Characteristics of rare earth element abundances in shallow marine continental platform carbonates of Late Neoproterozoic successions from India

摘要

We have studied the REE distribution in shallow marine continental platform carbonates belonging to two late Neoproterozoic basins of India. Their REE abundance patterns normalized by chondrite display well defined W-type tetrad effect. Based on chondrite-normalized Gd/Ho, La/Nd ratios, the REE abundance patterns have been classified into three groups. (Y/Ho) and (Y/Dy) concentration ratios reflect a combined effect of Y fractionation relative to neighboring trivalent REEs during carbonate precipitation from seawater and influence of continental contributions with chondritic ratios. Negative Ce anomalies recorded in Krol and Bilara carbonates resembles the Ce anomaly reported from shallow marine waters. However, absence of Ce anomaly and distinct positive anomalies in some of our carbonate samples reflect post-depositional redox condition related to Ce mobilization and preferential enrichment during early diagenesis. Variations in the REE abundance patterns may be attributed to contamination with terrigenous particulates having shale like REE abundances and post-depositional early diagenetic processes. [References: 45]