唐古拉地区拉卜查日组牙形石的发现、锶同位素组成及地层学意义

首次在唐古拉地区晚二叠世—早三叠世拉卜查日组中获得牙形石化石,其分子为Hindeodus typicalis、H.eurypyge和H.praeparvus。根据其地层意义并结合层序地层学及海平面变化研究,最终将研究区二叠系与三叠系界线的可能位置定在实测剖面的29层顶、30层底。基于此,作者系统测试了拉卜查日组中的碳酸盐岩87Sr/86Sr比值,结果表明,二叠系/三叠系界线附近87Sr/86Sr比值为0.707017~0.707032,显著小于国内外其他地区二叠系/三叠系界线附近87Sr/86Sr比值。造成这种差异的主要原因,可能是由于唐古拉地区二叠系/三叠系界线附近存在广泛的火山活动以及上扬子地区二叠纪广泛的玄武岩喷发等地方性事件。此外,剖面上锶同位素演化曲线与海平面变化曲线对比显示,87Sr/86Sr比值的最小值与初始海泛面基本一致,锶同位素演化曲线与海平面变化曲线有着很好的一致性,说明全球海平面变化是其最主要的控制因素。

The discovery of conodonts fossils and the strontium isotope composition of Labuchari Formation in Tanggula Range and their stratigraphic significance

Conodont fossils were found for the first time in the Late Permian Labuchari Formation in the Tanggula Range. The conodonts include Hindeodus typicalis, H. eurypyge and H. praeparvus. According to their significance and the investigation of sequence stratigraphy and sea-level changes, the Permian/Triassic boundary may be determined between the top of 29 and the bottom of 30 of the measured section. Here, the carbonatite ⁸⁷Sr/⁸⁶Sr ratios of Labuchari Formation were determined. At the Permian/Triassic boundary, ⁸⁷Sr/⁸⁶ Sr ratios are from 0.707017 to 0.707032, which are significantly lower than those in other areas. The main reasons for the remarkable difference might be the existence of extensive volcanic activities in Tangula Range at the Permian/Triassic boundary and the basalt eruptions in Yangtze region during the late Permian. In addition, the comparison between the strontium isotope curve and sea-level curve shows that the minimum ⁸⁷Sr/⁸⁶Sr ratio has a good consistency with the data of the first flooding surface, suggesting that global sea level change was the main factors controlling the strontium isotope.