川西地区中二叠世-中三叠世微量、常量元素与古环境、古气候关系研究

Study on Relationships between Paleoenvironment,Paleoclimate of Middle Permian-middle Triassic and Constant,Trace Elements in Western Sichuan

川西地区位于上扬子台地边缘,区内发育滨岸、缓坡型台地、镶边台地、陆棚-盆地及陆表海型台地共5种沉积体系。研究区中二叠统-中三叠统地层生物礁、滩相十分发育,拥有巨大油气勘探潜力。通过对研究区中二叠统-中三叠统地层中采集到的80件层位样品进行常量、微量元素测试,结合沉积体系分析,旨在探索本区古海平面升降、氧化还原条件、古气候及古盐度的演化规律。研究发现,本区古环境共经历了3个较大的相对氧化→相对还原→相对氧化旋回,但各沉积期存在若干短期的次级旋回;古气候总体为热带-亚热带气候,繁育了众多暖水型生物群落,在P与T交界处存在由温湿过渡为干热的1次重大变革。上述演化过程在岩性及生物群落特征上都有显著体现。

Western Sichuan is located in the edge of upper Yangtze platform, which is mainly composed of shoreland system, ramp platform system, rimmed platform system, shelf-basin system and epicontinental platform system. The reef-beach facies of Middle Permian-Triassic strata is very rich, owning huge potential for oil and gas exploration. By testing 80 samples from Middle Permian-Triassic strata, combined with the sedimentary systems analysis, the ancient sea level eustacy, oxidation-reduction conditions, paleoclimate and paleosalinity of evolution in study area were explored. The study found that paleoenvironment experienced 3 obvious relative oxidation-reduction cycles, but every deposition period have several secondary cycles; The whole paleoclimate is tropical-subtropical climate, breeding many warm water biotic communities the junction of Permian and Triassic having one time big arid-humid change. The above process had obvious reflections at lithology and characteristics of biotic communities.