Building a high resolution calcareous nannofossil biozonation using ranking and scaling (RASC)

The scope of this work is focused on enhancing the biostratigraphic resolution and quality of existing calcareous nannofossil zonations of the Cenozoic (e.g. Miocene and Late Paleocene-Late Eocene). Increasing biostratigraphic resolution is accomplished by the incorporation of non-traditional bioevents (e.g. C. gigas [influx]), and the reliability of bioevents is derived through the ranking and scaling (RASC) method. The ranked optimum sequence produced by RASC consists of bioevents with low standard deviation (i.e. reliable) and high standard deviation (i.e. unreliable). Section I outlines the methodology developed for defining and identifying bioevents, and performing RASC analysis on biostratigraphic data from the deepwater Gulf of Mexico. This RASC-derived ranked optimum sequence is successfully applied to an oil-producing Miocene Field (GoM). Section II is the primary component of this overall scope of work. This section builds on the general methodology outlined in Section I, but incorporates additional methods when interpreting bioevents in the ranked optimum sequence (e.g. merging/adjusting bioevents). In addition, Section II requires more extensive and detailed analysis and interpretation, as the author compiled quantitative calcareous nannofossil abundance data from Upper Paleocene-Middle/Upper Eocene sections in the North Atlantic (Sites 1051A/1052A) and deepwater Gulf of Mexico (KC 774 Unocal #1). The various traditional and non-traditional bioevents are identified from these three sections, in addition to bioevents identified from eight published datasets. Selected bioevents of the resulting ranked optimum sequence are deleted, merged or adjusted, and the final ranked optimum sequence is scaled to determine bioevent position in space/time. The most reliable bioevents within the scaled optimum sequence are assigned subzonal markers or zonal/subzonal co-markers. This final high-resolution calcareous nannofossil biozonation consists of 49 subzones within the Late Paleocene-Late Eocene (NP8-NP21). Section III focuses on the identification of paleoecological trends in Site 1051A and KC 774 Unocal #1, based on abundances of calcareous nannofossil groups (e.g. warm/oligotrophic and cool/eutrophic). The two sections demonstrate similar paleoecologic signals in portions of the Upper Paleocene and Lower Eocene, likely reflecting global thermal maxima events