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1.
洛川塬区土壤侵蚀变化表现出不同的侵蚀期,土壤侵蚀过程就是沟谷的发育过程。通过分析洛川塬区晚中更新世以来洛河阶地和沟谷黄土、古土壤记录的古地貌形态得出,560～460kaB.P.的第一侵蚀期洛河一级支流开始广泛形成;洛河较大的二级支流形成于250～200kaB.P.的第二侵蚀期;140～95kaB.P.的第三侵蚀期洛河形成了三级支流;洛川塬区众多的冲沟主要是全新世(10～0kaB.P.)以来形成的。分析了洛川塬区不同侵蚀期形成的沟谷地貌形态。以黑木沟为例,具体分析了黑木沟的发育过程和土壤侵蚀量变化。 相似文献
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基于地质过程，特别是沉积地质过程的理论和方法，利用遥感影像，结合实地测量的地貌与沉积记录、室内沉积分析和测年等资料，研究了玛纳斯河山麓冲积扇的演变过程，探讨了冲积扇演变对区域构造活动的响应。结果表明：（1）晚第四纪以来，玛纳斯河山麓冲积扇从第二排山麓到下游冲积平原，可划分为四期规模较大和三期规模较小的冲积扇，新冲积扇叠置和切割老积扇；（2）天山北麓第二排背斜带霍尔果斯、玛纳斯、吐谷鲁逆断裂-背斜带的间歇式差异升降运动是冲积扇演化的直接动力；（3）冲积扇是构造活动的特征地貌，其演化与山麓断层的构造活动性有明显的相关性。 相似文献
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晚更新世小江流域泥石流沉积特征及发育规律 总被引：1，自引：0，他引：1
泥石流沉积物作为晚更新世一种特殊沉积类型,是在特定的地质过程和地理环境中形成的。由于特殊的地理环境,泥石流沉积成为晚更新世小江流域主要的沉积类型,本文在研究了青藏高原东缘小江流域蒋家沟附近晚更新世不同时段泥石流沉积剖面沉积特征、化学元素及可溶盐成分的富集规律、CaCO3含量、pH值、有机质含量及植物花粉组合特征后发现,自末次间冰期到末次冰期,沉积物基质中可溶性盐在增多,花粉从以木本为主转变为草本为主,同时泥石流沉积层有变薄的趋势,反映了随气候变冷,泥石流有减少的趋势。 相似文献
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武都晚更新世泥石流堆积体的沉积相 总被引：3，自引：0，他引：3
本文以沉积学的方法,对武都晚更新世泥石流堆积体的地层剖面进行了划分对比,并建立了该期泥石流堆积体的综合地质柱状图,并较详细地研究了它们的沉积相特征。认为武都本期泥石流堆积体,是由与泥石流作用有关的泥流型洪积相、水流型洪积相以及与泥石流作用无关的冲积沉积相和黄土状土沉积相所组成。由此推断了它们的形成环境,探讨了泥石流发生、停歇与新构造作用及气候的关系,从而进一步划分了本次泥石流作用期的4次作用阶段。 相似文献
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基于5℃界限温度指标，利用羌塘自然保护区附近站点1971−2019年逐日平均气温、降水量和日照时数等资料，采用线性回归、Mann-Kendall检验方法和R/S分析等方法，分析了近49a自然保护区高寒草地牧草青草期及其水热气候资源的变化特征；预估了在RCP2.6、RCP4.5和RCP8.5三种排放情景下，未来80a（2021−2100年）牧草青草期的变化，以期了解和预测高寒草地生态系统的动态变化。结果表明：（1）近49a自然保护区平均每10a牧草青草期开始日提早2.81d，终止日推迟2.74d，天数延长5.56d；青草期积温、降水量和日照时数均表现为显著增加趋势，增幅分别为75.86℃·d·10a−1、15.84mm·10a−1和27.58h·10a−1。（2）在年代际变化特征上，20世纪70−90年代各站青草期开始日晚、终止日早、持续天数短、水热条件偏差；21世纪00−10年代截然相反，青草期开始日早、终止日晚、持续天数长、水热资源充沛。（3）M-K法检验显示，青草期开始日、终止日和天数的突变时间分别出现在2006年、1991年和1988年；青草期积温、降水量和日照时数分别在1988年、1999年和1981年也发生了由偏少变偏多的突变。（4）青草期要素的Hurst指数均大于0.5，表明未来青草期开始日提早、终止日推迟、天数延长，积温、降水量和日照时数均增加的变化趋势仍将持续。（5）在RCP4.5排放情景下，未来80a自然保护区牧草青草期开始日提早10d、终止日推迟9d、天数延长17d，这有利于牧草生长，牲畜抓膘，对牧业生产、草地生态系统恢复十分重要。 相似文献
6.
利用197l-2007年云南124站逐日降水资料计算雨季开始期,采用EOF(经验正交函数)分解和最大熵谱分析方法,研究云南雨季开始期的空间分布、时间演变及周期变化特征,并初步分析云南雨季开始期不同分布型与季风的关系,以期为指导春季农业生产提供依据。结果表明,全省雨季开始期一致偏早或偏晚为云南雨季开始期的最主要空间分布特征,其次为滇中及以东地区与滇西北及滇西南地区雨季开始期反向变化的空间分布型;雨季开始期全省一致分布型存在3～5a的显著周期变化,滇中及以东地区与滇西北及滇西南地区雨季开始期反向变化的空间分布型存在3～4a的显著周期变化;云南雨季开始期与同年5月孟加拉湾地区和南海地区OLR有显著的相关关系(P<0.05);南亚季风与南海季风强度指数对云南雨季开始期有重要的指示性意义。 相似文献
7.
晚更新世红土，由于它与Ｑ２红土的某些特征：如分布规律，构成地貌形态，母质成因等方面都有类同之处，故长期来人们习惯将它与Ｑ２红土上发育的土壤归并在同一个土类，只是在土属中加以区分。 相似文献
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青海官亭盆地黄河二级阶地的结构分析 总被引：1，自引：0，他引：1
通过对黄河上游官亭盆地地貌及古文化遗址的野外考察,分析了盆地中黄河二级阶地的结构,认为该阶地形成于全新世中期。距今4000年左右的史前洪水阶地上加积了一层平流沉积物,形成复合型阶地,其下部为基座阶地,上部为上叠阶地。 相似文献
12.
Twenty eight samples of peat, clay and silty clay from a tin mine exposure near Pantai Remis, Perak, Malaysia, were palynologically analyzed. Six pollen zones and eight subzones were delineated based on the dominant floral components. Accelerator mass spectrometry (AMS) radiocarbon and thermoluminescence datings on selected samples indicate late Pleistocene and older age. The occurrence ofPodocarpus imbricatus pollen suggests that the deposit is no older than late Pliocene. The fluctuation of sea level during the late Pleistocene is believed to be the main factor that influenced the development of vegetation at the Pantai Remis area. The presence of mangrove peat at depths between 13.0 m and 14.0 m, which overlies a freshwaterPandanus peat, indicates the position of a former shoreline at Pantai Remis when the area was inundated sometime during the last interglacial marine incursion. During this period of high sea level, thePandanus swamp was probably being gradually replaced by mangrove vegetation. The mangrove sequence is regarded as equivalent to the Kempadang formation. A slight drop in sea level sometime during the last glacial interstadial stage probably caused a small, open alluvial swamp to be developed over the mangrove forest. This freshwater deposit may be the equivalent of the Simpang formation. 相似文献
13.
