Abstracts / Quaternary International 279-280 (2012) 9–12090

to stress is compared to the results of ring-shear tests carried out on cor-responding materials under equal conditions.Control of all particle and model parameters allows an investigation of thedeformation patterns (distributed vs. discrete, viscous vs. plastic rheology)in a variety of subglacial conditions. The simulated data output allowsclose monitoring of progressive deformation, particle advection andintergranular mixing whereby all involved physical parameters are readilyavailable for continuous inspection and analysis. The preliminary resultsindicate that the effective pressure influences the mode of deformationand material rheology. High shear strain simulations show progressivevertical segregation of grain sizes.

THE GSSP OF “IONIAN” STAGE (EARLY-MIDDLE PLEISTOCENEBOUNDARY) AT THE MONTALBANO IONICO SECTION (SOUTHERN ITALY)

Neri Ciaranfi. Bari University, ItalyE-mail address: neri@geo.uniba.it

The Global Boundary Stratotype Section and Point (GSSP) of the “Ionian”Stage should be defined at a point “close” to the Matuyama-Brunhesreversal, in a marine section exposed on land. However, magnetic reversalis only one of multiple criteria for GSSP definition. The Montalbano Jonicosection, cropping out in the southern Apennine Foredeep, is a continuous,well exposed and astronomically tuned succession extended from 1.24 Mato 0.645 Ma. The section spans the interval from Marine Isotope Stage(MIS) 37 to 17/16 and covers, together with the Vrica Section, the sedi-mentary record of the entire Calabrian Stage. The section encompassesMIS19, whose base closely corresponds to the Matuyama/Brunhes boundary,a paleomagnetic reversal not yet recorded in theMontalbano sediments. Inthe section, the base of MIS 19 is close to the volcaniclastic layer V3,radiometrically dated at 801.2�19.5 ka and falls between the beginningand the end of temporary disappearance interval of Gephyrocapsa omegadated at 828 ka and 771 ka respectively. The sedimentary intervalincludingMIS 19 is represented by outer shelf deposits recording cyclic sealevel changes. A maximum flooding surface, highlighted by the occurrenceof Neopycnodonte paleocommunity, and the occurrence of the mesope-lagic tropical-sutropical Atlantic teleostean Bonapartia pedaliota, arecorrelated with MIS 19. Sedimentary evidences of glacio-eustatic sea levelrise correlated with MIS 19 andMatuyama/Brunhes boundary are also wellrecognizable in extremely different depositional systems and geographicareas, thus supporting the wide traceability of this oxygen isotope shift.We retain that the on set of MIS 19, in the Montalbano Jonico section, mayrepresent an appropriate stratigraphic horizon for the definition of theGSSP of the “Ionian” Stage, and fulfils indication of Remane et al. (1996) forboundary stratotype definition.

ADVANCES IN THE UNDERSTANDING OF THE BRITISH-IRISH ICE SHEETFROM THE GLACIAL LANDFORM RECORD

Chris D. Clark. University of Sheffield, United KingdomE-mail address: c.clark@sheffield.ac.uk

Palaeo ice sheets left behind a wide variety of evidence from which it ispossible to reconstruct elements of their spatial extent, thickness andvolume, and plot changes in these through time. Once a reasonableenvelope of ice sheet behaviour is constrained, the potential exists to gaininsights on how ice sheets and climate interact, and to use palaeo ice sheetreconstructions as a means of improving ice sheet modelling endeavours.Such knowledge is useful for understanding both Quaternary and futureclimate and associated cryospheric changes. However, the task is largebecause of the wide range of types of evidence (e.g. striae to relative sealevel indicators) and breadth of specialists required, including in glacialgeology and geomorphology, relative sea level, palaeoceanography, dating,geophysics, and numerical modelling. In this paper I review the centralcontribution that glacial geomorphological investigations havemade to icesheet reconstruction, drawing on examples from the Laurentide andFennoscandian Ice Sheets, but with a focus on recent advances in ourunderstanding of the British and Irish Ice Sheet. It is interesting that in thehistory of investigation of the BIIS that landform investigation had becomeneglected, relative to their use in reconstructing other palaeo ice sheets.More recently, new technologies with which to investigate landforms have

prompted a renewed mapping effort and along with data interpretationand synthesis tools have led to some significant advances in our under-standing of the changing extent and geometry of the ice sheet.

