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排序方式: 共有291条查询结果,搜索用时 16 毫秒
281.
黄河中游三趾马红粘土的岩石学研究及古气候意义——以陕西府谷老高川三趾马红粘土剖面为例 总被引:3,自引:0,他引:3
将岩石学研究方法引入三趾马红粘土研究中,利用薄片系统观察、电镜扫描、X-射线衍射、粒度分析及化学分析手段,对红粘土的岩石学、微结构及形态学进行较为细致的研究。结果表明,各粘土层下部的沉淀层系成壤过程中钙质从上部土壤中淋滤并向下迁移再沉淀的结果。土壤中粘化层的光性定向粘粒及淀积铁质粘胶膜的发育程度受古气候及淋滤作用强度的控制。红粘土形成过程中主要为干旱、半干旱-半湿润气候的草原疏林环境,也有湿润气候的森林环境出现。府谷老高川三趾马红粘土剖面记录了四个大的气候旋回 相似文献
282.
Junhuai Yang Dunsheng Xia Fuyuan Gao Shuyuan Wang Zixuan Chen Jia Jia Shengli Yang Zhiyong Ling 《地球科学进展》1986,35(8):863-877
The Yarlung Zangbo River is located in the southern Tibetan Plateau. Loess since the geological history and modern aeolian sand dunes are widely developed in the basin, bearing rich information on the aeolian processes and environmental evolution. In this work, we reviewed the main research progress of aeolian deposits in the Yarlung Zangbo River basin in recent years, and discussed the distribution characteristics, accumulation age, sediment characteristics and provenance and the possible formation mechanism of aeolian deposits and the history of aeolian activity. The results show that loess is mainly developed on the river’s terraces and some of the hilltops, and mostly formed since the last glacial maximum and mainly developed since Marine Isotope Stage 1 (about 14 ka BP), while aeolian sand deposit is mainly developed in the river’s wide valley, with relatively short accumulation time. The sediment particles mainly underwent mechanical transport and physical weathering, but chemical weathering was weak. Although the physical and chemical properties of sediments show some spatial changes, there still exist obvious local characteristics, which are closely related to the nearby surface sediments. Under the background of aeolian source, the local-source genesis of loess is generally recognized. The surface loose material at the bottom of valley is main material source of aeolian deposits. The evolution of aeolian activity is relatively complex. In addition to the regional climate change, the local environment is also an important factor affecting the aeolian activity and its regional difference. Based on the previous studies, we suggest that the systematic study on the physical and chemical properties of aeolian sediments, climate change since the Holocene and the impact of dust emission on human living environment should be strengthened in the future research. 相似文献
283.
The occurrence of red desert soil profiles developed on Nubian Sandstone in the Libyan Sahara is discussed. From an examination of profile morphology in the field and the position of the soils at 970 m on an old land surface, it would be possible to regard them as desert paleosols formed under a previous humid climatic phase during the Quaternary. However, an investigation of the mineralogy of the soils and the underlying parent rocks strongly suggests that the properties of the soils are largely dependent on the parent material. Both have identical patterns of kaolinite content, haematite as the main ferric oxide, and similar proportions of quartz silt and coarse quartz sand. Therefore, the use of kaolinite and ferric oxides in interpreting past soil-forming climates in arid regions needs to be carried out with caution, for in the present case such an interpretation would be unreliable. 相似文献
284.
Susan R.H. Zimmerman Crystal Pearl Sidney R. Hemming Kathryn Tamulonis N. Gary Hemming Stephanie Y. Searle 《Quaternary Research》2011,76(2):264-271
The type section silts of the late Pleistocene Wilson Creek Formation at Mono Lake contain outsized clasts, dominantly well-rounded pebbles and cobbles of Sierran lithologies. Lithic grains > 425 μm show a similar pattern of variability as the > 10 mm clasts visible in the type section, with decreasing absolute abundance in southern and eastern outcrops. The largest concentrations of ice-rafted debris (IRD) occur at 67–57 ka and 46–32 ka, with strong millennial-scale variability, while little IRD is found during the last glacial maximum and deglaciation.Stratigraphic evidence for high lake level during high IRD intervals, and a lack of geomorphic evidence for coincidence of lake and glaciers, strongly suggests that rafting was by shore ice rather than icebergs. Correspondence of carbonate flux and IRD implies that both were mainly controlled by freshwater input, rather than disparate non-climatic controls. Conversely, the lack of IRD during the last glacial maximum and deglacial highstands may relate to secondary controls such as perennial ice cover or sediment supply. High IRD at Mono Lake corresponds to low glacial flour flux in Owens Lake, both correlative to high warm-season insolation. High-resolution, extra-basinal correlation of the millennial peaks awaits greatly improved age models for both records. 相似文献
285.
During the Last Glacial Maximum (LGM), long valley glaciers developed on the northern and southern sides of the High Tatra Mountains, Poland and Slovakia. Chlorine-36 exposure dating of moraine boulders suggests two major phases of moraine stabilization, at 26–21 ka (LGM I — maximum) and at 18 ka (LGM II). The dates suggest a significantly earlier maximum advance on the southern side of the range. Reconstructing the geometry of four glaciers in the Sucha Woda, Pańszczyca, Mlynicka and Velicka valleys allowed determining their equilibrium-line altitudes (ELAs) at 1460, 1460, 1650 and 1700 m asl, respectively. Based on a positive degree-day model, the mass balance and climatic parameter anomaly (temperature and precipitation) has been constrained for LGM I advance. Modeling results indicate slightly different conditions between northern and southern slopes. The N–S ELA gradient finds confirmation in slightly higher temperature (at least 1 °C) or lower precipitation (15%) on the south-facing glaciers during LGM I. The precipitation distribution over the High Tatra Mountains indicates potentially different LGM atmospheric circulation than at the present day, with reduced northwesterly inflow and increased southerly and westerly inflows of moist air masses. 相似文献
286.
