湘黔地区下寒武统牛蹄塘组钡的差异富集及其与海洋环境关系的研究

Barium plays an important role in marine geochemical cycling that is closely associated with oceanographic changes. It is well known that the Niutitang Formation (or equivalents) of the lower Cambrian in Yangtze area is anomalously rich in barium (locally occurred as Ba-bearing ore deposits); however, its abundance and occurrence greatly vary tempo-spatially, likely in response to the unique oceanic conditions and barium cycling during the early Cambrian. Previous related studies mostly focused on the lower Cambrian strata-bound barite and witherite deposits in Yangtze area, on which several mechanisms were proposed. In contrast, less attention has been paid to the coeval Ba-rich non-ore horizons, limiting our understanding for the oceanic barium cycling, tempo-spatial differences of barium distribution and occurrence, and environmental constraints. In this context, this project will target the representative sections of the lower Cambrian Niutitang Formation in Guizhou and Hunan provinces, and aims to illustrate tempo-spatial differences in barium enrichment (abundance, occurrence, origin) and coupled oceanic environments, revealing the controls on the differential barium enrichment based on detailed sedimentological, mineralogical and geochemical studies. This study would help a better understanding for oceanic barium cycling and environmental settings during the early Cambrian, and barium mineralization in study area, which is of important significances on aspects of not only science but also application for ore predication.

钡在海洋地球化学循环过程中扮演着重要角色，并与海洋环境变化密切相关。扬子地区下寒武统（如牛蹄塘组）钡元素异常富集，但时空分异性显著（局部可成矿），可能反映了早寒武世特殊的海洋环境与钡循环过程。传统研究主要围绕下寒武统层状重晶石–毒重石矿床而开展，并提出了多种成因机制，但对于非成矿的钡富集层关注极少，限制了对海洋钡循环、时空分布及环境制约的准确认识。因此，本项目选择湘黔地区下寒武统牛蹄塘组代表性剖面为研究对象，通过沉积学、矿物学和沉积地球化学综合研究，查明钡富集（含量变化、赋存形式、成因类型）的时空差异及其与海洋环境背景变化的耦合性，揭示其富集规律及主控因素。此研究将有助于促进对早寒武世海洋钡循环及环境特征的理解，并增进对该地区钡成矿规律的认识，具有重要的科学意义及应用价值。

钡作为海洋生物地球化学循环的重要元素，在扬子地区下寒武统牛蹄塘组呈现出明显的时空差异富集（甚至成矿）特征，可能响应了海洋钡循环差异。因此，通过厘定牛蹄塘组钡的矿物样式、成因机理，结合海洋环境时空演化探讨钡差异富集的控制因素，有助于加强对深时海洋钡循环的认识，具有重要的研究意义。在此背景下，本项目针对湘黔地区代表性剖面的牛蹄塘组及相邻地层，通过详细的沉积学、矿物学和沉积地球化学等手段，综合研究了钡含量变化、矿物赋存形式和成因类型，建立了岩石及化学（C-S-Fe-P-Ba-Ca等元素或同位素）地层序列，揭示了海洋氧化还原性质、关键元素含量及生物生产力特征，探讨了钡差异富集特征及机制。据此，本项目揭示了贵州天柱地区牛蹄塘组层状重晶石矿床沉积特征，建立了冷泉成因模式；约束了遵义松林地区牛蹄塘组沉积环境，厘定了早期成岩作用特征；发现了湘西牛蹄塘组富含重晶石和钡铝磷石，后者是新发现的重要富钡矿物。此外，本项目进一步揭示出寒武纪早期仍然具有富硅海水特征，明确了黔东留茶坡组沉积时期海洋氧化还原性质，综述了钙同位素在古海洋研究中的应用及进展。上述研究表明，湘黔地区冷泉等富钡流体的异常输入（而非海洋硫酸盐浓度增加），叠加早期成岩作用过程，是牛蹄塘组钡差异富集的重要控制因素。这些研究将促进对埃迪卡拉纪—寒武纪时期海洋钡循环及成矿规律的认识，丰富对扬子地区海洋沉积环境演化、生物地球化学循环的理解，具有重要的科学意义。