WEATHERING PROXY VALIDITY AND IMPLICATIONS FOR NEW ENGLAND QUATERNARY SEDIMENTS

The Chemical Index of Alteration, or CIA, is a paleo-weathering proxy designed to measure the degree of chemical weathering in feldspar minerals. While it has been utilized extensively to answer questions regarding deep-time paleoenvironments, little research has been conducted on more recent study sites, inviting scrutiny of the sensitivity and resolution of this proxy and exposing a potential area for development. This research focused on applying the CIA proxy to both modern and Quaternary sediments in the Long Island Sound basin, two time periods which have been neglected in recent analyses. Specifically, the timing of the Laurentide Ice Sheet retreat has long been disputed, and this study investigated how this glacial/interglacial transition was reflected in the chemical weathering record. Using LiDAR to identify rimmed, circular depressions in north central Connecticut, a vibracore was taken from one of these depressions in late September 2022. The 2.5-m core was sampled at 3-cm intervals and analyzed using mudrock-calibrated XRF to obtain CIA values. Three main sedimentary units within the core mark the site’s transition from lake to wetland. Modern surface sediment from Long Island Sound and surrounding estuaries were also analyzed and their CIA values obtained in order to contextualize the resolution and sensitivity of the Quaternary chemical weathering signal. Data collected via XRF analyses show that samples from the bottom Unit 1 have an average CIA value of 69, the middle Unit 2 an average value of 73.4, and the top Unit 3 an average value of 82.4. The Ti/Al elemental ratio ranged from 0.0419 to 0.113 within the core, indicating these three units share the same provenance. These results are consistent with changing climate following the Last Glacial Maximum. These values offer useful insight into the sensitivity of the chemical weathering record as well as the timing of the Laurentide Ice Sheet retreat.