Richard H. Fillon¹, Barry Kohl², Harry H. Roberts³
(1) Texaco Inc, New Orleans, LA
(2) Tulane University
(3) Louisiana State University, Baton Rouge, LA

Abstract: Lowstand stratigraphic framework of the upper-slope, and down-slope Sediment Transport, Northeastern Gulf of Mexico

The lowstand depositional environment of the late Pleistocene Mobile River's Langiappe delta reflects an unusual combination of glacial low sea level, marine dominated shelf-edge deposition, and warm winter ocean temperatures, which supported a distinctive calcareous bank benthic foraminiferal assemblage ca. 19 KYBP (¹⁴C dates). Examination of the correlative interval in the critical transition zone that links the shelf-edge deposystem and the deep Gulf of Mexico has focused on a continuously cored borehole located on the upper slope in Viosca Knoll block 774. Benthic foraminifera, also uniquely indicative of winter warmth and calcareous banks or hard grounds have been found here as well; however, different species comprise the Langiappe and upper slope faunas, consistent with the contrasting inner and outer neritic lowstand environments inferred from the bathymetric relief. An abrupt juxtaposition of glacial and interglacial planktonic foraminiferal assemblages indicates that section, which should contain the ca. 10-12 KYBP Gulf-wide ¹⁸O meltwater event is very thin or missing. The hiatus corresponds to a distinctive seismic event that is traceable across the upper slope. Bi-directional downlap above this surface and reflector truncation below it meet criteria for recognizing a sequence boundary. Channel-levee seismic signatures immediately above the surface offer additional evidence of a direct link between the lowstand shelf-edge depocenter and slope-fan deposition. Warmer, less dense near-surface water in winter in the northern Gulf suggests a mechanism for enhanced hyperpycnal flows of cold turbid meltwater to the deep basin during lowstands.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana