中国古蚤属一新纪录

古蚤属 (Palaeopsylla Wagner,190 3) ,遍及古北界及相邻的东洋界。主要宿主为食虫目的鼠句鼠青科和鼹科。我国陈宁宇等 (1979)、张金桐等 (1984 )又相继建立了钝刺古蚤种团和短额古蚤种团。迄今我国共发现古蚤属 17个种 ,其中分布于云南省的达 10个种 [1,2 ] 。2 0 0 1年 8月 4日在新疆尼勒克县唐布拉天山森林草原带小鼠句鼠青 (Sorex minutus)体上采得一批跳蚤 ,经鉴定其中有 4 、4♀♀为鼠句鼠青古蚤种团 (Soricisgroup)鼠句鼠青古蚤斯塔克亚种 Palaeopsylla soricisstarki Wagner,1930。本亚种在国外分布于中亚 ,在原苏联分布很广 …     

云南省无量山自然保护区小型兽类群落结构及垂直分布研究

目的对云南省无量山自然保护区小型兽类群落结构、垂直分布及动物区系进行调查.方法采用铗日法,在云南无量山的4个垂直植被带:Ⅰ.暖温性针叶林和温性常绿阔叶林带(1 200～2 000m);Ⅱ.暖温性常绿阔叶林带(1 900～2 700m);Ⅲ.温性针阔叶混交林带(2 700～2 930m);Ⅳ.寒温性亚高山灌丛草甸带(2 930m及以上).分别捕捉取样,每带投铗数不少于1 100个,每日收集捕获的动物标本,分类鉴定登记计数.结果共捕获小兽26种 803 只,隶属于鼠科(Muridae)12种,松鼠科(Sciuridae)1种,鼩鼱科(Soricidae) 7种 ,鼹科(Talpidae)2种,猬科(Erinaceidae)1种,树鼩科 (Tupaiidae)1种和鼬科(Mustelidea)1种.其中东洋界有23 种,占88.46%;古北界3 种,占11.54% .无量山4个植被物种多样性指数分别如下:Ⅰ. 2.193 1;Ⅱ. 1.673 2;Ⅲ. 1.806 8 和Ⅳ. 1.796 6.云南省无量山小兽优势种主要由中华姬鼠(Apodemus draco)、大绒鼠(Eothenomys millet)、社鼠( Niviventer confucianus)、针毛鼠(N.fulvescens)、灰腹鼠 (N.eha)、锡金小鼠 (Mus pahari)、卡氏小鼠(M.caroli)、印度长尾鼩(Soriculus leucops)和中华新猬(Neotetracus sinensiss)组成.结论云南省无量山小兽群落物种多样性指数相对较高,群落相对稳定,存在着多种疾病的宿主动物.     

东方田鼠及其天然抗日本血吸虫感染的特性

东方田鼠 (Microtus fortis) [1 ]亦称米氏田鼠 (Microtusmichnoi kastschenko,1910 )或沼泽田鼠、远东田鼠、大田鼠、长江田鼠及湖鼠。属于啮齿目 ,仓鼠科 ,田鼠亚科 ,田鼠属 ,在我国分布甚广。我国的东方田鼠大致可分为 5个亚种 :分布于陕西、甘肃的指名亚种 (M.fortis fortis Büchner,1889)、分布于长江中下游的长江亚种 (M.fortis calamorum Thomas,190 2 )、分布于东北等地的黑龙江亚种 (M.fortis pelliceusThomas,1911)和辽宁亚种 (M.fortis fortis dolichoephalusMoril,1930 )以及福建亚种 [2 ] (M.fortis fujianensis hong,19…     

云南华坪县鼠疫疫源地调查实验室检测结果及风险分析

目的 调查处于滇川交界疑似鼠疫疫源地的华坪县鼠疫流行情况,为当地鼠疫的预防控制工作提供依据。方法 采集宿主动物及其体表寄生蚤样本,采集鼠疫指示动物血清,采用间接血凝实验(IHA)和酶联免疫实验(ELISA)两种方法对血清样本进行鼠疫F1抗体检测,采用反向间接血凝实验(RIHA)对自毙鼠脏器进行鼠疫F1抗原检测,对鼠脏器和蚤样本进行鼠疫菌分离培养。同时,对当地近年发生自毙鼠疫情、可疑病例情况进行回顾性调查。结果 共捕获小兽3目4科9属17种240只,居民区捕获率为1.58%,优势种为小家鼠(47.37%,9/19)和褐家鼠(26.32%,5/19);农耕区捕获率为10.85%,优势种为卡氏小鼠(23.08%)、黑缘齿鼠(12.22%)、灰麝鼩(11.76%)、白尾梢麝鼩(11.31%)、锡金小鼠(10.41%)和齐氏姬鼠(10.41%)。共检获小兽寄生蚤5科7属7种26匹,小兽平均染蚤率为10.83%,总蚤指数为1.53,居民区优势种为缓慢细蚤和印鼠客蚤相对较多,农耕区优势种为穗缘端蚤中缅亚种、近端远棒蚤二刺亚种和方叶栉眼蚤。共采集指示动物血清531份,其中犬血清491份、猫血清40份,...     

玉龙县及古城区鼠疫疫源地小型兽类构成及群落多样性特征

目的调查云南丽江玉龙县及古城区鼠疫自然疫源地小型兽类的构成及群落多样性特征,为鼠疫防控提供依据。方法在丽江玉龙县18个自然村和古城区9个自然村范围内,按鼠疫监测方案进行监测,捕获小型兽类进行种类鉴定。用群落生态学方法计算小型兽类的构成、多样性指数、均匀性指数、优势度指数和丰富度指数。结果共捕获小型兽类3目6科14属23种12 219只。其中啮齿目3科8属16种,食虫目2科5属6种,攀鼩目1科1属1种。群落多样性特征结果表明:三种不同生境的(Shannon–Wiener)多样性指数在1.148 9~1.493 0之间;(Pielou)均匀性指数在0.389 9~0.551 3之间;(Simpson)优势度指数在0.313 9~0.446 0之间;(Margalef)丰富度指数在2.031 4~2.311 9之间。Whittaker群落相似性指数比较结果,居民区与耕作地为极相似,居民区与林地、林地与耕作地为中等相似。结论丽江玉龙县及古城区鼠疫疫源地小型兽类以姬鼠(包括齐氏姬鼠、大耳姬鼠)、绒鼠(包括大绒鼠、玉龙绒鼠)、灰麝鼩、褐家鼠、黄胸鼠为优势种,群落多样性表明:居民区与耕作地为极相似,居民区与林地、林地与耕作地为中等相似。     

