Middle and Late Pleistocene glacial lakes of lowland Britain and the southern North Sea Basin

摘要

Focusing on lowland Britain and the southern North Sea Basin, this article reviews the sedimentary and geomorphic evidence for the main glacial lakes inferred during the Middle and Late Pleistocene and evaluates their impacts on drainage-basin development. Glacial lakes are best known from glaciations during Marine Isotope Stages (MIS) 12,6 and 2, although glacial lakes have also been inferred during MIS 10 and 4. Some lakes - for example, Bosworth, low-level Humber and the lakes of the eastern Fenland margin - are reconstructed from unequivocal sedimentary evidence, including rhythmites and subaqueous outwash, whereas others lakes - for example, Lapworth and Fenland - are inferred mostly from erosional features and remain to be substantiated. The largest known glacial lake developed in the southern North Sea Basin between an ice sheet to the north and a chalk bedrock ridge in the Strait of Dover area, first during the Anglian/Elsterian glaciation of MIS 12 and again during the late Wolstonian/ late Saalian Drenthe glaciation of MIS 6. The palaeohydological impacts of lake drainage are thought to include cutting of the Strait of Dover as a result of catastrophic drainage from the North Sea Lake during MIS 12, incision of a number of gorges and river valleys in England, and diversion or even reversal of major rivers such as the Thames and the proto-Soar/Avon system. Recently, varve chronologies have been correlated with the Greenland ice-core record, although caution is needed to discriminate between varves and non-annual rhythmites. Future work on Pleistocene glacial lakes needs to test chronologies of lake development by luminescence dating of glaciolacustrine sediments deposited in non-ice-proximal locations - (1) fine-grained rainout deposits and (2) wave-rippled sands deposited in shallow water -and to model the impacts of glacial isostasy in order to reconstruct lake extents. All of this work should be based on the rigorous application of sedimentology to interpret sedimentary facies and depositional environments.