HR: 0830h
AN: C31B-0403    [PDF]
TI: Insights Into the Drainage Characteristics of Pleistocene Ice Sheets in NW Europe Using 3D Seismic Reflection Data.
AU: * Lonergan, L
EM: l.lonergan@imperial.ac.uk
AF: Department of Earth Science and Engineering, Royal School of Mines, Imperial College London, South Kensington Campus, London, SW7 2AZ United Kingdom
AU: Collier, J S
EM: j.collier@imperial.ac.uk
AF: Department of Earth Science and Engineering, Royal School of Mines, Imperial College London, South Kensington Campus, London, SW7 2AZ United Kingdom
AU: Maidment, S
EM: susannah.maidment@imperial.ac.uk
AF: Department of Earth Science and Engineering, Royal School of Mines, Imperial College London, South Kensington Campus, London, SW7 2AZ United Kingdom
AB: We use commercial 3D seismic reflection data to image spectacular, cross-cutting, anastomosing valley systems formed by subglacial meltwater drainage in the Pleistocene of the North Sea, at ~58degN 1degE. Although the seismic data were collected to image deeper structures, the high resolution and quality of the data have allowed us to identify meltwater drainage systems formed at the base of different NW European Pleistocene icesheets in the top 400 ms of the data. The data volume comprises stacked, deconvolved and time migrated data, in 12.5 x 12.5 m bins sampled at 4 ms. The frequency bandwidth is 5-80 Hz (at the 20 dB point), giving a vertical resolution of ~ 8 m and lateral resolution of 12.5 m. Within the 12.5 by 8 km study area, four phases of cross-cutting valley incision can be identified. Individual valleys, which are 30-155m deep and 250-1200m wide, have the irregular longitudinal profile characteristic of meltwater incision under ice sheets. The first three phases are orientated N-S, whilst the youngest, fourth phase valleys and orientated E-W. The fourth phase valleys are also narrower and shallower than the older valleys. We speculate that the successive episodes of valley formation document a history of advance and retreat of an ice-sheet, probably during the Elsterian glaciation of northwest Europe. Detailed mapping of the valley morphology and the geometry of the infill has shown that the valleys were incised by a number of meltwater flow episodes, which were variable energy, probably high velocity and episodic. As a result the valleys were dynamic and long-lived, and they existed as depressions for long periods of time under the ice sheet. When the ice sheet retreated, they were filled with proglacial sediments. From our limited study area it appears that the first of these advances had a N-S orientated drainage network and generated a greater volume of subglacial meltwater than the second, whose drainage network was orientated in a more E-W direction and was characterised by lower velocity and volume meltwater flow events.
DE: 0935 Seismic methods (3025)
DE: 1827 Glaciology (1863)
DE: 9335 Europe
SC: Cryosphere [C]
MN: 2003 Fall Meeting