共查询到17条相似文献，搜索用时 125 毫秒
1.
泥河湾盆地岑家湾旧石器遗址的古地磁定年 总被引：3，自引：0，他引：3
通过对泥河湾盆地岑家湾旧石器地点进行的岩石磁学和磁性地层学研究表明, 岑家湾湖相沉积剖面的磁性矿物和剩磁载体是以磁铁矿为主; 少数时段沉积物含有磁铁矿和赤铁矿两种磁性矿物, 这类沉积物的特征剩磁是由磁铁矿和赤铁矿共同携带的. 磁组构测定证实了岑家湾剖面保存了原始沉积特征, 适合于磁性地层学研究, 其结果表明岑家湾旧石器地点的时代稍晚于Punaruu地磁漂移事件发生的时间(1.1 Ma). 结合东谷坨、马圈沟和小长梁剖面的研究结果, 可以确定早期人类在1.6, 1.3和1.1 Ma前后都在泥河湾地区生活过, 这一结果对认识早期人类迁徙与适应环境的能力是很有意义的. 相似文献
2.
3.
生物礁是重要的自然资源,在全球气候变化与碳循环中扮演了重要角色.磁性地层学是建立年代框架的有效手段,但是,由于生物礁沉积物中天然剩磁强度弱,南海地区生物礁的磁性地层学研究尚未很好展开.为此,本文利用西沙群岛西科1井乐东组生物礁沉积样品进行了详细的岩石磁学和磁性地层学研究.结果显示,西沙群岛乐东组记录了布容正极性时、奥杜维尔正极性时和松山负极性时.通过对比已有的钻孔资料,本文认为应基于岩石地层特征这一标准将西沙地区的乐东组埋深予以统一.在此基础上,综合磁性地层与~(230)Th定年结果,本文将乐东组的底界限定在~2.0 Ma. 相似文献
4.
以热磁分析为主,对中国北方泥河湾盆地更新世河湖相地层中灰绿色粉砂和灰黄色粉砂/细砂两种典型沉积物进行了详细的岩石磁学研究,有效确定了这两类沉积物中磁性矿物的种类、粒度特征以及加热过程中磁性矿物的变化过程和产物,并对其包含的古环境意义进行了初步探讨.灰绿色粉砂样品主要含有磁铁矿和赤铁矿两种磁性矿物,磁性相对较弱,颗粒相对较细;灰黄色粉砂/细砂主要含有磁铁矿和磁赤铁矿,磁性相对较强,颗粒相对较粗.在氩气环境中经700℃加热处理后,这两种沉积物中的绿泥石都分解,并生成超细粒（处于超顺磁和单畴颗粒区间）的磁铁矿,导致磁化率大幅升高.因此泥河湾盆地沉积物的热磁特征可以用来检测样品中绿泥石的相对含量,进而反映该地区化学风化作用强度的变化.此外,灰绿色粉砂样品中绿泥石含量比灰黄色粉砂/细砂样品的含量高,在氩气中加热后,磁化率升高幅度也较高,可能反映了化学风化相对较弱的沉积环境. 相似文献
5.
泥河湾层内易溶盐沉积及其环境意义 总被引：14，自引：0，他引：14
通过泥河湾古湖盆区４个地层剖面中易溶盐类沉积物的观察与实验分析,对泥河湾古湖的性质、演化阶段及其在地层划分和古环境复原上的意义有了新认识．泥河湾古湖至少是微咸水－半咸水湖,属于半干旱区的内陆湖泊．湖相层下段夹石膏层和石膏微薄层,易溶盐以 ＳＯ_２~（２－）和Ｃａ~（２＋）离子为主,代表古湖向硫酸盐湖阶段演化的趋向;上段易溶盐中Ｃｌ~－和Ｋ~＋,Ｎａ~＋离子占优势,证明古湖已向氯化物湖方向发展,虽未出现盐岩沉积,却代表本地区向更干旱的方向发展． 相似文献
6.
7.
8.
华北克拉通破坏的重要标志是岩石圈减薄、地幔性质转变以及伸展构造活动.长期以来这一重大地质事件发生的时代备受关注,目前已有大量地质、地球物理和地球化学研究结果,但对于华北克拉通破坏的准确时代,尚存争议.本文试图从地磁学的角度为华北克拉通破坏时代提供可靠约束.选取位于华北克拉通北缘的燕山造山带中段-承德盆地作为研究对象.磁性地层学研究结果表明研究剖面记录了三个磁极性段:下部正极性段(N2)、中部负极性段(R1)和上部正极性段(N1),与2004年地磁极性年表对比并结合129～128 Ma的火山岩同位素年龄(与B. Schoene 私人通信),认为剖面下部正极性段(N2)对应于M3n,负极性段(R1)对应于M1r,上部正极性段(N1)对应于M1n,由此得出承德盆地袁家庄剖面沉积作用起始年龄约为128 Ma.作为华北克拉通重要断陷盆地之一,承德盆地的沉积年龄可以为华北克拉通破坏时代提供有力约束.岩石磁学研究结果表明,研究剖面火山岩的剩磁载体十分复杂,可能与伴随华北克拉通破坏峰期出现的地壳变形、岩浆活动、地幔上涌、下地壳重熔等深部动力过程密切相关.综合分析结果表明,华北克拉通破坏的峰期为128～125 Ma. 相似文献
9.
