贵州新元古代冰期(Varanger)后环境演变与藻类的复苏

新元古代冰期引起生物大量绝灭 ,大绝灭后环境如何重建、生物怎样复苏是演化古生物学研究的重要课题。对贵州铜仁坝黄、瓮安北斗山剖面和台江五河剖面南沱冰碛岩之上连续沉积的陡山沱组底部的“碳酸盐岩帽”中藻类化石进行系统研究 ,并结合古海洋环境地球化学研究结果 ,认为冰期后生态环境恢复很快 ,藻类快速复苏 ,但藻类分异度低。“碳酸盐岩帽”沉积结束 ,藻类进入衰退期 ,到了陡山沱中晚期 ,藻类又进入顶盛期。而藻类的复苏、衰退与古海洋环境的δ13C ,δCe,δEu异常有着密切关系

ENVIRONMENTAL RECONSTRUCTION AND ALGAL RECOVERY AFTER NEOPROTEROZOIC GLACIATION (VARANGER), GUIZHOU

Neoproterozoic Varanger glaciation caused the extinction of Neoproterozoic life. But little work has been done on the relationship between environmental evolution and algal recovery after Neoproterozoic glaciation (Varanger). On the basis of the sedimentary stratigraphy of the Doushantuo and Nantuo formations in the Bahuang, Wuhe and Beidoushan sections, eastern and western Guizhou, geochemistry and algal fossils of the three sections have been studied in detail. The results show that the “ Carbonate Cap” was developed above the Nantuo tillite, and algal recovery took place at the upperpart of the “Carbonate Cap”. Though algal recovery is rapid, only Siphonophycus, Leiosphearidia and Trachysphaeridium, become abundant and are low in diversity. Algae decline on a small-scale above the “Carbonate Cap”. Algae developed in a radial style until the Middle-Late Doushantuo Stage. The algal recovery is related to δ 13C, δCe and δEu, with negative Ce anomaly and positive Eu anomaly at the lower part of the Doushantuo Formation. The data indicate that the seawater was of reduction-weak oxidation at the lower part of the “Carbonate Cap”. δ 13C values vary in the range of -8.0‰ ～ -7.5‰,showing that organism is rare. But Ce is of positive anomaly, and Eu is of negative anomaly at the upper part of the “Carbonate Cap”. δ 13C values vary in the range of -1.8‰ ～ -2.5‰,indicating that organism is abundant. The result is consistent with algae development at the upper part of the “Carbonate Cap”.