【摘要】 我们系统测定了新疆柯坪地区寒武纪和奥陶纪地层的海相碳酸盐样品的碳、氧和锶同位素组成,取得了沿地层剖面的同位素组成变化曲线。研究结果表明,柯坪地区寒武纪和奥陶纪海水中碳同位素变化曲线有6个δ¹³C负波动峰时期,它们与当时的全球生物灭绝事件和海退—海进事件的时间基本吻合,表明它们三者之间存在着必然的联系。在寒武纪和奥陶纪的大部分时间,锶同位素曲线较为平坦,反映出较少的地壳活动和板块构造作用。更多还原

【Abstract】 The authors systematically collected samples of marine carbonate rocks form the Cambrian and Ordovician strata in the Kalpin area, Xinjiang, and determined the C, O and Sr isotopic compositions and obtained the curves of C, O and Sr variations along the stratigraphic section. On the basis of the isotope data combined with the data biofacies and lithofacies and published information on the global Cambrian and Ordovician mass extinction events and regression-transgression events, the following conclusions can be drawn.There are six negative δ13C excursion peaks in the Cambrian and Ordovician seawater of the Kalpir. area. They are: early Early Cambrian, late Early Cambrian, late Late Cambrian, Arenig of Early Ordovician, Liandeilo of Middle Ordovician, and middle Caradoc-late-Caradoc of Middle Ordovician. All of them are basically coincident with the contemporary global mass extinction events and regression/transgression events, revealing the inevitable relationships among the negative δ13C excursion peaks in seawater, the global mass extinction events and regression/transgression events. As to the O isotopic data, it is difficult to make significant discussion because of influence and disturbance of diagenesis. The determined Sr isotopic ratios of seawater in the Kalpin area during the Cambrian and Ordovician are all consistent with the contemporary seawater values previously reported by W. H. Burke et al. In most parts of the Cambrian and Ordovictan, the Sr isotopic curve is flat, indicating that crustal activities and plate tectonic movements seldom occurred. The high Sr isotopic ratio occurring at the end of the Precambrian indicates the increase of components from old siliceous rocks in seawater and decrease of the rate of seafloor spreading. In the middle-late Middle Ordovician, the continual lowering of δ13C and 87Sr/86Sr ratios may be due to the integrative influence of some factors such as the global Taconic movement, glaciation and fall of the atmospheric temperature.更多还原