PALEORECONSTRUCTION OF THE CAMBRIAN-ORDOVICIAN TRANSITION USING OOLITE DEPOSITS ACROSS THE NORTHEASTERN UNITED STATES

Ooids are spherical, concentrically layered calcium carbonate grains less than 2 millimeters in diameter formed from agitating currents precipitating around a nucleus. Ooid grains serve as ideal paleoenvironmental proxies with ooid cortices recording paleooceanic conditions present during nucleation and cortical growth. The Cambrian and Ordovician Periods (504-443 million years ago) saw significant shifts in marine environments, transitioning from mass anoxia and euxinia during the Cambrian Extinction to radiating biodiversity during the Great Ordovician Biodiversification Event. During this time, transgressional periods flooded the Laurentia craton resulting in the deposition of oolitic strata within the shallow marine environment. Trower et al. 2020 utilized growth and abrasion formulas to calculate bathymetric parameters during ooid nucleation and precipitation.

This study utilizes ooid cortical stratigraphy as a paleoclimatic indicator to investigate the bathymetric conditions responsible for faunal and environmental changes during the Cambrian-Ordovician Transition. Petrographic analyses will be performed on lithologic samples collected from eighteen locations across Virginia, Maryland, Pennsylvania, New York, and Vermont. Geologic thin sections will be produced by slicing petrographic samples using a lapidary saw before being epoxied to glass slides and sanded to a thickness of 30 microns to reveal the ooids interior morphologic structure. Thin sections will be examined under a petrographic microscope and cortical thickness will be measured before being substituted into Trower’s equations to solve for unknown bathymetric conditions including salinity, temperature, and carbon saturation. Measuring oceanic conditions present during the formation, deposition, and diagenesis of ooid sediments will help fill gaps in climatic settings responsible for transitioning mass extinctions into mass biodiversification events.