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61.
Soft‐sediment deformation occurs in ancient eolian dune deposits, but understanding its extent and the conditions and forces behind the deformation often remains elusive. Here we gain insight into the aerial extent and environmental conditions related to intense soft‐sediment deformation, based on an exceptional three dimensional (3D) exposure of eolian dune deposits and preserved geomorphic landscape expressions in the Jurassic Navajo Sandstone at White Pocket, Vermilion Cliffs National Monument, Arizona. Deformation features include elongate northeast trending decameter‐scale mounds and raised ridges cored by deformed and upturned eolian dune sets, overlain by a massive blanket sandstone with breccia blocks. The geomorphic mounds display ~40–60 m spacing, roughly perpendicular to the southerly paleoflow dune foreset directions. The geometry of the deformation is imaged by oblique aerial photography using cameras mounted on a remote control airplane and high resolution panoramas with a robotic camera mount. We interpret the exquisitely preserved deformation features as liquefaction‐induced ground failure, consistent with theoretical and laboratory studies of deformation in saturated sand. A shallow water table affected by differential dune loading facilitated lateral spreading and failure. The transition to steady‐state flow liquefaction near the top of the shallow water table destroyed original sedimentary structure, creating a massive sand blanket that entrained brecciated blocks ripped up during flow. The water‐pressurized, upwelled sediment created the mounds (a relief inversion). In underlying deformed dune sets, deformation was intense but sedimentary structure was not obliterated as deformation progressed from initial cyclic mobility to strain‐softening, but ceased prior to steady‐state flow liquefaction. The spatial extent, topographic relief, and intensity of dynamic deformation suggest an origin of strong ground motion driven by long‐duration surface waves of a large earthquake (> Mw 7–8), possibly related to back arc thrusting from Jurassic subduction of the Pacific plate under North America. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
62.
通过对东濮凹陷北部古近系沙河街组的大量岩心观察和区域沉积-构造演化的分析,认为原地形
成的震积岩普遍发育,以独具特色的软沉积物同生变形构造为主,主要有液化砂岩脉、火焰构造、枕状构造、
球-枕构造、假结核、泄水构造、液化卷曲变形构造、液化水压破裂构造和粒序断层等,并综合出原地形成的
震积岩软沉积物同生变形构造的垂向序列,自下而上依次为液化砂岩脉段、液化角砾岩段、液化卷曲变形段、
震塌岩段以及液化均一层段,而球-枕构造和液化砂岩脉的形成主要与厚层泥岩夹砂岩有关,在震积序列的各
部位均可出现。在东濮凹陷古近系沙河街组中识别出液化角砾岩、震褶岩、震塌岩 ３种类型的震积岩。震积岩
的识别,为长期以来人们对东濮凹陷古近系沙河街组砂体沉积的 “ 重力流”与 “ 牵引流”以及相应盐岩成因的
“ 深水成盐”与 “ 浅水成盐”的争论,从岩石学特征方面提供了一些肯定或否定的证据,使这些问题逐渐趋于
明朗化。另外,震积岩是潜在的有利储集体,可能为东濮凹陷的勘探开发提供一个新的方向。 相似文献
63.
作者对浙西寒武系碳酸盐岩做系统调查时发现,在开化裴岭脚产出的大陈岭组碳酸盐岩中含有大量的液化泥晶脉、微同生变形构造、角砾岩及与之伴生的浊积岩等典型的地震-海啸沉积标志。根据震积岩特征及其在剖面上的分布,该地大陈岭期的地震活动可以分为两期:第一期以震积岩(A,液化亮晶脉和泥晶脉)、啸积岩(B,具丘状层理或平行层理的内碎屑白云质灰岩)、震浊积岩(C,具递变层理或鲍马序列且层面上有槽模构造的砾屑白云质灰岩或砂屑白云质灰岩)和背景沉积(D)组成的A-B-C-D沉积序列为特征;第二期为震积岩(A,液化亮晶脉和泥晶脉、震裂岩、震褶岩和内碎屑角砾岩等)和沉积背景(D)组成的A-D沉积序列。而在常山白石和芳村的大陈岭组剖面,上述特征不明显,但局部能看到液化变形构造。往南东至江山的碓边则不见震积岩特征。从震积岩的分布上分析,浙西大陈岭期的地震活动不受控于江绍深断裂,应与开化—淳安大断裂的形成有关,是开化—淳安大断裂形成于早古生代的一个证据。此外,值得一提的是,这是确凿的后震旦纪的“Molartooth”。 相似文献
64.
红丝石是产于山东临朐中奥陶统下部的一类具红色丝线状弯曲纹层的用于加工工艺品(砚台、笔筒等)的微晶碳酸盐岩。产有红丝石的这部分地层,厚约60m,被称为“红丝石层”。根据野外观测、室内鉴定及地震地质对比,从临朐红丝石层中识别出了具卷曲变形(包括塑性和半塑性变形)、环形纹层变形、微断裂(包括阶梯状和共轭微断裂)、震裂隙和震碎角砾等地震成因岩石构造的震积岩层。这些震积岩是中奥陶世古地震事件的记录,红丝石仅是古地震作用形成的一种常见的震积岩,由于在中奥陶世郯庐带内也有震积岩生成,因此认为这些地震记录是古郯庐带在中奥陶世强烈活动的证据。 相似文献
65.
川西南荥经坳陷开展了多口页岩气调查井及参数井(CYY1,YD1和YD2)的钻探。通过大量岩心观察和沉积构造特征分析,在中下奥陶统识别出大量软沉积变形构造及脆性变形构造,包括重荷模、火焰构造、球-枕构造等负载相关构造,液化砂岩脉、液化泥砾等液化构造,以及布丁构造、卷曲变形、震裂缝、震裂角砾、同沉积断层等,具有典型地震导致的同生及准同生构造变形特征。记录显示至少发生了2次地震事件,并引发海啸以及多次余震。该区震积岩的发现表明早中奥陶世曾发生明显的构造活动,是加里东早期都匀运动一次构造运动幕的响应,这对川中隆起具有重要意义。构造运动导致荥经坳陷周缘断裂活动并引发地震。地震对沉积地层的改造极大地改善了研究区油气储集层条件,更利于油气的运移。 相似文献