One of the goals of IGCP-464 Continental Shelves during the
Last Glacial Cycle, has been the investigation of the accumulation and preservation
of organic carbon deposited on shelf areas, and its possible later destruction
during subaerial exposure.
We here compare recently collected data from key shelf areas in northern
Australia, southern Iberia, southern Brazil and near the mouths of the
Irrawaddy River, Myanmar (Burma). In each case, organic-carbon contents,
C/N ratios and C-13/C-12 ratios of shelf sediments in well dated sediments
provide accumulation rates and allow calculation of the proportions of terrestrial-
and oceanic-derived carbon. For northern Australia (Gulf of Carpentaria),
the sedimentary succession is located in an isolation basin, and oscillates
between marine and lacustrine facies, and episodes of subaerial exposure.
There is substantial fluvial input in this area, with 24% of the total run-off
from the Australian continent entering the Gulf of Carpentaria. Our Myanmar
shelf example exhibits an even larger input of terrestrial sediment and
carbon.
The sequences showing clear evidence of subaerial exposure (pedogenesis)
display sediments with lowered organic-carbon contents, C/N ratios and C-13/C-12
ratios. We explore some of the systematics of this behaviour, including
in some cases, the complementary formation of soil carbonates.
CONTINENTAL SHELVES AND MODERN COASTAL ENVIRONMENTS:
WHAT CAN WE EXPECT DURING LOW STANDS OF THE OCEAN?
GARCÍA ADRIANA 1, CHIVAS ALLAN ROSS 1,
REEVES JESSICA M. 1, HOLT SABINE 1, CENDÓN DIONI
1, VAN DER KAARS SANDER 2
presenter's e-mail: adriana@uow.edu.au
1 - School of Earth and Environmental Sciences, University of Wollongong,
NSW 2522, Australia
2 - Centre for Palynology and Palaeoecology, School of Geography and
Environmental Science, Monash University, VIC 3800, Australia
Calcareous microfossils such as charophytes, ostracods and foraminifers
are indicative of marine/non-marine conditions which permit the distinction
of fresh water, inland saline, shallow to deep marine environments, and
coastal environments.
Modern tropical environments from Australia have been explored in order
to collect extant taxa and use them as analogues.
A detailed sampling around the Gulf of Carpentaria provided macrophytes,
ostracods, molluscs, sediments for palynological analyses and water samples.
These data will contribute substantially to the palaeoenvironmental reconstruction
of the Quaternary history of the Gulf of Carpentaria, including sources
of sediments, waters and pollen; biogeography and ecology of taxa present;
and the understanding of routes of colonisation.
The assemblages of charophytes, ostracodes and foraminifera of the longest
core collected from the Gulf of Carpentaria have been analysed. This core
of ~ 15m length comprises two non-marine/marine cycles and has been dated
at the base at 130 ka by OSL. Preliminary analyses of stable isotopes (d18O)
and d13C) have been performed on foraminifers from both marine and lacustrine
facies, and enable further distinction of several facies.
SHALLOW GAS IN SAN SIMON BAY (NW SPAIN)
GARCIA-GIL SOLEDAD 1, IGLESIAS JORGE 1
presenter's e-mail: sgil@uvigo.es
1 - UNIVERSITY OF VIGO
San Simón Bay is a small shallow basin located at the
innermost part of the Ria de Vigo. It consists of an N-S elongated embayment
of 10 km long and 4 km wide with a maximum depth of 10 m. Rande strait
connects this bay with the rest of the Ría de Vigo which has a N45E
of main axis. San Simón Bay has a clear tectonic control related
to a major N-S fault.
The most significant freshwater input comes from several relatively
small rivers that flow into San Simón Bay, which behaves as an estuary.
The rest of the ría is under strong oceanic influence (tides and
waves) and exhibits a residual circulation in two layers. Winds play an
important role in the circulation causing upwelling and downwelling cycles
with a strong seasonal pattern which provoke higher marine productivity
in summer than during winter.
