International Geological Correlation Program #464
Continental Shelves during the Last Glacial Cycle: Knowledge and Applications
Second IGCP 464 Annual Conference
and Cananeia, 30 August -3 September 2002
|DAY ONE, Friday 30 August 2003|
09:30 Opening business meeting
10:30 Coffee Break
SESSION 1 Chair: Wyss Yim
- Land bridges and isolation basins at the last glacial maximum around
Allan R. Chivas
11:30 - Submerged depositional terraces, a nearshore, "Mediterranean", depositional body possible indicator of LGM on steep shelves. ®
Chiocci F. L.
12:00 - Pedogenesis of subaerially exposed continental shelves during the last glacial maximum and the production of atmospheric greenhouse gases. ®
Wyss W.-S. Yim
12:30 – Lunch
14:00 – Poster Session
16:00 – Coffee Break
16:30 – Business Meeting
19:00 – Dinner
|DAY TWO, Saturday 31st August 2003|
08:30 – Excursion to Cananéia
20:00 – Dinner
|DAY THREE, Sunday 1st September 2003|
SESSION 2 Chair: Francesco L. Chiocci
- Southern Galicia continental shelf of NW Spain since the last glacial
Vilas, F., García-Gil, S., Diez, R., Durán, R.,Ferrín, A., Magariños, J., Iglesias, J.
09:30 - High-resolution seismic stratigraphy from the southern Galician shelf and its connection with the rías, NW Spain. ®
García-Gil, S., Vilas, F., Ferrín, A., Diez, R., Durán, R., Magariños, J., Iglesias, J.
- Sediment transfert and processes across the shelf and upper slope of
the Aquitaine Margin (Bay of Biscay, France). ®
Jean-Claude Faugères, Pierre Cirac
10:30 – Coffee Break
- Geochemical indicators of sediment accumulation in Guadiana estuary,
S.Portugal during the Holocene sea-level rise. ®
T.Boski, V. Santos Correia, E.Good, H.Martins
11:30 - Glacio-isostatic movements in the southern Baltic area. ®
12:00 - LGM lowstand and deglacial sea-level rise: the Sunda shelf
record compared with other sea-level curves. ®
K. Stattegger, T. J.J. Hanebuth
12:30 – Lunch
SESSION 3 Chair: Allan Chivas
- Late Pleistocene palaeo-environmental history from the Gulf of
Carpentaria, Australia: interpretation based on foraminifera, ostracoda
and charales. ®
Adriana García, Allan R. Chivas, Sabine Holt, Jessica Reeves Passos, R.F., Sousa, S.H.M., D'Agostino, L.F., Mahiques, M.M.
14:30 - Distribution of foraminifera in the SE Brazilian margin after
the last glacial maximum.
Passos, R.F., Sousa, S.H.M., D'Agostino, L.F., Mahiques, M.M.
15:00 - Paleoceanographic variations during the last 30.000 years: results from oxygen isotopes and total fauna with planktonic foraminifera and calcareous nannofossils. ®
Felipe A. L. Toledo, Karen B. Costa
15:30 – Coffee Break
- Carbonate sedimentation on Australia’s Western Margin. ®
Lindsay B. Collins
16:30 - Response of carbonate producers to sea-level oscillations in
the continental shelf and shelf edge, Bahia State, NE Brazil. ®
17:00 - Mid-latitude carbonate sedimentation on a volcanic island shelf (Pontine Islands, Tyrrhenian Sea). ®
E. Martorelli, F.L.Chiocci, G. Civitelli, C. Chimenz, G. Ventura, C. Altobelli, A. Balocco, A. Bosman, L. Cassata, M. Raspagliosi
17:30 - Relic carbonate deposits of the northwestern margin of India: record of sea level changes and neo-tectonic activity during the last glacial cycle. ®
V. Purnachandra Rao
18:00 - Glacial millennial-scale fluctuations in central African precipitation recorded in terrigenous sediment supply and freshwater signals offshore Cameroon. ®
Adegbie, A. T., Schneider, R. R., Röhl, U., Wefer, G.
20:00 – Dinner
|DAY FOUR, Monday 2nd September 2003|
SESSION 4 Chair: Don Gorsline
09:00 - Paleoenvironment of the Late Quaternary Pacific margin of Canada: influence on americas’ first humans. ®
Hetherington, Renée, Barrie, J. Vaughn, Reid, R.G.B., MacLeod, R.
09:30 – Human activity in relation to Late Holocene coastal changes of the Puck Lagoon. ®
Szymon Uscinowicz, Joanna Zachowicz, Grazyna Miotk-Szpiganowicz
10:00 - Main stages of the Southern Baltic development. ®
Regina Kramarska, Szymon Uscinowicz, Joanna Zachowicz
10:30 – Coffee Break
- Increased storminess at the Subboreal /Subatlantic transition in the
Galician continental shelf (NW Spain). ®
R. González-Álvarez, P. Bernárdez, L.D. Pena, G. Francés, S. García-Gil, F.Vilas, R. Prego
- The Holocene marine ingression in the lower Uruguay River. ®
Martin Iriondo, Daniela Kröhling
12:00 - The post-LGM transgressive surface in the northern region of
the Argentina continental shelf. ®
12:30 – Lunch
SESSION 5 Chair: Michel Mahiques
- Sea-level history since last glacial maximum inferred from
continental shelf morphology of Southern Brazil. ®
Iran Carlos Stalliviere Corrêa, Elírio Ernestino Toldo Jr.
14:30 - Palaeo-shorelines drowned by the last marine transgression on Campos Basin continental shelf, Brazil. ®
Silva, Cleverson G., Lopes, Anderson L. M.
15:00 – Interactions of sea level and tectonics on large scale bedforms preserved on a tropical shelf: the Rio Grande do Norte shelf, northeastern Brazil.®
Helenice Vital, Venerando E. Amaro, Karl Stattegger, Klaus Schwarzer, Werner F. Tabosa, Eugênio P. Frazão, Iracema M. Silveira, Luciano H.O. Caldas
15:30 - Coffee Break
- The paleo-valleys in southeastern Brazilian continental shelf: could
they be older than we thought?
Conti, L. A., Furtado, V. V.
16:30 - Holocene marine deposits: modelling self-weight consolidation. ®
N.Keith Tovey, Paul, M.A., Yap Chui-Wah, Simon Tovey
17:00 – Final business meeting
20:00 – Farewell dinner
|DAY FIVE, Tuesday 3rd September 2003|
08:00 – Return trip to São Paulo
1) GLACIAL MILLENNIAL-SCALE FLUCTUATIONS IN CENTRAL AFRICAN
PRECIPITATION RECORDED IN TERRIGENOUS SEDIMENT SUPPLY AND FRESHWATER
SIGNALS OFFSHORE CAMEROON. Adegbie, A. T., Schneider, R. R., Röhl,
U., Wefer, G.
LIST OF POSTER PAPERS
CONFERENCE ABSTRACTS (click on read dot to read the abstract)
GLACIAL MILLENNIAL-SCALE FLUCTUATIONS IN CENTRAL AFRICAN PRECIPITATION RECORDED IN TERRIGENOUS SEDIMENT SUPPLY AND FRESHWATER SIGNALS OFFSHORE CAMEROON.
Adegbie, A. T. (a) Schneider, R. R.(b) Röhl, U.b
(a) Nigerian Institute for Oceanography and Marine Research (NIOMR), P.M.B. 80108, Victoria Island, Lagos State, Nigeria. Fax: +234-1-2619517; Email: email@example.com (b) Fachbereich Geowissenschaften, Universität Bremen, Klagenfurter Strasse, D-28359 Bremen, Germany.
Evidence of rapid climatic oscillations like those observed in the Greenland ice cores and sediments from high latitudes of the northern Atlantic have been recognized in the pulses of terrigenous material to continental margin sediments off Cameroon. Fe/Ca ratios used as a parameter to quantify the relative proportions of terrigenous fluxes versus marine carbonate monitor the variability of the west African monsoon. They reveal the history of abrupt changes in precipitation over western and central Africa during last 52 kyr. These rapid changes are particularly pronounced during the last glacial period and occur at timescales of a few thousand years. Stable oxygen isotope (d18O) record of Globigerinoides ruber (pink) shows high negative values reflecting periods of high monsoon precipitation. The Fe/Ca pattern is very similar to the Dansgaard-Oeschger cycles from the Greenland ice cores. The good correspondence between the warm interstades of the Dansgaard-Oeschger cycles from the Greenland Ice Sheet Program (GISP2) ice core records and the high pulses of Fe/Ca sedimentation in our core suggest a strong teleconnection between the low latitude African climate and the high latitude northern hemisphere climate oscillations during the last glacial. This climatic link is probably vested in the west African monsoonal fluctuations that alters tropical sea surface temperatures, thermohaline circulations and in turn net export of heat from the south to the north Atlantic coupled with the variability of the low latitude southeast (SE) trade winds.
MOLLUSCAN ASSEMBLAGES FROM THE BONAERENSIAN NEARSHORE AND INNER CONTINENTAL SHELF (ARGENTINA) SINCE THE LATE PLEISTOCENE: PALAEOENVIRONMENTAL INTERPRETATION
M. Aguirre (1) R.A. Violante (2)
(1)Museo de Ciencias Naturales, Paseo del Bosque, 1900 La Plata, Argentina (2) Servicio de Hidrografía Naval, Av. Montes de Oca 2124, C1270ABV, Buenos Aires, Argentina.
A preliminary palaeoenvironmental study was performed
samples from corings at four stations off the Bonaerensian coasts
(Argentina, 36°58’34’’ to 37°50’48’’S; 56°41’09’ to
56°02’67’’ W) covering the time span since the Plio- Pleistocene
including the LGM
to Holocene. Three littoral cores (VC3-C; VC6-1- BC; LB12; between
m water depth) and one from the continental shelf (LB15 at 82m water
depth) provided a rich macroinvertebrate fauna showing to be
potentially useful for future, more detailed palaeoecological,
geochronological and geochemical studies aimed to characterize and
eventually differentiate pre and post-LGM deposits. A total of 31
molluscan species (20 bivalves and 19 gastropods) and an associated
fauna (bryozoans, polychaetes, balanids, polyplacophores) were
The molluscan fauna is similar to the modern along the Bonaerensian coasts, although differences in the relative abundance of the species in common are evident. Bivalves outnumber gastropods or are exclusive in all samples. All the taxa have modern representatives living along the Argentine or the Magellanean Zoogeographical Provinces, their stratigraphic distribution ranging from late Miocene and/or Pleistocene to Recent. The assemblages are also similar to those recovered in nearby Holocene and late Pleistocene littoral deposits (Aguirre, 1993).
As a whole the molluscs from all four cores suggest a littoral to shallow neritic or inner shelf depositional environment. Within the shallower cores (VC3- C and VC6-1-BC) the molluscan assemblages are more abundant and diverse and show close similarity to those characterizing the Holocene ridges from the nearby coastal area (at + 4m above m.s.l., 5-3 ka B.P.). Together with their good preservation and modern aspect they suggest a postglacial age for the 15 samples involved taken at 3 to 80 cm depth. They differ, however, by the abundance of Mactra spp (Bivalvia) in these cores vs. dominance of Littoridina australis (Gastropoda) in the Holocene coastal area, probably reflecting variations in salinity gradient (higher) and secondarily of substrate type (softer), depth (higher) and energetic (lower) conditions of the depositional environment offshore. The main difference between the shallower samples (VC3, VC6-1-BC, a few from LB12), some deeper ones from LB12 (at 80-130cm) and most LB15 samples (continental shelf; at 15-382cm) are the excellent preservation (most shells retaining even the original colour and shiny appearance of their living representatives), lower diversity and lower energetic palaeoenvironmental framework for the deeper ones.
Unfortunately, there is not as yet a full chronological control for the cores analysed, as no radiocarbon or aminoacid dates available refer to these samples, except for 14C dates from nearby stations which indicate ages younger than 15.000 years B.P. for the surface sediment cover (Richards and Craig, 1963, Parker and Violante, 1982). Lithological evidences supported by sismostratigraphic information (Parker et al., 1999) suggest that the surficial samples are of Holocene age (VC6-1-BC: upper VC3 and LB12) while the interval from 7 to 382 cm at core LB15 could belong to the late Pleistocene, including the LGM. A multivariate analysis (Q-Mode and R-Mode cluster analysis; Jaccard’s coefficient; UPGMA) support the palaeoenvironmental interpretation. The Q-mode showed three main biofacies (A-C) and subbiofacies: A (VC6-1, upper VC3 and LB12 samples: more diverse, sandy bottom, shallower water species; A1 of Holocene age), C (most LB15 samples: deeper, muddy bottom, lower energetic bivalve species, no gastropod taxa; Pleistocene) and B (most LB12 samples, intermediate in depth). The R-Mode dendrogram showed that the bivalve associatons are more informative than gastropods and support deeper, less energetic, perhaps colder environments (LGM ?) for C.
Some bivalves (Glycymeris longior Sow.; Brachidontes rodriguezi (d´ Orb.), Plicatula gibbosa Lamk.) are indicative of a very shallow environment (Biof. A) (less than 60m). The low taphonomic grade shown by some strong heavy bivalve shells (Pitar rostratus (Koch) indicates allochtony and a considerable abrasion due to transport from the beach zone or from sediments in deeper zones (A). One gastropod species (i.e., Anachis avara Say) (Biof. A) is today northwards displaced to warmer waters (Brazilian Subprovince) while one bivalve (i.e., Hiatella solida (Sow.) (Biof. C) is a typically cold water element of the Magellanean Province, probably indicative of the influence of the LGM along the continental shelf in this area (LB15).
On the basis only of the composition and taphonomic attributes of the molluscs recovered our evidence is insufficient to confirm or deny their late Pleistocene age within the LGM. Our preliminary data constitute a first approximation of this problem and further studies need to involve modern dating and stable isotope analysis of selected, best preserved and unaltered shells to reconstruct palaeoclimatic and palaeoenvironmental variations from LGM to present, with a precise chronological control for both the geological and palaeoecological data available. Probably the more abundant bivalve taxa (Mactra, Corbula, Nucula) are most appropriate to initiate both approaches.
Aguirre, M.L., 1993. Caracterización faunística del Cuaternario marino del noreste de la Provincia de Buenos Aires. Revista Asociación Geológica Argentina, 47(1): 31-54.
Richards, H. and Craig, J., 1963. Pleistocene Molluscs from the Continental Shelf of Argentina. 115 (6): 127-147.
Parker, G., Paterlini, C.M., Violante, R.A., Costa, I.P., Marcolini, S. y Cavallotto, J.L., 1999.
Descripción geológica de la Terraza Rioplatense (Plataforma Interior del noreste bonaerense). Servicio Geológico y Minero Argentino, Boletín N° 273, Buenos Aires.
GEOCHEMICAL INDICATORS OF SEDIMENT ACCUMULATION IN GUADIANA ESTUARY, S.PORTUGAL DURING THE HOLOCENE SEALEVEL RISE
T.Boski, V. Santos Correia, E.Good , H.Martins
CIMA – Centro de Investigação Marinha e Ambiental, Universidade do Algarve, 8000-117 Faro, Portugal
Guadiana is a major river on the Iberian Peninsula and
the terminal segment of its valley is cut deeply into the impervious
and faulted Upper Carboniferous schists and graywacks. Boreholes and
seismic profiles indicate that the paleovalley is 600 m wide and 70 m
deep below mean sea level, ca. 7 km inland from the mouth (Boski et
The depth of the incision, which is exceptional for the Gulf of Cadiz,
allows a good insight into the sedimentary record with a
high-resolution timescale. Several cored boreholes that reached the
pre-Holocene substratum were drilled in recent years in order to
recognize the architecture of sedimentary facies and to quantify the
organic carbon (OC) content trapped in sediments accumulating during
the drowning of the Guadiana fluvial valley. The results described in
the present study were obtained from a bore-hole drilled down to ca. 53
meters near the confluence of Beliche and Guadiana Rivers, located in
the intertidal zone of the latter. Three 14C datings performed on the
recovered samples indicate that the entire sedimentary sequence
accumulated over a period of ca 13-14 kyrs, representing one of the
longest postglacial sedimentary records in the nonglaciated areas.
About 80% of the Holocene sedimentary sequence was accumulated in
the first phase of the sea level rise which terminated ca. 6700 cal.
BP, at a rate of ca. 80 cm per century, and was followed by a much
rate of vertical accretion. The 10 lowermost meters, of this sequence,
which is lying on top of polimictic gravels, are mostly sandy with
intercalations of silty clay. The basal sands are mineralogically and
texturally immature but become progressively more quartzic and devoid
of mica towards the top of the horizon. The foraminifera fauna is
almost absent in this interval and when present, it consists of scarce
inner linings of benthic foraminifera. This environment maybe
interpreted as belonging to the transitional fluvial – estuarine phase
observed also in the basal sections of other boreholes in the Guadiana
area (Boski et al., 2002). In the remaining upper, almost entirely
finegrained section of the borehole, marked differences were found with
respect to several faunistic and geochemical parameters.
The lower segment that extends from the core bottom to ca. –20 m depth is characterized by a low abundance of calcareous benthic foraminifera, lower sulfur and OC content and a predominance of phytoplankton molecular biomarkers (Gonzalez Vila et al., 2002). These features may be representative of mudflat facies experiencing periods of frequent/prolonged submergence that were interrupted by several flood events that delivered coarser sandy sediments. Several peaks in the concentrations of redox sensitive elements point to the prevalence of reducing conditions. The upper segment, which comprises the top ca. 17 meters of the sediment column, is very rich in calcareous benthic foraminifera, and higher in sulfur, OC and resin biomarkers. Both higher sodium and sulfur content indicate the occurrence of evaporationdriven precipitation of halite and gypsum. Elevated OM contents relative to the lower segment (1.6% vs. 1.1% on average) can be associated with the increased erosion of land covered by coniferous forests, resulting in the delivering of vascular plant remains which are known to be more refractory than phytoplankton detritus.
In the study area, OC was buried at a rate of 178 g m-2 y-1 during the period of the fast sediment accumulation from 13 kyr cal BP to ca 6.7 kyr cal BP, decreasing to 80 g m-2 y-1 OC in the following, Upper Holocene sector. For the whole of the Guadiana River estuary the respective numbers are 182 and 56 g m-2 y-1 OC, giving a total mass of accumulated OC ca. 1.56 t. that corresponds to 100.6t ha-1 of OC accumulated over the considered period.
For comparison, in a similar study of OC accumulation rate changes during the Holocene conducted for Nakaumi Lagoon, Japan, Sampei et al. (1997) estimated OC accumulation rates to be 21-32 g m-2 y-1 from 8 to 6.5 kyr cal BP, and 11 g OC m-2 y-1 from 3 to 2 kyr cal BP.
BOSKI T., MOURA D., CAMACHO S., DUARTE R.D.N., SCOTT D.B., VEIGAPIRES C., PEDRO P., SANTANA P. (2002) - Postglacial sea level rise and sedimentary response in the Guadiana Estuary, Portugal/Spain border. Sedimentary Geology, 150, 103-121
GONZALEZ-VILA F.J., POLVILLO O., BOSKI T., ANDRÉS J.R. (2002) - A biomarker approach to the organic matter deposited in coastal estuarine sediments during Holocene: a case study in the Guadiana River estuary. Organic Geochemistry (in press).
SAMPEI Y., MATSUMOTO E., TOKUOKA T., INOUE D. (1997) – Changes in accumulation rate of organic carbon during the last 8,000 years in sediments of Nakaumi Lagoon, Japan. Marine Chemistry 58, 39-50
SEDIMENTARY RESPONSE TO RELATIVE SEA-LEVEL CHANGES DURING PRE AND POST-LGM IN THE DE LA PLATA RIVER AREA, ARGENTINA
Cavallotto, José Luis
Division of Marine Geology and Geophysics, Argentine Navy Hydrographic Office, Av. Montes de Oca 2124. C1270AVB, Buenos Aires, Argentina. E-mail: firstname.lastname@example.org
The present area of the de la Plata river and the
adjacent continental shelf in eastern Argentina were affected prior and
after the LGM by a coastline migration associated to relative sea-level
fluctuations. The processes occurred as a result of these events
conduced to sediment deposition in different sequences which have been
interpreted as systems tracks in the sense of Hunt and Turker (1992),
whose study reveals the occurrence of distinctive stages of sea-level
fall and rise.
Sea-level fall prior the LGM: During the sea-level fall occurred as a consequence of the last glaciation the ancient de la Plata river run along a narrow valley cut through a plain today submerged under the shelf. While the valley was excavated due to fluvial erosion, deposition took place in the neighborhoods of the river mouth in coastal barrier systems that prograded seaward (Violante et al, 2001). These deposits are today recognized in the sedimentary records as a forced regressive system tract.
Low-stand of sea-level at LGM: During the LGM, the river valley run aside the Uruguay and southern Brazil coasts and flowed into the sea in front of Rio Grande do Sul. As soon as sea-level reached its lowest position, the great volume of sediments transported by the river was deposited in deltaic bodies at its mouth, which include muddy prodelta facies extended further east in the upper slope (Urien and Ewing, 1974). These deposits constitute a lowstand wedge system tract.
