Ediacaran (Sinian) palaeogeographic reconstruction of the Upper Yangtze area, China, and its tectonic implications

ABSTRACT

The Ediacaran (ca. 635–541 Ma) was a critical period in Earth history, which saw a dramatic transformation in global biological, chemical and climatic conditions, making it one of the most intensively investigated time intervals worldwide. As the first mixed clastic–carbonate succession deposited on the Upper Yangtze Craton, the Ediacaran succession overlies Neoproterozoic continental rifts, and records a complex basin infill history. In this study, we focus on the tectonostratigraphic environment and basin infill process, integrating multiple data sets, including boreholes, outcrops, well correlations, seismic data, isopach maps and the spatial distribution of sedimentary facies. The Ediacaran System includes the Doushantuo Formation and overlying Dengying Formation which can be subdivided into four lithostratigraphic members (D1–D4). The Doushantuo Formation and D3 Member consist of mixed clastic–carbonate sediments, while carbonates predominate in the D1, D2 and D4 members. Intracratonic depressions and continental margin rifts dominated the Upper Yangtze area during the Ediacaran. During deposition of the Doushantuo Formation, the Upper Yangtze area contained a variety of environments, including terrigenous shorefaces, mixed tidal flats, lagoons, shelves, slopes and bathyal seas. A rimmed carbonate platform developed during deposition of the D1 and D2 members. The Deyang–Anyue Trough, which is related to post-rift subsidence in the intracratonic basin, began to develop in this interval. A relatively intense extension during deposition of the D3 Member resulted in intensification of intracratonic and continental margin rifting, creating distinct tidal flat, deep-water shelf, slope and bathyal environments. With the expansion of the Deyang–Anyue Trough during deposition of the D4 Member, the rimmed carbonate platform was divided into two segments. We suggest that the Deyang–Anyue Trough was a structurally controlled intracratonic rift-sag and likely arose from multiple episodes of rifting in the cratonic basement, as well as differential uplifting and exposure caused by the ongoing Tongwan Movement. Our model highlights the role of basement heritage on the structure and evolution of intracratonic rift-sag.

KEYWORDS:

• Palaeogeography
• intracratonic rift-sag
• erosional trough
• Doushantuo Formation
• Dengying Formation
• Upper Yangtze Craton

Research Highlights

• Two cyclical tectonostratigraphic transitions from mixed clastic-carbonate sediments to carbonates occur in the Ediacaran System.

• Ediacaran tectonic and depositional environments in the Upper Yangtze Craton were restored.

• The Deyang–Anyue Trough is interpreted as a structurally controlled intracratonic rift-sag that initially formed at the end of D2 Member deposition.

• This trough originated via multiple episodes of rifting in cratonic basement and episodic uplift associated with the Tongwan Movement.

Acknowledgments

We would like to thank the Sinopec Exploration Company and the PetroChina Southwest Oilfield Company for kindly supplying borehole, log and seismic data from the Sichuan Basin. We are grateful to the Chengdu Institute of Geology and Mineral Resources and Chengdu University of Technology for kindly supplying some outcrop data. We also greatly appreciate the precious comments and suggestions from Professors Robert J. Stern, Guochun Zhao, Xianhua Li, Andrei Khudoley, Simon Hohl and anonymous reviewers.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was financially supported by the National Key R&D Plan of China (2017YFC0601405) and the National Natural Science Foundation of China (Projects 41430316, 40739906, 41272237, 91755211, 41702110).