Evidence for a grounded ice sheet in the central North Sea during the early Middle Pleistocene Donian Glaciation

Carina Bendixen,Jørn B Jensen,Ole R Clausen,Rachel M Lamb,Lars O Boldreel,Mads Huuse

doi:10.1144/jgs2017-073

Abstract

Interpretation of 3D seismic data from the central North Sea yields evidence of a pre-MIS (Marine Isotope Stage) 12 grounded glaciation. The glaciotectonic complex shows buried push moraines resulting from the thrusting of multiple ice advance phases with horizontal shortening of 35 – 50%. The earliest feature observed within the complex, a hill–hole pair, represents the initial glaciation of the area. This is overlain and deformed by multiple thrust units with numerous inferred ice-flow directions. The thrust deformation observed shares characteristics with kinematic processes, push moraines and static gravity processes, seen as gravity spreading and contraction. The glaciotectonic complex in its entirety is interpreted to correlate to a pre-Elsterian glaciation, becaue of its stratigraphic position below central North Sea tunnel valleys, estimated to be Elsterian in age (MIS 12; 450 ka). The study proposes that the thrust complex correlates to the Donian glaciation in Russia (MIS 16; 600 ka) with ice sourced from Norway. The complex therefore represents a glaciation where a significant area of the central North Sea was covered by an ice sheet, 200 kyr prior to the Elsterian. This study highlights the fragmentary record of pre-Elsterian glaciations and the importance of incorporating offshore sedimentary archives and regional frameworks when reconstructing Pleistocene climate change.

Highlights

These glacial–interglacial cycles are seen from the onset of the Quaternary at 2.58 Ma (MIS 103); in NW Europe glaciogenic records from prior to the Elsterian glaciation are very scarce
This study takes advantage of the excellent coverage of the central North Sea by continuous 3D seismic data to fully investigate a glaciotectonic complex identified on high-resolution seismic data (Fig. 1) as probable pre-Elsterian in age
A previously unknown thrust complex has been observed on the high-resolution BroadSeisTM dataset covering an area of 700 km2 in the central North Sea, 57°16’N to 57°27’N and 0°55’E to 1°18’E (Figs 3 and 4)

Summary

Introduction

These glacial–interglacial cycles are seen from the onset of the Quaternary at 2.58 Ma (MIS 103); in NW Europe glaciogenic records from prior to the Elsterian glaciation are very scarce This is in part due to the lack of evidence preserved onshore, with much controversy over any potential pre-Elsterian deposits, owing to the overall erosional nature of the ice sheets in upland areas such that younger ice sheets have removed much of the evidence of any older ones that may have existed. The comparative lack of research into the Middle Pleistocene history of the central North Sea basin since the initial investigations during the 1980s and 1990s, despite the rapid increase in quality and quantity of the seismic data, has limited our understanding of any pre-Elsterian glaciation. In the central North Sea, Lower and early Middle Pleistocene deposits consist of a single seismostratigraphic unit, the Aberdeen Ground Formation. The top of the Aberdeen Ground Formation is defined by a regional glacial unconformity and dissection by a wide network of subglacial tunnel

Results

Discussion

Conclusion