Post-LGM sea-level rise: When the post-LGM transgression begun, the sea invaded the river mouth and installed a estuarine environment where clay flocculation processes took place at the fresh-salt water interface. As a result, a muddy depocenter was formed and migrated inland as sea-level rise progressed. Finally, a huge estuary occupied most of the fluvial valley. At the same time, in adjacent coastal areas the shoreline retreated and barriers moved inland. Littoral sandy sediment were reworked and redeposited as palimpsests. These processes continued until sea-level reached its highest position around +6 m above present level 6000 yrs ago. All these deposit constitute a transgressive system tract which overlie the transgressive surface modeled by the ravinement process.
High-stand of sea-level: As sea-level rise stopped and begun to fall coastal progradation became the most important process. In the upper part of the estuary a delta was built with sediments coming from the Paraná river, while beach ridges grew up in adjacent coastal area. As a result of these processes that accompanied the decreasing of sea-level down to its present position, the delta finally occupied most of the estuarine environment, while the coastal plain extended seaward by progradation of successive beach ridges systems. The resulting sedimentary body constitutes a highstand system tract.
Hunt, D. and Tucker, M., 1992. Stranded parasequences and the forced regressive wedge systems tract: deposition during base-level fall.
Sedimentary Geology, 81, 1-2.
Violante, R. A., Parker, G. y Cavallotto, J.L. 2001. Evolución de las llanuras costeras del este bonaerense entre la Bahía Samborombón y la laguna Mar Chiquita. Revista Asociación Geológica Argentina, 56, 1: 1-66.
Urien, C., M. and Ewing, M. 1974. Recent sediments and environments of Southern Brazil, Uruguay, Buenos Aires and Río Negro continental Shelf, in: The Geology of Continental Margins, IV. Recent Sedimentation (Eds C. A. Burk and C. L. Drake), Springer-Verlag: 157-177.
SUBMERGED DEPOSITIONAL TERRACES, A NEARSHORE, "MEDITERRANEAN", DEPOSITIONAL BODY POSSIBLE INDICATOR OF LGM ON STEEP SHELVES
Chiocci Francesco L.
Università "La Sapienza", Roma, Italy
Based on several different case-study in the Tyrrhenian
Sea (Italy), a model for formation of nearshore depositional body is
proposed, supported by high-resolution seismic, side scan sonar,
R.O.V., multibeam and gravity core data.
On steep continental shelves, an abrupt change in slope at -20/-30 m water depth marks the edge of a depositional terrace, barely described in literature. The terrace is the morphologic expression of a depositional body that can be up to 23/30 m thick, some 500/1000 m wide (in dip direction) and several km - or several tens of km - parallel to the coast. The inner structure of the body is always prograding and the slope of the foresets is like that of the frontal slope, witnessing the depositional nature of the terraced body.
The depositional terrace is often found where the bedrock creates steep seafloor (as on volcanic islands) and is usually made up of medium-coarse intrabasinal sediment, and the bioclastic fraction pre-dominates. The deposit typically lacks of any subaerial, paralic or foreshore sediment.
Different physical processes took place on the terrace i.e. wave reworking and sediment bypassing on terrace top, gravity flow and frontal accretion by avalanching on terrace slope, sediment draping at the base-of-the-slope/ transition to the shelf.
The deposit seems to be the very common in medium wave-energy, microtidal, siliciclastic environments as the Mediterranean Sea, where tectonics and/or volcanism creates conditions of very steep seafloor. As in active tectonic setting the deposit is likely to be uplifted, its knowledge can be important in interpreting outcrop examples of small-scale depositional body.
On the meantime, as the terrace is an extremely good paleo-sea level indicator, it can be used to define the depth of the Last Glacial Maximum.
LAND BRIDGES AND ISOLATION BASINS AT THE LAST GLACIAL MAXIMUM AROUND AUSTRALIA
Allan R. Chivas
School of Geosciences, University of Wollongong, NSW 2522, Australia
At and near the Last Glacial Maximum, at least three
large isolation basins existed near Australia, namely the Bass Basin,
Lake Carpentaria, and the Bonaparte Depression. Several studies of
these alternating marine and nonmarine basins demonstrate their use in
refining sea-level curves in the range 80 to 40 ka, during which time
estuarine and lacustrine sediments were accumulating. Such sediments
also permit the study of past monsoons in the period up to about 10 ka
BP, and include the period when the Australian monsoon became
re-established following the Last Glacial Maximum. During intervening
episodes there must have been
quite unusual sediment and tide dynamics in very shallow but areally
The current sill depths for the Bass Basin (Blom, 1988), between Tasmania and mainland Australia are -55 m in the east and -67 m in the west (see also Lambeck and Chappell, 2001). In the Gulf of Carpentaria, between northern Australia and the island of New Guinea, current sill depths are -53 m in the west and -12 m at Torres Strait. The Bonaparte Depression, offshore of northwestern Australia, is at a current water depth of up to 130 m and provides information on sea-levels and ice-volumes at the Last Glacial Maximum (Yokoyama et al., 2000; 2001).
Within the Gulf of Carpentaria, at lake-full stages, a lake with dimensions of 600 km x 300 km x 17 m depth existed. In some intervals, the fauna of the lake could be mistaken for a marine environment with foraminifera and coccoliths defying lengthy physical separation from the surrounding oceans (Chivas et al., 2001; and current work).
This presentation will focus on the dynamics and climatic implications from the Bonaparte Depression and the Gulf of Carpentaria. Recently (May 2001), longer cores (to 8.5 m) were collected from Bass Basin (Jock Keene, pers. comm.) and greater detail of its palaeoclimatic record is anticipated.
Blom, W.M. (1988). Late Quaternary sediments and sea-levels in Bass Basin, southeastern Australia – A preliminary report. Search, 19: 94-96.
Chivas, A.R., Garcia, A., van der Kaars, S., Couapel, M.J.J., Holt, S., Reeves, J.M., Wheeler, D.J., Switzer, A.D., Murray-Wallace, C.V., Banerjee, D., Price, D.M., Wang, S.X., Pearson, G., Edgar, N.T., Beaufort, L., De Deckker, P., Lawson, E. and Cecil, C.B. (2001). Sea-level and environmental changes since the last interglacial in the Gulf of Carpentaria, Australia: an overview. Quaternary International, 83-85: 19-
Lambeck, K. and Chappell, J. (2001). Sea level change through the last glacial cycle. Science, 292: 679-686.
Yokoyama, Y., Lambeck, K., De Deckker, P., Johnston, P. and Fifield, L.K. (2000). Timing of the Last Glacial Maximum from observed sea-level minima. Nature, 406: 713-716.
Yokoyama, Y., De Deckker, P., Lambeck, K., Johnston, P. and Fifield, L.K. (2001). Sea-level at the Last Glacial Maximum: evidence from northwestern Australia to constrain ice volumes for oxygen isotope stage 2. Palaeogeography, Palaeoclimatology, Palaeoecology, 165: 281-297.
MODELING THE SOUTHERN BRAZILIAN CONTINENTAL SHELF AS A "DEVIL'S STAIRCASE".
(1)Conti, L. A. (2) Baptista, M. S. (1)Furtado, V. V.
(1).Instituto Oceanografico, Universidade de São Paulo. (2). Instituto de Física, Universidade de São Paulo
Several works dealing with geomorphological analysis of
continental shelves have characterized the distribution of submerged
terraces and scarps, and their relation with periods of sea level
standstills during the late Quaternary period (post 18 kyears). These
works were responsible for the construction of sea-level curves and for
the better understanding of the late quaternary climate changes
dynamic. In this work, we go beyond the identification and
characterization of the distribution of the terraces, proposing a model
to the terrace features based on a identified pattern of development of
the bottom morphology as a consequence of the sea-level evolution.
The model is constructed based on data from the Southeastern Brazilian Continental Shelf. This Shelf is a typical sandy passive with the predominance of palimpsests sediments. The mean length is approximately 250km and the shelfbreak is located at 150m depth. The geology and topography of the emerge area have a very peculiar historical development, represented by the Mesozoic/Cenozoic tectonic processes that generated mountainous landscapes known as "Serra do Mar", extending parallel to the coastline (with mean altitudes of 800m). The coastline presents a complex pattern with the occurrence of several scarps intercalated with small coastal plains and pocket beaches. This particular characteristic determines the development of small size fluvial basins and estuaries conditioning a low input of modern sediments, what trend to preserve topographic signatures of the sea-level variations.
For the purpose of the present study, we select a few parallel profiles acquired from echo-sounding surveys. These profiles are transversal to the coastline and the isobaths trend, and extend from 20m to 120m deep. We observe that all considered profiles have in common the same similar series of sequences of high and low declivity, that we believe is somehow connected to sea-level standstills.Apparently, the Shelf geometry resembles a staircase, with randomly varying steps widths. However, assuming that the depth of each terrace represents a p/q frequency-locking between two global climate variables, which we believe to result in a temporary stabilization of the sealevel, we can classify each terrace with a number q. Through that, we were able to find a scaling power-law between the terrace width and the value of q. The finding of this scaling suggested us the existence of fractal pattern describing the terrace depths. We suggest this fractal geomorphological structure to be described by a Devil's Staircase, a Staircase with infinity steps in between two steps. This property gives the name "Devil" to the staircase, once an idealized individual would take an infinite time to go from one step to the other in case he wants to walk over all the possible steps.
The Devil's Staircase (DSC) is a fractal geometric structure whose step height position (depth in the sea-level geomorphological structure) represents the rotation number of a periodic responses of an oscillating dynamical system to a giving parameter (in this situation, we say the system is frequency-locked). As this parameter is varied different periodic responses appear (all being quantified by the rotation number) which stay stable to parameter variation up to a certain interval of values, the frequency-locked intervals. So, by varying the parameter value the rotation number stay fixed. Making a plot with the horizontal axis representing the parameter and the vertical axis representing the rotation number, a step is seen when the rotation number is kept fixed for parameter a variation. The interval size within which the system stay stable depends on two factors: the type of the periodic oscillation, and the amplitude of an external perturbation applied into the system. The rotation number is a rational number represented by the ratio p/q, physically interpreted as the ratio f1-1 / f2-1, where f1 and f2 are two frequencies of oscillations. Higher is q, smaller is the frequency-locked interval for which the system stay stable with the rotation number, given by p/q. As one changes the parameter in an oscillating dynamical system, the way specific frequency-locked oscillation appears follow a rule described by the a particular organization of rationals. This organization is represented by a Farey's Tree, which in short can be understood as a hierarchical organization of the many rationals in between two other rationals. If there are two frequented-locked intervals characterized by p/q and p'/q' respectively, there must exist an infinity number of other intervals which represent periodic oscillation with a given rotation number p''/q'' which is p/q < p''/q'' < p'/q'. However, among these infinity number of frequency-locked intervals (the steps in the staircase), there is one special interval, whose oscillation rotation number is given by p''/q''=(p+p')/(q+q'), which has an interval size greater than all the other possible frequency-locked intervals. The lengths of these intervals that follows the Farey's Tree rule have a fractal self-similar structure. In fact, there is an infinity number of fractal structures, characterizing the possible sequences of frequency-locked intervals.
The main premise that guide the application of DS model to the Shelf is that the relation between the depth and length of the terraces (and scarps) seems to obey the same pattern and rules described by a DSC, if the following hypothesis are followed: Given a terrace n with depth, dn, and length, ln,
(1) The frequency-locked interval is proportional to ln.
(2) There is a function F which applied into dn gives the frequency-locked ratio sn=pn/qn.
To find out what the function F is, we first use the fact that this function should have the same metric properties as the one described by the Farey's Tree rational organization, which lead to
 (dn+2 + dn)/dn= 1 = (sn+2 = s n )/ s n+1
Once we are dealing with experimental data, only a few terrace are observed, which means that the corresponding rational numbers (through hypothesis 1 and 2) can not be all. From the Farey's Tree theory, we know that:
 sn+1 = (pn + pn+2)/(qn + qn+2)
Therefore, combining Eq. 1 and Eq. 2, we obtain
 (K - 1) qn + 2. pn + (K - 1) qn + 2 pn + 2 = p nq2n+2
where K is the experimental data defined by
 K = (dn+2 + dn )/(dn+1)
In order to characterize the experimental DS, we do not
expect to have Eq.  satisfied. We only require that the difference
between the left and right side of this equation to be the lowest
possible, among all the possible values for pm and qm (with m= n, n+2),
for a given K. Doing so, we find the rationals associated with the
Table 1: Rationals associated with the terrace n. More deep and more in the past the terrace appeared. Using the model was possible to fit the rational numbers associated with each terrace, which are shown in the table 1. Fitting the given depth d with the found associated rationals sn, we find the function F that applied into d gives the frequency-locked rational s
 F(d) = 0.157(0.0026) + 0.00078157(4.05789 x 10-5)d
We also found a the length, l, of the terrace is a power-scaling law, with respect to q, for p=1, with a coefficient of approximately -4.5, what means that the terrace lengths are shorter than they could be, and therefore, the sea-level oscillations are not as stable, in time, as they can be. However, the branch 1/q (found for the terraces with n=1,3,5,6,8) of the Farey's Tree represent the more stable possible frequency-locked intervals within all the possible ones. In addition, as we go forward in time, the terraces are being represented by more stable intervals, once the branch 1/q has q decreasing with n. Therefore, it seems that the sea-level frequency-locked intervals are becoming more and more stable as time goes by. Finally, it should be noted that the identification of the DS in the Continental Shelf could model a very complicated interaction and coupling between Global Climate Variables (which are responsible for the stabilization of the sea-level) without actually the use of complex dynamical modelings, but only the knowledge of a particular hierarchical organization of the rational numbers within the interval [0,1].
THE PALEO-VALLEYS IN SOUTHEASTERN BRAZILIAN CONTINENTAL SHELF: COULD THEY BE OLDER THAN WE THOUGHT?
Conti, L. A. Furtado, V. V.
Instituto Oceanografico, Universidade de São Paulo.
The analysis of distribution of paleodrainage in
continental shelves has been done as an indicator of an evolution of
the relief during the last regressive period (post 18 kyears) when most
of the world shelves has been exposed to sub-aerial erosional
processes. Several works deal with this subject as an important tool in
order to characterize the tectonic control of shelves, as an indicator
of paleogeography of the sub-aerial surface and the hydrological regime
of regressive periods. It is accepted that, even covered by
transgressive deposits, it is possible to identify and classify the
paleovalleys in continental shelves surface relief since they has not
been submitted to strong tectonic processes or high depositional rates
what could mask, cover or distort the evidences of it.
This work has as an objective, the analysis of the distribution of the paleovalleys network at the southeastern Brazilian continental shelf. The paleodrainage network was extracted using the algorithm known by "single-flowdirection D8 method" from a digital terrain model that covered all study area. It allows flow from a cell to one of eight nearest neighbors based on the primary flow direction. Because flow can accumulate into a cell from several upslope cells, but only flow out into a single cell, this method can model a flow convergence in valleys, but not flow divergence in ridge. Due the very soft declivity angle of the continental shelf, and the fact of all surface is covered by transgressive sediments, it is impossible to extract quantitative parameters from the model since most of the topographic characteristics of the original erosive terrain is masked by transgressive deposits. However, the main flow axis direction still can be preserved and identified. In order to characterize the channels is subsurface in specific areas and correlate them with the paleovalleys extracted from the DTM, it was also analyzed a series of seismic lines from a sparker profiler
The drainage network generated to the whole continental shelf showed an excellent correlation with all actual drainage systems. It was generated 8 main basins systems; five of them are associated actual river systems while the other two do not present direct link with modern rivers. The biggest river system, the Ribeira de Iguape (RI), presents one clear paleo-valley beginning at the 25 meters isobath very well connected with the actual river month. Further south, approximately 5 kilometers, another valley feature runs seaward parallel to the first one. Based in the size of the valleys and their position, is reasonably to suppose that both features are linked with RI river. It was also observed in emerse area using satellite images that there is an clear indicator of abandoned channel from RI river characterized by wetlands and typical vegetation that converge to the second paleo-valley feature at the continental shelf.
The same characteristics can be observed at the northern part of the area with the "Juqueriquere" river. As the other case, there are two valleys features associated with the same river controlled by the presence of an island called São Sebastião. The first valley runs southward of the island while the second runs northward separated each other from more than 20 nautical miles. In both cases the valleys can be identifying also by subsurface features of cut and fill structures. In this case, the first valley (southern valley) reaches the isobath of 120 meters what coincide with the LGM and the second valley prolongates until 70 meters depth.
If we consider that in the glacial periods, the hydrological regime was at least as much wetter than today (in fact, evidences shows that it was considerably drier), it is hard to conceive the fact that two rivers could occupy the same fluvial basin in the paleo-coastal plain, so the most reasonable theory is that in both basins the different paleo-valleys were established at different cold periods.
SEA-LEVEL HISTORY SINCE LAST GLACIAL MAXIMUM INFERED FROM CONTINENTAL SHELF MORPHOLOGY OF SOUTHERN BRAZIL
Iran Carlos Stalliviere Corrêa, Elírio
Ernestino Toldo Jr.
Centro de Estudos de Geologia Costeira e Oceânica-CECO, Instituto de Geociências-Universidade Federal do Rio Grande do Sul (UFRGS*). Av. Bento Gonçalves,9500, Caixa Postal 15.001, 91501-970 Porto Alegre-RS, Brasil. Iran.email@example.com * Participant Institution of the Geology and Marine Geophysics Program-PGGM
A large number of continental shelves studied around
world exhibit sea level oscillations during the Late Quaternary as
shown by breaks or notches in seaward profiles. Almost all, those
presented are re-overwhelmed by bioclastic sediments and silisticlastic
analyses more thick as well as heavy minerals concentration presence.
Through detailed bathymetric chart elaborated on Brazilian South and
Southeast continental shelf about echo sound survey and bathymetric
profile perpendicular delineated to coastline till around –150m deep.
It is possible to observe five different declivity breaking situated
respectively –20/-25m, -32/-45m, -60/-70m, -100/-110m e –120/130m deep.
Such declivity breaking or marine terrace are observed over all
Brazilian South and Southeast continental
shelf from North area Cabo Frio (RJ) region to Chuí (RS) South
Using the paleoclimatic curve proposed by Servant (1984) for the central part of South America in the last 25,000 years BP, we observe that during the final Pleistocene regression and beginning Holocene transgression around 17,500 years BP, it’s weather was cold but from 16,000 to 11,000 years BP, it’s weather changed from humid to dry temperate during an interglacial period. A new glacial period happened between 11,000 and 10,000 years BP producing other new sea level stabilization. Around 10,000 and 9,000 years BP, weather became warmer causing a new rise in sea level followed by a cold weather in short time which made a little regression causing second sea level stabilization. Subsequently, the climate became humid. Between 8,000 and 5,000 years BP weather changed from humid to warmer humid. From 5,000 to 3,500 years BP climate changes from warmer humid to cold. Since 3,500 BP weather starting change to temperate warm. Temperature was risen and forests status developed. Rivers became more full flowing and drainage system was important. According Servant (1984) we can affirm that during cold periods sea level rises were slower making coastline stabilization in those places. In the study are continental shelf breaks in slope at –120/-130m deep, which are representatives about sea level in Holocene transgression. Starting cold time for –100/-110m, -60/-70m, -32/-45m e –20/-25m, when sea level had stabilization during transgression process making new coastline.
According variation sea level curve, proposed by Corrêa (1984), we can divide Brazilian South and Southeast continental shelf transgression event into four stages:
First stage: From 17,500 years BP to 16,000 years BP – Holocene transgression started around 17,500 years BP while sea level was –120/-130 m below its present level. At that time the continental shelf was almost totally emerged having a flat surface with many fluvial valleys. Lengthways that ancient coastline accumulated material is presenting formed for coarse sand originated from epoch fluvial drainage and for subjacent sediments re-worked. From 17,500 years BP to 16,000 years BP according Corrêa et al. (1992) and Corrêa (1996) sea level lifting was relatively fast presenting 2 cm/year speed that way maintaining ancient declivity coastline. That sea level was stabilized at –100/-110m deep where a new littoral system was formed.
Second stage: From 16,000 years BP to 11,000 years BP – Since 16,000 years BP sea level lifting was less fast till 11,000 years BP. According Corrêa et al. (1992) and Corrêa (1996) was 0.6 cm/year speed. In this stage were observed declivity breaks in –100/-110m and –60/-70 m deep. First one showed not so well maintained on studied field while second can be observed throughout area. Sediments at –60/-70m level is formed by coarse sands associated to bioclastic material of carbonatical composition and through many tests was observed peat bed presence. The heavy mineral contents on such level are the highest on continental shelf.
Third stage: From 11,000 years BP to 6,500 years BP – That third stage is featured by two declivity-breaking zones, which is localized in –32/-45m and –20/-25m deep. According Corrêa et al. (1992) and Corrêa (1996) coastline dislocating average speed that time was 1.6 cm/year. For coastline migration landward drainage channels starting to dislocate to East but they were continuing to give material to ancient continental shelf. Sands in a high grain size scale and for bioclastic material form the sediments re-cover such levels.
