This is unfinished work that has not been edited or peer reviewed by the Society. Updated 11th November 2022.

The Ice Age Misconception:

For a long time my understanding of the “Ice Age” was that glaciers formed in valleys to the north, the ice plucked fragments of rock from the valley walls and ground the rocks of the valley floor to form clay-like flour. These glaciers met to form an ice sheet one or two kilometres thick that travelled at a “glacially” slow pace with the rock fragments and flour within it. The ice sheet then melted dumping the rock fragments and flour as the Boulder Clay we can see in Holderness.

Like most geology, once you start to study it in detail in the field the truth turns out to be much more complex that the simple textbook explanations. How do we explain the distribution of the glacial erratics and why are they rounded rather than angular rock fragments? How do some delicate fossils and soft sediments inclusions survive the glacial transportation? Why are there distinct layers in the sediments? How do we explain the folding and faulting that can be seen in the rafts?

It is very tempting to draw straight lines on a map to show the origin of the erratics and then to think that was their direction of travel during the (single or last) “ice age”. I think that the glaciers did not travel in straight lines and they made several journeys. So an erratic may well have been moved and deposited several times during the Ice Ages, just like we often have to change trains to reach our intended destinations.

It is also tempting to assume that the erratics came from present day inland exposures, for example Hildoceras from Whitby and Speeton Clay from Speeton in a straight line. Yet there are so many Speeton Clay fossils to be seen that the present exposures do not seem to be big enough to be the simple single source. And there are no exposures of Chalk containing black flints; the Yorkshire flints are grey and brittle. The black flints must come from younger Chalk that was previously exposed in the bed of the North Sea when the area was dry land. And if that is the case then the North Sea could very well be the source of the Speeton Clay material and most of the Mesozoic erratics, and why not some Tertiary erratics? This would also explain why some erratics are not evenly distributed throughout Holderness.

Some results from the Flamborough Quaternary Research Group, with the help of Mark Bateman, imply that the Last Glacial Maximum in our region was relatively quite brief and that during that period the ice travelled to North Norfolk to deposit a similar diamict. Could it be that a decaying ice sheet actually speeds up rather than simply dumping its load of boulders and clay where it is. How many times have seen warnings of a skid hazard “mud on road” signs. Wet mud is slippery so just imagine a large wet ice cube moving over it!

When we start to log and measure the sediments in the cliffs of Holderness we realise that there is a lot of lateral variation and structural geology. There are beds of gravels and thinly layered beds. There are thrust planes, some of which may be due to rotational slumping, but even then these could be exploiting an original weakness in the deposits. There are complex folds and faults that are evident in exposures of Chalk rafts and the red band. Sometimes directional indicators imply that the glacier was travelling in the wrong direction. This all points towards the conclusion that the glacier was not simply carrying the sediment clasts but it was pushing sediment around and was this sediment previous diamicts and the marine, estuarine and freshwater sediments from what is now the North Sea. Please remember that the ancient Chalk cliff line ran from Bridlington to Hessle via Driffield, Beverley and Cottingham: Holderness was part of the North Sea!

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source (Hull Geological Society)