Wernbongam Stream Section and Quarry
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Geology & landscape
Geological Period: Devonian, Silurian · Rock Type: Sandstone
Description
Description A Silurian-Devonian section critical in interpreting the nature and timing of the change from marine to non-marine ('Old Red Sandstone') facies in south-west Wales. The site shows what has been interpreted as the conformable influx of non-marine facies prior to the end of the Wenlock, whereas traditionally the junction between Salopina bearing mudstones and 'Old Red' facies above had been taken to be an unconformity. A problematic site important in regional stratigraphic and sedimentary interpretation in the lower Palaeozoic. In layman's terms, the interest of this site may be expressed more simply, and such a statement is provided below. This should not be taken as definitive and further information as to details of the interest can be obtained from the Nature Conservancy Council. Some 400 million years ago a fundamental change took place which had a profound effect in shaping the geology of Wales. For a period of at least 200 million years before this much of Wales was covered by sea, and the thick deposits of mud and sands which accumulated in this environment were consolidated to form rock which was eventually uplifted by earth movements to stand above the sea as dry land. In broad terms, the Wembongam site demonstrates the change from sediments which are predominantly of marine origin to strata which were deposited in a freshwater environment. In other parts of Wales, this change was apparently accompanied by great upheavals in the Earth's crust, but this was not the case in the Wembongam area, where there was a gradual change from marine to a non-marine type of sedimentation. Wembongam is therefore of critical importance in the understanding and interpretation of this important event.