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FREWENS SANDSTONE, WYOMING, U.S.A.

The Upper Cretaceous Frewens is the basal member of the Frontier Formation on the western margin of the Powder River Basin. The Frontier Formation is an Upper Cretaceous (Cenomanian to Turonian) clastic wedge that prograded eastward from the Sevier mountain belt into the adjacent foreland basin. Units of the Frontier record the progradation of lowstand shorelines across the low-gradient floor of the Cretaceous Interior Seaway and subsequent transgressions. The Frewens Castle sandstone is composed of two elongate tidal sandstone bodies that are positioned directly above and slightly landward of a broader, more wave-influenced delta lobe. The bodies are at least 10 km long and 2-3 km wide, and overlap along a southeasterly trend. They fill an embayment confined to the south by the more lobate, wave-influenced Willow Sandstone and by a subtle structural uplift to the north. The Frewens sandstone is more tide-influenced and heterolithic than the other Frontier sandstones.  It iis interpreted as sand ridges deposited on the shoreface of a tide-influenced delta.  Accumulation rates in the Frewens were approximately 107m/my.

REFERENCES

Bhattacharya, J.P., and Willis, B.J., in review, Allostratigraphy of Cretaceous wave- and Tide-Influenced Lowstand deltas, Frontier Formation, Wyoming, USA: AAPG Bulletin 

Willis, B.J., Bhattacharya, J.P., White, C.D., Dutton, S.P., and Gabel, S.L. 1996, Lowstand deltas in the Late Cretaceious Frontier Formation of Central Wyoming: University of Texas at Austin, Bureau of Economic Geology, Deltas Industrial Associates field trip guidebook, 84 p.

Dutton, S.P., Wills, B.J., White, C.D., and Bhattacharya, J.P., in press, Outcrop characterization of reservoir quality and interwell-scale cement distribution in a tide -influenced delta, Frontier Formation, Wyoming, USA: Clay Minerals.

Willis, B.J., Bhattacharya, J.P., Gabel, S.L., and White, C.D., 1999, Architecture of a tide-influenced river delta in the Frontier Formation of central Wyoming, USA: Sedimentology, v. 46, p. 667-688. 

Bhattacharya, J.P., and Willis, B.J., 1996, Tide-Influenced Deltas in the Late Cretaceous (Cenomanian) Frewens Castle Sandstone, Belle Fourche Member, Frontier Fromation, Wyoming: The Universtiy of Texas, Bureau of Economic Geology, Deltas Industrial Associates Field Trip Guidebook

For more information contact Shirley Dutton.