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1.
西藏定结盆地叶如藏布东岸剖面为一套灰与灰白色黏土质砂、粉砂、细砂与粗砂层所组成的湖相沉积地层,厚约41. 3 m, ESR和U系测年数据显示该地层沉积时间介于距今551. 6 ~ 202. 4 ka的中更新世时期。该套地层的孢粉化石丰富,依据孢粉化石类型与丰度变化,自下而上可分为5个孢粉带。结合测年结果、孢粉和介形类记录,定结盆地中更新世的古环境变化阶段为：551. 6 ~ 448. 4 ka,气候温暖湿润,适宜植物生长;448. 4 ~ 375. 2 ka,气候向冷干转化;375. 2 ~ 291. 2 ka,气候波动频繁,呈现冷湿—冷干—冷湿的变化过程;291. 2 ~ 261. 0 ka,气候进一步趋于干冷;261. 0 ~ 202. 4 ka,气候波动频繁,表现为冷干—暖湿—冷干的变化过程。 相似文献
2.
《地层学杂志》2020,(2)
本文基于驻马店市控制性钻孔BK2的古地磁测试分析、ESR样品测试、孢粉分析,对该孔第四系进行研究。结果认为:BK2孔沉积了早更新世冲湖积地层、中更新世中期冲洪积地层,二者之间为不整合接触关系,缺失中更新世早期沉积地层以及中更新世晚期(含)以来沉积地层。早更新世和中更新世沉积的地层分界位于深度48.0 m处。其中,深度48.0—156.2 m属于早更新世中期、晚期沉积地层,深度1.5—48.0 m属于中更新世中期沉积地层。钻孔总体记录了早更新世中期(深度119.7—154.6 m)温干气候、晚期(深度48.0—119.7 m)冷干气候;中更新世中期(深度3.7—48.0m)温干气候,缺失中更新世早期的冷干气候记录。BK2孔第四纪地层沉积速率的变化是由该区域第四纪沉积气候环境演化和第四纪震荡性构造(升降)运动等共同作用的结果。 相似文献
3.
疏勒河下游安西古沼泽全新世沉积物粒度特征及其古气候环境意义 总被引：3，自引：1，他引：3
通过对安西古沼泽沉积物沉积特征分析,粒度特征分析,孢粉分析并结合年代学资料,研究了安西古沼泽全新世古沼泽进退演化过程、疏勒河中下游河川径流量的变化及河西走廊西部地区古气候环境变化特征。研究结果表明:晚更新世末至全新世河西走廊西部地区气候总体趋于暖湿,但气候冷干—暖湿波动频繁交替。安西古沼泽全新世沉积物4个粒度旋回:①366328 cm,328294 cm;②294240 cm,240206 cm;③206196 cm,196148 cm;④14854 cm,540 cm,可能代表河西走廊西部地区晚更新世末至全新世以来4个气候冷干—暖湿波动周期。 相似文献
4.
两护村ZKC1孔位于洞庭盆地安乡凹陷的东南部,孔内第四系(底部跨上新世)厚达294 m,为河流和湖泊沉积,自下而上依次为上新世—早更新世华田组、早更新世汨罗组、中更新世洞庭湖组、晚更新世坡头组以及全新统等。对ZKC1孔第四系进行了详细的孢粉分析,自下而上划分出16个孢粉组合带。ESR年龄和孢粉组合及其反映的气候特征指示华田组下段形成于上新世末。根据孢粉组合特征,结合构造—沉积演化和区域气候背景,重塑洞庭盆地上新世末以来的气候演化过程:上新世末期由孢粉带Ⅰ和Ⅱ指示具暖干气候。早更新世经历了凉干(孢粉带Ⅲ、Ⅳ)→暖湿间凉干(孢粉带Ⅴ～Ⅶ)→冷干间温湿(孢粉带Ⅷ～Ⅹ)→暖较湿(孢粉带Ⅺ,Ⅻ)的气候演变过程。中更新世早期无孢粉样品(洞庭湖组下部砾石层),其沉积环境暗示冷干气候条件;中期由孢粉带ⅩⅢ反映出暖稍湿的气候特征;晚期因构造抬升缺失沉积,同期湿热化事件指示暖湿气候。晚更新世早期缺乏沉积,据区域对比应为寒冷气候;中期由孢粉带ⅩⅣ指示温较湿的气候特征;晚期缺失沉积,系寒冷气候下区域海平面下降所致。全新世经历了暖稍湿(孢粉带ⅩⅤ)→暖稍干(孢粉带ⅩⅥ)的演变。上述气候演变过程与ZKC1孔化学蚀变指数曲线反映的气候演变过程以及中国东部第四纪气候演化基本吻合。以孔深140 m为界,上部孢粉数量显著高于下部,种属也更为丰富。这一变化很可能对应于一次重要的地质事件,其成因有待今后深入研究。 相似文献
5.
