• 责任者：He Tianchen (State Key Laboratory for Mineral Deposits Research ; School of Earth Sciences and Engineering ; Nanjing University ; Nanjing 210093 ; China) ; Ling Hongfei
• 刊名：Geological Journal of China Universities
• 出版年：2013
• 卷期：19(4)
• 关键词：硅质岩 ; silicolite ; 岩石地球化学 ; lithogeochemistry ; 安徽 ; Anhui Province
• 页码：p.620-633
• 图表：6 illus., 3 tables, 86 refs.
• 分类号：0803
• issnNo：ISSN1006-7493
• isbnNo：CN32-1440/P

     To determine the origin of silica in terminal Ediacaran chert, we have undertaken a variety of sedimentary geochemical proxies, in conjunction with geological features, on well-characterised Piyuancun chert at Lantian section from southern Anhui province. The Piyuancun cherts are typical marine siliceous deposits with microcrystalline structure and high content of SiO2. Silica constituting the chert is partially derived from submarine hydrothermal fluid, indicated by geochemical ratios of Fe/Ti  20 and A1/（AI＋Fe） 〈 0.4, as well as position in A1-Fe-Mn triangular diagram. However, Y/Ho ratios close to seawater from modern open sea and seawater-like rare earth element distribution patterns demonstrate that the sedimentary water body of Piyuancun chert primarily sourced from seawater. The isotope compositions of silicon and oxygen illustrate no variation trend stratigraphically whilst relatively high δ30Si values indicate that Piyuancun cherts were formed by chemical precipitation of dissolved silica from seawater rather than direct precipitation from hydrothermal fluid. Moreover, estimated values from oxygen isotopic geothermometer are also consistent with normal coeval seawater temperature. Bottom seawater was first mixed with silicarich submarine hydrothermal fluid and subsequently driven by upwelling to relatively acidic waters far away from hydrothermal activity center. As a result, silica within the regional seawater became over-saturated and thus precipitated. Extensively existence of microfossils and algae mats including Palaeopascichnus fiumenensis in Piyuancun chert indicates the thriving ocean paleo- productivity. Acidic substance produced through degradation of organic matter and biodegradation process would have, to some extent, dropped the solubility of dissolved silica in seawater and thus promoted the deposition of Piyuancun chert.