Print this pageAbstract: Teapot Delta of Western Powder River Basin, Wyoming
Well logs and adjacent outcrops allow the reconstruction of the Teapot delta which filled part of the western margin of the western Interior Seaway during Late Cretaceous time.
1. Initial infill of the sea floor was by deposition of prodelta wedges that slope seaward. Time lines dip east (seaward), as younger prodelta wedges were deposited on the outer edges of the delta. Three hundred ft (91 m) of these rocks (compacted) were deposited and raised the depositional surface of the sea floor to near wave base. 2. About 70 ft (21 m) of delta-front sandstones then were deposited on the platform of prodelta deposits in higher energy marine settings.
3. The last stage of delta formation was the most complex and included at least three major depositional settings. (a) The type Teapot sandstone represents delta plain deposits and is composed of highly variable channel sandstones which are slumped, irregularly cross-bedded, and highly carbonaceous. Root zones, lignites, thin coals, and a wide variety of other rock types were deposited on the delta plain. (b) Seaward from the delta plain, a belt of marine bars is present above the delta-front sandstones. These irregular bars are as much as 85 ft (26 m) thick, homogeneous, irregular in outline, and have abrupt edges. Ophiomorpha and other marine burrows are present. These marine bars would be exceptional traps for oil and gas in the deep basin. (c) Seaward from the marine bars, Teapot andstones, as at Kaye and Well Draw oil fields, are slope deposits because the sandstones in cross section slope eastward (seaward) just as other prodelta deposits slope. Time lines in the slope sandstones dip eastward (seaward) as younger deposits were added to the east side of the depositional slope by a strong western sediment source (the Teapot delta).
AAPG Search and Discovery Article #90971©1976 AAPG-SEPM Rocky Mountain Sections 25th Annual Meeting, Billings, Montana