对许家窑泥河湾组两个平行剖面的高分辨率古地磁研究结果发现,在剖面的中下 部存在厚度约 １０ｍ（未见底）的巨厚负向极性带．根据正负极性带的相对位置及组合关系并 结合剖面附近相关层位火山豆的Ｋ－Ａｒ绝对年龄值进行分析认为,该负向极性带应为松山反 向极性时带．此结果否认了作者关于在遗址剖面底部存在Ｂｌａｋｅ反向极性偏移的结论．由此 推断,分布在许家窑一带的泥河湾组年代应为早更新世晚期至中更新世早中期． 相似文献
10.
利用埃及北部Faiyum盆地获得的高取芯率沉积物岩芯,进行沉积物多种磁性参数的测量,结合有机碳、介形虫、粒度等分析,在AMS14C加速器测年的基础上,建立全新世以来湖泊沉积物磁性特征变化的时间序列.结果表明,粒度效应以及沉积后的各种次生作用对沉积物的磁性特征没有明显的影响,磁性变化主要反映了沉积物不同来源组成的相对变化.全新世前沉积物磁性较弱,主要含不完全反铁磁性矿物,与周边沙漠的物质相似,结合其粒度特征,沉积物来源应以近源物质为主.全新世早中期(约10 5.4 ka BP)沉积物磁性变化相对稳定,有机质含量也较高,指示了来自尼罗河较为稳定的物质供应;而大约5.4 ka BP尤其最近约4.2 ka BP以来,磁性的明显变化反映了流域降水减少情况下,来自青尼河物质贡献的相对增加;最近约2.0 ka BP以来沉积物的磁性变化,则更多地与盆地人类活动的强化有关.总体而言,Faiyum盆地全新世以来的环境演变主要受控于全新世以来尼罗河与盆地的水力学联系.即:全新世前盆地未与尼罗河连通时,沉积物主要来源于周边沙漠的风成物质;而受全新世早-中期来流域季风降水增加的影响,泛滥的尼罗河为盆地提供了相对稳定的物质供应,湖泊也处于高湖面;全新世晚期以来,随着流域干旱化的加剧,尼罗河与盆地的连通性开始减弱,来自高磁性的青尼罗河物质贡献开始相对增加.最近约2.0 ka BP以来,虽然仍有人工运河连接尼罗河与盆地,但沉积物磁性的显著变化更多地反映了盆地人类活动的不断强化. 相似文献
11.
The fluvio-lacustrine sequences in the Nihewan Basin of North China (known as the Nihewan Formation) are rich sources of Early Pleistocene Paleolithic sites and mammalian fossils (known as the Nihewan Fauna sensu lato), which offer an excellent opportunity to investigate the evolution of early humans and land mammals in East Asia. Also abundant mammalian fossils provide clues about the general environmental and climatic setting of early humans. Among the Nihewan Fauna (sensu lato), the Daodi Fauna is one of the most complete and oldest in the eastern Nihewan Basin: seven mammalian fossil-bearing layers in the Nihewan Formation have been described. Except for a biostratigraphy, however, precise age control on the Daodi Fauna has remained unavailable. Here we report a new magnetostratigraphic record that stringently constrains its age. The seven fossil-rich layers span an age range of ca 2.5–1.8 Ma between the Gauss–Matuyama boundary and the termination of the Olduvai polarity subchron. Combining our new and recently published paleomagnetic data, we further establish a Pleistocene magnetochronology of the fauna and Paleolithic sites in the Nihewan Basin. Age ranges of about 2.5–0.5 Ma for the faunas and 1.7–0.3 Ma for the Paleolithic sites are deduced, which span most of the Pleistocene. The chronological framework and calculated proportions of mammals that were adapted to different environments indicate that mixed settings of dominant grasslands and subordinate forests continued at least from 2.5 to 0.5 Ma for early human occupation in the basin, similar to the mixed open savannah and woodland habitats of early humans in Africa. The Nihewan hominins consistently adopted a simple Oldowan-like technology (i.e., Mode 1 core and flake technologies) from at least ca 1.7 to 0.3 Ma. A more advanced Acheulean technology (Mode 2) has not been found in the Nihewan Basin, although it started to emerge in the Bose Basin of South China at ca 0.8 Ma. This implies that multiple groups of hominins distinguished by differential stone-tool-making capabilities may have coexisted in China after 0.8 Ma. 相似文献
12.
