The sedimentological record of a late Jurassic transgression: Rona Member (Kimmeridge Clay Formation equivalent), West Shetland Basin, UKCS

Late Jurassic sandstones form important potential reservoirs within the West Shetland Basin. They were deposited predominantly in deep marine environments although subaerial and shallow marine facies are also present. Data from 23 exploration wells show, however, that it is a heterogeneous unit ranging from coarse-grained pebbly sandstones to mudstones. The facies identified (cohesionless debris flow, high and low density turbidites, upper and lower shoreface) and their vertical transitions are considered typical of fan delta deposition, initially in a subaerial environment and later under progressively more marine conditions. To explain the facies distribution it is suggested that footwall uplift on the Rona and Judd Faults (Rona Ridge and associated basement highs) was responsible for the supply of coarse-grained material to isolated fan deltas. Transgression eventually resulted in: flooding of the basement highs, cut off of sediment supply and deposition of finer-grained sediments. -from Authors