Geochemical characteristics and the significance of two major coal‐bearing strata claystones from the Datong Coalfield (North China). Issue 5 (4th January 2022)

• Record Type: Journal Article
• Authors: Liu, Linsong; Li, Jintao; Zhang, Jing; Hao, Riwa; Kang, Xingjian; Liu, Qinfu
• Is Part Of: Geological journal. Volume 57:Issue 5(2022)
• Page Start: 1938
• Page End: 1956
• Publication Date: 2022-01-04
• Subjects: diagenetic process -- parent rock -- sedimentary environment -- sedimentary kaolinitic claystone -- tonstein; Geology -- Periodicals; 551
• DOI: 10.1002/gj.4389
• Languages: English
• ISSNs: 0072-1050

Abstract

Abstract : This study aims to investigate the significance of the geochemical differences and the factors that control the geochemistry of two major types of coal‐bearing stratum claystones (sedimentary kaolinitic claystone [SK‐claystone] and tonstein). The SK‐claystone and tonstein derived from the Taiyuan Formation of the Upper Carboniferous coal‐bearing strata in the Datong Coalfield of North China have been comprehensively analysed using X‐ray powder diffractometer, scanning electron microscopy, X‐ray fluorescence, and inductively coupled plasma mass spectrometry. The results showed that the SK‐claystones and tonsteins exhibit similar SiO2 content; however, the content of Al2 O3 in tonsteins is higher than that in SK‐claystones, whereas the TFe2 O3 and K2 O content in tonsteins are lower than those in SK‐claystones. These findings are consistent with the mineral composition analysis of the samples. The SK‐claystones and tonsteins have different parent rocks, as shown by the Al2 O3 /TiO2 ratios, diagram of Zr/TiO2 versus Nb/Y, and chondrite‐normalized rare earth element patterns. The palaeosalinity indexes (B/Ga and Sr/Ba) and palaeoredox proxies (Mo and U enrichment factors as well as U/Th ratios) indicate that both SK‐claystones and tonsteins were formed in freshwater suboxic–oxic environments. The kaolinite in SK‐claystones and tonsteins is formed via the deposition or crystallization of aluminium‐rich weathering products and alteration of volcanic ash, respectively. In summary, the different parent rocks and diagenetic processes are the main factors differentiating the geochemical characteristics of the two types of claystones. Our study links the different types of elemental enrichment features to the geological genesis of the two types of claystones, indicating that the trace elemental enrichment characteristics can be used as indicators for distinguishing the SK‐claystone and tonstein in the Datong Coalfield as well as other similar coalfields. Abstract : This study presents a comparative study on the geochemical characteristics of two types of coal‐bearing strata claystones in the Late Paleozoic of North China. The model for the formation of sedimentary kaolinitic claystone and tonstein shows that the geochemical characteristics of claystones controlled by parent rock type and diagenetic process. The different trace element enrichment characteristics can be used as an important indicator for discriminating the coal‐bearing strata claystones.