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Facies Changes of the Eutaw Formation (Coniacian-Santonian), Onshore to Offshore, Northeastern Gulf of Mexico Area

Kaiyu Liu
Department of Geological Sciences, University of Alabama, Tuscaloosa, Alabama, 35487

The Upper Cretaceous Eutaw Formation in the eastern Gulf Coastal Plain represents marginal marine to marine deposits that accumulated during a Late Cretaceous (Late Coniacian-Santonian) transgression. Eutaw facies vary significantly from updip to downdip on the Late Cretaceous continental shelf. A regional correlation of the Eutaw Formation from the outcrop area to the outer shelf area based on wireline logs and nannofossil biostratigraphic data illustrates facies changes on the continental shelf.

Two surfaces that have chronostratigraphic significance were correlated to constrain the Eutaw strata in a sequence stratigraphic framework: a maximum flooding surface in the Mooreville Chalk, which is stratigraphically above the Eutaw Formation, and a sequence boundary (the Tuscaloosa-Eutaw contact) at the base of the Eutaw Formation. The sand facies of the Eutaw Formation were found to grade basinward into chalk facies assigned to the Selma Group. The Eutaw-Selma contact, a diachronous surface, was interpreted to have formed as part of a series of higher order transgressive events.

Regional structures had major impacts on the deposition of sediments on the Late Cretaceous continental shelf, especially on the deposition of the transgressive deposits of the Eutaw Formation. A large lagoon or bay existed during the Late Coniacian-Santonian transgression, which contributed to impounding sand sediment on the northern side of the basin and resulted in shale sediment deposition in the basin proper and south of the basin.


AAPG Search and Discovery Article #90080©2005 GCAGS 55th Annual Convention, New Orleans, Louisiana