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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 311

Last Page: 312

Title: Cincinnatian Series--Model for Cyclic and Episodic Deposition of Carbonates and Shales on a Storm-Dominated Ramp: ABSTRACT

Author(s): Rick C. Tobin, Wayne A. Pryor

Article Type: Meeting abstract


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Upper Ordovician (Cincinnatian) strata in Ohio, Indiana, and Kentucky were deposited as cyclic sequences. Three types of cycles are represented: thin, graded storm cycles, moderately thick megacycles (carbonate to shale sequences), and thick shoaling-upward cycles (shale-rich, grainstone-poor facies that grade upward into shale-poor, grainstone-rich facies).

Cincinnatian strata were deposited on a gently sloping, shallow-marine carbonate ramp. Sedimentation was episodic; periods of in-situ carbonate accumulation were frequently interrupted by storm events. Tropical storms affected sedimentation and benthic ecology in seven ways by: (1) eroding sediments; (2) transporting allochthonous clays and silts onto a carbonate ramp; (3) winnowing, transporting, and redistributing carbonate sediments; (4) generating downslope gravity flows; (5) mixing benthic fauna from different communities; (6) periodically interrupting the process of community succession; and (7) creating favorable conditions for the evolution and success of opportunistic species.

Because of the excellent preservation of episodic storm events and their influence on sedimentation and paleoecology, the Cincinnatian Series is recognized as an example of an ancient storm-dominated, carbonate ramp. The following characteristics are diagnostic of storm domination in the rock record: (1) abundant storm sequences occur in all facies; (2) storm sequences are variable; (3) inner shelf facies have thin, discontinuous bedding; (4) rudites dominate in inner shelf facies; (5) fine grainstones are concentrated in outer-shelf facies; (6) textural inversions are common; (7) carbonate rock types are widely variable; (8) storm-generated structures occur in all facies; (9) in-situ faunal communities are rare; and (10) most beds contain a mixture of fossil-preservational states.

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