宁夏中卫市沙坡头区啮齿动物及其体外寄生虫调查

目的了解宁夏中卫市沙坡头区啮齿动物及其体外寄生虫的种群组成与数量分布,为预防鼠传疾病提供基础数据。方法采用鼠疫动物和昆虫监测方法,分类鉴定捕获的鼠和蚤并统计计数。结果共发现啮齿动物3目6科9属12种130只,其中子午沙鼠Meriones meridianus(占37.69%)、三趾跳鼠Dipus sagitta(占29.23%)和小毛足鼠Phodopus roborovskii(占12.31%)为优势种,长尾仓鼠Cricetulus longicaudatus(占6.92%)、长爪沙鼠Meriones unguiculatus(占5.38%)、阿拉善黄鼠Spermophilus dauricus alaschanicus(占2.31%)、草兔Lepus capensis(占1.54%)和大沙鼠Rhombomys opimus(占1.54%)为常见种;在沙坡头旅游区首次发现有大沙鼠R.opimus分布,为宁夏新记录,发现跳蚤3科6属7种,其中同形客蚤指名亚种Xenopsylla conformis conformis(占74.51%)为优势种,秃病蚤田鼠亚种Nosopsyllus laeviceps ellobii(占9.35%)、长突眼蚤Ophthalmopsylla kiritschenkoi(占8.50%)和细钩双蚤Amphipsylla tenuihama(占6.80%)为常见种,人蚤Pulex irritans(占0.28%)、长吻角头蚤Echidnophaga oschanini(占0.28%)和双蚤属未定种Amphipsylla sp.(占0.28%)为稀有种。结论中卫市沙坡头区啮齿动物及其体外寄生蚤种类丰富,沙坡头旅游区广泛分布有长爪沙鼠Meriones unguiculatus及同形客蚤指名亚种Xenopsylla conformis conformis,其数量较多;该地区基本具备动物鼠疫流行的条件,需高度重视、适时监测。     

2001～2010年广州市鼠疫宿主动物及其媒介种类的监测及评价

目的分析广州市鼠疫宿主动物及其媒介的种群构成及数量分布情况,为制定鼠疫防控策略提供依据。方法采用夜笼法。在广州市12区、县级市设置监测点,对捕获鼠类及捡获蚤类进行鉴定,计算鼠密度;计算鼠带(染)蚤率和蚤指数;用鼠疫IHA法检测鼠疫F1抗体。结果 10年间共捕获鼠形动物8 891只,分属2目2科4属9种。其中啮齿目动物8 285只,食虫目动物606只,总鼠密度(捕获率)为11.25%;在1 185只鼠形动物中发现染蚤鼠243只,捡获蚤811只。发现蚤类4种,主要蚤种为印鼠客蚤;平均鼠染蚤率为20.51%,总蚤指数为0.68;未查出鼠疫F1抗体。结论未发现鼠间鼠疫流行迹象。褐家鼠仍是广州市主要鼠种。主要蚤种是印鼠客蚤。     

广州市2006～2007年鼠疫宿主动物监测结果分析

目的 了解广州市鼠疫宿主动物的种群构成及数量分布情况.为鼠疫防治T作积累基础资料.方法 采用夜笼法.对捕获鼠类及检获蚤类进行鉴定;计算鼠带(染)蚤率和蚤指数;用鼠疫IHA法检测鼠疫FI抗体.结果 捕获鼠形动物1 709只,分属2目2科4属7种.其中啮齿日动物1 615只,食虫目动物94只,总鼠密度(捕获率)为10.39%,鼠密度(捕获率)为9.83%:在194只鼠形动物中发现染蚤鼠40只,检获蚤84只,鼠体表蚤经鉴定为印鼠客蚤、猫栉首蚤;鼠染蚤率为20.62%,总蚤指数为0.43;黄胸鼠蚤指数为0.56;未查出鼠疫FI抗体.结论 褐家鼠仍是广州市主要鼠种,主要蚤种是印鼠客蚤,未发现鼠间鼠疫流行迹象.     

克拉玛依地区的利什曼病 Ⅲ.大沙鼠体内利什曼原虫的形态及其对实验动物致病力的研究

在新疆克拉玛依的小拐和白碱滩两地,从20只大沙鼠的耳组织徐片上查出9只有利什曼原虫的感染。经测量69个原虫,平均大小为4.71±0.71×2.35±0.44μm,t试验结果显示,该地大沙鼠体内的利什曼原虫较沙鼠利什曼明显为小,与硕大利什曼原虫的形态比较,也有显著不同。 动物实验感染结果表明,该地大沙鼠体内的利什曼原虫在接种到BALB/c小鼠的足垫皮下后。可使小鼠产生皮肤溃疡和转移性皮肤损害,小鼠最后死于全身性感染。在远交系小鼠(昆明株)的足垫组织内,利什曼原虫可引起足垫局部短期肿胀,旋后消退,在外观正常的足垫皮下组织内,原虫可持续7个月以上。当原虫被注入黑线仓鼠的睾丸内后,产生睾丸局部感染,利什曼原虫主要寄生在鼠睾间质部位的巨噬细胞内,在曲细精管内的一些塞氏细胞中也有原虫寄生,偶而也发生转移性皮损。在长爪沙鼠耳组织内,原虫能持续14个月以上,并且可使鼠耳发生溃疡。 上述各项观察和实验结果表明,克拉玛依大沙鼠体内的利什曼原虫在形态大小、对4种实验动物所致的病变都与沙鼠利什曼原虫不同,对自然宿主大沙鼠的耳组织和远交系小鼠的致病力又与硕大利什曼原虫相异。作者认为,该地大沙鼠耳组织感染的利什曼原虫可能是一个新种(或新亚种),宜通过进一步的实验研究,来确定它分类上的地位。     