Fourth Stage: From 6,500 years BP to present time – This final stage by Holocene transgression was featured by transgress sand stratum and shelf mud. The fluvial deep had a considerable reduced grade. That period sea level had passed present sea level twice. First time when it rose +5m around 5,100 years BP followed by a regression which reached the lowest point (-6m) approximately 5,100 years BP. Second time in 3,000 years BP when sea level reached +4m level over present time followed by a regression/ transgression. Since (2,300 years BP) sea level started to come back till reach present level.
Corrêa,I.C.S.1990a. Analyse morphostructurale et evolution paleogeographique de la plate-forme continentale Atlantique sudbrésilienne (Rio Grande do Sul-Brésil). Université de Bordeaux I, Talence- France. Thèse de Doctorat. N1477. 314p.
Corrêa, I.C.S. 1990b. Variations de la Ligne de Rivage Depuis 17.500 ans BP sur la Plate-Forme Continentale du Sud du Brésil. In: Colloque de L'Union des Océanographes de France,16. Roscoff-França. Programme et Activits..., Roscoff-França. p.15.
Corrêa,I.C.S. 1996. Les variations du niveau de la mer durant les derniers 17.500 ans BP: l’exemple de la plate-forme continentale du Rio Grande do Sul-Brésil. Marine Geology, 130:163-178.
Corrêa, I.C.S.; Baitelli, R.; Santos, H.N.; Ade, M.V.B. 1989. Sea Level Change in South-Brazilian Continental Shelf. In: International Symposium on Global Changes in South America During the Quaternary. São Paulo-SP. Special Publication..., São Paulo-SP. 1:245-249.
Corrêa,I.C.S.; Baitelli,R.; Ketzer,J.M.; Martins,R. 1992. Translação horizontal e vertical do nível do mar sobre a plataforma continental do Rio Grande do Sul nos últimos 17.500 anos BP. In: Congresso da Associação Brasileira de Estudos do Quaternário,3. Belo Horizonte-MG. Anais...., ABEQUA, Belo Horizonte-MG. P.225-240.
Kowsmann, R.O.; Costa, M.P.A.; Vicalvi, M.A.;Coutinho, M.G.N.; Gamboa, L.A.P. 1977. Modelo da sedimentação holocênica na plataforma continental sul-brasileira. In: Projeto REMAC-Evolução sedimentar holocênica da plataforma continental e do talude do sul do Brasil. Rio de Janeiro, CENPES.p.7-26 (Sérire Projeto REMAC 2).
Servant,M. 1984. Climatic variations in the low continental latitudes during the last 30.000 years. In: Morner,N.A. & Karlen,W. (ed). Climatic changes on a yearly to millennial basis. D.Reidel Publishing Company. Boston. p.117- 120.
* Financial support was also provided by the CNPq (Process 470106/01-8 and 300116/80).
STRATIGRAPHIC AND GEOMORPHOLOGIC INDICATORS OF LATE PLEISTOCENE-HOLOCENE SEA-LEVEL CHANGES ON THE ALGARVIAN SHELF, SOUTHERN PORTUGAL
Dias, J.M.A.(1) Lobo, F.J.(1) González, R.(1)
Hernández-Molina, F.J.(2) Mendes, I.(1) Fernández-Salas,
L.M.(3) Díaz del Río, V.(3)
(1) CIACOMAR-Univ. Algarve,Olhão, Portugal (2) Dpto Geociencias Marinas y Ordenación del Territorio, Univ. Vigo, Vigo, Spain (3) Instituto Español de Oceanografía (IEO), Fuengirola, Spain
A sector of the continental shelf of the Gulf of
Cádiz (southwest Iberian Peninsula) has been chosen to find
evidences of recent sea-level changes. The Algarvian shelf, located
westwards of the Guadiana river mouth, is characterised by the absence
of significant fluvial feeders, and only minor streams provide
sediments. In spite of
this regional setting, the analysis of highresolution seismic profiles
collected over the shelf has shown several significant incised-valley
systems. However, some of these channels seems to be buried and/or not
connected with the most recent regressive wedge, which has been related
with the sea-level fall/lowstand that occurred during isotopic stage 2
(Hernández-Molina et al., 2000). The main erosive channels that
be related with the last glacial maximum occur on the inner and middle
but they are not identified farther seaward, probably because of
seismic coverage These channel infillings erode older Pleistocene
Pliocene regressive wedges, and are overlain by post-glacial
The study of backstepping wedges located above the isotopic stage 2 regressive wedges also gives information about post-glacial sea level changes (Roque, 1998). Our results suggests that the post-glacial transgression occurred in a step-like manner, as several transgressive parasequences related with periods of sea-level rise deceleration have been identified.
A period of regional coastal progradation probably occurred at the early stages of the post-glacial transgression. In relation with this progradational event, a period of fault movement is evidenced in our records. Later, a period of accelerated sea-level rise led to a rapid coastline migration and to the landward translation of depositional environments. The lower seafloor gradients on the shelf sectors located to east and to the west of Faro favoured the transgression in those settings, where depositional systems are characterised by coastal barriers, aggradational coastal plains and high-energy infralittoral deposits, especially to the west of the study area. The identification of terrace-like features to the east of the study area provides some indications of the positions reached by the coastline during the middle to late post-glacial transgression. In contrast, the high gradients of the shelf sector located in front of Faro conditioned reduced coastline translations and a moderate development of transgressive parasequences.
Finally, the internal architecture of the prograding wedge composing the Holocene Highstand Systems Tract reveals a complex history in terms of highfrequency sea-level change. Two main asymmetric cycles characterised by prolonged falls and rapid rises can be identified. These cycles seem to be modulated by higher frequency cycles. During the first major cycle, the existence of accommodation space permitted the preservation of progradational-aggradational packages or a sigmoid configuration. In contrast, the second and more recent major cycle is characterised by the dominance of progradational wedges, whereas short rises do not seem to have been registered.
The database was collected through several oceanographic surveys (Golca, Fado and Wadi Ana), jointly organized between the Universidade do Algarve and the Instituto Español de Oceanografía.
The research benefited from the following projects: Emerge (Odiana Program), PB-91-0622-C03/Golca and PB94-1090-CO3/Fado (Spanish Marine Science and Technology Program). The second author also benefited of a Post-Doctoral Research Grant (Reference SFRH/BPD/5616/2001) given by the Fundação para a Ciência e Tecnologia (FCT), Portugal. This study is part of the research project IGCP nº 464 entitled “Continental Shelves during the Last Glacial Cycle: Knowledge and Applications”.
Hernández-Molina, F.J., Somoza, L. and Lobo, F.J. (2000) Seismic stratigraphy of the Gulf of Cádiz continental shelf: a model for Late Quaternary very high-resolution sequence stratigraphy and response to sea-level fall, in Hunt, D., and Gawthorpe, R.L.G., eds., Sedimentary Responses to Forced Regressions: Geological Society Special Publications, 172, 329-361.
Roque, A.C. (1998) Análise morfosedimentar da sequência deposicional do Quaternário Superior da plataforma continental Algarvia entre Faro e a foz do Rio Guadiana. Dissertação, Univ. Lisboa, 221 pp.
MARINE ISOTOPE STAGE 5
TERRACES AND CORAL BIOHERMS AT LAS ANIMAS, BAJA CALIFORNIA SUR, MEXICO
Teresa De Diego-Forbis (1) Robert G. Douglas1 Enrique Nava Sanchez (2) Jay Banner (3) Lawrence Mack (3) Donn S. Gorsline (1)
(1) Department of Earth Sciences, University of Southern California, Los Angeles, CA, 90089-0740, USA; (2) Centro Interdisciplinario de Ciencias Marinas-Instituto Politecnico Nacional, La Paz, BCS, Mexico; (3) Department of Geological Sciences, University of Texas, Austin, Texas, USA
The Las Animas area is an open embayment located along
the western edge of Bahia La Paz, between Punta Coyote and San Juan de
la Costa about 50 km north of La Paz, Baja California Sur, Mexico. The
locale is a narrow coastal plain 1-3 km wide typically with low sea
cliffs along the shore cut by wave action into dissected terrace
deposits of Late Pleistocene age resting unconformably on the shallow
water-lagoonal San Isidro Formation of Late Miocene age. The deposits
vary in thickness from 0.5 up to 10 m laid down in pre-existing
channels and depressions in the San Isidro erosional surface. The
sequence begins with a basal conglomerate with oyster shells resting
unconformably on the eroded San Isidro, overlain by poorly bedded
molluscanrich bioclastic sands and coral rubble, beds of massive
Porites in life position, and coral-rhodolith sands and marls. Beach
sands and gravels and coastal dunes cap the sequence.
Samples of Porites californicus selected for U/Th dating (thermal ionization mass spectrometry method) are well-preserved aragonite (98-99%; confirmed by x-ray diffraction and scanning electron microscopy and by staining with cobalt nitrate), although some skeletal material has a thin (1-3mm) coating of silica, presumably deposited by ground water. Coral samples were broken up and cleaned prior to radiometric analysis.
Preliminary results yield U/Th ages of 137-208 ka but the corals have initial 234U values in excess of modern seawater values. This indicates opensystem behavior and uncertainty associated with the ages. Using the correction of Gallup et al. (1994) model dates of 123-125 ka were obtained for the upper samples and 131 ka for the middles samples from the massive Porites unit. If the model ages are accurate, this suggests that the corals grew during maximum sea level high stands of Marine Isotope Stage (MIS) 5e. U/Th ages for the base of the terrace unit are pending.
Filed relationships suggest that the terraces are cut by NE-SW trending normal faults with small displacement. Elevations at the top of the massive coral beds are 15-28 m above present-day sea level and the terraces dip gently seaward. Global sea level during MIS 5e was about 4 m above present-day sea level (McCulloch and Esat, 2000) and assuming coral growth reached sea level, the terraces have been uplifted 11-24 m (rate of 9-20 cm/ka). However, the distance to the paleoshore line and common subtidal to neritic mollusks suggest that the coral thickets lived several meters below their contemporary sea level, and so the total post-5e uplift rate may exceed 30 m (rate of 24 cm/ka). These uplift rates are significantly higher than rates measured on terraces at El Coyote (Sirkin et al., 1990) and in the Bahia Concepcion region (Ledesma and Johnson, 2001).
The area represents a narrow subtropical carbonate-dominated shelf during MIS 5e where limited coastal drainages delivered little terrigenous sediment and bioclastic formation dominated. The contemporary offshore extent of the terraces cannot be accurately defined but probably was no more than another 1-2 km, the width of the present shelf on this margin.
Gallup, C. D., Edwards, R. L. and Johnson, R. G., 1994, The timing of high sea levels over the past 200,000 years, Science, 263:796-800.
Ledesma-Vazquez, J. and Johnson, M. E., 2001, Miocene-Pleistocene tectonosedimentary evolution of Bahia Concepcion region, Baja California Sur, Mexico, Sedimentary Geology, 144:83-96
McCulloch, M. T. and Esat, T., 2000, The coral record of the last interglacial sea levels and sea surface temperatures, Chemical Geology, 169:107-129.
Sirkin, L., Szabo, B. J., Padilla-A, G., Pedrin-A., S. and Diaz-R., E., 1990, Uranium-series ages of marine terraces, La Paz Peninsula, Baja California Sur, Mexico, Coral Reefs, Springer Verlag, 9:25-30.
AND PROCESSES ACROSS THE SHELF AND UPPER SLOPE OF THE AQUITAINE MARGIN
(BAY OF BISCAY, FRANCE)
Jean-Claude Faugères Pierre Cirac
University Bordeaux I, DGO, UMR-CNRS « EPOC », Avenue des Facultés, 33405 Talence, France e-mail : firstname.lastname@example.org
The Aquitaine shelf, in the bay of Biscay, is a
storm-dominated shelf similar to the US Californian shelf. Its width
decreases from the north (120 km) where the Gironde river delivers a
significant amount of fine-grained sediments (up to 106 t/year),
towards the south (45 km) where today only minors rivers are present.
Terrigenous supply coming from the erosion of the Pyrenean Chain or the
Massif Central may have been very abundant during the Quaternary low
sea-level episods. Two major canyons, one in the mid part and the other
one in the very south of the continental margin, are major conduits for
the transfert of sediments towards the deep. During the last 2 decades,
numerous data – bathymetric data, swath mapping, side scan sonar, 3,5
kHz and high to very high resolution seismic lines, and box-, piston-
and vibro-cores were collected in order to determine 1-the modern
deposit distribution and processes of transfert and deposition, 2- the
geometry and evolution of the sediment wedge deposited during the last
climatic cycle, and the sea level control ; 3- the role of the canyons
and instability processes in the transfert of sediment across the shelf
The modern sediments (upper Holocene) consist in a thin veneer of sands (1 to 2 m thick) overlying coarse-grained deposits (Cirac et al., 2000). This sand sheet is shaped by various bedforms (furrows, sand patches, large dunes and ripples). The overall architecture is considered as the result of the stacking of several storm beds with material reworked from Pleistocene coarse-grained sediments. Sedimentary motion is low and toward the continent in the inner shelf as shown by a 14 year record (10 to 100 m for the sandy dunes) ; it seems seaward but has not been yet quantified in the deeper shelf, where it would be induced by the very high amplitude storms.
In the north and very south of the shelf, the Mio-Pliocene substratum suffers deformations that are associated with distensive or strike-slipe (?) faults. These structures seem to control the trend of the valleys and canyons incised into the substratum, and are associated with a fluvial erosional surface.
The soft sedimentary cover overlying the Mio-Pliocene substratum has a variable thickness decreasing north to south (20 m to 50m as an average) and from the outer to the inner shelf (i.e. 150 m to a few metres in the very south). It represents the last climatic cycle and is interpreted as a fourth order stratigraphical sequence. Three units have been distinguished in the north (Cirac et al., 1997):
1- regressive perched shelf low stand wedges and incised valley fill ; complex geometry of some valley infill suggest a stepped infill history with alternating phases of deposition and erosion (Lericolais et al., 2001);
2- early transgressive infills
3- outer shelf transgressive sand bodies and middle-inner shelf backstepping parasequences that suggest a stepped post-glacial sea level rise. In the southern outer shelf, five regressive parasequences bounded by erosional surfaces (fith order sequence) are observed in the regressive unit 1. However, the transgressive units are similar in the north and south of the median-inner shelf.
Most of the sediments that are transported into the deep margin is then delivered during the low sea level periods.
The 2 canyons present in the region play a different role in the transfert of sediment toward the deep. The canyon of Cap Ferret develops only down the lower continental slope and a network of convergent minor canyons and slope incisions. It mainly works during low sea level stands with coarse- to finegrained turbidites transported toward the rise and abyssal. Only very diluted fine-grained flows may be trapped there during high sea-level where hemipelagite are the predominant deposits with lower sedimentation rate (Crémer et al., 1999). The canyon of Capbreton, in the very south, has its head very closed to the cost line, and cut deeply into the shelf and continental slope with a meandering course (Cirac et al., 2001). Despite the absence of a major river directly connected with the head of the canyon, it is active during high sealevel stand. As recently demonstrated (Mulder et al., 2001), alongshore currents and very high storm-derived currents may transport sands into the head and shelf part of the canyon course, and induce turbidity currents along the canyon.
Deposit instability also favours the transfert of shelf and shelf break sediments toward the deep, in the form of chutes, slides and slumps in the vicinity and in the flanks of the canyons, especially in the south. There in the shelf break and upper slope, gravity-driven deposit deformation interactive with turbidity or contour current depositional processes are responsible for the settling of a large field of wavy bedforms that reflects a slow and complex process of sediment transfert (Faugères et al., in press).
OF THE SEA-LEVEL FLUTUATIONS ON THE EVOLUTION OF THE RIVER POTENGI
ESTUARY AND ADJACENT CONTINENTAL SHELF
Eugênio Pires Frazão (1,2,3) Helenice Vital (1,2,3,4)
(1)Departamento de Geologia, Universidade Federal do Rio Grande do Norte (UFRN), Natal – RN, 59072- 970, Brazil (e-mail: email@example.com) (2) Programa de Pós-Graduação e Pesquisa em Geodinâmica e Geofísica - PPGG - UFRN (3) PRH-ANP 22 (4) Pesquisador do CNPq
Holocene marine levels higher than the present one are
known on the brazilian coastline, mainly in the central, southeast and
southern regions of the country. Several authors have already presented
curves of the relative sea-level variation based on over 700 ages
achieved by radiocarbon, by using geological, biological and
prehistoric indicators (Suguio, 1999). Some authors, as Oliveira et
al., (1990); Bezerra et al., (1998) and Barreto et al., (2001) make
reference to the performance of erosion or retraction (transgression)
cicles and progradation (regression) to the relative sea-level
variation in the State Rio Grande do Norte. These authors support the
theory that in the Brazilian Northeast, the curve of Salvador (BA) is
taken as reference since it is based on over 50
datations of indicators found in an area of about 60 Km of the seashore.
On the coastline and inner continental shelf of the State of Rio Grande do Norte between the estuary of the Ceará-Mirim River, in the municipal district of Ceará-Mirim, and the Barreira do Inferno, in the municipal district of Pirangi, exist two beach sandstone stripes named “beachrocks” which were dated by Oliveira et al., (1990) respectively in aged the older beachrocks are closed to the continent - 6.250 a BP and the younger are more distant from the continent - 4.700 a BP; later Bezerra et al.,(1998) and Barreto et al., (2001) built curves this region (Fig. 01).
According to Frazão and Vital (in the printing press), bathimetric and sonographic studies are essencial instruments to identify the beach sandstones submerged in the inner continental shelf. Based on the sonographic study in the River Potengi estuary accomplished by Frazão and Vital (in the printing press), we can conclude that the River Potengi estuary didn’t low off in the same place where it is found nowadays, since on its mouth there is a stripe of beachrocks showing that, during their development, didn’t flow over there any river like the Potengi River.
To help in the identification of these beachrocks, it was used a rate of bands 7/4-5/3-4/2 of the sensor ETM+ of the Landsat 7, combined in RGB. The image was handled previously with the use of enhancement techniques and special filters in order to emphasize the visualized features.
Due to the absence of morphosedimentary and morphostratigraphic data of the coastal plain of Rio Grande do Norte near the River Potengi estuary, the sedimentation evolutive pattern is based on the integration of the absolute datation data in beachrocks, aeolic deposits and marine terraces.
The coastal plain of Rio Grande do Norte bear the River Potengi estuary, is presently on a transgressive phase, with field systems of recent coastline aeolic dunes (Fig. 02) and of active cliffs of the coastal plateau (Fig. 03) suffering a continuous erosive process, forming marine abrasive platforms on the deposits of the Group Barreiras and mangroves. At the same time, there is the fulfilling of the estuary systems and development of estuarine and tide channels.
BARRETO, A.M.F.; SUGUIO, K. & BEZERRA, F.H.R. 2001. Comparação das Curvas de Variação do Nível Relativo do Mar no Holoceno do Litoral Norte-Riograndense entre si e com outras Curvas do Brasil. In: VIII CONGRESSO DA ASSOCIAÇÃO BRASILEIRA DE ESTUDOS DO QUATERNÁRIO, Mariluz, Imbé-RS, 2001. Boletim de Resumos. Imbé, ABEQUA. p.106-108.
BEZERRA, F.H.R.; LIMA-FILHO, F.P.; AMARAL, R.F.; CALDAS, L.H.O. & COSTA-NETO, L.X. 1998. Holocene coastal tectonics in NE Brazil. In: STEWART, I.S. & VITA-FINZI, C. (eds) Coastal Tectonics. Geological Society, London, Special Publications, 146, 279-293. FRAZÃO, E.P. & VITAL, H. Estudo Batimétrico e Sonográfico do Estuário do Rio Potengi – RN. (in the printing press)
OLIVEIRA, M.I.M.; BAGNOLI, E.; FARIAS, C.C; NOGUEIRA, A.M.B. & SANTIAGO, M. 1990. Considerações sobre a geometria, petrografia, sedimentologia, diagênese e idade dos “beachrocks” do Rio Grande do Norte. In: XXXVI CONGRESSO BRASILEIRO DE GEOLOGIA. Natal, Anais, SBG. 2, p.621-634.
SUGUIO, K. 1999. Recent progress in Quaternary geology of Brazil. Episodes, 22: 217-220.
Fig. 01. Aerial view during the low tide two beachrock stripes, named beachrock 1 (BR-1) and beachrock 2 (BR-2) on the Meio beach.
Fig. 02. Recent active dune sussering under erosive process on the beach of Genipabú.
Fig. 03. Active Cliff located at Barreira do Inferno sussering under coastal erosion.
