# Geochemistry and Evolutionary Characteristics of Rare Earth Elements in Ordovician Carbonate-Evaporite Rocks of the Central-Eastern Ordos Basin, Central China

## TL;DR

This study examines how rare earth elements behave in ancient carbonate-evaporite rocks during seawater evaporation in China's Ordos Basin.

## Contribution

The study reveals that REEs in evaporite rocks are not tied to detrital minerals but likely exist in fine particles or mineral defects.

## Key findings

- REEs show a consistent distribution pattern despite low overall content in the C-G-S system.
- Light REEs are enriched with negative Eu anomalies, indicating non-isomorphic substitution in mineral structures.
- REEs migrate significantly during dolomitization from limestone to dolomite.

## Abstract

This study aims to reveal the geochemical behavior characteristics
of rare earth elements (REEs) in the process of seawater evaporation
and concentration by analyzing the REEs and their variation characteristics
in different stages of rocks from the rock system of carbonate-gypsum-salt
(C-G-S system) of the Ordovician in the central-eastern Ordos Basin,
China. The results indicate: despite the low overall content of REEs
in the endogenous deposition process of the C-G-S system in this area,
a relatively consistent REEs distribution pattern is still exhibited
in different types of rocks formed in different stages of seawater
evaporation and concentration, showing a relative enrichment of light
rare earth elements (LREEs) and obvious negative europium (Eu) anomalies;
and its REEs content is not directly related to the content of continental
source detrital minerals. All this means that REEs do not enter the
crystal structure of the main rock-forming minerals mainly in the
form of isomorphous substitution during the mineral crystallization
process but are more likely to aggregate in the form of extremely
fine particles, exist in the lattice defects and mineral surfaces
of the main rock-forming minerals, or be enclosed by subsequent growth
of mineral crystals. Also, during the dolomitization transformation
from limestone to dolomite, REEs undergo relatively significant outward
migration.