Calcium Isotopes in the Saint Agatha Kettle Lake Deposits of Southern Ontario

Emma-Dawn Ferguson, The University of Western Ontario

Abstract

The St. Agatha kettle lake deposits, ON, Canada, contain a thick section of endogenic marl and coeval shelly fauna. Marl accumulation occurred from ~13,500 to ~8,200 cal yrs BP. This study examines controls on marl and shell δ^44/42Ca, element ratios (Mg, Fe, and Ba), δ¹⁸O, δ¹³C, and ⁸⁷Sr/⁸⁶Sr ratios of marl calcite, shell aragonite, groundwater, and bedrock as proxies for paleolacustrine conditions. Results for Interval A (532.0 to 475.0cm) indicates a cooler, wetter climate, lower primary lake productivity and higher lake levels. Interval B (475.0 to 345.0cm) marks the onset of a closed lake system, warming climate, and perhaps Ca-limitation on marl calcite δ^44/42Ca. Data for Interval C (345.0 to 192.0cm) suggest a reduction in lake depth, increased lakewater evaporation and greater lake productivity which continues into Interval D (192.0 to 128.0cm) before marl precipitation ceases. Marl calcite δ^44/42Ca is likely controlled by non-equilibrium processes in this freshwater system.