PETROGRAPHIC ANALYSIS OF SANDSTONES AND CONGLOMERATES FROM THE NANUSHUK AND TOROK FORMATIONS, SLOPE MOUNTAIN, ALASKA

The mid to Late Cretaceous Nanushuk and Torok formations are located at Slope Mountain, North Slope, Alaska. The Torok Formation, comprised of marine sediments, underlies and interfingers with the lower Nanushuk Formation as part of a deltaic succession. The Nanushuk Formation is generally divided into upper and lower units: the lower Nanushuk comprises shallow marine mudstones and sandstones, whereas the upper Nanushuk consists of marginal marine to terrestrial sediments. These Aptian-Cenomanian sediments were derived from the exhumation of the Brooks Range and the filling of the Colville foreland basin. This project examines thin sections from the Nanushuk and Torok formations at Slope Mountain in an attempt to expand on an original study aimed at understanding how the Cretaceous landscape responded to tectonic and climate forcing through the description of sediments and facies classifications. My work supplements previous work at Slope Mountain by tracking changes in provenance and sedimentary texture within thin sections. I use the Gazzi-Dickinson point count method to study 10 thin sections from Slope Mountain and compare them to previous work in the area. I distinguish 19 point counting categories, with a traditional emphasis on quartz, feldspar, and lithic composition. The changes seen within these sections, in conjunction with previous facies analyses, help with the interpretation of the contrasting effects of facies control and regional changes in provenance caused by evolution of the Brooks Range. In addition, I compare my results to thin sections from the Straight Cliffs Formation in Southern Utah. The Late Cretaceous Straight Cliffs Formation was deposited in a similar foreland basin setting, and provides important contrasting data points to the Alaskan results.