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