宜昌市医学淡水贝类调查初报

1种类经检索鉴定所收集的淡水贝类隶属为1纲4科12属22种,其名录是:腹足纲Gastropoda前鳃亚纲Prosobranchia觹螺科HydrobiidaeA钉螺属Oncomelania(Gredler)1)钉螺指名亚种Oncomelania hupensis hupensis(Gredler)2)钉螺丘陵亚种Oncomelania hupensis fausti(Bartsch)B拟钉螺属TriculaBenson3)泥泞拟钉螺Tricula humida(Heude)4)齿拟钉螺Tricula odonta Liu et Zhang5)小口拟钉螺Tricula microstoma Liu et ZhangC豆螺属ButhyniaLeach6)赤豆螺Bithynia fuchsian(Moёllendorff)7)檞豆螺Buthynia misella(Moёllendorff)D小豆螺属B…     

新疆出血热病毒免疫荧光试验检测结果报告

目的了解新疆出血热(XHF)的自然界分布状况。方法对采自塔里木盆地、准噶尔盆地、伊犁谷地和东疆盆地23个县(市)的96份病原材料分别接种Vero-E6细胞,病原材料经细胞培养后,胰酶消化制备细胞片,应用免疫荧光试验(IFA)对细胞片进行病毒检测。结果96份病原材料中,检出新疆出血热病毒颗粒阳性材料16份,分布地区包括巴楚、于田、轮台、民丰、尉梨、莫索湾、吐鲁番和木垒。结论巴楚、于田、轮台、尉梨、莫索湾和木垒地区存在新疆出血热的自然界分布,而民丰和吐鲁番仅从羊血液标本中查出阳性,不能说明该地区存在新疆出血热的自然界分布。     

新疆准噶尔盆地荒漠大沙鼠鼠疫自然疫源地调查研究概述

本文概述了世界沙鼠鼠疫自然疫源地及其主要宿主.新疆准噶尔盆地荒漠自1956年调查大沙鼠(Rhombomys opimus)鼠疫自然疫源地以来,曾检验大沙鼠8 139只,其体外寄生蚤50 054只,结果均为阴性.2005年首次于准噶尔盆地荒漠大沙鼠体内及其寄生蚤(Xenopsylla minax, Echidnophaga oschanini)分离到14株鼠疫菌.该鼠疫菌的生化和毒力测定结果:麦芽糖、阿胶糖、甘油阳性,鼠李糖和脱氮阴性,其毒力差距很大(LD50为<10～>108),其主要特征与中亚荒漠鼠疫菌的生化特征相同,也和内蒙古长爪沙鼠鼠疫菌生化相同.以大沙鼠的生物学特性和流行病学特点及其体外寄生蚤和检出鼠疫菌的数量及生化毒力测定等结果,可以判定新疆准噶尔盆地荒漠为大沙鼠鼠疫自然疫源地.     

乌鲁木齐市沙鼠鼠疫疫源地夜行鼠类调查

目的掌握乌鲁木齐地区准噶尔盆地古尔班通古特沙漠南缘荒漠戈壁啮齿动物及其体外寄生物本地和自然感染情况。方法在戈壁荒漠生境内捕夜行鼠,进行鼠密度、鼠体蚤调查,实验室进行鼠疫四步检验。结果居民区和荒漠区过渡地带布夜行夹200夹次,捕鼠17只。其中三趾跳鼠11只,占61.1%,为主要鼠种,柽柳沙鼠和西伯利亚五趾跳鼠各3只,占17.6%,红尾沙鼠1只,占5.9%,从自毙三趾跳鼠及柽柳沙鼠体外寄生蚤同行客蚤各分离出鼠疫菌1株。结论传播多种自然疫源性疾病的啮齿动物在该区域均有分布,而三趾跳鼠是参与动物鼠疫流行的主要鼠种。     

塔里木盆地荒漠型黑热病宿主动物调查研究

目的调查并查找新疆塔里木盆地荒漠型黑热病自然疫源地的宿主动物。方法参考世界卫生组织(WHO)黑热病宿主动物的5个标准,采用流行病学方法查明荒漠型黑热病患者被感染的主要生境;采集疫区不同生境优势动物,以特异性抗体检测方法筛查抗体阳性动物;调查疫区不同生境白蛉密度和传播媒介吴氏白蛉自然感染利什曼原虫的感染率;采用特殊培养基和敏感动物从患者、阳性动物和吴氏白蛉中分离利什曼原虫,开展分子遗传学相似性鉴定;以吴氏白蛉开展优势动物吸血实验,查找吴氏白蛉的供血宿主;对照黑热病宿主动物的5个标准,根据上述实验调查结果,采用排除法确认天然宿主动物,同时确认荒漠型黑热病疫区的核心区;黑热病暴发时在核心区及其周边以杀虫剂灭蛉,与对照区比较,根据两个区的实际控制效果和时间,最后确定宿主动物。结果荒漠型黑热病患者被感染的生境是胡杨柽柳生境及其相邻农田;胡杨柽柳生境的优势动物为塔里木兔(Lepus yarkandensis)、子午沙鼠(M.meridianas)、毛脚三趾跳鼠(D.sagitta)和科氏三趾矮跳鼠(S.crassicada);共获得16种动物1374份样品(野生动物1137份、家畜237份),只有塔里木兔(45/485)检出抗利什曼原虫阳性个体,从塔里木兔分离出4株利什曼原虫(4/485)。在疫区的所有生境中,只有胡杨柽柳生境中的塔里木兔的抗体阳性率和吴氏白蛉的利什曼原虫感染阳性率最高;吴氏白蛉只能吸到塔里木兔和大耳猬的血,吸血率分别为9.5%和3.3%;塔里木兔的利什曼原虫分离株与当地黑热病患者和传播媒介吴氏白蛉分离株的乙酰氨基葡萄糖磷酸转移酶(NAGT)核基因鉴定结果显示相似性100%,属婴儿利什曼病2型;自2008年黑热病暴发以来,实验区飞机喷洒杀虫剂灭蛉一次,连续7年无流行,对照区流行2次,每次流行持续2年。结论所有动物中只有塔里木兔与WHO规定的黑热病宿主动物的5个标准最接近,传播媒介吴氏白蛉的供血宿主实验是验证天然宿主动物的重要方法;荒漠型黑热病患者被感染的生境是查找黑热病宿主动物的关键区域,即胡杨柽柳核心区及其相邻农田;核心区灭蛉是长期有效控制黑热病流行的重要措施,能为证明荒漠型黑热病宿主动物提供重要证据。     

