INVESTIGATING THE CARBON ISOTOPE RECORD OF THE END-BOTOMIAN MASS EXTINCTIONS: NEW DATA FROM THE SHADY DOLOMITE OF SOUTHWEST VIRGINIA

The late early Cambrian end-Botomian mass extinctions (513 to 509 Ma) were one of the first extinction events to affect animal life on our planet. These mass extinctions affected the reef-forming archaeocyathids, small shelly fauna, other reef-associated benthos and trilobites and roughly correspond to the emplacement of the Kalkarindji Large Igneous Province (LIP) now found in present-day Australia. An abrupt, negative carbon isotope excursion found in the Cambrian successions of northern Siberia also coincides with the end-Botomian extinctions. One hypothesis links this negative carbon isotope excursion to ¹³C depleted CO₂ emissions from the Kalkarindji LIP. Alternatively, this negative isotope excursion may be a local signal, driven by higher rates of organic matter remineralization in the water column during the extinction events. Since the global versus local nature of this δ¹³C excursion has not been assessed, the potential driving mechanisms behind it remain unresolved.

Here we will present carbon isotopic data from the age-equivalent Upper Shady Dolomite of the southwestern Virginia. The Early Cambrian Shady Formation in southwest Virginia represents a unique opportunity to study this end-Botomian interval as it represents 1) a relatively continuous and thick stratigraphy succession through the Early Cambrian 2) previous work has identified the extinction interval and 3) has confirmed that carbonate components in the Shady Formation carry Cambrian seawater signals. This new record from the paleocontinent of Laurentia will assess the local versus global nature of the end-Botomian carbon isotope excursion which has implications for the environmental drivers behind this excursion and the extinction events.