THE CHARATERISTICS OF Ce ANOMALIES IN WEATHERING CRUSTS OF CARBONATE ROCKS AND ITS FORMATION MECHANISM

In this paper,Ce geochemical behavior has been studied systematically through REE mass transport coefficient,REE combining states and water chemistry of cave drip waters.In the upper part of weathering profiles,Ce 3+ is oxidized into Ce 4+ and hydrated,then mainly co-precipitated with Fe-Mn oxides and partly adsorbed by clay minerals,showing positive anomalies,whereas at the rock-soil boundary,Ce shows intensively negative anomalies.Two reasons are considered to be responsible for this phenomenon.Firstly,soil samples inherited Ce negative anomalies from the basement carbonate rocks.Secondly,more important reason is that in the weathering process Ce is more stable than the other LREEs and the Ce content in the downward leaching solution is much less than the other LREE contents such as La and Nd,resulting in intensively negative Ce anomalies when LREE are super-enriched at the rock-soil boundary.Consequently,the authors excluded the possibility of Ce migrating downward by the preferential formation of complexes with HCO_3- ligand.