The Bytham river reconsidered

Abstract

The English Midlands is one of the most important regions for British Pleistocene geology. The Middle Pleistocene glacial sediments of the region, termed the Wolston Formation, overlie deposits of a pre-existing river system, the Baginton Formation. The latter are characteristically composed of quartz-rich sediment derived from underlying Triassic bedrock. This SW–NE aligned proto-Soar system was overridden by the Wolstonian ice. Its lack of terraces or discrete sedimentary units implies that the river can only have existed for a limited period. The deposits accumulated during a period of climate change from boreal (?interstadial) to subarctic conditions. A reinterpretation of these sediments as the headwaters of a pre-Anglian ‘Bytham river’, aligned towards East Anglia across the Fenland, where they were linked to the Ingham Formation deposits, found favour for two decades. This was especially so when the Wolston Formation sediments were reassigned to the earlier, Anglian Stage. However, recent work has shown that the ‘Bytham river’ could not have existed in the form suggested by some authors since pre-Anglian-age fluvial sediments are absent from the eastern Fenland margin, except possibly certain deposits at High Lodge, Suffolk. Therefore a re-examination of the evidence is required.It is concluded that the Wolstonian glaciation (late Saalian, Marine Isotope Stage [MIS] 6) indeed post-dates that during the Anglian Stage (Elsterian, MIS 12). In addition, it appears that the Baginton (proto-Soar) stream, as originally conceived, almost certainly did not exist before the early Wolstonian (early Saalian) Stage, following a significant period of fluvial incision. Rather than being aligned towards East Anglia, the substantial proto-Soar flowed into south Lincolnshire and thence potentially to the North Sea via the Wash and the Silver Pit depression. By contrast, the pre-Anglian Ingham Formation deposits of central East Anglia were almost certainly deposited by a separate proto-Trent river that drained the East Midlands over an extended period as a left-bank Thames' tributary. Together these conclusions reinforce the view that the main drainage alignment in southern England during the pre-Anglian period was NW to SE parallel to the regional tilt of the landmass.