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首页> 外文学位 >Petrography and geochemistry of Pennsylvanian black shales in offshore and nearshore stratigraphic settings in Midcontinent and Illinois Basins.
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Petrography and geochemistry of Pennsylvanian black shales in offshore and nearshore stratigraphic settings in Midcontinent and Illinois Basins.

机译：中大陆和伊利诺斯盆地近海和近岸地层环境中宾夕法尼亚黑页岩的岩石学和地球化学。

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摘要

Although all Midcontinent Pennsylvanian black shales were once regarded as shallow water deposits, the widespread, phosphatic, conodont-rich black shales that lack benthic fossils and lie stratigraphically between marine transgressive and regressive limestones in a cyclothem (T-R sequence) are now recognized as offshore sediment-starved condensed-section deposits, which accumulated slowly in anoxic water below a pycnocline. In contrast, less widespread phosphate- and conodont-poor black shales that typically overlie coals (or other flooding surfaces), tend to grade vertically and laterally into shoreline/terrestrial deposits and often contain a sparse benthic fauna probably formed under conditions of organic overload in nearshore dysoxic environments. Recently, Coveney et al. (1991) suggested that some widespread, conodont- and Mo-rich black shales interpreted as offshore shales by Heckel (1977) were deposited rapidly in a shallow shoreline environment. This dissertation investigated several black shales of different stratigraphic settings in the Middle-Upper Pennsylvanian succession of midcontinent North America in order to characterize their petrography and geochemistry in an attempt to clarify the emerging depositional models for black shales and to constrain the possibilities as to what the geochemical evidence actually means. The black facies of offshore shales included in this study (from the Midcontinent and Illinois Basins) display lenticular lamination, with lenses composed of a fine “hash” of quartz crystals (that may be compacted radiolarians) within an organic-rich clay matrix containing fine quartz silt. The SEM microfabric of offshore shales has an overall preferred orientation of clay flakes. Geochemical analysis shows that offshore black shales are enriched in metals and have V/(V + Ni) values suggesting an anoxic-to-euxinic depositional environment. In contrast, nearshore shales display variable and often random SEM particle orientation, contain abundant plant fragments and coarser quartz grains, and have significantly lower metal concentrations and V/(V + Ni) values suggesting dysoxic depositional environments. Petrographically and geochemically, the much debated Mecca Quarry black shale fits the characteristics of offshore black shales in the Illinois Basin, and thus was probably deposited in an environment similar to that of other Illinois offshore shales, which is the more variable, shoreline-influenced (as opposed to shoreline-located), nearer-shore edge of the overall offshore black shale environment.
机译：尽管宾夕法尼亚州中部的所有黑色页岩曾经被认为是浅水沉积物，但广泛的，富含磷酸盐，牙形石的黑色页岩缺乏底栖化石，并且地层间位于海侵和退回石灰岩之间（TR层序），现已被认为是近海沉积物。饥饿的凝结断面沉积物，这些沉积物在比可可林以下的缺氧水中缓慢积累。相比之下，磷酸盐和牙形石贫乏的黑色页岩通常分布在煤层（或其他洪水表面）上，往往在垂直和横向上分级为海岸线/陆地沉积物，并且通常包含稀疏的底栖动物群，可能是在有机超载条件下形成的。近岸缺氧环境。最近，Coveney等。 （１９９１）认为，Ｈｅｃｋｅｌ（１９７７）解释为近海页岩的一些分布广泛的，牙形和富钼的黑色页岩在浅海岸线环境中迅速沉积。本论文研究了北美中部宾夕法尼亚州中上宾夕法尼亚地区的几套不同地层环境的黑色页岩，以表征其岩相学和地球化学特征，以试图阐明新兴的黑色页岩沉积模型，并限制可能存在的黑页岩。地球化学证据实际上意味着。这项研究中（来自中大陆和伊利诺伊盆地）的近海页岩的黑色相显示出透镜状的层状结构，透镜由细的“哈希”石英晶体（可能是压实的放射线虫）组成，并富含有机物的粘土基质中。石英粉砂。海上页岩的SEM微观结构总体上优先选择粘土薄片。地球化学分析表明，离岸黑色页岩富含金属，并且具有V /（V + Ni）值，表明存在缺氧到富余的沉积环境。相比之下，近岸页岩显示出变化且通常是随机的SEM粒子方向，包含丰富的植物碎片和较粗的石英颗粒，并且金属浓度和V /（V + Ni）值明显较低，表明存在缺氧的沉积环境。在岩石学和地球化学方面，备受争议的麦加采石场黑色页岩符合伊利诺伊盆地的海上黑色页岩的特征，因此可能沉积在与其他伊利诺伊州海上页岩相似的环境中，即海岸线变化<斜体>受影响的（而不是海岸线-位于），是整个离岸黑色页岩环境的近岸边缘。

著录项

  • 作者

    Bisnett, Angela Jean.;

  • 作者单位

    The University of Iowa.;

  • 授予单位 The University of Iowa.;
  • 学科 Geology.
  • 学位 Ph.D.
  • 年度 2001
  • 页码 469 p.
  • 总页数 469
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;
  • 关键词

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