Cyclic alternation of proximal and distal storm facies: Kope and Fairview Formations (Upper Ordovician), Ohio and Kentucky
- Univ. of Cincinnati, OH (United States)
The Upper Ordovician Kope and Fairview Formations and the Bellevue Tongue of the Grant Lake Limestone exposed in the Cincinnati, Ohio region, represent storm-dominated sedimentation on a prograding, intracratonic ramp. The upper Kope-lower Fairview transition zone (25 m thick) is an outer to intermediate ramp lithofacies and is composed of numerous (1-3 m thick) shallowing-upward subtidal cycles. Bedding cycles are composed of two depth-controlled facies: (1) a shale-dominated distal facies and (2) a fossiliferous proximal facies. The distal facies records low-energy, largely single-storm events and consists of thin graded shale beds, nearly in situ fragile-fossil accumulations, thin parautochthonous packstones, and quartzose siltstone beds. Siltstones contain abundant storm-depositional indicators: tool-marked soles, gutter casts, mud-filled scours, hummocky lamination, and hummocky bedforms. The proximal facies represents deposition in an energetic, storm-wave-swept environment and consists of amalgamated sets of thick-bedded, fine- to coarse-grained skeletal grainstones and packstones with low-angle cross-lamination, megaripples, and shale lithoclasts. Sedimentary structures and paleocurrent patterns from both facies record deposition under a combined flow regime with the unidirectional current vector oriented in the offshore direction. Three scales or orders of sedimentary cyclicity are recognized in the study area. Meter-scale bedding cycles are considered fifth-order parasequences (20-100 Ka duration) and stack into genetically related parasequence sets. Analysis of Fischer plots suggest that cycle thickness and subfacies composition was controlled by both accommodation and siliciclastic sediment supply.
- OSTI ID:
- 6237665
- Journal Information:
- Journal of Sedimentary Petrology; (United States), Journal Name: Journal of Sedimentary Petrology; (United States) Vol. 63:2; ISSN 0022-4472; ISSN JSEPAK
- Country of Publication:
- United States
- Language:
- English
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