Interpretation of new high resolution seismic records (2004 survey)
has allowed mapping of shallow gas accumulations and gas seeps in San Simón
Bay (Ría de Vigo). X-ray photographs and voids of cores are semi-indirect
evidences of gassy sediments. Furthermore, bubbles of gas coming out from
the seabed of this bay have been recorded for a first time in the rain.
Analyses (GC-MS) of bubble samples confirm the presence of methane.
Concerning to the generation of gas in San Simón Bay, it is
suggested that there are three different sources of biogenic gas: (1) microbial
methane generation from the organic matter accumulated in the subtidal
sediments, (2) drainage of an ancient peat horizon located under the present
intertidal sediments and (3) fluids migration throughout faults.
It is interpreted that the present location of the peat horizon and
the cemented beach facies correspond to variations in the relative sea-level.
These variations in San Simon Bay are due to the combination of tectonic
and the global rise of sea level occurred after the last glacial episode.
CONTINENTAL
SHELF EVOLUTION DURING THE LAST GLACIAL CYCLE - INFLUENCE ON HUMAN CULTURE
HETHERINGTON RENÉE 1
presenter's e-mail: reneehet@uvic.ca
1 - University of Victoria
The fourth IGCP 464 working group "Influence on Human Culture"
acknowledges that not only do humans influence continental shelf evolution
- as in Hong Kong harbour (Chan & Yim 2001; Yim 2001, 2003; China)
- but that continental shelf evolution has influenced human culture, behaviour,
and migrations over the last glacial cycle (LGC). Shelf areas underwent
significant changes during the LGC. Flat, lowstand coastal plains emerged
that were suitable for human settlements. Rapid sea-level rise resulted
in coastal retreat of more than 100 m per year, and the damming of the incised
valleys by transgressive littoral barriers caused rivers to flood and coastal
marshes and swamps to form.
Changes in the paleoenvironment and paleogeography of the shelf has
led IGCP 464 researchers from Italy (Enzo et al. 2001), South Africa (Franceschini
& Compton 2001), France, USA, and Canada (Faure et al. 2002), Poland
(Kramarska et al. 2002, 2003; Uscinowicz & Miotk-Szpiganowicz 2001;
Uscinowicz et al. 2002, 2003; Zachowicz 2001, Zachowicz et al. 2003), Korea
(Park & Kim 2003), and Australia (Garcia et al. 2001, 2002, 2003; Holt
et al. 2003; Reeves et al. 2003; Van Der Kaars et al. 2003) to suggest
links and influences between LGC induced changes and human occupation,
expansion, and regional economic and cultural development. Researchers
from Argentina (Cavallotti et al. 2004; Nami 2001; Torra 2001; Violante
2001, 2002; Aguirre & Violante 2002; Violante & Parker 2004), Brazil
(Lima, de Souza, de Mahiques 2002, de Mahiques et al. 2003), Russia (Patyk-Kara
2003), and Canada (Hetherington et al. 2001, 2002, 2003, 2004; Josenhans
2001; Fedje 2003; Hetherington & Weaver 2003; Al-Suwaidi et al. 2003;
Fladmark 2003; Jackson 2003; Ward et al. 2003; Wilson et al. 2003), are
comparing their findings in an effort to provide insights into early human
habitation and peopling of the Americas. IGCP 464 researchers from France,
Belgium, Romania, and the United States are investigating how catastrophic
flooding of the Black Sea 7,500 years ago may have played a role in the
spread of early farming into Europe and much of Asia and influenced the
deluge account in the Babylonian epic of Gilgamesh and, in turn, the story
of Noah in the Book of Genesis (Lericolais et al. 2001; 2003; Ryan et al.
2003).
This presentation will briefly highlight a few IGCP464 research initiatives
before providing a case study of the Late Quaternary Pacific Margin of Canada
and the peopling of the Americas.
