Black shale deposition and faunal overturn in the Devonian Appalachian basin: Clastic starvation, seasonal water-column mixing, and efficient biolimiting nutrient recycling

Integrated geochemical data suggest that black shale deposition in the Devo nian Genesco Formation of western New York was initiated by the coincidence of siliciclastic starvation and the intensification of seasonal water colu mn stratification and mixing. Once established, however, black shale deposi tion was maintained through efficient recycling of biolimiting nutrients wh ich enhanced primary productivity. Recycling efficiency was achieved throug h a positive feedback loop of oscillating benthic redox conditions that enh anced N and P regeneration from sediments, sustained high primary productiv ity by returning nutrients to the photic zone during mixing, and ensured a downward flux of organic matter that drove or enhanced the episodic develop ment of benthic anoxia during stratification. This feedback was ultimately disrupted by rising siliciclastic influx, which diluted organic matter and restored benthic redox stability. The abrupt overturn of diverse, long-stan ding Appalachian basin marine communities may have been the result of troph ic resource destabilization during Geneseo deposition.