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δ^(18)O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δ^(18)O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δ^(18)Ow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。
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.δ 18 O values range from -7.96‰, VPDB to -11.35‰, VPDB, and δ 13 C 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 δ 18 O values are recognized as(-9.04±0.18)‰, VPDB and(-8.0±0.11)‰, VPDB from the sample CL-11C4. Subsequently, the δ 18 O w 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.
作者
刘芮岑
李祥辉
胡修棉
LIU RuiCen;LI XiangHui;HU XiuMian(School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China)
出处
《沉积学报》
CAS
CSCD
北大核心
2018年第6期1169-1176,共8页
Acta Sedimentologica Sinica
基金
国家自然科学基金项目(41372106
41672097)~~
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
oxygen isotope
paleoprecipitation
pedogeniccalcrete
Late Cretaceous
Chaling Basin