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Geological significance of rare earth elements in marine shale during the Late Ordovician–Early Silurian in Sichuan Basin, South China
Author(s) -
Lu Bin,
Qiu Zhen,
Zhang BaoHua,
Li Jian,
Tao HuiFei
Publication year - 2021
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.4027
Subject(s) - terrigenous sediment , oil shale , geology , ordovician , pyrite , rare earth , geochemistry , clay minerals , rare earth element , sedimentary rock , paleontology , mineralogy
Rare earth elements (REEs) record a large amount of geological information, and serve as a good geological indicator that can effectively predict the palaeoclimate, palaeoenvironment, and palaeotectonic evolution of the sedimentary rocks. The REEs and major elements of 94 marine shale samples obtained from the Late Ordovician to the Early Silurian at Shuanghe (SH) and Qiliao (QL) sections in Sichuan Basin were analysed in this study. Results showed that the major elements of Al 2 O 3 , K 2 O, and TiO 2 were mainly controlled by clay minerals associated with terrigenous detrital, but the SiO 2 and Na 2 O were not influenced by clay minerals. In addition, ΣREE values obtained at Shuanghe and Qiliao sections during the Late Ordovician–Early Silurian were close to those of North American Shale (NASC) composites (173.2 ug/g). REEs were characterized by light rare earth elements enrichment, but heavy rare earth elements depletion. Furthermore, the NASC‐normalized REE patterns were similar with a little difference at Shuanghe and Qiliao sections. The following conclusions were drawn by studying REE indicators associated with source, redox condition and the mechanism of organic matter enrichment: (a) ΣREE showed strong positive correlations with TiO 2 , Al 2 O 3 , K 2 O, and Na 2 O, but exhibited relatively poor correlations with Fe 2 O 3 and P 2 O 5 . These results suggested that REEs in the marine shale mainly occurred in clay minerals, but also were influenced by pyrite, phosphates, and other minerals. (b) Ce/Ce* showed that marine shale during the Late Ordovician–Early Silurian was mainly deposited under anoxic condition in Sichuan Basin and the reduction intensity at Qiliao section was stronger than Shuanghe section. (c) The diagram between La/Yb and ΣREE and the Ce/Ce* values indicated that the detrital minerals in the marine shale were mainly derived from the sedimentary rocks and deposited in the same continental margin environment with a complex composition. (d) The controlling factors of organic matter enrichment were different at Shuanghe and Qiliao sections and the depositional environment controlled the organic matter accumulation and preservation of the organic‐rich marine shale.