Abstract: Sequence Stratigraphic Framework and Depositional Variations of Early Miocene Lowstand Systems Tracts, Southwestern Louisiana

LUNEAU, BARBARA A.; JEFFREY A. MAY; and JOSEPH J. GARBEE, GeoQuest Reservoir Technologies, Denver, CO

Facies of early Miocene lowstand systems tracts comprise a large portion of the remaining exploration potential for deep untested objectives in southwest Louisiana. This complex and highly variable section is contained within six major depositional sequences deposited from 21.9 to 16.5 million years ago; each sequence ranges in duration from 0.5 to 1.5 million years. Regional well-log, seismic, and biostratigraphic correlation and mapping of the sequence stratigraphic framework defines the occurrence and extent of lowstand facies that filled intraslope basins across southwest Louisiana's coastal zone.

From oldest to youngest, the six sequences are correlated to Cristellaria R, Lenticulina hanseni, Siphonina davisi/Planulina palmerae, Marginulina ascensionensis, Cristellaria A/Discorbis B, and Gyroidina 9 biozones. Within onshore and state water areas, the five oldest sequences contain regionally correlative lowstand systems tract components. Almagamated, massive turbidite facies of basin floor fan complexes are not recognized in the two oldest Miocene depositional cycles, but become more common in the younger part of the section. Deep-water fan and channeled levee facies of slope fan complexes and deltaic facies of prograding complexes are well developed throughout the early Miocene section.

Syndepositional fault movement and salt withdrawal controlled thickness trends, facies patterns, sandstone content, and the position and trend of the shelf-slope break. Sandstone-rich basin floor fans, slope fans, and prograding deltaic complexes are best developed in intraslope basins where paleobathymetric confinement and accommodation were greatest.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas