IngentaConnect Geochemical signature and related climatic-oceanographic processe...

Abstract:

A sediment sequence which may contain the early Albian OAE 1b was investigated in a deep-water (3800 m) open-ocean environment at Site 417D, western North Atlantic Ocean. Redox cycles, which contain black shale intervals and occur in the early Albian M. gracilis radiolarian Biozone, were studied in order to show processes and climate-associated controlling factors during the deposition of early Albian sediments. The black shale intervals are characterized by the enhanced accumulation and preservation of marine-derived organic matter as determined by Rock-Eval pyrolysis and organic petrology. The presence of laminated sediments, the relationships between organic carbon, iron and total sulfur, pyrite size analysis and trace-metal enrichment indicate the periodic prevalence of anoxic conditions in the pore waters, which may at times have extended to the sediment/water interface. Changes in the mineralogical composition throughout the black shale-dominated interval, i.e., quartz content and clay-mineral assemblage, resulted in the variation of the major-element chemistry and probably reflect cyclic climatic changes in northern Africa combined with flooding of coastal lowlands during an overall transgressive phase in the early Albian. The geochemical signatures observed at different scales demonstrate a genetic link between the climate system on land and processes in the deep ocean during the deposition of black shales in deep-water environments of the western North Atlantic. Copyright 2001 Academic Press

Keywords: Oceanic Anoxic Event 1b; black shales; redox conditions; climate forcing; early Albian; North Atlantic

Language: English

Document Type: Research article

Affiliations: Department of Geology, Zülpicher Str. 49a, Cologne, 50674, Germany:

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Geochemical signature and related climatic-oceanographic processes for early Albian black shales: Site 417D, North Atlantic Ocean