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Studies of the provenances, facies, and subsidence histories of Upper Cretaceous and lower Tertiary strata in conjunction with flexural modeling document the tectonic origin and sedimentary evolution of the northern Green River basin in western Wyoming. The area evolved from being part of the Sevier foreland into a nonmarine intermontane basin with the uplift of the Wind River and Gros Ventre Ranges during late Cretaceous time, and by early Tertiary time, subsidence and sedimentation related to these uplifts dominated the northern Green River basin. Sandstone compositions and paleocurrent data indicate an abrupt change in provenance at the beginning of Paleocene time, marking the progressive uplift and erosion of the Wind River and Gros Ventre highlands. Sandstones changed from dominantly sedimentary lithic compositions to dominantly feldspathic compositions when the crystalline core of the Wind River Range was breached. Similarly, paleocurrent trends changed from southeasterly flow directions southward and southwestward, as both the Gros Ventre and Wind River uplifts flooded the basin with detritus. The alluvial sandstone architecture of Upper Cretaceous and lower Tertiary rocks was analyzed in order to document the interaction of allocyclic controls and depositional facies as related to the subsidence history of the basin. This approach proved to be successful only where complicating factors, such as climate and source lithology, could be adequately constrained. Analyses of facies within the lenticular sandstone and shale sequence (Campanian) and the Hoback Formation (Paleocene) suggest deposition during rapid subsidence. The alluvial architecture of Eocene strata (Pass Peak and Wasatch formations) of the Hoback area cannot be easily interpreted in terms of subsidence. Rapid subsidence is indicated for the LaBarge Member of the Wasatch Formation in the Big Piney-LaBarge area. Subsidence analysis for the Hoback, Pinedale anticline, and LaBarge areas documents the patterns and timing of tectonically induced subsidence. A subsidence event occurring at approximately 120 to 115 Ma was probably related to thrusting in the Idaho-Wyoming thrust belt. Another subsidence event at approximately 90 Ma may indicate initial uplift of the Wind River block. The very rapid subsidence event in the Pinedale anticline area during Maastrichtian time is not evident in subsidence curves from the Hoback and LaBarge areas, and thus is probably a manifestation of loading by the Wind River thrust. Rapid subsidence during Paleocene time in the Hoback area is attributed to loading from the Darby thrust and Gros Ventre uplift. Two-dimensional profiling of the northern Green River Basin shows that the basin can be effectively modeled as a flexural depression resulting from extrabasinal and intrabasinal loading on an elastic lithosphere. Two distinct models were used to confirm regional compensation and the flexural response to loading of the lithosphère. Modern basin geometry analysis tested for regional compensation by comparing modeled deflections with observed basin geometry for a given load configuration. Sediment thickness profiling was used to determine the maximum thickness of sedimentary rocks that could have accumulated in the tectonic depression resulting from Darby, Prospect, and Wind River thrusting (assuming instantaneous uplift and adequate sediment supply). Both models are consistent with the concept of basin-margin tectonic loading as the main cause of subsidence in the Green River basin.

Abstract Geologic features along the Hoback River Canyon in central western Wyoming illustrate tectonic effects and stratigraphic and structural evidence for dating thrusts and later listric normal faults in part of the Idaho-Wyoming Thrust Belt and adjacent Foreland. Figure 1 and Table 1 combine to show that major thrusts in the Thrust Belt young in thedirection of tectonic transport, in this case from west to east, the oldest being the Paris Thrust and the youngest the Prospect. The preeminent features, logged below and visible from the highway (Fig. 2) are, west to east, the Hoback Fault (listric normal), Bear Thrust, Prospect (=Cliff Creek=Jackson) Thrust and Game Hill Thrust. These are capitalized on Table 1. The site description begins on the west at Hoback Junction, 13 mi (21 Km) south of Jackson, Wyoming, on U.S. 187-189. It follows U.S. 187-189 east from there for 16 mi (26 km) with four stops enroute (Fig. 2). It crosses from south-central Teton County into northwestern Sublette County within U.S. Geological Survey Camp Davis and Bull Creek 7½-minute tomographic and geologic map quadrangles. Small-scale colored geologic map and cross-section sheets, which include the site, are in the pocket at the back of Dorr and others, 1977. A detailed road log of this area is given by Spearing and Steidtmann (1977).

Abstract Very large scale, trough cross-stratification in sandstone units of the Casper Formation is well exposed along Sand Creek in the southernmost Laramie Basin, Wyoming (Fig. 1). The exposures of features described herein are located in the SW¼, Sec.31, T.13N., R.74W. and the E½, Sec.l, T.12N., R.75W.(Fig. 1). This locality is included in a field trip guide by Steidtmann and Weimer (1976); photographs of the features mentioned herein are in Steidtmann (1974, 1976).

Abstract Depositional style of the middle Eocene Bridger Formation on the south flank of the Wind River Range, Wyoming, changed in response to volcanism to the north in the Absaroka volcanic field. Lower Bridger sediments were deposited in a fluvio-deltaic environment during the waning stage of Lake Gosiute. Channel lag sediments, trough crossbedding and well developed epsilon crossbed-ding indicate a high sinuosity (meandering) stream pattern. In contrast, upper Bridger sandy channels are simple to multistory ribbons composed dominantly of trough cross-strata. Tuffs and tuffaceous siltstones form channel fills and overbank deposits and constitute a major portion of the unit. Upper Bridger deposition occurred under a variety of sediment/water ratios, from debris flow to normal turbulent stream flow. Gravels in the upper Bridger contain well rounded clasts that were derived from the Absaroka volcanic field. Paleocurrents indicate that these volcanic epiclasts were transported across the Wind River Range through a low divide into the basin. This low divide in the range served as a node for avulsion, and rapid deposition caused formation of short-lived channels. Syndepositional movement along the Continental fault zone in the study area provided intrabasinal control on upper Bridger deposition. On adjacent fault blocks, the South Pass Formation overlies upper Bridger strata and disconformably overlies lower Bridger strata. The disconformity omits 80 m of upper Bridger section. In the upper Bridger on the downthrown block there is a coarse clastic wedge that may have been reworked off the adjacent uplift. Paleocurrents deflect around the upthrown block, suggesting the faulting was contemporaneous with upper Bridger deposition.

Abstract Facies analysis of the Lenticular Sandstone and Shale Sequence in the northern Green River basin, Wyoming provides the basis for testing the concept that subsidence controls fluvialsandstone architecture. This sequence consists of three genetic facies including (1) low sinuosity fluvial channel sandstones of both ribbon and multistory geometries, (2) levee and splay complexes, and (3) interfluve swamp, bog, and lake deposits. The fluvial channels are thick (>5 m), lenticular bodies consisting of fine to mediumgrained sandstone with basal scour lags. The absence of point bar lateral accretion surfaces and the low variance of paleocurrent directions suggest low sinuosity. Ubiquitous levee and splay sandstones are thin (0.5 m) and contain smallscale trough crossbedding and microtrough crosslamination. The interfluve rocks consist of dark gray mudstone, carbonaceous shale, thin coal beds, and thin, nonmarine micritic limestone. We interpret these deposits to be the products of a fixedchannel fluvial system that developed in a rapidly subsiding foreland basin. High subsidence rates are indicated by the large proportion of overbank mudstone, ribbon to multistory channel geometries and lack of paleosol horizons. Subsidence analysis (backstripping) also shows that basin subsidence was rapid during the Campanian and therefore that the architecture of the Lenticular Sandstone and Shale Sequence may have been tectonically controlled. We attribute this subsidence to regional flexure induced by tectonic loading during major thrust emplacement to the west.