Evaluation of Ar-Ar ages of Individual Mica Grains for Provenance Studies of Loess, Long Island, NY A Thesis Presented by

of the Thesis Evaluation of Ar-Ar ages of Individual Mica Grains for Provenance Studies of Loess, Long Island, NY by Jian Zhong Master of Science in Geosciences State University of New York at Stony Brook 2001 Loess in a one-meter thick section on the SUNY Stony Brook Campus has been studied for grain size distribution and provenance. The loess provenance has been evaluated using single crystal Ar/Ar muscovite and biotite ages. The grain size distribution of loess shows three modes at fine sand (250 microns), silt (20 microns), and clay (<2 microns). There are also occasional pebbles up to 5 cm in diameter in the loess. The size distribution of the clay and silt fractions of the sediment resemble that of loess in many parts of the world. The size distribution of the fine sand in the loess resembles that of the immediately underlying glacial sand unit and the sand in the underlying gravely till. It is proposed that sand in the loess on Stony Brook campus might be wind blown sand or derived from the underlying sand and till by the combined action of cryoturbation and faunalturbation. Mica has been also dated for samples in a section from Caumsett State Park, Lloyd Harbor, New York about 25 miles west of the campus that includes Cretaceous sands, glacial outwash sand and gravel, and loess.