BIOSTRATIGRAPHY AND DEPOSITIONAL ANALYSIS OF A GULF OF MEXICO DEEP WATER BOREHOLE, ALAMINOS CANYON BLOCK 627

A deep water borehole in the northwest Gulf of Mexico, Alaminos Canyon Block 627, has been biostratigraphically analyzed using Late Miocene through Late Pleistocene calcareous nannofossils. Assemblage composition was tabulated and species abundances were estimated for the interval. The results of this study reveal changes in depositional environment in the western Gulf of Mexico. High nannofossil abundance values, from the Late Miocene through the Middle Pliocene suggest a condensed section, which is associated with a deep basin environment. Above this point, nannofossil abundances decline and reworked Cretaceous species are observed from the Late Pliocene through the Late Pleistocene. Reworked Cenozoic species were also found in the Late Pliocene just above the extinction of Discoaster tamalis. These observations may be associated with the development of a mass transport complex and subsequent sustained influx of clastic sediment into the area.