Dated shorelines of late Pleistocene pluvial Lakes Lahontan (Great Basin Desert, northwest Nevada) and Mojave (Mojave Desert, eastern California) provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late Pleistocene to early Holocene. Two sets of alluvial fan systems have been mapped: the Stillwater fans, feeding Lake Lahontan; and the Zzyzx fans, feeding Lake Mojave. Their contrasting morphologies suggest different responses of the two fan systems to late Pleistocene to early Holocene climatic change. At the time the Stillwater fan systems underwent minimal sedimentation, with the catchment hillslopes apparently stable. The Zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes. There was a major phase of hillslope debris-flow activity, followed by fanhead trenching and distal fan progradation. Both areas were wetter and colder in the late Pleistocene than they are today, but during the transition to the Holocene the Zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the Southwest. Vegetation reconstructions for the late Pleistocene to the early Holocene suggest that catchment hillslopes in the Mojave supported a desert shrub vegetation, but those in the Stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations. Contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the Pleistocene to Holocene climatic transition. After the falls in lake levels of Lakes Lahontan and Mojave in the early Holocene, both areas underwent aridification, resulting in reductions in hillslope vegetation cover. Increased storm runoff led to fanhead trenching and distal progradation of the alluvial fans. Variations in fan style at that time may relate primarily to base-level conditions resulting from different gradients on the exposed lake shores. 相似文献
14.
利用放射性碳对中国变性土的年代确定 总被引：1，自引：0，他引：1
LIU Liang-Wu 《土壤圈》1996,6(2):147-153
Vertisols,which are mainly developed on fluvial and lacustrine deposits and basalt,are extensively distributed in China.66 samples of them for radiocarbon dating were collected across 5 porvinces and 1 autonomous region,ranging from warm-temperate to subtropical and tropical zones in China.The soil organic matter was dated via surface horizon,black soil horizon and dark-colour horizon of the vertisols,whereas carbonate through calcareous concretions and dispersed carbonate in soil profile using radiocarbon method.The present article elucidates the dates of genetic horizons,and of surface and buried vertisols as well.14C dating indicates that the surface vertisols were formed during the end of the late Pleistocene.ca.15600 years ageo.Correlation between depth of sampling and measured 14C age shows that age characteristics of the vertisols of China are close to those of West Germany,Italy,TUrnisia,Australia and Argentina,However,two buried vertisols developed on fluvial and lacustrine deposits were formed during different geological periods,The buried soils in warm-temperate zone were formed in the mid Holocene,while those in subtropics were buried at 12930 years B.P., and formed in the end of the late Pleistocene. 相似文献
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作者认为分布在起伏台地区中更新统沉积物上的黑土(无石灰反应,有机质丰富,几乎全部耕垦)和平原中部晚更新统和近代冲积物上的淡黑钙土(强石灰反应,有机质少,常混有盐斑),其发生学上的差异主要是成土母质和年龄的不同。后者远较前者为年幼。淡黑钙土是按沼泽→草甸→草甸淡黑钙土→淡黑钙土的过程形成的。现代气候条件下,植被制约着草甸土类的发生方向。不论是由于天然的或人为的任何原因,一旦植被破坏,随着蒸发的加强,即便地下水的矿化度不高,也能形成强碱性、结构极坏的苏打盐(碱)土。按照土壤发生的观点,合理利用碱性草原和改良苏打盐(碱)土的原则,应是保护和恢复植被。 相似文献
16.
青藏铁路K1533路基风蚀防治措施效益研究 总被引：1，自引：0，他引：1
对青藏铁路K1533处高立式沙障和石方格沙障防风固沙的效益进行了研究,结果表明:高立式沙障可有效地降低防护区的风速,风速降幅范围在第1沙障后为14.63%~86.15%,第2沙障后为41.93%~97.91%,第3沙障后为22.80%~87.40%;同时降低了防护区的侵蚀量,高立式沙障后的侵蚀量和对照区相比,第1沙障后的侵蚀量仅占对照区的21.75%,第2,3沙障后的侵蚀量和对照区相比,其值缩小了数十倍到数百倍。石方格区的侵蚀量减幅更大,和对照区相比,相同高度的侵蚀量缩小了数十倍到数百倍甚至数千倍。高立式沙障、石方格沙障措施相结合使用,对于防治风蚀具有十分显著的作用,对保护风沙区铁路工程免遭风沙危害具有非常重要的作用。 相似文献
17.
van Dijk C Ebbenhorst-Selles T Ruisch H Stolle-Smits T Schijvens E van Deelen W Boeriu C 《Journal of agricultural and food chemistry》2000,48(2):132-139
The relationships between the redox potential of the brine, during fermentation of white cabbage into sauerkraut of two early and two late fermentation processes, and the changes in the amount of sugars, organic acids, the redox potential of the brine and of the ascorbic acid redox couple, and pH are described. The trend in the change of the redox potential of the brine is the same for all four fermentation processes studied. In the first phase a sharp decrease in redox potential is followed by an increase in redox potential. In the second phase the redox potential is rather constant. This second phase is followed by another decrease in redox potential, which stabilizes at a minimum value, the third phase. It was observed that sugar fermentation and acid production mainly took place during the first and third phases, probably representing, respectively, the heterogeneous and homogeneous fermentation processes. 相似文献
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The genesis, evolution, and paleoecology of soils of the Early Valdai interstadials were investigated in the Aleksandrov quarry (Kursk oblast), a key section of the Late Pleistocene deposits in the periglacial area of the East European Plain. The soils developed in the uppermost parts of the buried hollows (investigated in 2009) were compared with the soils developed in the lower parts of the same hollows (investigated in 1988). The data obtained suggest that the soils in the upper parts of the hollows were developed under wetter and, at the same time, more percolative water regime than the soils in the lower parts of the hollows. These soils were formed in a semihumid climate under the forest-steppe vegetation. Forest groves existed in the upper parts of the erosional network amidst herbaceous meadow steppes. In general, the soil cover pattern of the Early Valdai interstadials corresponded to the modern soil cover pattern within the analogous landscapes. 相似文献
19.
鸡粪中的有机酸及其对土壤速效养分的影响 总被引：32，自引：1，他引：32
通过室内模拟实验研究了鸡粪堆腐过程中有机酸的种类、含量和变化规律。结果表明 ,鸡粪腐熟过程中会形成和累积大量的有机酸 ,在堆腐的第 5周 ,最高含量可达88 3cmolkg- 1DM ;不挥发性有机酸在堆腐的第 3周和第 5周分别达到两个高峰 ,挥发性有机酸在第 6周和第 9周分别达到高峰 ,堆腐 9周后 ,鸡粪中的有机酸大大降低。鸡粪在堆腐的过程中产生大量的丁二酸及其衍生物等低级脂肪酸等。土培试验表明 ,这些酸在活化土壤磷素方面具有不可忽视的作用 相似文献
20.
Soil evolution over the Quaternary period in a semiarid climate (Segre river terraces,northeast Spain) 总被引：1，自引：0，他引：1
A macro- and micromorphologic study was done on the soils from a stepped sequence of seven dated fluvial terraces in the lower Segre river valley (Lleida, northeast Spain) under a present-day semiarid Mediterranean climate. The soils have evolved from the Holocene through the early Pleistocene, providing an excellent morphostratigraphic framework for evaluating time-dependent factors influencing soil formation in a dry and calcareous environment. Throughout the chronosequence, some properties are regularly age-related specially carbonatation in subsurface horizons. The carbonates occur mainly as micrite, and although microsparite and sparite also appear in the oldest soils, they are replaced by fine-grained calcite by dissolution–reprecipitation processes (micritization process), which is active at present. Some pedological paleofeatures as the presence of sparite and recarbonated argillans in oldest terrace can be interpreted as the reflex of climatic changes during the Quaternary. In spite of this climate variability, the soils display progressive and systematic patterns of carbonate accumulation: on the lowest terraces, the soils do not yet have secondary carbonates but in the beginning Late Pleistocene calcic horizons, with carbonate pendents, are developed; these pendents increase its thickness with age although pendent growth rates decreases from Late Pleistocene to Middle Pleistocene. In the middle of the Late Pleistocene, calcic horizons evolved to petrocalcic horizons, which increase its thickness in the Middle and specially in Early Pleistocene. The presence of calcic and petrocalcic horizons is the primary basis for soil classification. This criterion is applicable not only to the soils of the lower Segre river basin, but also to many soils throughout the semiarid Mediterranean region. 相似文献