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The Ediacaran–Cambrian Phosphogenic Episode is the Earth's first true phosphogenic event and resulted in worldwide phosphate deposits, which occurred during the processes of the Neoproterozoic Oxygenation Event. The Ediacaran Doushantuo Formation (ca. 635–551 Ma) of Weng'an area in central Guizhou, South China, contains two economic phosphorite beds (the Lower and Upper Phosphorite Beds). This paper presents a detailed stratigraphic, sedimentological and mineralogical study of multiple outcrop and drill core sections of the Doushantuo Formation across the Weng'an area, and identified 11 lithofacies and 4 types of phosphatic grains. Significant differences in lithofacies and grain types between the upper and lower phosphate deposits are observed, indicating that the two sets of phosphate deposits are the products of two distinct phosphogenic processes. The Lower Phosphorite Bed mainly consists of banded and laminated phosphorites, contains micro-oncoids formed by microbially-mediated precipitation and peloids formed by in-situ chemically oscillating reactions, indicating a biochemical and chemical enrichment of phosphorus to sediments during the Early Ediacaran Period. The Upper Phosphorite Bed is mainly composed of carbonaceous, massive, and stromatolitic phosphorites, contains bioclasts (phosphatized spheroidal fossils), and intraclasts formed by hydrodynamic agitation, suggesting that the major accesses of phosphorus to sediments were the remineralization of organic P. Deposition of the two economic phosphorite beds was controlled by two sea-level cycles. Such differences have also been documented in contemporaneous phosphate-bearing successions in Brazil and Mangolia, indicating a significant shift in global phosphogenic mechanism during the early and middle Ediacaran, which may be due to the changes in redox conditions in seawater, associated with the Neoproterozoic Oxygenation Event. These regional active P-cycle processes could produce more free oxygen, which may have contributed to the upcoming Phanerozoic global oxidation. [ABSTRACT FROM AUTHOR]

The terminal Ediacaran Dengying Formation in the eastern Yangtze Gorges area, South China is well known for hosting diverse Ediacaran-type macrofossils and trace fossils. However, the depositional processes of this carbonate succession are still poorly known. Here we present detailed sedimentological data on the Dengying carbonates in four sections across the eastern Yangtze Gorges area, with an emphasis on tempestites in limestones of the Shibantan Member of Dengying Formation that have largely been overlooked. The Shibantan limestones in the studied sections contain extensive autochthonous microbial mats and storm-related deposits, including calcirudite, individual swaley cross-stratified calcarenites, hummocky cross-stratified fine- to very fine-grained calcarenites, normally graded calcarenites, calcarenite-calcisiltite beds in discrete units, and soft-sediment deformed beds. The spatial variation of facies suggests that the Shibantan Member was deposited on a carbonate ramp with an intra-ramp lagoon. With the upward shallowing of water depth and progradation of storm-generated sediments, the ramp gradually become steeper, as characterized by the occurrence of soft-sediment deformation structures and graded bedding in the middle of the member. The abundance of tempestites in the Shibantan limestones suggests that the Shibantan Basin was located in low-latitude regions frequently affected by tropical storms, consistent with previous paleogeographic reconstructions. Storm events probably brought nutrients into the environment and contributed to the rapid burial and preservation of macrofossils. The Shibantan limestones thus provide another example of a massflow-related taphonomic window for the Ediacaran organisms that is comparable to the fossil preservation style in the Ediacaran siliciclastic rocks. • Eight facies have been recognized from the Dengying Formation. • Tempestites are abundant in the Shibantan limestones. • The Shibantan Member was deposited on a carbonate ramp with an intra-ramp lagoon. • The Shibantan Basin was located in low-latitude regions affected by tropical storms. • Storm events contributed to the preservation of Ediacaran-type fossils. [ABSTRACT FROM AUTHOR]