共查询到19条相似文献，搜索用时 140 毫秒
1.
近20年来, 古DNA研究技术和方法已迅猛发展.目前从古人类残骸中获取DNA序列, 进而讨论人类的演化、亲缘关系和迁移成为分子人类学的一个重要方向.本研究对采自陕西临潼仰韶文化6 000多年前的姜寨遗址第一期和第二期文化层中的古人类残骸进行古DNA提取、扩增和测序, 获得了169 bp的线粒体高变控制区Ⅰ的古DNA片段, 与现代西安人同源性序列有2个位点的突变.另外, 通过在不同实验室进行重复性实验和系统发育分析等方法详细地论证了所获得的DNA序列的可靠性.在所研究的6个姜寨遗址样品中有3个样品获得古DNA序列, 古DNA的提取成功率为50%, 高于一般的古DNA研究材料的提取率, 说明姜寨遗址的人类残骸是研究古DNA的理想材料, 为今后从分子水平上研究姜寨遗址及其他同地区仰韶文化遗址的古人类墓葬及中国古人类分子演化关系奠定了基础. 相似文献
2.
基于瞬变电磁法(TEM)的西昆仑地区多年冻土厚度探测与研究 总被引：5，自引：4，他引：1
多年冻土厚度对于多年冻土的区域分布和环境效应具有重要控制和指示意义. 应用瞬变电磁法(TEM)对青藏高原西昆仑地区的多年冻土下限进行了探测, 并结合钻孔资料分析了该研究区域多年冻土厚度的分布特征. 结果表明:研究区域多年冻土厚度随地形、地质条件的差异表现出显著的空间差异性. 沿着219国道从509道班到奇台达坂的高山峡谷区, 随着海拔的升高, 多年冻土从无到有, 而且, TEM探测到的多年冻土厚度从不到10 m到接近100 m, 平均厚度约为55 m; 自界山达坂向东到拉竹龙的低山丘陵区, 除部分区域发育融区外, 多年冻土厚度一般在50 m左右, TEM探测显示多年冻土平均厚度约为58 m; 进入甜水海盆地, 多年冻土厚度普遍超过60 m, TEM探测到靠近湖泊的盆地中心地带多年冻土平均厚度可达110 m. 多年冻土厚度随地温的降低呈显著的线性增加趋势, 10 m深度地温平均每降低1 ℃, 多年冻土厚度增加29 m. 多年冻土的厚度随海拔的升高显著增加, 同时局地因素对多年冻土的发育有显著影响, 其内在机制需要进一步研究. 相似文献
3.
黄河源区冻土特征及退化趋势 总被引：17，自引：8，他引：9
黄河源区位于青藏高原多年冻土区东北部边缘地带,是季节冻土、岛状多年冻土和在大片连续多年冻土并存地带.多年冻土层在垂向分布上有衔接状和不衔接状两大类.不衔接状又可分为浅埋藏(8m)、深埋藏(8m)和双层多年冻土等形式.从20世纪80年代以来,源区气温以0.02℃.a-1增温率持续上升,人类经济活动日益增强,导致冻土呈区域性退化.多年冻土下界普遍升高50～80m,最大季节冻深平均减少了0.12m,浅层地下水温度上升0.5～0.7℃.冻土退化总体趋势是由大片状分布逐渐变为岛状、斑状分布,多年冻土层变薄,冻土面积缩小,融区范围扩大.部分多年冻土岛完全消失变为季节冻土. 相似文献
4.
气候变暖背景下青藏高原多年冻土层中地下冰作为水"源"的可能性探讨 总被引：6，自引：4，他引：2
多年冻土中含有大量地下冰,全球气候变暖势必导致多年冻土退化,地下冰融化,部分水分被释放并参与到区域水循环之中,改变了区域水文状况.冻土退化-释水的过程在监测上面临较大困难,无法提供直接让据,但其长期累计的效果在宏观水文过程中表现显著.为此,利用近年来青藏高原部分湖泊水位变化监测以及地区水文情势变化研究成果,探讨了在气候变暖背景下,多年冻土层中的地下侣冰作为一种潜在水"源"的可能性.结果表明:多年冻土退化较强烈地区,补给源头在多年冻土区的封闭湖泊水位上涨、地下水位上升,排除其它补给量增加的可能性后,多年冻土地下冰很可能是补给水量增加的原因之一. 相似文献
5.
