| 湖南茶陵盆地晚白垩世古降水氧同位素 |
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| 引用本文： | 刘芮岑,李祥辉,胡修棉.湖南茶陵盆地晚白垩世古降水氧同位素[J].沉积学报,2018,36(6):1169-1176. |
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| 作者姓名： | 刘芮岑 李祥辉 胡修棉 |
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| 作者单位： | 南京大学地球科学与工程学院, 南京 210023 |
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| 基金项目： | 国家自然科学基金项目（41372106，41672097） |
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| 摘 要： | 在岩相、阴极发光分析基础上，对湖南茶陵盆地戴家坪组成壤钙质结核进行了碳、氧同位素测试，重建了该区晚白垩世古降水的氧同位素。分析结果显示，戴家坪组发育钙质古土壤，背景岩性以洪积扇环境下形成的副砾岩为特征；钙质结核主要由棕红色微晶方解石基质和浅红色方解石脉构成，前者的阴极发光呈微弱橘红色或不发光，后者发光呈明亮橘黄色；钙质结核的δ18O值（VPDB）介于-7.96‰~-11.35‰之间，δ13C值（VPDB）为-7.30‰~-8.24‰。综合方解石构成、阴极发光和氧同位素表明，钙质结核存在两期方解石沉淀作用。依据氧同位素分布特征，在样品CL-11C4的δ18O值（VPDB）中识别出2条大气方解石线（MCLs），分别为（-9.04±0.18）‰和（-8.03±0.11）‰。进一步根据古纬度和地表温度，估算出茶陵地区晚白垩世晚期的大气降水δ18Ow值（VSMOW）为-5.76‰~-6.80‰，与北美近似纬度地区同期的降水一致，为白垩纪水文循环模型及古大气环流模拟提供了基础参考数据。
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| 关 键 词： | 氧同位素 大气降水 成壤钙质结核 晚白垩世 茶陵盆地 |
| 收稿时间： | 2017-11-30 |
Late Cretaceous Oxygen Isotope of Paleoprecipitation in Chaling Basin,Hunan Province |
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| Institution: | School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China |
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| Abstract: | Based on the analyses of lithofacies and cathodo luminescence(CL) images, we measured the carbon and oxygen isotopic ratios of pedogenic calcretes from the Late Cretaceous Daijiaping Formationin Chaling Basin, Hunan province and estimated the paleoprecipitation-oxygen isotopes. Results show that the Daijiaping Formation is characterized by calcisols with in paraconglomerates, which were deposited in an alluvial fan environment along the mountain foot.Calcretes mainly consist of a reddish-brown calcite matrix and light-red calcite vein, corresponding to dull reddish-orange CL or non-luminescence and bright orange CL, respectively.δ18O values range from -7.96‰, VPDB to -11.35‰,VPDB, and δ13C values from -7.30‰, VPDB to -8.24‰,VPDB. The integration of calcite composition, CL, and oxygen isotopes indicates two stages of calcite precipitation have ever been experienced by the calcretes.From the oxygen isotope data, two meteoric calcite lines (MCLs) of δ18O values are recognized as(-9.04±0.18)‰, VPDB and(-8.0±0.11)‰, VPDB from the sample CL-11C4. Subsequently, the δ18Ow values of the Late Cretaceous paleoprecipitation are estimated from -5.76‰, VSMOW to -6.80‰, VSMOW at low paleolatitude (~17.4°N) for the Chaling Basin, consistent with those from the similar latitude in North America and providing basic reference data for the Cretaceous greenhouse hydrologic cycle model and paleoatmospheric circulation simulation. |
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