Plio-Pleistocene Planktonic Foraminiferal Biostratigraphy, Paleo-oceanography, and Sediment Accumulation Rates, Northeastern Gulf of Mexico

Ronald E. Martin, Glenn W. Johnson, Brenda Spotz

The planktonic foraminiferal biostratigraphy has been analyzed for Ocean Drilling Program's hole 625B (Leg 100), drilled to a total sub-bottom depth of 235 m south of De Soto Canyon in the northeast Gulf of Mexico. The hole penetrated to at least early Pliocene (zone N19), as indicated by the Globigerina nepenthes LAD (~ 3.7 Ma) at 182 m.

Preliminary seismic sections of the Plio-Pleistocene sediments of the continental slope in the northeast Gulf suggested a relatively continuous depositional record. However, sediment accumulation rates have fluctuated in parallel with paleo-oceanographic changes. Percent coarse (~ 63 µm) carbonate fraction (mainly planktonic foraminiferal tests) in hole 625B shows high-frequency, low-amplitude fluctuations from the Pliocene to the Jaramillo paleomagnetic event (~ 900,000 y.B.P.), whereupon low-frequency, high-amplitude fluctuations occur to the Holocene. Low-frequently, high-amplitude fluctuations correspond primarily to increased amplitude of sea level fluctuations and terrigenous dilution during low sea level stands.

Percent abundance of Globorotalia menardii and percent coarse carbonate fraction in the uppermost 18 m reflects oxygen isotope stages 1-5 and therefore, primarily, ice volume and, secondarily, water temperature. However, the lack of a strict correspondence between G. menardii abundance, percent coarse carbonate fraction, and planktonic-benthic ratios (presumed dissolution indicator) lower in the hole indicates that G. menardii abundance peaks reflect not only eustatic sea level changes and water temperature but possibly also productivity (upwelling) and/or differential dissolution. Preliminary results of factor analysis of foraminiferal assemblages are also presented.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.