THE BOOK
Some of the ideas discussed in this blog are published in my new book called "The Stonehenge Bluestones" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
To order, click
HERE

Friday 1 July 2022

Middle England: three glaciations.


The suggested maximal glaciation limit for southern England.  The white line represents the Anglian (MIS-12) limit usually accepted as the maximum -- but scattered erratics occur all the way to the blue line in a landscape much altered by denudation.

Something new from Jim Rose and his colleagues.  This is a highly complex and somewhat intimidating paper describing a site (Clipsham) in the East Midlands where there are two tills separated by a weathered horizon with organic materials.  So -- evidence of two glacial episodes separated by an interglacial.  But the really interesting thing, from our point of view, is the conclusion that there was an even earlier glaciation of unknown extent -- in which the ice margin might have extended south of the "accepted" glacial maximum in Anglian (MIS-12) times.

Quote:
"Clipsham provides evidence for the presence of three glacial episodes across this part of eastern Midland England. The first is inferred from the traces of erratic material in the periglacial Pickworth Gravels. The low frequency of such material suggests that the glacial deposits, with the exception of a few residual clasts, had been stripped from the landscape before the erosion of the now buried channel and deposition of the Pickworth Gravels. All that can be said is that lowland Midland England was glaciated and subsequently eroded before the glaciation that deposited the Bozeat Till (the second glacial episode). The third glacial episode is represented by the Oadby Till."


Organic and soil material between tills in east-midland England – direct evidence for two episodes of lowland glaciation in Britain during the Middle Pleistocene
James Rose, Jenni Turner, Elaine Turton, James B. Riding, Adrian Palmer, John K. Wright, Jonathan R. Lee, Nicholas S. J. Q. Bullimore.  2021. Jnl Quat Science.
First published: 18 May 2021
https://doi.org/10.1002/jqs.3307

Here is the abstract:

ABSTRACT

This paper provides a record and analysis of a site in east-midland England, at which organic and soil material are found between two Middle Pleistocene tills. This is the first discovery of its kind in the area, and demonstrates unequivocally that the region was glaciated on two separate occasions, something that has long been inferred and articulated, but not actually demonstrated. The landforms, sediments and soils are studied with respect to their geomorphological, lithological, pedological, palaeobotanical and structural properties. The organic and soil material along with soil structures indicate, sequentially, a periglacial climate, a long period of warm temperate weathering and a cool temperate climate. Evaluation of this evidence in terms of existing published work identifies a number of problems with existing models and suggests that the most likely model for the glacial history of this part of midland England is an early Middle Pleistocene glaciation which is represented only by trace erratics, a Marine Isotope Stage (MIS) 12 age glaciation which moved across the area from the NW and deposited a chalk-free till, and an MIS 8 age glaciation that transported and deposited an upper chalky till from the NE.

We can set this paper alongside others relating to the glaciations of  Eastern England and the Midlands, as mentioned in this post:


and this one:



As I have said earlier, within the Anglian glacial limit, most of the older deposits or free erratics left lying about would have been incorporated into the deposits attributed to the Anglian Glaciation (MIS-12) -- but outside that limit there would just be "a few residual clasts" that survived hundreds of thousands of years of  denudation and destruction -- probably from the MIS-16 glacial episode.  For example, we can cite the clasts and boulders found on Salisbury Plain........

PS.  In the literature there are occasional references to a "Stonehenge moraine" -- I have mentioned this on this blog.  In 1903 William Judd wrote, concerning the ancient glaciation of Salisbury Plain:  "Many tracts where the boulder clay was thin have probably been swept quite bare of the formation, except for the large boulders that would be left behind."  He also suggested that Stonehenge was built where there was a mix of sarsens and bluestones scattered across the landscape.  He said that the combination of shapes, colours and textures to some degree decided the site and "suggested the architectural features of the noble structure....."
                                                                                                                              
                                                                                                                                                                              

No comments: