沉积学报2025，Vol.43Issue(5)：1796-1813,18.DOI:10.14027/j.issn.1000-0550.2025.048
贵州瓮安磷矿区寒武系牛蹄塘组元素地球化学特征及意义
Elemental Geochemical Characteristics and Significance of the Cambrian Niutitang Formation in the Weng'an Phosphate Mining Area,Guizhou Province
摘要
Abstract
[Objective]The early Cambrian period represents a significant epoch of geological and biological trans-formation in Earth's history.This period witnessed not only the emergence of numerous skeletal-bearing metazoans but also the formation of significant metal mineral deposits.The Niutitang Formation,widely distributed across South China,represents an important stratigraphic unit from this period.Researching the characteristics of elemental geo-chemistry in Niutitang Formation reflects not only the environment of sedimentation and deposition of this period,but also it is significant to the exploration of early life evolution and environmental synergy.[Methods]By means of petro-logical,mineralogical,and geochemical analysis of the Shantun section in Weng'an,Guizhou,the sedimentary envi-ronment of the Niutitang Formation is discussed.[Results]The Niutitang Formation in the Weng'an phosphate min-ing area of Guizhou is clearly divided into the upper phosphate rock and black shale members,with the polymetallic layer located at the transition between these two lithological sections.The Niutitang Formation biota is located in the upper part of the polymetallic layer and at the bottom of the black shale that covers it,suggesting a close relationship between the appearance and prosperity of the Niutitang Formation biota and the special geological event represented by the polymetallic layer.Irregular dolomite debris is commonly found at the bottom of the upper phosphate rock mem-ber,with overlying phosphate rock and polymetallic ore developing gravel debris structures,and the morphology of glauconite is commonly irregular,which reflects the stronger hydrodynamic force of the local environment of the an-cient ocean at that time.Barite lenses and pyrite laminations are developed in the polymetallic layer and the black shale overlying it.Pyrite,chalcopyrite,and sulfide nickel minerals are commonly found coexisting in the ore,which are consistent with the characteristics of modern ocean floor hydrothermal black chimneys.The geochemical V/Cr and Ni/Co characteristics of the Niutitang Formation indicate that the ancient marine environment during its sedimentary period was anoxic or hypoxic,which is consistent with the sedimentary characteristics of the Niutitang Formation.However,a series of abnormal values were observed in the upper part of the upper phosphate rock member,the polymetallic layer,and the black shale bottom layer closely covering it:V/Cr,Ni/Co,U/Th(U/Th>1),P,and vari-ous trace element contents reached their peak,and Sr/Ba(Sr/Ba<1)reached its lowest value.In this layer,samples exhibit clear negative Ce anomalies and slight enrichment of light rare earth elements.Additionally,a sample in the middle of the black shale member showed a positive Eu anomaly.These rare earth element characteristics fall be-tween hydrothermal fluids and typical seawater.In summary,the geological event represented by the polymetallic lay-er is a hydrothermal upwelling activity event in ancient oceans.Hydrothermal activity can be divided into three dis-tinct stages,with the second stage having the highest hydrothermal composition and being highly consistent with paleontological records.[Conclusions]The geochemical characteristics of the elements further prove the existence of submarine hydrothermal activity during this period.Based on this,a comprehensive reconstruction of the paleoenvi-ronmental evolution model of the Niutitang Formation biota before and after its appearance in the Weng'an phosphate mining area was conducted,taking into account the sedimentary geological background.关键词
寒武系底部/牛蹄塘组生物群/多金属层/热液活动/充氧事件Key words
bottom of the Cambrian,Niutitang Formation biota/polymetallic layer/hydrothermal activity/oxygenation event分类
天文与地球科学引用本文复制引用
庞艳春,林丽..贵州瓮安磷矿区寒武系牛蹄塘组元素地球化学特征及意义[J].沉积学报,2025,43(5):1796-1813,18.基金项目
国家自然科学基金项目(41173058,41872007)National Natural Science Foundation of China,No.41173058,41872007 （41173058,41872007）
