Article: Upper Albian ammonites from ODP Leg 171B off northern Florida

ODP Leg 171B investigated the sediments of the Blake Plateau off northern Florida and recovered 36 Upper Albian ammonites - one from Site 1050C, the others from Site 1052E. This unusually large number of specimens from an ODP site permits the dating of the interval between 668 to 621 m below sea-floor at Site 1052E as late Late Albian, Stoliczkaia (S.) dispar ammonite zone. This zone is indicated by the genera Mortoniceras and Stoliczkaia (S.). Site 1050C (Interval 171B-1050C-31R-3, 0.80-0.86 m) cannot be dated more precisely than Late Aptian to Mid Cenomanian by ammonites. The fauna is cosmopolitan. Tetragonites jurinianus and Puzosia myoriana are widely distributed forms. Kossmatella muhlenbecki was thought to be restricted to a fairly small area around the Mediterranean, but the record off northern Florida presented here, indicates that it is not an endemic species; this is also true for Hemiptychoceras subgaultinum in the Albian. The event-like character of the ammonite-bearing interval at Site 1052E is unique. It is overlain by a laminated claystone succession; the top of this sequence is considered to represent maximum flooding (Oceanic Anoxic Event, OAE 1d). Ammonites perhaps profited from an increased nutrient supply derived from flooded coastal plains during a continuous transgression.