Petrological and geochemical characteristics of the botryoidal dolomite of Dengying Formation in the Yangtze Craton, South China: Constraints on terminal Ediacaran “dolomite seas”

Wang, Jingbin; He, Zhiliang; Zhu, Dongya; Liu, Quanyou; Ding, Qian; Li, Shuangjian; Zhang, Dianwei

doi:10.1016/j.sedgeo.2020.105722

Cited by 32 publications

(11 citation statements)

References 83 publications

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“…Terrigenous input likely alters the depositional archives of ancient carbonates, especially the Precambrian samples (Tostevin et al, 2016;Hood et al, 2018), which should be carefully screened before they are analyzed for paleo-environment reconstruction. According to previous studies (Bau et al, 1997;Webb and Kamber, 2000;Ling et al, 2013;Wang et al, 2020;Lan et al, 2022b), the REE + Y data can preserve the paleo-environmental significance if Al < 0.35%, Zr < 4.00 ppm, Th < 0.10 ppm, Sc <1.00 ppm, and REE <4.00 ppm. The maximum Al, Th, Zr, Sc and REE concentrations of the studied samples are respectively 0.328%, 0.073 ppm, 3.094 ppm, 0.337 ppm and 3.393 ppm, which are below the thresholds above.…”

Section: Geochemical Data Reliability Analysismentioning

confidence: 86%

“…Previous studies concluded the general depositional architecture of the Gaoshiti -Moxi area as a rimmed carbonate platform (Liu et al, 2015;Li et al, 2020;Wang et al, 2020;Zhou et al, 2020). From west to east, the Z 2 dn 4 develops deep-water facies, platform margin mound-shoal facies, platform interior shoal and tidal flat, with distinct lithological differences (Zou et al, 2014).…”

Section: Geological Settingmentioning

confidence: 93%

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Terminal Ediacaran microbialite lithofacies associations with paleo-environmental constraints in a high-frequency sequence stratigraphic framework of Sichuan Basin, SW China

Zhou

Li²

2023

Front. Earth Sci.

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The terminal Ediacaran shallow marine microbialites are significant for paleo-environment reconstruction and petroleum exploration. Their depositional and paleo-environmental characteristics during high-frequency sea-level fluctuations were paid less attention, which limited the understanding of their evolution and related reservoir characterization. Microbialites from the fourth member of the upper Ediacaran Dengying Formation, Gaoshiti-Moxi area, Sichuan Basin, SW China are important records for studying their lithofacies associations and paleo-environmental constraints in high-frequency depositional sequences. Petrographic and geochemical analyses (in-situ major and trace elements and carbon and oxygen isotopes) indicate microbialites depositional and paleo-environmental evolution on a rimmed platform within a fourth-order depositional sequence. From late TST (transgressive systems tract) to early HST (highstand systems tract), thick-bedded dark-grey dolomudstone-thin-bedded spotted thrombolite dominates the platform margin; while thick-bedded dark-grey dolomudstone-thin bedded dark-grey wavy stromatolite dominates the platform interior. From late HST to early TST of the next fourth-order sequence, the platform margin is dominated by thick-bedded spotted thrombolite—dolograinstone, while the carbonate interior is dominated by thin-medium-bedded layered thrombolite—light-grey wavy stromatolite. Salinity correlates well with microbialite lithofacies associations: the platform interior layered thrombolite and wavy stromatolite enriched lithofacies associations are characterized by higher salinity than that of the platform margin spotted thrombolite enriched lithofacies associations. The microbialite lithofacies associations are less constrained by redox: platform interior layered thrombolite and wavy stromatolite enriched lithofacies associations are slightly more reduced than the platform interior spotted thrombolite enriched lithofacies associations. The redox analysis of the microbialites also indicates low oxygen levels of shallow marine in the study area during terminal Ediacaran, with possible oxygenation at the Ediacaran-Cambrian boundary. The study suggests that the terminal Ediacaran microbialite development was controlled by both high-frequency sea-level fluctuations and paleo-environmental factors such as salinity and redox. Platform margin spotted thrombolitic reefs from late fourth-order HST to next early fourth-order TST serve as favorable microbialite reservoirs. Platform interior layered thrombolites and wavy stromatolites are regarded as potential reservoirs, which deserve more detailed depositional-paleo-environmental research.

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Section: Geochemical Data Reliability Analysismentioning

confidence: 86%

Section: Geological Settingmentioning

confidence: 93%

Terminal Ediacaran microbialite lithofacies associations with paleo-environmental constraints in a high-frequency sequence stratigraphic framework of Sichuan Basin, SW China

Zhou

Li²

2023

Front. Earth Sci.

