Cosmogenic dating of Midlands erratics

 

Timing and dynamics of Late Wolstonian Substage ‘Moreton Stadial’ (MIS 6) glaciation in the English West Midlands, UK
Sebastian M. Gibson,
Mark D. Bateman,
Julian B. Murton,
Timothy T. Barrows,
L. Keith Fifield and
Philip L. Gibbard
Royal Society Open Science: 29 June 2022

https://doi.org/10.1098/rsos.220312

https://royalsocietypublishing.org/doi/10.1098/rsos.220312

There are now 6 cosmogenic dates for erratic boulders in the Midlands. These are reported by Seb Gibson and his colleagues in their big paper on the Wolstonian glaciation of the Midlands.  In the table below, the top 3 dates are new determinations, and the bottom three are corrected from Phillips et al (1994).  There is one anomaly, as yet unexplained:  52,000 yrs BP for sample WAR-01.  The others are strongly suggestive of a substantial glacial episode in the Midlands in the Wolstonian, in which the ice was more extensive than that of the Anglian glaciation.  (The line showing maximum Anglian ice extent has been withdrawn northwards.....)

Gibson, Sebastian M.; Bateman, Mark D.; Murton, Julian B.; Barrows, Timothy T.; Fifield, L. Keith; GIBBARD, Philip L. (2022): Supplementary material from "Timing and dynamics of Late Wolstonian Substage ‘Moreton Stadial’ (MIS 6) glaciation in the English West Midlands, UK". The Royal Society. Collection. 

Quote:

Glaciation during the late Middle Pleistocene is widely recognized across continental northwest Europe, but its extent and palaeoenvironmental significance in the British Isles are disputed. Although glaciogenic sediments at Wolston, Warwickshire, in the English West Midlands, have been used to define the stratotype of the Wolstonian Stage, their age has been variably assigned between marine isotope stages (MIS) 12 and 6. Here we present sedimentological and stratigraphical observations from five sites across the English West Midlands whose chronology is constrained by new luminescence ages from glaciofluvial sediments, supplemented by cosmogenic 36Cl exposure dating of erratic boulders. The ages suggest that between 199 ± 5 ka and 147 ± 2.5 ka the British Ice Sheet advanced into the English West Midlands as far south as Moreton-in-Marsh, Gloucestershire. This advance is assigned to the Moreton Stadial of the Late Wolstonian Substage. Dating of the glaciation to this substage allows correlation of the Moreton Stadial glacial deposits in the English West Midlands with those of the Drenthe Stadial during the Late Saalian Substage across continental northwest Europe.

Quote from main article text:

4.2.2. Exposure dating

The new and revised exposure ages are presented in table 8, ages are presented with internal errors and external errors in brackets. The ages scatter more than expected and suggest that some of the boulders may not be in situ. All but one of the ages fall between 225 and 100 ka. The ages rule out deposition before the Wolstonian Stage and during the Early-to-Middle Wolstonian Substage (ca MIS 10–8). Weathering is unlikely to be the cause of the scatter, but periglacial action during the last glacial cycle could conceivably have heaved boulders. Erratics dated by Phillips et al. were brought in by Wolstonian Stage ice but are only directly related to glacial diamicton at Calcott Hill (Sample GB-B1) 

Three of the dates are corrected from this paper in 1994:
Phillips FM, Bowen DQ, Elmore D. 1994 Surface exposure dating of glacial features in Great Britain using cosmogenic chlorine-36: preliminary results. Mineral. Mag. 58, 722-723. (doi:10.1180/minmag.1994.58A.2.113) 

This map shows the revised glacial limits across England, the North Sea and the Netherlands.  Note that  the Anglian (MIS-12) ice is shown as less extensive than shown in earlier speculative limits for the Midlands, and Wolstonian ice is shown as more extensive.  Wolstonian ice also pushed much further south across the Netherlands. The reasons for these substantial differences in ice cover are not yet explained.