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The AAPG/Datapages Combined Publications Database
GCAGS Transactions
Abstract
Depositional Facies and Eustatic Effects in the Upper Cretaceous (Maastrichtian) Ripley Formation, Central and Eastern Alabama
Michael C. Skotnicki (1), David T. King, Jr. (2)
ABSTRACT
In central and eastern Alabama, the Maastrichtian Ripley Formation (40 to 123 m thick) is comprised of six depositional facies: (1) barrier-island shoreface/tidal-inlet fill sands; (2) back-barrier lagoon/marsh siltstones; (3) storm-generated lagoonal sand beds; (4) back-barrier tidal-flat/lagoonal claystones; (5) lower shoreface sands; and (6) inner-shelf deposits. The Ripley is divided into two genetic packages of facies; the genetic packages are bounded by stratigraphic breaks of eustatic origin. The basal Ripley break is correlated with the end-Campanian (c. 74 Ma) eustatic sea-level drop, and the middle Ripley break (separating the two genetic packages) marks the mid-Maastrichtian (c. 71 Ma) sea-level drop. The basal and middle Ripley breaks are low-relief erosional surfaces distinguished by facies discontinuities and thin conglomeratic lag deposits. The break at the top of the Ripley has a maximum erosional relief of 67 m in the outcrop area studied (83 m in the shallow subsurface) and is mantled by a conglomeratic lag bed up to 80 cm thick. The break at the top of the Ripley represents a Late Maastrichtian (c. 68 Ma) sea-level fall estimated to have been nearly 95 m.
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