linktoigcp464webpage    I nt ernational Geological Correlation Program #464  IGCPhammer

Continental Shelves during the Last Glacial Cycle: Knowledge and Applications

Discussion Forum



During the First Annual Conference of IGCP464 it was decided to mantain an ongoing scientific discussion apart from the Meetings.
Such discussion will occur through written contributions to this electronic forum. Individual will be listed in chronological order.

If you wish to participate in the debate, send a written message to francesco.chiocci@uniroma1.it . In it please cite the subject of the forum you wish to contribute.
 To be effective to the discussion, ENSURE YOUR MESSAGE HAS IS CONCISE AND WELL FOCUSED.
The moderator(s) reserve the right to decide if and how to publish the contributions.




THEMES DECIDED AT THE HONG KONG MEETING AS PRIORITIES FOR THE START-UP OF IGCP464 PROJECT

geological markers to define LGM position on shelves
glacio- and hydro- isostasy on shelves
role of shelves in the carbon cycle
compilation of shlef characteristics around the world



IGCP464 WORKING GROUP

Physical stratigraphy
 leader: Gilles Lericolais , France  
Chemical Stratigraphy
leader: Allan Chivas , Australia
Applied Aspects
(i.e. economic deposits, engineering and geotechnical studies)
leader: Wyss Yim , China
Influence on human culture
leader: Renée Hetherington , Canada
The working group leader will act as covener, asking for contributions on specific aspects of the w.g. themes






DISCUSSION FORUM



Glacio- and hydro- isostasy on shelves
DEFINITION OF THE THEME (by F.L.Chiocci):A major goal is the production of reliable maps of coastlines at the LGM and other key eustatic/climatic moments, that will take into account the glacio/hydro-isostatic movements. Often models of vertical movements of continental margin take into account only some of the following: 1) tectonic subsidence due to local or regional effects (specially in active margins); 2) load subsidence and compaction due to the growth of the depositional wedge along the margin; 3) glacio-isostatic rebound due to ice retreat; 4) hydro-isostasy due to sea level rise. Moreover the models often consider effects deriving from selected data (i.e. in the Mediterranean the effect of the fenno-scandinavian ice cap is considered but not the ice cover on the Alps). Apart for the problem of  groundtruthing the models (see further discussion forum) a discussion is needed to define which factors are effective at which geographical scale in controlling the subsidence of the outer shelf/ shelf break region.











Geological markers to define LGM position on shelves

DEFINITION OF THE THEME (by Francesco L. Chiocci): the definition of LGM coastline is one of the main goal og the Project. It has relevant consequences to: 1) maximum amount of exposed land (a rough estimate of ..% has been given); 2) creation of land bridges for human migrations; 3) changes in coastal currents and littoral drifts, etc.
At present the estimate of the LGM coastline is quite rough, i.e. the present-day -100 or -120m isobaths (or whatever the d 18 people tell us was the minimum) is taken and the shoreline is assumed to have been there. This simple procedure may oversimplify the reality as tectonics, glacio-isostasy, hydro-isostasy and even erosion at the shelf break may result in processes more complicated than previously assumed. Only geological evidences will provide an indisputable data on the position of the LGM (i.e. eustatic minimum) shoreline. Once defined with geological data, it would be possible a) to define the processes controlling subsidence at the shelf edge;
b) to extrapolate the information at a global scale; c) to test the isostatic models produced for continental margins .


To build-up a database for discussion in these theme, you are asked to give a brief description of which are in your experience, the most reliable indicators of the eustatic minimum reached during LGM (one message for each item) on the left column and to give data in the right column

LGM palaeo-sealevel indicators
LGM palaeo-sealevel depths in specific areas
Study area, type of evidence, depth below present-day sea level, presumed range of confidence











Role of shelves on carbon cycle
DEFINITION OF THE THEME (by Wyss Yim):