CONTROLS ON THE LOCATION OF GLACIAL OVERDEEPENING

Chris D. Clark. University of Sheffield, United KingdomE-mail address: c.clark@sheffield.ac.uk

Glacial overdeepenings have yet to be systematically studied. In thisinvestigation, we examined the location and form of several hundred glacialoverdeepenings, and analyse controls on overdeepening location. The aimofthe study is to elucidate the glaciological and geomorphological processesthat control overdeepening development, and assess the importance ofoverdeepenings in glacial systems. This will allow significant improvementsin our knowledge of glacial systems and landscape evolution, as well aspotentially permit us to gauge the influence of this phenomenon on thedynamic response of glaciers, which is coupled to climate.The investigation made use of GIS tools to analyse NASA Shuttle RadarTopography Mission (SRTM3) and General bathymetric chart of the oceans(GEBCO 30 arc-second) digital elevation models. Preliminary researchfocused on the Labrador Province of Canada (and adjacent coastal region),and has so far examined whether changes in glacial valley cross-sectionalarea drive overdeepening formation, via influencing basal ice velocities.The hypothesis predicts that a strong local to glacier-wide associationwould frequently be observed between the location of glacial confluences(localised ice acceleration) and overdeepening.Initial results indicate a strong statistical relationship between the locationof glacial confluence and overdeepening, with nearly twice as manyintersections apparent thanwould be expected by random coincidence. Asmany as 50% of identified confluences contain at least one overdeepening.Research is now concentrating on quantifying how glacial valley cross-sectional area affects overdeepening size. This study aims to providesystematic data on overdeepenings and which could subsequently be usedas a test of numerical models of glacial erosion. Better models will improveour understanding of the glacial system.

PALAEOGEOGRAPHIC MAPS OF THE RETREAT OF THE LAST BRITISH-IRISH ICE SHEET

Chris D. Clark. University of Sheffield, United KingdomE-mail address: c.clark@sheffield.ac.uk

During the last glacial the ice sheet that subsumed most of Britain, Irelandand the North Sea attained its maximum extent by 27 ka BP andwith an icevolume sufficient to raise global sea level by ca. 2.5 m when it melted. Wereconstruct the demise of this British-Irish Ice Sheet (BIIS) and presentpalaeoglaciological maps of retreat stages between 27 – 15 ka BP. Thewhole land area was investigated using remote sensing data to mapmoraines, meltwater channels, eskers, and drumlins. For the continentalshelf, seabed bathymetric data were used to map numerous largemoraines. From an integration of this mapping of glacial geomorphology(> 26,000 landforms) with previously published evidence, compiled in theBRITICE database, and from more recent sources, we derive a pattern ofretreat for the whole BIIS. Along with a recently compiled database ofrelevant dates (881 examples) that constrain the timing of retreat, thepattern information is deciphered to produce a best-estimate of thepalaeogeography of the shrinking ice sheet. Pattern information reveals anice sheet mainly comprised of a shelf-parallel configuration from SWIreland to NE Scotland but it spread far enough to the south to incorporateoutlying ice domes over Wales, the Lake District and Kerry. Final disinte-gration was into a number of separate ice caps, rather than reduction asa single mass, and paradoxically, retreat was not always back to highground. Rates of ice loss were found to vary widely over space and time(e.g. 65 - 260 km3 per year) and the role of ice streams and calving losses ofmarine-based sectors are considered. Retreat rates of up to ca. 150 ma-1

were found for some ice streammargins. Our reconstruction, when viewedfrom the opposite perspective, documents when fresh land becameexposed for exploitation by plants, animals and Humans, and records forhow long such land has been available for soil and geochemical develop-ment and ecological succession.