MIOCENE BIOSTRATIGRAPHIC TRANSECT BETWEEN ALAMINOS CANYON AND MISSISSIPPI CANYON, GULF OF MEXICO

The Miocene sediments of two deep water boreholes from the northern Gulf of Mexico, Alaminos Canyon (AC) Block 627 and Mississippi Canyon (MC) Block 555, have been biostratigraphically analyzed using calcareous nannofossils. Assemblage composition was tabulated and species abundances were estimated. Because samples were retrieved by rotary drilling methods, only last occurrence datums of biostratigraphic markers were used. The results of this study reveal changes in depositional environments and sedimentation rates across the northern Gulf of Mexico. High nannofossil abundance values and low sedimentation rates in the Alaminos Canyon area suggest a condensed section, associated with a deep basin environment. Mississippi Canyon exhibits lower nannofossil abundance and higher sedimentation rates, approximately by a factor of ten, compared to Alaminos Canyon. Increased sediment volumes are almost certainly due to input from the Mississipi River. One anomaly was observed in the lower part of the section at Mississippi Canyon between the interval defined by Sphenolithus belemnos and Dictyococcites biscetus suggesting a fault which has shortened the section. A biostratigraphic cross-section of the two boreholes was created that depicts these changes across the northern Gulf of Mexico.