Compilation of shelf characteristics around the world
A major goal of IGCP 464 is the classification of continental shelves, via the definition of end members, and the establishment of a common terminology. To this end, the following researchers will act as co-ordinators for particular regions for which old and new basic data need assembly and synthesis in order to classify shelves.  Collins and Chivas (Australia), Hanebuth (East Pacific), Voraya (India), Compton and Shaw (Africa), Chiocci and Gvirtzman (Mediterranean), Lericolais (North-east Atlantic), Polnyak (Arctic Eurasia), Josenhans (Arctic North America and north-west Atlantic), de Mahiques (Caribbean and South-east Atlantic), Gorsline (North-east Pacific), de Mahiques to contact Chilean colleagues (for south-east Pacific), Chivas and Violante (Antarctica).
DEFINITION OF THE THEME (By Francesco L. Chiocci):











Physical stratigraphy

 

leader: Gilles Lericolais , France  



DEFINITION OF THE THEME (by Gilles Lericolais):The relative importance of climate vs. sea-level change on continental and nearshore marine successions has become increasingly important in recent years. Recent studies of the ice cores (Greenland, Iceland and Antartic) have offered many insights into Holocene climatic dynamics. Despite the abundance of continental records of Holocene climate, few have sufficient chronological control and sampling resolution to compare with the ice-core findings. As the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets and their effects on the Earth's surface. The disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans, which probably disturbed the ocean's thermohaline circulation and, hence, global climate. Sea-level increases bear witness to the melting of continental ice sheets. In parallel with ice-core studies, coral reef sections have been accurately dated and have provided sea level fluctuation curves. Ice cores are restricted to pole location or glaciers and could be considered as regional indicators. Corals often overlie active subduction zones, where tectonic movements are large and often discontinuous (especially in New Guinea), so the apparent sea-level records may be contaminated by a complex tectonic component. Recent developments in sequence stratigraphy, mostly in the area of very high resolution seismic data acquisition and interpretation and computer modelling allow empirical reconstructions of changes through time, as geometric representations of former erosional or depositional surfaces and could play a key role in understanding the relative importance of climatic vs. sea-level controls. Sequence stratigraphy is the study of genetically related strata within a chronostratigraphic framework.
This approach emphasises (1) recognition of key surfaces of erosion and/or sediment starvation, (2) description of sediment packages relative to their time-stratigraphic associations, and (3) genetic interpretation of sedimentary cycles. High Resolution Sequence stratigraphy provides a guide for observation and prediction and integrates observation at a log, core or outcrop scale. This guide can be used to locate good samplings on continental shelves in order to decipher the sea level prints an records. The last an easiest sequence to consider is without any doubt the last 4th order sequence installed since the Last Glacial Maximum.













Chemical Stratigraphy



leader: Allan Chivas , Australia


DEFINITION OF THE THEME (by Allan Chivas):












Applied Aspects
(i.e. economic deposits, engineering and geotechnical studies)
  

leader: Wyss Yim , China


DEFINITION OF THE THEME (by Wyss Yim):












