Origins and maturity of organic matter in mid-Cretaceous black shales from ODP Site 1138 on the Kerguelen Plateau |
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| Authors: | Philip A Meyers Jong-Gwon Yum Sherwood W Wise |
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| Institution: | 1. Marine Geology and Geochemistry Program, Department of Geological Sciences, The University of Michigan, 1100 North University Avenue, Ann Arbor, MI 48109-1005, USA;2. Department of Geology, Florida State University, Tallahassee, FL 32306-4100, USA |
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| Abstract: | We have conducted elemental, isotopic, and Rock-Eval analyses of Cenomanian–Santonian sediment samples from ODP Site 1138 in the southern Indian Ocean to assess the origin and thermal maturity of organic matter in mid-Cretaceous black shales found at this high-latitude location. Total organic carbon (TOC) concentrations range between 1 and 20 wt% in black to medium-gray sediments deposited around the Cenomanian–Turonian boundary. Results of Rock-Eval pyrolysis indicate that the organic matter is algal Type II material that has experienced modest alteration. Important contributions of nitrogen-fixing bacteria to the amplified production of organic matter implied by the high TOC concentrations is recorded in δ15N values between −5 and 1‰, and the existence of a near-surface intensified oxygen minimum zone that favored organic carbon preservation is implied by TOC/TN ratios between 20 and 40. In contrast to the marine nature of the organic matter in the Cenomanian–Turonian boundary section, deeper sediments at Site 1138 contain evidence of contributions land-derived organic matter that implies the former presence of forests on the Kerguelen Plateau until the earliest Cenomanian. |
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| Keywords: | Cenomanian&ndash Turonian Boundary Event Black shales Sediment δ15N Organic δ13C Rock-Eval pyrolysis TOC/TN ratio |
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