FIELD EXCURSION

Field Excursion



Field Excursion

Introduction to geology and geomorphology of western Carmarthen Bay

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates. In modern times, geology is commercially important for mineral and hydrocarbon exploration and for evaluating water resources; is publicly important for the prediction and understanding of natural hazards, the remediation of environmental problems, and for providing insights into past climate change; plays an essential role in geotechnical engineering; and is a major academic discipline. Geology is also a hobby for those who enjoy collecting various rocks, minerals and/or fossils.

Carmarthen Bay is formed by the estuaries of the rivers Taf, Twyi and Gwendraeth where they enter the sea between the Carboniferous Limestone headland of Worms Head on the Gower Peninsula and Caldey Island. The bay includes several subunits that would warrant selection as coastal geomorphology GCR sites in their own right. It is unusual, however, in containing features that are relatively uncommon in England and Wales and in being very little disturbed by human activity.

Figure 1

Description of sites visited and features observed including annotated sketches and/or photographs

Apart from the coasts of north Norfolk and Holy Island, Carmarthen Bay contains the largest assemblage of unmodified sandy beaches in England and Wales, but it has received very limited attention in the literature. North (1929) and Steers (1946a) concentrated mainly upon the hard-rock coastline and the evidence of changes in sea level. Savigear (1952) saw the eastward growth of the Pendine beach as controlling slope development on the abandoned cliffs behind the beach and marsh. Kahn (1968), Potts (1968), Jago (1980) and Jago and Hardisty (1984) described the sediments and the geomorphological processes that act upon individual parts of the site. Barber and Thomas (1989) have considered the whole bay in terms of sediment transport and its effects on the beaches. Emerged ('raised') beaches and periglacial and fluvioglacial deposits occur at several points around the bay and many writers have considered the Quaternary history of the area and Campbell and Bowen (1989) provide a comprehensive summary.

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Discussion of appropriate methods of study

Consideration of processes at other GCR sites led to the decision to treat the whole of Carmarthen Bay as a single unit in the GCR, defined by the low-water limits of the intertidal zone at Ragwen Point and Rhossili. In addition, the cliffed coast around Worms Head, which is an important site in its own right, was integrated with the larger Carmarthen Bay GCR site. The site includes all the intertidal sand banks of the bay and the channels between them. The seaward boundary crosses the channels at their most seaward extent. Because the processes that affect the site extend into deeper water, an appropriate geomorphological boundary lies along a straight line from Ragwen Point to ...