Towards a More Refined Lower Miocene Calcareous Nannofossil Biostratigraphy in the Gulf of Mexico

Brandi Harkins¹, David K. Watkins¹, and Michael J. Styzen^2
1Dept. of Geosciences, University of Nebraska-Lincoln, Lincoln, NE
²BEAST - EP Solutions, Shell International Exploration and Production, Houston, TX

A need for high resolution, reliable calcareous nannofossil biostratigraphy in lower Miocene Gulf of Mexico sediments has increased due to deep water exploration and attempts to target intervals below salt with poor seismic resolution. Published zonation schemes elsewhere either target first occurrence datums or use species that do not work in the Gulf. However, few published biostratigraphic analyses have targeted the Gulf of Mexico and this interval in particular, with their focus concentrated on the upper Miocene through Pleistocene; knowledge that does exist is industrial and proprietary.

Five industry provided GOM cores have been examined with morphometric and statistical analysis and then correlated to enhance current biostratigraphy. Primary and secondary datums and events are defined for the lower Miocene through the last appearance datum of Helicospheara ampliaperta based on regional and basin correlation. Abundances, last occurrence datums, morphological data, assemblage changes, and evolutionary trends, particularly of Cyclicargolithus, Reticulofenestra, and Helicospheara species, provide these datums and events. Regional and basin-wide unconformities are also documented, then correlated, and percent abundance counts used as a proxy for sequence stratigraphy.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas