Early Triassic Sediments and Their Tectonic Controlling Factors,Western Qinling

Key words: 
• turbidite /
• megabreccias /
• tectonic controlling factor /
• Early Triassic /
• Western Qinling

Abstract: The early Triassic deposits consist of chaotic megabreccias,conglomerates, slump deposits,turbidites, deep-water limestones and calcareous mudstones.From bottom to top, sediments show four sedimentary cycles controlled by tectonic process. A single sedimentary cycle is composed of chaotic megabreccias, conglomerates,turbidite, slump deposits,deep-water limestone and calcareous mudstones upward. Based on the directional structures of turbidite and slump deposits, continental margin slope dipping to the west-south, the palaeocurrent direction ranges from 220°to 260°.This indicates that on the north plate margin existed an extensional tectonic setting along Luqu-Chenxian in Early Triassic, which is related to the rollback caused by the subduction of the Yangtze plate towards the north.The subduction causing the roll-back process made the north plate margin form a series of normal faults. This also made the early formed shallow water platform factes break,collapse and slide along the steep slope,at last they deposited in the deep water basin and formed the chaotic megabreccias,conglomerates deposits which slid and slumed at the later,and the turbidite,at the relatively stable period, formed the deep water limestone and calcareous mudstone.In another tectonic active period,the similar sediments deposited in the deep water basin.So,the early Triassic deposits were obviously controlled by the tectonic process.