LATE PLEISTOCENE PALAEO-ENVIRONMENTAL HISTORY FROM THE GULF OF CARPENTARIA, AUSTRALIA: INTERPRETATION BASED ON FORAMINIFERA, OSTRACODA AND CHARALES
Adriana García Allan R. Chivas Sabine Holt
School of Geosciences. University of Wollongong. NSW, Australia. E-mail:firstname.lastname@example.org
The Gulf of Carpentaria, located in the northern part
of Australia is an epicontinental sea with maximum water depth of 70 m.
Australia's separation from Papua New Guinea by Torres Strait to the
is only 12 m deep, and the Arafura Sill connecting with the Indian
to the West is 53 m deep. During glacial times when the sea level
about 130 m, connection with the ocean was severed and a palaeo-lake
"Lake Carpentaria" developed in the basin. Six sediment cores ranging
six to fifteen m long where obtained, spanning the last 125 ka (Last
and two non-marine/marine transitions have been identified. A
approach based on foraminifers, ostracods, nannofossils, pollen and
and geochemistry is under development to produce an accurate
The results obtained for the upper six metres of the two longest cores (MD-31 and MD-32) are discussed. The results include the systematic analyses of the assemblages of calcareous microfossils (foraminifers, ostracods and charophytes), and the palaeo-environmental reconstruction based on those taxa. The analyses spans between the time of the last regression (~ 75 ka) up to the last transgression (~ 9.7 ka), including the Last Glacial Maximum time (~ 20 ka).
During the development of the palaeo-lake Carpentaria we obtained two different results in relation with the location of the cores. Core MD-31 located in the west of the basin, has a higher topographic position and has been therefore subjected to major fluctuations in lake level, changing from saline lake to freshwater lake to saline lake to a time of highly saline events within dry periods. Core MD-32, collected towards the east of the basin, is located in the deeper part of the basin, and therefore appears to always have had water, so we have a nice sequence of facies from estuarine environment to a saline lake disconnected from the ocean to a freshwater lake. These changes are evident in the palaeo-biota. Euryhaline taxa such as Ammonia sp., Leptocythere sp., Cyprideis sp. and Pistocythereis sp., were replaced by an association of Ammonia sp., Helenina sp., Cyprideis sp., and Ilyocypris sp., indicating that salinity diminished. The disconnection of the lake from the ocean, increased the freshwater input, and the biota changed to an assemblage of taxa of fresher- water affiliation represented by Ammonia tepida, Ilyocypris sp., Cyprinotus sp., Cypretta, Darwinula sp., together with charophytes Chara vulgaris, C. zeylanica and Lychnothamnus barbatus. Lamprothamnium sp., a euryhaline genus, is present in only one level, indicating fluctuating environment. After the last transgression, when the fully marine conditions were restored, the assemblages changed to a highly diverse fauna of foraminifers and ostracods of marine affiliation (including several species of Textularia, Bolivina, Asterorotalia, Pararotalia, Ammonia, Neonesida, Paranesidea, Cyteroptheron, Echinocythereis).
HIGH-RESOLUTION SEISMIC STRATIGRAPHY FROM THE SOUTHERN GALICIAN SHELF AND ITS CONNECTION WITH THE RÍAS, NW SPAIN.
García-Gil, S. Vilas, F. Ferrín, A.
R. Durán, R. Magariños, J. Iglesias, J.
Dpto. Geociencias Marinas, Facultad de Ciencias, Universidad Vigo, 36200-Vigo, Spain. email@example.com
The topographic grain of the western Iberian margin is
the result of Triassic rifting between Europe, Africa and North America
which preceded the opening of the north Atlantic during Jurassic-Early
Cretaceous. Metamorphic and plutonic rocks dominate along the coast
followed westwards by the ‘Galicia Interior Basin’ and the ‘Western
The Galician Shelf is segmented into small tectonic units, mostly by
dextral strike-slip faults ( WSWENE), roughly perpendicular to the
as well as N -S and NE-SW faults.
The study area (Fig. 1) includes the continental shelf from Miño estuary (41º 55’ N) up to Ría de Muros (42º 50’ N). The shelf in this region is narrow (30-50 km wide) with a poorly defined shelf-break that occurs at depths of 160- 180 m. North of 42º 30’ (Ría de Arousa) the shelf narrows and the shelf-break is clearly defined. This sector is characterized by the named Rías Baixas that are structurally controlled incised valleys, bounded by steep hills (horsts). In order to establish the geologic framework from southern Galician Shelf and its connection with the Rías Baixas, high-resolution seismic lines were acquired and interpreted covering an area of 3250 km2 approx. The profiles were recorded using a 4500 Joules EG&G multi-electrode Sparker (167 km, 1997 survey) and 100-300 Joules Uniboom EG&G 234 (850 km, 2001 survey). In addition to geophysical data a deep well (3538 m) PMB-1 drilled by ENIEPSA (1984) has been tied.
High-resolution seismic stratigraphy analysis has allowed us to recognize 8 stratigraphic units bounded by 6 major unconformity surfaces (Fig. 2). Facies and ages obtained from PMB-1 well have been tentatively correlated with the different seismic units. From oldest to youngest these would be: 1- Granite Basement (BG); 2 - Jurassic (J); 3 - Cretaceous (C); 4 - Upper Oligocene-Lower Miocene (T1); 5- Lower Miocene-Middle Miocene (T2); 6- Upper Miocene- Pliocene (T3); 7- Pleistocene (Q1); 8- Upper Pleistocene-Holocene (Q2). This interpretation conveys us to establish that the first stratigraphy record within the Rías would correspond to Miocene sediments overlaying the Palaeozoic basement. Three 3rd order Miocene sequences and two Quaternary (3rd and 4th order) are distinguished. Based on the Mesozoic-Cenozoic Cycle Chart (Haq et al., 1987) we have grouped and identified three 1st order Megacycles: I. LOWER ZUNI (LZ) – Jurassic; II. UPPER ZUNI (UZ)- Cretaceous; III. TEJAS – Tertiary-Quaternary. Tejas lies on the underlying (I and II) as an angular unconformity and has been mapped in detail showing its depocenter on the shelf close to Ría de Arousa. Tejas Megacycle in the Galician margin shows the TB1, TB2 and TB3 2nd order supercycles. The boundary between 3rd order cycles (3.8 and 3.9) and the Last Glacial Maximum (LGM) surface has been distinguished within TB3. The geological history of the Galician Shelf is highly complex, and it is documented in the sedimentary sequences, faults, folding and erosional horizons that resulted from rifting and spreading events, sea-level fluctuations, subsidence and the effects of climate changes.
*Contribution 263 of the EX-1 Research Group to REN2000-1102MAR, PGIDT00PXI30105PR,BT2000-0877 & PGIDT00MAR0103PR Spanish Projects.
Figure 1. Map of the Rías Baixas and Galician continental shelf showing locations of seismic reflection profiles. RSP=Sparker lines, L=Uniboom lines, Dots=Shipeck samples, PMB1=Pontevedra Marino B1 well.
Figure 2. Sparker seismic reflection profile (see Fig. 1 for location). BG= granite Basement, J=Jurassic, C=Cretaceous, T1-T2-T3=Tertiary, Q1=Pleistocene, Q2=Last Glacial Maximum Sequence.
PALEOENVIRONMENTAL INTERPRETATION OF VIBRACORES FROM THE INNER SHELF OFF THE ‘RIA DE AVEIRO’ (NORTHERN PORTUGAL)
R. Gonzalez J.M.A Dias F. Lobo I. Mendes
CIACOMAR-Universidade do Algarve, Avenida 16 de Junho s/n, 8700-311 Olhão, Portugal
Large parts of the Northern Portuguese inner shelf are
considered to be areas lacking in Holocene deposits, as the high energy
of the rising sea-level of the Atlantic Ocean erased lowstand and
transgressive deposits. As a consequence, evidence for the Holocene
sea-level rise is mostly limited to sparse geomorphological features,
such as paleo-terraces.
Estimates of Holocene sea-level changes show that the transgression reached the inner shelf only during the past 9000 years, rising at a rate with a rate of 0.01m per year at 6000 - 9000 years before present, and stabilising around 5000 to 3000 years ago, only shifting by a few meters around the present sea-level (Dias, 1987).
Twenty-two 3m long vibracores were taken at water depths between 18- 27m in an area of approximately 5x7 km off the Ria de Aveiro.
The top x decimetres of the cores was found to be dominated throughout the area by fining upward sand and gravel, containing a heterogeneous mixture of quartz sand, and a variety of lithoclasts (carbonates, schists, magmatic, and metamorphic rocks) ranging in size from sand to cobbles. Poor rounding of clasts and the ubiquitous presence of mica points at a not too far source. It can be speculated that this upper layer is modern and formed during storms, mixing the uppermost part of the sedimentary column, and later precipitating in form of a fining upward sequence as the storm energy waned.
The lower two thirds of cores are dominated by sand, composed almost essentially of quartz, as well as significant amounts of mica. Layers of very coarse sand to fine gravel-sized lithoclasts can be found in intervals. Where the contrast between finer and coarser sediments is high enough the cores show thick complex sequences of several cross-bedding hierarchies, from decimetre thick sheets, to millimetric laminated sand layers.
The top metre of cores in the central-eastern area closest to the modern shore-line is dominated by fine and very fine quartz sand with substantial amounts of silt and in some cases clay. Some horizons contain small branches and plant fragments. Many of these beds, and units below or above, show evidence for bioturbation. The most likely candidate as a source of fine-grained river sediments is the Vouga River, which nowadays deposits the bulk of its sediments into the Ria de Aveiro.
The top of these sediments underlying the modern gravel and sand sheet at a depth of 0.24-0.29 m revealed ages of 4890 ± 40 years. According to sealevel curves, this area of the shelf would have been already part of the inner shelf / infralittoral at this time.
It can be speculated that these fine-grained layers represent pro-deltaic deposits from the Vouga, possibly sheltered from the high-energy wave regime of the Atlantic by sand bodies (subtidal sand shoals or ridges), which were later eroded.
Dias, J.M.A. (1987): Dinâmica sedimentar e evolução recente da plataforma continental Portuguesa setentrional. PhD. Thesis, Univ. Lisbon, 384 pp.
Dias, J.A., Boski, T., Rodrigues, A. & Magalhães, F. (2000) – Coast line Evolution in Portugal since the Last Glacial Maximum until Present – A Synthesis. Marine Geology, 170:177-186.
INCREASED STORMINESS AT THE SUBBOREAL/SUBATLANTIC TRANSITION IN THE GALICIAN CONTINENTAL SHELF (NW SPAIN)
R. González-Álvarez (a), P.
Bernárdez (a), L.D. Pena (a), G. Francés (a), S.
García-Gil (a), F. Vilas (a), R. Prego (b)
(a) Dpto. de Geociencias Marinas y O.T., Facultad de Ciencias, Universidad de Vigo, 36200 Vigo, Spain (b) Grupo de Biogeoquímica Marina, Instituto de Investigaciones Marinas (CSIC), 36208 Vigo, Spain
Sedimentological (grain size, total and organic carbon,
and total nitrogen), micropaleontological and opal content analyses
were performed in a 96 cm gravity core (CGPL00-1) retrieved from the
outer Galician continental shelf (NW of Spain, 42º5’15.115’’N,
9º3’46.380’’W, 130.8 m water depth) in order to reconstruct the
hydrodynamic evolution during the last 3,000 years.
Grain size along the whole core presents a general decreasing trend from the bottom to the top but two well-differentiated sections can be observed throughout the core. The lower half (96-55 cm) consists mainly of glauconitic sand overlaying a basal interval of bioclastic gravel 2 cm thick. Internal laminations and thin sandy mud intervals were observed, although sometimes blurred by bioturbation. A muddy sand interval 8 cm thick separates the aforementioned sand from the green mud sediments recorded in the upper half of the core.
The complete section represents a fining upwards sequence embracing two smaller sequences. The lower one is a fining upwards sequence from bioclastic gravel to silty clay sediments located at 30 cm. The upper one is a coarsening upwards sequence marked by the decrease of clay abundance, and the increase of medium and fine silt, and, in a lower extent, of sand.
The chronological framework of the core is based on four accelerator mass spectrometry (AMS)-14C ages. The obtained age for a shell of Acanthocardia cf. aculeata (Linné, 1758) from the bioclastic gravel interval is 9033 cal. BC. The remaining three measurements were performed on planktonic foraminifera tests picked at 70, 60 and 26 cm. The obtained calibrated ages were 907 cal. BC, 898 cal. BC and 1399 AD, respectively.
According to the obtained ages, and mineralogical, sedimentological and micropaleontological features the whole sandy interval has been deposited in a short period. Such sand sediments have been deposited by recurrent storm ebb currents between fair-weather wave base and storm wave base. In agreement with this interpretation, the basal bioclastic gravel interval is constituted by reworked material deposited as a lag by the strongest storm influence. On the other hand, weaker currents at the end of a storm event deposited the sandy mud intercalations. According to the age model, the sharp sedimentary change observed at 47 cm took place between 885-756 cal. BC, coinciding with the Subboreal/Subatlantic transition (van Geel et al., 2001). This transition is characterised by a sharp rise of atmospheric D14C content caused by a sudden decline of solar activity (Kilian et al., 1995) leading to a strong shift from relatively continental (warm and dry) to a more oceanic climate regime (cool and wetter). The climate instability associated with the Subboreal/Subatlantic transition was linked to an intensification of mid-latitude storm tracks (van Geel et al., 2001).
During the Subatlantic period low energy processes permitted the sedimentation of mud on the outer Galician continental shelf. High organic carbon and opal content recorded throughout the mud interval reflects enhanced productivity caused by upwelling processes. Under current conditions fine sediments are resuspended and transported to the outer shelf during winter storms. Coarser sediments are transported southwards and inshore only by more violent storms coming from the West (Dias et al., 2002), starving the outer shelf of relatively coarse sediments.
Contribution 259 of the EX-1 group to REN2000-1102 MAR, PGIDT00MAR30103PR, and PGIDT00PXI30105PR projects.
Dias, J.M.A., Gonzalez, R., Garcia, C. and Diaz-del-Rio, V., (2002) Sediment distribution patterns on the Galicia-Minho continental shelf, Progress in Oceanography, 52, 215-231.
Kilian, M.R., van der Plitch, J. and van Geel, B., (1995), Dating raised bogs: new aspects of AMS 14C wiggle matching, a reservoir effect and climate change, Quaternary Science Reviews, 14, 959-966.
van Geel, B., Renssen, H. and van der Plicht, J., (2001) Evidence from the past: solar forcing of climate change by way of cosmic rays and/or by solar UV?, Proceedings of the Workshop on Ion-Aerosol-Cloud Interactions. J. Kirkby (Editor), CERN, Geneva.
THE LATE QUATERNARY PACIFIC MARGIN OF CANADA: INFLUENCE ON AMERICAS’
Hetherington, Renée (a,b,c)* Barrie, J. Vaughnb,(c) Reid, R.G.B.(d) MacLeod, R.(c)
(a)Department of Geography, University of Victoria, Victoria, BC, Canada, V8W 3N5 (b) School of Earth and Ocean Sciences, University of Victoria, BC, Canada, V8W 3N5 (c) Natural Resources Canada, Geological Survey of Canada, PO Box 6000, Sidney, BC, Canada, V8L 4B2 (d) Department of Biology, University of Victoria, Victoria, BC, Canada, V8W 3N5 *Corresponding author: firstname.lastname@example.org
The coastlines along Canada’s north Pacific continental
shelf were impacted by rapid changes in sea-level and climate during
the Late Quaternary, a result of crustal displacement, induced by the
weight of continental and alpine glaciers as they advanced and
retreated across the region. Consequently, the position of coastlines
changed, both substantially and swiftly; the degree and direction of
those changes were dependent on where coastlines were situated relative
to glacial ice. Many Late Quaternary coastlines are now submerged
beneath coastal waters. A few, however,
have been found above sea-level along the fringe of the Queen Charlotte
Islands (QCI) and the British Columbia (BC) mainland. Molluscs,
and published sub-bottom profiles, combined with geo-spatial
interpolation modeling are used to deduce sealevels, outline the
influence of glacially-induced crustal displacement, and reconstruct
the paleoenvironment of the northeast Pacific Late Quaternary
The complex pattern of crustal displacement and resultant local sea-level change has important implications to the region’s ability to support an early migrating coastal people. The “Coastal migration” hypothesis for the peopling of the Americas, implies that the first people’s of North and South America migrated down the Pacific coast, however no evidence dating earlier than 10,000 14C years BP (Dixon, 2001) has yet been discovered along the northeast Pacific coast of North America. The coastal migration hypothesis presumes that the Queen Charlotte Islands (QCI) / Hecate Strait region, along Canada’s west coast had a suitable climate and the right combination of natural resources to make habitation possible. However, the complexity of sea-level change, including the influence of isostatic rebound and glacial advance and retreat, has made paleoenvironmental reconstruction difficult.
Our research indicates that after ~14,000 14C years BP, and prior to 12,640 +/- 50 14C years BP (Archer, 1998), glacial ice began retreating from Dixon Entrance north of the QCI. Humans were prevented from navigating northern QCI and Dixon Entrance until sometime after 14,000 14C years BP due to presence of ice. Prior to this any migrants would have skirted the outer QCI. By 12,640 +/- 50 14C years BP (Archer, 1998), Dixon Entrance was ice-free, providing clear navigation east to the BC mainland where edible molluscs colonized a productive gravel and cobble beach. Crustal uplift persisted in Hecate Strait between 12,750 and 8,750 14C years BP, suggesting a fixed icefront and continued ice presence on the BC mainland until at least 10,000 14C years BP (Clague, 1981; Clague and James, 2002). Lowered eustatic sea-level combined with crustal uplift permitted terrestrial conditions to develop on two emergent coastal plains; one extended eastward from QCI, and the other developed in QC Sound, extending northward from Vancouver Island. A resulting landbridge connected the BC mainland to the QCI, facilitating faunal, floral and potential human land-based migration.
The presence of intertidal molluscs in Late Quaternary sediments indicates not only that the ice was gone (Conway et al., 1999), but also that an accessible food source was present. Early coastal habitation sites would likely have been located in close proximity to resource-rich shorelines and estuaries. Edible molluscs, quick to recolonize once sedimentation rates and sea-surface temperatures were conducive, and pelagic marine fish such as Clupea harengus pallasi, and potentially other edible fish and sea mammals were available to provide subsistence resources for early inhabitants in Hecate Strait by at least ~13,210 14C years BP. In all probability caribou, brown and to a less extent black bear, and other beach-combing mammals such as ringed seal and otters, along with gulls and crows, scavenged the beach (Fedje, 1996; Fedje et al., 1996; Heaton et al., 1996). Between 10,890 14C years BP and 10,250 14C years BP, cooler sea-surface temperatures reduced edible molluscan biomass (Hetherington and Reid, 2002 submitted) in the “Hecate Sea”, potentially requiring early peoples to migrate greater distances to collect coastal resources and increase their reliance on land-based resources.
Numerous resource-rich coastal zones and estuaries in Hecate Strait and QC Sound have been cored and dated, and although these would make excellent potential early archaeological site locations, they are now drowned and difficult to access. The intersection between paleocoastlines obtained from paleogeographic reconstruction maps and present-day subaerial topography provides the location of potential subaerially exposed early archaeological sites. Paleocoastlines of particular interest lie along the west coast of QCI, where early migrants likely first travelled and the westernmost sites along the BC mainland, where the effects of glacial ice are reduced.
Archer, D.J.W., 1998. Early Holocene Landscapes on the north coast of B.C. [abs.], 31st annual meeting Canadian Archaeological Association, Victoria, BC, p. 34.
Clague, J.J., 1981. Late Quaternary geology and geochronology of British Columbia, Part 2: Summary and discussion of radiocarbon-dated Quaternary history, Geological Survey of Canada, Paper 80-35, 41 pp.
Clague, J.J. and James, T.S., 2002. History and isostatic effects of the last ice sheet in southern British Columbia, Quaternary Science Reviews 21, p. 71-87.
Conway H., Hall, B.L., Denton, G.H., Gades, A.M., and Waddington, E.D. ,1999. Past and future grounding-line retreat of the West Antarctic Ice Sheet, Science 286, p. 280-283.
Dixon, E.J., 2001. Human colonization of the Americas: Timing, technology and process: Quaternary Science Reviews 20, p. 277-299.
Fedje, D.W., 1996. Early Holocene archaeology at Richardson Island, Haida Gwaii. Paper presented at the 29th Annual Meeting of the Canadian Archaeological Association, Halifax.
Fedje, D.W., McSporran, J.B., and Mason, A.R., 1996. Early Holocene Archaeology and Paleoecology at the Arrow Creek sites in Gwaii Haanas, Arctic Anthropology 33, p. 116-142.
Heaton, T.H., Talbot, S.L., and Shields, G.F., 1996. An ice age refugium for large mammals in the Alexander Archipelago, southeastern Alaska, Quaternary Research 46, p. 186-192.
Hetherington, R. and Reid, R.G.B., 2002. Molluscan insights into the marine ecology and changing climate of the Late Pleistocene – Early Holocene northeastern Pacific, submitted to Canadian Journal of Zoology, 2002.
