湘西寒武纪早期黑色岩系中干酪根的 稀土元素地球化学特征
REE Geochemistry of Kerogen from Early Cambrian Black Rock Series in Western Hunan

湘西寒武纪早期黑色岩系中富含源于上层海水生物体的有机质,其稀土元素（REE）特征不被碎屑物质干扰,能有效地反映海洋上层水体的古环境特征.样品中作为有机质主体的干酪根的重稀土富集、Ce负异常、Y正异常和Eu无明显异常等特点与现代海水一致，其特征可能反映古海洋上层水体的氧化还原信息.扬子地台各相区沉积剖面底部可能出现滞流（或硫化）环境,随后沉积环境逐渐氧化.全岩样品中Ce的负异常可能由有机质提供,Ce／Ce*值由剖面底部的较低值向上逐渐升高可能意味着海洋上层水体含氧量的逐渐上升,而海水含氧量逐渐升高或许是由寒武纪早期海洋底部硫化环境的减弱所导致.
Organic matter from Early Cambrian black rock series in western Hunan was derived fromorganisms in the euphotic zone.For not interfered by the detrital component,REE geochemistry of organic matter can demonstrate paleoenvironmental characteristics of the upper seawater.As the main part of organic matter,kerogen is fully consistent with the modern seawater like REE pattern which shows a progressive enrichment towards the heavier REE,depletion of Ce,positive anomalies of Y and no obvious anomalies of Eu.The characteristics of kerogen may trace paleoredox condition of upper seawater.The euxinic encironment may have arised in the lower part of sections in the Yangtze area,and the depositional condition may have shifted to gradual oxidization in the upper part of sections.The negative Ce animalies of bulk rocks are most probably derived from organic matter input.Gradual increase of Ce/Ce* values indicates increasing oxygen content of upper seawater,and weakening of euxinic environment of bottom seawater may result in rising of oxygen content of upper seawater