POSTGLACIAL EVOLUTION OF THE WESTERN ARCTIC SHELF
ENVIRONMENTS
IVANOVA ELENA V. 1
presenter's e-mail: eivanova@geo.sio.rssi.ru
1 - Shirshov Institute of Oceanology RAS
The high-resolution study of benthic foraminiferal assemblages
in several cores from shelf depressions suggests different paleoenvironmental
evolution of the glaciated Barents Sea shelf and the non-glaciated eastern
Kara Sea shelf during the postglacial time. Lithostratigrafic evidence
confirmed by AMS 14C datings show that the recovered time span is about
17-18 cal ka in the north-eastern Barents Sea and about 12 cal ka in the
eastern Kara Sea. Generally rare foraminiferal occurrence in sediments of
the Barents Sea ice sheet deglaciation points to unfavorable benthic habitat.
A proximal glaciomarine environment characteristic for the early deglaciation,
with almost permanent sea-ice cover throughout the newly formed marine basin,
and abundant fine suspended matter delivery from melting glaciers hinted
biological productivity, thus restricting the food supply for benthic communities.
During the main deglaciation phase, when the ice sheet retreated above sea
level, foraminiferal assemblages became more diverse, and some increase in
abundance occurred at rather short intervals of enhanced bottom-water ventilation
that resulted from oxygen supply by downslope brine-induced nepheloid flows.
The warm and saline subsurface Atlantic water inflow into the Barents Sea
via troughs and an appearance of short ice-free seasons promoted plankton
bloom. In both seas, the benthic foraminiferal assemblages demonstrate high
values of opportunistic species which tolerated the stressed environments.
However, a significant percentage of brackish species is found in Preboreal
sediments from the Kara Sea due to river run-off influence. The most dramatic
change in the Barents Sea environments is fixed at Preborial to Holocene
boundary when normal marine conditions established throughout the basin resulting
in a strong increase in bioproductivity. The evolution of periglacial eastern
Kara Sea was more gradual with an increase of marine elements percentage
in foraminiferal assemblages during the Early Holocene sea-level rise, until
~ 7 cal ka. In both basins, variations in Holocene assemblages respond to
climate driven changes in sea-ice conditions, food supply, bottom-water ventilation,
and other paleoceanographic parameters. The variability also reflects oscillations
in the Atlantic water input into the basins and in river run-off, the latter
being especially pronounced in the Kara Sea affected by an increased Siberian
rivers discharge during the Middle Holocene.
GLOBAL CHANGE AND
SUBMARINE GROUNDWATER DISCHARGE
KONTAR EVGENY 1
presenter's e-mail: ekontar@ocean.fsu.edu
1 - P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences
Global Change can refer to a number of processes. It certainly
means (a) that a phenomenon is observed to be changing in many different
parts of the world; and (b) that a process is linked to some large-scale
phenomenon like climate. Submarine groundwater discharge (SGD) and its associated
nutrient contributions to the coastal zone are closely related to both definitions.
While SGD has been estimated to be a small fraction of the global freshwater
flux, such inputs are estimated to be much more important in semi-enclosed
and inland seas. Recent estimates, for example, attribute 50% of the total
freshwater flow into some inland seas to groundwater inputs! (i.e., Aral
Sea, INTAS projects 1003 & 1014). In addition, since nutrient concentrations
are often much higher in groundwater than river water; net fluxes can be
higher even when the flow is lower. We hypothesize that many of the water
quality and associated problems effecting coastal zone environments around
the world today may be related to past and on-going contamination of terrestrial
groundwater because those groundwater are now encroaching upon the coastal
zone. For example, chronic inputs of fertilizers and sewage on land over
the past several decades has resulted in higher groundwater nitrogen concentrations
which, because of slow yet persistent discharge along the shorelines, eventually
results in coastal marine eutrophication. Such inputs may thus be responsible
for the increased occurrences of coastal hypoxia, nuisance algal blooms,
and all the associated consequences, which have direct human dimensions.
We thus suggest that some of the more important "Changes in Coastal Zones
and Inland Waters," a research priority, may be influenced by groundwater
discharge, an invisible and overlooked pathway between land and sea. On July
20, 2001, during the 6th Scientific Assembly of the IAHS in Maastricht, the
Netherlands, we had a productive meeting, discussing and organizing the IUGG
Inter-Association Commission "Groundwater-Seawater Interactions" (CGSI),
with representatives from the International Association for the Physical
Sciences of the Ocean (IAPSO) and the International Association of Hydrological
Sciences (IAHS), to help to facilitate and coordinate research in this highly
interdisciplinary subject. During the IUGG Congress in Sapporo, Japan (July
2003) the CGSI was reorganized to have more than 130 members. Study of the
direct discharge of groundwater into the ocean is an emerging science.
