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To refine Unocal’s Gulf of Mexico deepwater Miocene biozonation, a statistically rigorous methodology was applied to an extensive micropaleontological database of wells penetrating the Miocene. Over a two-year period, we analyzed, in an integrated manner, the stratigraphic distribution of calcareous nannofossil and foraminiferal species that resulted in improvements in age dating and correlation for both exploration- and development-scale projects. Our approach was to first begin with a detailed evaluation and validation of bioevents of many hundreds of Miocene-age taxa using hardcopies of species distribution charts (BugCAD plots), followed by analysis of results processed through specialized computer software (IPS and BioSlot). This process yielded the placement of the more common types of bioevents (i.e., species range tops and bases), and in addition aided in the recognition of new, useful, subordinate bioevents (e.g., first downhole increases). All bioevents were then analyzed using the ranking and scaling probabilistic sequencing method (RASC), and the correlation and scaling in time method (CASC). The RASC/CASC methods resulted in the most probable order, termed the “optimum sequence” for the Miocene-age biostratigraphic events. This optimum sequence has been empirically validated by its successful application to correlations of previously drilled wells currently in production in a deepwater Gulf of Mexico field.

Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones

SEPM Special Publication No. 93, Copyright © 2009

SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 337–342.

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