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Paleogeographic reconstructions and stratigraphy of the Upper Thumb Member of the Horse Spring Formation, western Lake Mead, NV.

机译：内华达州米德湖西部马斯普林地层上拇指成员的古地理重建和地层学。

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摘要

This study focuses on the upper Thumb Member stratigraphy of the western Lake Mead Domain within the central Basin and Range region. The central Basin and Range is an east-west trending corridor extending from the southwestern edge of the Colorado Plateau west to the Sierra Nevada. During the Miocene epoch, the Horse Spring Formation was deposited into a single or multiple basins before and during Basin and Range extension. The Thumb Member of the Horse Spring Formation (∼17/16.5 Ma -- 14.5 Ma in the western Lake Mead area) records much of the early syndepositional deformation in the Lake Mead region and will be the focus of this study. The upper Thumb Member (∼15.5 -- 14.5 Ma) is a laterally extensive, dominantly sandstone unit containing several interbedded tuff units that have been dated and/or correlated throughout the basin.;This study concentrates on the development of, and sedimentation in, basins and sub-basins that were formed by the normal and strike-slip faulting that accommodated large-magnitude crustal extension within the central Basin and Range. Basin stratigraphy and paleogeography was assessed by studying facies changes, both laterally and vertically. The sedimentologic and stratigraphic data obtained as part of this study aided in better understanding the controls on sedimentation and the effects of faulting within the basin. The effects of paleoclimate and paleotopography were also evaluated with respect to sedimentation rates and deposition of the upper Thumb Member into these basins.;Due to the numerous tuff units present throughout the strata of the upper Thumb Member, geochronologic correlations were made along with correlations based on lithostratigraphy. These correlations were then used to create paleogeographic reconstructions of the basin at progressive time intervals.;Six paleogeographic maps were made to represent depositional environments and facies distributions over significant time intervals or at a specific time-slice focused on one well-dated and extensive tuff unit. The upper Thumb Member section was divided into intervals based on important tuffs that were correlated throughout the basin or marker beds such as a distinct megabreccia and associated debris flow deposit. The paleogeographic maps presented are as follows: 1) 15.5 -- 15.4 Ma, which spans from the upper contact of the middle Thumb Member conglomerate to just below the crystal rich tuff, 2) 15.35 Ma time-slice, which depicts the basin at the time of the crystal rich tuff deposition, 3) 15.35 -- 15.09 Ma, which spans from the crystal rich tuff to the crystal poor tuff, 4) 15.09 -- 14.8 Ma, which spans from the crystal poor tuff to the Christmas tree tuff, 5) ∼ 14.7 Ma time-slice, which depicts the basin at the time of megabreccia 4 and debris flow 2 deposition, and 6) 14.8 -- 14.5 Ma, which spans from the Christmas tree tuff to the contact of the Thumb Member with the Bitter Ridge Limestone Member.;The upper Thumb Member records the onset of faulting in the Gale Hills along the Government, West Fortress, and Southern Gale Hills normal-oblique faults between 15.5 and 15.35 Ma. The right-lateral Las Vegas Valley shear zone propagated into the study area between 15.35 Ma and 15.0 Ma. The Bitter Spring Valley fault became active after ∼ 14.8 Ma. The White Basin fault is active starting at ∼14.5 Ma. These faults were responsible for the initial creation of sub-basins within the Thumb Member basin and significantly influenced deposition both during and after Thumb Member deposition.
机译：这项研究的重点是中部盆地和山脉地区西部米德湖地区的上部拇指成员地层。中部盆地和山脉是一条东西向的趋势走廊，从科罗拉多高原的西南边缘一直延伸到内华达山脉。在中新世时期，马泉组在盆地和范围扩展之前和期间沉积到一个或多个盆地中。马泉组的拇指成员（米德湖西部地区约为17 / 16.5 Ma-14.5 Ma）记录了米德湖地区的大部分早期沉积变形，将成为本研究的重点。上部拇指构件（〜15.5-14.5 Ma）是侧向广泛的砂岩单元，包含几个相互交错的凝灰岩单元，这些单元在整个盆地中都已过时和/或相关联;该研究的重点是由正断层和走滑断层形成的盆地和子盆地，这些断层容纳了盆地中部和山脉的大幅度地壳扩展。通过研究横向和纵向的相变来评估盆地地层和古地理。作为这项研究的一部分而获得的沉积学和地层数据有助于更好地了解沉积物的控制和盆地内断层的影响。还评估了古气候和古地形对这些盆地中上部拇指构件的沉积速率和沉积的影响。由于上部拇指构件的整个地层中存在大量凝灰岩单元，因此进行了地质年代学相关性和相关性在岩画上。这些相关性随后被用于以渐进的时间间隔创建盆地的古地理重建。制作了六张古地理图以表示在重要的时间间隔内或在特定时间段上的沉积环境和相分布，重点是一个良好的时间范围和广泛的凝灰岩单元。根据重要的凝灰岩，在整个盆地或标志层（如明显的角砾岩和相关的泥石流沉积物）相关的基础上，将上部大拇指构件部分划分为多个间隔。呈现的古地理图如下：1）15.5-15.4 Ma，其范围从中部拇指成员砾岩的上接触点到恰好在富含水晶的凝灰岩之下，2）15.35 Ma的时间切片，描绘了盆地的盆地。富含水晶的凝灰岩沉积时间，3）15.35-15.09 Ma，从富含水晶的凝灰岩到较差的凝灰岩，4）15.09-14.8 Ma，从富含水晶的凝灰岩到圣诞树的凝灰岩， 5）〜14.7 Ma的时间切片，描绘了角砾岩4和泥石流2沉积时的盆地，以及6）14.8-14.5 Ma，其范围从圣诞树凝灰岩到拇指成员与Bitter Ridge石灰岩成员。；上部Thumb成员记录了沿政府，西要塞和南部Gale Hills正常倾斜的断层在15.5至15.35 Ma之间的大风山断裂的发生。右侧的拉斯维加斯谷剪切带在15.35 Ma至15.0 Ma之间传播到研究区域。苦泉谷断裂在约14.8 Ma之后开始活动。白盆地断裂始于〜14.5 Ma。这些断层是造成拇指成员盆地内盆地形成的初步原因，并且在拇指成员沉积期间和之后都对沉积产生了重大影响。

著录项

  • 作者

    Cains, Amanda Ila.;

  • 作者单位

    Northern Arizona University.;

  • 授予单位 Northern Arizona University.;
  • 学科 Geology.;Sedimentary Geology.
  • 学位 M.S.
  • 年度 2014
  • 页码 243 p.
  • 总页数 243
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 新闻学、新闻事业;
  • 关键词

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