中国西北地区和毗邻中亚诸国以及外蒙的一个重要传播媒介-斯氏白蛉Phlebotomus(Larroussius) smirnovi Perfiliew,1941

目的进一步证实分布在中国新疆、甘肃和内蒙的"硕大白蛉吴氏亚种"和"吴氏白蛉"是斯氏白蛉的异名. 方法对中国新疆、甘肃和内蒙的"硕大白蛉吴氏亚种"和"吴氏白蛉"标本与包括同模标本在内的哈萨克斯坦、吉尔吉斯坦的斯氏白蛉标本以及在内蒙新捕获的中国标本做了分类学的详细对比研究,查清了这一白蛉的全球地理分布结果在冷延家、Lane及Lewis(1987)所做研究的基础之上,取得更加详实的证据,依据当代白蛉分类学进一步地证明了"硕大白蛉吴氏亚种"和"吴氏白蛉"应是斯氏白蛉[P. (La.) smirnovi Perfiliew,1941]的同物异名.对中国这一蛉种的澄清,开辟了国际共用有关此蛉科研成果和防制经验的的道路. 结论斯氏白蛉1941年发现于哈萨克斯坦和吉尔吉斯坦.它的分布连续地自中亚向东,经中国的新疆、甘肃和内蒙直达外蒙.中国的"吴氏白蛉"首先在准噶尔和塔里木盆地之西的新疆发现,而且它连续地分布在此二盆地的东西两侧.这一事实否定了Artemiev和Neronov (1984)认为吴氏白蛉是斯氏白蛉自中亚和哈萨克斯坦向东在横过准噶尔和塔里木盆地的迁徙过程中,演化而形成为独立的新种"吴氏白蛉",而后才进入中国和蒙古的假说.     

新疆额尔齐斯河流域及其毗邻山地蜱螨区系调查

到目前为止,在新疆北部额尔齐斯河流域及其毗邻的阿尔泰山地、萨吾尔山东段和准噶尔盆地北部共发现蜱5属11种;革螨6科15属33种,其中外贝加尔巨鳌螨Macrocheles transbaicalicus和欧亚异肢螨 Poecilochirus eurasiaticus是新疆地区首次记录的种类;恙螨4周4种。本文记述这些蜱螨的地理分布和宿主种类,并介绍了有关蜱类的医学意义。     

碘缺乏病与地理环境—昆仑山山前洪积—冲积平原调查研究报告

1987～1990年,我们在新疆塔里木南部昆仑山山前洪积-冲积平原进行了地理环境与碘缺乏病关系调查研究,昆仑山为海拔平均高度6000米的山脉,5200米以上终年覆盖积雪。昆仑山山前洪积-冲积平原地表覆盖第四纪沉积物,厚度约800～1100米,为坡降度2.5～5.4‰的山前倾斜平原。平原近山的南部地区地表覆盖物为卵、砾石,向北逐渐变为砂土并与沙漠相连接、第三纪早期,和田绿洲及以西的大部分地区曾受古海海浸,形成古叶尔羌海湾。平原地区气侯干旱,年平均降水量仅28.9～65.0毫米,蒸发量2198～2790毫米;年平均气温11～12.1℃。区内34条河流,总径流量152亿立方米。叶尔羌河为其中最大河流,年径流量为63.74亿立方米;其次为和田河,年径流量44.58亿立方米。河流均发源于昆仑山脉,居民居住区多位于海拔1650米以下有地面水供饮用及灌溉的绿洲内。地表水含碘量均低,其中平原下部水碘为2.6μg/L,高于平原中部(1.47μg/L)及上部1.14μg/L)。浅层地下水含碘量高于地表水,平原不同部位的水碘均值为2.43～8.57μg/L;深层地下水含碘最高,均值为12.23μg/L。碘缺乏病的病情分布与水碘基本吻合。平原上部两村庄居民甲状腺肿患病率为49.2％和53.51％,克汀病患病率为1.24％和1.46％;平原中部7个村落居民甲状腺肿患病率为6.69％～50.0％     

Late Oligocene–early Miocene birth of the Taklimakan Desert

As the world’s second largest sand sea and one of the most important dust sources to the global aerosol system, the formation of the Taklimakan Desert marks a major environmental event in central Asia during the Cenozoic. Determining when and how the desert formed holds the key to better understanding the tectonic–climatic linkage in this critical region. However, the age of the Taklimakan remains controversial, with the dominant view being from ∼3.4 Ma to ∼7 Ma based on magnetostratigraphy of sedimentary sequences within and along the margins of the desert. In this study, we applied radioisotopic methods to precisely date a volcanic tuff preserved in the stratigraphy. We constrained the initial desertification to be late Oligocene to early Miocene, between ∼26.7 Ma and 22.6 Ma. We suggest that the Taklimakan Desert was formed as a response to a combination of widespread regional aridification and increased erosion in the surrounding mountain fronts, both of which are closely linked to the tectonic uplift of the Tibetan–Pamir Plateau and Tian Shan, which had reached a climatically sensitive threshold at this time.Surrounded by the Tian Shan to the north, the Pamir to the west, and the West Kunlun to the south, the Taklimakan Desert is the world’s second largest sand sea (Fig. 1). Located far from any major source of moisture, and shadowed by Tibetan and central Asian mountain ranges, the Taklimakan is deprived of rainfall, with mean annual precipitation not exceeding 50 mm (1). Provenance studies suggest that mineral dust from the Taklimakan Desert contributes substantially to the global aerosol system, allowing it to play a significant role in modulating global climate on various time scales (2, 3). The formation of the Taklimakan Desert therefore marked a major environmental event in central Asia during the Cenozoic, with far-reaching impacts. Furthermore, determining when and how the desert formed holds the key to better understanding the nature of tectonic–climatic linkage in this critical region. However, the time at which the Taklimakan Desert came into existence has been strongly debated, with estimates ranging from only a few hundreds of thousands to a few million years ago (1, 4–8).Open in a separate windowFig. 1.Location map. (A) Topographic map showing the western portion of the Taklimakan Desert (Tarim Basin) and the surrounding mountain ranges with major active faults. The location of the studied Cenozoic sedimentary sections at Aertashi, Kekeya, and Mazatagh are shown by stars. (B) Map showing the location of the Tarim Basin (TB), Junggar Basin (JB), and Chinese Loess Plateau (CLP). Qin’an loess section (QA) is marked by a red star.In the context of this study, we define desertification to represent not only the formation of a significant sand sea but also the generation of a dynamic eolian system that supplied voluminous mineral dust on regional and even global scales. Evidence of desertification in the geological past is preserved in sedimentary sequences within, and along the margins of, the present-day Taklimakan Desert that lies within the Tarim Basin (Fig. 1). Recent geochronological work, mostly based on the magnetostratigraphy of these sedimentary sequences, proposed ∼3.4 Ma to 7 Ma for the initiation of the Taklimakan (4–8). Precise dating of these terrestrial rocks has largely been hampered by lack of dateable material. In this study, we report a newly identified volcanic tuff from two sedimentary sections along the southwestern margin of the Tarim Basin. Radioisotopic dating of the volcanic minerals provides a robust age for the sections, and therefore we are able to determine the age of the Taklimakan Desert more precisely.     

