Carbon Isotope Negative Excursion of the Sturtian Glacial Sediments in the Nanhua Basin and its Geological Significance
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摘要: 新元古代Sturtian冰期(~ 717-660 Ma)在全球范围内广泛发育,在南华盆地中也有良好的记录,但是目前对冰期的碳循环过程研究较少。为了了解Sturtian冰期期间的碳同位素特征,选取黔东松桃地区高地ZK2115钻孔为研究对象,对Sturtian冰期期间沉积的铁丝坳组进行高分辨率的有机碳和无机碳同位素(δ13Ccarb和δ13Corg)测试,结果显示δ13Ccarb值在-9.29 ‰和-3.37 ‰之间变化(平均值-7.24 ‰),具有明显的负偏,δ13Corg值在-33.63 ‰和-23.35 ‰之间变化(平均值-29.29 ‰)。此外,δ13Ccarb和δ13Corg具有明显的正相关关系,表明地层中的无机碳同位素组成不受成岩作用的影响,δ13Ccarb代表了Sturtian冰期期间南华盆地中溶解的无机碳(dissolved inorganic carbon; DIC)库的碳同位素组成,并且地层中的有机质主要是通过光合作用形成的,有机质中固定的碳主要来源于海水中的DIC库。结合已发表的铁丝坳组TOC含量(平均值0.25 %),这意味着在冰期这种极端气候条件下,光合作用虽然仍在进行,但是其速率比较缓慢,产生有机质的量相对较少。本文对Sturtian冰期沉积物中碳同位素组成的研究也有助于进一步探讨冰期的碳循环过程,同时也为深入理解极端气候条件下的古海洋环境及生物地球化学循环提供依据。
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关键词:
- Sturtian冰期 /
- 铁丝坳组 /
- 碳同位素 /
- 南华盆地
Abstract: The Neoproterozoic Sturtian Glaciation (~ 717-660 Ma) developed widely across the world, which was well recorded in the Nanhua Basin, but the study of carbon cycling during this period has been lacked. To understand the characteristics of carbon isotope compositions during the Sturtian Glaciation, this study focuses on the drillcore ZK2115 in Songtao area, eastern Guizhou Province, and the high-resolution organic and inorganic carbon isotopes (δ13Corg and δ13Ccarb) of the syn-Sturtian Tiesi’ao Formation are analyzed. The results show that the values of δ13Ccarb vary between -9.29 ‰ and -3.37 ‰ (mean -7.24 ‰), indicating the genitive excursion. The values of δ13Corg vary between -33.63 ‰ and -23.35 ‰ (mean -29.29 ‰). Besides, there is a positive correlation for the δ13Corg and δ13Ccarb values, indicating that the inorganic carbon isotope compositions are not affected by the diagenesis, and can be used to reflect the original carbon isotope signals of the syn-Sturtian Nanhua Basin. Combined with the low TOC contents (mean 0.25%) of the Tiesi’ao Formation, showing that the photosynthesis still existed under the extreme glacial conditions with low rates, and the contents of the generated organic matter are low. The research of carbon isotope compositions in this study can be used to explore the carbon cycling during the Sturtian Glaciation and can also provide evidence for the paleo-marine environment and biogeochemical cycle under extreme climatic condition.-
Key words:
- Sturtian Glaciation /
- Tiesi’ao Formation /
- carbon isotope /
- Nanhua Basin
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