鄂北中生界多尺度、多类型、多成因软沉积变形构造的研究

A set of soft sediment deformation structure with characteristics of multi-scales, multi-types, multi-genesis, multi-layers, multi-periods, multi-locations, and multi-combinations was developed among the Jurassic and Cretaceous strata within a 300 kilometers long, 30 kilometers wide zone near Dongsheng–Hangjinqi-Wuhai district and the northeast suburb of Dongsheng, northern Ordos basin. Its feature of large scale, multiple type, high density and broad distribution is so rare that the dish structures there in lower Cretaceous glutenite can develop a width up to 10 meters and a height more than 2 meters. Heights of the soft deformation folds formed by large sliding deformations can also be developed up to several meters, with a visible continuous length of more than one hundred meters. In addition, there are a large number of meso-and micro-scale soft deformation structures (including several classifications that never reported). More attentions should be deserved as many of the large soft-sediment deformation structures were developed among the medium (1.5-2.5 meters thick) massive conglomerate layers with horizontal occurrences (fully shows that the former liquefication was very strong), which was rarely reported previously. Through detailed study of geometry features, formation mechanisms and spatial distribution rules of those soft sediment deformation structures, it can not only offer precious information for the research of Mesozoic tectonic movements and their evolutions(many large soft sediment deformation structures were related to earthquakes) in Ordos basin and Midwest China, but also supply important data for the study and exploration of the oil & gas resources in Ordos basin.

鄂尔多斯盆地北部的东胜—杭锦旗—乌海一带的300km长、30km宽的区带内及东胜东北郊的侏罗系和白垩系地层中发育了一套多尺度、多类型、多成因、多层段、多期次、多地点、多组合的软沉积变形构造。尺度之多、类型之多、密度之大、分布面积之广实属罕见，如下白垩统砂砾岩中的碟状构造的宽度最大可达10m以上，高度可达2m以上；大型的滑动变形形成的软变形褶皱高度也可达数米，可见连续长度达百余米。更为值得注意的是：许多大型软沉积变形构造发育在水平状的中厚层（厚度多在1.5-2.5m）块状砾岩中（充分表明当时的液化非常强烈），这在以前很少见报道。通过详细研究这些软沉积变形构造的几何学特征、形成机制及空间分布规律可以为丰富和完善沉积学基础理论和为鄂尔多斯盆地和中国中西部中生代的大地构造运动（许多大型的软沉积变形构造与强烈地震有关）及其演化提供宝贵资料，甚至还可以为鄂尔多斯盆地油气资源的研究和勘探提供重要的资料

鄂尔多斯北部的下白垩统中发育了一种不寻常的软沉积变形构造，它们与碟状构造非常相似。这种构造主要发育在鄂尔多斯市至杭锦旗的G109国道100余公里长的公路两侧的一些露头中。这种构造发育在下白垩统的一套黄褐色或灰白色的中厚层砾岩或砂砾岩中，在竖截面上其边缘翘起、中部平坦或下凹，与典型的碟状非常相似；所以，我们也把它称之为“碟状构造”。这种碟状构造的尺度总体很大，小型者的宽度一般在1~3m，高度多在0.5~1.5m，中大型者的宽度一般在5~6m，最大可近10m；高度多在1~1.5m，少数可达2m；其两侧翘起程度不同，有倾角小于45°的倾斜边，有倾角在45°~75°的陡斜边，还有倾角75°~90°的近直立边，甚至有大于90°的翻卷边；碟状构造之间为泄水形成的液化充填体，竖直面上多呈漏斗形、倒三角形、少数呈盘形狭缝形、花瓶形、柱形或浅盘形，其宽度多在数十厘米，大者可达2~3m，甚至更宽。岩性与碟状构造的主体岩性截然不同，为棕红色泥岩、泥质粉砂岩，由于风化淋滤这些泄水充填的棕红色泥岩、泥质粉砂岩呈黄褐色松散粉砂状，极易碎。.碟状构造一般发育在黄褐色或灰白色的中厚层辫状河砾岩或砂砾岩中，其底部多为湖相棕红色（有时夹少量灰色）泥岩或砂质泥岩，但由于液化流动而多呈块状，极易碎。碟状构造常与砂岩岩脉、液化脉、软变形层理或软变形褶皱等共生。碟状构造系泥底辟泄水形成的，认为是受强烈地震扰动所致，地震强度可达8~9级、甚至更高。地震与鄂尔多斯北部中生代强烈的构造运动有关。