Cwm Crymlyn Road Section
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Geology & landscape
Geological Feature: Rock Outcrop · Geological Period: Ordovician
Landscape processes: Glacial
Description
Description This is the only permanent exposure of the recently discovered Tremadoc rocks in South Wales, which here yield a rich fauna of anisograptid graptolites, trilobites and inarticulate brachiopods, indicative of the Clonograptus tenellus Zone. Several of the trilobite genera have never previously been recorded from Britain, and show close links with Argentinian faunas. A key site in studies of the distribution of earliest Ordovician rocks and their faunas. 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 Countryside Council for Wales. Cwm Crymlyn is of considerable importance since it provides the only permanent outcrop of Tremadoc rocks anywhere in South Wales. These strata were deposited as a blanket of mud on the sea floor some 500 million years ago when much of Wales lay beneath the sea. The site has yielded a rich assemblage of fossils, some of which occur nowhere else in Britain. The fossils described from this locality, which represent the earliest forms of life to exist in the Ordovician period of geological time, include a group of marine arthropods known as trilobites (which are now extinct), graptolites (colonial organisms which were particularly abundant in early geological times) and a variety of shelly fossils. Some species of trilobite show a close similarity to forms described from Argentina, the site is of importance in an international as well as a national context.