Abstract 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.

Abstract An unconventional application of traditional similarity coefficients, the similarity curve, is presented to assist in the identification and interpretation of stratigraphic discontinuities. Similarity curves are generated for an entire stratigraphic sequence by comparing each sample to the sample immediately above it in stratigraphic sequence. Similarity coefficients are calculated for each sample pair on the basis of their contained foraminiferal assemblages, and a similarity curve is then generated for the stratigraphic section. By examining the breaks in these curves and comparing the total assemblage similarity curve to similarity curves generated individually for planktonic and benthic groups, we interpret candidates for discontinuities from a well in the Gulf of Mexico. Furthermore, we discuss these discontinuities and relate them to factors such as potential sea-level change, changes in sedimentation locus, and dissolution effects.