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Friday, 30 March 2018

On glacial cycles

A composite map of the assumed Anglian Celtic Ice Sheet flowlines and maximum extent. Could it be that this is simply a "best shot" at unravelling what went on during four glacial phases over a quarter of a million years?  

A big new paper has just been published in Nature Scientific Reports which throws new light on the glacial cycles in northern Europe -- assembling a vast array of new dating evidence. The authors are Tobias Lauer and Marcel Weiss. Key info:

Timing of the Saalian- and Elsterian glacial cycles and the implications for Middle – Pleistocene
hominin presence in central Europe

by Tobias Lauer & Marcel Weiss

NATURE SCIENTIFIC REPORTS (2018) 8:5111, 12 pp.


By establishing a luminescence-based chronology for fluvial deposits preserved between the Elsterian- and Saalian tills in central Germany, we obtained information on the timing of both the Middle Pleistocene glacial cycles and early human appearance in central Europe. The luminescence ages illustrate different climatic driven fluvial aggradation periods during the Saalian glacial cycle spanning from 400–150 ka. The ages of sediments directly overlying the Elsterian till are approximately 400 ka and prove that the first extensive Fennoscandian ice sheet extension during the Quaternary correlates with MIS 12 and not with MIS 10. Furthermore, the 400 ka old fluvial units contain Lower Paleolithic stone artefacts that document the first human appearance in the region. In addition, we demonstrate that early MIS 8 is a potential date for the onset of the Middle Paleolithic in central Germany, as Middle Paleolithic stone artefacts are correlated with fluvial units deposited between 300 ka and 200 ka. However, the bulk of Middle Paleolithic sites date to MIS 7 in the region. The fluvial units preserved directly under the till of the southernmost Saalian ice yield an age of about 150 ka, and enable a correlation of the Drenthe stage to late MIS 6.

Here is one of their key diagrams:

It's quite detailed.  Click to enlarge.  The authors confirm that the first big extension of the Fennoscandian Ice Sheet into Germany occurred in MIS12 and not MIS10, making it earlier than some others have suggested.  That's the big glaciation otherwise referred to as Elsterian, Mindel or Anglian -- the one assumed to have been the GBG (Greatest British Glaciation) about which we have talked on many previous occasions.  The date of this glaciation is again confirmed as around 450,000 years ago.

But look at the next glaciation -- named the Saalian / Riss / Wolstonian episode, shown here as spanning a vast time span from 400,000 to 125,000 years BP.  There are four discrete glacial or cooling episodes within it, all showing up in the marine isotope record as MIS10, MIS8, MIS6 and one other temperature dip that has not been labelled.  Between these are the warmer episodes including MIs7 and MIS9.

Now let's look at another glacial cycle diagram which is in common currency:

The climate curve is very similar, but look at the labelling of the glacial episodes.  On this diagram it is the Anglian Glaciation that is shown as incorporating four discrete glacial episodes, with the Wolstonian Glaciation shown as a single glacial episode spanning the period 200,000 - 140,000 years ago.

The Devensian Glaciation is shown more or less conventionally, with a deteriorating climate -- with oscillations -- after 100,000 yrs BP culminating in the glacial maximum around 20,000 yrs BP and then a very rapid warming and glacial collapse.  That's a scenario which I confirmed in my doctorate work in West Wales in 1962-65 -- with many other confirmations from other field workers.

There are clearly some major labelling issues here.........

So was the Anglian Glaciation a short, sharp one or one that was very prolonged, with many ice-front oscillations over more than a quarter of a million years?

Watch this space.......

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