青藏铁路沿线多年冻土分布特征及其对环境变化的响应 总被引：1，自引：0，他引：1
针对青藏高原特殊的自然气候条件,按照地形、地貌把青藏铁路沿线多年冻土分为15个区段,并分别介绍了各个区段多年冻土特征. 结果表明：在外界环境变化,包括全球气候变暖及工程活动的双重效应下,青藏铁路沿线多年冻土及其存在状态发生了极大变化,这些变化主要包括年平均气温升高、多年冻土退化、热融灾害增加、寒区工程病害不断加剧等. 多年冻土及其存在状态发生变化不但导致生态环境恶化,而且对青藏铁路沿寒区工程的安全运营、维护及发展提出新的挑战. 相似文献
6.
热融湖影响下多年冻土退化的数值模拟 总被引：2，自引：0，他引：2
在柱坐标下,运用带相变的数值热传导模型,预测了千年尺度上热融湖对多年冻土退化的影响。预测结果表明,受热融湖的影响,湖底下部及周围多年冻土温度状态发生了较大变化。在湖深相同的情况下,湖底年平均温度越高,对多年冻土的热扰动越明显。当湖底年平均温度等于0℃时,湖底下部及周围多年冻土一般不会形成融化层,只可能引起地温升高;当湖底年平均温度大于0℃时,多年冻土不但温度升高,上限下移,而且可能形成融化层,最终导致多年冻土可能被融穿。湖底年平均温度越高,地温增加越快,融穿多年冻土的时间越短。在湖底年平均温度相同的情况下,水深差异对多年冻土退化的影响不明显。 相似文献
7.
多年冻土区水泥稳定砂砾基层抗冻性能研究 总被引：2，自引：1，他引：1
多年冻土地区路面使用过程中的许多病害与基层状况直接相关.水泥稳定砂砾作为我国传统的半刚性基层材料,在多年冻土地区公路路面结构中得到了普遍运用.为研究水泥稳定砂砾不同水泥掺量、不同养生龄期下的抗冻性能,通过提出合理的抗冻试验方法分别进行了水泥稳定砂砾冻融温度、冻融时间、冻融次数、试件的养生龄期及抗冻指标方面的试验研究. 结果表明：水泥剂量越高,水泥稳定砂砾冻前、冻后的抗压强度值越高,说明其抗冻性能越好;水泥稳定砂砾从28 d开始抗压强度、冻融后抗压强度及冻融后劈裂强度都明显增加,证明水泥稳定砂砾从28 d开始已具有一定的抗冻性. 提出的抗冻试验方法和指标要求适合多年冻土地区半刚性基层材料,有一定的实用价值. 相似文献
8.
内蒙古中部早白垩世地层发育,含植物化石较好,但经系统描述和报道的材料并不多。对固阳城西茜连脑包一带下白垩统的植物化石进行了系统采集,化石采自固阳组灰黑色泥岩以及灰绿色、黄绿色粉砂质泥岩中。在对植物化石进行系统鉴定及描述的基础上,探讨了化石植物的埋藏环境。其中保存于灰黑色泥岩中的植物化石形态较为完整,且泥岩指示弱水动力条件,因而这些化石可能为近原地埋藏;而保存于粉砂质泥岩中的化石保存较为破碎,且粉砂质泥岩表示水动力较强的环境,故这些化石可能经过水流搬运,为异地埋藏。通过以上化石的保存状态及岩性特征,可知茜连脑包一带早白垩世固阳组化石埋藏类型为近原地埋藏和异地埋藏两种,且植物化石指示较温暖湿润的古气候环境。 相似文献
9.
