ABSTRACT: Sequence Stratigraphy Interpretation of the Central Shelf Area, Offshore Louisiana

Barbara Radovich, Timothy Powell, Mark Lovell Robert Mitchum, Jr.

Sequence stratigraphy methods are demonstrated on a Halliburton regional seismic line and several well logs near the Eugene Island-Ship Shoal border off the central Louisiana shelf area of the Gulf of Mexico. The example shows five sequences of Pliocene-Pleistocene age interpreted by synthesizing log character, biostratigraphy and seismic character. These sequences show the complete range of shallow water to deeper water systems tracts, demonstrating a significant presence of lowstand wedge sediments high onto the present-day shelf.

The study area shows exceptional development of the transgressive systems tract between the 2.4and 3.0-m.y. sequence boundaries. This is evidenced by apparent truncation on seismic and corresponds to an overall shaly unit which contains several parasequences identified in well logs. The individual sands of the parasequences are easily correlated from well to well. The Lenticulina 1 paleo picks fluctuate between the 1.6 and 2.4-m.y. sequences but generally occur near the top of the 2.4 m.y. transgression. The 2.4-m.y. sequence boundary is deeply incised and filled with lowstand wedge prograding sands and shales. The 3.0, 3.8, and 4.2-m.y. sequences show an increasing thickness of lowstand wedge sediments and mounded slope fan seismic character with some channelized "gull wing" developm nt. Several sands with blocky log character are interpreted as channelized portions of the slope fan. Updip along the sequence boundary, the proximal slope fan seismic facies character becomes dominant, i.e., much more laterally continuous seismic reflectors with few mounds.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990