根据珠江三角洲GZ-2孔测年结果、岩相特征和孢粉地层信息推断,该地区全新统约在6.0 ka BP开始沉积, 全新统孢粉组合特征与更新统相比有明显的区别,表明全新世与更新世的气候相比有明显变化。孢粉与沉积信息揭示,全新世本区气候基本以暖湿为主,气候波动不大,在5.0～2.4 ka BP表现最为热湿,在2.4～1.9 ka BP相对偏凉干,随后恢复暖湿。在这些相对较明显的波动中还包含有次一级的微弱波动。除了反映气候变化,孢粉信息也指示了一定的沉积环境变迁以及人类活动信息。该区在中全新世经历了一次明显的海侵过程,进入晚全新世后人类活动对三角洲植被和环境的影响加剧, 期间水深逐渐变浅,沉积环境由河口湾、浅海、滨海潮滩逐渐演变为三角洲平原,区域气候的变化与海平面变化趋势基本一致。 相似文献
6.
西藏定结盆地叶如藏布东岸剖面为一套灰—灰白色粘土质砂、粉砂、细砂与粗砂层所组成的湖相沉积地层,厚约41.3m,该套地层中产丰富的介形类化石,含10属26种,ESR测年数据显示地层沉积时间介于543.8~184.0 kaBP的中更新世时期。本文首次报道了该盆地中更新世时期(543.8~184.0 kaBP)的介形类,据介形类属种类型与丰度值变化,自下而上可分为6个化石组合;结合ESR测年结果,讨论了定结古湖近360 ka的沉积环境与气候变化:543.8~437.9 kaBP,湖区气候偏凉湿,降水较多,湖面较宽,水体较深,但水温不高,水质为微咸水;437.9~347.7 kaBP,湖区气候较上一时期变得寒冷,水体变小,湖水向咸化发展;347.7~264.2 kaBP,气候较上一时期变得更冷,湖泊水体扩大,湖水含盐度减少,向淡化方向发展;264.2~254.9 kaBP,湖区气候更加寒冷,水体温度变得更冷,湖泊水体先缩小后逐渐增大;254.9~239.0 kaBP,湖泊水体减少,湖区气候较前一阶段变暖;239.0~184.0 kaBP,湖水较上一时期有所扩大,淡化明显,湖泊周边环境依然比较寒冷。 相似文献
7.
亚洲内陆荒漠化和干旱化与中国西部人类生存环境和社会可持续发展密切相关。中国西部地区的气候自晚更新世以来经历了多次冷暖、干湿变化，研究其晚更新世古气候变化，有助于预测未来气候的变化趋势。文章分析了宁夏南部清水河盆地晚更新世中晚期的孢粉记录，结果显示孢粉序列可从下至上划分为4个组合带，反映了该地区晚更新世中晚期植被和气候变化规律。研究表明研究区晚更新世中期(75～50 ka B.P.)是植被以蒿属为主的干草原，气候温凉偏干；晚更新世晚期(25～15 ka B.P.)由荒漠草原-干草原和疏林草原交替出现逐渐过渡到荒漠草原，该时期冬季风呈现逐渐增强的趋势，致使气候逐渐变冷变干，气候类型由温凉偏湿过渡到冷干。宁夏南部清水河盆地晚更新世中晚期孢粉记录的深入研究对于正确认识黄土高原自然环境历史演变和黄土高原治理决策的制定具有重要指导意义。 相似文献
8.
萨拉乌苏河流域位于我国北方沙漠/黄土过渡带和生态脆弱带,它对全球变化反映非常敏感,是研究全球变化的理想区域。本文根据地质测年、气候地层对比,以及地层中气候代用指标的分析,将萨拉乌苏河流域地层和气候变化划分为全新统的风成相与湖相沉积(0~11.5kaBP),早、中期气候较暖湿,晚期气候较干旱;上更新统城川组的风成相沉积(11.5~80kaBP),气候干旱寒冷;上更新统萨拉乌苏组的湖相沉积(80~140kaBP),气候温暖较湿润;中更新统上部的河流相与风成相互层(140~190kaBP),气候冷干与温凉半干旱波动;中更新统上部的冲洪积沉积(190~220kaBP),气候较暖湿等阶段。指出自中更新世晚期以来气候发生频繁波动,无论是暖湿还是冷干阶段,气候都波动频繁,气候变化不稳定性明显。 相似文献
9.
