Sedimentary Environment of the Early Ordovician in Danzhai, Guizhou

Yu Pei, Youbin He, Jinxiong Luo, Yantao Zeng, Zhan Wen
2017 Open Journal of Yangtze Oil and Gas  
This study analyzes the variations in trace element contents and ratios, the distribution patterns of rare earth elements, and the sedimentary environment and its evolution in the Early Ordovician. In particular, the analysis is based on measured section of the Qingjiang Village located in Nangao Town, Danzhai County, Guizhou Province. The analysis also considers thin sections and the characteristics of C, O isotopes. The lower part of the Tongzi Formation has a simple lithology and mainly
more » ... ogy and mainly consists of light gray to gray thin-medium bedded muddy dolomite and dolomicrite with a few dolarenites and dolorudites. The upper part of this formation includes gray thin-medium bedded fine crystalline dolomite and gray massive bioclastic limestone. Only a fraction of gray massive fine crystalline limestone, sparry calcarenite, and calcirudite are on top of the upper part. The Honghuayuan Formation is generally composed of light gray to gray medium-thick bedded or massive bioclastic limestone, reef limestone, and calcarenite with a few sandstones at the bottom. The δ 18 O PDB values of 18 samples are less than −11‰; in addition, the Pr/Pr* and Ce/Ce* ratios are greater and less than 1, respectively. These data reflect a sedimentary environment. The lower part of the Tongzi Formation might have been formed in an evaporite platform, which was then transformed into a restricted one, which featured a dry climate, a shallow water depth, and an insufficient amount of oxygen. By contrast, the upper part of the formation was deposited in an open platform, which featured a humid climate and relatively increased water depth and reducibility. During the sedimentary period of the Honghuayuan Formation, the water energy further increased, the climate became humid, the water depth increased, and the reducibility increased. Correspondingly, the sedimentary environment, which originally comprised littoral facies that slowly developed into an open platform and into a platform marginal bank, gradually evolved into a platform How to cite this paper: Pei
doi:10.4236/ojogas.2017.23009 fatcat:t3x6biv5qrgsnfmqy4qvg4gvdu