RETRACTED: Sedimentary characteristics and origin of dolomitic ooids of the terminal Ediacaran Dengying Formation at Yulin (Chongqing, South China)

Abstract

Abstract The Ediacaran was a crucial transition period in the evolutionary history of the Earth. Ediacaran ooids in the Dengying Formation from the Yulin section in southwestern China are important archives of paleoenvironmental information. Although these ooids have been totally dolomitized, the cortical fabric characteristics are locally preserved well, indicating that these ooids were mimetically replaced. The common occurrence of concentric–radial fabrics and low level of Sr concentrations (60.3 ± 8.8 ppm) in the studied ooid cortex is more likely suggestive of a primary low-Mg calcite mineralogy and that a calcite sea might exist during deposition of the second member of the Dengying Formation. In situ geochemical data for the ooid cortices obtained by laser ablation inductively coupled plasma mass spectrometry show that these ooids have middle rare earth element enrichment (PrN/SmN = 0.7 ± 0.1 and SmN/YbN = 1.5 ± 0.4) and high Fe contents (8200 ± 1800 ppm). This suggests ferruginous pore waters, which were related to the selective or preferential absorption and release of REEs by Fe-Mn oxyhydroxides.