摘要
陕西富平中—上奥陶统赵老峪组发育了一套半远洋的以薄板状和页状泥晶灰岩夹重力流碳酸盐岩为特征的斜坡相地层。重力流沉积按成因可划分为直移滑移体、滚动滑移体、碎屑流角砾灰岩、颗粒流角砾灰岩和浊流灰岩五种类型。笔者曾对其中能指示古斜坡和古流向的沉积构造、砾石长轴走向及古网格虫迹长轴方向进行了大量的实地测量。研究表明,该区在中、晚奥陶世时有一个向东南方向倾没的古斜坡,并存在着顺坡下流的重力流和平行斜坡等深线流动的等深流。
The Fuping region of Shaanxi Province lies to the eastern sector of the Weibei uplift in the southern margin of Ordos Basin. During the early Ordovician epoch, the Weibei area and the North China's platform is a unitary shallow water carbonate platform in which a suite of shallow water carbonate rock was deposited.Up to the middle-late ordovician epoch, the region subsided and become a continental margin of the back-arc basin and a suite of deep water carbonate rock was deposited. And the features of lithologic characters are lanellar and laminar micritic limestone, interbeded with the gravity-flow limestones.According to the origin, the gravity-flow limestones can be subdivided into five rock types, ( 1 ) translational slides; ( 2 ) rotational slides) ( 3 ) debris flow breccia limestones; ( 4 ) grain flow breccia limestones, and ( 5 ) turbidity current limestones.
Through observation and by surveying, the authors discovered that the slump structures of the translational slides, the undulations of superface and long dimensions of breccia limestones in the rotational slides, the dips of long dimesions of breccia limestones with grade and maximal flattened surface, current ripples,cross-laminations and trace fossils and so on, all can be used to judge the directions of the ancient continental slope and paleoflow.The studies have demonstrated that during the sedimentary period of the Zhaolaoyu Formation,the regional paleoslope was the southeast,and the gravity-flow deposits were-developed at the downward slope.The flow direction of the contourite was approximately swl5-20.It appears that there was probably an open oceanconnected with the Qinling ocean trough in the south of this region.
关键词
沉积
古斜坡
古流向
奥陶世
Zhaolayu Formation, gravity-flow, contour, Paleo-slope, Paleoflow direction