本文将西藏札达盆地河湖相地层重新划分为第四系下更新统香孜组(Qp1-1x)、新近系上新统古格组(N22g)和上新统托林组(N21t)。河湖相地层的古地磁法和ESR法测年结果表明,札达盆地内河湖相沉积地层的形成时代为新近纪上新世—第四纪早更新世。根据该套河湖相地层沉积演化和其中的孢粉组合特征、河湖相沉积中所发现的各种古动植物化石等的综合分析,笔者对札达盆地上新世—早更新世的古植被、古环境与古气候演变进行了探讨。结果表明,札达地区上新世—早更新世气候经历了从湿热—温暖潮湿—偏冷潮湿—寒冷干旱的变化,以及植被从森林—灌木—草原的逐渐演化。可将札达盆地上新世—早更新世环境演化划分为7个大的阶段,其总体特征是15.4~4.4Ma,札达地区处于亚热带湿热气候环境;24.4~3.95Ma,为暖温带温暖潮湿气候;33.95~3.5Ma,为偏凉潮湿阶段,气候开始转冷;43.5~3.2Ma,为温暖潮湿阶段;53.2~2.9Ma,气候转为偏冷潮湿阶段;62.9~2.57Ma,该阶段气候偏冷而干旱,整体较为干冷;72.57~1.36Ma,气候寒冷而干旱。表明自上新世—早更新世,该区的古气候环境在逐渐变干、变冷的总趋势上,经历了多次明显的冷暖与干湿波动。 相似文献
10.
通过对青藏高原昆仑山垭口盆地磁化率、频率磁化率环境重要参考指标的分析,并与黄土—古土壤和深海δ18O记录的气候变化进行对比,结合剖面的岩性特征和年代序列以及前人所获得的粒度和孢粉资料,揭示了3.6Ma～0.5Ma期间昆仑山垭口盆地气候变化经历了6个不同的阶段:3.6Ma～2.48Ma气候相对冷干,2.48Ma～2.14Ma气候偏凉湿,2.14Ma～2.07Ma气候相对冷干,2.07Ma～1.16Ma气候总体相对较湿润(其间有数次冷干波动),1.16Ma～0.78Ma气候偏冷干以及0.78Ma～0.5Ma气候向冷湿发展。 相似文献
11.
Between 1985 and 1991, two new mountain protected areas (MTNPA) covering more than 35,000 km2 and based on participatory management models — the Makalu-Barun National Park and Conservation Area, Nepal, and Qomolangma Nature Preserve, Tibet Autonomous Region — were successfully established through the collaborative efforts of Woodlands Mountain Institute and conservationists in China and Nepal. Characteristics common to both projects include the importance of establishing (1) effective rationales, (2) local support constituencies, (3) a senior advisory group, (4) a task force, (5) linkages between conservation and development, and (6) fund raising mechanisms. The lessons derived from the experiences of Woodlands Mountain Institute are of significant value to others in preserving MTNPA. Increased collaboration and communication between all interested in conservation, however, will remain a critical component for expanding mountain protected area coverage to throughout the world. 相似文献
12.
Most sulfide-rich magmatic Ni-Cu-(PGE) deposits form in dynamic magmatic systems by partial melting S-bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components, and generation of barren to weakly-mineralized immiscible Fe sulfide xenomelts into which Ni-Cu-Co-PGE partition from the magma. Some exceptionally-thick magmatic Cr deposits may form by partial melting oxide-bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components, and generation of barren Fe ± Ti oxide xenocrysts into which Cr-Mg-V ± Ti partition from the magma. The products of these processes are variably preserved as skarns, residues, xenoliths, xenocrysts, xenomelts, and xenovolatiles, which play important to critical roles in ore genesis, transport, localization, and/or modification. Incorporation of barren xenoliths/autoliths may induce small amounts of sulfide/chromite to segregate, but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors (PGE > Cu > Ni > Co and Cr > V > Ti, respectively) is required to make significant ore deposits. Silicate xenomelts are only rarely preserved, but will be variably depleted in chalcophile and ferrous metals. Less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma. Denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma, but may aid downward sulfide transport by increasing the bulk density of the magma. Sulfide wets olivine, so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets, but other silicates and xenoliths may not be wetted by sulfides. Xenovolatiles may retard settling of – or in some cases float – dense sulfide droplets. Reactions of sulfide melts with felsic country rocks may generate Fe-rich skarns that may allow sulfide melts to fractionate to more extreme Cu-Ni-rich compositions. Xenoliths, xenocrysts, xenomelts, and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas, and are more likely to be preserved in less dynamic (less turbulent) systems/domain/phases than in more dynamic (more turbulent) systems/domains/phases. Massive to semi-massive Ni-Cu-PGE and Cr mineralization and xenoliths are often localized within footwall embayments, dilations/jogs in dikes, throats of magma conduits, and the horizontal segments of dike-chonolith and dike-sill complexes, which represent fluid dynamic traps for both ascending and descending sulfides/oxides. If skarns, residues, xenoliths, xenocrysts, xenomelts, and/or xenovolatiles are present, they provide important constraints on ore genesis and they are valuable exploration indicators, but they must be included in elemental and isotopic mass balance calculations. 相似文献
13.
