Abstract
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 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 δ18OPDB 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 marginal reef.
Highlights
The Early Ordovician section in the Qingjiang Village of Nangao Town in Danzhai County, Guizhou Province shows clear stratigraphic boundaries (Figure 1), complete layers, reliable depositional marks, and abundant fossils
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
This section is an excellent carrier of the sedimentary environment evolution in southeast Guizhou and partially reflects the Early Ordovician tectonic evolution of South China
Summary
The Early Ordovician section in the Qingjiang Village of Nangao Town in Danzhai County, Guizhou Province shows clear stratigraphic boundaries (Figure 1), complete layers, reliable depositional marks, and abundant fossils. To gain further insights into reservoir development characteristics and strengthen petroleum geology research by exploring the basic issues related to reservoir formation and the potential of marine oil and gas exploration in the south, we must clarify the characteristics and evolution of the sedimentary environment. Biostratigraphy researches, such as trilobites, corals, conodonts and so on, are conducted in the Early Ordovician of Guizhou Province [10] [11] [12] [13] [14]. This study discusses the Early Ordovician paleoenvironment, including paleoclimate, paleosalinity, paleowater depth, paleoxygenation facies, and its evolution in the Danzhai region of Guizhou on the basis of petrology characteristics and by synthetically using C, O isotopes and trace elements
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