贵州地区南沱冰期的冰下化学风化作用及其对海洋磷富集的意义  

Subglacial Chemical Weathering and its Significance in Marine Phosphorus Enrichment during Nantuo Ice Age in Guizhou Province

作　　者：顾尚义[1] 毕晨时[1] 

机构地区：[1]贵州大学资源与环境工程学院,贵州贵阳550025

出　　处：《贵州大学学报（自然科学版）》2015年第6期22-28,共7页Journal of Guizhou University:Natural Sciences

基　　金：国家自然科学基金资助项目(编号41162003)

摘　　要：新元古代南沱冰期海洋磷浓度出现了大幅度的升高,这可能对该冰期后的生物圈、水圈和大气圈演化均产生了影响,但磷浓度升高的原因尚不清楚。贵州不同沉积相区的南沱组岩石中普通存在的层理构造和砾石较高的磨圆度特征,细粒碎屑组分的化学蚀变指数(CIA)数值具有较大变化范围,表明南沱冰期存在明显的气候波动。细粒碎屑组分的CIA值与P2O5/Al2O3值呈显著的负相关关系,说明磷主要来源于化学风化作用。鉴于南沱冰期的雪球地球背景,作者提出南沱冰期可能存在着复杂的冰下水文系统,具备进行冰下风化作用的条件。由于南沱冰期水体处于缺氧环境,所以生物及铁氧化物对磷的吸收和吸附甚微。冰下风化作用释放的磷被搬运进入海洋中逐渐累积,含量得以增加。Neoproterozoic Nantuo Ice Age witnessed elevated marine phosphorus concentration and may play an important role in the thereafter evolution of biosphere, hydrosphere, and atmosphere. However, the reason for the increase of marine phosphorus during this period remains unknown. Both sedimentary rocks bedding structures and widespread rounded gravels or pebbles and a large range variation of Chemical Index of Alteration （CIA） in fine-grained parts of diamictite in Nantuo Formation Nantuo Ice Age. Significantly negative correlation between CIA indicated warm and cool climate oscillation during values and P205/Al2O3 implied that phosphorus was released from source rocks during chemical weathering. In the context of snowball earth, the continents were almost covered by ice and/or snow for millions of years, it is suggested that complicated subglacial drainage system and subglacial chemical weathering existed in Nantuo Ice Age. Owing to the prevailing anoxic condition and weak biological activities, most phosphorus released by subglacial weathering was transported into oceans and be- came enriched in the oceans as a result of limited retention by iron oxides and living organisms.

关 键 词：磷 南沱冰期 化学蚀变指数 气候波动 冰下风化作用 

分 类 号：P595[天文地球—地球化学]