TESTING THE IMPACT OF FOREST EVOLUTION ON THE ORGANIC MATTER COMPOSITION OF APPALACHIAN BASIN MARINE BLACK SHALE

Middle and Upper Devonian Appalachian Basin (AB) strata record the evolutionary development and ecological expansion of vascular land plants concurrent with widespread marine black shale. Based on this timing, Algeo and others published several seminal papers proposing that terrestrial plant evolution and marine black shale are related: the expansion of taller terrestrial floras with deeper root systems enhanced terrestrial weathering/soil formation and terrestrial to marine nutrient fluxes leading to eutrophication, black shale formation, and marine extinction. Although prior studies have examined the production and preservation of organic matter (OM) in Devonian black shale, few employed large-scale, high temporal resolution geochemical transects across the AB.

Our project aims to decipher the terrestrial versus marine OM contribution to latest Givetian-earliest Frasnian AB black shale along a transect from the northern AB to the more open ocean-influenced southern AB; this approach will spatially and temporally constrain terrestrial OM flux to marine settings during forest evolution. We are compiling an integrated dataset of weight percent organic carbon, carbon isotopes, and biomarkers from core and outcrop; a sub-project is testing the accuracy of outcrop-derived organic geochemical analysis relative to better-preserved core. The first phase of the project is focused on the northern and central AB Geneseo and Burket black shales of NY, PA, and WV. Weight percent organic carbon measurements are comparable between nearby outcrop and core in NY, and among samples from NY, PA, and WV. Isotope data from the Geneseo Formation (NY, Cargill #17 Lansing core) shows that δ¹³C_ORG values become isotopically lighter up section to ~-29.5‰ in the black shales of the lower Geneseo. Subsequently, beginning with the mid-Geneseo Fir Tree depositional sequence and up through the basal Lodi sequence, δ¹³C_ORG becomes heavier to values ~-27.5 as turbidites become more common. This suggests that Geneseo Formation black shale OM has a primarily marine source. This pattern will be compared to δ¹³C_ORG values from PA and WV that are in preparation as well as preliminary biomarker results. The final integrated dataset will improve our understanding of the terrestrial-marine teleconnection during forest evolution.