THE HOLOCENE MARINE INGRESSION IN THE LOWER URUGUAY RIVER
Martin Iriondo Daniela Kröhling
CONICET – Facultad de Ing. y Cs. Hídricas, Univ. Nac. del Litoral; CC 217 (3000) Santa Fe. Argentina.
The Uruguay is one of the large rivers in South
its basin covers an area of 365,000 km©˜ in S Brazil, W Uruguay
NE Argentina. The lower reach of the river underwent ingressions of the
Atlantic ocean during periods of high sea levels. Coastal deposits of
Holocene and Eemian ingressions are registered up to the city of
Concepción del Uruguay (32°30´ lat.S; 58°20´
long.W), located 400 km upstream of the present sea border.
The river joints the Paraná river at the rear part of the Río de la Plata, forming a littoral complex built by the Paraná during the Holocene (Iriondo and Scotta, 1979). Besides that system, recent investigations show that several littoral units are directly linked to the Uruguay river. A 20 km long marine terrace is preserved at the latitude of 32°50´S at both sides of the river. The surface of the terrace has an altitude of 10 m.a.s.l.; it is covered by a thin carpet of alluvial deposits of upper Pleistocene/Holocene age. Provisorily, an Eemian age is attributed to the terrace. In the lower segment, the river fills a large depression 85 km long and 5 to 12 km wide.
The highest level of the Holocene ingression formed there beach ridges at the mouth of the Río Negro (33°25´ lat.S) and along the Uruguayan coast to the south; the beach ridges form barriers closing the outlets of a series of small rivers. At the right bank the sand drift formed a 25 km long lagoon, into which flowed the two major rivers of the area (Gualeguaychú and Tala). North of the Río Negro, the left bank of the gulf underwent a dominant wave erosion. A raised plataform with a notch at the back was described in the Fray Bentos area (Iriondo and Kröhling, in press), where the notch is 3 m deep, and 1.5 m high, with a mean altitude of 3 m above present sea level in the cliff. Upstream of the gulf the river developed a 65 km long estuary, in which a tide plain was formed, probably during the upper Holocene. Minor estuaries join the major system at the confluences of tributaries.
At present this littoral system is subject to a fluvial dynamics. The tide plain is now transformed in a delta system with distributary pattern in which the channels develop lateral levees and produce accretion in several areas forming new islands. The lowermost part of the river is wide (6 to 7.5 km) and shallow (between 1 and 3 m) subject to the influence of tides and southeastern winds. A particular feature in that sector is the existence of a very narrow (400 to 800 m) and deep channel, with depths from 10 to 18 m.
A 1:100,000 scale map of the Holocene ingression was produced during the study of the area.
Iriondo, M. and E. Scotta (1979). The evolution of the Paraná River delta. In: K. Sugio, M. Fairchild, L. Martin and J. Flexor (eds.): Proceedings of the 1978 International Symposium on Coastal Evolution in the Quaternary, INQUA, pp. 405-418. Sao Paulo.
Iriondo, M. and D. Kröhling (in press). Cambios ambientales en la cuenca del Uruguay (desde el Presente hasta dos millones de años atrás). Colección Ciencia y Técnica, Universidad Nacional del Litoral; 350 pp.
MAIN STAGES OF THE SOUTHERN BALTIC DEVELOPMENT
Regina Kramarska Szymon Uscinowicz Joanna Zachowicz
Polish Geological Institute, Branch of Marine Geology
Deglaciation of the Southern Baltic started 14,000
with the retreat of the ice sheet from positions at the Gardno End
moraines (Uscinowicz 1999). During the retreat of the ice sheet across
the Southern Baltic area local marginal lakes were formed. Between c.
12,8 ka BP Bornholm Basin and Gdansk Basin ice margin lakes became
connected. The total thickness of the Late Pleistocene, varved,
and homogeneous deposit locally with dropstones is about 10 m in the
central parts of the deepwater basins. To the north the Baltic Ice Lake
was limited by the retreating ice sheet. Melt waters were directed
westward through the Danish Straits. Further retreat of the ice sheet
a new route for the melt waters through the lowlands of central Sweden,
and resulted in fast draining of the Baltic Ice Lake. Retreat of the
Baltic Ice Lake marked itself in some places by a prograding sandy
structures. This stage of the Baltic Sea ended c. 10,300 years BP
The connection with the ocean across the central Sweden and eustatic ocean level rise caused an inflow of salty water and transgression. This events at the break of Pleistocene and Holocene begun the new stage in the Baltic Sea evolution — the Yoldia Sea stage. Transgression is marked by erosional top of Baltic Ice Lake deposits. Traces of erosion found, in general, between 60 and 45 m isobaths. Yoldia Sea greyish brown clay have been retained only in the deepest parts of the basins (Kramarska et al. 1995).
The glacioisostatic uplift of Scandinavia at a higher rate than the eustatic ocean level rise, close the connection of the Yoldia Sea with the ocean at the Late Preboreal. The reservoir transformed c. 9.7 ka BP into a freshwater lake— the Ancylus Lake —next stage of the Baltic Sea. Closing of the connection with the ocean did’t stop transgression in the southern part of the Baltic. The transgression was due to higher uplift rates in the north than in the south. Within the deepwater basins the greyish-brown Yoldia deposits gradually pass into light grey clays of the Ancylus Lake. They contain numerous dots and laminations of ferrous sulphides. The Ancylus Lake clays have been retained only at depths exceeding 65 m. Ancylus Lake transgression took up areas of bottom up to the present 30-28 m depth. Places lying shallower than 25 m were still land.
At the end of Boreal period, due to the eustatic ocean level rise, salt water started to flow into the Baltic through the Danish Straits. Between the Ancylus Lake and the stage of Litorina Sea a transient phase called the Mastogloia Sea is distinguished and dated to the Late Boreal. Accretion of muddy deposits, started in deep water basins at the Late Boreal (Mastogloia stage), continues without break through Atlantic period, during the Litorina Sea stage. On the edges of the deep-water basins the beginning of the Litorina transgression is marked by erosion caused by the inflow of salt water, and to the beginnings of permanent haline stratification. Transgression of the Litorina Sea took up these parts of the present shallow water area which from the beginning of the Late Glacial were a land. Transgression was accompanied by erosional processes. Pleistocene surface is often covered by sandy gravely deposits which form an erosional pavement. The Litorina transgression ended about 5,0-4,5 ka BP attaining a level similar to the present one. After the sea level became stabilized in the Early Subboreal, the stage of the contemporary Baltic, the Post–Litorina Sea began. The thickness of Litorina and Post–litorina muddy deposits reaches 4–5 m. Litorina and Post-Litorina Sea sand cover is of small thickness, only rarely does it exceed 2 m.
Björck S., 1995: A review of the history of the Baltic Sea, 13.0-8.0 ka BP. Quaternary International, Vol. 27: 19-40.
Kramarska R., Uscinowicz Sz., Zachowicz J., 1995: Quaternary. in: J., E., Mojski et al. (eds.). Geological Atlas of the Southern Baltic. Polish Geological Institute, Sopot-Warszawa: 22-30.
Uscinowicz Sz. 1999: Southern Baltic area during the last deglaciation. Geological Quarterly 43 (2): 137-148.
SHALLOW SEISMIC REFLECTORS AND UPPER QUATERNARY SEA LEVEL CHANGES IN THE NORTHERN INNER SHELF OF THE STATE OF SÃO PAULO, SOUTHEASTERN BRAZIL
Andréa França Lima (1) Luis Antonio
Pereira de Souza (2) Michel Michaelovitch de Mahiques
(1) Institute of Oceanography of the University of São Paulo 05508-900 Praça do Oceanográfico, 191 São Paulo, SP, BRAZIL E-mail: email@example.com Institute of Technological Research of São Paulo
In Southeastern Brazil, at least two Quaternary sea
level rise events can be recognised in the coastal region. One, named
Cananéia, presented its maximum at approximately 120,000 yr. BP
and reached a maximum of 8.0 m above the present sea level. The other,
named Santos, had its maximum at 5,100 yr. BP and reached a maximum of
5.0 m above the present sea level. These events were separated by a
regressive event, correlated to the Würm- Wisconsin (maximum at
18,000-yr. BP), when the sea level dropped approximately 130 meters
below the level present on the Southeastern Brazilian margin. According
to the Sequence Stratigraphy it corresponds to a Type 1 discordance. On
the Southeastern Brazilian coastal plains, despite the existence of
several Quaternary sea-level curves
that are based on shellmidden ("sambaquis") and Vermetidae positions,
especially for the last 7,000 years, little information is available on
the buried deposits of coastal submerged areas.
In a restricted area of the northern inner shelf of the state of São Paulo (Southeastern Brazil), seismic sequences may be recognised that can be correlated to relative sea level change events and interpreted in terms of models of Quaternary coastal change. The analysis of seismic profiles reveals the existence of four units, separated by three regionally correlated reflectors. The study area comprises Flamengo and Palmas bays, two small and shallow (0-20 m) semi-enclosed marine environments, that are connected by a strait, 35 m deep and 500 m wide, called Boqueirão da Ilha Anchieta.
The reflector R1 defines the uppermost sequence (Unit U1). It is fairly flat and it exhibits conspiquous changes in internal reflection pattern, running parallel in the outer part of the bay and being transparent in the inner part. A core collected in the inner part of the study area presents a sharp contact, situated at 360 cm depth, which separates an uppermost dark grey sandy mud lithofacies, rich in organic carbon, and with variable amounts of plant debris and calcium carbonate, from lowermost light grey quartzose sand facies, very poor in organic carbon and calcium carbonate. These basal sediments present bioturbations as a major sedimentary structure. These structures are believed to be formed by Callichirus major, which is a very common crustacean that lives in the inter-tidal zone of sandy shores. A C14 dating provided an age of 7470 ± 60-yr. BP for a shell collected immediately below the contact between the two lithofacies.
In most of Boqueirão area U1 as well as deeper units are completely eroded. The second unit (Unit U2) overlies an irregular erosive reflector (R2). Cut-and-fill, prograding reflectors, chaotic structures and dipping internal reflectors characterise the basal part of the unit. Its topmost part is mainly characterised by transparent and parallel reflection patterns. In the inner parts of the bay, R2 and R3 onlap the acoustic basement.
Reflector R2 could be interpreted as an erosional surface developed after the maximum of the Cananéia Transgression up to the time of the maximum late Pleistocene regression, which occurred at 18,000 yr. B.P. Thus, Unit U2 probably corresponds to late Pleistocene alluvial and coastal plain sediments developed during isotopic stages 4 to 2. The several channels observed in U2 can be correlated to the residual deposits formed by the coarse fraction which is redeposited over the wave ravinement surface generated during the marine transgression.
Reflector R3 separates the deepest sedimentary units (U3 and U4) and its non erosive shape characterises it. Unit U3 and the uppermost sequence of U4 present a high variability of internal reflection patterns.
According to the evolutionary model for the coast of the State of São Paulo, we can interpret units U3 and U4 as representing the Pleistocene sequence correlated to the Cananéia deposits or even to older sequences. R3 could represent either an erosional surface, as an abrupt change in the sedimentation pattern, as for R1.
The analysis of Boqueirão Strait profiles reveals the occurrence of two important erosional events, indicated by the shape of the present bottom surface and by reflector R3. The reflector R3 shows a pattern that is similar to the present surface bottom. Thus, we may assume that the bottom dynamic processes that were responsible for the development of R3 were the same as those, which maintain the bottom shape of the Boqueirão as it is at present. Admitting that the scour of the Boqueirão is correlated to high sea level, we can assume that R3 was developed during a high sea level period, possibly correlated to the maximum of the Cananéia event (ca. 120,000 yr. B.P.), when the sea level reached up to 8 meters above the present sea level.
Despite their absence from the emerged coastal deposits, at least two sedimentary units can be identified below reflector R3 (U4 and underlying deposits) and above the acoustic basement. Assuming that U4 corresponds to the transgressive deposits correlated to the Cananéia event, we can associate the lowermost sedimentary sequences to older transgressive-regressive deposits. In the Rio Grande do Sul coastal plain (southward of the study area), two other Pleistocene sedimentary sequences are found, which were associated with isotopic stages 8 and 10 or 6 and 8. Thus, we may correlate the lowermost deposits of the study area to one of these sequences.
POST-GLACIAL STEP-LIKE SEA LEVEL CHANGES IN THE WESTERN PACIFIC: SIGNIFICANCE OF THE RAPID MELT-WATER PULSES (1A, 1B, 1C, AND 1D)
J. Paul Liu John D. Milliman
School of Marine Science, College of William & Mary, Gloucester Pt. VA, 23062, USA E-mail: firstname.lastname@example.org
The Yellow Sea (YS) and East China Sea (ECS), an end
member of modern epicontinental seas, are the largest shallow marginal
shelf seas in the western Pacific Ocean, together with the Sunda shelf
in the South China Sea (SCS). They are located on the tectonically
stable margins, and represent the typical far-field sites where have
less ice-induced deformation in contrast with the formerly glaciated
regions (near-field sites). Because of their shallow depths, low
gradient and large sediment input from the adjacent continents, they
have been more likely to preserve more detailed post-LGM sea-level
transgressed and climate changed events. The post-glacial
hydro-isostatic effects are also less due to the huge nearshore
sediment accumulation from Yangtze and Yellow Rivers.
The newly defined sea-level curve (Fig. 1) based on the data from the YS, ECS, Sunda [Hanebuth et al., 2000] and Bonaparte(2) shelves shows that post- LGM sea level rose through a series of rapid flooding events (50-100 mm/y), separated by a series of slow rises (2-6 mm/y). The early post-LGM appears to have been marked by two separate periods (19.1-18.8 and 18-17.6 ka cal BP) when sea level rose 7- to 9-m from –120 m to –110m then –102 m [Hanebuth et al., 2000; Yokoyama et al., 2000], which we term melt water pulse–2a (mwp- 2a) and mwp-2b. By about 15 ka cal BP, sea level had reached about –100 m, and seawater began to enter the YS, ECS and SCS. A rapid rise during MWP- 1A occurred between 14.3 –14.1 ka cal BP, when sea level jumped from –94 m to –74 m (~100 mm/yr). At the end of this flooding event, the sea water had reached the southern edge of the north YS, after which sea level rose again slowly (6 mm/yr) from –72 m to –60 m. Beginning about 11.6 ka, sea level again jumped, from –60 m to –42 m at 11.4 ka (MWP-1B), resulting in a rapid westward flooding (~90 mm/yr) of the NYS and initial entrance into the Bohai Sea. Sea-level rise then again stagnated (between -42m to -36 m) for about 1.9 k yrs. Starting about 9.5 ka, the sea-level advanced again from –36m to –16 m at 9.0 ka (MWP-1C: > 40 mm/yr), after which most of BS, YS, and ECS had been submerged. Then another slowdown occurred between 9.0-8.0 ka when sea level rose from -16m to –10m. The last major transgression happened between 8.0 and 7.2 ka (MWP-1D), and resulted in Holocene highstand of at least +2 to 4 m along most of Chinese and Korean coastlines. Sea level during these rapid rise intervals may have back-stepped landward by as much as 500 m/yr horizontally, whereas during the long periods of stable or slowly rising sea level, shoreline regression may have been only a few m/y.
Depositional sequence structures on this Yellow Sea shelf show strong landward horizontal changes, instead of the vertical changes. The first major Yellow River deltaic system was developed in the north YS together with the decelerated sea-level rise after MWP-1B event (Liu et al, 2002), and the intensified summer monsoon and subsequent increased river discharge at about 11 ka. The second subaqueous delta was built in the south YS between 9-7ka during another slackened sea level after MWP-1C. Then modern subaqueous and subaerial deltas in the west Bahai Gulf have been formed during the sea-level highstand after the last jump of MWP-1D.
Hanebuth T., K. Stattegger, and P.M., Grootes, (2000). Rapid Flooding of the Sunda Shelf: A Late-Glacial Sea-Lvel Record, Science, 288, 1033-1035.
Liu, J.P., Milliman, J.D., and Gao, S. (2002), The Shandong mud wedge and post-glacial sediment accumulation in the Yellow Sea. Geo-Marine Letters, 21: 212-218.
Yokoyama, Y., Lambeck, K., Deckker, P.D., Johnston, P. and Fifield, L.K. (2000) Timing of the Last Glacial Maximum from observed sea-level minima. Nature 406: 713-716.
Figure 1: A proposed western Pacific sea-level curve derived from East China Sea, Yellow Sea, Sunda shelf and Australian data. Depth ranges for intertidal and subtidal indicators are assumed to be 5 m, and depth ranges for shallow marine indicators are 20 m. Most 14C dates are AMS-derived and have been converted to calendar years using the program of Calib4.3.
CONTRASTING STYLES OF
HOLOCENE HIGHSTAND DEPOSITION ON THE
GUADIANA SHELF, GULF OF CÁDIZ, SOUTHWEST IBERIAN PENINSULA
Lobo, F.J.(1) González, R.(1) Dias, J.M.A.(1) Hernández-Molina, F.J.(2) Díaz del Río, V.(3) Fernández-Salas, L.M.(3) Mendes, I.(1)
(1) CIACOMAR-Univ. Algarve, Avenida 16 de Junho s/n, 8700-311 Olhão, Portugal (2) Dpto Geociencias Marinas y Ordenación del Territorio, Univ. Vigo, 36200 Vigo, Spain (3) Instituto Español de Oceanografía (IEO), Puerto Pesquero s/n, 29640 Fuengirola, Spain
The Holocene highstand sedimentation is relatively well
known in a sector of the Gulf of Cádiz continental shelf (Nelson
et al., 1999), e.g. southwards of the Guadalquivir river. However,
previous stratigraphic studies of the shelf sector influenced by the
Guadiana river have mainly focussed on its late Quaternary evolution
(Hernández-Molina et al., 2000, Lobo et al., 2002), or on the
late Pleistocene depositional sequence (Roque, 1998). An extensive grid
of high-resolution seismic profiling collected in several oceanographic
surveys (Golca 93, Fado
9611 and Wadi Ana 2000) has been used to characterise recent highstand
sedimentation patterns in the shelf sector adjacent to the Guadiana
The study area includes the eastern Algarvian shelf (southern Portugal)
the Spanish shelf located between the Guadiana and Guadalquivir river
In terms of Holocene highstand sedimentation, three main depositional environments have been recognised:
1) Inner shelf prodeltaic wedges. They are highly reflective deposits which show moderate thickness and develop in front of the river mouths, the most significant of them being the Guadiana deposit. They can be considered as wave-dominated deltas, whose moderate development could be related to a sand supply only significant during flooding events and to an active wave regime, which prevents from significant aggradation.
2) The Faro-Tavira infralittoral prograding wedge. It could be considered the equivalent of inner shelf prodeltaic wedges in a sector where fluvial supply is minimal. It presents a complex internal architecture, as eastwards of Faro is characterised by lower sigmoid facies evolving upwards to oblique tangential facies. The most complete record of its internal stratigraphy is identified westwards of Faro, where numerous minor scale progradational/aggradational events are recognised. Their complex internal architecture suggests that these deposits are highly sensitive to high frequency Holocene sea-level changes.
3) The middle to outer shelf muddy deposit. An aggradational deposit with laterally variable thickness covers wide extensions of the middle to outer shelf in the study area. Its transparent configuration suggests a dominant muddy composition with intercalations of coarse-grained sediments. This significant deposits seems to have been constructed from the fine-grained fluvial supply coming from the Guadiana river and to minor extent from other smaller rivers. The influence of the south-east moving Atlantic Inflow on shelf sedimentation is evident, as maximum depocenters are deflected in that direction. However, the identification of significant depocenters westwards of the Guadiana river suggest that current reversal may take place, probably in relation with seasonal changes.
The database was collected through several oceanographic surveys (Golca, Fado and Wadi Ana), jointly organized between the Universidade do Algarve and the Instituto Español de Oceanografía. The research benefited from the following projects: Emerge (Odiana Program), PB-91-0622-C03/Golca and PB94-1090-CO3/Fado (Spanish Marine Science and Technology Program). The first author also benefited of a Post-Doctoral Research Grant (Reference SFRH/BPD/5616/2001) given by the Fundação para a Ciência e Tecnologia (FCT), Portugal. This study is part of the research project IGCP nº 464 entitled “Continental Shelves during the Last Glacial Cycle: Knowledge and Applications”.
Hernández-Molina, F.J., Somoza, L. and Lobo, F.J. (2000) Seismic stratigraphy of the Gulf of Cádiz continental shelf: a model for Late Quaternary very high-resolution sequence stratigraphy and response to sea-level fall, in Hunt, D., and Gawthorpe, R.L.G., eds., Sedimentary Responses to Forced Regressions: Geological Society Special Publications, 172, 329-361.
Lobo, F.J., Hernández-Molina, F.J., Somoza, L., Díaz del Río, V. and Dias, J.M.A. (2002) Stratigraphic evidence of an upper Pleistocene TST to HST complex on the Gulf of Cadiz continental shelf (southwest Iberian Peninsula), Geo-Marine Letters, DOI 10.1007/s00367-002-0103-0.
