INVESTIGATING CARBONATES IN THE SEDIMENTARY RECORD OF CONESUS LAKE, LIVINGSTON COUNTY, NY

The sedimentary record of the Finger Lakes archives a long history of annual sedimentation influenced by environmental and biological factors. Conesus Lake is the westernmost Finger Lake in New York, consisting of nearly isolated north and south basins. The north basin has few tributaries, resulting in a lower sedimentation rate and variable autochthonous sedimentation. Harmful cyanoalgal blooms regularly occur during the late summer in Conesus Lake, often with precipitation of calcite (whiting). Here, we investigate the carbonate record in the north basin to determine the role of calcium carbonate production through its deep-rooted history in Conesus Lake.

Piston and Bolivia cores were collected from the northeast basin at a depth of 1.4 meters, resulting in a total of 1.53 meters of archived sediments. The cores were split, imaged, and analyzed for magnetic susceptibility and X-ray fluorescence (XRF) using a multi-sensor core logger. An initial core description was developed from 30 smear slides, and SEM/EDS analysis was used to characterize grain size, texture, and composition.

High concentrations of clastics and pennate diatoms occurred in the upper 30 cm with minimal varve carbonate sedimentation. In contrast, the remaining 1.23 m has varved micritic calcite with an increased abundance of centric and pennate diatoms. Varve intervals show micritic calcite deposition during spring-summer months with strongly biogenic re-suspended sediment in winter months. Calcite minerals occur as both shelly material and as nano to < 5-micron scale scalenohedral, rhombohedral, and sheet-like morphologies. The calcite textures and grain size within the core suggest the calcite sediments are predominantly biogenic, with evidence of carbonate diagenesis overprinting the biogenic signal. Preliminary analysis of ‘whiting’ precipitants shows rhombohedral calcite similar to the textures seen in the archive and form in association with cellular material. Varve disruption occurred over the last century from human-caused environmental changes impacting the lake chemistry, water cycle, and sedimentation/precipitation rates. The recent history of calcite precipitation has a limited record within the core, making connections to a decade-long record of ‘whiting’ challenging.