澳大利亚悉尼中新世古土壤形成时期的古气候特征  

MIOCENE PALEOSOL IN SYDNEY, AUSTRALIA AND ITS PALEOCLIMATIC SIGNIFICANCES

作　　者：王涛[1] 刘秀铭[1,2,3] 吕镔[1] 陈家胜 郭晖[4] 

机构地区：[1]福建师范大学地理科学学院,福建省湿润亚热带山地生态重点实验室——省部共建国家重点实验室培育基地,福州350007 [2]福建师范大学地理研究所,福州 350007 [3]Department of Environment and Geography,Macquarie University,Sydney NSW 2109, Australia [4] 甘肃省油气资源研究重点实验室(中国科学院地质与地球物理研究所兰州油气资源研究中心) 中国科学院油气资源研究重点实验室,兰州 730000

出　　处：《第四纪研究》2015年第4期997-1005,共9页Quaternary Sciences

基　　金：国家自然科学基金项目（批准号：41210002和41402149）和福建省教育厅中青年教师教育科研项目（批准号：JB14017）共同资助

摘　　要：澳大利亚悉尼地区普遍分布着一套中新世早期（17Ma B.P.）发育的砖红壤地层,本文选取该古土壤剖面作为研究对象,进行了常量元素、岩石磁学和土壤色度测试.通过化学蚀变指数（CIA）、磁化率（x）、磁性矿物居里温度（TC）、土壤红度（a ＊）等环境代用指标,结合现代土壤诊断学特征进行综合分析,得出以下结论：1）该中新世古土壤形成时期地表化学风化作用十分强烈,悉尼地区当时可能为湿热的热带气候,通过古土壤化学风化指数对悉尼地区当时降水量进行半定量重建,年平均值高达1471.22mm;2）丰富的降水使土壤发生脱硅富铝铁过程,铁、铝氧化物沿地层自上而下淋溶淀积,在剖面底部富集形成铁结核和铁盘层;3）该古土壤剖面自上而下磁性矿物种类发生规律变化,磁性矿物由磁铁矿→磁赤铁矿化的磁铁矿→磁赤铁矿→赤铁矿逐渐转变,尤其是磁赤铁矿和赤铁矿的大量富集,说明古土壤形成时期对应着一种高温氧化环境.Early Miocene paleosols, dated back to 17Ma B.P., are prevalently distributed in Sydney area, of which laterite strata was previously thought to form in tropic environments with high temperature and humidity. However, the Australia plate did not yet drift to current position during the Early Miocene, when Sydney paleolatitude was at 45°-50°S, thus belonging to temperate zone. So, what were the paleoenvironments like during the laterite developing period is still in controversial. In order to better understand and investigate the paleoclimate of Sydney during the Early Miocene, a typical paleosol profile （33.743269°S, 151.305244°E） with laterite was taken, which was located at the Long Reef Beach （LRB） town （northeast of Sydney）. The profile as depth as 6.9m from top to bottom and was divided into three parts： Holocene Mollisol part （HM, 0 -1.2m） , Miocene Uhisol part （ MU, 1.2- 5.2m） and Miocene Laterite part （ ML, 5.2 - 6.9m）. Contents of macrocelement （ SiO2, Fe2O3, Al2O3, MgO, CaO, Na2O and K2O） , the property of rock magnetism （including low field magnetic susceptibility （X） , saturation isothermal remanent （SIRM）, saturation magnetization （Ms） , and anhysteretic remanent magnetization （ARM） in room temperature, magnetic hysteresis loops, and thermomagnetic analysis （i.e. M-T ＆ K-T curves） ） and the soil chromaticity （L＊ , a＊ , and b＊ ） for all the samples （n = 55） were measured. The results suggest that ： （1） The average chemical index of aheration （ CIA, indicating chemical weathering degree） of LRB paleosol is 95.26, which is comparable with the Late Pleistocene paleosols developed on basalt in north Hainan Island. The high CIA of LRB section indicates strong chemical weathering on the Earth surface during the Early Miocene. The calculated mean annual precipitation during the Early Miocene 1471.22mm in Sydney area is close to current precipitation in Hainan Island （1400-1800mm） as well. （2） Si dropped but Fe and A

关 键 词：古土壤 古气候 元素地球化学 岩石磁学 土壤色度 

分 类 号：P318[天文地球—固体地球物理学] P534.621[天文地球—地球物理学]