Graphic Correlation of Plio-Pleistocene Sequence Boundaries, Gulf of Mexico: Oxygen Isotopes, Ice Volume, Sea Level, and Water Mass Structure

R. Martin, R. R. Fletcher

Graphic correlation of Plio-Pleistocene Globorotalia-based zonal boundaries reveals changes in sediment accumulation rates that reflect seismic sequence boundaries previously recognized by other workers using integrated seismic, well-log, and biostratigraphic data bases. Graphic correlation of Globorotalia-based datums is a first step in teasing apart the effects of ice volume (sea-level change, temperature) and water mass structure (upwelling, productivity). Pleistocene zones appear to primarily represent the repeated invasions (from the Indian Ocean) and regional (Atlantic) extinctions of Globorotalia menardii (and reciprocal contractions and expansions of G. inflata). The migrations were a response to latitudinal shifts in water masses of the Atlantic Ocean driven by c anges in northern and southern hemisphere ice volume and shifts in the position of the Subtropical Convergence and Antarctic Polar Front. The occurrence of Globorotalia may also be related to the depth and periodic reorganization of the thermocline (upwelling, productivity, temperature), which may account for discrepancies between the ecozonation and the oxygen isotope curve below oxygen isotope stage 5. Abundance and shape changes (indicative of water mass reorganization) of Globorotalia spp. in deep sea cores could be related to high resolution records of sea-level change from the continental margin that would allow separation of the effects of ice volume, temperature, and water mass structure that are confounded both in the oxygen isotope record and the Globorotalia curve. Prior to the onset of major northern hemisphere ice sheets, the Pliocene Globorotalia curve indicates changes in water mass structure in response to closing of the sthmus of Panama and fluctuations in volume of Antarctic ice sheets.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995