Origin of Park City (Phosphoria) cycles in Bighorn basin
The Franson and Ervay cycles of the Permian Park City Formation in the Bighorn basin developed in response to both eustatic fluctuations and the changing climatic regimes associated with these fluctuations. The basal phosphatic shales (Meade Park and Retort members) and cherty siltstones (Rex and Tosi cherts) in these cycles were deposited during major transgressive events under the influence of cold, upwelling, deep oceanic currents and semitropical/tropical climatic conditions. The overlying carbonate units (Franson and Ervay Members) were deposited during sea level stabilization and regional marine regressions in warm marine waters and under hot, arid climatic conditions. During these periods of carbonate deposition, shallow marine ramp systems developed. Widespread, low-energy, restricted-marine environments extends across most of the Bighorn basin, except to the southwest, where normal marine environments existed, and along the east flank of the basin, where peritidal carbonates and lagoonal/salina red beds and evaporites developed. The smaller clastic/carbonate cycles that comprise the Franson and Ervay members developed during minor sea level changes and as a result of shifts in the major water currents in the basin and the normal short-term processes involved in shoal development and destruction. The imprint of the varying climatic conditions on these sequences is manifest in the vertical decrease in clastic content and gradation from more normal marine to restricted marine carbonate facies upward through all cycles, the development of tepee structures and then dissolution features in peritidal deposits, and the precipitation of evaporites in the lagoonal sequences.
- Research Organization:
- Lithologic and Stratigraphic Solutions, Inc., Denver, CO
- OSTI ID:
- 7230344
- Report Number(s):
- CONF-8609129-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 70:8; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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