UPPER QUATERNARY STRATA OF THE UPPER CONTINENTAL-SLOPE, NORTHEAST GULF-OF-MEXICO - SEQUENCE STRATIGRAPHIC MODEL FOR A TERRIGENOUS SHELF EDGE

The shallow subsurface of the upper slope, northeastern Gulf of Mexico , shows abrupt changes in depositional environments, sequence stratigr aphy, and sedimentation rates reflecting Pleistocene to Holocene glaci oeustasy, Stratigraphic change is recorded in lithologic, sedimentolog ic, biostratigraphic, and oxygen isotopic data from a nearly continuou s 245.5 m core from Viosca Knell Block 774, a gamma-ray log of the bor ehole, and high-resolution seismic-reflection data. Mud with minor san d at the base of the boring (245.5 to similar to 136 m) was deposited during several sea-level cycles corresponding to isotope stages 13 to 8, and includes a thick, probable stage 10 unit. A thick, coarsening u pward deltaic mud and sand at similar to 136-59.9 m likely was deposit ed during oxygen isotope stage 8 glaciation, The section upward from s imilar to 59.9 m contains: a deltaic silt and sand probably deposited during stage 8; a transgressive sand shoal recording the stage 8-7 tra nsition; highstand mud and sand of stage 7; a relatively thin stage 6 lowstand mud and sand; stage 5 highstand mud and sand; stage 4-2 mud a nd sand; and Holocene sandy silt. Almost all contacts between systems tracts are transitional in core. Inferred lowstand deposits are lithol ogically and sedimentologically variable, reflecting degree of delta p rogradation and subsequent erosion, and consist of sand and (or) mud, Thicker, coarser intervals at the site represent shelf-margin deltas l ikely deposited during falling sea level, Falling sea level and lowsta nd sediment is characterized by mostly middle to inner neritic benthic foraminifera, cool-temperature planktonic foraminifera, and high oxyg en isotopic values of the planktonic foraminifera Globigerinoides rube r. Transgressive and highstand systems tracts are thin. Rising-sea-lev el sections and highstand condensed intervals consist of clay or silt with carbonate concretions and with numerous pyritized microfaunal tes ts and small burrows. Condensed sections also contain abundant microfa una, mostly warm temperature planktonic foraminifera, outer neritic to upper bathyal benthic foraminifera, and transitional to interglacial delta(18)O values of Globigerinoides ruber, Some sandy turbidites appe ar to be interbedded with highstand mud.