摘要
本文采用化学蚀变指数(CIA)系统研究了鄂尔多斯盆地西缘中晚侏罗世地层,并探讨古气候变迁对大规模砂岩型铀矿成矿作用的影响。研究显示,中侏罗世早期巴柔期(大致为延安组沉积期)样品CIA值总体较高,介于70.4～73.5之间,反映温暖湿润气候条件、中等化学风化程度的古气候条件。中侏罗世巴通期(直罗组下段沉积期)样品CIA值波动较大,介于65.6～79.8之间,并呈锯齿状震荡下降,说明该时期古气候环境经历了由暖湿向半湿润、半干旱的交替变化。中侏罗世晚期的卡洛维期(直罗组上段沉积期)样品CIA值下降明显,介于58.9～72.4之间(主要集中于60～70之间),平均值为66.4(n=14),远低于巴柔期和巴通期样品的CIA平均值(分别为72.8和71.9),反映相对稳定的半湿润、半干旱气候环境;直罗组上段底部的突变界面C3为古气候环境由暖湿向半湿润、半干旱转变的关键界面。进入晚侏罗世CIA突然骤降(58.9),随后增高(65.9～69.4),然后再次骤降(54.2),指示牛津期(安定期)很可能存在剧烈、短暂的变冷事件。
The method of Chemical Index of Alteration(CIA)is applied to the researches of Middle-Late Jurassic strata and discussion of paleoclimate changes. The experimental data show that samples during Middle Jurassic Bajocian(Yan,an Formation period) are characterized by high CIA values, ranging from 70.4~73.5, implicating the warm-temperate humid climate and medium chemical weathering. The 65.6~79.8 CIA values of the samples from Middle Jurassic Bathonian(Low-Zhiluo Formation)reflects alternate appearance of change from warmtemperate humid climate to semi-arid and semi-humid climate. CIA values of the samples from Callovian(UpperZhiluo Formation)fall to 58.9~72.4(focus on 60~70;average value 66.4, n=14), away below the average CIA values of samples from Bajocian to Bathonian(72.8 and 71.9), reflecting a stable semi-arid and semi-humid climate.The transform boundary which climate change from warm-temperate humid climate to semi-arid and semi-humid climate is C3-boundary that below Upper-Zhiluo Formation. The CIA values between Middle Jurassic and Late Jurassic chang from 58.9 to(65.9~69.4), and then low down to 54.2, which reflect the possibility of ephemeral colding event.
作者
张天福
张云
苗培森
俞礽安
李建国
金若时
孙立新
ZHANG Tian-fu;ZHANG Yun;MIAO Pei-sen;YU Reng-an;LI Jian-guo;JIN Ruo-shi;SUN Li-xin(Tianjin Center, China Geological Survey, Tianjin 300170, China;Laboratory of Non-fossile Energy Minerals, China Geological Survey Tianjin Geological Survey Center, Tianjin 300170, China)
出处
《地质调查与研究》
2018年第4期258-262,279,共6页
Geological Survey and Research
基金
国家973项目"中国北方巨型砂岩型铀成矿带陆相盆地沉积环境与大规模成矿作用(2015CB4530006)"
国家重点研发计划课题"北方含铀盆地深部铀富集规律与成矿预测(2018YFC0604203)"
