Palynological and bulk geochemical constraints on the paleoceanographic conditions across the Frasnian–Famennian boundary, New Albany Shale, Indiana

Abstract

Abstract A down-core record of stable isotope and geochemical results is integrated with palynofacies (kerogen) data from the New Albany Shale (Indiana) to reconstruct environmental changes that occurred across the Frasnian–Famennian boundary. Preliminary interpretations are focused on developing several multiproxy linkages that will potentially lead toward a more robust understanding of the occurrence and significance of phytoplankton assemblage variations during the Late Devonian, a time of widespread black shale formation. Development of such linkages will potentially provide a more comprehensive assessment of the various controls on 1) primary production, and 2) carbon sequestration in a large, low-paleolatitude intracratonic basin. An abrupt change in the geochemical and biotic proxies for particulate organic matter across the Frasnian–Famennian boundary coincides with a distinct lithological change, characterized by laminated, brownish-black Famennian mudstones unconformably overlying alternating bioturbated, greenish-gray and non-bioturbated, dark-gray Frasnian mudstones. Elemental and isotopic profiles reflect different patterns of production, degradation, and removal of organic carbon in the two shale facies. A shift from acritarch- to prasinophyte-dominated waters across the boundary indicates the overall importance of bathymetric fluctuations, chemico-physical conditions, and nutrient availability related to eustatic sea-level change. A positive δ 13 C V-PDB shift of 1.1‰ across the boundary is interpreted to be correlative with the global Upper Kellwasser Event. A preliminary model is proposed to explain the sustainable primary production during times of maximum flooding, thereby enhancing organic preservation during black shale formation.