Isotopic anomalies at the Precambrian-Cambrian boundary

该项目最初的目的是阐明前寒武纪/寒武纪界线事件的性质。然而，在与伊朗地质学家小组联合研究的过程中，实际的实地工作计划进行了重组，并扩大到整个古生代地段。因为认为P/C边界事件只能通过与F/F边界、P/T边界等其他古生代边界事件的比较来刻画。关于古生代世界的化学地层学和环境变化，我们取得了以下主要结果1。碳同位素负值和正值均在P/C界面下方和正下方被识别。前者和后者被解释为对应于前寒武纪动物群的大规模灭绝和古生代动物群的爆炸性多样化。此外，在晚寒武世地层中还观察到了强烈的正异常。上泥盆统中度负碳异常可能与法门期/法拉斯期边界事件有关。石炭-二叠纪碳同位素组成的旋回变化可能反映了冰川-间冰川旋回。球粒陨石标准化的稀土元素模式显示出有趣的长期变化。寒武纪爆发期出现强烈的Ce负异常，而其余古生代剖面呈正常模式，表明寒武纪大爆发与含氧洋相有关，而整个古生代洋相则以还原环境为特征。

This project was originaly intended to elucidate the nature of the Precambrian/Cambrian boundary event. However, the actual field work plans were reorganized and expanded towards the entire Paleozoic sections in the course of the joint study with the Iranian geologist group. Because the P/C boundary event was believed to be characterized only through the comparison with the other Paleozoic boundary events such as F/F boundary and P/T boundary. We have obtained the following major results concerning the chemo-stratigraphy and environmental changes of the Paleozoic world.1. Negative and positive carbon isotopic anomaly have been recognized just below and bove the P/C boundary. The formaer and the latter are interpreted to correspond to mass extinction of Precambrian fauna and explosive diversification of the Paleozoic type fauna. Moreover, strong positive anomaly was observed in the late Cambrian strata.2. Moderate negative carbon anomaly in the upper Devonian is probably attributed to the Famenian/Frasnian boundary events.3. Cyclic changes in carbon isotopic composition recognized in the Carboniferous-Permian may reflect the glacier-interglacier cycles.4. Chondrite-normalized REEs patterns show interesting secular variations. Strong negative Ce anomaly occurs in the Cambrian explosion intervals whereas the remaining Paleozoic sections show normal pattern, suggesting that the Cambrian explosion was associated with oxygenated ocean while the entire Paleozoic ocean was characrerized by reducing environment.