Nelson, C.H., Baraza, J., Maldonado, A., Rodero, J., Escutia, C.,and Barber Jr., J.H. (1999) Influence of the Atlantic inflow and Mediterranean outflow currents on Late Quaternary sedimentary facies of the Gulf of Cadiz continental margin, Marine Geology, 155, 99-129.
Roque, A.C. (1998) Análise morfosedimentar da sequência deposicional do Quaternário Superior da plataforma continental Algarvia entre Faro e a foz do Rio Guadiana. Dissertação, Univ. Lisboa, 221 pp.
USE OF GEOGRAPHIC INFORMATION SYSTEMS (GIS) TO MANAGE MULTI-SOURCE DATA ON A COMPLEX SHELF ENVIRONMENT: APPLICATION TO PONTINE ISLANDS (TYRRHENIAN SEA)
Department of Earth Science, University of Rome “La Sapienza”, Italy
Sedimentary dynamics on continental shelves can be
studied with a number of different techniques, such as geophysical
prospections (side scan sonar, high resolution reflection seismic,
multibeam), seafloor sampling (dredge, grab, coring), in situ
investigations (ROV, divers). When sedimentation pattern is complex,
with frequent lateral changes, the amount and complexity of data can be
very high. In this case, the use of Geographic Information Systems
(GIS) will be useful, up to indispensable, to manage the multi-source
information on a geographical base.
An experience of the use of a GIS system was performed in the Pontine Islands continental shelf where morphoacoustic, sedimentological, seismostratigraphic, paleontological and petrographical studies are still in progress, to realise a geological map of the marine areas.
The studied shelf surrounds a group of volcanic islands and is characterised by complex morphology, quite steep seafloor, shelf-break at 100- 150 m of water depth, frequent rock outcrops; sedimentation is almost exclusively intrabasinal, with a prevailing biogenic component. The whole area is characterised by short-range lateral changes in sediment size and components due to local hydrodynamics, morphology and proximity with rock outcrops. GIS technology was used in all steps of the research, from survey planning, to data analysis, to interpretation of sedimentary dynamics, to presentation of the data. The system allowed an integrated management of raster images, vectorial and alphanumeric data on a georeferenced environment. The data used are: side scan sonar records and literature raster images; batymethric and navigation vectorial data; grab, cores, dredges, ROV videos and diver sampling alphanumeric informations.
During survey planning and execution, a digital database of existing data was realised, both for literature informations (digitizing calibrated and georeferenced maps) and data previously collected and available for the study.
Data integration with other base maps, as bathymetric-morphoacousticsedimentological maps, allows a quick recognition and selection of less investigated or more interesting areas, with an automated computing of point coordinates and length of ship course; for this purpose it is necessary to refer all the data to the same geodetic system: as new data will be positioned with GPS system, the referenced system used was UTM WGS84.
For data analysis, a multilayer map has been created yelding the integration of data of different nature. For example, side scan sonar and sedimentological-ROV data integration yields to groundtruthing the relationship between sonar facies and textural-sedimentological properties of sediments, as well as, side scan sonar and bathymetric data integration yields to discriminate between morphological contribute and seafloor roughness contribute to backscatter intensity. Moreover the alphanumeric data underwent statistical analysis (i.e. correlation matrix and multivariate analysis) to highlight pattern, trend, peculiar situation. The alphanumeric data were used to produce thematic maps of sedimentologic, minero-petrographic and paleontologic results. Point Range Varying Size maps were used to interpret the sand-gravel compositional analysis results to highlight the geographic distribution and relative quantity of the organic (calcareous algae, bryozoa, planktonic and benthonic forams etc.) and terrigenous components (k-feldspar, glauconite, volcanic glass, rock fragments, mica etc. Pie Chart maps were used to represent different textural classes of sediments, in order to correlate these data with side scan sonar interpretation and minero-paleontologic results.
During data interpretation the availability of different kind of data allowed an integrated interpretation of the morphology, sedimentology and ecology of the different areas. The possibility to easily correlate textural or main component characters of sediment with ROV or side scan images gave an invaluable interpretative tool, the literature maps can be compared with trend derived from newly acquired data, alphanumeric data pertaining to sediment characters can be cross-correlated with seafloor slope and depth.
MID-LATITUDE CARBONATE SEDIMENTATION ON A VOLCANIC ISLAND SHELF (PONTINE ISLANDS, TYRRHENIAN SEA)
E. Martorelli* F.L.Chiocci* G. Civitelli* C.
Chimenz° G. Ventura^ C. Altobelli˙ A. Balocco˙ A. Bosman* L.
Cassata˙ M. Raspagliosi˙ *
Dept. of Earth Sciences, University of Rome “La Sapienza” ° Dept. of Animal and Human Biology, University of Rome “La Sapienza”; ^ Geological Survey of Italy, Rome ˙University of Rome “La Sapienza”
Mid-latitude continental shelves are usually
characterized by terrigenous deposits whereas carbonate sedimentation
is relatively uncommon. However if sediment supply from the continent
is low, such as in islands shelves or submarine banks, carbonate
sediment may become predominant; due to the uneven distribution of the
controlling factors, complex sedimentation patterns characterize these
areas. Pontine Islands, located 22 km offshore mainland (41° N
Latitude, Central Tyrrhenian Sea, Italy), have a narrow, steep and
morphologically complex continental shelf, frequently punctuated by
rock outcrops. In this area since 1997 a research project for submarine
geological mapping purposes, funded by the Geological Survey of Italy,
is ongoing. A large amount of different kind of data was collected
(more then 250 km2 of side scan sonar records, 700 km of high
resolution seismic profiles, over 240 grab samples, 80 rock samples and
68 ROV films plus multibeam, gravity cores) in order to reconstruct
through a multidisciplinary approach the sediment distribution and
shelf evolution during Late Quaternary. The research consists in a
morphoacoustic, seismostratigrapic, sedimentological, paleontological,
minero-petrographical characterization of the continental shelf
deposits and rock outcrops. Sediments texture is generally coarse,
ranging from sandy-gravel to gravely-muddy-sand; finer sediments (mud)
were found only on the continental slope. Generally the coarse fraction
is mainly made up of biogenic clasts including: calcareous algae,
bryozoa, planktonic and benthonic forams, pteropoda etc. The
terrigenous fraction, which is made up of volcanic clasts (i.e.
volcanic glass, volcanic rock fragments, etc.), is in general
and becomes prevalent only in finer sediments.
Carbonate sediment is dominated by different groups at different depths: in very shallow water the biogenic component is at its minimum; in shallow water (40-80m) the association of bioclasts is dominated by fragments of calcareous algae; in intermediate water mollusks, echinoderms and benthonic forams bioclasts dominate, their size becoming finer offshore; finally deeper (>200m) and finer sediments are dominated by pteropoda and planktonic forams association; on the shelf break area (150 m) a well-defined crinoiddominated facies is present.
Altough such distribution highlights the rule of bathymetry and texture as controlling factors, this simple relationship between biogenic composition and water depth/grain size is only a general rule and was observed in a few areas.
Actually, side scan sonar data reveals that sediment distribution is extremely complex and highly controlled by proximity to rock outcrops (partially or totally bioencrusted) and local hydrodynamic factors (i.e. current on saddles and wave action on coast facing main storm direction).
The distribution of sediment and the identification of controlling factors will be described. Some example is given hereafter.
Rocks outcropping on a smooth seafloor covered by fine sediments, show a recurrent sediment distribution pattern, i.e. they are surrounded by a ringshaped belt of coarse biogenic sediment separated from finer sediments by a sharp boundary. Such rock–related coarse biogenic sediments extent in all sectors around the island but are more developed in the 50-120 m bathymetric range highlighting a major productivity of biogenic debris in this depth range.
In areas characterized by current action, side scan sonar data show a peculiar sonar facies with high backscatter belts (without any morphological relief) lying on a low-medium backscatter seafloor. High backscatter belts are produced by rhodolites concentration on a sandy biogenic sediment (mainly calcareous algae fragments). Rhodolite belts seem to be normal respect to main current direction, develop in water depth ranging between 30 and 70-80 m and are more frequent in saddle areas.
DISTRIBUTION OF FORAMINIFERA IN THE SE BRAZILIAN MARGIN AFTER THE LAST GLACIAL MAXIMUM
Passos, R.F. Sousa, S.H.M. D'Agostino, L.F. Mahiques,
Institute of Oceanography of the University of São Paulo 05508-900 Praça do Oceanográfico, 191 São Paulo SP BRASIL
Finantial support by Fapesp In this paper we present
the results of the analysis of the distribution of foraminifers in the
continental shelf and upper slope of Southeastern Brazil. Twenty seven
box-core samples, located in transects perpendicular to the coast,
between the depths of 100 and 500 meters were analysed for foraminifer
assemblages as well as for abiotic parameters (grain-size, organic
matter, calcium carbonate and C and N stable isotopes).
Sediment samples were wet sieved and the specimens retained between the 0.250 mm and 0.125 mm were used for identification. A total of 300 specimens were identified and counted in each sample.
The distribution of recent foraminifer assemblages is controlled by depth, mainly for the species Bulimina aculeata and Bulimina marginata, both indicators of nutrient availability (Debenay & Redois, 1997). It seems that these species also exhibits a latitudinal variation, with decrease of their abundance towards the north. Values of d13C in the organic fraction show a similar pattern.
Between the Cape of Santa Marta and São Sebastião Island Cassidulina laevigata is the dominant species mainly along the 100 meter isobath. The presence in the SE Brazilian shelf of this species, considered as a cold water indicator (Boltovskoy et al., 1980), seems to reflect the northward displacement of Patagonean waters. Between the São Sebastião Island and the Cape Frio, the species Cibicidoides sp. and Globocassidulina subglobosa are predominant, and the latter one is more abundant in the 500-m isobath.
The abundance of planktonic foraminifers is almost constant along the isobaths with an increase of planktonic foraminifers towards the slope. The Globigerinoides ruber , typical of tropical waters, and Globigerina bulloides, present in subtropical assemblages, are the most frequent planktonic species. An exception to this pattern is found in the outer slope southward of São Sebastião Island where C. laevigata is the most frequent species. The higher abundance of C. laevigata in the 500-m isobath seems to be related to the meandering pattern of the Brazil Current and its consequent displacement of shelf waters towards deeper areas (Mahiques et al. 2002).
The foraminifera species observed in the recent sediments are also identified in sediments older than 10,000 years B.P. However, important changes in species frequence can be detected when we compare recent and old foraminifera assemblages An example of this fact, is the decrease of the frequence of Bulimina marginata and Cassidulina laeviagata in the shelf and slope after LGM. Other fact to be considered is the relative decrease of Globigerinoides ruber and Globigerina bulloides in the sediments older than 10,000 years B.P. The occurrence in these sediments of Neogloboquadrina pachyderma and Turborotalita humilis, typical of cold and temperate waters, respectively, seems to reflect lower sea surface temperatures during the Last Glacial Maximum.
Boltovskoy, E., Guissani, G., Watanabe, S., Wright, R. 1980 Atlas of benthic shelf foraminifera os the southwest Atlantic. Dr. W. Junk bv Publishers. The Hague. 147p.
Debenay, J-P., Redois, F. 1997 Distribution of the twenty seven dominant species of shelf benthic foraminifers on the continentl shelf, north of Dakar (Senegal). Marine Micropaleontology, vol. 29 p. 237-255.
Mahiques, M.M., Silveira, I.C.A., Sousa, S.H.M., Rodrigues, M. 2002. Post-LGM sedimentation on the outer shelf – upper slope of the northernmost part of the São Paulo Bight, southeastern Brazil. Marine Geology, 181:387-400.
RELIC CARBONATE DEPOSITS OF THE NORTHWESTERN MARGIN OF INDIA: RECORD OF SEA LEVEL CHANGES AND NEO-TECTONIC ACTIVITY DURING THE LAST GLACIAL CYCLE
V. Purnachandra Rao
National Institute of Oceanography Dona Paula-403 004, Goa, India
Relic carbonate deposits occur abundantly on the
carbonate platform and in the Gulf of Kachchh of the northwestern
margin of India. The carbonate platform lies on the outer shelf between
80 and 100 m
water depth, covering an area of about 28,000 sq. km. Bathymetric
across 11 E-W profiles indicate sea floor irregularities of the
top average 15 m relief on the northern part, but can be more ~20-30
m relief in the southern part. Buried pinnacles of 6 - 8 m high were
at the eastern edge of the platform. Pinnacles about 2 to 6 m height,
or coalesced pinnacles separated by flat floors also occur and are
by mounds and coalesced mounds in the seismic profiles. The individual
mounds are about 5 km wide and 6 m high, and the coalesced mounds are
8 to 15 km wide and 4 to 20 m high. The Gulf of Kachchh is on the inner
shelf and its sea floor is highly irregular with 10 m high relief
Tidal currents of 4-6 m high operate in the Gulf. The maximum depth in
the Gulf is 40 m.
The relic deposits on the carbonate platform are largely aragonite sands. Indurated sediments, shell zone comprising of oyster shells and dolomite crusts, however, also occur at different places. Thin sections of the aragonite sands indicate that some of these sands are Crustacean faecal pellet-dominated, while others are oolite-dominated. Halimeda-dominated and pelletal/oolitic limestones and indurated aragonite muds, similar to hardground deposits, occur closer to the seaward edge of the platform. Dolomite, high-magnesium calcite and quartz are dominant minerals in dolomite crusts occurring at 64 m depth on the northeastern edge of the platform. Thin sections, SEM and stable isotope studies of the crust indicate the presence of irregularly laminated dolomitized cyanobacterial filaments with trapped detritus and formation of the crusts in shallow, hypersaline conditions. The samples recovered at different stations from the Gulf of Kachchh are large sheet limestones encrusted by 0.5 to 1.0 cm thick dolomite crusts, 3 cm size lense-shaped dolomite crusts and corals belonging to Favidae family (Leptastrea transversa).
Twenty-eight radiocarbon ages, including three AMS ages were obtained for different carbonate deposits of the platform. The conventional radiocarbon ages are younger than that of the AMS ages by 500 to 800 years for the samples of the same station. The age of the aragonite sands from 15 stations ranges from 12,440 to 6,730 yr BP (7.6 to 14.2 ka). The sands at trough portions of the mounds are older than at the crest. The ages of the limestones mostly lie between 9,920 and 11,480 14C yr BP (10.99 ka to 13.28 ka). Coralline algal nodules (dated 12,000 14C yr BP) occur beneath the aragonite sands dated at 7,630 14C yr BP (7.56 ka). The largest shells have oldest ages (11,920 14C yr BP). The AMS age of the dolomite crust is 17,250 14C yr BP (20.34 ka). The ages of the dolomite crusts at 35 m and 25 m in the Gulf of Kachchh are 12,650 14C yr BP (14.44 ka) and 10,660 14C yr BP (12.47 ka), respectively. The corals at 25 m are dated 10.81 ka.
Despite the platform is off the major rivers carbonate sedimentation continued from 17,250 yr BP to 6,730 yr BP. The depth and age of the dolomite crusts on the platform suggest that, unlike other continental shelves, the carbonate platform was at shallow depths during the LGM. The time interval (between 12,440 yr BP and 6730 yr BP) during which the oolites formed on platform corresponds to 80 m rise of sea level on the glacio-eustatic sea level curve. This implies that oolites may not be considered as sea level indicators and even form at deeper depths. The younger ages on the platform than that of the ages on glacio-eustatic sea level curve for the corresponding depth suggest subsidence of the platform. On the other hand, the Gulf of Kachchh was inundated atleast by 15 ka. The depth and ages of the samples in the Gulf are not consistent with that on the glacio-eustatic sea level suggesting that the Gulf uplifted sometime after 10.81 ka. There seems to exist an isostasy between the subsidence of the platform and upliftment of the Saurashtra or in particular Gulf of Kachchh.
PALAEO-SHORELINES DROWNED BY THE LAST MARINE TRANSGRESSION ON CAMPOS BASIN CONTINENTAL SHELF, BRAZIL.
Silva, Cleverson G. Lopes, Anderson L. M.
Laboratório de Geologia Marinha – LAGEMAR Departamento de Geologia, Universidade Federal Fluminense (email@example.com)
The morphology of the continental shelf on Campos
on the northern Rio de Janeiro and southern Espirito Santo States,
reflects its geological evolution in association with the sedimentary
erosional processes related to the Quaternary marine tansgression
observed during the last 20.000 years. Offshore the cities of
Macaé and Cabo de São Tomé the seaward protruding
isobaths, from 10 to 80 meters, represents an ancient delta lobe with
superimposed drowned palaeo-lagoons represented by encircling depth
contours around 50 meters depth. Conspicuous escarpments are located in
depths of 25 to 30 meters, 80 to 90 meters and 100 to 115 meters and
are interpreted to represent palaeo-shorelines drowned by the marine
transgression. Some of these features were previously reported by other
studies (Kowsmann et al.,
1978 apud Kowsmann e Costa, 1979, Alves et al.,1980 , Dias et al.,
Silva, 1987, Côrrea, 2001).
The irregular shelf seabed morphology to the north of the Paraíba do Sul river mouth extends northwards to the latitude of Vitória city. In this area numerous circular topographic highs are formed by coralline algal reefs growing over limonite concretions, marking the extension of a very shallow waveabrasion platform cut over the Barreiras Group Tertiary red-beds. Three large submarine channels cut across the entire continental shelf, from 10 to 50 meters, in the E-W direction.
Some of these features might be associated with variations of the rate of se-level changes during the course of the marine transgression as observed on the 230Th/234U sea-level curve of Fairbanks et al. (1990). The ages of the escarpments can be extrapolated from this curve, considering its present depth, resulting in ages of 18,500 B.P. for the external escarpment (100 to 115 m), 12,500 B.P. for the escarpment at 60 to 80 meters and 8,500 B.P. for the escarpment located along detphs of 25 to 30 meters.
ALVES, E. C., GORINI, M. A., RODRIGUES, P. C. H. SILVA C. 1980. Estudo da sedimentação quaternária na região entre o Rio Doce e Cabo Frio. 31° Congresso Brasileiro de Geologia, 515 - 529.
CÔRREA, A. C. T. 2001. Estudo de feições morfológicas do assoalho marinho na plataforma externa da Bacia de Campos pela interpretação de imagens de side scan sonar, de perfis batimétricos e de amostras litológicas. Niterói. Universidade Federal Fluminense, Departamento de Geologia. Tese de Mestrado. 77p.
DIAS, G. T. M., GORINI, M. A., GALLEA, C. G., MELLO, S. M., DELLAPIAZZA, H. 1982. Bancos de arenito de praia (beach rocks) submersos na plataforma continental SE brasileira. 32° Congresso Brasileiro de Geologia, 1540 - 1546.
KOWSMANN, R. O. e COSTA, M. A. 1979. Sedimentação quaternária da margem continental brasileira e das áreas oceânicas adjacentes. Rio de Janeiro, PETROBRÁS. CENPES. DINTEP, 55p. (Série Projeto REMAC, n.8).
SILVA, C. G. 1987. Estudo da evolução geológica e geomorfológica da região da Lagoa Feia, RJ. Rio de Janeiro. Universidade Federal do Rio de Janeiro, Instituto de Geociências. Tese de Mestrado.
LGM LOWSTAND AND DEGLACIAL SEA-LEVEL RISE: THE SUNDA SHELF RECORD COMPARED WITH OTHER SEA-LEVEL CURVES
K. Stattegger* T. J.J. Hanebuth**
* Institute for Geosciences, University of Kiel, Olshausenstr. 40-60, 24118 Kiel, Germany ** Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany
The Sunda Shelf (SE-Asia) as one of the largest shelf
areas in the world offers excellent conditions by its extension, low
gradient, high supply of terrigenous organic-rich sediment, tectonic
stability, and thin Holocene sediment-cover for the reconstruction of
the LGM sea-level lowstand and subsequent flooding. From a detailed
sediment core and seismic transect (-70 to -126 m modern water depth,
mwd) we developed a high-resolution sea-level curve. Detailed AMS-14C
datings of in situ mangroves and of other plant remnants from tidal
deposits provided a high-resolution age control.
Late-LGM tidal flat deposits cored at -116 m modern water depth yielded an age of 21020 +/-330 y BP. Recently, slightly younger ages of 20600 and 19970 +/- 340 y BP have been measured on two samples from the same core 6 metres deeper in the same tidal-flat environment. This would indicate a glacial sea-level lowstand value of -122 m (+/- 2(?) metres tidal range). The slight age reversal points at a rapid build up of a more than 6 metres thick tidal succession within a few hundreds of years beyond the 14C age-resolution, taking into account some contamination by older plant material as well as maximum dating uncertainties. It is not clear if this corresponds to a first rapid sea-level rise, and how much can be attributed to the aggradation of the tidal system. Corings deeper than -120 m mwd revealed only erosional gaps around the LGM.
