DEVONIAN CARBONIFEROUS SEDIMENTARY EVOLUTION OF THE CLAIR AREA, OFFSHORE NORTH-WESTERN UK - IMPACT OF CHANGING PROVENANCE

The Clair Group was deposited in a Devonian-Carboniferous rift basin at the edge of the present day north-west European shelf west of the Shetland Islands. The West Shetland Basin, in which the Clair area lies, therefore provides the most westerly record of Devonian-Carboniferous environments in northern Britain and allows comparison with the Orcadian basin to the east. Palaeogeographical time slices are presented based on sedimentological studies of core, electrical logs and heavy mineral assemblages. The basin underwent two cycles of increasing endorheism (internal drainage) in a Devonian continental rift, followed by a cycle of increasing humidity as high sinuosity streams were succeeded by marginal marine environments in the Carboniferous. The two lower cycles of increasing endorheism are separated from the upper cycle by an important field-wide unconformity. This stratigraphic break is accompanied by a major change in provenance from small intra-rift drainage networks and deserts depositing polycyclic minerals, to much enlarged drainage systems transporting first-cycle, unstable minerals from catchments reaching far beyond the Devonian rift.