The fluid mud flow deposits represent mud caps of Holocene hybrid event beds from the widest and gentlest shelf
The fluid mud flow deposits represent mud caps of Holocene hybrid event beds from the widest and gentlest shelf
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流体泥浆流沉积物代表了来自最宽和最平缓陆架的全新世混合事件层的泥盖
DOI：
10.1016/j.margeo.2019.06.004
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发表时间：
2019-09
期刊：
影响因子：
2.9
通讯作者：
Fu Chao
中科院分区：
文献类型：
--
作者：
Shan Xin;Shi Xuefa;Qiao Shuqing;Jin Lina;Otharan German A.;Zavala Carlos;Liu Jianxing;Zhang Yingqiu;Zhang Dan;Xu Taoyu;Fu Chao
沉积物重力流沉积物顶部的泥帽的内部结构至今尚未探索。在最宽、最平缓的陆架（东海陆架）上，我们识别出了四个混合事件层。划分出块状砂、混乱泥和均质泥3种岩相类型。均质泥代表这些混合事件层的泥帽。在均质泥浆和混沌泥浆中进行的扫描电子显微镜显示存在符合砂级碎屑的泥浆聚集体（泥浆碎屑）。聚集体的化学分析表明，存在丰富的石膏/硬石膏和粘土矿物成分，以及残余的石英，白云母和长石，表明与侵蚀事件和内碎屑起源的起源。垂向缩短、变形及泥质碎屑孔隙的发育表明，沉积物的侵蚀埋藏较浅，泥质沉积物仍处于松散状态，水饱和状态。在泥帽中不存在背景沉积，因为我们在岩心图像和X射线照片中没有观察到任何生物扰动间隔。在均质泥浆中缺乏层状泥浆和同沉积遗迹化石，表明其起源与流体泥浆流有关。如以前的实验所证明的，泥帽可能与头部侵蚀和剪切的泥质泥石流/泥流的上表面，产生一个缓慢移动的流体泥流。我们的研究进一步证实，在以泥浆为主的H3分区的混合事件层中不存在层压砂/粉砂（H4分区）。泥质泥石流/泥流的头部侵蚀不允许形成层状H4分裂，这是因为由母泥质泥石流衍生的流体泥流主要由小于30 μm的颗粒组成，可以有效地阻尼湍流。对流体泥流存款样品进行的粒度分析落入了Pelagites/hemipelagites区（T区），表明流体泥流沉积也是T区的候选者，该区域不一定反映非应力环境下的沉积。
The internal fabric of mud caps, which are on top of sediment gravity flow deposits, remains unexplored so far. We identified four hybrid event beds on one of the widest and gentlest shelf (East China Sea Shelf). Three types of lithofacies, including massive sand, chaotic mud and homogeneous mud, were distinguished. Homogeneous mud represents mud caps of these hybrid event beds. Scanning electron microscopy performed in both homogeneous mud and chaotic mud has revealed the presence of mud aggregates (mud clasts) conforming sand-size clasts. Chemical analyses of the aggregates show the presence of abundant gypsum/anhydrite and clay mineral components as well as relicts of quartz, muscovite and feldspar, suggesting an origin related to erosional events and an intraclast origin. The vertical shortening, deformation together with the pore spaces of mud clasts indicate a shallow burial depth of erosion, where mud sediments were still unconsolidated and water-saturated. No background sedimentation is present in the mud caps, because we did not observe any bioturbated interval in core images and X-radiographs. The lack of laminated muds and synsedimentary trace fossils in the homogeneous muds suggest an origin related to fluid mud flows. As proved on previous experiments, the mud caps could be related to head erosion and shearing of the muddy debris flow/mud flow's upper surface which generated a slower moving fluid mud flow. Our study further confirms that no laminated sand/silt (H4 division) would be present in hybrid event beds with mud-dominated H3 division. Head erosion of muddy debris flow/mud flow would not allow laminated H4 division to form, because the fluid mud flow derived from the parent mud-dominated debris flow was mainly composed of grains smaller than 30 μm which can effectively damp turbulence effectively. Grain size analysis performed on samples from fluid mud flow deposit fall into pelagites/hemipelagites area (T area), suggesting that fluid mud flow deposits are also a candidate for T area, and the area does not necessarily reflect a deposition under un-stressed environment.
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