REE geochemistry of kerogen from Early Cambrian black rock series in western Hunan

Organic matter from Early Cambrian black rock series in western Hunan was derived from organisms 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 environment 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 anomalies 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.