Late Laramide tectonic fragmentation of the eastern greater Green River Basin, Wyoming

Abstract

Frontispiece. Aerial photograph with view to the northeast, emphasizing an asymmetric anticline (Beer Mug Anticline; cored by Pennsylvanian Tensleep Ss. and flanked by Permian Goose Egg Fm.) thrust atop a less obvious, synformal anticline (Ellis Ranch Anticline of Taylor, 1996; cored by Triassic Red Peak Fm. and stratigraphically overlain by the white, more clearly defined, Triassic Alcova Ls.). The steeply north-dipping thrust fault between the anticlines (Indian Spring Fault) is exposed only near the photo's lower-left corner, and it strikes northeastward from there, hidden by the slopes of erosional debris. The camera is above the northern edge of the eastern Hanna Basin, and the general view is across southern parts of the adjacent Freezeout Hills. This image was selected for use as the Frontispiece jointly because of its clarity and for being emblematic of the extraordinary degree of Laramide structural complexity characteristic of the Hanna Basin area-and particularly so along the basin's northern and southern margins. For structural details,

A new stratigraphic framework and constraints for the position of the Paleocene–Eocene boundary in the rapidly subsiding Hanna Basin, Wyoming

“…Main retreat of the Western Interior Seaway from this area in the late Maastrichtian is marked by the beach and shore-face deposits of the Fox Hills Sandstone. Leaf margin analysis and several marine incursions documented in the Upper Cretaceous Medicine Bow and Upper Cretaceous-Paleocene Ferris deposits suggest that the Hanna Basin remained at or near sea level until at least the early or middle Eocene (Dunn, 2003;Wroblewski, 2003Wroblewski, , 2004Boyd and Lillegraven, 2011;Cather et al, 2012;Lillegraven, 2015). Deposits progressively change from marginal marine and coastal plain to increasingly fluvial, paludal, and shallow lacustrine (Fig.…”

“…Initially, the Hanna Basin was part of the Greater Green River Basin, later isolated into smaller subbasins by localized uplifts of the Laramide orogeny during the mid to late Paleocene ( Fig. 1; Ryan, 1977;Blackstone, 1993;Perry and Flores, 1997;Secord;Kraatz, 2002;Wroblewski, 2003;Lillegraven, 2015;Smith et al, 2015b;Loope and Secord, 2017). The emergence of these uplifts influenced provenance and sedimentation patterns indicating predominantly local sources after this time (LeFebre, 1988;Blackstone 1993;Perry and Flores, 1997;Lillegraven et al, 2004;Peyton and Carrapa, 2013).…”

Interactions of A Paleocene River, A Rising Fold, and Early-Diagenetic Concretions

“…The Hanna and Carbon basins, relatively small structural basins located in southeastern Wyoming, were tectonically active from Late Cretaceous to middle Eocene time (Blackstone 1983(Blackstone , 1993Merewether 1983;Love 1970;Lillegraven et al 2004;Lillegraven 2015). Before widespread deformation in the Paleocene and middle Eocene, these basins were part of a much larger depositional basin including the Greater Green River Basin to the west and the Laramie basin to the east (Lillegraven et al 2004;Lillegraven 2015). The Hanna and Carbon basins are now separated by the Simpson Ridge anticline, a west-vergent structure that plunges NNE and is exposed at the surface for about 25 km (Fig.…”

“…2), as much as 7 km of Upper Cretaceous to lower Eocene strata are present in the Ferris and Hanna formations. These rocks accumulated in the span of about 10 Myr (Lillegraven 2015) and are dominated by sandstones, siltstones, and shales, but also contain numerous lignites and coals. All previous authors have attributed the great thickness of the Ferris and Hanna formations to syndepositional tectonism, but there is considerable disagreement concerning the relationship between surface drainages and active structures (Ryan 1977;Lillegraven and Ostresch 1988;Wroblewski 2006;Lillegraven et al 2004).…”

“…Ferris strata accumulated near the western margin of the Cannonball Sea (Wroblewski 2006;Boyd and Lillegraven 2011), but fluvial strata and hiatuses in the Hanna Formation may record the sinuous pathway of the Paleogene ''California River'' (Davis et al 2010) through Wyoming's Laramide uplifts on its way to the western Gulf of Mexico (Blum and Plecha 2014;Sharman et al 2017). Lillegraven (2015) provided highly detailed geologic maps, cross sections, and voluminous field notes on the structure and stratigraphy of the eastern portion of the Greater Hanna basin, including most of the Carbon basin (Fig. 2) that have aided this study.…”