PROPERTIES AND SOURCE REGION OF IGNEOUS AND METAMORPHIC GLACIAL SEDIMENT DEPOSITED IN CENTRAL NY

Much of the surface geology of Oswego County, NY consists of unconsolidated sediment, either glacial till or lacustrine sands and gravel deposited by the Laurentide Ice sheet during the last glacial period. Based on previous work, this till was determined to consist largely of gravel to cobble-sized sediment eroded from local clastic sedimentary rock formations such as the Oswego Sandstone and the Queenstown formations. However, approximately 20% of this surface sediment is not sedimentary, but rather felsic plutonic igneous and medium to high grade metamorphic rock. This portion of sediment has clearly been eroded from other sources of bedrock not local to the Oswego area. It is probable that this sediment was transported from points north, likely the Western Adirondacks, Thousand Islands, and Grenville terrains in Southeastern Ontario, Canada, north of Lake Ontario and directly north of our study area. Determining the origin of these sediments could help to understand ice flow direction as well as weathering and erosion patterns and rates.

Clasts of igneous and metamorphic rocks ranging from approximately 10-30 cm were collected from eight sites along two glacial drumlins, located at Rice Creek Field Station (RCFS) and Oswego Middle School (OMS), both located in Oswego, NY. Samples from several crystalline erratics located at these sample sites were also collected for analysis. Igneous and metamorphic bedrock, with similar mineralogy and texture to crystalline sediment at RCFS, was collected from outcrops in the Adirondacks and Thousand Island regions for comparison to the glacial sediment from OMS and RCFS. All rock samples were categorized based on the modal abundance of major minerals visible in hand samples and cut clasts. Thin sections were analyzed via optical and electron microscopy, with SEM/EDS and XRD being used to further constrain mineralogy and determine bulk geochemistry. XRF analyses were also conducted to determine trace element concentrations in an effort to better correlate samples to possible source regions. Analyses show that glacial deposits in Oswego appear to contain at least some sediment derived from metasedimentary bedrock in northern NY.