鄂尔多斯盆地西北缘中奥陶系世发现等深岩丘
- 收稿日期:
2025-06-23
- 网络出版日期:
2025-11-04
摘要: 【目的】鄂尔多斯盆地西缘及南缘奥陶系等深流沉积极为发育，沉积现象丰富，是等深流沉积研究的理想地区。在鄂尔多斯盆地西缘奥陶系克里摩里组发现了一种特殊的等深流沉积，即等深岩丘。【方法】通过野外露头测量、薄片及古水流等资料，研究了等深岩丘的形成机理。【结果】（1）研究区泥晶、粉晶及含泥等深流沉积极为发育。岩性主要为深灰色斑状薄层泥晶及粉晶石灰岩，界面多为波状，透镜状较为明显，断续顺层分布；水平层理、波状层理及侵蚀面较为常见；生物碎屑较多，生物扰动及潜穴发育；古水流方向为北东向，大致平行斜坡。（2）等深流沉积具丘状外形，呈北西-南东向展布，大致平行岸线，为较为典型的等深岩丘。（3）等深岩丘内发育次级等深流丘状体，具有明显的丘状外形，岩性为泥晶及粉晶石灰岩，下部及上部为含泥石灰岩夹极薄层泥岩。厚度152 cm，可分为11期，内部发育4个小型丘状体，丘状体内部发育一系列进积沉积，整体呈细-粗-细沉积序列。生物扰动及潜穴极为常见。（4）等深岩丘可分为早期萌生、中期成型及晚期衰减三个阶段。其主要为高能等深流的次生环流作用而成。高能的等深流在向北东运动过程中，螺旋型次生环流可发生侵蚀及沉积作用而形成等深流水道。同时，逆时针运动的次生环流可对沉积物进行搬运，在等深流水道向海盆一侧形成丘状等深流沉积。【结论】本研究明确了等深岩丘的沉积特征、形成过程，进而建立了其沉积模式，不仅为等深岩丘的研究增加了又1实例，还可帮助研究区等深流环流系统的重建及古环境的恢复。
Mounded Contourite in Middle Ordovician, northwestern Margin of Ordos Basin
- Received Date:
2025-06-23
- Available Online:
2025-11-04
Abstract: [Objective]Contourites well developed along southern and western margin of Ordos Basin, where sedimentary characteristics very abundant. It is ideal area of research contourites. The mounded contourite, a special type of contourite formed in Kelimoli formation of Ordovician in western margin of Ordos Basin. [Methods] Using outcrop, thin section, and paleacurrent, mechanism of mounded contourites had been researched.
[Results] (1) Micrite-, calcisiltite-, and muddy contourites are well favour in the study area. The lithology is mainly dark grey motted thin micrtici and calsisiltitic limestone with wavy boundary. They are lenticular-shape with unstabe along layer. Horizontal-, wavy- bedding, erosive surfaces are usually founded. Bioclastic fragments are relative rich. Bioturbation and burrow are well developed. And the paleocurrent direction is northeast, paralleling to slope. (2) Mounded contourites are mounded shape, and NW-SE orientation, about parallel to slope. (3) Contourites dunes developed in mounded contourites showing mounded shape are micrite and calcisiltite, some muddy limestone interbedded very thin mudstone in lower and upper parts. The thickness of mounded contourites being fine-coarse-fine cycle, is 152 cm, can be divided into 11 units. 4 small mounded contourites developed with a series progradation. Bioturbation and burrows are usually formed. (4) The mounded contourite can be divided into early initial, middle formative and late decline stages. They were resulting from secondary flow showing helical feature when high energy contour current moved northeastward. Helical flow can lead to erosion and deposition and form moat. Anticlockwise secondary flow also can transport sediment, and develop mounded contourite on the side of moat facing to deep sea basin. [Conclusion] This study demonstrate characteristics, processes, and depositional model of mounded contourite, not only add one example of mounded contourites, but also help to reconstruct contour current circulation and recover the palaeoenvironment.
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