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