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“…Petrographic observations show that the matrix dolomites and dolomite cements have been diagenetically altered to different extents. The micritic, stromatolitic and oolitic dolomites are generally considered to have been dolomitized syn‐depositionally under near‐surface conditions (Hood & Wallace, 2012; Cui et al ., 2019) with the dolomitizing fluid being derived from contemporaneous seawater (Hood & Wallace, 2012; Wang et al ., 2020). The fine crystals and weak luminescence in the micritic and stromatolitic dolomites seemingly support this primary hypothesis (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…The fibrous–radial dolomite cement is suggested to be syn‐depositional or formed shortly after sediment deposition and has been used as a rock record for the purposes of palaeoceanographic reconstruction (Wang et al ., 2020). However, petrographic evidence shows that the early cement co‐occurred with the saddle dolomite filling in pores and vugs and has bright luminescence in the outer zones of the dolomite crystals (Fig.…”

Section: Discussionmentioning

confidence: 99%

A clumped isotope diagenetic framework for the Ediacaran dolomites: Insights to fabric‐specific geochemical variabilities

Lu,

Koeshidayatullah,

et al. 2023

Sedimentology

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While marine dolomites formed under near surface conditions have been considered to be potentially reliable archives of past oceanic conditions, this interpretation comes with significant challenges because diagenetic alteration frequently produces diverse fabrics with large geochemical variability. It has been suggested that the Ediacaran dolomites in South China (Hamajing Member, Dengying Formation) recorded the oceanic conditions present at the time they formed, yet these dolomites are composed of five different fabrics (stromatolitic, micritic, oolitic, saddle dolomites and fibrous–radial dolomite cements) and show large variations in multiple geochemical isotope proxies (carbon, oxygen, clumped, magnesium and the sulphur of carbonate‐associated sulphate). This study establishes a paragenetic sequence for these dolomites by combining the clumped and the oxygen isotopic compositions, thereby assessing whether they are geochemically representative of the original seawater. Using this diagenetic framework, the micritic and stromatolitic dolomites show a closed‐system behaviour (low water–rock ratios; <0.3) and are largely resistant to the hydrothermal alteration during late diagenesis. In contrast, the ooid and cement fabrics have been affected by the hydrothermal fluid precipitating saddle dolomite in the open‐system condition with the high stimulated water–rock ratios (>1). Furthermore, in a closed‐system environment, the elevated δ24Mg and δ34S values in the stromatolitic dolomite reflect the isotopic Rayleigh fractionation that enriches the 26Mg and 34S through rock‐buffered recrystallization, coupled with microbial sulphate reduction. These results demonstrate that the complex signals in early marine dolomite should be carefully evaluated when used as a palaeoproxy.

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“…The thrombolite dolostone is characterized by an irregular microbial-like texture, interlayers of dark and light color mixed fabric (Figure 4c), and botryoidal structure (BS) [54] (Figure 4c) with non-fabric selective dissolution vugs that are filled by multiple stages of isopachous dolomite cements and crystalline dolomite (CD) (Figure 4d). The initial fibrous dolomite cement (FD-I) vertically encircles the boundaries of pores or grains (Figure 4d), showing dull-dark orange luminescence (Figure 4e).…”

Section: Petrological Characteristicsmentioning

confidence: 99%

Diagenesis and Reservoir Evolution Model of the Ediacaran Dengying Formation in the Sichuan Basin: Evidence from Laser Ablation U-Pb Dating and In Situ Isotope Analysis

et al. 2022

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The microbial dolomite of the Ediacaran Dengying Fm., Sichuan Basin, SW China is endowed with abundant oil and gas resources. A complex diagenetic history greatly complicates the development of such microbial dolomite reservoirs, and has severely restrained hydrocarbon exploration. This study focused on key field profiles in Eastern Sichuan and aimed to decipher the origin and evolution of dolomites, using novel techniques, including elemental mapping, laser ablation U-Pb dating as well as carbon, oxygen, and strontium isotope analyses. Additionally, we compared the diagenesis and reservoir development model for the Dengying microbial dolomites of the Central Sichuan to other areas, with the aim to provide practical guidance for oil and gas exploration across the entire Sichuan Basin. Our results have shown that the Ediacaran microbial dolomite in Eastern Sichuan experienced four stages of diagenetic modification–specifically: (1) syn-sedimentary dolomitization; (2) penecontemporaneous cementation of fibrous dolomite cement; (3) bladed dolomite and brown-dark very fine crystalline dolomite cementation during the Ordovician; and (4) fine crystalline dolomite and medium-coarse crystalline dolomite cementation during the Silurian-Devonian. Petrology and geochemistry data imply that each diagenetic phase of dolomitization was mainly sourced from marine-dominated fluids. The influence of tectonically related fluids was rarely noted. Significantly, U-Pb ages of these dolomites reveal that the history of dolomite infill to pores within the Eastern Sichuan Basin clearly post-dated that in the Central Sichuan region, resulting in high porosities (6%–11%) that favored hydrocarbon accumulation. This study suggests that the platform margin at the eastern edge of the Xuanhan-Kaijiang paleo-uplift is favorable as the next key exploration target for microbial dolomites in the Sichuan Basin.

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Petrological and geochemical characteristics of the botryoidal dolomite of Dengying Formation in the Yangtze Craton, South China: Constraints on terminal Ediacaran “dolomite seas”

Cited by 32 publications

References 83 publications

Terminal Ediacaran microbialite lithofacies associations with paleo-environmental constraints in a high-frequency sequence stratigraphic framework of Sichuan Basin, SW China

Terminal Ediacaran microbialite lithofacies associations with paleo-environmental constraints in a high-frequency sequence stratigraphic framework of Sichuan Basin, SW China

A clumped isotope diagenetic framework for the Ediacaran dolomites: Insights to fabric‐specific geochemical variabilities

Diagenesis and Reservoir Evolution Model of the Ediacaran Dengying Formation in the Sichuan Basin: Evidence from Laser Ablation U-Pb Dating and In Situ Isotope Analysis

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