The project consists of a detailed, regional chronostratigraphic, sedimentologic, and sequence stratigraphic analysis of nonmarine rocks in the Upper Jurassic - Lower Cretaceous Morrison, Cloverly, and Kootenai Formations and the equivalent strata of the Gannett Group. In order to integrate sequence stratigraphic analysis with the marine record of the foreland basin, the study will include bounding marine rocks in the Sundance (Jurassic) and Thermopolis (Cretaceous) Formations. Areas of data collection include the Powder River basin and Black HIlls, the Idaho-Wyoming thrust belt, and the area surrounding Great Falls in west-central Montana. Detailed facies analysis, point counts of petrographic thin sections and conglomerate clast counts, outcrop mapping of fluvial channel complexes, subsurface-to-surface correlations of geophysical well logs, detailed magnetostratigraphy, and fission- track dating of euhedral zircons from selected ash-rich horizons will be performed. The principal results of this data base will be a complete chrono - and lithostratigraphic framework for the Morrison-Cloverly sequence and its equivalents to the west and north of Wyoming. The Data base will span an area covering - 250,000 km , from the proximal part of the basin to near its eastern terminus. Among other important results will be (1) a sequence - stratigraphic framework for nonmarine rocks in both underfilled and overfilled parts of foreland basins; (2) a new chronostratigraphically controlled model for early filling of the Cordilleran foreland basin; and (3) new and more complete understanding of the extrinsic (tectonic, eustatic, climatic) controls on the early Cordilleran foreland basin. The results also will provide one of the largest data bases for comparison with available and developing geophysical models for foreland basins.
