Mike Horne FGS
Glaciations
The Quaternary has been a time of fluctuating temperatures resulting in glaciations in the higher latitudes.
For the UK this has led to periods of glaciation, perigacial conditions and warmer spells.
The study of Quaternary geology in northern Britain has been compared with calculating how many times a blackboard has been cleaned. Each cleaning if the blackboard wipes out most of the writing; each glaciation scrapes away previous deposits.
The affects of glaciation vary accoring to original landscape. In high mountainous and hilly areas there is accumulation of glaciers, with resultant weathering and erosion. In lower areas there is the deposition of the material carried by the glaciers. And in front of the glacier there are perigacial conditions.
The highland landscape will be altered by the glaciers - valleys will be deepened and change from a 'V' to a 'U' shape, peaks will become more exaggerated and pointed; hills in the path of the glacier will become more rounded and streamlined.
In East Yorkshire we are more concerned with the deposits resulting from glaciation - so here are some definitions of jargon-words you might come across:-
Anglian - the Ice Age which had most affect on the UK
Boulder Clay - another name for Till. A mixture of erratic boulders and silty clay deposited by a glacier.
Devensian - the last Ice Age -
Cross-bedding - bedding in sands and gravel that is on a slope cause by deposition of dunes from fast flowing water or wind.
Diamict (or diamicton) - see Boulder Clay (Diamict is the new formal term for a sediment with two or more distinctive size fractions of various origins, not necessarilly glacial. I suspect that all tills are dicamicts but not all diamicts are tills.)
Drumlin - streamlined hill that has been reshaped by subsequent ice advance
Erratic - a rock or fossil in the "wrong place" that has been transported by a glacier.
Esker - sedimentary deposits from a stream flowing from tunnels under a glacier - often including cross-bedded sands and gravels
Holocene - the last 10 000 years
Ice Wedge Casts - V-shaped masses in the top of earlier sediments; filling a crack caused by annual freeze/thaw under periglacial conditions.
Ipswichian - the warm interglacial before the Devensian Ice Age
Kettle-Hole - depression caused by the melting block of ice that is trapped in sediments.
Mere - lake filling a Kettle-Hole
Moraine - till deposits - may be classified further into Terminal Moraine - left at the point of furthest advance of a glacier; Lateral Moraine - deposited at the sides of the glacier; Medial Moraine - deposited by the middle of the glacier; Recessional Moraine - deposited as the glacier melts and retreats; Ground Moraine - deposited under the glacier.
Periglacial conditions - frozen ground not covered by a glacier; may partly thaw in the summer.
Raft - a (sometimes distorted) piece of erratic soft sediment within a till.
Till - see Boulder Clay.
Varve - thinly layered silts and clays, representing annual accumulation in a quiet lake - more being deposited in the warmer summers than colder winters.
Link to a Quaternary time-scale
further reading -
Wilson R C L, S A Drury & J L Chapman 2000. The Great Ice Age. Climate Change and Life. Routledge, London and the Open University. 267pp, isbn 0415194829. library - 550.60901.
Williams MAJ, D L Dunkerley, P De Deckker, A P Kershaw & T Stokes 1993. Quaternary Environments. Edward Arnold, London. 256pp
copyright Mike Horne - October 2016