三峡地区二叠系牙形石的U-Th-Pb定年及古海水信息

利用激光剥蚀电感耦合等离子质谱(LA-ICP-MS)对三峡地区二叠系茅口组牙形石的U-Th-Pb同位素年龄进行测定。结果表明该地层中牙形石的208Pb/232Th放射年龄为269±44,Ma,207Pb/235U放射年龄为256±39,Ma,接近二叠系茅口组的生物地层年龄。206Pb/238U的年龄为196±6,Ma,虽然准确度较高,但与前人推测的地层年龄相比偏低。此外,作者对牙形石的稀土元素(REE)组成进行了分析,并且发现牙形石的REE组成和Ce异常与古海水氧化还原条件有一定的相关性,可以指示古海水的信息。

U-Th-Pb dating and paleoseawater information of the Permian conodont of Three Gorges area

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to establish radiometric U-Th-Pb ages and produce the records of rare earth elements (REE) of conodont of the Permian Maokou Formation in the Three Corges area. Fourteen spots on the sample indicate a radiometric ~(208)Pb/~(232)Th age of 269±44 Ma and a radiometric ~(207)Pb/~(235)U age of 256±39 Ma, which are consistent with the biostratigraphic ages of the Permian Maokou Formation. The age of ~(206)Pb/~(238)U is 196±6 Ma, which is relatively lower compared with the stratigraphic ages predicted by preresearchers. The paleochemical characteristics of paleoseawater from the Permian conodont were reconstructed through contrastive researches of REE and Ce anomalies. The resuts show that geochemical characteristics of the conodont may be regarded as a useful proxy to reconstruct the paleoenvironment.