Geochemistry of upper Miocene Kudankulam limestones, southern India

Concentrations of major, trace, and rare-earth elements (REE) were measured in shallow marine limestone samples of the upper Miocene Kudankulam Formation, southern India, in order to investigate the geochemical variations among various litho-units. The CaCO3 content is higher in algal limestone (AL; 92 +/- 1, n = 3) and elastic limestone (CL; 90 +/- 2, n = 3) than sandy shell limestone (SSL; 81 +/- 1, n = 3). All trace elements exhibit lower concentrations than post-Archean Australian Shale (PAAS) values, except one SSL sample. Large variations in SigmaREE content are observed among CL, SSL, and AL (similar to14-142, similar to68-124, and similar to38-98, respectively). Almost all limestone samples analyzed from the Kudankulam Formation show a small negative cerium anomaly (Ce/Ce* similar to0.8-0.9), except one AL sample, which lacks this cerium anomaly (Ce/Ce* similar to1.04). Variations in Ce anomalies and SigmaREE contents in Kudankulam limestone samples are mainly controlled by the amount of terrigenous sediments and diagenetic behavior. Shale-normalized REE patterns and (La/ Yb)(s), La/Sc, La/Th, and Th/Sc ratios suggest that the detrital sediments present in the limestones were probably derived from felsic source rocks. The observed low content of U (0.9 +/- 0.5, n = 9) and U/Th (0.2 +/- 0.1, n = 9) ratio in these limestones are probably related to an oxygen-rich environment.