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ABSTRACT: Facies Stratigraphy and Relative Sea-Level History--Upper Cretaceous Eutaw Formation, Central and Eastern Alabama

David T. King, Jr.

The Upper Cretaceous (late Santonian-early Campanian) Eutaw Formation crops out in an east-west-striking belt in the inner Coastal Plain of Alabama. Facies arrangement within the Eutaw indicates a regional paleoshoreline having depositional strike approximately parallel to and coincident with the present outcrop belt. The Eutaw Formation (40 to 120 m thick) rests disconformably on incised valleys (a type 1 unconformity) occurring at the top of the underlying Cenomanian-early Turonian nonmarine Tuscaloosa Formation. The Eutaw is topped by an erosional discontinuity that has slight relief and a discontinuous conglomeratic lag. In the outcrop and shallow subsurface, the Eutaw Formation has four main paralic and nearshore facies that are arranged in two discontinuity-bounded enetic packages of facies (or parasequences) both of which developed in a single eustatic cycle. The Eutaw facies are: carbonaceous and ostried-rich clayey silts

(= back barrier); planar, trough, and low-angle cross-bedded medium-fine sands (= barrier island); fossiliferous bioturbated fine sands (= lower shoreface); and calcareous clays, silts, and sands (= inner shelf). The lower genetic package of the Eutaw Formation is bounded below by the Tuscaloosa disconformity (a flooding surface) and is bounded above by a low-relief intraformational facies discontinuity. The intraformational facies discontinuity is likely a parasequence boundary developed at maximum eustatic high-stand in latest Santonian. The lower genetic package is mainly a transgressive sequence of back-barrier, barrier-island, lower-shoreface, and inner-shelf facies. The upper genetic package is mainly a progradational sequence encompassing the same set of facies as the lower gen tic package.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990