An examination of freshwater euselachian fossils from the Maastrichtian lower and upper Hell Creek Formation, and the Bug Creek Anthills (Cretaceous-Paleogene boundary), and the early Paleocene (Puercan) Tullock Member of the Fort Union Formation of Montana, USA, revealed seven taxa: Lonchidion selachos , Protoginglymostoma estesi , Chiloscyllium , Restesia americana , Ischyrhiza avonicola , Myledaphus pustulosus n. sp., and Dasyatis (Dasyatidae). Squatirhina americana is redescribed to the new genus Restesia based on unique crown morphology. Dasyatis is only reported from the Paleocene. This is in contrast to the other collected taxa, which are only known from the Cretaceous. Ischyrhiza is not reported in our samples from the Hell Creek Formation despite earlier erroneous claims; however, the taxon is present in a sample from the Bug Creek Anthills. We suggest that this taxon infrequently moved into the freshwater rivers to forage. Lonchidion selachos occurs only in the upper Hell Creek Formation, and we hypothesize that the upper Hell Creek localities were deposited during a warm interval, as the paleodistribution of L. selachos shifted significantly to the north during warmer periods in the Santonian and Campanian. Of the taxa found in the Hell Creek Formation and the Bug Creek Anthills, only Myledaphus is found in Paleogene deposits; however, specimens are extremely rare. The occurrence of Myledaphus in the Paleogene is suggested to be due to the occurrence of reworked material.

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 Microfossils from Cretaceous coal-bearing strata can be used to establish key stratigraphic surfaces that mark marine flooding events with intermediate-frequency (fourth-order) and high-frequency (fifth-order) periodicities. We document several examples of this cyclicity from the transgressive and regressive facies at the land–sea transition of the Greenhorn Marine Cycle on the Colorado Plateau. Estuarine strata from the upper Cenomanian Dakota and middle Turonian Straight Cliffs Formations yield four primary fossil assemblages: Assemblage A, the lagoonal assemblage, comprising a rich agglutinated foraminiferal population of Trochammina and Verneuilinoides and brackish ostracodes and molluscs in a skeletal shell accumulation; Assemblage B, the proximal estuarine assemblage, comprising the brackish ostracode Fossocytheridea , charophytes, and smooth admetopsid gastropods within bituminous coal zones giving rise to distal estuary with the addition of brackish gastropods and sparse agglutinated foraminifera in sandy marlstones; Assemblage C, the open-bay (distal estuarine) assemblage, comprising the ostracodes Fossocytheridea posterovata , Cytheromorpha , Looneyella , and Cytheropteron , the foraminifera Trochammina and Ammobaculites , and ornate brackish molluscs in calcareous shelly mudstones; and Assemblage D, the marsh, comprising an exclusive population of the foraminifera Trochammina , Miliammina , and Ammobaculites in rooted lignites. Intermediate flooding surfaces are marked by normal marine taxa that are superimposed on the background of a primary marginal marine assemblage. In general, intermediate flooding events approximate lithologic and biostratigraphic boundaries and record basin-wide paleoenvironmen-tal changes with the advancing Greenhorn Sea. We correlate coal zones from the coast to maxima in calcium carbonate and planktic foraminifera in the offshore. The intermediate cycles approximate ammonite biostratigraphic zones and therefore maintain periodicities within the 100–400 kyr bandwidth. The onshore–offshore correlations suggest that a regional and perhaps global sea-level mechanism controlled the stratigraphic position of the coal zones. Superimposed on the intermediate cycles are higher-frequency cycles that represent short-lived flooding events. As many as six high-frequency cycles constitute an intermediate cycle, and therefore periodicities fall within an approximate 10–25 kyr range. The general asymmetry of the packages suggests that a combination of oceanographic, climatic, and autogenic processes influenced the high-frequency stratal architecture. Overall, the primary mechanism controlling the stratigraphic position of the coals was tectono-eustasy. Compactional processes and/or climate modulations contributed to the observed internal coal-zone cyclicity that we interpret as a secondary coal-forming process.

Full article available in PDF version.

Abstract The Bridge Creek Limestone Member of the Greenhorn Formation records maximum eustatic rise of the Greenhorn Marine Cycle, and the maximum aerial extent reached by the Western Interior Seaway. Limestone-shale couplets reflecting Milankovitch-style climatic cycles, and abundant laterally persistent bentonites, within a highly refined biostratigraphic framework based primarily on rapidly evolving cosmopolitan molluscan taxa, allows the development of a very detailed system of event-isochron stratigraphy divided into intervals of 100,000 yr or less. The Bridge Creek Limestone Member can be divided into three informal subdivisions (lower, middle, and upper) based on overall lithologic characteristics and slope forming profile. These precisely correlate to the upper Hartland, Jetmore, and Pfeifer members in central Kansas and reflect changes in marine environments and sedimentation style corresponding to the periods just prior to, during, and after maximum transgression respectively. The development and preservation of cyclic sedimentation during deposition of the Bridge Creek Member is largely the result of slow rock accumulation rates of 0.5 to 1.0 cm/1000 years across the central Western Interior. The combination of widespread deposition, numerous chronostratigraphic marker-beds, and a highly refined regional and global biostratigraphy make the Bridge Creek Limestone Member a magnificent natural laboratory for detailed ecologic, evolutionary, biogeographic, and oceanographic studies.

Abstract The Pueblo-Canon City area provides an outstanding opportunity to study well exposed sections of the marine and marginal marine stratigraphie units which make up the Kiowa-Skull Creek (Late Albian), Greenhorn (latest Albian-Middle Turonian), and Niobrara (Late Turonian -Early Campanian) Cyclothems. Each of these cyclothems represents a third-order eustatic fluctuation that produced regionally synchronous transgression and regression in the Western Interior Seaway. Extensively studied exposures along the Canon City hogback and in the dissected Rock Canyon Anticline west of Pueblo are easily accessible and contain the most typical examples of the stratigraphie units in these cyclothems found in Colorado. Numerous, detailed and interdisciplinary studies of this Cretaceous section have been completed (see papers in this volume and references therein) which collectively allow the dynamics of large-scale Cretaceous eustatic cycles to be interpreted and modeled for epicontinental seas. In view of these factors, the Pueblo-Canon City area has become the standard mid-basin reference section for the Kiowa-Skull Creek, Greenhorn, and Niobrara Marine Cycles. The field trip will examine outcrops of each stratigraphie unit in the Kiowa-Skull Creek, Greenhorn, and Niobrara Cyclothems in the Pueblo-Canon City area. Field examination will focus on high-resolution stratigraphie concepts, facies characteristics, geochemical profiles, and inferred depositional environments. Discussions will emphasize a broad range of possible interpretations and current controversies regarding the depositional history of these cyclothems. The prevailing theme of this excursion will be cyclic sedimentation as expressed in Cretaceous marine and marginal marine facies of the Western Interior Seaway. Detailed discussion of each outcrop section can