Earth Science Frontiers ›› 2020, Vol. 27 ›› Issue (4): 294-301.DOI: 10.13745/j.esf.sf.2020.4.46

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Genesis of bird's-eye structure in the Triassic Dongmaanshan Formation in Chaohu, Anhui Province

XU Liang(), CHEN Tianhu, GAO Yang, CHEN Ping, XIE Qiaoqin, ZHOU Yuefei*()   

  1. Key Laboratory of Nanominerals and Pollution Control of Anhui Higher Education Institutes, School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China
  • Received:2019-09-15 Revised:2020-04-15 Online:2020-07-25 Published:2020-07-25
  • Contact: ZHOU Yuefei

Abstract:

Bird's-eye structure is a special structure in carbonate stratum indicative of the sedimentary environment of supratidal-intertidal zone. A layer of bird's-eye structure is widely developed in the bottom of the Triassic Dongmaanshan Formation in Chaohu, Anhui Province, but its mineralogy, geochemistry and genesis are still poorly understood. Here, we used optical microscope, X-ray diffraction (XRD), Raman spectroscopy and LA-ICP-MS to investigate the mineralogy and geochemical characteristics of bird's-eye structure in the Dongmaanshan Formation. The results showed that the major mineral in bird's-eye structure was calcite, enriched in Sr, REE, etc., with decreasing crystalline size from the core to edge; while the major matrix mineral was dolomite, containing enriched Fe, Cu, Ti, etc. The contents of quartz, clay minerals and organic matters in matrix were higher than in bird's-eye core. These results demonstrated that bird's-eye structure in the Dongmaanshan Formation developed as a result of calcite formation, from matrix re-precipitation in cavities formed by accumulation and decomposition of sedimentary organic matters after Ca separation in the diagenetic stage due to dolomitization.

Key words: Dongmaanshan Formation, bird's-eye structure, dolomitization, mineralogy, geochemistry, Chaohu, Anhui

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