Origins and maturity of organic matter in mid-Cretaceous black shales from ODP Site 1138 on the Kerguelen Plateau

• Published in: Marine and petroleum geology Vol. 26; no. 6; pp. 909 - 915
• Main Authors: Meyers, Philip A., Yum, Jong-Gwon, Wise, Sherwood W.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.06.2009; Elsevier
• Subjects: Black shales; Cenomanian–Turonian Boundary Event; Earth sciences; Earth, ocean, space; Exact sciences and technology; Hydrocarbons; Marine; Marine geology; Organic δ 13C; Rock-Eval pyrolysis; Sediment δ 15N; Sedimentary rocks; TOC/TN ratio; Indian Ocean; Kerguelen Plateau; PSE, South Indian Ocean, East Indian Ridge, Kerguelen Plateau; ISW, Indian Ocean; TOC/TN ratio; Black shales; Rock-Eval pyrolysis; Cenomanian–Turonian Boundary Event; Sediment δ 15N; Organic δ 13C; Senonian; Mesozoic; C; bacteria; latitude; Rock-Eval; N; preservation; Santonian; pyrolysis; Organic δ; Upper Cretaceous; oxygen; organic carbon; clastic rocks; Sediment δ; black shale; thermal maturity; geologic sections; maturity; Cenomanian; concentration; Cretaceous; sedimentary rocks; Turonian; prokaryotes; organic materials; alteration; Phanerozoic; Cenomanian-Turonian Boundary Event
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/j.marpetgeo.2008.09.003

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 δ 15N 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.