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    羌塘盆地晚三叠世古地理反转及其对烃源岩的控制作用

    Late Triassic paleogeographic inversion and its control on source rocks in the Qiangtang Basin, Xizang (Tibet)

    • 摘要:研究目的】差异构造演化对羌塘盆地晚三叠世-早侏罗世烃源岩发育特征及空间展布的影响及意义。【研究方法】本文从沉积演化的角度,讨论了羌塘盆地晚三叠世构造转换的沉积记录。【研究结果】研究表明,晚三叠世,羌塘盆地发生了明显的沉积转换,表现为中三叠世-晚三叠世的海退序列转换为早侏罗世的海侵序列。与此同时,该时期羌塘盆地也发生了重要的古地理反转,表现为北羌塘由中三叠世的海相沉积逐渐转化为晚三叠世的陆相沉积,而南羌塘则由中三叠世的陆相沉积转化为晚三叠世的海相沉积。【结论】羌塘盆地晚三叠世的沉积转换和古地理反转控制了烃源岩的分布,晚三叠烃源岩主要受前陆盆地控制,发育于北羌塘的深水区,盆地周缘则发育含煤系烃源岩。早侏罗世烃源岩主要受被动大陆边缘盆地控制,发育于南羌塘的深水区,在南羌塘北部的潟湖环境发育含油页岩烃源岩。

       

      Abstract: This paper is the result of petroleum geological survey engineering. Objective Effect and significance of various tectonic history on the development characteristics and spatial distribution of source rocks in the Qiangtang Basin during the Triassic-Jurassic. Methods In the present study, we discuss the sedimentary records of the Late Triassic tectonic inversion. Results The Middle Triassic sequence has typically shallowing-upward changes and a marine regression related regional uplift. However, the Early Jurassic sequence displays typically deeping-upward changes due to the tectonic subsidence and transgression. We also identify paleogeographic inversion during the Late Triassic in the Qiangtang Basin. In the northern Qiangtang depression, the pre-existing (Middle-early Late Triassic) marine depositional areas turned into terrestrial units during the Norian. In contrast, the previously (Middle Triassic) terrestrial part of the sourthern Qiangtang depression became marine units. Conclusions Our study suggests that the distribution of source rocks in the Qiangtang Basin was mainly controlled by the sedimentary change and paleogeographic inversion during the Late Triassic. The Late Triassic source rocks were probably related to the foreland basin and developed in the deep water area of the northern Qiangtang depression, while the coal-bearing source rocks were developed around the basin. The Early Jurassic source rocks are probably related to the passive continental margin basin and developed in the deep-water area of southern Qiangtang depression. Oil shale-bearing source rocks are well developed in the lagoon in the northern part of Southern Qiangtang depression.

       

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