重庆东部地区寒武系龙王庙组碳、氧同位素特征及其意义  

Characteristics and significance of carbon and oxygen isotopes of the Cambrian Longwangmiao Formation,eastern Chongqing

作　　者：杨雪琪[1,2] 钟大康[1,2] 任影[1,2] 谢瑞[1,2] 姜杨锦丰 蒲强 钟泞聪 唐自成[1,2] Yang Xueqi Zhong Dakang Ren Ying Xie Rui Jiang Yangjinfeng Pu Qiang Zhong Ningcong Tang Zicheng(College of Geosciences, China University of Petroleum （Beijing） , Beijing 102249 State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum （Beijing） , Beijing 102249)

机构地区：[1]中国石油大学(北京)地球科学学院,北京102249 [2]中国石油大学(北京)油气资源与探测国家重点实验室,北京102249

出　　处：《古地理学报》2017年第5期865-878,共14页Journal of Palaeogeography：Chinese Edition

摘　　要：在野外露头和镜下薄片观察分析的基础上,对重庆东部地区下寒武统龙王庙组83个碳酸盐岩样品的碳、氧同位素进行测试,并分析了其所保留的海水原始信息的有效性。结果表明,扣除无效数据后,重庆地区龙王庙组δ^(13)C值分布在-4.300‰~2.694‰之间,平均值为-0.031‰;δ^(18)O值分布在-9.880‰^-0.100‰之间,平均值为-7.396‰;纵向上,碳同位素值整体呈现先降低后升高的趋势,底部、中上部及顶部为正值且变化幅度小;中下部整体为负值且波动幅度大,正、负漂移事件频发。古环境恢复结果显示,龙王庙期重庆东部地区整体处于海相沉积环境,海水盐度在龙王庙组早期较低,晚期较高;海水温度主要介于20~30℃之间,属温暖或炎热的亚热带气候;龙王庙期共经历3期海退—海侵作用,海平面上升、海洋生产力增加、有机碳快速埋藏使得海洋中13C含量升高,反之则使其降低。龙王庙组沉积中期与末期,δ^(13)C值负偏,水体较浅,盐度较高,是白云岩发育的最有利阶段。To eveluate the paleoceanographic information recorded in the stratigraphic record,carbon and oxygen isotope analyses were conducted for 83 carbonate rock samples from the Longwangmiao Formation of the Lower Cambrian along with outcrop study and thin section analysis. The results（ excluding inva-lid samples） show that the δ^13C values of carbonate rocks in Longwangmiao Formation vary from-4. 300‰ to 2. 694‰ with the mean value of-0. 031‰ and the δ^18O values vary between-9. 880‰ and-0. 100‰ with the average of-7. 396‰. The vertical variation of δ^13C shows a decrease trend followed by an increase trend from bottom to top of the studied interval. The carbon isotopic composition is characterized by negative values with frequent occurrences of positive or negative excursions at the lower to middle part of the formation and positive values with small fluctuation at the other parts. The reconstruction of palaeo-ocean environments shows that marine environment was developed around the eastern Chongqing area during the Lower Cambrian Longwangmiao stage. The salinity of seawater was low during the Early Longwangmiao stage and high during the later stage. Sea water temperature mainly ranged between 20℃ and 30℃,suggesting a warm to hot subtropical climate. Three stages of regression-transgression cycles through Longwangmiao stage were identified. When sea level rises,increased marine productivity and fast burial of organic carbon result in an increase of δ^13C value. In the case of dropping sea level,the δ^13C value decreases. During the middle to late Longwangmiao stage,the negative shift of δ^13C value,low seawater level and the high salinity provide favorable conditions for the development of dolomites.

关 键 词：碳、氧同位素 古海水温度和盐度 地质意义 龙王庙组 重庆东部地区 

分 类 号：P597[天文地球—地球化学]