Browsing by Subject "Maastrichtian"
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Item Dynamic stratigraphy and sediment partitioning of high-supply fluvial succession in Maastrichtian source-to-sink system(2013-05) Ned, Allison Marie; Steel, R. J.; Olariu, CornelThe sediment budget and paleogeography was reconstructed for the Maastrichtian fluvial to coastal plain Lance Formation (>200m thick) that developed coevally with the shoreline/shelf Fox Hills Sandstone (>200m thick) and deep-water Lewis Shale (>750m thick) in a complete source-to-sink system in the Washakie and Great Divide Basins of south central Wyoming. The system initiated during the final Western Interior Seaway (WIS) transgression and the onset of the Laramide Orogeny rapid subsidence (>2km in 1.9 My) that largely outpaced sediment flux into the basin so the system became and remained a deep-water (>500m water depth) basin beyond the Lance-Fox Hills shelf prism. The active tectonic setting and rapid subsidence caused the Lance fluvial and coastal plain deposits to aggrade and accumulate behind the generally rising shoreline trajectory of the Fox Hills Sandstone. The depositional succession is subdivided into 15 clinothem units and the Lance Formation is best exposed in outcrops in clinoforms 10, 11, and 12. Subsurface analysis correlates key stratigraphic surfaces across the basin to define the sediment budget and clinoform architecture. Field analysis along clinoform 12 on the east side of the basin details facies and paleohydraulic dimensions. Sediment partitioning shows the regressive and transgressive systems tracts (RST and TST) form complementary wedges such that the RST thickens basinward and the TST thins basinward, reflecting the preferential storage of sediment. Channels measured in the field and subsurface datasets are similar in thickness (2m-16m) and suggest braided channel morphology with channel belts from 6.2-8.4km. N/NE paleocurrent trends departing from the subsurface dataset and previous studies of the system provide evidence of possible tidal influences in a developed shoreline embayment or an east to west supply from the basement-cored Rawlins and Sierra Madre Uplifts in the east. The fluvial Lance Formation paleogeography associated with the RST and TST is primarily driven both by modest, Late Cretaceous relative sea level changes and sediment supply linked to the tectonic setting and climate.Item Letter to Cesare Emiliani from H.B. Stenzel on 1951-11-03(1951-11-03) Stenzel, Henryk B.Item Letter to Ehrhard Voigt from H.B. Stenzel on 1961-10-10(1961-10-10) Stenzel, Henryk B.Item Letter to Erle G. Kauffman from H.B. Stenzel on 1970-03-13(1970-03-13) Stenzel, H.B.Item Letter to G.T. James from H.B. Stenzel on 1962-10-11(1962-10-11) Stenzel, H.B.Item Letter to H.B. Stenzel from Bill Berggren on 1958-07-11(1958-07-11) Berggren, William A.Item Letter to H.B. Stenzel from M.J. Meijer on 1963-05-08(1963-05-08) Meijer, M.J.Item Letter to H.B. Stenzel from William A. Berggren on 1961-02-04(1961-02-04) Berggren, William A.Item Letter to H.B. Stenzel from William A. Berggren on 1961-03-06(1961-03-06) Berggren, William A.Item Letter to H.B. Stenzel from William A. Berggren on 1962-07-06(1962-07-06) Berggren, William A.Item Letter to Jorgen Wind from H.B. Stenzel on 1950-02-16(1950-02-16) Stenzel, Henryk B.Item Letter to Lloyd W. Stephenson from H.B. Stenzel on 1935-09-18(1935-09-18) Stenzel, Henryk B.Item Taxonomic revision of latest Cretaceous North american basal neonithischian taxa and a phylogenetic analysis of basal ornithischian relationships(2012-05) Boyd, Clint Aaroen; Clarke, Julia A.The systematic relationships of basal ornithischian dinosaurs remain contentious, especially the position of basal neornithischians (i.e., ‘hypsilophodontids’). Prior analyses of basal ornithischian relationships have been hampered by the fact that the hypodigm material of many basal neornithischian taxa is fragmentary, denying access to character data crucial to resolving their relationships. The recent discovery of several new basal neornithischian taxa and the referral of more complete specimens to known taxa provide important new data pertinent to resolving these relationships. The results of this study supplement those recent advances by improving our understanding of the anatomy and systematic relationships of basal neornithischian taxa from the Late Cretaceous of North America. These new insights are accomplished through a taxonomic revision of the Maastrichtian taxa Bugenasaura and Thescelosaurus, a detailed anatomical description of the cranial anatomy of Thescelosaurus neglectus based on the referral of a specimen that includes a nearly complete skull (NCSM 15728), and description of a new basal neornithischian taxon from the Kaiparowits Formation (Campanian) of Utah. All of these new data are compiled into a dataset composed of 255 characters for 65 terminal taxa (all species exemplars) focused on assessing basal ornithischian relationships. The recovered strict consensus topology is the most highly resolved, stratigraphically congruent phylogenetic hypothesis of basal ornithischian relationships yet proposed. This analysis places all basal neornithischians except Hypsilophodon foxii outside of Cerapoda, substantially reducing the taxonomic contents of Ornithopoda. A new clade containing fourteen basal neornithischian taxa is recovered as the sister taxon to Cerapoda and includes all North American basal neornithischians from the Cretaceous. The historical biogeography of Ornithischia is also reconstructed using a method that incorporates time calibrated branch lengths that represent the implied missing fossil record of each taxon. The results of this analysis support two dispersals of neornithischian taxa into South America during the Cretaceous: one consisting of basal iguanodontians dispersing from Australia (possibly via Antarctica) and a second consisting of basal neornithischians dispersing from Asia through North America.