从地球生物学角度讨论华南中二叠世海相烃源岩缺氧沉积环境成因模式

探讨陆棚环境缺氧沉积的成因, 对查明海相优质烃源岩时空分布、恢复地史时期古环境演化具有重要意义.华南地区中二叠世栖霞组有机质丰富, 出现多方面缺氧沉积特征, 同时多门类底栖生物繁盛, 其成因一直令人困惑.简要介绍了陆棚浅海缺氧环境的生物特征及古氧相划分, 分析了栖霞组一个由纹层状灰岩和块状灰岩组成的典型的沉积序列的古氧相特征.块状灰岩的生物特征和地球化学特征均指示常氧沉积环境; 而纹层状灰岩的生物特征偏向常氧相, 沉积地球化学特征偏向厌氧相, 体现了陆棚缺氧沉积环境水体溶氧量不稳定的特点.栖霞组沉积特征表明, 栖霞组缺氧沉积环境的频繁出现与较高的生物产率有关.结合区域古地理和古特提斯古海洋背景, 认为华南地区中二叠世缺氧环境的成因与当时陆海分布格局和古海洋表面洋流系统有关. 

Geobiological Interpretation of the Oxygen-Deficient Deposits of the Middle Permian Marine Source Rocks in South China:A Working Hypothesis

To decipher the origin of oxygen-deficient shelf deposits is significant for tracing the distributions of marine hydrocarbon source rocks and interpreting the evolution of depositional environments. The origin of the Middle Permian Chihsia Formation from South China remains a puzzle for long, with its evident oxygen-deficient features associated with diverse benthos. This paper introduce briefly the nature of oxygen-deficient shelf environment as well as subdivision of related paleoxygenation facies, and shows a typical Chihsian depositional sequence with ecological and geochemical features. Massive bioclastic limestone from the middle of the sequence was believed to be formed under the aerobic conditions, supporting by both ecological and geochemical features. However, a contradictory conclusion is observed for "laminated" limestones from the lower and upper parts of the sequence; the aerobic ecological signal was associated with the anoxic geochemical record. The association of contradictory signals in ecology and geochemistry was here interpreted as the instability of paleoxygenation condition in shelf environment, caused by enhanced paleoproductivity. Repetitive occurrence of oxygen-deficient condition might have been stemmed from paleo-Tethyan currents flowing across the South China.