Transect 2 – North Sea

newtransect2Transect Leader:

David Evans (University of Durham)

Transect Personnel:

David Evans, Mark Bateman, David Roberts, Colm O’Cofaigh, Alicia Medialdea, C Clark, L Callard, R Chiverrell, M Burke

Fieldwork and activities:

  • 13 accesible sites have been sampled for OSL dating, each one representing a stratigraphic record of onshore advance of the North Sea Lobe.  Three further sites have been identified for drilling, and offshore samples will be collected during Cruise JC 123, Summer 2015

  • During Summer 2015, Cruise JC 123 surveyed a significant swathe of the North Sea in order to investigate the offshore hisotyr of the British-Irish Ice Sheet.  8 sub-transects were identified in order to explore key quations relating the ice extent, de-coupling of the BIIS and Norwegian Ice Sheet and the retreat pattern of the BIIS.

Background

Although the type site for the LGM glaciation of Britain is on the Holderness coast at Dimlington, very poor chronological control is otherwise available for the pattern of advance and recession by the North Sea Lobe (NSL), the major outlet of the British-Irish Ice Sheet whose potentially dynamic and pulsed behaviour has been the subject of considerable speculation due to limited chronological control on marginal oscillations. Not only the dynamics but also the configuration of this large outlet of the BIIS are poorly understood, and existing palaeoglaciological reconstructions depict a glaciologically improbable configuration, with east coast-parallel flow that requires a buttressing ice mass in the North Sea despite the lack of unequivocal evidence for such a shelf-based ice mass1,2. An alternative scenario is that the forebulge of the Scandinavian Ice Sheet could have confined the flow of the NSL3, although this remains untested. Our understanding is hampered by a lack of knowledge of offshore sediment-landform assemblages and a dearth of dates on their emplacement. Ice flow directional indicators reveal a clear pattern of onshore, radial flow by the western margin of the NSL, which deposited prominent till sheets, moraines and ice-dammed lake sediments, but offshore limits are related only tentatively to the extent of the weakly chronologically constrained Bolders Bank Formation4, and marginal recession patterns and rates are unknown. Because of the late marine inundation of the North Sea during immediate deglaciation, there is no glacimarine or glacioisostatic record of ice sheet recession along the eastern England coast, but the region was subject to glacial loading nonetheless and therefore would have been extensively flooded by proglacial lake waters, as evidenced by the extensive glacilacustrine sediments in the onshore stratigraphies. The chronology of extent and depth changes and potentially significant role of this lake in forcing ice sheet recession is entirely unknown.

Existing chronology

In the Holderness type area for the last glaciation, two radiocarbon dates produced in the 1960s on subtill organics have recently been supplemented by OSL dates on stratified glacifluvial and glacilacustrine sediments between two overlying tills, indicating two phases of ice advance at 21.7–16.2 ka and then at 16.2-15.5 ka BP3. The first phase of advance is coincident with climate warming in the Greenland icecore record, whereas the second coincides with cooling but dates to a time when the BIIS had retreated back to its dispersal centres, thereby indicating that the whole eastern sector of the BIIS was oscillating out of temporal sequence with the rest of the ice sheet. The two onshore advance phases of the North Sea Lobe, which are manifest in other stratigraphies further north such as Sandsend near Whitby, have therefore been related to ice stream marginal responses to internal ice sheet dynamics, rather than climatic forcing. They are potentially indicative of surge activity, although independent diagnostic criteria for surging are presently unavailable due to poor knowledge of seabed geomorphology. Our present knowledge of ice marginal recession patterns and chronology is depicted in Figure 1, which includes existing dates as dots and interpolated sequential ice limits. The area of proposed investigation is identified by the red box and covers the significant offshore area in terms of seabed morphology and datable deglacial sediments, together with the immediate onshore sites known to contain excellent stratigraphic records of NSL marginal activity.

Proposed work and inventory of dates

OSL dating of onshore stratified sediments relating to NSL maximum limits, recession and readvance. Recession from numerous inset, glacitectonized subaqueous fans on Holderness5 will be dated using the fan deposits at Frodingham, Berrygate Hill, Barmston, Skipsea, Gembling, Filey Bay and Flamborough Head. Lake sediments in the west and east of the Vale of Pickering will be used to date the high and low stands of glacial Lake Pickering. Similarly, the ice-contact deposits relating to Glacial Lake Humber and the recession of ice from the Humber Gap will be dated. At Sansend, near Whitby, lake and glacifluvial deposits lying between two tills will be dated. Glacial Lake Wear sediments and possible equivalents will be dated in the Durham coast sections and inland brickpits, thereby providing a pattern and chronology of Tyne Gap and Tweed ice stream separation (total = 50 OSL dates). Multiple AMS radiocarbon dates will be obtained on individual marine shells recovered from the North Sea tills in order to determine a maximum constraint on the timing of deglaciation of the North Sea Basin. Previous applications of this technique indicate that a minimum of 10 dates are required on each local stratigraphic unit (total = 30 radiocarbon dates).

Offshore coring transect from the Durham coast to North Norfolk, in order to assess the ice flow parallel chronology of recession. This will involve the collection of 10 cores spaced equidistantly along the N-S transect over a 24 hour cruise period. The contingency is for a total of 3-4 radiocarbon dates per core (total = 30-40 radiocarbon dates). A number of offshore cores are archived by the BGS, but are of variable quality and have not been collected with ice sheet retreat chronologies along the east coast in mind and therefore require investigation before their content can be used to augment our programme of sampling. Additionally, our project partners at Bergen will be coring the seabed in the eastern half of the southern North Sea, thereby providing age constraints on the recession of the eastern margin of the NSL.

3. Offshore swath bathymetry along the Holderness coast to assess the existence of ridges similar to that of the onshore Withernsea Till, regarded as the limit of a significant ice sheet readvance4, in addition to potential surge geomorphology. These data will complement the work of our Bergen project partners in the eastern half of the southern North Sea and thereby provide a spatially comprehensive analysis of the bed and retreating margins of the whole NSL.

References

  1. Carr, S.J., Holmes, R., van der Meer J.J.M. & Rose, J. 2006: The last glacial maximum in the North Sea: Micromorphological evidence of extensive glaciation. Journal of Quaternary Science 21, 131-153.
  2. Clark, C. D., Hughes, A. L. C., Greenwood, S. L., Jordan, C. & Sejrup, H. P. 2011: Pattern and timing of retreat of the last British-Irish ice sheet. Quaternary Science Reviews. doi:10.1016/j.quascirev.2010.07.019.
  3. Bateman, M. D., Buckland, P. C., Whyte, M. A., Ashurst, R. A., Boulter, C. & Panagiotakopulu, E. 2011: Re-evaluation of the Last Glacial Maximum typesite at Dimlington, UK. Boreas, 10.1111/j.1502-3885.2011.00204.x.
  4. Davies, B.J., Roberts, D.H., Bridgland, D.R., O Cofaigh C. & Riding, J.B. 2011: Provenance and depositional environments of Quaternary sediments from the western North Sea Basin. Journal of Quaternary Science, in press.
  5. Evans, D.J.A. & Thomson, S.A. 2010: Glacial sediments and landforms of Holderness, eastern England: a glacial depositional model for the North Sea lobe of the British-Irish ice sheet. Earth Science Reviews 101, 147–189.