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

Middle-Upper (Givetian-Frasnian) Devonian strata in the Appalachian Basin record the evolutionary development and ecological expansion of vascular land plants concurrent with widespread black shale deposition. Based on this timing, Algeo and others published a series of seminal papers proposing that terrestrial plant evolution and marine black shale are related: the expansion of taller terrestrial floras with deeper root systems would have increased terrestrial weathering/soil formation and terrestrial-to-marine biomass fluxes, thereby resulting in eutrophication, black shale deposition, and marine benthic fauna extinction. Although a variety of studies have investigated the production and preservation of organic matter in Devonian black shales, few have employed large-scale geochemical transects across the Appalachian Basin.

Building on previous studies of terrestrial-marine teleconnection onset, we hypothesize that: 1) an increased influx of terrestrial biomass into marine settings during the Givetian-Frasnian transition is recorded stratigraphically; and, 2) the proportion of terrestrial-to-marine organic matter in black shale decreases with proximity to open-ocean settings on the continental margin and distance from terrestrial ecosystems. Our current study focuses on Appalachian Basin marine strata, and includes the Geneseo, Burket, Millboro, Blocher, Portwood, Trousdale, and New Albany black shales. In these shales, we are compiling an integrated organic and inorganic carbon isotopic, biomarker, total organic carbon (TOC), and redox-sensitive trace elemental dataset to constrain the spatio-temporal flux of terrestrial organic matter. Preliminary data from the Geneseo Formation (New York) shows that δ¹³C_CARB values become isotopically lighter up section, from 1 to -6‰. This trend corresponds to a global shift to lighter values, which may indicate a widespread increase of terrestrial-to-marine flux of isotopically light carbon at this time. Paleoredox proxies indicate low-oxygen conditions, but interpretation is complicated by a shallowing-upward change from black shale to gray shaly siltstones resulting from Catskill Delta progradation. This study will provide a robust dataset for understanding the onset of terrestrial biomass influx to marine settings.