The mid-Cretaceous (Albian-Cenomanian) boundary in the central United States traditionally is placed at a major unconformity that records a withdrawal of marine waters from the Western Interior Seaway. Although this unconformity can be located with reliability in many areas of western North America and the Gulf Coast, its placement along the eastern margin of the interior seaway is more problematical. Largely as a matter of convenience, unconstrained by biostratigraphic data, the base of Cenomanian strata has been placed at the base of the sandstones of the Dakota Formation in its type area of eastern Nebraska and western Iowa, where they overlie Paleozoic and Precambrian rocks. Palynological evidence from Dakota sections in the type area now suggests that the mid-Cretaceous unconformity may instead be traceable to a horizon within the formation, separating the upper Woodbury Member from the lower Nishnabotna Member. If this interpretation proves to be correct, the Nishnabotna is chronostratigraphically and depositionally equivalent to Albian units such as the Newcastle and Muddy Sandstones of Wyoming and the subsurface “J” Sandstone of the Denver Basin. Given the historical development of the use of the term “Dakota,” this suggested interpretation also calls into question the advisability of continuing to include the Nishnabotna Member within the Dakota Formation.

The historic type area of the Dakota Formation lies along the Missouri and Big Sioux River Valleys in northeast Nebraska and northwest Iowa, in the eastern margin area of the Western Interior Province. The type Dakota sequence is characterized to provide a basis of comparison with supposed “Dakota” sections elsewhere in the Western Interior. The general sequence includes (1) a lower sandstone-dominated Nishnabotna Member with coarse-grained and conglomeratic facies, and (2) an upper mudstone-dominated Woodbury Member with sandstone channel bodies and lignites. The depositional sequence is interpreted to record, in ascending order: (1) aggradation of coarse-grained braided and proximal meanderbelt fluvial systems; (2) an episode of lowered base levels, channel incision, and widespread pedogenic alteration; (3) aggradation of channels and flood-basin sediments in meander-belt fluvial systems; and (4) upward transition into deltaic and marginal-marine facies. The Woodbury Member is of Cenomanian age, and is interpreted to have aggraded in response to sea-level rise in the adjacent seaway during transgressive phases of the Greenhorn Cyclothem, with progressive eastward displacement of nonmarine by marine facies. The age of the lower Dakota sequence is known with less certainty, but is probably upper Albian in part. Aggradation of lower Nishnabotna fluvial systems may be related to sea-level rise during transgression of the Kiowa–Skull Creek Cyclothem, although the possibility that the entire Dakota sequence is post-Kiowa cannot be completely discounted. Based on the type sequence, usage of the term Dakota Formation should be restricted to include only eastern-derived detrital sequences and should exclude marginal-marine or marine facies of the Kiowa–Skull Creek Cyclothem. Usage of the term “Dakota” for western-derived sedimentary sequences in the Rocky Mountain area is discouraged.

Abstract The Kaiparowits Basin, located mostly within Grand Staircase–Escalante National Monument, preserves an outstanding record of Late Cretaceous sedimentation in a foreland basin setting. Hosted in these rocks is one of the most continuous and complete records of this period’s ecosystems known from any one geographic area in the world. Recent work in the basin has emphasized macrovertebrate remains and documented many new sites of high scientific value. Recent stratigraphic studies have further refined our knowledge of the depositional systems and chronostratigraphic relationships. Provided is an overview of some of these recent advances, along with the necessary background to provide context .

ABSTRACT Strata preserved within the Sevier foreland basin of North America contain a suite of lithologic variations influenced by hinterland tectonic processes. Using U-Pb detrital zircon geochronology, we compared provenance signals of Upper Jurassic and Lower Cretaceous strata from a west-to-east, foredeep-to-forebulge-to-backbulge depozone transect across the state of Wyoming and evaluated major tectonic mechanisms operating during the early evolution of the Sevier orogeny. Our data included new and compiled U-Pb detrital zircon ages ( n = 6013) from 50 localities that were integrated into a revised chronostratigraphic framework and subsidence history for the basin. At the onset of the Sevier orogeny, we found evidence for uplift and erosion of early Mesozoic and late Paleozoic strata within the nascent Sevier fold-and-thrust belt. This event occurred prior to the Aptian Stage of the Early Cretaceous and is recorded by the coordinated progradation of coarse-grained fluvial systems across the overfilled foreland basin. Continued emplacement of thrust loads in the hinterland generated accommodation in excess of sediment supply, a condition likely exacerbated by a relative reduction of siliciclastic sediment supply due to greater unroofing of Paleozoic carbonates during the Aptian and Albian Stages of the Early Cretaceous. This led to an underfilled condition characterized by widespread calcareous lacustrine deposition across much of the foredeep depozone and condensed stratigraphic intervals in the forebulge and backbulge depozones. During the late Albian–earliest Cenomanian, fluvial systems sourced in the Appalachians invaded the foreland basin from the east, followed by the rapid incursion of the Western Interior Seaway, driven by accelerated thrust emplacement, flexural subsidence, and potentially the onset of dynamic subsidence.