Paleogene Calcareous Nannofossil Bioevents from the Fold Belts of the Deep-Water Central Gulf of Mexico
Richard A. Denne, 2007. "Paleogene Calcareous Nannofossil Bioevents from the Fold Belts of the Deep-Water Central Gulf of Mexico", The Paleogene of the Gulf of Mexico and Caribbean Basins: Processes, Events and Petroleum Systems, Lorcan Kennan, James Pindell, Norman C. Rosen
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Although the Oligocene to middle Eocene sediments of the fold belts of the deep-water central Gulf of Mexico are generally condensed and fossiliferous, many open-ocean and nearshore calcareous nannofossil markers are very rare or non-existent, necessitating the use of non-standard markers and assemblage changes (bioevents). These bioevents are based on species’ highest occurrences, consistent last occurrences, downhole abundance increases, morphometric changes, and acmes. Forty-five bioevents have been identified in the Oligocene to Middle Eocene of the northern Gulf Basin (onshore and offshore) utilizing 52 calcareous nannofossil species. As 10 of these horizons are based on nearshore forms and not recognized in the deep-water, 35 bioevents have been found in the deep-water Gulf of Mexico. This compares to the 14 zones and subzones of the standard nannofossil zonation schemes. Twenty-six additional species have been determined to be useful as zonal “flags.”
The lower Eocene and upper Paleocene sediments are expanded and contain few nannofossils. Seventeen bioevents have been identified in the northern Gulf Basin utilizing 25 calcareous nannofossil species. Due to the low fossil abundances and possible unconformities, only 10 of these bioevents have been found in the deep-water Gulf of Mexico. There are 12 standard zones and subzones within this interval, but 10 of the zonal boundaries are defined by species’ bases, and therefore not reliable in a petroleum industry context. Thirty-three additional species are useful as zonal “flags”. The lower Paleocene section is generally either very condensed or missing, with the exception of the K/T boundary debrite.