Abstract:
Neogene calcareous nannofossils were sampled from seven industry drill core sequences and eleven Syracuse University piston cores taken on the carbonate ramp slope in the northeast Gulf of Mexico. Detailed range charts for each core were constructed in order to establish a biostratigraphic framework of the study area. More section was found to be present in coreholes CH 30-43, CH 31-44, CH 35-46, anc CH 34-47 than had been previously reported in the literature. It is hoped that information from this study can be used by both academia and industry to establish a Neogene reference section for the Gulf Coast and to provide ground truth for seismic stratigraphic sequences. Presently, the study is helping to provide a foundation for an ODP proposal to drill continuous coreholes in the west Florida shelf and slope areas. Continuous cores are needed to determine the cause of the hiatuses noted in the EXXON drill cores and to better understand the correlation of the offshore sediments and the Gulf coastal land formations. Stratigraphic discontinuities were delineated in the middle and upper Miocene of EXXON core holes CH 29-42, CH 30-43, CH 31-44, CH 32-45, CH 35-46, CH 34-47, and CH 33-48. Seismic stratigraphic analysis suggests that a middle Miocene hiatus was caused by the formation and invigoration of the Loop Current. A late Miocene hiatus, best documented in EXXON corehole CH 30-43, may have been induced by a severe sea level drop during the Tortonian 7-10 Ma). The Syracuse piston cores each contain continuous Pleistocene nannofossil sequences. These cores are useful for studying the effect of the modern Loop Current on the formation of the West Florida carbonate ramp. In collaboration with others, Pleistocene climatic fluctuations have been documented from a combination of pteropod, foraminiferal, nannofossil, stable isotope, and sediment data. Reworked Cretaceous nannofossils and aragonitic pteropod-rich sediments with large insoluble residues and total aragonite contents were deposited during glacial intervals. Sandy, calcitic sediment with abundant planktonic foraminifera accumulated during interglacial periods. The Loop Current, which formed by the tectonic closure of the Isthmus of Panama, indirectly influenced Pleistocene sedimentation through upwelling where it impinges on the slope, and continues to dominate sedimentation in the study area today.