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首页> 外文期刊>Organic Geochemistry: A Publication of the International Association of Geochemistry and Cosmochemistry >Origins and accumulation of organic matter in expanded Albian to Santonian black shale sequences on the Demerara Rise, South American margin
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Origins and accumulation of organic matter in expanded Albian to Santonian black shale sequences on the Demerara Rise, South American margin

机译：南美边缘Demerara Rise的扩展的阿尔比至桑顿黑页岩序列中有机质的起源和积累

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摘要

Ocean Drilling Program Leg 207 recovered thick sequences of Albian to Santonian organic-carbon-rich claystones at five drill-sites on the Demerara Rise in the western equatorial Atlantic Ocean. Dark-colored, finely laminated, Cenomanian-Santonian black shale sequences contain between 2% and 15% organic carbon and encompass Oceanic Anoxic Events 2 and 3. High Rock-Eval hydrogen indices signify that the bulk of the organic matter in these sequences is marine in origin. However, delta C-13(org) values lie mostly between -30 parts per thousand and -27 parts per thousand, and TOC/TN ratios range from 15 to 42, which both mimic the source signatures of modern C-3 land plants. The contradictions in organic matter source indicators provide important implications about the depositional conditions leading to the black shale accumulations. The low delta C-13(org) values, which are actually common in mid-Cretaceous marine organic matter, are consequences of the greenhouse climate prevailing at that time and an associated accelerated hydrologic cycle. The elevated C/N ratios, which are also typical of black shales, indicate depressed organic matter degradation associated with low-oxygen conditions in the water column that favored preservation of carbon-rich forms of marine organic matter over nitrogen-rich components. Underlying the laminated Cenomanian-Santonian sequences are homogeneous, dark-colored, lower to middle Albian siltstones that contain between 0.2% and 9% organic carbon. The organic matter in these rocks is mostly marine in origin, but it occasionally includes large proportions of land-derived material. (c) 2006 Elsevier Ltd. All rights reserved.
机译：海洋钻探计划第207条腿在赤道西大西洋Demerara Rise的五个钻探地点恢复了阿尔比亚至桑顿时期富含有机碳的粘土的厚层序列。深色，精细层压的西诺曼尼亚-桑顿尼亚黑色页岩序列含有2％至15％的有机碳，涵盖了海洋缺氧事件2和3。高岩石-评估氢指数表明这些序列中的大部分有机物为海洋起源。但是，δC-13（org）值大多在千分之-30到千分之-27之间，TOC / TN比在15到42之间，都模仿了现代C-3陆地植物的来源特征。有机质源指标的矛盾为导致黑色页岩堆积的沉积条件提供了重要的启示。低δC-13（org）值实际上在白垩纪中期海洋有机物中很常见，这是当时盛行的温室气候和相关的加速水文循环的结果。较高的C / N比（这也是黑色页岩的典型特征）表明与水柱中低氧条件相关的有机物降解降低，这有利于保存富含碳的形式的海洋有机物而不是富含氮的组分。叠层的Cenomanian-Santonian序列之下是均一的，深色的，中低阶的Albian粉砂岩，含0.2％到9％的有机碳。这些岩石中的有机物主要来自海洋，但偶尔也包含很大比例的陆源物质。 （c）2006 Elsevier Ltd.保留所有权利。

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