GEOCHEMICAL AND SEDIMENTOLOGICAL INVESTIGATION OF A LACUSTRINE TRIASSIC LAGERSTÄTTE IN THE COW BRANCH FORMATION OF THE DANVILLE-DAN RIVER BASIN

The North American Atlantic passive margin contains a number of early Mesozoic lacustrine basins that are part of the Newark Supergroup. These lacustrine deposits contain sedimentary facies attributed to Milankovich cyclicity, making them an excellent archive of Early Mesozoic climatic and environmental conditions. Additionally, these basins contain substantial accumulations of organic-rich facies making them potential targets for energy production. One of these lacustrine basins, the Triassic Danville-Dan River basin, is of specific interest, due to its preservation of lacustrine cycles in combination with a wide range of fossil flora and fauna. Specifically, the organic-rich shales of the Cow Branch Formation include a 3 cm thick bed of perfectly preserved soft-bodied insects, known hereafter as the Triassic Lagerstätte. Beds adjacent to the Lagerstätte contain other well-preserved fossils, like the reptile Tanytrachelos. Given the variety of lithofacies and preserved biota present, the depositional environment of the Lagerstätte, and more broadly the Cow Branch Formation, is disputed.

The aim of our research is to investigate the sedimentology and geochemistry of the Cow Branch Formation in the Danville-Dan River basin to determine the paleoenvironment of the lake. Specifically, we will test whether a chemocline existed within the lake, and if so, its chemistry and dynamics through the sedimentary cycles. Initial analysis will be completed from two cores through the Cow Branch formation, taken from the Virginia Solite Quarry. The cores overlap stratigraphically and contain the Lagerstätte, totaling approximately 7 meters through a lacustrine cycle. The cores will be slabbed, described, and analyzed for various geochemical measures including total organic carbon (TOC), pyrite sulfur contents, as well as iron speciation and the isotope composition of pyrite sulfur and organic carbon. The combined sedimentological and geochemical results will allow us to make more educated statements about lake depth and chemistry overall. Understanding the paleolake chemistry will assist with interpreting the depositional environment of the lake, which could have implications for the oil/gas industry, as well as for the scientific community seeking to further investigate the East Coast Mesozoic rift basins.