The Late Triassic Blue Anchor Formation and the initial Rhaetian marine transgression in south-west Britain

Summary The Blue Anchor Formation of the Upper Trias in south-west Britain is divided into two members. The lower (Rydon Member) was deposited in an evaporitic lacustrine environment whilst the upper (Williton Member) was deposited in a shallow marine environment and represents the initial marine transgression into south-west Britain late in the Triassic Period. Sedimentological and clay mineralogical evidence indicates that the Williton Member is bounded by erosional disconformities and, at present, can only be positively recognised in North Somerset.