Previous work has shown that the location and flow patterns of the major early Cretaceous rivers in the medial and distal parts of the CCFB were controlled, in part, locally by syndepositional intra-basinal faulting. This study will elucidate precisely how this faulting influenced channel geometries (e.g widths, depths, sinuosities, channel patterns), hydraulics (e.g channel slopes, velocities, discharges), and the distribution of associated channel-bar, channel-belt, and floodplain deposits. These parameters will be compared and contrasted in (i) medial and distal setting within the CCFB, (ii) in places where the rivers were located essentially on or adjacent to known structures versus places where the structures were several kilometers away, and (iii) where the rivers locally crossed the structures versus where they paralleled them. Results of this study should be valuable for those who attempt to model how intra-basinal tectonism is manifested n the accumulation of nonmarine fill in the medial and distal parts of foreland basins. Moreover, this work will be the first of its kind to document quantitatively the effects of localized syndepositional faulting on pre-Quaternary fluvial sedimentation.
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 willbe (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.
Previous work has shown that the location and flow patterns of the major early Cretaceous rivers in the medial and distal parts of the CCFB were controlled, in part, locally by syndepositional intra-basinal faulting. This study will elucidate precisely how this faulting influenced channel geometries (e.g widths, depths, sinuosities, channel patterns), hydraulics (e.g channel slopes, velocities, discharges), and the distribution of associated channel-bar, channel-belt, and floodplain deposits. These parameters will be compared and contrasted in (i) medial and distal setting within the CCFB, (ii) in places where the rivers were located essentially on or adjacent to known structures versus places where the structures were several kilometers away, and (iii) where the rivers locally crossed the structures versus where they paralleled them. Results of this study should be valuable for those who attempt to model how intra-basinal tectonism is manifested n the accumulation of nonmarine fill in the medial and distal parts of foreland basins. Moreover, this work will be the first of its kind to document quantitatively the effects of localized syndepositional faulting on pre-Quaternary fluvial sedimentation.
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 willbe (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.
Geology, Petrology, Sedimentology, Stratigraphy