RAPID
TRANSGRESSIONS INTO SEMI-ENCLOSED BASINS SINCE THE LAST GLACIAL MAXIMUM
LERICOLAIS GILLES 1, CHIVAS ALLAN ROSS 2,
CHIOCCI FRANCESCO LATINO 3, USCINOWICZ
SZYMON 4, BO JENSEN JORN 5, LEMKE WOLFRAM 6,
VIOLANTE ROBERTO ANTONIO 7
presenter's e-mail: Gilles.lericolais@ifremer.fr
1 - IFREMER France
2 - School of Geosciences, University of Wollongong, NSW 2522, Australia
3 - Dipartimento Scienze della terra, Università di Roma "La Sapienza"
P.le Aldo Moro 5, 00185, Roma, Italy
4 - Polish Geological Institute, Branch of Marine Geology Ko_cierska
5 st., 80-328 Gdansk, Poland
5 - Geological Survey of Denmark and Greenland, Øster Voldgade
10, DK-1350 Copenhagen K, Denmark
6 - Institution: Baltic Sea Research Institute Street: Seestr. 15 Postal
code: D-18119 Rostock-Warnemünde German
7 - Argentina Hydrographyc Office Av. Montes De Oca 2124, (C1270ABV)
Buenos Aires, Argentina
One of the objectives of the IGCP 464 project is to compare
and contrast the global development of continental shelves, particularly
with respect to the Last Glacial Maximum (LGM) with a real will to complement
with a high-temporal-resolution the plaeoclimate variability since the LGM.
Semi-enclosed basin margins represent good candidates for preservation in
their sedimentary records of abrupt changes climatically or tectonically
related, often unrecorded or obliterated by global modifications. Abrupt
Sea-level rises have been recorded in many different semi-enclosed basins
around the world. The link to rapid transgressions is easy to do, even if
the mechanisms are completely different. Large and rapid releases of freshwater
from ice sheets since the LGM to sensitive areas may also arise from several
mechanisms. The last deglaciation provides the level of preservation necessary
to identify specific mechanisms of ice-sheet forcing and attendant climatic
responses. The presentation will summarise results presented during a special
session of the project which concern focussed on rapid transgressions into
semi-enclosed basins since the LGM. Different examples will be discussed
as the Carpentaria Basin, in northern Australia, Argentinean semi-enclosed
basins, the Baltic Sea and the Black Sea. The Carpentaria Basin, in northern
Australia is at low latitude, and far from the direct influence of ice sheets.
Here, the critical sill depth (currently -53m wrto sea level) defines changes
between marine and lacustrine sedimentation, and provides independent evidence
of global sea-level changes. Evolution of the Argentinean basins was mainly
conditioned by the post-LGM relative sea-level rise as well as by littoral
dynamic factors that fluctuated following the succession of climatic and
eustatic events. The Baltic Sea has been covered during the LGM by an ice
sheet up to 3km thick, and the subsequent isostatic re-adjustment after deglaciation
far outpaced the global postglacial sea-level rise. The Black Sea, a semi-enclosed
basin which connections with the global ocean are restricted by the Bosphorus,
Dardanelles and Gibraltar Straits, was directly supplied with the melt water
of the first deglaciation event by major Eastern Europe rivers. The Black
Sea has encountered complex water level fluctuations with high lake levels
occurring during wet and melting period after the LGM and low lake levels
occurring during drier conditions as the Younger Dryas was for this region
LATE QUATERNARY EVOLUTION
OF THE INNER SHELF OFF SÃO SEBASTIÃO, SOUTHEASTERN BRAZIL:
IMPLICATIONS FOR THE BRAZILIAN SEA-LEVEL CURVE
DE MAHIQUES MICHEL 1, KLEIN DANIEL ANDREAS
1, RODRIGUES MARCELO 1, FURTADO
VALDENIR VERONESE 1
presenter's e-mail: mahiques@usp.br
1 - Institute of Oceanography - University of São Paulo
The Quaternary evolution of the Brazilian coast has been the
object of recent evaluation mainly concerning the Holocene sea-level curve.