Late Miocene episodic lakes in the arid Tarim Basin,western China

The Tibetan Plateau uplift and Cenozoic global cooling are thought to induce enhanced aridification in the Asian interior. Although the onset of Asian desertification is proposed to have started in the earliest Miocene, prevailing desert environment in the Tarim Basin, currently providing much of the Asian eolian dust sources, is only a geologically recent phenomenon. Here we report episodic occurrences of lacustrine environments during the Late Miocene and investigate how the episodic lakes vanished in the basin. Our oxygen isotopic (δ¹⁸O) record demonstrates that before the prevailing desert environment, episodic changes frequently alternating between lacustrine and fluvial-eolian environments can be linked to orbital variations. Wetter lacustrine phases generally corresponded to periods of high eccentricity and possibly high obliquity, and vice versa, suggesting a temperature control on the regional moisture level on orbital timescales. Boron isotopic (δ¹¹B) and δ¹⁸O records, together with other geochemical indicators, consistently show that the episodic lakes finally dried up at ∼4.9 million years ago (Ma), permanently and irreversibly. Although the episodic occurrences of lakes appear to be linked to orbitally induced global climatic changes, the plateau (Tibetan, Pamir, and Tianshan) uplift was primarily responsible for the final vanishing of the episodic lakes in the Tarim Basin, occurring at a relatively warm, stable climate period.Once part of the Neo-Tethys Sea, indicated by the Paleogene littoral-neritic deposits with intercalated marine strata (1), the Tarim Basin in western China (Fig. 1) has experienced dramatic environmental and depositional changes during the Cenozoic. The eventual separation of the basin from the remnant sea probably occurred during the middle to late Eocene (1, 2), and since then, terrestrial sedimentation and environment have prevailed. Today, the basin has relatively flat topography with elevation ranging between 800 and 1,300 m above sea level (asl), surrounded by high mountain ranges with average elevation exceeding 4,000 m. Hyperarid climate prevails with mean annual precipitation <50 mm and evaporation ∼3,000 mm. Active sand dunes occupy 80% of the basin, forming the Taklimakan Desert, the largest desert in China and the second largest in the world (3). Thick desert deposits in the basin also provide a major source for dust storms occurring in East Asia (4).Open in a separate windowFig. 1.Digital elevation model of the Tarim Basin and surrounding mountain ranges. The studied 1,050-m sediment core is retrieved from Lop Nor (1), at a relatively low elevation (∼800 m asl) in the eastern basin. Also indicated are locations of previous studied sections, near Sanju (2), Kuqa (3), and Korla (4) in the basin.The Tibetan Plateau uplift, long-term global cooling, and the associated retreat of the remnant sea during the Cenozoic, through their complex interplay, may have all contributed to the enhanced aridification in the Asian interior and eventually the desert formation (2, 5–11). Although the onset of Asian desertification is proposed to have started in the earliest Miocene (12, 13), prevailing desert environment in the Tarim Basin, currently providing much of the Asian eolian dust sources (4), is only a geologically recent phenomenon (9). Previous lithological and pollen studies (9, 14, 15) suggest that the currently prevailing desert environment started probably at ∼5 Ma. However, what kind of environmental conditions prevailed before that and how the dramatic changes occurred largely remain elusive.To better decipher the aridification history, we used a 1,050-m-long, continuous sediment core retrieved from Lop Nor (39°46''0''''N, 88°23''19''''E) in the eastern basin (Fig. S1). The core site has a relatively low elevation (∼800 m asl) (Fig. 1) and thus effectively records basin environment. Previous study sites came from elevated basin margins (9, 14). The core mainly consists of lacustrine sediments with associated fluvial-eolian sands (Fig. 2). The core chronology was established previously based on paleomagnetic polarity (15). The total 706 remanence measurements on the continuous sediment profile allow straightforward correlation with the CK95 geomagnetic polarity timescale (16) and identification of 14 normal (N1–N14) and 13 reversal (R1–R13) polarity zones over the last 7.1 Ma (Fig. S1). The CK95 timescale is largely consistent (within a few ky) with that inferred from marine archives (17) over the last 5.23 Ma, and before 5.23 Ma a practical measure of chronological uncertainty was estimated to be within ∼100 ky (18), assuring that the terrestrial records can be directly compared with marine records and orbital changes at the timescale of >100 ky. The derived chronology yields an average sedimentation rate of ∼200 m/Ma at lower sections (>1.77 Ma), allowing high-resolution studies of the desertification history at the critical interval.Open in a separate windowFig. 2.Records of δ¹¹B, δ¹⁸O, TOC, and CaCO₃ changes in the Lop Nor profile. Representative photos show lithological changes mainly from lacustrine bluish gray argillaceous limestone to fluvial-eolian brown/red clayey silt, as shown in the lithological column with visual colors indicated (15). High levels and large fluctuations of proxy values occurred only before ∼4.9 Ma, and since then, those remain low and within a small range, largely similar to modern conditions. The transition from episodic occurrences of lacustrine phases to prevailing desert environments thus appears to be permanent and irreversible.Boron and oxygen isotopes from carbonates are important environmental indicators (19–25) and used here to infer the environmental evolution in the Tarim Basin. We also present total organic carbon (TOC), calcium carbonate (CaCO₃), ostracod, and grain size records to substantiate the isotopic evidence (SI Materials and Methods). Our δ¹¹B profile shows substantial, stepwise changes over the last ∼7.1 Ma (Fig. 2). Carbonate δ¹¹B values were −5.0 ± 1.6‰ (n = 3) before 6.0 Ma, increased