Neogene-Holocene Mixed Carbonate-Siliciclastic Deposition in Eastern Gulf of Mexico with Earlier Analogs

L. J. Doyle, S. D. Locker

The Neogene to Holocene history of the eastern Gulf of Mexico reveals a complex interplay between carbonate and siliciclastic sedimentation that may help interpret and explain many ancient deposits. Well data from the Florida Panhandle have been correlated with over 1,900 mi of high-resolution seismic reflection profiles collected on a 2-mi grid as part of a major geophysical program sponsored by GECO Geophysical Company, Inc. Data show a shift from flat carbonate sequences to prograding sequences about a major Neogene unconformity. Below that unconformity, carbonate sedimentation was dominant; afterward sediments became progressively more siliciclastic, grading into the Apalachicola delta and a surficial quartz sand sheet. The quartz sand grades laterally into the west F orida carbonate margin, bounded on the east by fine quartz sand beaches and terrace deposits of the Florida peninsula and on the west by the massive siliciclastic Mississippi fan. Siliciclastic sediments must have advanced and retreated across the carbonate shelf with sea level rise and fall. DSDP Leg 9 cores and seismic profiles suggest that, periodically, portions of the west Florida and probably Yucatan margins have failed, injecting massive carbonate gravity deposits into the deep Gulf of Mexico. These deposits have become intercalated into the Mississippi fan. Examples of quartz sand-filled channels in carbonate rocks and carbonate gravity deposits within siliciclastic (e.g., south Pyrenean basin and some deposits of the Permian basin) are found in the ancient record where they prov de excellent isochronous marker beds as well as good potential reservoirs for hydrocarbons.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.