Actually most of the data on Brazilian coastal evolution relate to the
Late Holocene; very little information is available regarding the position
of the sea-level prior to 7,500 years B.P. and a considerable amount of
information about the position of the sea-level has been obtained by association
from other areas of the world. This is particularly critical for the Isotope
Stage 3, for which no reliable information about the maximum sea-level had
yet been obtained.
In this study we have used three sedimentary cores as well as a beach-rock
sampled in the region off São Sebastião, on the Souttheastern
Brazilian shelf, to interpret the evolution of the area during the Late
Quaternary giving special attention to the sea-level change curve. The cores
were analysed for coarse fraction, calcium carbonate, organic carbon, total
nitrogen and sulphur content and carbon isotope values. Calcium carbonate
samples (foraminifer and beach rock) were used for radiocarbon datings.
For samples younger than 20,000 years the ages were calibrated using the
SW Atlantic reservoir correction for marine samples.
The base of one of the cores (TSSB-1), at a depth equivalent to 7 meters
below the present sea-level, consisting of a dark olive gray mud with sparse
carbonate fragments and containing the foraminifer Elphidium sp. and the
ostracod Cyprideis, has been dated at 39,500±750 years B.P., corresponding
to Isotope Stage 3. Compositional and isotopic values allow this sequence
to be recognised as characteristic of a mixohaline environment. Sedimentation
of this sequence continued up to ca. 10,000 years B.P. through a progressive
change of the environment to fresh water conditions.
The Holocene marine ingression in the area is registered after 8,250
years B.P. when a beach rock, located 13 meters below the present sea-level
was deposited. In the region of the core samplings marine conditions were
established only after ca. 6,000 years B.P. as revealed by compositional
and isotopic data.
Our results have enabled us to make good the lack of information as
to the position of the sea-level in a relatively tectonically stable area
of the SW Atlantic Ocean. They also represent the first sure indication of
the maximum sea level on the Brazilian coast during Isotope Stage 3.
LOWSTAND DEPOSITIONAL TERRACES SURROUNDING
WESTERN PONTINE ARCHIPELAGO (TYRRHENIAN SEA)
MARTORELLI ELEONORA 1, CHIOCCI FRANCESCO LATINO
1, PAZZINI ALFREDO 1
presenter's e-mail: eleonora.martorelli@uniroma1.it
1 - Dipartimento di Scienze della Terra, Università degli Studi
di Roma "La Sapienza"
Lowstand depositional terraces (LDTs) are prograding sandy wedges,
characterized by limited thickness (some tens of meters), with internal
foreset dipping 5°-9° (Chiocci and Orlando, 1996). They develop
parallel to the isobaths close to the shelf break and have been always recognized
on steep shelves, mainly located around volcanic islands or in tectonic settings.
In volcanic island settings, LDTs represent the main, sometimes the
exclusive, depositional bodies occurring over the volcanic bedrock on the
shelf.
The detailed study of the LDTs give indications on 1) the depositional/climatic
condition during glacial time 2) the vertical movement of the continental
margin, 3) the occurrence of present or sub-present erosional conditions
of canyon heads.
A detailed description of LDTs recognized in Western Pontine Archipelago
has been done by Chiocci and Orlando (1996). For geological mapping purposes,
new high resolution seismic data (Sparker and Chirp) have been collected
and a re-interpretation of existing data have been performed. As a result
a detailed map of distribution and thickness of the LDTs is now available.
In particular a LDT develops, almost continuously, around Palmarola,
Ponza, Zannone islands and Botte Rocks, above an erosional unconformity
clearly depicted in almost all the area.
The unconformity truncates a substratum mainly made up of volcanic
rocks. However, in some areas (i.e. northern part of the archipelago and
Botte Rock), below the unconformity the presence of deeper reflectors suggest
the occurrence of older lowstand depositional terraces. These areas are thus
believed to represent subsiding zone where older units were preserved from
erosion by lowering them below the maximum depth reached by Upper Pleistocene
sea level lowstands.
Last LDT (thought to be formed during last glacial maximum) reaches
the maximum thickness close to the shelf break. Main depocenters are located
offshore the northern part of Ponza-Zannone saddle (with thickness of about
50 m) and S-SE of Ponza Island (with thickness of about 40 m).
In some areas LDT seems to have a quite complex relation with instability
processes as the terrace edge may be controlled in part by slope gradient
but the post-depositional erosive activity of gullies and canyon heads may
shallow it as well.
CHIOCCI F.L. and ORLANDO L. (1996). Lowstand terraces on Tyrrhenian
Sea steep continental slopes. Marine Geology, 134, 127-143.
FACIES SYSTEM
OF THE BARENTS SEA SINCE THE LAST GLACIAL MAXIMUM TO RECENT
MURDMAA IVAR 1
presenter's e-mail: murdma@sio.rssi.ru
1 - P.P.Shirshov Institute of Oceanology
Late Weichselian continental moraine facies unconformably overlie
the rough basement topography of the Barents Sea shelf. In shelf depressions,
a blanket of proximal glaciomarine facies was deposited above the moraine
during the initial deglaciation phase (ca. 16-13 ka BP) when the Barents
Sea ice sheet detached from the bottom resulting in iceberg calving, and
seawater first penetrated into deep troughs. The facies comprise marine moraine,
diamicton composed of iceberg rafted debris (IRD) and glacier meltwater load,
as well as debris flow deposits. Although very rare, but persistent foraminiferal
fauna and saline pore water are evidence of a marine environment. Overlying
distal glaciomarine facies represented by various laminated flow deposits
are formed during the main deglaciation phase (ca. 13-10 ka BP). Absence
of IRD in laminated fine-grained sediments suggests glacier front retreat
above the sea level. Glacier meltwater discharge became the main sediment
source. Appearance of oxidized sediments and ferruginous hardgrounds indicates
ventilation of the bottom water possibly related to enhanced brines activity.
The latter also induced gravity flows and transferred meltwater isotope
signals from the sea surface to the bottom where they are fixed in benthic
foraminiferal tests. Onset of the Holocene marine environment led to a
dramatic increase in such indicators of enhanced biological productivity
as organic carbon content, foraminiferal abundance and species diversity,
bioturbation, and microbial sulfate reduction. Holocene sediments are represented
by clay or silty clay of depression facies contrasting with wave- and current-transported
sand on near-shore shoals and with thin discontinuous veneer of residual
coarse-grained bank summit facies enriched in IRD and characterized by locally
rich benthic fauna. Lateral near-bottom suspended matter transport by waves,
bottom currents, and low-density nepheloid flows mainly controls the facies
diversity and variations in thickness of the Holocene sediment cover. Maximum
thicknesses (up to 20 m or more) are fixed in fjords. Holocene sections up
to 3-5 m thick occur in local depressions, where they show high organic matter
content and relatively rich benthic foraminiferal fauna. Facies of wide deep
lowlands and gentle slopes are characterized by thin (<1 m) Holocene sediments
with low organic matter content and absence of microfossils, possibly owing
to their dissolution in conditions of slow sedimentation.
ARE EMERGED SHELVES
A SOURCE FOR LOESS?
SMYKATZ-KLOSS BETTINA 1, ZOELLER LUDWIG R.
2, ANTOINE PIERRE 3
presenter's e-mail: ludwig.zoeller@uni-bayreuth.de
1 - University of Bonn, Geography Dept.
2 - University of Bayreuth, Chair for Geomorphology
3 - UMR CNRS 8591 - Laboratoire de Géographie Physique, Meudon
Textbooks of geology and geomorphology mostly regard glacial
outwash plains as the main source of loess. The thickest loess units of
the world are, however, too far remote from vast glacial outwash plains.
Therefore, other possible sources have been suggested in the literature.
Shelves emerged due to glacio-eustatic sea-level drop have seldom been discussed
as source areas. In many parts of the world shelves are covered by unconsolidated
fine-grained detrital sediments which can easily be blown out. The English
Channel, e.g., was identified as a significant source area of loess in north-western
France by heavy mineral analysis and geomorphologic observations. For loess
areas further remote from the coast-line heavy minerals may, however, fail
to prove a loess contribution from emerged shelves.
We compared last glacial loess-paleosol sequences from the Picardie
historical landscape (NW France) and the rolling land "Pleiser Huegelland"
east of the city of Bonn, Germany, situated at the decline of the Rhenish
Massif towards the Lower Rhine Embayment. Geochemical, isotopic and mineralogical
methods (including microprobe SEM) as well as microscopic investigation
of microfossils have been applied.
We found evidence (trace minerals, microfossils) for littoral or shallow
marine sediments delivering detrital grains to loess accumulations in areas
under investigation, the Picardie (as expected) and the surroundings of
Bonn. For the latter, a (dominant) local source (primarily periglacial fluvial
terraces of the southern Lower Rhine Embayment) is distinguished from a remote
source including emerged littoral or shallow marine sedimentary environments.
The far-travelled component cannot be quantified at this stage of our studies,
but its qualitative proof may trigger further research into the role of
emerged shelves as a source of atmospheric dust. Sea-level change, with regard
to this perspective, would not only appear as a result of climate change,
but also give rise to a positive feed-back to climate change due to the
effects of dust on atmospheric radiation parameters.
PALAEOENVIRONMENTAL
EVOLUTION OF THE NORTHERN ARGENTINA CONTINENTAL SHELF DURING THE POST-LGM
TRANSGRESSION
VIOLANTE ROBERTO
ANTONIO 1
presenter's e-mail: violante@hidro.gov.ar
1 - argentina hydrographic service
Littoral and shallow-marine deposits accumulated during the
marine cycle that followed the Last Glacial Maximum constitute the uppermost
stratigraphical unit in the northern part of the Argentina continental shelf
and adjacent coastal plains. This unit is considered, from the sequence stratigraphy
viewpoint, as a depositional sequence that includes two system tracts: transgressive
and high-stand. The probable existence of a low-level system tract on the
outer margin of the shelf was still not confirmed. System tracts are formed
by a succession of depositional systems that represent sedimentary environments
such as barriers, beach ridges, coastal lagoons, marshes and estuaries.
The study allowed to interpret the sea-level fluctuations and palaeoenvironmental
evolution occurred in the region over the last 18.000 to 20.000 years.
SUB-AERIAL EXPOSURE OF CONTINENTAL SHELVES DURING
GLACIAL PERIODS AND THE TERMINATION OF ICE AGES
YIM WYSS WAI-SHU 1
presenter's e-mail: wwsyim@hku.hk
1 - Department of Earth Sciences, The University of Hong Kong, Hong Kong
SAR, China
The sub-aerial exposure of continental shelves during glacial
periods is suggested to provide a mechanism for the production of atmospheric
carbon dioxide significant enough to cause the abrupt termination of ice
ages. The processes operating leading to such changes include:
(1) Acid-sulphate soil development in exposed siliciclastic shelves.
(2) Karstification of exposed coral reefs.
(3) Karstification of exposed carbonate platforms.
The massive release of carbon dioxide provides the triggering mechanism
needed for switching the earth from a full glacial mode back into an interglacial
mode (Yim et al., 2002). This is supported by the dramatic increase in carbon
dioxide and methane content in the Vostok ice core following the glacial
periods of MIS 2, 6, 8, 10 and 12 (Petit et al., 1999).
References -
Petit, J.R., Jouzel, J., Raynauld, 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., Stievenard, M. (1999). Climate and atmospheric
history of the past 420,000 years from the Vostok ice core, Antarctica.
Nature 399: 429-436.
Yim, W.W.-S., Chan, L.S., Hseih, M., Philp, R.P., Ridley Thomas, W.N.
(2002). Carbon flux during the last interglacial cycle in the inner continental
shelf of the South China Sea off Hong Kong. Global and Planetary Change
33: 29-45.
18O values. The early Holocene sediments everywhere showed
high MS associated with high AIR and low OC, CaCO3 and 