Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China

Abstract

The terminal Ediacaran Dengying Formation (c. 551.1–538.8 Ma) in South China is one of two successions where Ediacara-type macrofossils are preserved in carbonate facies along with skeletal fossils and bilaterian animal traces. Given the remarkable thickness of carbonate-bearing strata deposited in less than 12.3 million years, the Dengying Formation holds the potential for construction of a relatively continuous chemostratigraphic profile for the terminal Ediacaran Period. In this study, a detailed sedimentological and chemostratigraphic (δ13Ccarb, δ18Ocarb, δ13Corg, δ34Spyrite, and 87Sr/86Sr) investigation was conducted on the Dengying Formation at the Gaojiashan section, Ningqiang County of southern Shaanxi Province, South China. Sedimentological results reveal an overall shallow-marine depositional environment. Carbonate breccia, void-filling botryoidal precipitates and aragonite crystal fans are common in the Algal Dolomite Member of the Dengying Formation, suggesting that peritidal facies were repeatedly karstified. The timing of karstification was likely early, probably soon after the deposition of the dolomite sediments. The presence of authigenic aragonite cements suggests high alkalinity in the terminal Ediacaran ocean. Geochemical analysis of micro-drilled samples shows that distinct compositions are registered in different carbonate phases, which should be considered when constructing chemostratigraphic profiles representative of true temporal variations in seawater chemistry. Integrated chemostratigraphic data suggest enhanced burial of organic carbon and pyrite, and the occurrence of extensive marine anoxia (at least in the Gaojiashan Member). Rapid basinal subsidence and carbonate accumulation during a time of elevated seawater alkalinity and increased rates of pyrite burial may have facilitated the evolutionary innovation of early biomineralizing metazoans.

Formation, diagenesis and palaeoenvironmental significance of upper Ediacaran fibrous dolomite cements

“…These cements have lengths from 100 to 2000 μm and a maximum width of 10 μm, respectively, and exhibit botryoidal crystal fabrics (Fig. D) and square crystal terminations (Cui et al ., ). The fibrous texture is partly lost in some samples (Fig.…”

“…Fibrous dolomites are exceptionally well‐preserved in the upper Ediacaran ( ca 551·1 to 548·0 Ma) Dengying Formation in the Sichuan Basin, China. Due to their potential significance as archives of Ediacaran palaeoenvironmental properties, these fabrics have been debated in the literature, with topics including: (i) the precursor mineralogy (Lin et al ., ; Mou et al ., ; Peng et al ., ; Qian et al ., ; Cui et al ., ; Ding et al ., ); and (ii) the parent fluid (freshwater: Shi et al ., ; Qian et al ., , mixed waters: Xiang et al ., , or seawater: Hao et al ., ; Mou et al ., ; Peng et al ., ; Cui et al ., ; Ding et al ., ). Here, a multi‐proxy, fabric‐specific data set is shown to help elucidate these controversies and provide the foundation for more sophisticated interpretations.…”

Calcium isotopes as a record of the marine calcium cycle versus carbonate diagenesis during the late Ediacaran

“…Calcite pseudomorphs after gypsum have been reported from the Dengying Formation, South China, which is contemporaneous with the Nama Group (Cui et al, 2019;Duda et al, 2016;Lu et al, 2013). Alteration of oceanic crust 1.5*10 12 = seawater…”

“…If instead, recrystallisation occurs under fluid-buffered conditions, the buried calcite can acquire a new δ 44 Ca that reflects the smaller ∆ 44 Calocal between newly precipitated calcite and the pore fluid (Ahm et al, 2018;Higgins et al, 2018) (Figure 5b). Sedimentological, geochemical and fluid inclusion data suggest that the majority of primary carbonate minerals precipitating globally were aragonitic in the terminal Ediacaran (Brennan et al, 2004;Cui et al, 2019;Grotzinger et al, 2005;Zhuravlev and Wood, 2008). If aragonite is the dominant carbonate precipitate from the oceans globally, and if the buried carbonate minerals retain a low δ 44 Ca during sediment-buffered recrystallisation, then more 40 Ca overall is removed from the ocean, and the δ 44 Ca of the ocean should be higher (Blättler and Higgins, 2017).…”

Avances recientes en la comprensión del sistema de vida terrestre del Ediacárico tardío en China meridional y el Ártico siberiano

“…Data source: δ 15 N data , δ 238 U data , all the other data . Modified after Cui et al (2016bCui et al ( , 2019. Figure 2.--Integrated litho-, bio-, and chemo-stratigraphy of the Khatyspyt Formation at the 0601 and 0605 sections, Arctic Siberia, Russia.…”