Triggers and characteristics of Late Triassic deep-lacustrine synsedimentary deformation structures in Ordos Basin
Qiu Xinwei1,2, Liu Chiyang2, Wang Jianqiang2, Deng Yu2, Wang Feifei2, Mao Guangzhou3
1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, CAS, Guangzhou 510640;
2. State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069;
3. College of Geological Science & Engineering, Shandong University of Science and Technology, Qingdao 266510
Various synsedimentary deformation structures are found in deep lake zone through detail study on outcrop and core sections of Upper Triassic Yanchang Formation in Ordos Basin.Syndepositional sandstone dikes,ridges,veins,minor faults and folds are found in outcrops section; Sandstone rumpled structures,sand muddy breccia structures,minor faults and sandstone veins are found in cores,based on the detail descriptive characteristics and analysis these structures of sequence,we propose a paleoseismic trigger to explain the various synsedimentary deformation structures,and the paleoearthquakes induced sand body at delta front along slope slump,a lot of flame structures and Bouma sequence are found.Detailed study of its distribution characteristics of that seismites and volcanic ash sediments in temporal is almost the same period in development; Slump turbidite formed after seismites and volcanic ash sediments,indicating that earthquakes,volcano eruption or deep thermal effect led to the basin basement subsidence,increasing in terrain elevation and later seismic prompted the formation of turbidites.Synsedimentary deformation structures are mainly locating in south and southwest of Ordos Basin,and the intensity decreased from southwest to northeast.Comprehensive comparison the same period adjacent orogenic belt evolution and the distribution characteristics of synsedimentary deformation structures in deep lake,suggest synsedimentary deformation structures coupled response of the Qinling collision orogenic process and deep heat effect,indicating a deep lacustrine corresponds to the basin with a relative activity dynamics setting,which played an important role in development of high-quality hydrocarbon source rocks.