Deposition of sedimentary organic matter in black shale facies indicated by the geochemistry and petrography of high-resolution samples, Blake Nose, western North Atlantic
Published:January 01, 2001
Charles E. Barker, Mark Pawlewicz, Emily A. Cobabe, 2001. "Deposition of sedimentary organic matter in black shale facies indicated by the geochemistry and petrography of high-resolution samples, Blake Nose, western North Atlantic", Western North Atlantic Palaeogene and Cretaceous Palaeoceanography, Dick Kroon, R. D. Norris, A. Klaus
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A transect of three holes drilled across the Blake Nose, western North Atlantic Ocean, retrieved cores of black shale facies related to the Albian Oceanic Anoxic Events (OAE) 1b and 1d. Sedimentary organic matter (SOM) recovered from Ocean Drilling Program Hole 1049A from the eastern end of the transect showed that before black shale facies deposition organic matter preservation was a Type III–IV SOM. Petrography reveals that this SOM is composed mostly of degraded algal debris, amorphous SOM and a minor component of Type III–IV terrestrial SOM, mostly detroinertinite. When black shale facies deposition commenced, the geochemical character of the SOM changed from a relatively oxygen-rich Type III–IV to relatively hydrogen-rich Type II. Petrography, biomarker and organic carbon isotopic data indicate marine and terrestrial SOM sources that do not appear to change during the transition from light-grey calcareous ooze to the black shale facies. Black shale subfacies layers alternate from laminated to homogeneous. Some of the laminated and the poorly laminated to homogeneous layers are organic carbon and hydrogen rich as well, suggesting that at least two SOM depositional processes are influencing the black shale facies. The laminated beds reflect deposition in a low sedimentation rate (6m Ma−1) environment with SOM derived mostly from gravity settling from the overlying water into sometimes dysoxic bottom water. The source of this high hydrogen content SOM is problematic because before black shale deposition, the marine SOM supplied to the site is geochemically a Type III–IV. A clue to the source of the H-rich SOM may be the interlayering of relatively homogeneous ooze layers that have a widely variable SOM content and quality. These relatively thick, sometimes subtly graded, sediment layers are thought to be deposited from a Type II SOM-enriched sediment suspension generated by turbidites or direct turbidite deposition.
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Western North Atlantic Palaeogene and Cretaceous Palaeoceanography
Palaeogene and Cretaceous palaeoceanography has been the focus of intense international interest in the last few years, spurred by deep ocean drilling at Blake Nose in the North Atlantic as well as the need to use past climate change as input for modelling future climate change. This book brings together a number of review papers that describe ancient oceans and unique events in the Earth’s climatic history and evolution of biota. The papers show evidence of periods characterized by exceptional global warmth such as the Late Palaeocene Thermal Maximum and Cretaceous anoxic events. Geochemical records and modelling will make the reader aware that these periods were forced by greenhouse gases. This information is essential for understanding the response of the ocean—climate system to the current input of fossil fuels. In this sense, the book contributes to the understanding of fundamental aspects of Earth’s climate, the carbon cycle, and marine ecosystems. A number of papers describe massive mass wasting deposits resulting from the energy released by the bolide impact at the Cretaceous—Tertiary boundary as well as the geochemistry of the boundary itself. Additional papers cover aspects of cyclostratigraphy and biostratigraphy of Palaeogene and Cretaceous records.
This book will be of interest to a broad audience of Earth Scientists interested in Palaeogene—Cretaceous palaeoceanography, extreme climate modelling, Cretaceous—Tertiary boundary, Late Palaeocene Thermal Maximum, Cretaceous anoxic events, as well as those specifically interested in radiolarian, dinoflagellate and coccolithophorid stratigraphy.