Association of a Seismic Reflector and Upper Cretaceous Sediment in the Bay of Biscay

Résumé du livre

Geological and geophysical investigations have been carried out over a small seamount near 45°N, 8°W in the central part of the Bay of Biscay. Recordings made with an airgun seismic profiler have suggested that the feature has been formed as a result of folding of a sequence of stratified sediments, which may be composed largely of turbidites, and by later deposition of accoustically more uniform pelagic material. The fold movements apparently took place before a series of turbidites nearly 1 kilometre thick was laid down to form the Biscay Abyssal Plain. A strong seismic reflector marking the top of the distorted stratified sequence is generally covered by thick sediments, but in two places it apparently outcrops at the sea floor. Samples of cocolith ooze of Maestrichtian age were obtained by gravity coring and dredging in one of the outcrop areas. It is suggested that the strong seismic reflector is approximately Maestrichtian in age and may record an important change in the sedimentary regime in the deep parts of the Bay of Biscay near the Mesozoic-Tertiary boundary. This occurrence of relatively old sediment does not conflict with current ideas on the formation of the Bay of Biscay by an anticlockwise rotation of Spain in late Jurassic-early Cretaceous times.