多年冻土区高寒草甸根系分布与活动层温度变化特征的关系 总被引：4，自引：3，他引：1
多年冻土区植物根系的地下分布格局是其适应高寒、反复冻融作用等特殊环境条件的重要体现.针对目前青藏高原高寒植物根系研究不足的现状,对青藏铁路沿线高寒草甸植物群落根系的分布特征及多年冻土活动层地温变化等进行调查观测.研究高寒植物群落根系在活动层土壤中的垂直分布特征,重点探讨多年冻土活动层温度变化对于高寒植物根系分布和格局的影响,揭示植物根系对冻土环境变化的响应特征及其对逆境条件的适应策略.研究结果表明:活动层季节性冻融对于高寒植物和地下根系分布格局具有深刻的影响,多年冻土表层最先具备适宜根系生长的温度和水分条件,导致高寒草甸根系分布浅层化,生物量大量累积在土壤表层,并随深度增加而减少.高寒草甸地下平均总根量为3.38 kg·m-2,0~10 cm土层根量密度平均为21.41 kg·m-3,约占地下根系总量的63.4%.高寒草甸植物群落具极高的根茎比,活动层长期的低温环境增加了根系的干物质总量和高寒植物总的生物产量.活动层0℃以上积温是根系分布的主要影响因子. 相似文献
10.
寒区环境中的古DNA分子 总被引：1，自引：0，他引：1
寒区埋藏环境常年处于负温条件下,土壤冻结或冰的形成过程产生封闭作用,可以隔离造成埋藏生物遗体同DNA氧化分解的氧气之间的接触.由于液态水含量极大地减少和冰胶结作用,使得主要依赖于液态水而发生的生物大分子的化学分解以及生物降解反应作用减慢,有机体没有成岩过程中降解以及水解作用,从而使古DNA分子可以得到较好的保存.目前绝大多数关于古DNA研究的重要成果所使用生物材料均来自寒区环境,最为引人注目的有关猛犸象、棕熊和企鹅化石古DNA的研究.这些研究分别从个体、种群和同一种群在不同时间尺度上描绘了它们与现代生物种之间的亲缘关系、过去发生的生物迁移和空间隔离以及特定生物分子水平上的时间演化.从目前来看,大量的生物标本很好地保存在那里,以至于单一考贝基因都可以获得,因此是获取古DNA并获得相应遗传信息的理想地区. 相似文献
11.
Selective preservation of soil organic matter in oxidized marine sediments (Madeira Abyssal Plain) 总被引：1，自引：0，他引：1
Carme Huguet Gert J. de Lange Jack J. Middelburg Jaap S. Sinninghe Damsté Stefan Schouten 《Geochimica et cosmochimica acta》2008,72(24):6061-6068
In ocean margin sediments both marine and terrestrial organic matter (OM) are buried but the factors governing their relative preservation and degradation are not well understood. In this study, we analysed the degree of preservation of marine isoprenoidal and soil-derived branched glycerol dialkyl glycerol tetraethers (GDGTs) upon long-term oxygen exposure in OM-rich turbidites from the Madeira Abyssal Plain by analyzing GDGT concentrations across oxidation fronts. Relative to the anoxic part of the turbidites ca. 7-20% of the soil-derived branched GDGTs were preserved in the oxidized part while only 0.2-3% of the marine isoprenoid GDGT crenarchaeol was preserved. Due to these different preservation factors the Branched Isoprenoid Tetraether (BIT) index, a ratio between crenarchaeol and the major branched GDGTs that is used as a tracer for soil-derived organic matter, substantially increases from 0.02 to 0.4. Split Flow Thin Cell (SPLITT) separation of turbidite sediments showed that the enhanced preservation of soil-derived carbon was a general phenomenon across the fine particle size ranges (<38 μm). Calculations reveal that, despite their relatively similar chemical structures, degradation rates of crenarchaeol are 2-fold higher than those of soil-derived branched GDGTs, suggesting preferential soil OM preservation possibly due to matrix protection. 相似文献
12.
13.
