Stratigraphy, sedimentology, sandstone body architecture, and ichnology of the Ferris and Hanna formations, Hanna Basin area, southern Wyoming

The Ferris (latest Maastrichtian-Danian: 66-63 Ma) and Hanna (Danian-early Thanetian: 62-55 Ma) formations in southern Wyoming's Hanna and Carbon basins have traditionally been considered entirely continental deposits. The presence of newly recognized tidal and marine (or brackish-water), indicators in multistoried sandstone bodies of both formations strongly suggests that previous reconstructions of the region's paleogeography are in error. Rather than migrating hundreds or thousands of kilometers to the east and south, the Western Interior Sea remained in the vicinity of southeastern or south-central Wyoming during the latest Cretaceous (68-65 Ma) and Paleocene (62-58 Ma).; Short-term changes (10s–100s of k.y.) in local base level (sea level) were probably caused by tectonic activity associated with Laramide adjustment of the Hanna Basin block in relation to Simpson Ridge Anticline, the Granite Mountains, and the Medicine Bow/Sierra Madre uplift. Since the Hanna Basin behaved as a rigid block, with the Rawlins Uplift representing its hanging wall, patterns of fluvial sedimentation are different than those proposed for flexural basins. Uplift of the western Hanna Basin resulted simultaneous fluvial incision and base level fall in the west, while transgression and base level rise characterized the east. Paleovalleys filled with mixed fluvial and estuarine channel belts preserve low-diversity marine ichnofaunas and selachian (shark and ray) paleofaunas.; The orectolobiforms (carpet and zebra sharks) Cretorectolobus and Cederstroemia occur in the lower Ferris Formation, representing the first reported Maastrichtian occurrence of each. A new species of dasyatid (stingray) occurs in estuarine deposits of the middle Ferris Formation (∼64.5 Ma).; By the middle-late Paleocene, tectonic separation of the Hanna Basin from the sea (caused by uplift of Simpson Ridge) resulted in sediment starvation and lacustrine deposition. A previous episode of tectonic uplift of Simpson Ridge resulted in early Paleocene (64-63 Ma) reversal of the overall easterly drainage through the basin, and lacustrine flooding. Basal Hanna Formation (62-58 Ma) paleovalleys can be traced from the central Hanna Basin into the eastern Carbon Basin, where tidal facies and marine fossils are more abundantly preserved. In the northeastern Hanna Basin, ∼1,500 m of alluvial deposits (preserving abundant crayfish burrows) accumulated as the Freezeout Hills uplifted during the middle Paleocene (62-59 Ma).