CAI Baoquan & LI Qiang . Department of History Xiamen University Fujian China . Institute of Vertebrate Palaeontology Palaeoanthropology Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2004,47(5)
The Nihewan (Nihowan) Basin is well known in the world for producing abundant mammal fossils and paleoliths. As one issue of the program 搕he early hominid evolution and environmental background in East Asia?a biostratigraphic survey was made in July 2001, and a large number of mammal fossils were un-earthed and 5 lithic artifacts were recognized from the Majuangou gully in the Nihewan Basin, Hebei Prov-ince, North China. 1 Stratigraphic section The new site is located on the south bank… 相似文献
13.
It draws much attention of scientists how early hu- mans occupy and adapt to the rigorous climate and environment at high northern latitudes in East Asia after they stepped out of Africa, passed West Asia and finally arrived in East Asia[1-4]. Reliable age determi- nations of Paleolithic sites from northeastern Asia not only help to find out the earliest occupation of early humans in this region, but also relate to the founda- tion of the overall framework of human origin and migration[1-8]… 相似文献
14.
As one of the most important regions for early human occupation in East Asia, Nihewan Basin in North China is well-known for an abundance of archaeological sites with ages spanning the last 2 Ma. In recent 10 years, more than 27 new archaeological localities have been discovered from the Yuxian (sub-basin of Nihewan), and all of them are with no age control. The lack of reliable ages for these localities affects our understanding for the evolution of the stone-tool technology in the Nihewan Basin. As many localities were founded in the river terrace, the fluvial terrace sequence of the Huliu River (main river of the Yuxian) was investigated. Based on single-grain post-infrared infrared stimulated luminescence (pIRIR) procedure on potassium (K-) feldspar, our results reveal that the formation ages of three Huliu River terraces are 139.6–115.7, 19.7–5.5, and <0.9 ka, respectively. On the basis of these pIRIR ages, the formation of the fluvial terrace sequence may provide informative constraints on the human occupation in the Huliu River terrace in the Nihewan Basin, if a clear stratigraphic correlation is established between the archaeological sites and the dated terrace deposits. 相似文献
15.
Observation and experimental analysis of soluble salt deposit along four profiles across the strata deposited in Nihewan paleolake
basin enabled us to recognize the nature and evolution stages of the Nihewan paleolake and its significance in stratigraphical
division and pa-leo-environmental reconstruction. The Nihewan paleolake was at least a weak-saline to semi-saline lake and
represents an intracontinental lake in the semi-arid region. The lower member of sedimentary strata in the paleolake contains
gypsum layer and gypsum lamellae. Soluble salt is mainly composed of SO
4
2-
and Ca2+ ions, representing a trend of the paleolake evolving into a stage of sulfate lake. The upper member of the strata has predominantly
Cl-, K+, and Na+ ions in soluble salt, indicating a starting development of the paleolake to chlorite lake, but no salt rock was deposited,
indicating a drying trend of the area. 相似文献
16.
Hua Zhao Yanchou Lu Chengming Wang Jie Chen Jinfeng Liu Hongliang Mao 《Quaternary Geochronology》2010,5(2-3):159-163
The Nihewan Formation, consisting of thick fluvio–lacustrine sediments with abundant mammalian faunas and Paleolithic remains, is widely distributed in the Nihewan Basin, northern Hebei Province, China. In this study the fluvio–lacustrine sediments of the Nihewan Formation and the loess–paleosol sequence evident in the Haojiatai Section were dated by recuperated OSL (ReOSL) of fine-grained quartz (Wang, X.L., Lu, Y.C., Wintle, A.G., 2006a. Recuperated OSL dating of fine-grained quartz in Chinese loess. Quaternary Geochronology 1, 89–100.). The preliminary ReOSL dating results show that: (i) the loess–paleosol sequence in the upper part of the profile started to develop at about 128 ka ago; (ii) the unconformity separating the loess–paleosol from the underlying Nihewan Formation represents a sedimentation break of about 130 ka. On the basis of the ReOSL dates and related stratigraphic evidence it is proposed that the ancient Lake Nihewan dried shortly after about 266 ka. 相似文献
17.
Rock magnetic measurements of Nihewan sediments from Xujiayao section demonstrate that magnetite, hematite and maghemite are
dominant remanent magnetization carriers. Monitoring the variations of magnetic susceptibility (MS) and saturating isothermal
remanent magnetization (SIRM) at low temperature are the attractive ways of detecting the presence of magnetite, maghemitization
and superparamagnetic grain sizes. Low-temperature MS investigations suggest that susceptibility enhancement for Xujiayao
samples is mainly due to the remarkable presence of SD/MD magnetite to some degree though some magnetite grains have been
partially oxidized at some depths. It is tentatively concluded that both SD/MD magnetite and hematite are of detrital origin
and carry a characteristic remanent magnetization (ChRM), whereas maghemite can be attributed to be chemical origin, overprinting
a reversed polarity component of Matuyama age. 相似文献