CLAY MINERAL INVESTIGATION OF GLACIAL TILL IN GREAT GULLY, CAYUGA COUNTY, NEW YORK

Recent geologic mapping and field investigations in Great Gully, west central Cayuga County by the New York State Geological Survey has documented a well-preserved record of glacial sediments. Glacial stratigraphic sections in excess of 34 meters comprise glacial-lacustrine and fluvial sediments, and multiple diamicton units interpreted as glacial tills. Newly collected chronologic data suggest the glacial tills represent multiple glacial cycles in the region. As a baseline assessment, clay minerals separated from these glacial tills were analyzed using a Rigaku Miniflex X-ray diffractometer. Samples were prepared according to the procedure of Moore and Reynolds (1997). Ten different samples from four laterally continuous, stratigraphically correlative till units were processed. The amount of clay varied as a percentage of mass. The clay samples ranged in color from pale yellowish brown (10YR 6/2) to light brown (5YR 6/4) to light brownish gray (5YR 6/1), and are inferred to reflect variation in oxidation state and/or trace mineral abundance. The clay mineral composition of the tills was very uniform throughout the units. Chlorite and illite were the primary clay minerals detected. No quartz was identified, however, there were traces of calcite in some of the lower samples. No significant variation in the chlorite to illite ratio was observed. The implications of uniform clay mineralogy in till units that vary by as much as 50ka suggest that weathering conditions and/or parent material were similar for all glacial cycles in the region.