Influence of paleo-Trade Winds on facies patterns of the Cambrian Shanganning Carbonate Platform, North China
Influence of paleo-Trade Winds on facies patterns of the Cambrian Shanganning Carbonate Platform, North China
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DOI：
10.1016/j.palaeo.2019.109556
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发表时间：
2020-08
期刊：
影响因子：
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通讯作者：
Chen Hu;Zhang Yuanfu;Jijun Tian;Wenfeng Wang;C. Han;Haichao Wang;Xin Li;Shuo Feng;Chao Han;T. Algeo
中科院分区：
文献类型：
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作者：
Chen Hu;Zhang Yuanfu;Jijun Tian;Wenfeng Wang;C. Han;Haichao Wang;Xin Li;Shuo Feng;Chao Han;T. Algeo
中国克拉通北部山甘宁碳酸盐岩台地在寒武纪处于信风带，影响了其相的发育。近年来，从这些单元中回收了大量的钻井岩心，但这一大型(约2.0亿×105km2)碳酸盐台地体系的沉积环境和相结构尚未详细报道。在这项研究中，我们综合了从露头和钻芯中收集的沉积学和磁性组构数据，以记录SCP内微相和相组合的变化，推断SCP的古风向和约束其古地理位置，并评价风成对台地发育的控制。这项分析记录了属于六种组构类型(泥岩、板岩、包岩、砂砾岩、框架岩和白云岩)的大量碳酸盐微相，以及较为罕见的硅屑沉积。这些微相属于代表潮坪、开阔台地、台地边缘、斜坡和深盆地沉积环境的相组合。磁化率(AMS)测量的各向异性得到了早、中、晚寒武世的平均古流方向，分别为距古北114°、63°和83°(±30°)，在13个地台边缘地点中有12个相对一致，所有矢量都被校正为寒武纪后~150°的NCC顺时针旋转。这些风向与SCP从早寒武世的古赤道以南到中寒武世的古赤道以北的位置一致。古信风影响了整个地台的相模式，产生了明显的迎风-背风分带。上风边缘以分选较好的蚝粒砾岩、珊瑚和海藻海绵骨架岩为主，背风边缘以分选较差的橄榄粒砾岩和细粒生物碎屑沉积为特征。本研究的创新之处在于：1)结合微相和AMS分析建立古风模式及其对古碳酸盐岩台地的影响；2)记录整个海盆的可量化沉积物性质的迎风-背风变化；3)约束寒武纪NCC的古半球位置。
The Shanganning Carbonate Platform (SCP) of the North China Craton (NCC) was located in the Trade Winds belt during the Cambrian, which influenced its facies development. In recent years, numerous drillcores have been recovered from these units, but the depositional environments and facies architecture of this large (~2.0 × 105km2) carbonate platform system have not yet been reported in detail. In this study, we integrate sedimentological and magnetic fabric data collected from outcrops and drillcores in order to document variation in microfacies and facies associations within the SCP, to infer paleowind directions and constrain the paleogeographic location of the SCP, and to evaluate eolian controls on platform development. This analysis documented numerous carbonate microfacies belonging to six fabric types (mudstone, wackestone, packstone, grainstone, framestone, and dolostone) along with rarer siliciclastic sediments. These microfacies belong to facies associations representing tidal flat, open platform, platform margin, slope, and deep basinal depositional environments. Anisotropy of magnetic susceptibility (AMS) measurements yielded mean paleocurrent directions for the Early, Middle, and Late Cambrian of 114°, 63°, and 83° (± ~30°) from paleo-north, respectively, that were relatively consistent for 12 out of 13 platform-margin sites, all vectors being corrected for a post-Cambrian ~150° clockwise rotation of the NCC. These wind orientations are consistent with the SCP shifting from south of the paleo-Equator in the Early Cambrian to north of it by the Middle Cambrian. Paleo-Trade Winds influenced facies patterns across the platform, producing a distinct windward-leeward zonation. The windward margin is characterized by well-sorted oolitic grainstone, as well as (favositids) coral and (dasycladacean) algal-sponge framestone, and the leeward margin by poorly-sorted oolitic wackestone-grainstone and fine bioclastic sediments. The present study is innovative in 1) integrating microfacies and AMS analyses in order to establish paleowind patterns and influences on an ancient carbonate platform, 2) documenting windward-leeward variation in quantifiable sediment properties across the SCP, and 3) constraining the paleo-hemispheric location of the NCC during the Cambrian.