蓟县中-新元古界剖面团山子组-景儿峪组碳氧同位素演化特征及其沉积环境与构造意义

Characteristics of the carbon and oxygen isotopes of the Tuanshanzi Formation-Jingeryu Formation from the Meso-Neoproterozoic section in the Jixian County and constraints on depositional-tectonic environment

对华北克拉通北缘蓟县中-新元古界碳酸盐岩进行了系统的碳、氧同位素研究,共获得有效碳、氧同位素数据376组。团山子-景儿峪组岩石学特征、碳氧同位素组成特征对沉积-构造环境具有良好的协同指示意义:δ^(13)CVPDB和δ18OV-PDB曲线变化幅度很小,δ^(13)C多数介于-1‰~+1‰,δ^(18)O多数介于-4‰~-6‰。显著的δ^(13)C负值出现于团山子组、高于庄组和铁岭组下部,显著的δ^(13)C正值出现于杨庄组/雾迷山组界线以及景儿峪组。通过对比研究认为,团山子期经历了大规模裂解事件,与区内团山子期末-大红峪期强烈火山作用事件相吻合;杨庄晚期-雾迷山早期经历了沉积环境突然变化,导致生物爆发式发育;景儿峪组碳同位素变化范围介于-0.90‰~+3.70‰,与扬子克拉通神农架群1.4~1.0 Ga碳同位素波动范围存在部分重合,有可能填补待建系(1.35~1.00 Ga)的部分空白。

A systematic study of C and O isotopic composition was conducted on the Tuanshanzi Formation to Jingeryu Formation(1.4~1.0 Ga)in The Jixian strata profile on the northern margin of the North China Craton.A total of 376 valid data of C and O isotopic composition were obtained.The lithological characteristics and C and O isotopic composition supplement each other for understanding the depositional-tectonic environment.Theδ^(13)CV-PDB andδ^(18)OV-PDB mainly vary from-1‰to+1‰and-6‰to-4‰respectively.Apparentδ^(13)C negative values appeared in the Tuanshanzi Formation,the Gaozhuang Formation and the lower part of the Tieling Formation.Apparentδ^(13)C positive values appeared boundary of the Yangzhuang Formation and Wumishan Formation,and the Jingeryu Formation.Synthesizing every evidence including C and O isotope data,it is concluded that a largescale breakup event occurred from the Tuanshanzi period,in coupling with the strong volcanic activities initiated from the end of the Tuanshanzi period,and depositional environment changes abruptly around the Yangzhuang-Wumishan boundary,leading to a bio-resuscitation event.Theδ13C variation range(0.90‰~+3.70‰)of the Jingeryu Formation partially overlaps with theδ^(13)C fluctuation range of the Shennongjia Group(1.4~1.0 Ga)from Yangtze Craton,which means the Jingeryu Formation may fill up part of the stratigraphic hiatus in the time range of 1.35~1.0 Ga.