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Depositional environments in an arid, closed basin and their implications for oil and gas exploration; the Lower Permian Fengcheng Formation in the Junggar Basin, China

Yu Kuanhong, Cao Yingchang, Qiu Longwei and Sun Peipei
Depositional environments in an arid, closed basin and their implications for oil and gas exploration; the Lower Permian Fengcheng Formation in the Junggar Basin, China
AAPG Bulletin (September 2019) 103 (9): 2073-2115

Index Terms/Descriptors
Abstract

The Fengcheng Formation is a nonmarine, carbonate-dominated succession that formed under arid climatic conditions in a hydrologically closed basin. Two transects and two seismic profiles were examined, the characteristics and environmental significance of different lithofacies were studied, and a model of depositional environment divisions was proposed. The sedimentary model involved an alkaline lake in which the depositional environments consisted of a shallow saline lake margin, slope, saline lake center, and steep lake margin from northeast to southwest. The perennial central salty lake was located in the southwestern part of the study area, whereas there were widespread, low-gradient lake margins in the northeast, east, southeast, and southern parts of the study area. Lake-level fluctuations had a major influence on the shallow saline lake system and complicated the depositional environments in these areas. The deposits are derived from bedrock reworking, volcanic eruptions, and authigenic minerals that precipitated from brine during the hypersaline phase. Fine-grained terrigenous clastic sediments, volcanic ashes and dusts, and authigenic minerals mixed in the depocenter (concentration center of the brine pool), which was covered by high-salinity brines, and the depositional environment was anoxic as a result of salinity-based brine stratification. A thick sodium carbonate succession occurred in the depocenter of the ancient Mahu lake, where bedded sodium carbonate alternated with fine-grained, organic-rich tuff or tuffaceous hydrocarbon source rocks. Microorganisms bloomed in the alkaline, high-salinity brine, and the organic matter was well preserved, which is similar to those modern alkaline saline lakes in eastern Africa and western North America. Thus, the Permian Fengcheng Formation contains source rocks that formed in an alkaline saline lake.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 103
Serial Issue: 9
Title: Depositional environments in an arid, closed basin and their implications for oil and gas exploration; the Lower Permian Fengcheng Formation in the Junggar Basin, China
Affiliation: China University of Petroleum (East China), School of Geosciences, Laboratory of Deep Oil and Gas, Qingdao, China
Pages: 2073-2115
Published: 20190915
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 132
Accession Number: 2019-088991
Categories: StratigraphyEconomic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., strat. cols., geol. sketch maps
N46°00'00" - N46°19'60", E85°25'00" - E86°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 2019
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