Local Foraminiferal Faunas: The Key to Enhanced Stratigraphic Resolution in Expanded Cenozoic Sections of the Gulf Coast Basin: ABSTRACT

ABSTRACT Local foraminiferal faunas are categorized and described from selected stratigraphic sections of the Gulf Coast Basin, including the lower Pleistocene (Nebraskan), lower Pliocene, the Marginulina ascensionensis and Siphonina davisi/Planulina palmerae zones of the lower Miocene and the middle Oligocene Hackberry zone. Several different types of local faunas are recognized: these include calcareous and arenaceous local extinctions and acmes, planktic floods, reoccurring faunas, zones of reworking, flags and deep-water (bathyal) locals. Locals are best delineated through high resolution biostratigraphic and paleoenvironmental analyses, and are most useful in field or well-to-well studies, especially along paleoenvironmental strike. General methods for establishment of local foraminiferal zones are discussed. Three unrelated microfossil groups, ostracodes, palynomorphs and nannoplankton, are compared to foraminifera for local correlation potential. Foraminifera are judged to be the most successful group due to great abundance, high species diversity and tolerance for all marine environments. Although local zonations are not limited to expanded sections, their greatest utility is recognized there because many major productive intervals in the Gulf Coast Basin are located in expanded sand-rich sections between major biostratigraphic events. Local foraminiferal faunas are significant to subdivision of thick stratigraphic sequences by providing additional correlative events, and in areas of rapid sedimentation where others markers may be diluted or rare. Deep-water local foraminifera may have more widespread utility due to global uniformity of environmental conditions in the bathyal zones.