The Clava Shelley Till Controversy
MFC Paper 04 by SM Ross 1975
Some 80 years ago, the discovery near Clava at a height of 169m O.D. of bands of clay containing marine shells created much excitement and debate amongst geologists — so much so that the deposits were the subject of a detailed investigation by the committee of the British Association. The committee members could not agree on the origin of the deposits, but a majority of them were of the opinion that the clay had been laid down in situ as a marine deposit. This suggested that there was a marine transgression to at least 160m prior to the advance of the last ice sheet, and the argument has continued ever since.
In the past few years there have been considerable advances in the understanding of glacial processes, largely stemming from careful studies in the field of existing glaciers. Under permafrost conditions, large rafts of frozen sediment can be plucked intact from the land surface by a glacier, moved up shear planes into the ice, and transported away from the source region. Another feature now accepted is that during summer melting surface waste material or till can become so waterlogged on top of the impervious frozen layers below that it will flow downhill like porridge. These materials can be found in recognisable form after the retreat of the ice.
Dr. J. D. Peacock of the I.G.S. has recently re-examined the deposits at Clava and in his report concludes:—
“Few exposures near Drumore of Clava show a succession of glacio—fluvial deposits and material interpreted as flow till. These strata overlie shelly till which apparently lies at the same horizon as the Clava Marine Clay. The latter is thought to be a raft enclosed in the shelly till, which is interpreted as melt—out rather than lodgement or flow till“.
- PEACOCK J. D. 1975 Depositional Environment of Glacial Deposits at Clava, North East Scotland. Bull. Geol. Surv. Gt. Brit. No. 49 – p 31.