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

Abstract

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.

Experimental REE partitioning between calcite and aqueous solution at 25.DEG.C. and 1atm: Constraints on the incorporation of seawater REE into seamount-type limestones

“…In estimating REE abundances in ancient seawater, it is desirable to select carefully marine limestone samples without detritus such as seamount-type limestones (Kawabe et al, 1991;Tanaka et al, 2003), which show well-preserved seawater features. Continental shelf-type limestone can also be used, but it is necessary to examine carefully whether it preserves the seawater signature, because it could be easily affected by terrigenous materials (Mazumdar et al, 2003).…”

Trace and rare-earth element behaviors during alteration and mineralization in the Attepe iron deposits (Feke-Adana, southern Turkey)

“…So, a negative Ce anomaly is a common phenomenon for the marine basins. Soluble Ce 3+ under oxidation condition changes to insoluble and thermodynamically stable Ce 4+ (Mazumdar et al, 2003). Subsequently preferential scavenging of Ce 4+ through organic and inorganic (δ-MnO 2− and/or Fe-oxyhydroxides) particulates causes negative Ce anomaly in seawater, which is then inherited by carbonates that formed in this seawater (Elderfield and Greaves, 1982;De Baar et al, 1985;Hu et al, 1988;, Wilde et al, 1996Mazumdar et al, 1999;Ohta and Kawabe, 2000;Fernández-Nieto et al, 2003;Mazumdar et al, 2003;Chen et al, 2006;Yu et al, 2009).…”

“…Subsequently preferential scavenging of Ce 4+ through organic and inorganic (δ-MnO 2− and/or Fe-oxyhydroxides) particulates causes negative Ce anomaly in seawater, which is then inherited by carbonates that formed in this seawater (Elderfield and Greaves, 1982;De Baar et al, 1985;Hu et al, 1988;, Wilde et al, 1996Mazumdar et al, 1999;Ohta and Kawabe, 2000;Fernández-Nieto et al, 2003;Mazumdar et al, 2003;Chen et al, 2006;Yu et al, 2009). In addition, Ce anomaly in carbonate sediments may have resulted from post-depositional mobilization of Ce during early diagenesis owing to its redox-sensitive nature Holser, 1997;Shields and Webb, 2004;Mazumdar et al, 2003). Although the characteristic data of the host rock suggest an original marine carbonate, there are also indications of mixing of hydrothermal exhalative fluids with the ambient seawater and/or early diagenetic effects.…”

“…Ce gets fractionated from other trivalent REE in the marine environment owing to its unique redox chemistry (De Baar et al, 1985;Mazumdar et al, 2003). So, a negative Ce anomaly is a common phenomenon for the marine basins.…”

Depositional and post-depositional setting of Maastrichtian limestone, Ariyalur Group, Cauvery Basin, South India: a geochemical appraisal

“…The Kallankurichchi limestones are clustered in the IIIa region, which indicates positive Ce and negative La anomaly. According to Mazumdar et al (2003), absence of Ce anomaly or positive Ce anomaly in some samples may be attributed to enrichment of Ce relative to other REE 3? through mobilization of Ce as Ce 3?…”