RARE EARTH ELEMENT GEOCHEMISTRY OF CENOZOIC CARBONATES DURING DOLOMITIZATION

Rare earth elements plus yttrium (REY) in marine carbonates have the potential to trace ocean conditions over geologic times. However, the dolomitization effect on REY patterns including the cerium anomaly remains debatable due to a scarce of laboratory constraints under Earth-surface conditions, and a lack of well-characterized recent dolomitization event. The XK-1 drill core from the Xisha Island of the South China Sea is among the well-characterized marine carbonates. Previous studies have identified seven pure dolomite layers interbedded with low magnesium calcite in the Miocene carbonate sediments, providing an ideal natural laboratory for studying dolomitization. Here we report the data of trace elements including REY of Xisha marine carbonates. To avoid contaminations from detrital phases, we applied sequential leaching protocols to these carbonates before elemental analysis. The results show that PAAS-normalized REY of both dolomite and calcite carbonate exhibit a uniform modern seawater-like REY pattern, with mild light rare earth elements depletion, significantly negative Ce and positive Y anomalies. This suggests dolomite may preserve primary REY signals from seawater, regardless of diagenetic alteration. The influences of hydrothermal activity could be excluded due to the absence of Eu anomaly, while a lack of correlations between Ce/Ce* and Y/Ho with Al could rule out significant terrigenous input. Increases in Y/Ho ratios and total REY concentrations with depth suggest possible burial diagenesis, yet its effect is minor. Overall, this study demonstrates dolomization may not necessarily modify the precursor REE pattern preserved in carbonates, therefore dolomite potentially acts as a recorder of past seawater REY patterns.