川东北旺苍地区栖霞组地球化学特征及其古环境意义

Geochemical characteristics and paleo-environmental implications of Middle Permian Qixia Formation in Wangcang, northern Sichuan

张运周 徐胜林 陈洪德 林良彪 董翼昕 余瑜 张瑶

ZHANG Yunzhou XU Shenglin CHEN Hongde LIN Liangbiao DONG Yixin YU Yu ZHANG Yao

成都理工大学 沉积地质研究院, 成都 610059 2. 油气藏地质及开发工程国家重点实验室(成都理工大学), 成都 610059 3. 中国石化 西南油气分公司 石油工程技术研究院, 四川 德阳 618000

Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China 2. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Chengdu University of Technology), Chengdu, Sichuan 610059, China 3. Petroleum Engineering Technology Research Institute, SINOPEC Southwest Oil and Gas Branch Company, Deyang, Sichuan 618000, China

为研究川东北地区中二叠统栖霞组沉积期古环境，对川东北旺苍地区鹿渡坝剖面进行了野外露头观察，开展了室内镜下薄片鉴定与地球化学分析。结果表明，栖霞组19件样品δ13C和δ18O呈现离散型，不具有线性关系，且均满足δ18O > -6‰，Mn/Sr ≤ 0.6、Fe/Sr < 3、MgO/CaO < 0.125，可作为古环境分析的可靠对象。陆源元素Al2O3和TiO2含量低，且呈强烈正相关，ΣREE与Σ（Al2O3+TiO2）有较强烈的正相关，结合其他相关的主量元素和微量元素特征（V/（V+Ni）和U/Th的相关性等）表明，栖霞组形成于缺氧-贫氧环境；Sr/Ba介于21.9~261.9之间，说明海平面相对较高，故陆源物质含量稀少，且沉积时期陆源碎屑物受古水深的控制；碳、氧同位素揭示古海洋温度介于17.62~28.43℃，古盐度介于129.07~135.21，MgO/CaO比值介于0.007~0.029，揭示沉积古环境主体为相对温暖的热带潮湿气候，水深在小范围内呈震荡式变化，经历过2次海侵-海退旋回。

The sedimentary paleoenvironment of the Middle Permian Qixia Formation in northeastern Sichuan Basin was studied based on outcrop observations and laboratory analyses. The data correlations of the δ13C and δ18O of 19 samples from the Qixia Formation showed that there was no linear relationship between them. The samples are reliable targets for paleoenvironmental analyses since δ18O > -6‰, Mn/Sr ≤ 0.6, Fe/Sr < 3, and MgO/CaO < 0.125. The contents of terrigenous elements (Al2O3 and TiO2) are low, and are strongly and positively correlated. The ΣREE and Σ(Al2O3+TiO2) also showed a positive relationship. The characteristics of other main and trace elements indicated that the Qixia Formation was formed in a hypoxic or oxygen-depleted environment. The Sr/Ba value ranges from 21.9-261.9, indicating that the sea level was relatively high, so the terrigenous material content is low, and the terri-genous detrital sediments were controlled by paleo-water depth during sedimentation. The carbon and oxygen isotopes revealed that the ancient oceanic temperature ranged from 17.62-28.43℃, the paleosalinity ranged from 129.07-135.21, and the ratio of MgO/CaO ranged from 0.007-0.029, revealing that the paleoenvironmental climate was relatively warm and humid. Water depth fluctuated within a small range and experienced two transgressive and regressive cycles.

国家自然科学基金青年科学基金项目（41602107）和成都理工大学中青年骨干教师培养计划（JXGG201537，JXGG201538）资助。

https://doi.org/10.11781/sysydz201802210