Ice streaming in the Amery Ice Shelf system over the Neogene

Abstracts / Quaternary International 279-280 (2012) 346–461356

reworked shells from the ‘Irish Sea Till’, and OSL dates from deglacialoutwash overlying the Irish Sea Till all provide support for an extensive lastIrish Ice Sheet which covered much of the area of the Older Drift at the lastglacial maximum. Ice sheet advance and till deposition along the southcoast of Ireland dates to after w24 cal ka with deglaciation shortlythereafter. This interpretation is consistent with published ice-rafteddebris records from the western margin of the ice sheet which showmaximum glaciation at 24 cal ka BP and major deglaciation by 23 cal ka BP.Multibeam swath bathymetry data collected through the Irish NationalSeabed Survey offshore of southwest Ireland suggest that the ice sheet wasgrounded on the inner-mid shelf. Thus most of southern Ireland wasglaciated during the LGM and the moraine belts which have traditionallybeen interpreted as marking the last glacial limit such as the South IrelandEnd Moraine are recessional features formed during ice sheet retreat.

ICE STREAMING IN THE AMERY ICE SHELF SYSTEM OVER THE NEOGENE

Philip O’Brien. Macquarie University, AustraliaE-mail address: phil.obrien.ant@gmail.com

The Amery Ice Shelf ice drainage system has a history of glaciation goingback to the Palaeogene. Ice flow was strongly controlled by underlyinggeological structure, following the Lambert Graben and excavating thesedimentary basin it contains. A change in seismic reflector geometry,cutting of a cross shelf trough and growth of a trough mouth fan indicatethe onset of ice streaming in the early Pliocene (w3.9-3.6 Ma). The icestream orientation indicated by the direction of Prydz Channel is almostnormal to underlying basement structures suggesting deflection of themain drainage to the west by ice from the eastern side of Prydz Bay. Shelfedge trajectories on seismic reflection data from the Prydz Channel and itsfan suggest episodes of glacial bed erosion followed by some verticalaggradation, while debris was still being transported to the shelf break atthe base of the ice. Seaward dipping topsets reflect loading of the slope byfan deposition and compaction of fan sediments, while the apparent cyclesmay result from sea level cycles affecting subglacial deposition. Episodes ofice retreat from the shelf edge saw deposition of thin mud units on the fansurface and open water extending hundreds of kilometres inland of thepresent ice shelf edge. The section in ODP Hole 1167 indicates that thePrydz Channel ice stream ceased advances to the shelf edge some time inthe mid Pleistocene. Deforming beds with megaflutes extended out togrounding zone wedges in the mid shelf during the late Pleistocene. Thismid Pleistocene change in behaviour could stem from deep excavation ofthe inner shelf, reduced moisture transport into the interior, and thechange from 41 ka to 100 ka climate cycles. The changes in ice behaviour inthe Amery system over the Neogene suggest that changes in precipitationon a regional scale should considered when trying to understand theevolution of major drainage basins and ice streams.

ENVIRONMENTAL CHANGE AND THE EXPANSION OF LATE NEOLITHICCULTURES IN CENTRAL AND WESTERN EUROPE: AN OVERVIEW OFTHE EVIDENCE PROVIDED BY HIGH-RESOLUTION PALAEOECOLOGICALRECORDS

Michael O’Connell. National University of Ireland, IrelandE-mail address: michael.oconnell@nuigalway.ie

An overview of environmental change associated with Funnelbeakercultures (Trichterbecherkultur, TBK), i.e. the first farming peoples thateffected the Neolithization of a large part of northern Europe, will bepresented. As the first farmers in northern central Europe and Scandinavia,they introduced domesticated animals and cultivated plants into theseparts of Europe and accorded them,what was to become, a central definingrole in human nutrition. Megalithic tomb construction was anotherimportant feature of the TBK cultures that was shared with Neolithiccultures of Atlantic Europe. Of particular relevance in this regard is theexpansion of Neolithic cultures into Britain and Ireland that was sostrongly characterised by megalithic-tomb construction and that coin-cided, to a considerable degree, with the TBK cultures in continentalEurope. The farming activities of these peoples, who were responsible forthe final stages of the Neolithization of Europe, resulted in varying degrees

