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本文从岩性、岩相、旋回及演化等方面讨论陕西焦坪侏罗系延安组和直罗组的沉积特征。岩性特征表明,延安组属灰色复陆屑建造,直罗组为红色复陆屑建造。根据沉积剖面结构、成因标志划分出河床滞留、河床、天然堤、决口扇、河漫滩、洪泛平原和岸后沼泽等相,组成具二元结构的旋回。作者重点剖析J_(1-2)y_2和J_2Z_1二段的剖面结构,确定前者为高弯度河,后者为低弯度河。延安组属于气候温湿、沼泽发育的冲积平原,后期转向半干旱气候。古河流由低弯度河向高弯度河,接着又向小型高弯度河方向演化。低弯度河两侧利于成煤。直罗组属半干旱气候的冲积平原,演化特征与上述情况相似,但无沼泽沉积。总之,本区随着构造向稳定状态发展,建造由构造控制转变为古地理控制。
This paper discusses the sedimentary characteristics of the Jurassic Yan’an and Zhiluo formations in Jiaoping, Shaanxi Province from aspects of lithology, lithofacies, cycle and evolution. The lithological characteristics show that the Yan’an Formation is composed of the gray complex continental litter and the Zhiluo Formation is the red complex continental litter. Based on the sedimentary profile structure and genesis sign, the sediments of riverbed, riverbed, natural dike, crevasse, floodplain, flood plains and shore swamp are divided to form a cycle with binary structure. The author focuses on analyzing the section structure of the J_ (1-2) y_2 and J_2Z_1 sections, confirming that the former is a high-crooked river and the latter is a low-crooked river. The Yan’an Formation belongs to the alluvial plain where the climate is warm, humid and marsh, and turns to semi-arid climate later. The ancient river flows from low-crooked river to high-crooked river and then to small-high-crooked river. Low curvature of the river on both sides conducive to coal. The Zhiluo Formation belongs to the alluvial plain in the semi-arid climate. Its evolution characteristics are similar to the above, but no swamp deposition. In short, as the structure developed toward a steady state, the construction turned from tectonic control to paleogeographic control.