广东肇庆奥陶系砂泥岩沉积环境的地球化学表征

以砂泥岩样品的常量/微量元素地球化学特征分析为主要手段,探讨广东肇庆地区奥陶纪沉积环境,为尚显薄弱的云开古陆北缘下古生界沉积学研究提供佐证。以"相当B含量"、Ga、K、Rb、V、Sc等元素组分及其比值为判别指标,分析研究区奥陶系碎屑岩沉积的古水体性质和古环境变化。结果表明,奥陶纪早-中期(缩尾岭群沉积期)海水明显淡化、富氧;奥陶纪晚期(三尖群沉积期)以半咸水-正常咸水为主,水体还原性增强。结合地层岩相特征,认为研究区在奥陶纪期间整体为云开古陆东北缘的滨-浅海,早期可能存在受淡水影响的海陆过渡环境,例如三角洲或河口湾,晚期由于海平面上升逐渐成为浅海陆棚。研究结果有助于进一步了解云开古陆周缘奥陶纪沉积演化,并为开展更为详细的沉积学研究提供参考。

Elemental Geochemistry Evidence for Sedimentary Environment of Ordovician Siltstones in Zhaoqing, Guangdong Province

The elemental geochemistry of siltstone and mudstone samples collected from the outcrops of the Ordovician in Zhaoqing, Guangdong Province, is described and discussed, thus providing evidence for the sedimentary environment nearby the "Yunkai ancient land". The major and trace element compositions, such as B, Ga, K, Rb, V and Sc, were discussed and used to unravel the geochemical features of paleo-sea water. The results showed the obvious dropping of paleosalinity and oxygenization of sea water during the Early-Middle Ordovician when the Suoweiling Formation (SWL) was deposited. Conversely, the Sanjian Formation (SJ) was deposited in a weakly oxidative or reducing environment, in which the paleosalinity varied from brackish to normal saline, in the Late Ordovician. These features, in combination with the lithofacies characteristics, suggested that the SWL siltstones in the study area would form in a coastal or transitional environment, such as deltas or tidal flats with predominant contributions from freshwater, nearby the "Yunkai ancient land". By subsequent transgression in the Late Ordovician, the SJ siltstones and mudstones would form in a neritic shelf. The results may help us to understand the sedimentary evolution of the Yunkai block and provide reference materials for further detailed studies.