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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]

Focuses on a study of the geochemical characteristics of the independent cadmium deposit at Niujiaotang, Duyun, Guizhou, China. Geological characteristics of the deposit; Distribution and mode of occurrence of cadmium; Geochemical characteristics of the fluid inclusions in the deposit; Summary.

Phosphorite of the Ediacaran Doushantuo Formation accumulated in the central Guizhou province during the Neoproterozoic-Cambrian Phosphogenic Event, producing the first true phosphorite giant in Earth history. Deposition is interpreted to have occurred on a wave-dominated epeiric platform along the northern margin of the Qianzhong Uplift. Lithofacies stacking patterns and two paleokarst surfaces record phosphogenesis through at least two sea-level cycles. As in younger Phanerozoic epeiric sea phosphorites, the delivery of upwelled phosphorus is interpreted to have stimulated phosphogenesis in a range of shallow-water environments. Ten phosphatic and associated lithofacies are recognized in the Doushantuo Formation. Wavy and horizontal laminated pristine facies were the locus of phosphogenesis and reflect the authigenic precipitation of francolite in accumulating fine sediment. Granular, cross-stratified phosphorite is interpreted to have been produced through storm-wave winnowing of pristine facies and the subsequent transport, redeposition, and concentration of phosphatic peloids into economic beds. Beds with the highest concentration of phosphorus formed in shallow, wave-agitated environments around paleo-topographic highs. Paragenetic analysis suggests that secondary meteoric processes further enriched the phosphorus content (>35 wt%) of these granular beds during sea-level lowstands. Such aerially extensive, upwelling-related phosphorite contrasts Paleoproterozoic and Neoproterozoic phosphatic deposits. Throughout much the Proterozoic francolite precipitation was restricted to shallow-water, photosynthetic oxygen oases where redox sensitive phosphogenic processes were focused in the sediment. The Doushantuo Formation is interpreted to record the oxygenation of the water column and concomitant expansion of phosphogenic environments during the Neoproterozoic Oxygenation Event. This progressive ventilation of the deep ocean forever changed the biogeochemical cycling of phosphorus in the marine realm and set the stage for the deposition of phosphorite giants that punctuate the Phanerozoic stratigraphic record. [ABSTRACT FROM AUTHOR]

• The Doushantuo glaucony have consistent and high K 2 O with low but variable TFe 2 O 3 , consistent with Al–Fe substitution during glauconitization. • The wide occurrence of glaucony documents a generally suboxic early diagenetic environment on the seafloor. • The lack of a negative Ce anomaly in phosphorites confirms deposition and diagenesis in suboxic environments. • Apatite-glaucony association in lower Doushantuo Formation resulted from Fe-redox driven diagenesis. Major phosphogenic events took place in the late Paleoproterozoic and the Ediacaran, both of which followed an episode of atmospheric oxygenation. These apparent coincidences have led to suggestions that the Precambrian phosphorus cycle was partly regulated by oceanic redox conditions, although direct evidence is lacking. In this paper, we report the discovery of glaucony in drill cores from the phosphorite-rich Ediacaran Doushantuo Formation at Weng'an, South China, which provides new insights into redox conditions and geochemical cycles during the deposition and early diagenesis of the lower Doushantuo Formation. The presence of flaser and lenticular bedding in the sandstones suggests deposition in a tidally-influenced shallow water environment. Apatite is present as millimeter-scale flasers in sandstones, but more commonly as intraclastic grains. Glaucony typically occurs as interstitial aggregates cementing and replacing detrital minerals and phosphatic grains, with an upsection decrease in abundance. The Doushantuo glauconies have consistently high K 2 O (7.5–9.6 wt%). In particular, phosphorite-hosted glaucony has generally higher total iron (TFe 2 O 3) than sandstone-hosted glaucony, consistent with Al3+–Fe3+ substitution in the octahedral site, as supported by Raman peaks slightly shifted towards lower wavenumbers for higher Fe content. A decrease in detrital input probably resulted in limited Al availability during early diagenesis, which in turn led to the waning of glaucony upsection. The phosphate grains do not show any negative Ce anomalies, consistent with precipitation of authigenic apatite in suboxic environments with insignificant preferential remobilisation of Ce during deposition and early diagenesis. REE + Y features show variable diagenetic REE enrichment in phosphorites, but identical concave-down patterns. The wide occurrence of glaucony cement further documents the presence of a generally suboxic early diagenetic environment on the seafloor, which was in active exchange with bottom seawater. Slight fluctuations of redox states in the porewater and bottom water would have promoted the cycling of Fe, enrichment of phosphate and REE, and extensive glaucony authigenesis. Therefore, the glaucony-bearing phosphorites in the Doushantuo Formation are a direct result of Fe-redox driven diagenesis. Apatite-glaucony association likely forms in suboxic environments and is considered as a useful mineralogical proxy for paleoredox conditions on the Precambrian ocean floors. [ABSTRACT FROM AUTHOR]