PARAGENETIC SEQUENCING OF FRESHWATER TUFA REEFS, FAYETTEVILLE GREEN LAKE, NEW YORK

Green Lakes State Park, located 13 km east of the city of Syracuse, New York, contains two meromictic lakes, Green Lake and Round Lake. Meromixis in both lakes is due to calcium- and sulfate-rich groundwater discharge sourced from bedrock dissolution, resulting in salinity stratification. The entire water column is supersaturated with respect to calcite. Thus, sedimentation primarily results from spring/summer whiting events (calcite precipitation) in the mixolimnion. Thrombolytic tufa reefs, rare in freshwater lakes, are abundant around the shoreline of Green Lake reaching depths of at least 16 meters. A small cluster of tufa also occurs in Round Lake but are submerged about 2 meters below the waterline. Several previous studies focused on the role microorganisms play in their formation, using petrography and scanning electron microscopy. This study focuses on describing the paragenetic sequence of facies observed in a tufa core collected from Green Lake in 2019. Preliminary results indicate at least three main facies; primary tufa, calcite cements, and calcareous sediment. Volumetric quantification and 3D visualization of each, and pore space, was conducted using a Zeiss Xradia 520 Versa CT scanner. The primary tufa is composed of both thrombolytic and stromatolitic textures. Several calcite cements occur, including isopachous fibrous coatings and drusy void-filling cements. Sediment infill, while abundant in some pores is absent elsewhere. This may indicate periods of slow tufa growth allowing sediment, settling through the water column or reworked by waves, to fill some pores. Each facies were targeted for carbon and oxygen isotope analyses to potentially distinguish differing water sources, such as groundwater and lake water, or formation mechanism. Further research of these deposits can investigate the spatial relationship between large tufa structures, and sites of significant groundwater influx. Quantitative and qualitative analysis of the modern tufa reefs in Green Lake, collected in situ, can provide a valuable tool for understanding past depositional environments of other tufa preserved within the geologic record.