The sea-level curve of the deglacial sea-level rise from 21000 to 11000 y BP therefore shows one or two periods of accelerated sea-level rise (Hanebuth et al., 2000): After the possible initial rapid rise around 20500 yr BP, and a moderate sea-level rise up to -96m until 14600 y BP, a highly accelerated rise occurred between 14600 and 14300 yr BP from -96 to -80 m corresponding to the meltwater pulse 1A. Then sea-level rise slows down again.
In a general discussion, the new data from the Sunda-Shelf are compared with records from Barbados (Fairbanks, 1989; Bard et al., 1996), Tahiti (Bard et al., 1996), and the Bonaparte Gulf (Yokoyama et al., 2000) for the depth of the LGM-lowstand and for the deglacial sea-level rise. A LGM minimum lower than -130 m claimed from the Bonaparte Gulf record is not supported by the other records and is controversely discussed by other modelers (Peltier, 2002). There is a generally good agreement with the Barbados-curve, but a higher resolution of meltwater pulse 1A, and a general age shift of 300 to 400 years towards higher ages in the Sunda curve. The Tahiti curve starts only at 13800 (U/Th) y BP, this is after meltwater pulse 1A.
Sea-level curves derived from wide low-gradient shelves far from glacial epicentres have some advantages over reconstructions from coral reefs. Sealevel governed migration of nearshore environments can be easily detected, ages can be precisely controlled by AMS-radiocarbon dating of plant remnants for the last 50000 y. Coral-reefs show extensive karstification during lowstands, reef growth does not necessarely reach intertidal waterdepths and can not follow rapid sea-level rises.
Bard, E. et al., (1996) Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge, Nature, 382, 241-244.
Fairbanks, R.G., (1989) A 17,000-year glacio-eustatic sea level record: influence of glacial melting dates on the Younger Dryas event and deep ocean circulation, Nature, 342, 637-642.
Hanebuth, T., Stattegger, K., and Grootes, P.M., (2000) Rapid flooding of the Sunda Shelf: a late-glacial sea-level record, Science, 288, 1033-1035.
Peltier, W.R., (2002) Comments on the paper of Yokoyama et al. (2000), entitled “Timing of the Last Glacial Maximum from observed sea-level minima”, Quaternary Science Reviews, 21, 409-414.
Yokoyama, Y. et al., (2000) Timing of the Last Glacial Maximum from observed sea-level minima, Nature, 406, 713-716.
RESPONSE OF CARBONATE
PRODUCERS TO SEA-LEVEL OSCILLATIONS IN THE CONTINENTAL SHELF AND SHELF
EDGE, BAHIA STATE, NE BRAZIL
Departamento de Ecologia e Recursos Naturais. Universidade Federal do Espirito Santo. Vitória, Brazil. firstname.lastname@example.org
The continental margin of Bahia extends from about
12.5º S to 18º S. It is under the influence of the Brazil
Current (BC), which is characterized by warm (c. 28º C, saline
(35%0) and clean offshore waters (< 25g/l). Nearshore waters are
generally stirred by waves, which promotes widespread resuspension of
coastal sediments. The depositional environment can be considered to be
wave and storm dominated. The inner shelf area varies from pure
siliciclastic sands to mixed carbonate-siliciclastic sands, with an
important contribution of corals and crustose red algae forming reefs
near the shore (Leão et al. 2002); the calcareous green algae
Halimeda is locally abundant. Although the middle and outer shelf vary
in composition according to the proximity of large rivers,
the contribution of carbonate sediments tends to increase offshore,
free-living calcareous red algae is the main carbonate producer.
bivalves, bryozoans, foraminifera or Halimeda may dominate over the
red algae, associated to variable amounts of siliciclastic sands.
Recent surveys carried out in 2001 along the continental shelf and upper slope of Bahia State aimed to investigate the seabed morphology and sedimentary deposits and whether these could reveal relative sea-level changes. The first part of this investigation (April 2001) aimed to investigate an area of 2800 square kilometers of continental shelf in detail. The second investigation was part of a large survey undertaken by the Brazilian Navy using the N.O. Antares (October to December 2001), which concentrated on the acquisition of physical oceanographic data. At depths shallower then 200 m samples of surface sediments were taken for an investigation of present hydrodynamic energy and related sedimentary deposits.
The bathymetric data shows a gently sloping continental shelf with numerous banks. These banks were interpreted to have developed due to the growth of calcareous red algae. The interlocking development of branching freeliving forms of calcareous red algae seems to favor the development of banks in wave dominated environments, whilst current dominated environments seem to favor the formation of sand ribbons (Testa 1999).
The shelf break is generally found at about 50 m water depth, and is marked by steep slopes and escarpments, which cut down to 100 m through the shelf edge. The shelf edge is also marked by wide, rounded seabottom features, at present covered by calcareous red algae, although samples of the coral Agaricia agaricites, a shallow water coral, were also collected from waters as deep as 72m. The shelf edge also shows widespread areas of stabilized sediments due to the development of two distinct communities: thinly laminated crusts of calcareous red algae and rhodoliths, and the in situ production of Halimeda. The latter seems to be associated with the pinnacles positioned near to the shelf edge, as result of in situ production and sedimentation, as the rhyzoids of Halimeda help to trap and stabilize the sediments.
The true origin of these submarine features is uncertain, as we lack subsurface data (cores beyond a few cm penetration or high resolution subbottom profiles), but undoubtedly further studies will yield important information about the history of South Atlantic sea-level oscillations. In addition, these data also shed some light on the understanding on how the carbonate system found along the Brazilian continental margin responds to sea-level oscillations. This is particularly with regard to the creation of the accommodation space necessary build one of the largest, most continuous carbonate shelves in the world.
The aim of this paper is to present a series of new data and to suggest some interpretations concerning a portion of the Brazilian continental shelf. It is anticipated that in this forum these results can be discussed critically and compared with findings from other parts of the South Atlantic province.
The first part of this work was sponsored by W.S.Atkins (U.K.). The second part myself and students are indebted to the Brazilian Navy, in the name of Comander Ferreira de Lima, for allowing us to take part of the Oceanographic Survey Oceano Leste 1.
PALEOCEANOGRAPHIC VARIATIONS DURING THE LAST 30.000 YEARS: RESULTS FROM OXYGEN ISOTOPES AND TOTAL FAUNA WITH PLANKTONIC FORAMINIFERA AND CALCAREOUS NANNOFOSSILS.
Felipe A. L. Toledo Karen B. Costa
Bolsistas Rhae - projeto MAPEM, Instituto de Geociências - UFRGS.
During the Last Glacial Maximum (LGM), continental
paleotemperatures suggest a significant cooling at low latitudes (i.e.
Guilderson et al. 1994, Stute et al. 1995), while tropical/sub-tropical
Sea Surface Temperature (SST) remained warm (i.e. Colinvaux et al.
1996, Behling and Lichte 1997), suggesting that the low-latitude ocean
might behaved as a warm water pool that is relatively stable through
This study was designed to test the hypothesis of stability of water temperature by examining marine microfossils and isotopic evidences for hydrological changes during the last 30 kyr on the Brazilian Continental Margin. We used three sediment cores (SAN-76, ESP-08 and CMU-14) from sites located between 7°S and 25°S latitude along the margin.
This work includes the oxygen isotopic analysis in planktonic foraminifera tests. These data made it possible to identify the international marine stratigraphy of isotopic stages for the late Pleistocene-Holocene. The study also based on quantitative analysis of planktonic foraminifera and calcareous nannofossil. The combined analysis allowed us to infer hydrological variations for the studied area, as changes in the depth of the mixed layer and thermocline/nutricline in the last 30 kyrs. The results, using Q-mode factor analysis on assemblage data for planktonic foraminifera and calcareous nannofossils, indicate the presence of an approximately 12 kyr cycle that might be responsible for the sub-Milankovitch changes.
The paleotemperatures obtained by factor analysis agree with the temperature differences previously described by CLIMAP project for the LGM and Holocene, with ~ 2°C variations. Except for the deglacial interval between the LGM and 13-9 kyrs in the core SAN-76 at 24°S, the temperature difference is 4°C. This temperature contrast is larger than that for the LGM-Holocene in this core. The faunal variations suggest that the hydrological conditions in the southwestern South Atlantic Ocean were not stable during the deglacial transition from LGM to Holocene.
Possible causes for the observed oscillation in the hydrography in the last 30 kyrs, include changes in the positions of the Intertropical Convergence Zone (ITCZ) and the Subtropical Gyre. The contact zones between the Brazil and Malvinas Current, the Brazil Current and coastal currents flow, in a complex pattern of meanders and eddies. These cyclonic cold-core eddies “travel” along the Subtropical Gyre with cold and rich-nutrient waters. The presence of these eddies, associated with the changes in the depth of thermocline/nutricline recorded by the calcareous nannofossil Florisphaera profunda, were a likely cause for the oscillation indicated by the microfossil data.
Behling, H. and Lichte, M. (1997) Evidence of dry and cold climatic conditions at glacial times in tropical southeastern. Quaternary Research, 48, 348-358.
Colinvaux, P.A., Oliveira, P.E.D., Moreno, J.E., Miller, M.C. and Bush, M.B. (1996) A long pollen record from lowland Amazonia: forest and cooling in glacial times. Science, 274, 85-88.
Guilderson, T.P., Fairbanks, R.G. and Rubenstone, J.L. (1994) Tropical temperature variations since 20.000 years ago: Modulation interhemispheric climate change. Science, 263, 663-665.
Stute, M., Forster, M., Frischkorn, H., Serejo, A., Clark, J.F., Schlosser, P., Broecker, W.S. and Bonanai, G. (1995) Late glacial stage and Holocene tropical ice core records from Huascaran, Peru. Science, 269, 46-50.
THE ORIGIN OF THE ‘PAMPEANO
FORMATION’ (PLEISTOCENEHOLOCENE) AT THE ARGENTINA PLAINS AND
SURROUNDING AREAS: AN APPROACH
Roberto Torra Nistal
Facultad de Ingeniería, UNNE. Av. Las Heras 727, 3500, Resistencia, Chaco, Argentina E-mail: email@example.com
Argentina' geologists think that the sedimentary
terrains that cover the central and north territories of the Argentina
country correspond to a very well define eolian geologic-sedimentologic
main silty grain sized deposit that is related with processes that
developed the loessial blanket ‘pampas’ sediment. This occured during
the Pleistocene up to Holocene ages. This is generalically named as
‘The Pampeano Formation’ (Ameghino, 1881; Frenguelli, 1921). These
processes were of eolical origin and gave place to an apparent typical
and widely loess formation (Figure 1). These soft friable horizontal
bodyassemblage sediments are composed of very fine sand and/or fine
silty quartz grains (predominantly) as well as few-potency flat-lenses
of mixed muddy-silty weathered lithofacies. These lasts facies are
extremely common in the studied Argentine ‘pampas’ plains area. The
typical color-blanket-sediment-rock is darkbrown or clear-brown
coloured. The thickness of the blanket-rock ranges between 1 up to 30
m in average.
This apparent loess sedimentary body was currently knowed as the ‘Pampeano Formation’ (Figure 2). The records of the deposit envelope the last giant vertebrate paleontological fossil bonds. The giant vertebrates disappearance dates back to approximately 11,500 BP.
This formation is so extense that covers about of 1,050,000 km2, embracing Argentina (central and north sectors), Paraguay (west sector) and Bolivia (east sector).
Most researchers assume the hypothesis that the origin of this formation was typically eolical in origin. The materials were carried from the Andean ranges and Patagonia plateau by the south and west winds (e.g. Ameghino, 1881; Frenguelli, 1921; Gallet et al., 1998; González Bonorino, 1966; Iriondo, 1999; Sayago, 1999; Teruggi, 1957). In such a case the parent and/or reservoir rocks are unexplicable if we taken in consideration the huge volume of materials considered herein.
Until now, not any alternative was presented to explain the origin of this wide sedimentary body (first regional order).
During the last 8 years detailed regional studies focused on this mantlerock help us to know something else about its features and genesis. The investigations were performed using field detailed reconnaissance, exhaustive mapping and monitoring by means of remote sensing satellite imagery (LANDSAT TM 5 and LANDSAT +ETM 7) in specific regions (NEA, NOA) and/or satellite image windows (SAC-C Satellite Mission) (Figure 1). On the other hand, rigurous analyses of about 5,000 m of registers got from drill-core logs were analysed and interpreted employing the sequential stratigraphy model.
The field lithological-structural studies revealed that the relation between the infralying littoral marine sediments and the overlying Pampeano mantlerocks is quite conformable and transitional (Figures 2, 4). The blanket mantlerock didn’t present any class of structures and/or features of eolian action within the mantle-body sediments (Torra, 2002).
The detailed sampling and analyses of more than 100 samples, laterly studied by geochemical in-dry FRX trace elements (more than 1,500 major and trace elements values), revealed that the ‘eolian theory’ may be considered in a different way with a reasonable interpretation (Torra, 2001; 2002; Figures 2, 3).
Upon the studies performed by this author, the apparent succession of sedimentary beds (interpreted as a mantle-rock) related to the ‘Pampeano Formation’ should correspond to a typical ‘in situ regolithic loess formation’ in accord with Kemp (2001) and Smalley et al. (2001). Moreover, the ‘in situ regolithic loess formation’ comes from the littoral shallow marine Miocene transgression system tracts deposits, specially from sediments that represent the lasts HST sequences (Middle-to-Upper Miocene age). In such a way the parent rock of the ‘Pampeano Formation’ correspond to an in situ disaggregate (biotical, mechanical and/or chemical weathering) marine mudrock beds as well as tempestite offshore sand bodies, lenses muddy beds and/or very fine sand beds lithofacies deposits (Torra, 2001, 2002).
A typical calcrete body is frequently present, in many places very well developed, as laminar and/or mottled caliche forms, elsewhere in the ‘pampas’ plains. In general the calcrete irregular bodies are present to depths which ranges from 2 to 10 meters in average. The thickness varies from centimetres to meters (Figure 3).
The problem with the single term ‘loess’ is that this word implies an accuracy geological procces of genesis (Pye, 1995). Because of this, I propose that the origin of the ‘Pampeano Formation’ corresponds to an ‘in situ regolithic loess mantle-rock (an in situ horizontal blanket deposit) formation’ that derives from littoral shallow marine sediments of Miocene age. The thesis for such origin corresponds exactly with the previous detailed geochemical analyses studies which linked the marine succession with the Quaternary mantle-rock (Torra, 1999, 2000a,b, Torra, et al., 2000) (Figures 3, 4).
There is a lack of knowledge concerning to the continued failed small-tomedium gravity dams and bridges and the intrinsic sedimentologic characteristics related with mechanical behaivioring of the ‘Pampeano Formation’ which lies at the Argentina plains. This fact has an enourmous importance for the regional hidrologic and mineral exploration as well as for the use and management of the soil erosion, vegetate coverage, irrigation, forestation and soil conservation. The above statement results will probably produce a great effect not only for the basic studies of this ‘in situ regolithic loess mantle-rock’ (blanket) but because basic and applied studies are the Bergbaustudenten Osterreich. Special Abstracts Volume. p 138. Leoben Torra, R. (2001) Origin and evolution of the continental giant 'Chaco-Pampeano' shelf (Argentina): their evolution and morphology from the Miocene to present day. International Geological Correlation Program (IGCP 464). Abstracts Volume. 1st Annual Conference. pp 49-50. Hong Kong Torra, R. (2002) Sedimentología de las areniscas de la Formación Ituzaingó en el sector norte y oeste de la Mesopotamia, Argentina. Unpublished Doctoral Thesis. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Universidad Nacional de Tucumán. Vol. II. 495 p. Tucumán
HOLOCENE MARINE DEPOSITS: MODELLING SELF-WEIGHT CONSOLIDATION
N. Keith Tovey(1), Paul, M.A.(2), Yap Chui-Wah (3)
Simon Tovey (4)
(1) School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK (2) School of Life Sciences, Heriot Watt University, Edinburgh, EH14 4AS, UK (3) Singapore Government, Singapore (4) 101 Media Ltd, Keswick Hall, NR4 6TJ, Norwich, UK
It is widely recognised that Continental Shelf deposits
hold critical information regarding recent geological sequences and
provide opportunities for palaeo-climatic reconstruction. However,
relatively little attention has been paid to the consequences of
self-weight consolidation of the recent clayey marine sediments, and
recent studies (e.g. Tovey and Paul, 2002) have demonstrated that
errors in the determination of sedimentation rates of Holcene sediments
based on simple linear models can be significant and often may be in
error by a factor of two or more.
This paper has two functions. Firstly it extends the work of Tovey and Paul, by incorporating further data from other locations around the world which support a more general relationship between the consolidation parameters (e1 the void ratio at unity stress, and the compression index Cc).
e1=0.8483 + 2.7226 Cc
This is demonstrated in Fig, 1 where the original data
of Tovey and Paul is supplemented by data from elsewhere. This
relationship which has a high coefficient of correlation at 0.98,
extends over a wider range of compression index from 0.2 to 2 and may
be represent by:-
Tovey and Paul emphasised the importance of this relationship as e1 is rarely reported for sediments, and yet is needed in decompaction routines. This relationship provides a convenient route to estimate these values with a high degree of confidence.
Furthermore, Tovey and Paul suggested, contrary to established ideas, that excess pore pressures may develop in deep Holocene sediments. This paper also attempts to explore the situation further to examine whether or not such excess pore pressures could remain undissipated and thereby account for the higher than projected moisture content seen at depth within such samples. While there is no doubt that full dissipation of excess pore pressure will occur at the surface as each new layer is laid down, similar pressures will also develop at depth, and because of the relatively long path lengths to a free drainage surface it is probable that full dissipation may not be achieved before the next layer is sedimented.
Models using annually incremented sediment layers indicate that for marine Holocene sequences thicker than around 2m excess pore pressures do indeed persist and continue to increase with each annual increment. Evidence from Hong Kong suggests that the sequences are draining only in an upward direction, while the sequence from Osaka in Japan suggests double drainage, and this difference in behaviour appears to be linked with the borehole records .
Tovey, N.K. and Paul, M.A. (2002). Modelling self-weight consolidation in Holocene sediments. Bulletin of Engineering Geology and The Environment, 61: 21-33.
Fig.1 Data from additional sites appears to confirm a
unique relationship between e1 and Cc.
HUMAN ACTIVITY IN RELATION TO LATE HOLOCENE COASTAL CHANGES OF THE PUCK LAGOON
Szymon Uscinowicz (1) Joanna Zachowicz (1) Grazyna
(1) Polish Geological Institute, Branch of Marine Geology (2) Gdansk University, Department of Geomorphology and Quaternary Geology
Archaeological sites of different age are known from
of Puck Lagoon situated in the north-western part of the Gulf of
of them; Neolithic settlement in Rzucewo and submerged remains of
medieval harbour in Puck are the best investigated and strictly related
to history of sea-level rise and shoreline displacement during the Late
Holocene. According to pollen analyses the first appearance of man in
the vicinity of present day Puck Lagoon took place in the Atlantic
period (Uscinowicz & Miotk-Szpiganowicz 2002). The same data
indicate increasing human activity in the beginning of Subboreal
period. Radiocarbon dating of
archaeological artefacts and pollen data from cultural layers indicates
the beginning of the settlement at c. 4400-3700 years BP (Krol 1997).
The Cerastoderma sp shells from the base of marine sand at the 0.24-
m bsl. are dated at 3435±30 years BP. If sand with gravel and
shells are from storm layer it is probably that sea-level in Puck
c. 4000 years BP was at least c. 1.0-1.2 m lower than today. The date
beginning of seal hunters settlement correlate well with the period
water in the Puck Lagoon reached the level nearly as a recent one.
Archaeological underwater investigations in the vicinity of Puck town are carried on since 1978. Wooden constructions consisting of oak logs and numerous poles, driven into the lagoon floor, as well as wrecks of boats, have been found in the area. The radiocarbon dates of harbour remains and wrecks, which now are 0.5 to 1.2 m below water surface, are from IX to XIII century. One of the more controversial issues is whether or not there was a rapid sea level rise of c. 1–1.5 m approximately 1000 years ago, the potential effect of which would have been the destruction of the mediaeval harbour in Puck (Zbierski 1986). That supposition is in contradiction to the radiocarbon dates of marine shells from the shore c. 1000 m. north-west from submerged harbour remains. Cerastoderma sp shells found in the base of beach sands at the level from 0.07 m. asl to 0.09m. bsl. are dated by 14C method at 720±25 years BP (GdA-166). The core taken c. 10 m. from the shore shows 26 cm of sand with Cerastoderma sp. and Hydrobia sp. shells laying on peat dated on Atlantic period. The age of Cerastoderma sp. shells is 835±25 years BP (GdA-167) and Hydrobia sp. is 945±25 years BP (GdA-168). Both shells samples are from the layer of 0.37-0.45 m. bsl. Those data shows clearly those c.1000 years ago water level in the Puck Lagoon was very similar like today. The conclusion is supported by pollen spectra of peat from the cores taken on the beach c. 7 km to the south-east from discussed archaeological site. The pollen spectrum from the base of peat layer (0.26-0.27 m bls.) indicates richness of the pollen grain of plants related to the corn cultivation. (Zachowicz, unpublished data). This type of economical activity is known in the region since 1000 years BP. In the upper surface of this peat (0.12-0.17 m bsl.) dated on 600±75 years BP (Gd-15217) in pollen spectrum appear more pollen grains typical for wet meadows. This fact, and appearance of brackish and marine diatoms indicate that sea level was c. 0.2-0.3 m below present. Thus the destruction of the mediaeval Puck Harbour (e.g. Zbierski 1986) are now shown not to be due to a rapid rise the sea level approximately 1000 years ago. The present position, relatively far from the shore, of the harbour remains could be explained by coastal erosion. The Atlantic and Subboreal peat outcrops on the lagoon bottom and shore c. 100- 200 m. west from the construction remains are recently strongly eroded, in spite of reeds abundance protected the shore against the waves.