rapidly to ∼11‰ at 4.9–6.0 Ma, and then stayed at roughly the same level (10.7 ± 2.2‰, n = 25) for the remaining 4.9 Ma. Higher-resolution δ¹⁸O, TOC, and CaCO₃ profiles generally confirm the pattern observed in the low-resolution δ¹¹B one (Fig. 2). The δ¹⁸O values remained low, ranging from −10‰ to −4‰ over the last 4.9 Ma. However, δ¹⁸O values frequently oscillated between −10‰ and 5‰ before that. Similarly, the TOC profile shows consistently low organic carbon content (0–0.2%) after 4.9 Ma and large fluctuations (0–1.0%) before then. The CaCO₃ profile also indicates consistently low values (0–25%) after 4.9 Ma and large fluctuations (0–50%) earlier (Fig. 2).The multiple proxy records strongly suggest that critical environmental changes must have occurred at ∼4.9 Ma. δ¹¹B values of carbonates from marine sources differ substantially from those of nonmarine carbonates (19–21). δ¹¹B values after 4.9 Ma are close to those from marine carbonates, but values before 6 Ma fall into the range of lacustrine carbonates (22). Positive δ¹⁸O values before 4.9 Ma also indicate lacustrine environments at that time. Carbonates from modern lakes in arid and semiarid regions of northwestern China show similar positive δ¹⁸O values (23), due to strong evaporation processes. High TOC and CaCO₃ contents (Fig. 2) further support that lacustrine environments existed in the basin before ∼4.9 Ma. δ¹⁸O values after 4.9 Ma are comparable to those in Cenozoic soil carbonates (24) and ancient marine carbonates in the Tarim Basin (25). However, the accompanying carbonate δ¹³C values throughout the record, ranging from −4‰ to 1‰ (Dataset S1), are significantly higher than those from Cenozoic soil carbonates reported (26), essentially ruling out the possibility of soil carbonate source. Using modern prevailing desert environment in the basin as an analog, the combined δ¹¹B and δ¹⁸O evidence thus suggests that the sediment deposits in the basin after 4.9 Ma must be eolian-fluvial in origin and their sources, at least carbonate grains, came from weathered ancient marine carbonates in nearby regions.Sedimentological and stratigraphic patterns in other exposed sections from different parts of the basin (9, 14) share great similarity with the Lop Nor core profile (Fig. S1). Episodic lacustrine mudstones and/or siltstones during the Late Miocene were present in all sections and were replaced by fluvial-eolian deposits later. Studies of ostracod assemblages (27) also suggest a shallow paleolake with brackish water environments in the northern basin during the Late Miocene. Changes in the depositional environment from our Lop Nor profile alone could be plausibly explained by a shift in basin center due to tectonic compressions, as evidenced from the slightly uplifted central basin (Fig. 1). However, similar temporal changes occurring basin-wide at ∼4.9 Ma argue against it. Instead, our results, together with previous studies (5, 14, 15, 27), suggest that paleolakes were widely present in the low lands of the basin during the Late Miocene, much different from currently prevailing desert environments with a few scattered small lakes. The existing evidence, although still limited (Fig. 1), would point to the occurrence of a possible megalake in the Tarim Basin during the Late Miocene.Three high-resolution records, δ¹⁸O, TOC, and CaCO₃, further suggest that lacustrine environments before ∼4.9 Ma were not permanent (Fig. 2). These large fluctuations indicate frequent switches between lacustrine and fluvial-eolian environments in the basin. High proxy values, δ¹⁸O in particular, appear to indicate lacustrine environments, whereas low values, similar to ones after 4.9 Ma, correspond to fluvial-eolian deposits. This is consistent with lithological features at this interval, showing argillaceous limestone intercalated with clayey layers (15), the occurrence of ostracod assemblages (Fig. 3) from lacustrine sediments, grain size changes (Fig. S2), and detrital carbonate grains identified in photomicrographs of fluvial-eolian deposits (Fig. S3).Open in a separate windowFig. 3.δ¹⁸O fluctuations linked to eccentricity and obliquity orbital variations at 4.5–7.1 Ma. Lacustrine phases (high δ¹⁸O) generally correspond to periods of high eccentricity and obliquity. Fluvial-eolian environment (low δ¹⁸O, highlighted with gray bars), developed more around 6.5, 6.1, 5.7, and 5.2 Ma, at a ∼400-ky eccentricity beat. The red bar indicates the last occurrence of lacustrine environment at ∼4.9 Ma. Occurrences of ostracod assemblages with total number >100 are also indicated.To further investigate such episodic changes, we performed spectral analysis on the δ¹⁸O record over the interval 4.5–7.1 Ma. Strong spectral power at orbital frequencies were identified, with periods of ∼400 ky throughout the interval, ∼41 ky particularly at 6–6.5 Ma, and ∼100 ky at 5–6 Ma and 6.5–7.1 Ma (Fig. S4). Precessional ∼20-ky power might also have existed but was relatively weak and discontinuous. Lacustrine phase as indicated by high δ¹⁸O values and ostracod assemblages generally occurred at periods of high eccentricity and obliquity (28) (Fig. 3). At 6–6.5 Ma, δ¹⁸O shows clear correspondence to orbital obliquity variation (Fig. 3A). Additionally, the number of low δ¹⁸O values (fluvial-eolian environment) occurred more around 6.5, 6.1, 5.6, and 5.2 Ma, at a ∼400-ky beat following orbital eccentricity variation (Fig. 3B). The cluster of high δ¹⁸O values (>0‰) at 4.9–5.0 Ma signals the last occurrence of lacustrine environments in the basin. Our orbital association thus allows us to precisely determine the timing of desert formation at ∼4.9 Ma, ∼400 ky (an eccentricity cycle) later than the age inferred from basin margins (9, 14) and yet all occurring at eccentricity minima (Fig. 3B). As high eccentricity and obliquity generally correspond to warm conditions at orbital timescales, lacustrine (wet) phase could be associated with warm periods, consistent with the notion that cooler conditions would reduce moisture in the atmosphere and enhance continental drying (10, 11). We recognize that the chronological uncertainty from