Depositional Styles from Miocene through Pleistocene in the

JESSE L. HUNT, Jr. and GRANT BURGESS.
Minerals Management Service, 1201 Elmwood Park Boulevard, New Orleans, Louisiana 70123
e:mail jesse_hunt@smtp.mms.gov, grant_burgess@smtp.mms.gov
Reprinted from GCAGS Transactions, v.45

The Minerals Management Service, U.S. Department of the Interior, has recently classified the producible sands from the approximately 1,100 fields across the northern Gulf of Mexico into groups of genetically related plays defined by production, chronostratigraphy, lithostratigraphy, and structure. Each field was assigned a structural code, and each producible sand was classified by depositional environment. Correlation of the type logs with biostratigraphic and seismic data established 13 chronozones from lower Miocene to upper Pleistocene. Sands within each chronozone were classified as transgressive, aggradational, progradational, or submarine fan facies. Hydrocarbon plays encompassing all discovered resources were mapped for each chronozone.

This paper describes the distribution and continuity of hydrocarbon plays in the Louisiana OCS comprised of discovered resources in sands deposited by the ancestral Mississippi River delta. Pronounced changes in depositional styles and hydrocarbon-prone areas are observed from the lower Miocene through the Pleistocene as the ancestral Mississippi River delta migrated basinward and across offshore Louisiana.

Lower Miocene hydrocarbon plays are restricted to the western portion of the Louisiana shelf. A marked eastward migration of the depocenters occurred in middle Miocene. During the upper Miocene, the depocenter began migrating to the west and extended significantly basinward. Throughout the Pliocene and Pleistocene the depocenter migrated basinward and westward. The distributions of known hydrocarbon plays provide an organized framework for exploration analogs.

The following figures correspond to the figures referenced in the Complete Text above:

Figure 1.	Chronostratigraphic subdivisions and biostratigraphic zones used for the Gulf of Mexico. Modified from Reed et al (1987).
Figure 2.	Depositional facies, sand-body characteristics, and associated idealized SP log shape.
Figure 3.	LM 1 (lower Miocene - Lenticulina hanseni) facies distribution map.
Figure 4.	LM 2 (lower Miocene - Siphonina davisi) facies distribution map.
Figure 5.	LM 4 (lower Miocene - Marginulina "A") facies distribution map.
Figure 6.	MM 4 (middle Miocene - Gyroidina "K" to Amphistegina "B") facies distribution map.
Figure 7.	MM 7 (middle Miocene - Cibicides opima to Bigenerina humblei) facies distribution map.
Figure 8.	MM 9 (middle Miocene - Textularia "W" to Bigenerina 2) facies distribution map.
Figure 9.	UM 1 (upper Miocene - Discorbis 12) facies distribution map.
Figure 10.	UM 3 (upper Miocene - Cristellaria "K" to Robulus "E"/Bigenerina "A") facies distribution map.
Figure 11.	LP (lower Pliocene - Textularia "X") facies distribution map.
Figure 12.	UP (upper Pliocene - Buliminella 1) facies distribution map.
Figure 13.	LPL (lower Pleistocene - Valvulineria "H" to Lenticulina 1) facies distribution map.
Figure 14.	MPL (middle Pleistocene - Angulogerina "B") facies distribution map.
Figure 15.	UPL (upper Pleistocene - Hyalinea "B") facies distribution map.