Influence on human culture

leader: Renée Hetherington , Canada



DEFINITION OF THE THEME (by Renée Hetherington): Continental shelf evolution since the LGM has influenced the paleogeography and paleoenvironment of continental shelves worldwide.  Very rapid changes in sea-level combined with climate change impacted the location and productivity of littoral zones.  The formation and subsequent melting of continental ice sheets resulted in eustatic sea-level changes and isostatic crustal uplift and subsidence.   Changes in relative sea-level varied depending on the amount of water locked up in glaciers and proximity to ice sheets. Landbridges, coastal plains, paleoseas, paleolakes, and paleorivers formed and were rapidly inundated as eustatic sea-level rose, or were subaerially exposed during post-glacial rebound, subsequent to the melting of continental ice sheets. Paleoshorelines shifted in response to changing relative sea-levels.  Sea-surface temperatures and ocean currents were also impacted by climate change and altered paleogeography.  The influence of eustatic and isostatic changes on continental shelves, and the productivity of coastal zones is critical to understanding how humans were impacted by climate change during the last glacial cycle.  Where were new coastal plains and littoral zones located?  How productive were littoral zones during and subsequent to glaciation?  How rapidly did coastal zone productivity fall or rise as a result of climate and geographic changes?  How did humans respond and adapt to changes in their habitat?  What, if any, were the resultant impacts of human culture on the environment?  How did environmental changes influence human culture, behaviour, subsistence, and migration. These questions and the factors influencing human cultures on the continentel shelf during the Last Glacial Cycle, are the focus of this working group over the course of this project. Interdisciplinary insights are encouraged
May 25, 2002 FROM: Francesco d'Errico, CNRS Bordeaux, France
 No doubt that our and your projects are twins  or, at least, soul brothers. In few words, we are 1) creating a  comprehensive database of the C14 dates from archaeological sites dated to  the OIS 2 and 3 (ca 5400 dates so far, includig direct dates obtained from  painted caves - one of which has an entrance 27 m below the present sea  level !), and other information concernig each site (altitude, latitute,  open air, shelter, cave etc. cultural affiliation etc.). In the meanwhile,  some of us are carrying a number of analyses in marine cores, mostly collected off hte Iberian margin. In particular the high resolution pollen  record, with the other proxies, is providing the opportunity to study the  continental response to the D.H. climatic varibility. New analysis will be  soon conducted on the Marmara sea and in the Gascony gulf. We have  published a paper, presented several communication at conferences, and are  preparing two others.
 I would like to know what specific methods and data you or other members of  your group are using to assess the issue of the impact of continenetal  shelf evolution on cultural changes and if you have, or know where we can  find precise maps (and related software) of the evolution of the  continental shelf for Europe. If they exist.
 Incidentally, I lead a ESF/CNRS projet in the framework of the program  Origin of Human, language, and languages, and one or two projects of this  program work on the relationship between the first colonisation of  Australia and the implication of this for the origin of language and behavioral modernity. You can find information on this visint the site OHLL  (origine de l'homme, du language et des langues" of the CNRS
 I hope we will find ground for collaborations.
Francesco d'Errico, PhD  Charge de recherches au CNRS  UMR 5808 du CNRS,Institut de Prehistoire et de Geologie du Quaternaire  Batiment B18- Geologie, Av. des Facultes, 33405 Talence, France  Phone 33 (0)5 56842628, Fax 33 (0)5 56848451,  e-mail: f.derrico@iquat.u-bordeaux.fr web site: http://www.iquat.u-bordeaux.fr/paleo-art Home: 18 allee G. Brassens, 33600 Pessac, tel. 33 (0) 556458409
June 16, 2002 FROM: Renée Hetherington c/o Natural Resources Canada
Researchers participating in the project use molluscan, faunal, pollen, foram and sedimentological evidence in marine cores and highstand deposits to provide indications of climate and sea level change along the west coast of North and South America, the Black Sea, and locations in the southern hemisphere.  Interpretations of these data provide information about ice extent, the existence of coastal plains, and massive flooding events during and subsequent to the last glaciation.
* In the northern hemisphere Ice sheets blocked the path of early migrators; whereas coastal ice free plains provided opportunities for habitation and migration of early human, animal and floral populations.  The identification of ice extent and timing thus provides important constraints to the movement and habitation patterns of peoples during the Late Quaternary and Early Pleistocene.  Furthermore ice sheets likely separated linguistically and genetically similar populations for thousands of years.
* I used ESRI's ArcInfo Geo-spatial Analyst software to map the paleogeography of the west coast of Canada.  You can visit ESRI's website at: www.esri.com <http://www.esri.com> .
* I am currently unaware of maps showing continental shelf evolution in Europe in its entirety.  However, some of our members are working on paleogeographic reconstructions at specific locations.  I will raise this issue at our next meeting and would like to see a compilation of all research.  One of the goals of IGCP is to provide global continental shelf evolution maps - a difficult objective to achieve, but we will discuss the mechanisms for development at our next meeting.
Thank you for your interest in our project.  I would appreciate receiving reprints you may have available relating to your research.  If you have additional inquiries or questions that you would like addressed at our meeting in São Paulo in August please do not hesitate to contact me.

Renée Hetherington c/o Natural Resources Canada, Geological Survey of Canada. 9860 West Saanich Road, P.O. Box 6000, Sidney, B.C.,V8L 4B2, E-mail: rhetheri@pgc-gsc.nrcan.gc.ca <mailto:rhetheri@pgc-gsc.nrcan.gc.ca> Tel: 250-363-6302





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