Cycle symmetry and its causes, Cisco Group (Virgilian and Wolfcampian), Texas
- Univ. of Texas, Austin, TX (United States). Dept. of Geological Sciences
181 transgressive-regressive cycles composed of nonmarine and marine carbonate and siliciclastic rocks of the Cisco Group on the Eastern Shelf, Texas, display complex characteristics at both hemicycle and full-cycle scales. They are delineated on the basis of successive changes of depositional environments, stratal boundary relations, and stratigraphic position. Transgressive and regressive stratigraphic environment gradients are defined as the magnitude of environmental shift divided by thickness for each hemicycle. They indicate the rates of lateral environmental shifts during transgression and regression. Cycle symmetry index is defined as the ratio between transgressive and regressive stratigraphic environment gradients. It provides a measure of stratigraphic response to controlling processes. Five Cisco cycle types defined by the type of component lithofacies display the stratigraphic response mainly to noncyclic allogenic and autogenic processes. The cycle types have varying magnitude, thickness, and symmetry. They also vary in lateral extent and in abundance. A process-response model of cyclic sedimentation of the Cisco Group on the Eastern Shelf is established. It emphasizes the interplay between autogenic and allogenic processes at the sub-cycle scale. Understanding interactions among glacio-eustasy, climate, shelf subsidence, sediment supply, and depositional dynamics during various stages of transgression and regression is central to a clearer comprehension of the observed variations in cycle characteristics.
- Sponsoring Organization:
- Texas Univ., Austin, TX (United States); Geological Society of America, Boulder, CO (United States)
- OSTI ID:
- 428188
- Journal Information:
- Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes, Vol. 66, Issue 6; Other Information: PBD: Nov 1996
- Country of Publication:
- United States
- Language:
- English
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