the geomagnetic polarity timescale before 5.23 Ma, within ∼100 ky (18), could confound our association of wet phase with high obliquity, although it is unlikely affected at the 400-ky eccentricity beat. However, the opposite association, wet phase with low obliquity, and the combination with high eccentricity, would require a different, yet unknown mechanism that is inconsistent with the orbital theory of Pleistocene ice ages.Superimposed on the orbitally episodic changes, the δ¹⁸O record also shows a long-term trend of deteriorating lacustrine conditions at 4.9–7.1 Ma. As δ¹⁸O values indicate two depositional environments, lacustrine and fluvial-eolian, the range of δ¹⁸O changes (between −10‰ and 5‰) does not vary much over this period (Fig. 3). Rather, the duration of high δ¹⁸O vs. low values would reflect the long-term trend. The mean δ¹⁸O values over 40-ky and 400-ky intervals both show a decreasing trend, with dominant lacustrine phase before 6.1 Ma, more developed fluvial-eolian environment at 5.7–6.1 Ma, a return to slightly better lacustrine environment at 5.3–5.7 Ma, and lacustrine phase permanently vanished around 4.9 Ma (Fig. 4).Open in a separate windowFig. 4.Long-term δ¹⁸O changes compared with global climatic conditions and regional tectonic activities. Global benthic δ¹⁸O (29) and northwestern Pacific SST (30) records show minimal long-term changes at 4–7 Ma, whereas occurrences of detrital apatite fission track ages (35) in northern western Kunlun peaked, and the Tarim episodic lakes gradually vanished. The dark thick lines are their 400-ky running means, and the light green line on δ¹⁸O represents the 40-ky running mean.The gradual disappearance of the Tarim episodic lakes could be potentially explained by the two driving forces, plateau uplift (the Tibetan Plateau, Pamir Plateau, and Tianshan) and long-term global cooling. However, the long-term global climate was relatively warm and stable during this period (Fig. 4). The global benthic δ¹⁸O record (29) shows that much of the Miocene cooling occurred between 15 and 11 Ma, and the cooling between 8 and 5 Ma was minimal. Supporting this view, sea surface temperature records from the northwestern Pacific (30) show that almost no cooling occurred between 6 and 4 Ma (perhaps further to 3 Ma) (Fig. 4). Particularly, the mean global climate (29, 30) was even warmer at 4.1–4.5 Ma than at 5.7–6.1 Ma, whereas lacustrine phase permanently disappeared after ∼4.9 Ma (Fig. 4), indicating decoupling of the lake evolution from global climate. Therefore, long-term global cooling might have played a subordinate role in the lake disappearance.Instead, the growth of surrounding mountain ranges (Tibetan, Pamir, and Tianshan) may have blocked moisture from the west and south, changed air circulations, and eventually led to the permanent lake disappearance within the basin. Today, the Tarim Basin receives limited moisture from westerlies (31) through the Pamir and Tianshan Ranges (and perhaps from the Indian Ocean in summertime as well). Although the Indo–Eurasian convergence since the Late Eocene resulted in high elevations of the Tibetan Plateau and, to a lesser degree, surrounding mountains including Pamir and Tianshan by the mid-Miocene time (8), tectonic activities in broad areas around the Tarim Basin appear to be rejuvenated since the Late Miocene. Tectonic deformations during the Late Miocene–Early Pliocene inferred from growth strata, sedimentary facies changes, and low-temperature thermochronologic studies occurred in Tianshan to the north of the Tarim Basin, in the Kunlun Mountains to its south and the Pamir to its west (32–35). Syntectonic growth strata from the foreland basins of the Kunlun and Tianshan Ranges (32) show that strong crust shortening and potential mountain uplift initiated ∼6.5–5 Ma and lasted to the Early Pleistocene (Fig. S5), similarly reported in northern Pamir (33). Cenozoic sequences in the Pamir–Tianshan convergence zone, changing from an arid continental plain to an intermountain basin by ∼5 Ma, support surface uplift of the west margin of the Tarim Basin (34). Occurrence of detrital apatite fission track ages from West Kunlun Ranges (35) also peaked at ∼4.5 Ma (Fig. 4). Thus, the reactivated uplift of Pamir and West Kunlun Ranges and northward movement of Pamir during the Late Miocene–Pliocene would progressively block moisture into the basin and enhance regional aridity to a certain threshold to terminate lacustrine environments even during warm periods with favorable orbital configuration. Although inconsistencies indeed exist in linking regional climatic and environmental changes to tectonic events (8), the final vanishing of the Tarim episodic lakes is better explained by tectonic factors.Therefore, our multiple-proxy results consistently show that the Taklimakan sand sea began to form at ∼4.9 Ma and that the transition into prevailing desert environment was permanent and irreversible. The episodic occurrences of lacustrine environments at favorable climatic conditions (warm periods) during the Late Miocene suggest that uplifted mountain ranges then were not high enough to effectively block moisture from being transported into the basin. The transition from episodic lacustrine environments to prevailing desert deposits was gradual, from 7.1 Ma (or earlier beyond our record) to 4.9 Ma, for which we suggest that although long-term global cooling enhanced the overall aridification in the Asian interior during the Late Cenozoic (10, 11), plateau uplift played a more important role in finally drying up the episodic lakes within a relatively warm, stable climate period, thus decoupling regional climate temporally from a global trend. Our high-resolution records thus demonstrate that regional climate in the Tarim Basin reached a critical state in the Late Miocene, with the dual effects from global climate conditions and regional tectonic settings then. With global climate remaining relatively stable and warm entering the Pliocene, by ∼3–4 Ma (Fig. 4), drying up of episodic lakes at ∼4.9 Ma could thus be largely attributed to rejuvenated tectonic activities.     

