Tectonic Stress Field Characteristics And Its Transition Laws And Tectonic-Sedimentary Framework In Mesozoic Ordos Basin

ABSTRACTThe tectonic stress field characteristics, transition laws and its control to sedimentation are revealed in the paper based on studying structural features and tectonic-sedimentary framework in the Mesozoic Ordos basin.It suggests that the NE-SW stressing is the main characteristic of the tectonic stress field in Indo-Chinese epoch in Ordos basin and the NW-SE stressing in Yanshan epoch after studying regional distributing joints. There is a gradual transition process between the two tectonic stress fields and the main transition period is the Fuxian-Yan'an period in Lower-Middle Jurassic.The changes in tectonic-sedimentary framework record the transition process. In Upper Triassic the preponderant extending direction of the sedimentary facies belts is NW-SE in Ordos basin. As a whole there are uplifts in the north of the basin and depressions in the south. The depocenter and center of subsidence lie in the south of Ordos basin. But in Upper Jurassic and Lower Cretaceous period uplifts are located in the east of the basin and depressions in the west. The sedimentary facies belts extend along nearly SN. The depocenter and center of subsidence have been transferred to the west of Ordos basin.Structural features have recorded the stress distribution state of two instantaneous stress fields. One is the stress field in Upper Triassic when Late Indo-China movement happens, the other is in Upper Jurassic when Middle Yanshan movement happens. Energy releases during tectonic movement and accumulates along with sedimentation. Transition of tectonic stress fields influences sedimentary framework and sedimentary framework reflects transition of tectonic stress fields.