GEOCHEMICAL PROVENANCE OF CLASTIC SEDIMENTARY ROCKS FROM THE WESTERN CORDILLERA: UTAH, COLORADO, WYOMING, OREGON, AND CALIFORNIA

One of the central goals of sedimentary petrology is the identification of provenance. Provenance is critical for deciphering the tectonic history of ancient basins and has been applied to both terrane analysis and basin analysis. Provenance is also an important factor in petroleum exploration, because of the role provenance and tectonic setting play in controlling the distribution and quality of petroleum systems elements, particularly reservoir, within sedimentary basins.

Determining provenance is relatively straightforward for conglomerates and breccias, where large intact samples of source are preserved as clasts. For sandstones, the process is more cumbersome and time consuming. Geochemical provenance studies focus on the nature of the source terrane and the tectonic setting of the depositional basin, and provide a general characterization of the nature of the source and the tectonic setting of the basin, whereas isotopic and detrital zircon studies suggest particular terranes from which the sediments may have been derived.

Dickinson et al. (1983) divided sandstones into three main categories using petrographic methods: continental block, recycled orogen, and magmatic arc. This project uses a selection of the same basins studied by Dickinson et al. (1983) to determine if these sandstone suites can be classified into similar groups using whole rock of major and trace elements geochemistry. Whole rock samples are analyzed using XRF and ICP-MS; CO2 is determined independently to correct for both detrital and diagenetic calcite, which makes the results directly comparable to point count data produced by the Gazzi-Dickinson method. We report here on geochemical data from 14 separate basins in the Rocky Mountain and Pacific coastal regions, and compare our results to those obtained by traditional petrographic methods.