Pliocene-Pleistocene Evolution of Central Offshore Louisiana

James E. Geitgey

Central offshore Louisiana (the South Additions of Eugene Island, Ship Shoal, and South Timbalier) was the site of shelf-margin progradation through the Pliocene-Pleistocene. Two distinct depositional settings developed concurrently in that region: a series of shelf-margin deltaic complexes to the west, and an inter-deltaic shelf to slope system to the east. The two different depositional settings can be recognized by differing structural and stratigraphic elements that, in conjunction, characterize and distinguish each.

A series of paleobathymetric maps for successive intervals through the Pliocene-Pleistocene documents the development of a conspicuous seaward bulge in the paleontologically defined shelf margins in the area of Eugene Island. Overall, the maps illustrate the southerly progradation of the entire shelf margin through the South Additions during the Pliocene-Pleistocene. Mapping the distribution of successive sands and interpreting log character establishes that well-developed, extensive sands are present shoreward of each shelf margin to the west in Eugene Island, and equivalent bathyal section to the east in South Timbalier and eastern Ship Shoal is relatively sand poor.

Structurally, the pattern of faulting in the shelf-margin deltaic systems is that of a complex network of arcuate growth faults. To the east, in South Timbalier, a relatively small number of extensive strike-oriented fault systems are recognized.

The variations in the geologic expression of the two depositional settings are also manifested in the geographic and stratigraphic patterns of hydrocarbon production established to date and would need to be considered to make the best use of remaining exploration potential.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.