Abstract
The Late Permian on the periphery of the Songliao Basin, eastern Inner Mongolia, is an important hydrocarbon source rock system. Its sedimentary environment plays an important role in the evaluation of hydrocarbon prospects in the area. Unfortunately, until now, the interpretation of the sedimentary environment of this area has been controversial. We investigated the Late Permian sedimentary environment by studying the sedimentary characteristics and geochemistry. Based on these investigations, we conclude that the Linxi Formation is mainly composed of clastic sediments, interbedded with limestone lenses, with bioherm limestone at the top of the formation. Inner-layer marine fossils (calcium algae, bryozoans, and sponges) and freshwater and blackish water microfossils (bivalves) are all present, indicative of a typical shallow water sedimentary environment with an open and concussion background. In terms of geochemistry, the formation is relatively light rare Earth enriched, with significant positive Eu anomaly, slight positive La and Y anomaly, weak positive Gd anomaly, and lack of Ce anomaly. The average B/Ga ratio of the mudstone is greater than 3.3, and the average Sr/Ba ratio of the limestone is greater than 1.0. The range of the 87Sr/86Sr ratio is from 0.707285 to 0.707953. The range of δ13C values is from −4.0‰ to 2.4‰. The sediment assemblages, rare Earth elements, trace elements, and 87Sr/86Sr and C isotopes of the formation indicate that the Linxi Formation formed in a marine sedimentary environment and occasional marine-terrestrial transitional facies. The formation can be further divided into littoral facies, neritic facies, bathyal facies, and delta front.
Highlights
Introduction e eastern part of InnerMongolia in China is located on the junction of the Sino-Korea Plate and the Siberian Plate
Zhang et al and Tian et al concluded that the Linxi Formation formed in a marine sedimentary environment, based on the presence of marine fauna and bioherms in the exposed sections of the Late Permian Linxi Formation in the Linxi area [2, 3]. e other interpretation was that the Late Permian Linxi Formation deposited in terrestrial lake sedimentary environment, according the development of the freshwater bivalve fossils and Angara flora of the Late Permian Linxi Formation in the Linxi area [4,5,6]
rare Earth elements (REEs) + Y concentrations were normalized to the Post-Archaean Australian Shale (PAAS) composite [16]. e total REE content (ΣREE) of the sediments in the Linxi Formation ranges from 10.07 μg/g to 195.69 μg/g with an average of 76.56 μg/g
Summary
Introduction e eastern part of InnerMongolia in China is located on the junction of the Sino-Korea Plate and the Siberian Plate. Since the 20th century, different interpretations have been put forth concerning the paleogeographic environment of the Linxi area of eastern Inner Mongolia during the Late Permian. He et al interpreted the sedimentary environment of the Linxi Formation, according to the lithology, sedimentary structure, and paleontology of an exposed section in Linxi County. Zhang et al and Tian et al concluded that the Linxi Formation formed in a marine sedimentary environment, based on the presence of marine fauna and bioherms in the exposed sections of the Late Permian Linxi Formation in the Linxi area [2, 3]. Previous studies formed some conclusions concerning the Permian sedimentary environment of eastern Inner Mongolia, especially in the Linxi area, some issues still require clarification. is is mainly due to the fact that the fossil types are not consistent throughout the formation and that determining the sedimentary environment of a complete set of formations based on environmentally meaningful typical fossils, sedimentary structures, or bioconstructions has its limitations. is research study investigates the Late Permian Linxi Formation’s sedimentary environment, by analyzing the sedimentary characteristics and the geochemical characteristics of the Linxi Formation in the Linxi area, eastern Inner Mongolia
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