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首页> 外文学位 >Development of the Rocky Mountain foreland basin: Combined structural, mineralogical, and geochemical analysis of basin evolution, Rocky Mountain thrust front, northwest Montana.
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Development of the Rocky Mountain foreland basin: Combined structural, mineralogical, and geochemical analysis of basin evolution, Rocky Mountain thrust front, northwest Montana.

机译：落基山前陆盆地的发展：盆地演化的结构，矿物学和地球化学分析，落基山逆冲前缘，蒙大拿州西北部。

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摘要

The sub-Middle Jurassic unconformity exhumed at Swift Reservoir, in the Rocky Mountain thrust belt of Montana, exposes structures that call for a re-evaluation of the deformation history at this locale. The unconformity separates Late Mississippian Madison Group carbonate (∼340 Ma) from the transgressive basal sandstone of the Middle Jurassic (Bajocian-Bathonian) Sawtooth Formation (∼170 Ma). Fieldwork established that northwest-trending, karst-widened fractures (grikes) are filled with cherty, phosphatic sandstone and conglomerate of the Sawtooth Formation and penetrate the Madison Group for 4 meters below the unconformity. Clam borings, filled with Sawtooth sandstone, pierce the unconformity surface, some of the fracture walls, and also perforate rounded clasts of Mississippian limestone that lie on the unconformity surface within basal Sawtooth conglomerate. Following deposition of the overlying foreland basin clastic-wedge, the grikes were stylolitized by layer-parallel shortening and buckled over fault-propagation anticlinal crests in the Late Cretaceous-Paleocene fold-and-thrust belt. The model proposes that the grikes record uplift and erosion followed by subsidence as the Rocky Mountain foreland experienced elastic flexure in response to tectonic loading at the plate boundary farther to the west during Early Jurassic; the forebulge opened strike-parallel fractures in the Madison Group that were karstified. The grike system contributes to the secondary porosity and permeability of the upper Madison Group; a major petroleum reservoir in the region. Grikes acted as fluid pathways during basin evolution as seen from the clay mineral assemblage and fluid inclusions contained within the grike fill. Mixed-layer illite-smectite (I/S) indicates that the grikes did not exceed 210° C (complete smectite-illite transition). The illite likely resulted from supersaturated fluids flushing through the foreland at the onset Laramide orogeny and may have been coincident with hydrocarbon migration. Hydrocarbon inclusions contained within the grike cements were trapped at temperatures ranging from 110°-170° C; correlative with the clay temperature calculations. Recognition of the fractures as pre-middle Jurassic revises previous models, which related them to Cretaceous fracturing over the crests of fault-propagation folds, substantially changing the understanding of the hydrocarbon system.
机译：在蒙大拿州落基山冲断带的斯威夫特水库中发现了侏罗纪次中部不整合面，露出了需要重新评估该位置变形历史的构造。不整合面将中晚期侏罗纪（Bajocian-Bathonian）锯齿形海床（〜170 Ma）的密西西比阶麦迪逊组碳酸盐（〜340 Ma）与海侵基底砂岩分开。野外工作确定，西北趋势，岩溶加宽的裂缝（碎石）充满了锯齿状的钙质，磷化的砂岩和砾岩，并在不整合面下方穿透了4米的麦迪逊群。充满锯齿状砂岩的蛤lam钻孔刺穿不整合面，一些裂缝壁以及密苏里州石灰岩的圆形圆形碎屑，这些碎屑位于基底锯齿砾岩的不整合面上。上覆前陆盆地碎屑楔沉积后，通过层状平行起皱将砂砾钉化，并在晚白垩世-古新世褶皱-冲断带中的断层传播背斜波峰上弯折。该模型提出，在侏罗纪早期，岩石山记录了隆起和侵蚀，然后下沉，因为落基山前陆响应于更西面的板块边界的构造荷载而经历了弹性挠曲。前隆在麦迪逊组中形成了与岩溶有关的走向平行的裂缝。碎屑系统有助于麦迪逊组上部的次生孔隙度和渗透率。该地区主要的石油储藏库。从盆地填充物中的粘土矿物组合和流体包裹体来看，在盆地演化过程中，石充当了流体通道。混合层伊利石-蒙脱石（I / S）表明，该砂砾未超过210°C（完全蒙脱石-伊利石转变）。伊利石可能是由于拉拉米德造山运动开始时通过前陆冲刷过饱和流体引起的，并且可能与烃运移同时发生。水泥中包含的碳氢化合物夹杂物的捕集温度范围为110°-170°C；与粘土温度计算相关。侏罗纪前中侏罗世对裂缝的认识修改了以前的模型，使它们与断层传播褶皱顶上的白垩纪裂缝有关，从而大大改变了对油气系统的认识。

著录项

  • 作者

    Ward, Emily M. Geraghty.;

  • 作者单位

    University of Montana.;

  • 授予单位 University of Montana.;
  • 学科 Geology.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 188 p.
  • 总页数 188
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;
  • 关键词

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