Krol D. 1997: Excerpts from Archaeological Research at Rzucewo, Puck Region. In: D. Krol (Ed.) The Built Environment of Coast Areas during the Stone Age. The Baltic Sea-Coast Landscapes Seminar. Session No.1, Gdansk.
Uscinowicz Sz., Miotk-Szpiganowicz G., 2002 — Holocene Shoreline Migration in the Puck Lagoon (Southern Baltic Sea) based on the Rzucewo Headland case study. Landform Analysis Vol. 4.
Zbierski A., 1986: Problems connected with wide-scope investigations into the beginning of the Port of Puck. Peribalticum IV, GTN: 122-142.
GLACIO-ISOSTATIC MOVEMENTS IN THE SOUTHERN BALTIC AREA
Polish Geological Institute, Branch of Marine Geology, Gdansk, Poland
The glacio-isostatic rebound of the Southern Baltic area have been reconstructed by comparison of the latest relative sea level curve of the Southern Baltic (Uscinowicz 2000) with eustatic curves of the ocean level (Fairbanks 1989, Blanchon & Show 1995, Mörner 1976). For Late Pleistocene and Lower Holocene, comparison was possible only for periods when the Baltic Sea had connection with the ocean and water levels were equal. According to Svensson (1991) and Björck (1995) it happened at c.12.5-12.4 ka BP, 11.0-10.9 ka BP, 10.2-10.1 ka BP and 9.7-9.6 ka BP. Since 8.5 ka BP, when Baltic had permanent connection with the ocean, comparison had been done for every 500 years. Since c. 3.0 ka BP the Southern Baltic relative curve and ocean eustatic curves have covered each other (Blanchon & Show 1995, Mörner 1976) or shown constant difference –2.5m (Fairbanks 1989). Because of using for comparison three eustatic curves, the curve showing result of a subtraction (glacio-isostatic rebound) was established by mathematical approximation. The best fitting curve is given by function:
Because of available data about level changes of Baltic
Sea only since c. 13.0 ka BP this curve has shown only second half of
glacio-isostatic rebound. The total history of glacio-isostatic rebound
of the area can be reconstructed only by extrapolation of calculated
part of the curve basing on general knowledge about glacio-isostatic
movements (Peltier et al. 1978, Mörner 1980, Dawson 1992) and
about deglaciation of northern Poland and Southern Baltic (eg. Mojski
1993, 1995, Uscinowicz 1999).
The basic assumptions for reconstruction are as follow. The restrained rebound started most probably c. 17.5-17.0 ka BP during the deglaciation of northern Poland. Transition from restrained rebound to essential uplift took place c. 14.0 at the beginning of the Southern Baltic deglaciation and during that time the area had to be higher then ocean level.
According to this assumptions and to calculated part of glacio-isostatic rebound curve, approximated uplift during the phase of restrained rebound was c. 20 m and rate of uplift increased up to c. 15 mm/y at 14.0 ka BP. The basic uplift took place between 14.0 and c. 11.0 ka BP. At that time the area was uplifted c. 85 m with max. rate of c. 45 mm/y at c. 12.4-12.2 ka BP, just after ice-sheet retreat from the Southern Middle Bank. At c. 11.0 ka BP rate of uplift decreased to c. 16 mm/y. The residual uplift ended c. 9.4-9.2 ka BP. Fast termination of the residual uplift was related most probably to hydro- and sedimento-isostasy caused by early phases of the Baltic Sea. Total uplift between 17.5-17.0 and 9.4-9.2 ka BP reached c. 120 m.
The forebulge with amplitude of c. 2-3 m migrated across the Southern Baltic between 9.2-7.0 ka BP and between 7.0-4.0 ka BP subsidence up to c.2 m occurred. However, range of these movements was rather small and is close to accuracy of estimations. Since c. 4 ka BP the Earth crust is rather stable, and if neotectonic movements of other origin occur, they are of a small range.
Time of termination of glacio-isostatic rebound of the Southern Baltic area is confirmed by seismoacoustic records. In the Bornholm Basin, some fault zones were active still in the Early Holocene. Dislocations of the top of Pleistocene Baltic Ice Lake clays are observed up to c. 6-7 m and top of Early Holocene Ancylus Lake clays – up to 3-4 m.
Björck S., 1995: A review of the history of the
Baltic Sea, 13.0-8.0 ka BP. Quaternary International, Vol. 27: 19-40.
Blanchon P., Shaw J., 1995: Reef drowning during the last deglaciation: Evidence for catastrophic sea-level rise and ice-sheet collapse. Geology, Vol. 23, No. 1: 4-8.
Dawson A., G., 1992: Ice age Earth, Late Quaternary geology and climate. Routledge, London, New York: 293.
Fairbanks R., G., 1989: A 17,000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deepocean circulation. Nature, Vol. 342: 637-642.
Mojski J. E., 1993: Europa w plejstocenie. Wydawnictwo PAE. Warszawa.
Mörner N., A., 1976: Eustatic changes during the last 8000 years in view of radiocarbon calibration and new information from the Kattegatt region and other northwestern European coastal areas. Palaeogeogr., Palaeoclimatol, Palaeoecol. 19: 63-85.
Peltier W., R., Farrell W., E., Clark J., A., 1978: Glacial isostasy and relative sea level: a global finite element model. Tectonophysics, 50: 81-110.
Svensson N. O., 1991: Late Weichselian and Early Holocene shore displacement in the Central Baltic Sea. Quaternary International, Vol. 9: 7- 26.
Uscinowicz Sz. 1999: Southern Baltic area during the last deglaciation. Geological Quarterly 43 (2): 137-148.
Uscinowicz Sz. 2000: Late Glacial and Holocene of the southern Baltic shoreline displacement. “Geoindicators” – Symposium and Field Meeting. Poland, September 2000, IUGS &GSA: 36-37
SOUTHERN GALICIA CONTINENTAL SHELF OF NW SPAIN SINCE THE LAST GLACIAL MAXIMUM.
Vilas, F. García-Gil, S. Diez, R. Durán,
R. Ferrín, A. Magariños, J. Iglesias, J.
Dpto. Geociencias Marinas, Facultad de Ciencias, Universidad Vigo, 36200-Vigo, Spain. firstname.lastname@example.org
The study area includes the continental shelf from
Miño estuary (41º 55’ N) up to Ría de Muros
(42º 50’ N). It extends from the inner parts of the Rías
Baixas ( Vigo, Pontevedra, Arousa and Muros) up to the -200 m
bathymetry on the shelf. The shelf in this region is narrow (30-50 km
More than 850 km of high-resolution seismic lines were acquired and interpreted covering an area approx. 3250 km2 . The seismic data were recorded with a 300 joule Uniboom EG&G, a 3,5 kHz O.R.E. mud profiler, a 500 kHz Klein 595 side scan sonar run at the same time. In addition to geophysical data 30 vibrocorers (5 m length) and 702 Shipeck superficial samples have been recovered.
Detailed maps of sediment distribution at the present sea floor have been performed for each one of the Rías and the adjacent shelf. The application of side scan sonar techniques has allowed the high resolution seafloor mapping being able to determine the accurate distribution of outcrops, sediment and bedforms.
High-resolution seismic stratigraphy analysis has allowed us to recognize the Last Glacial Maximum (LGM) erosive surface in both, the continental shelf and within the Rías. The LGM ( 18 ky BP) appears as an smoother erosive surface in the continental shelf than into the Rías. This represents an important unconformity surface (Figure) developed over the Pleistocene Sequence ( Q1) within the Rías and in most of the shelf. Nevertheless, there are places where the LGM palaeorelief is directly developed on the Tertiary and even Mesozoic sediments (García-Gil et al., in this symposium). Therefore, the LGM would represent the basal surface of a 4th order sequence.
In the Rías, taking into the account the unconformity surfaces (hiatus and sequence boundaries) have allowed us to distinguish two 5th order sedimentary sequences (S1 and S2) into the 4th order LGM sequence (Q2 in this symposium). The boundary between S1 and S2 sequences is a stratigraphy unconformity which correlates with the Younger Dryas cold event ( approx. 10,500 ky BP) representing the beginning of the Holocene sedimentation.
It is noticeable the occurrence of gas-related features in the youngest Holocene sequence (S2). In addition to common gas accumulations, the present sea-floor also shows ‘small’ oval pockmarks due to gas escapes. Fluids expulsions from the sea bed into the water column can be detected on the echosounder and 3.5 kHz records.
Contribution 263 of the EX-1 Research Group to REN2000-1102MAR, PGIDT00PXI30105PR, BT2000-0877 & PGIDT00MAR0103PR Spanish Projects.
THE POST-LGM TRANSGRESSIVE SURFACE IN THE NORTHERN REGION OF THE ARGENTINA CONTINENTAL SHELF
Roberto A. Violante
Argentine Navy Hydrographic Office, Division of Marine Geology and Geophysics. Av. Montes de Oca 2124, C1270ABV Buenos Aires, Argentina
At the LGM the northern continental shelf of Argentina
was a broad and very gentle sloping subaerial plain. The post-LGM
transgression which begun in the area around 18.000 years ago produced
a progressive flooding of that surface and a consequent coastal
retreat. The ravinement process was responsible for the modelling of
the transgressive surface, whose final configuration was the result of:
1) The relief and lithological constitution of the pre-transgressive
surface. 2) The rate of relative sea-level rise. 3) The balance between
erosion and deposition at each stage of the transgression.
With the onset of the transgressive event the ancient rivers mouths located at the present shelf edge were first transformed into estuaries, while adjacent coastal areas formed by littoral barriers begun to migrate inland. As transgression progressed these processes moved upslope and the shoreline retreated in response to coastal erosion. At the same time deposition occurred in different places. Estuaries and coastal lagoons were the main sites where sediments became trapped. In interfluvials near the coast soil evolution was interrupted when sea-level reached that place. Alluvial aggradation replaced erosive processes in fluvial channels due to the progressive loss in capacity of sediment transport as a result of the rising of base-level. Offshore depositional processes acted below the wave-action zone. All these events occurred without interruption till the sea-level reached its highest position (3 or 4 meters above present level) around 6.000 years ago.
As a consequence, a post-LGM depositional sequence developed. Its sedimentary records show distinctive characteristics: near the shelf edge the most complete transgressive stratigraphic successions are found, composed of estuarine, littoral and marine sediments deposited during the entire time that transgression lasted. In the opposite side, in the continent, they are represented by fluvial sequences in the valleys and eolian deposits covered by soils in interfluvials. In intermediate positions between both locations, that is in most of the shelf, the post-LGM sequence shows incomplete stratigraphic sections composed of littoral to marine sediments deposited after the moment that sea level reached the place, but previous transgressive stages are not represented. Instead, fluvial deposits and paleosoils are located there, which represent the time elapsed since the glacial epoch when interfluvials were exposed to subaerial action to postglacial times before the submergence of the place.
The post-LGM sequence overlies pre-LGM sequences. Both sequences can be easily differentiated in shelf areas through their seismic character as reflected in high-resolution and low-penetration reflection seismic records, as well as through the textural characteristics when their sediments are observed in submarine cores. Pre-LGM sediments are mainly eolian to lacustrine, semiconsolidated, brownish, reddish and tawny loess-like deposits; paleosoils and partially cemented hardgrounds are common features; fluvial or littoral sands can also be found. Post-LGM sediments are mainly littoral to shallow marine, no consolidated, yellowish, greenish and grayish sands and muds with variable amounts of shells; sands in the top of the sequence are considered as relict or palimpsestic; fining-upwards sandy to silty fluvial deposits with similar colours can also be part of the lowest levels of the sequence.
The transgressive surface (represented by the boundary between both units) has in consequence different characteristics depending on the place of observation: it can be located under a marine sequence, below or in between a fluvial sequence or in between a paleosoil. The transgressive surface constitutes a erosional unconformity that is therefore time-transgressive with the highest age (around 18.000 years old) at the shelf edge and the lowest (around 6000 years old) in the coastal plain. Since pre-transgressive sediments are onlapped upslope by progressive younger transgressive deposits, the unconformity represents a stratigraphic hiatus that is minimum in the deepest areas of the shelf and maximum in the coastal plain.
INTERACTIONS OF SEA LEVEL AND TECTONICS ON LARGE SCALE BEDFORMS PRESERVED ON A TROPICAL SHELF: THE RIO GRANDE DO NORTE SHELF, NORTHEASTERN BRAZIL
Helenice Vital(1,2,3,4,5) Venerando E. Amaro (1,2,3,4)
Karl Stattegger (6) Klaus Schwarzer (6) Werner F. Tabosa (1,2,4)
Eugênio P. Frazão (1,2,4) Iracema M. Silveira (1,2)
Luciano H.O. Caldas (6)
(1).Universidade Federal do Rio Grande do Norte, (2).Programa Pós-Graduação em Geodinâmica e Geofísica, (3).Dept. Geologia, (4).PRH-ANP 22, (5). CNPq Researcher, (6).Christian Albrechts Universität, Kiel, E-mail: email@example.com
Large scale bedforms located on the inner continental
shelf of the northern Rio Grande do Norte State, have been analyzed in
detail by integrating high-resolution seismic (BOOMER), and side scan
sonar data, sediment samples and remote sensing (6 to 25 m water
The northern Rio Grande do Norte margin is characterized by a tectonic fabric that is inserted on the offshore Potiguar Basin, which underwent a complex evolution, merging elements from both the Equatorial and the Southern Atlantic tectonics zones. This domain belongs to a larger complex in PETROBRAS oil exploration research. E-W compression released along preexisting faults trending NE-SW, making this one of the most seismically actives regions of Brazil.
The approach used remote sensing technology on a large scale with Landsat TM/ETM+ satellite data integrated through a GIS database with highresolution acoustic images and sediment samples.
High-pass filtering applied to single visible or infrared bands highlighted some important offshore morphologic features such as rock lines and subaquatic dunes, some of them strongly oriented probably sustained by structurally controlled blocks edges. Regional lineaments maps of coastal zone obtained by directional filtered images combined with actual land forms features and drainage system showed a indisputable evidence of continuity offshore of these morphostructural lineaments. The signatures of these bottom features are well recognized on BOOMER, echosound and side scan sonar records. Our findings indicate that the complex interaction of tectonics and sea level strongly affects the delivery, accumulation, and preservation of sediments on this area.
Work funded by: PROBRAL 150-02 (CAPES/DAAD), MARPETRO (FINEP/CTPETRO/PETROBRAS), MAMBMARE (CNPq/CTPETRO).
PEDOGENESIS OF SUBAERIALLY EXPOSED CONTINENTAL SHELVES DURING THE LAST GLACIAL MAXIMUM AND THE PRODUCTION OF ATMOSPHERIC GREENHOUSE GASES
Wyss W.-S. Yim
Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China (Email: firstname.lastname@example.org)
The pedogenesis of subaerially exposed continental shelves is suggested to have played a role in the production of atmospheric greenhouse gases causing a change in the earth’s climate. During the Last Glacial Maximum (LGM), coral reefs contracted towards the equator. Both fossilized coral reefs and carbonate platforms exposed became sites of karstification resulting in the release of carbon dioxide into the atmosphere through weathering. In siliciclastics-dominated inner continental shelves such as the northern South China Sea off Hong Kong, subaerial exposure of seafloor muds of marine isotope stage (MIS) 5 age resulted in the release of carbon dioxide and methane. Carbon dioxide was produced by acid-sulphate soil development through sulphuric acid reacting with biogenic carbonates while methane was generated through the bacterial decomposition of fossilized plant matter. The release of these two greenhouse gases may be the triggering mechanism needed for switching the earth from a full glacial mode back into an interglacial mode. Such a mechanism is supported by the dramatic increase in both carbon dioxide and methane content in the Vostok ice core following the LGM (Petit et al., 1999). Methane generation in pre-Holocene shelf sediments is supported by seismic profiles showing areas of the seabed affected by acoustic turbidity while microfabric studies of palaeo-desiccated crust developed in the upper part of MIS 5 muds (Tovey and Yim, 2002) also supported the conclusions drawn.
Petit, J.R., Jouzel, J., Raynaud, D., Barkov, N.I., Barnola, J.-M., Basile, I., Bender, M., Chappellaz, J., Davis, M., Delaygue, G., Delmotte, M., Kotlyakov, V.M., Legrand, M., Lipenkov, V.Y., Lorius, C., Pepin, L., Ritz, C., Saltzman, E., Joiuzel, Stievenard, M. (1999). Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399: 429-436.
Tovey, N.K., Yim, W.W.-S. (2002). Desiccation of Late Quaternary inner shelf sediments: microfabric observations. Quaternary International 92: 73-87. ;
activity in relation to Late Holocene coastal changes of the Puck
Szymon Uscinowicz, Joanna Zachowicz, Grazyna Miotk-Szpiganowicz
of the Late Quaternary Pacific margin of Canada: influence on americas’
Hetherington, Renée, Barrie, J. Vaughn, Reid, R.G.B., MacLeod, R.
Carbonate sedimentation on Australia's Western Margin Lindsay B. Collins
|Marine isotope stage 5 terraces and coral biohermes at Las
Animas, Baja California Syr, Mexico
Teresa De Diego-Forbis, Robert G. Douglas, Enrique Nava Sanchez, Jay Banner, Lawrence Mack, Donn S. Gorsline
a) A regional meeting at Gdansk, Poland (8 – 10 May 2003) – this meeting will have two thematic sessions and a 1-day excursion (contact: Szymon Uschinowitz).
b) A regional meeting in Vancouver, Canada (25 – 28 May 2003). This is being arranged as a tripartite meeting with a special session focussing on the early inhabitation of the NE Pacific Margin. It is intended to be interdisciplinary and focus on the importance of the continental shelf to humans (contact: Renée Hetherington).
a) Which courses would be of relevanceMichel De Mahiques indicated that short courses would be welcomed at the University of São Paulo as perhaps part of the graduate program.
b) Who should give them
c) To whom should they be given
a) A list of their project-relevant publications for 2001 and 2002.Allan also reminded participants that they must acknowledge/credit their work as a contribution to IGCP-464 when writing research papers; and that this is viewed as a key indicator of activity by IGCP/UNESCO.
b) A list of scientific co-operation arising as a result of the project, e.g. joint research, scientific personnel exchanges, joint publications, etc.
c) A list of their research facilities and capabilities that are available for collaborative research.
These were discussed again to see if there were further courses, which might be added. The microfabric analysis was added by Keith Tovey after he had given several short presentations to individual participants of a technique known as grey-level morphology, which is a non-destructive testing method for an automatic particle size analysis directly from photographs. Karl Stattegger indicated a willingness to prepare a short course on palaeoceanography.Seismic Stratigraphy
X-Ray Diffraction Methods
GIS and remote sensing
- Relevance of the shelves
- Geology of the shelves
- Mechanisms of sea-level change
- High-resolution seismics
- Other geophysical methods
- Sediment sampling
- Non-destructive core analysis
- Sedimentology studies
- Geochemical studies
- Sedimentary petrography, including microfabric analysis
- Palaeontological studies
- Geotechnical studies
- Dating techniques
- Applications of GIS to shelves
- Sea-floor imaging
a) Medium for publication (e.g. electronic/paper) – former would be easier to update8. Concluding Remarks
b) Scale of the maps.
c) Format of data for inclusion in maps
d) Accuracy of definition of LGM coast line. – different key might be used e.g.
I. One symbol to represent high quality data from very localised areas which have been fully corrected for tectonic movements
II One symbol derived from regional analyses which while being reasonably accurate in itself, might not be entirely relevant for a very localised area within the region
III One symbol – perhaps a dotted line showing LGM shorelines where data can be inferred from good bathymetric data
IV Blank areas where no information is available Such maps would also have the function that they would clearly identify areas to which future research should be directed.
|Visit to butantan 1||
on the way to cananeya
|| Fileldtrip 1
|Visit to butantan 2||
|| Fieldtrip 2
|Visit to butantan 3|| lecture room
|| conference dinner
| Chopstik show/1
| They are making
him up (Chiocci)
|| Polish sea horse
| Italian sea
|| Polish sea
horsess *** (Zachowicz)
|| Sleeping Torra
|| Tired people
| Argentina sea
|| Brazilian sea
horse (de Maquies)
|| Who is the true
| Australian sea
|| Italian sea
|| Strange couple
|| Sticky Rice
(le riz coulè)