About a basin—The Palaeogene pull-apart fluvial Bovey Basin, South Devon, UK

The Bovey Basin in south Devon, UK, provides an instructive example of a Palaeogene pull-apart basin with a complex fluvial sedimentary fill. The basin, one of three that lie along the NW-SE-trending Sticklepath Fault Zone, is filled by about 1200 m of sediment, of which about the lower 700 m (mainly lower Bovey Formation) is concealed. The main Bovey Basin is separated from a smaller sub-basin (the Decoy Basin) south of Newton Abbot. Two main lithofacies are present in the Bovey Formation: lignite-clay; and clay-sand, with subordinate lithofacies of red-mottled clay and sand; and gravel and conglomerate. The upper 500 m or so of the sedimentary infill (middle and upper Bovey Formation) is divided into 10 members. Deposition in the basin was by a variety of fluvial processes, notably floodplain clays and sands deposited by meandering rivers; forest swamps with associated short-lived shallow lakes; and (mainly in the upper Bovey Formation) braided stream sands and gravels that formed mainly on alluvial fans. Lignites in the basin formed from plants that grew in place in forest swamps, a revision of the long-held view that the lignitic material was transported into the basin from forests of the conifer Sequoia couttsiae growing outside the basin on adjacent uplands. Newly discovered ichnofabrics occur in some lignitic sequences and probably represent root traces (rhizoliths).