利用多年冻土区湖相沉积物中埋藏植物稳定碳同位素组成重建大气CO2浓度 总被引：5，自引：5，他引：5
沉水植物碳同位素分馏同水中溶解无机碳浓度有一定的关系，因而可以通过青藏高原多年冻土区的湖相沉积物中埋藏沉水植物－－龙须眼子菜（Potamogeton pectinatus)植物屑的碳同位素组成重建该地大气CO2浓度的变化情形，研究结果表明，该地在9．17－6．77ka BP间，大气CO2浓度是整个研究时间段中最低的，其后在6．77－4．56ka BP时期大气CO2浓度增加，在4．56－2．17ka BP之间，大气CO2浓度是整个研究时间内CO2浓度最高的阶段，植物屑的碳同位素组成反映了溶解无机碳浓度的变化，从而可用以重建大气CO2浓度的变化情况。 相似文献
14.
古环境DNA(ancient environmental DNA,简称ancient eDNA)指保存于古环境样品中的生物古DNA(ancient DNA,简称aDNA).与直接从古代生物遗存内获取的单一物种古DNA不同,古环境DNA为多种生物的混合DNA,常常以小片段DNA分子形式吸附在腐殖质和矿物颗粒上,主要从粪化石、牙结石、肠道残留物、冰川、冻土、泥炭、湖泊、海洋、洞穴和遗址沉积物等环境样品中获得.古环境DNA研究自1998年开始兴起,经历了早期的DNA条形码(DNA barcoding)古代物种鉴定,到DNA宏条形码(DNA metabarcoding)古代生物类群恢复,再到近期的鸟枪法宏基因组(shotgun metagenomic)古生态系统重建等发展历程,目前已形成了完善的研究体系,可以完成对古环境样品中大部分动物、植物和微生物物种的检测.相比于传统的动植物化石形态鉴定手段,古环境DNA研究具有样品用量少、方法简单快捷、不依赖于化石、一次实验可以确定大量物种信息等优势.目前,国际上的古环境DNA研究在古生态环境重建、古代农业发展、古代人类食性、人类扩散历史和人类活动对环境影响等环境考古领域的应用都取得了良好的进展并发表了大量成果,但国内相关研究还少有报道.本文综述了古环境DNA技术的发展、研究方法、应用方向及存在的问题等内容,认为随着古环境DNA研究技术的日趋完善,其在环境考古学中的应用前景也将更加广阔. 相似文献
15.
Ulyantsev A. S. Belyaev N. A. Bratskaya S. Yu. Romankevich E. A. 《Doklady Earth Sciences》2018,482(2):1357-1361
The concentration and molecular composition of phenols, lignin derivatives, were analyzed. The material for the study was sampled from bottom sediments and subaqueous perennial frozen rocks from a well drilled in the Buor-Khaya Gulf of the Laptev Sea. The analysis was undertaken on the basis of calculation of the molecular factor. The principal difference in the molecular composition of organic matter is shown. This difference is manifested in the decrease in the total concentration of the vanillic lignin derivatives in the thawed formations in comparison with the perennial frozen rocks. This phenomenon is explained by activation of the bacterial transformation of organic matter caused by thawing of the subaqueous permafrost. It was established that the weight percentage of lignin in the organic matter of the analyzed sediments is 17% Corg.
相似文献16.
Pleistocene sediments and soils exposed at Stebbing in central Essex, England are described, analysed and interpreted. The sand and gravel units above Eocene London Clay and Upper Pliocene Red Crag are shown to be a high level member of the Kesgrave Formation, with a surface immediately beneath that of the Westland Green Gravels, which are tentatively assigned to the Pre-Pastonian ‘a’ Stage of the British Quaternary succession. The rubified, argillic soil developed in the surface of these fluvial deposits is a composite of the Valley Farm and Barham Soils and displays micromorphological evidence of several phases of clay illuviation, gleying and clay coating disruption. Originally truncated and buried beneath Anglian gelifluction deposits, cover sand and till, the soil has been exhumed in most places by subsequent erosion. The full succession, however, is preserved within large gulls that formed by periglacial cambering prior to this erosion. More recent loess incorporation and pedogenesis have modified the exhumed soil and the materials within the gulls. 相似文献
17.