From the Cover: Eleventh-century shift in timber procurement areas for the great houses of Chaco Canyon

An enduring mystery from the great houses of Chaco Canyon is the origin of more than 240,000 construction timbers. We evaluate probable timber procurement areas for seven great houses by applying tree-ring width-based sourcing to a set of 170 timbers. To our knowledge, this is the first use of tree rings to assess timber origins in the southwestern United States. We found that the Chuska and Zuni Mountains (>75 km distant) were the most likely sources, accounting for 70% of timbers. Most notably, procurement areas changed through time. Before 1020 Common Era (CE) nearly all timbers originated from the Zunis (a previously unrecognized source), but by 1060 CE the Chuskas eclipsed the Zuni area in total wood imports. This shift occurred at the onset of Chaco florescence in the 11th century, a time with substantial expansion of existing great houses and the addition of seven new great houses in the Chaco Core area. It also coincides with the proliferation of Chuskan stone tools and pottery in the archaeological record of Chaco Canyon, further underscoring the link between land use and occupation in the Chuska area and the peak of great house construction. Our findings, based on the most temporally specific and replicated evidence of Chacoan resource procurement obtained to date, corroborate the long-standing but recently challenged interpretation that large numbers of timbers were harvested and transported from distant mountain ranges to build the great houses at Chaco Canyon.The high desert landscape of Chaco Canyon, New Mexico was the locale of a remarkable cultural development of Ancestral Puebloan peoples, including the construction of some of the largest pre-Columbian buildings in North America (1) (Fig. 1). The monumental “great houses” of Chaco Canyon reflect an elaborate socioecological system that spanned much of the 12,000-km² San Juan Basin from 850 to 1140 Common Era (CE) (2). These massive stone masonry structures required a wealth of resources to erect, including an estimated 240,000 trees incorporated as roof beams, door and window lintels, and other building elements (3). The incongruity of the great houses located in a nearly treeless landscape has led archaeologists and paleoecologists to investigate the origins of timbers used in construction (4–9). Beyond the simple curiosity driving this question, the answer has important implications for understanding the complexities of human–environmental interactions, the sociopolitical organization, and the economic structure of Chacoan society (10–12).Fig. 1.Aerial view of Pueblo Bonito, the largest of the Chaco Canyon great houses. Image courtesy of Adriel Heisey.The first excavators of the great houses in the early 20th century speculated that construction timbers were harvested locally, perhaps resulting in deforestation of the surrounding landscape (13). Paleoecological studies conducted during the late 1970s and early 1980s, however, showed that ponderosa pine (Pinus ponderosa), the primary tree species used in construction, was not abundant enough at the relatively low elevations (1,800–2,000 m above sea level) of Chaco Canyon and nearby mesas to support timber demand (14–16). Spruce (Picea spp.) and fir (Abies spp.), which account for tens of thousands of construction beams, have been absent from Chaco Canyon for at least 12,000 y and could have only been logged from distant, higher-elevation sites (2,500–3,450 m above sea level) (4). An inadequate supply of timbers in Chaco Canyon and its immediate surroundings during Puebloan occupation strongly suggests long-distance procurement from surrounding mountain ranges, where all three conifers now grow in abundance. This inference was corroborated by strontium isotope (⁸⁷Sr/⁸⁶Sr)-based sourcing. Through a comparison of ⁸⁷Sr/⁸⁶Sr values from great-house timbers to ₈₇Sr/₈₆Sr values from conifer stands growing today in mountains surrounding the San Juan Basin, two studies concluded that the Chuska Mountains (75 km west) and Mount Taylor (85 km southeast) were the most likely sources for spruce, fir, and ponderosa pine trees (6, 7). Recently, the explanation of long-distance timber transport and the related interpretations of ⁸⁷Sr/⁸⁶Sr evidence have been challenged and an alternative has been proposed that most great-house timbers (particularly ponderosa pine) were just as likely to have originated from nearby and low-elevation sites within, east, and south of Chaco Canyon (8, 9).We assessed probable timber origins independently from previous efforts by applying tree-ring width-based sourcing techniques to a set of 170 beams from our archives at the University of Arizona. These beams comprise six tree species from seven great-house structures (17) (Fig. S1). Each site chronology, as the average of 40–100 trees, represents tree-ring growth patterns peculiar to an individual landscape. This method of identifying the probable origin of timbers has been applied widely in Europe in the study of archaeological and nautical timbers and artifacts, musical instruments, and paintings on oak panels (17–20). These techniques are underused in North America, but recent efforts in the northeastern United States have revealed distant, inland sources for 18th- and 19th-century nautical timbers (21, 22).Table S1.Number of sourced beams by species and great-house structureFig. S1.An example of sourcing a great-house beam via tree-ring-width methods. (A) An individual beam (black line), the ponderosa pine JPB-88 from Pueblo del Arroyo, and the Chuskas chronology (red line). (B) Bivariate plot comparing the ring-width indices of ...Tree-ring sourcing can only be applied where tree growth patterns are distinguishable between the potential locations of origin. In the southwestern United States tree growth primarily responds to regionally coherent winter precipitation (23, 24), and as a consequence trees across the region tend to share roughly half of their interannual variability (25). Differences between site chronologies are predominantly attributed to variations in topography and subregional-scale climate conditions (26).We compared great-house beams to the site chronologies of eight potential harvesting areas surrounding the San Juan Basin. Chaco Canyon was not included as one of our sites because it lacked enough remnant wood from the Chaco era to build a local site chronology. To assess the efficacy and accuracy of the tree-ring sourcing method within the San Juan Basin, we tested whether tree-ring growth patterns could be distinguished between the various mountain ranges surrounding Chaco Canyon by applying sourcing methods to living trees of known origin (SI Text and Fig. S2).Table S2.Tree-ring sites used to evaluate tree-ring-based sourcing in the San Juan BasinFig. S2.Evaluation of dendroprovenance in the San Juan Basin. (A–F) Each tile provides a different test for a set of modern trees (green triangles). Circle sizes are proportional to the number of trees (labeled in the circle) sourcing to a given location. ...