Ice-rafted erratics, Norfolk

Palaeo-rivers and site locations in the southern North Sea.  The theory is that glaciers from Scotland and Scandinavia flowed into the northern part of the basin, and that there was a floating / calving ice front from which icebergs transported debris southwards, to be dumped or dropped on tidal or freshwater mud flats........

This is an interesting paper, dealing with a number of small erratic clasts (up to 15 kg in weight) found in sediments on the Norfolk coast.  These are of course very different from the giant erratics found on the coasts of Devon and Cornwall, and the geomorphological / sedimentological setting is very different too.  But an interesting paper, reminding us that there were some very old glaciations and that erratics were carried by glacier ice -- and also in mobile icebergs in deep water -- southwards towards the Straits of Dover.  So our thoughts turn to the strange erratics found on the coasts of the English Channel -- might they have come from the North Sea at a time of substantially higher RSL?

Something to think about........

 https://nora.nerc.ac.uk/id/eprint/14695/1/Larkin_et_al.pdf

Nigel R. Larkin, Jonathan R. Lee & E. Rodger Connell. 2011. Possible ice-rafted erratics in late Early to early Middle Pleistocene shallow marine and coastal deposits in northeast Norfolk, UK. Proc. Geol. Assoc. 

Abstract

Erratic clasts with a mass of up to 15 kg are described from preglacial shallow marine deposits (Wroxham Crag Formation) in northeast Norfolk. Detailed examination of their petrology has enabled them to be provenanced to northern Britain and southern Norway. Their clustered occurrence in coastal sediments in Norfolk is believed to be the product of ice-rafting from glacier incursions into the North Sea from eastern Scotland and southern Norway, and their subsequent grounding and melting within coastal areas of what is now north Norfolk. The precise timing of these restricted glaciations is difficult to determine. However, the relationship of the erratics to the biostratigraphic record and the first major expansion of ice into the North Sea suggest these events occurred during at least one glaciation between the late Early Pleistocene and early Middle Pleistocene (c. 1.1−0.6 Ma). In contrast to the late Middle (Anglian) and Late Pleistocene (Last Glacial Maximum) glaciations, where the North Sea was largely devoid of extensive marine conditions, the presence of far-travelled ice-rafted materials implies that earlier cold stage sea-levels were considerably higher.

=========================

6. Conclusions

Concentrations of erratics within WCF (Wroxham Crag Formation) coastal deposits at Sidestrand and West Runton in northern East Anglia are considered the product of melt-out from (possibly grounded) icebergs.

The provenance of the erratics implies that these icebergs were derived from glaciers that were eroding bedrock in the Southern Uplands, Midland Valley and southern Grampian Highlands of Scotland, and Oslofjord in southern Norway.

The age of these erratic-bearing beds can be broadly constrained to a period from the late Early Pleistocene to early Middle Pleistocene interval (c. 1.1–0.6 Ma, a time period that spans the ‘Menapian’ (MIS 34)) to late ‘Cromerian Complex’ (MIS 16) stages.

These erratics demonstrate both the existence of restricted glaciations in Scotland and Norway, and their periodic expansion into the North Sea Basin prior to the maximum extent of the ice sheets during the Anglian Glaciation (MIS 12) of the Middle Pleistocene.

This research supports the work of Sejrup et al. (1987) and Ekman (1999) that argues that both the BIIS and SIS were active in the North Sea Basin on at least one occasion well before the Anglian stage of the Middle Pleistocene.

The deposition of the erratic-bearing beds during these early glaciations appears to coincide with higher glacial sea-levels than occurred during the late Middle and Late Pleistocene.

==============

https://www.northfolk.org.uk/geology/erratics.html

The formation of the Straits of Dover comes into the frame here too:

https://brian-mountainman.blogspot.com/2017/04/the-creation-of-straits-of-dover.html

Gibbard, P. Europe cut adrift. Nature 448, 259–260 (2007).
https://doi.org/10.1038/448259a

The initiation of the megaflood responsible for the cutting of the Straits of Dover.  Note that in the North Sea the water level is assumed to have been substantially higher that that in the proto-English Channel.  Note also the large icebergs running aground and dropping erratics!