Rare earth elements in clay-sized fractions: Implications for weathering fingerprint from parent materials to soils
Xianming Zhang,
Yuntao Jing,
Wanfu Zhao,
Yongjun Jiang,
Dong-Xing Guan,
Hongxia Du,
Ying Qian,
Fei Ye,
Wancang Zhao
Affiliations
Xianming Zhang
Chongqing Key Laboratory of Karst Environment & School of Geographical Sciences of Southwest University, Chongqing 400715, China
Yuntao Jing
Chongqing Key Laboratory of Karst Environment & School of Geographical Sciences of Southwest University, Chongqing 400715, China; School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
Wanfu Zhao
Ningxia Institute of Land Resources Survey and Monitor, Yinchuan 750002, Ningxia Hui Autonomous Region, China
Yongjun Jiang
Chongqing Key Laboratory of Karst Environment & School of Geographical Sciences of Southwest University, Chongqing 400715, China
Dong-Xing Guan
Zhejiang Provincial Key Laboratory of Agricultural Resources and Environment, Institute of Soil and Water Resources and Environmental Science, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China
Hongxia Du
College of Resources and Environment, Southwest University, Chongqing 400715, China
Ying Qian
Chongqing Key Laboratory of Karst Environment & School of Geographical Sciences of Southwest University, Chongqing 400715, China
Fei Ye
Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of China, Nanjing 210042, China
Wancang Zhao
Chongqing Key Laboratory of Karst Environment & School of Geographical Sciences of Southwest University, Chongqing 400715, China; Corresponding author.
Rare earth elements (REEs) have gained attention as tracers of pedogenic processes over the last few decades. Clay-sized fractions (CSFs, < 2 μm) may play a crucial role in hosting REEs. To better understand the pedochemical signals of REEs in clay-sized phases, such as iron oxides and phyllosilicates, we analyzed REE speciation in CSFs of carbonate rocks (limestone), clastic rocks (sandstone and shale), and their derived saprolites. Our results quantified the REE content (41.2–144.6 mg kg−1) and speciation in CSFs of parent materials, revealing that REEs were primarily hosted in amorphous iron oxides (Feox1), followed by crystalline iron oxides (Feox2) and phyllosilicates. Compared to parent materials, saprolites derived from carbonate rocks exhibited more than a two-fold enrichment of REEs in major clay-sized phases, confirming the role of CSFs as REE sinks during carbonate rock weathering. Furthermore, the initial REE patterns of CSFs of carbonate rocks underwent alteration throughout the weathering process, likely due to water–mineral interactions. Our findings suggest that REEs in CSFs record the weathering fingerprint for soils derived from carbonate rocks, while they are indicative of provenance for soils originating from clastic rocks.