Although fatty acids and alcohols in plant polyesters can be useful indicators of organic matter provenance in soils and sediments, interpretation is limited by uncertainty in: (i) the distribution of lipids among plant species and their organs (e.g. leaves and roots) and (ii) the extent to which plant lipid composition is recorded in soils and sediments. In this study, we compare lipids in leaves, roots and soils from 11 temperate tree species. Base hydrolysis was used to release ester-bound lipids and solvent extraction was then used to recover both hydrolysable and “free” lipids. Leaf and root lipid composition varied substantially among the tree species and we highlight differences among evergreen conifers, deciduous broadleaved angiosperms and a deciduous conifer (Larix decidua). Some of the variation appears to be linked to the morphology and lifespan of leaves and roots. Soils preserved much of the variation in the leaf and root lipid composition of the overlying tree species. Yet, the concentration of some lipids in soil diverged from their concentration in tree leaves and roots, reflecting an undocumented input from understory plants and other plant organs (e.g. seeds) or variation in the extent of lipid preservation in soil. Finally, by comparing leaf and root lipid composition, our results help constrain the attribution of lipids to each of these plant organs. This allowed us to evaluate the utility of leaf-derived lipids as plant type biomarkers and to document a substantial contribution of root-derived lipids to soil beneath all 11 tree species. 相似文献
18.
The post-depositional changes of the onshore 2004 tsunami deposits on the Andaman Sea coast of Thailand 总被引：2，自引：1，他引：1
Witold Szczuciński 《Natural Hazards》2012,60(1):115-133
The Indian Ocean tsunami flooded the coastal zone of the Andaman Sea and left tsunami deposits with a thickness of a few millimetres
to tens of centimetres over a roughly one-kilometre-wide tsunami inundation zone. The preservation potential and the post-depositional
changes of the onshore tsunami deposits in the coastal plain setting, under conditions of a tropical climate with high seasonal
rainfall, were assessed by reinvestigating trenches located along 13 shore-perpendicular transects; the trenches were documented
shortly after the tsunami and after 1, 2, 3 and 4 years. The tsunami deposits were found preserved after 4 years at only half
of the studied sites. In about 30% of the sites, the tsunami deposits were not preserved due to human activity; in a further
20% of the sites, the thin tsunami deposits were eroded or not recognised due to new soil formation. The most significant
changes took place during the first rainy season when the relief of the tsunami deposits was levelled; moderate sediment redeposition
took place, and fine surface sediments were washed away, which frequently left a residual layer of coarse sand and gravel.
The fast recovery of new plant cover stabilised the tsunami deposits and protected them against further remobilisation during
the subsequent years. After five rainy seasons, tsunami deposits with a thickness of at least a few centimetres were relatively
well preserved; however, their internal structures were often significantly blurred by roots and animal bioturbation. Moreover,
soil formation within the deposits caused alterations, and in the case of thin layers, it was not possible to recognise them
anymore. Tsunami boulders were only slightly weathered but not moved. Among the various factors influencing the preservation
potential, the thickness of the original tsunami deposits is the most important. A comparison between the first post-tsunami
survey and the preserved record suggests that tsunamis with a run-up smaller than three metres are not likely to be preserved;
for larger tsunamis, only about 50% of their inundation area is likely to be presented by the preserved extent of the tsunami
deposits. Any modelling of paleotsunamis from their deposits must take into account post-depositional changes. 相似文献
19.
古代生物分子与分子考古学 总被引：14，自引：0，他引：14
分别论述了从古DNA，古蛋白质，类脂化合物等古代生物分子的尺度去研究人类的起源和迁移，动，植物的家养和驯化过程及早期农业的发展，考古点动植物骸的精确鉴定，新的定年技术以及古气候的变化等与考古学相关的许多重要问题，对分子考古学及其应用进行综述，并就在我国开展分子考古学研究提出了展望。 相似文献