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Thursday, 5 January 2017

Late Pleistocene Putorana





As usual, when you start to dig, treasures come up.......... and I have found a host of references to the late Pleistocene in the vicinity of the Putorana Plateau.

Here is some key info from a big 2004 paper written by a host of field workers led by John Inge Svendson.  The paper can be accessed via ResearchGate.


Late Quaternary ice sheet history of Northern Eurasia
Quaternary Science Reviews 23 · January 2004, pp 1229-1271
John Inge Svendsen et al

https://www.researchgate.net/publication/223294900_Late_Quaternary_ice_sheet_history_of_Northern_Eurasia

EXTRACT

3.3. Putorana Plateau

At least once during the Quaternary an ice sheet advance from the Kara Sea inundated this mountain
area (Fig. 2). The occurrence of granite erratics reflects ice flow across northern Taimyr and onto the Putorana Plateau and a very thick shelf-centered ice sheet at that time (Urvantsev, 1931).  Even though this glacial event is poorly dated a major glaciation is thought to have occurred during the Saalian when the ice sheet terminated far south on the adjacent lowland in West Siberia. Two younger moraine belts that encircle the Putorana Plateau indicate that the glaciations were more restricted
during the Weichselian than during the foregoing glaciation (Fig. 2).  The outer moraine system in north-eastern Putorana was originally dated to the LGM on the basis of several radiocarbon dates from beneath the corresponding till (Isayeva et al., 1976). The same age was suggested for the Onyoka morainic belt along the southern slope of the plateau (Isayeva, 1984). The Onyoka moraines merge with the moraines trending east west across the Yenissei valley to the West Siberian Plain. This chain of moraines is therefore considered to be contemporaneous with the last shelf-centered glacia-
tion that inundated the West Siberian Plain, which according to our interpretation occurred during the Early Weichselian (Astakhov, 1992).

The inner system of morainic ridges, termed the Norilsk Stage, is represented by horseshoe-shaped end moraines encircling the western ends of deep fjord-like lakes. Sachs (1953) and other geologists considered the Norilsk moraines products of alpine glaciation, whereas Isayeva (1984) thought that these spectacular features were deposited by outlet glaciers which drained a substantial ice cap covering the flat plateau.  A Younger Dryas age was suggested for the Norilsk Stage (Kind, 1974), but more recent investigations indicate that it is older. Pollen diagrams from long cores retrieved from the bottom sediments of Lake Lama, situated on the proximal side of the Norilsk moraines (Fig. 2), suggest that lacustrine sedimentation started well before 17 ka (Hahne and Melles, 1997).  Judged from seismic records there are more than 20 m of lacustrine sediments below the 19 m long cored sequence.

Hahne and Melles (1997) therefore assume that the youngest till in these lake basins is of Middle Weichselian age, which implies that the Norilsk moraines predate the LGM. This is supported by geomorphologic observations, proposing that the maximum extent of the LGM glaciers is
represented by moraines higher up in the valleys (Bolshiyanov et al., 1998).


Late Quaternary ice sheet history of Northern Eurasia. Available from: https://www.researchgate.net/publication/223294900_Late_Quaternary_ice_sheet_history_of_Northern_Eurasia [accessed Jan 5, 2017].

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Here are some of the key maps from the paper:



The sequence which is gradually being worked out appears to show a succession of glacial phases, with each glaciation smaller than the last.  Pre-Saalian (including the Anglian?) glaciations were very extensive, with the Putorana Plateau well and truly incorporated int the Eurasian ice sheet.  The plateau was well covered too in the late Saalian, and during the Weichselian, interestingly enough, there appear to have been three phases, with maxima around 90 ka, 60 ka and 20 ka.  Each phase was smaller than the last -- although it is doubtful that the ice completely wasted away between each phase.  The early and mid Weichselian phases here appear to be well supported by the evidence -- but it's worth remarking that if there were ice expansions in the UK at this time, the evidence is difficult to find because the ice expansion of the LGM was larger than anything that went before.

Around 90 ka the plateau was incorporated into the larger Eurasian ice sheet; around 60 ka (following an interglacial) the plateau was the centre of a local ice sheet (as it must have been on many prior occasions); and at the time of the LGM around 20 ka, there were just a few small local ice caps and glaciers on the plateau.

There has been surprisingly little comment in the literature about the morphological effects of these phases -- I'll look at this in a bit more detail in another post.





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