Coral reefs are often constrained by diagenesis as a sound environmental archive. The correct understanding and evaluation of diagenesis is the key to the paleoenvironmental reconstruction of coral reefs. The diagenesis of coral reefs mainly includes cementation, dissolution, neomorphism and dolomitization etc. On the one hand, the diagenesis itself can record the paleoenvironment that coral reefs underwent, such as sea-level fluctuation, climate change, change of sea water, hydrothermal alteration, microbial activity and so on. The diagenetic evolution thus can be used for the reconstruction of paleoenvironment change. On the other hand, diagenesis also destroys the original environmental information which recorded of coral reefs recard, and it is necessary to know the degree of the impact of diagenesis. In the future, we should pay more attention to the study on the relationships among diagenesis, modern climate, sea-level change, atmospheric water transformation and microbial activity. It can provide more accurate and longer time series of paleoenvironmental information that coral reefs recorded. 相似文献
287.
Jessica D. Tomkins Dermot Antoniades Scott F. Lamoureux Warwick F. Vincent 《Journal of Paleolimnology》2008,40(1):577-582
We describe a method for preserving the upper sediments of fragile sediment cores during transport from field sites and assess
potential effects on subsequent laboratory analyses. This method addresses the need to minimize disturbance to the surfaces
of unfrozen sediment cores used for paleoenvironmental or other high-resolution sedimentological analyses during transport.
A polymer gel (sodium polyacrylate) applied above the sediment surface acts as a barrier to movement while also preserving
surface undulations. The gel seal can preserve even exceptionally fine sedimentary structures (<0.2 mm) in the upper sediments
of lacustrine and fiord sediment cores, but may react with organic material (e.g. algal mats) present on some sediment surfaces.
This reaction creates an adhesive layer at the gel’s base but it can be handled effectively during sampling. The gel seal
minimizes surface deformation and preserves surficial sediments better than traditional seals made of water-absorbent floral
foam, wax or paper towel. In addition to permitting detailed sedimentary and subfossil investigations of the sediment–water
interface, this method shows no detectable effects on measurements of total organic carbon or total nitrogen values in the
sediment. This method is inexpensive, non-hazardous and applicable to many coring systems and sediment types. 相似文献
288.
Limnological and sedimentary processes at Sawtooth Lake,Canadian High Arctic,and their influence on varve formation 总被引:1,自引:0,他引:1
Pierre Francus Raymond S. Bradley Ted Lewis Mark Abbott Mike Retelle Joseph S. Stoner 《Journal of Paleolimnology》2008,40(3):963-985
This paper synthesizes data collected to document the modern limnological and sedimentary processes in South Sawtooth Lake
located on northern Ellesmere Island, Nunavut, Canada. Field observations show that the finely laminated sediments deposited
in the distal basin are formed by the settling of overflows and interflows, and in rare occasions, by non-erosive hyperconcentrated
density flows. Thin-sections of these sediments allowed for the classification of the sedimentary fabrics into six facies,
each representing different limnological processes. The sediments in this distal basin are considered to be continuous and
annually laminated (varved) based on radioisotope analyses, and both limnological and sedimentological evidence. 相似文献
289.
As a typical alluvial-proluvial fan area in the Qaidam Basin, Nuomuhong is important to the research on paleoclimate reconstruction in proluvial fan areas and basin climate change and ecological protection. This paper analyzes features of ~2H, ~3H, ~(18) O and ~(14) C isotopes in Nuomuhong and reconstructs paleoclimate in this area. According to the results: since 28 ka B.P., the ground average temperature decreases and then increases in the Qaidam watershed, reaching the lowest in 17.7 ka B.P. before increasing gradually. In the past 30 000 years, average temperature has changed ranged from 1 ℃ to 5 ℃ in this area; the lowest temperature was different from today's temperature only by 3 ℃. This shows that climate conditions and natural environment in this area have been relatively stable in the past 30 000 years. 相似文献
290.
昆特依盐湖氯同位素特征及古气候意义 总被引:14,自引:0,他引:14
于1994-1996年,采用高精度正热电离质谱测定氯同位素(δ37Cl)的方法,对青海柴达木盆地昆特依盐湖区的盐湖卤水、湖底盐类矿物、油田水以及该地区的盐类沉积物钻孔剖面的δ37Cl值进行了初步研究。结果表明,该地区的δ37Cl值(卤水)变化范围在-2.05‰—1.04‰,盐湖卤水的δ37Cl值较低,这与卤水的相对密度及pH值有关;盐类沉积钻孔剖面的δ37Cl值呈现自下而上逐渐降低的趋势,这一变化与该地区的古气候变化有关。盐类沉积的δ37Cl值研究将会对高原干旱、蒸发环境条件下湖相沉积古气候演化的研究提供一种新的手段。 相似文献