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首页> 外文期刊>Palaeogeography, Palaeoclimatology, Palaeoecology: An International Journal for the Geo-Sciences >Nannofacies analysis as a tool to reconstruct paleoenvironmental changes during the Early Toarcian anoxic event
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Nannofacies analysis as a tool to reconstruct paleoenvironmental changes during the Early Toarcian anoxic event

机译：纳米相分析是重建早期Toarcian缺氧事件期间古环境变化的工具

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The black shales of lower Toarcian (Schistes Carton in France, Jet Rock in England, Posidonia Shale in Germany) are sediments formed by fine alternations of millimetric to sub/millimetric clear and dark laminae. A study of polished core surfaces (Dottemhausen core, SW Germany) was carried out in SEM in order to characterize the micro-fabrics of different laminae and their content in nannofossils. Two main intervals were recognized where fabrics and nannofossil content are significantly different. In the clay-rich interval, characterized by high wt.%TOC and a large negative carbon isotope excursion (both in carbonates and organic matter) the dominant micro-fabrics are well foliated or lumpy, giving evidence of the absence or reduction of benthic life. Nannofossils are scarce and only concentrated in discrete laminae separated by large, abiotic intervals. Assemblages are indicative of a deep nutricline, but sporadic nutrient inputs occurred, as demonstrated by fluctuation in abundance of specimens of the Biscutaceae. Nutrients were probably delivered to the German basin via riverme influx. Different sized framboids of pyrite were recognized in this interval, the smallest ones (- 2 mu m) being probably precipitated in an anoxic and sulphidic water column. The clay-rich interval was likely deposited during low sea level in a restricted basin. These conditions were followed by a sea-level rise and better water-mass circulation within the German basin. Sedimentation records an increase in carbonate deposition, organic matter content decreased, and carbon isotopes came back to pre-excursion values. Micro-fabrics became less markedly laminated, pyrite framboids nearly disappeared, and rich and diversified nannofossil assemblages are recorded. Sea-water conditions were probably highly fluctuating, as indicated by alternation of intervals dominated in turn by Schizosphaerella spp., flourishing under generally oligotrophic conditions, where nutrients were temporarily available in surface waters due to storms, and by Crepidolithus spp., a deep-dweller. The results of this work fit well with a silled-basin model. (c) 2007 Elsevier B.V. All rights reserved.
机译：下Toarcian的黑色页岩（法国的Schistes Carton，英国的Jet Rock，德国的Posidonia页岩）是由毫米级到亚/毫米级的透明和深色薄层的精细交替形成的沉积物。在SEM中对抛光的芯表面（Dottemhausen芯，德国SW）进行了研究，以表征不同薄片的微纤维及其在纳米化石中的含量。认识到两个主要的时间间隔，其中织物和纳米化石含量明显不同。在富含粘土的区间内，其特征在于高的TOC％重量和较大的负碳同位素偏移（在碳酸盐和有机物质中均如此），主要的微纤维很好地形成叶状或块状，从而证明了底栖生物的缺乏或减少。 Nannofossils稀少，仅集中在以较大的非生物间隔隔开的离散薄片中。集合体表明营养素很深，但是出现了零星的营养输入，这由Biscutaceae的标本数量波动所证明。营养物可能通过河水涌入德国盆地。在此间隔内可以识别出不同尺寸的黄铁矿黄铁矿，最小的（-2微米）可能沉淀在缺氧和硫化水柱中。富含粘土的层段可能是在限制海盆低海平面期间沉积的。在这些情况之后，德国盆地内海平面上升，水质环流改善。泥沙记录表明碳酸盐沉积增加，有机质含量降低，碳同位素恢复到偏移前的值。微织物变得不那么明显地层压，黄铁矿的泡沫几乎消失了，并且记录了丰富多样的纳米化石组合。海水状况可能波动很大，如由裂殖壶菌（Schizosphaerella spp。）依次控制的间隔变化，在一般的贫营养条件下旺盛的营养状况（由于暴风雨，地表水中的养分暂时可用）和深海隐藻（Crepidolithus spp。）。居住者。这项工作的结果非常适合于孤立盆地模型。 （c）2007 Elsevier B.V.保留所有权利。

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