of incursion into the natural environment that is reflected in a variety ofproxies and, above all, in pollen records. In recent years, several new high-resolution pollen diagrams with good chronological control, provide newpossibilities of improving our understanding of how these late Neolithicpeoples changed the environment and how they, in turn, reacted toenvironmental change. Central questions that will be considered includeregistration of initial farming impacts in the pollen records, insights intothe changes effected in local and regional woodland cover and composi-tion, the duration of phases of impact, and the long-term consequences ofNeolithic farming for woodland dynamics and pedogenesis. Considerationwill also be given to climate change in the mid Holocene, and the role thatclimate may have played in influencing patterns of human activity anddevelopments in the natural environment.

VARIABILITY IN RIVER RUNOFF AND DUST ACCUMULATION IN WCENTRAL ASIA DURING THE PAST w2000 YEARS

Hedi Oberhaensli. GeoForschungsZentrum Potsdam, Telegrafenberg. D-14,GermanyE-mail address: oberh@gfz-potsdam.de

The tributary rivers Amu Darya and Syr Darya contribute major amounts ofwater to the hydrological budget of the endorheic Aral Sea. Processescontrolling the flow of water into rivers in the headwater systems in TienShan (Kyrgyzstan) and Pamir (Tajikistan) are therefore most relevant. Lakewater mineralization is strongly dependent on river discharge and hasbeen inferred from spectrometrically determined gypsum and other saltcontents. Comparison of high-resolutionmineralization datawith tree ringdata, other proxies for tracing temperature and snow cover in NW China,and accumulation rates in the Guliya Ice Core indicate that mineralizationover the past w2000 years in the Aral Sea reflects snow cover variabilityand glacier extent in Tien Shan and Pamir (at the NW and W edges of theTibetan Plateau). We observed that the runoff decreased between AD 100-300, AD 1150-1250, AD 1380-1450, AD 1580-1680 and during several lowfrequency events after AD 1800.We assessed the late Holocene minerogenic aerosol deposition distribu-tion of the grain size of detrital particles and the bulk sediment flux fromthe Aral Sea at high resolution. Two processes are mainly relevant for thedetritic input because fine silt-size fractions and Ti, Fe and K were posi-tively correlated with Component 1 (C1), and clay-size fractions werepositively correlated with Component 2 (C2). We propose that silt-sizefractions and, in particular, the grain-size fraction ratio (6-32 mm/2-6 mm)are associated with airborne processes in the Aral Sea region, while theclay-size fractions (C2) are transported into the lake by sheetwash duringheavy rainfalls, particularly in spring. Our results show that the bulksediment deposition fluxes were extremely high during the Little Ice Age(LIA; AD 1400-1780), which may be related to increased dust deposition.Deposition was low during AD 1-350; between AD 720 - 1400, includingthe Medieval Warm Period (MWP, AD 755 – 1070), and since the AD 1940s.

FLUVIAL INCISION BY SEASONAL ICE AND SNOW MELTWATER DURINGINTERGLACIAL-GLACIAL CLIMATIC TRANSITION IN LORRAINE, FRANCEAND SAARLAND, GERMANY

Serge Occhietti. CERPA Université Nancy2, FranceE-mail address: serge.occhietti@gmail.com

In the Eastern Paris Basin and its Hercynian margins, Quaternary steppedterraces are preserved, especially along the main valleys (Moselle,Meurthe, Sarre), and related to a slow continental uplift and a discontin-uous deepening of the valleys allocated to climatic changes. Incision byrivers into previous alluvial sediments and the underlying bedrock occursduring interglacial-glacial climatic transitions and at the end of late glacialphases. In the upper reaches of rivers directly fed by glacial meltwater fromthe Vosges Massif, the late glacial erosional phases are the strongest, asobserved in the St-Dié basin. In the middle reaches of rivers, the mainerosional phase seems to occur during the warm to cold climatic transi-tion; but the related processes were not specifically studied. In Lorraineand Saarland, the erosional contact at the base of the terrace deposits hasbeen observed on excavations. The typical sequence of sediments over the