Abstract: Late Pleistocene Sedimentation and Meltwater Influx in the Central Gulf of Mexico: Stratigraphic Signals

Megan Jones, Barun Sen Gupta

Frequency variations of planktonic foraminiferal species in the Y1 biostratigraphic unit (16.5-11 kyr) indicate that the meltwater discharge into the northwestern Gulf of Mexico extended as far as 500 km south of the location of Galveston. In seven piston cores, two salinity-sensitive species, Globigernoides ruber, a commonly used faunal indicator of the meltwater spike, and Neoglobequadrina dutertrei exhibit frequency increases in the Y1 subzone, the base of which generally coincides with the base of the meltwater spike. Our data do not confirm the findings of previous workers that the frequency of G. ruber decreases significantly between the northern and the central Gulf during a meltwater event, and conversely, that the frequency of M. du ertrei, a deeper-dwelling species, increases. At two sites closest to the meltwater source (both with expanded sections), a faunal dilution is apparently related to the influx of terrigenous material (29 cm/kyr). Other sites just to the west show the lowest sediment accumulation rates (4 and 6 cm/kyr), whereas sites farther south show little variation (11-15 cm/kyr), suggesting either an altered sedimentation pattern (related to different sources or transport barriers) or undetected hiatuses within these cores.

Judging by its major-element composition, the glass from an ash layer (Y8 subzone) in one of our cores is indistinguishable from that in the high-K rhyolitic ash and pumice (SC-7, H-tephra and ash flow) of the Los Chocoyos Ash (84 ka) in Guatemala. Using this marker, the average sediment accumulation rate for the glacial Y-Zone is about 7 cm/kyr.

Average Holocene sedimentation rates (28 cm/kyr) generally decrease with increasing distance from the Mississippi delta, but again the lowest rates occur in the central part of the study area, as in the glacial subzone Y1.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas