Full
ZHOU Yuan,born in 2002,Ph.D. candidate,is engaged in researches on sedimentology and petroleum field development geology. E-mail: zhouyuan@student.cup.edu.cn.
Outline
The Neoproterozoic represents a critical interval in the evolution of the Earth surface system,during which oceans transitioned from low-oxygen,microbially dominated conditions to a stratified and progressively oxygenated state,accompanied by profound reorganization of seawater chemistry and carbonate depositional systems. Marine dolomite cements,owing to their synsedimentary to early diagenetic modes of formation,have been widely used to reconstruct Neoproterozoic seawater chemistry;however,their formation mechanisms and principal controlling factors remain debated. This study synthesizes petrographic observations together with multiple geochemical proxies,including C,O,Sr,Mo,U,and Mg isotopes,from globally representative Neoproterozoic carbonate successions,to systematically evaluate the petrographic characteristics and paleoenvironmental significance of marine dolomite cements. The stratigraphic comparisons indicate that,despite regional variations in cement morphologies and isotopic compositions,the timing of dolomite precipitation and associated genetic patterns are broadly comparable,suggesting a dominant control by a common global seawater chemical background. Multi-isotopic records further demonstrate that Neoproterozoic seawater chemistry did not remain in a long-term steady state,but evolved dynamically in response to tectonic reorganization,glacial-interglacial oscillations,and variations in continental weathering fluxes. The widespread occurrence of dolomite therefore does not reflect a single,persistently existing “dolomite sea,”but instead records the episodic emergence of favorable chemical conditions during different tectonic-climatic stages. Dolomite precipitation windows are inferred to have been opened under a relatively elevated Mg/Ca background,when low sulfate concentrations,high alkalinity,and appropriate redox conditions acted in concert. Neoproterozoic tectonic-climatic processes modulated seawater end-member inputs and material cycling,allowing such precipitation windows to recur at the global scale and thereby accounting for the anomalous abundance of marine dolomite during this interval. This study systematically clarified the key controlling mechanisms of Neoproterozoic marine dolomite formation from a multi-scale and multi-isotope perspective,providing important constraints for reconstructing the chemical evolution of ancient oceans and understanding the co-evolution of the Earth’s surface system in deep time.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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