河南省济源盆地下侏罗统鞍腰组重力流沉积特征及其构造意义*

在详细野外剖面工作的基础上,通过岩性特征、沉积构造及沉积序列等的系统观察研究,发现济源盆地下侏罗统鞍腰组重力流沉积由滑塌沉积、砂质碎屑流沉积和浊流沉积构成。滑塌沉积以砂岩和泥岩的混杂、岩层的滑动变形以及泥岩呈碎块被卷入砂岩层中为特征;砂质碎屑流沉积常呈厚层块状,颗粒分选和磨圆较差,杂基较多,可见漂浮于层内的石灰岩砾石;常见的浊流沉积分为2种类型: 具有明显正粒序结构的浊流沉积和砂泥岩薄互层的浊流沉积,可用鲍马序列来描述。鞍腰组重力流沉积可划分为3个沉积序列: 序列A记录了滑塌沉积→砂质碎屑流沉积→浊流沉积→深湖沉积的转换过程;序列B表现为砂质碎屑流与浊流沉积的叠覆;序列C由浊流及湖泊沉积构成,并经历了由序列A→序列B→序列C的沉积演化过程。重力流的形成受秦岭造山带于早侏罗世沿三门峡—鲁山—舞阳断裂发生逆冲推覆作用的控制,其沉积演化指示了秦岭造山带造山作用由强到弱的过程。

Sedimentary characteristics and tectonic significance of gravity flow deposits of the Lower Jurassic Anyao Formation in Jiyuan Basin,Henan Province

On the basis of the detailed field work,the authors focus on the gravity flow deposits of the Lower Jurassic Anyao Formation of Jiyuan Basin,Henan Province. Deposits of slump,sandy debris flow and turbidity current are identified through the systematic researches on lithologic characteristics,sedimentary structures and sequences. Slump deposits are characterized by the mixed sandstones and mudstones,sliding deformation and convolute mudstone fragments. The sandy debris flow deposits are usually of massive structures. The grains with matrix supported are poor sorted and rounded. Limestone gravels are often floating in the sandstone strata. The most common turbidity current deposits can be divided into two types: One with nomal grading beddings and the other is composed of thin interbedded sandstones and mudstones. They all can be described with the Bouma sequence. Three evolutive sequences of the gravity flow deposits are identified from the bottom to the top. Sequence A records a conversion of slump deposits into sandy debris flows,then into turbidity currents and finally into deep lacustrine deposits. Sequence B represents superimposition of sandy debris flows and turbidity currents. Sequence C is composed of turbidity currents and deep lacustrine deposits. The gravity flow deposits are controlled by the thrusting of Qinling Orogen along the Sanmenxia-Lushan-Wuyang fault during the Early Jurassic. The sedimentary evolution of the gravity flow deposits can be used to demonstrate the waning orogensis of the Qinling Orogen.