14.
《Chemical Geology》2007,236(1-2):13-26
We examined the coprecipitation behavior of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides under two different fluoride forming conditions: at < 70 °C in an ultrasonic bath (denoted as the ultrasonic method) and at 245 °C using a Teflon bomb (denoted as the bomb method). In the ultrasonic method, small amounts of Ti, Mo and Sn coprecipitation were observed with 100% Ca and 100% Mg fluorides. No coprecipitation of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides occurred when the sample was decomposed by the bomb method except for 100% Ca fluoride. Based on our coprecipitation observations, we have developed a simultaneous determination method for B, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by Q-pole type ICP-MS (ICP-QMS) and sector field type ICP-MS (ICP-SFMS). 9–50 mg of samples with Zr–Mo–Sn–Sb–Hf spikes were decomposed by HF using the bomb method and the ultrasonic method with B spike. The sample was then evaporated and re-dissolved into 0.5 mol l− 1 HF, followed by the removal of fluorides by centrifuging. B, Zr, Mo, Sn, Sb and Hf were measured by ID method. Nb and Ta were measured by the ID-internal standardization method, based on Nb/Mo and Ta/Mo ratios using ICP-QMS, for which pseudo-FI was developed and applied. When 100% recovery yields of Zr and Hf are expected, Nb/Zr and Ta/Hf ratios may also be used. Ti was determined by the ID-internal standardization method, based on the Ti/Nb ratio from ICP-SFMS. Only 0.053 ml sample solution was required for measurement of all 9 elements. Dilution factors of ≤ 340 were aspirated without matrix effects. To demonstrate the applicability of our method, 4 carbonaceous chondrites (Ivuna, Orgueil, Cold Bokkeveld and Allende) as well as GSJ and USGS silicate reference materials of basalts, andesites and peridotites were analyzed. Our analytical results are consistent with previous studies, and the mean reproducibility of each element is 1.0–4.6% for basalts and andesites, and 6.7–11% for peridotites except for TiO2. 相似文献
15.
Models have become so fashionable that many scientists and engineers cannot imagine working without them. The predominant use of computer codes to execute model calculations has blurred the distinction between code and model. The recent controversy regarding model validation has brought into question what we mean by a ‘model’ and by ‘validation.’ It has become apparent that the usual meaning of validation may be common in engineering practice and seems useful in legal practice but it is contrary to scientific practice and brings into question our understanding of science and how it can best be applied to such problems as hazardous waste characterization, remediation, and aqueous geochemistry in general. This review summarizes arguments against using the phrase model validation and examines efforts to validate models for high-level radioactive waste management and for permitting and monitoring open-pit mines. Part of the controversy comes from a misunderstanding of ‘prediction’ and the need to distinguish logical from temporal prediction. Another problem stems from the difference in the engineering approach contrasted with the scientific approach. The reductionist influence on the way we approach environmental investigations also limits our ability to model the interconnected nature of reality. Guidelines are proposed to improve our perceptions and proper utilization of models. Use of the word ‘validation’ is strongly discouraged when discussing model reliability. 相似文献
16.
I. Bejarano-Ramirez Jose M. Jurado R. Muñiz-Valencia Á. Alcázar Silvia G. Ceballos-Magaña A. Olivos-Ortiz O. Rangel 《International Journal of Environmental Science and Technology》2017,14(6):1333-1342
The contents of As, Cd, Cu, Cr, Mg, Mn, Ni, Pb and Zn have been determined in sediment and water samples from Valle de las Garzas estuary and Port Manzanillo (Colima, Mexico) using ICP-AES. The concentrations of these elements were used for a comparative study to determine the distribution of heavy metals and to evaluate which elements reflect natural or anthropogenic backgrounds. For this purpose, seven sampling points were selected: Four of them correspond to the lagoon, and three were situated in the port. Statistical analysis of the mineral content was assessed. Initially, data comparison was assessed by statistical tests for each variable. Principal component analysis was then applied considering the influence of all variables at the same time by obtaining the distribution of samples according to their scores in the principal component space. In this way, four studies were carried out: (1) study of sediments collected during the dry season; (2) study of sediments collected during the rainy season; (3) comparative study between sediments from rainy and dry season; and (4) study of water composition collected during rainy season. From the results of the performed analyses, it can be concluded that metals distribution pattern reflected natural and anthropogenic backgrounds (e.g., sediments from the lagoon, situated at the beginning of the rain channel, presented high contents of Zn and Cu, perhaps related to anthropogenic activities or the influence of igneous sediments). 相似文献
17.
《Geoforum》2017
This article advances critical geographies of youth through examining the spatiality implicit in the imagined futures of young women in rural India. Geographers and other scholars of youth have begun to pay more attention to the interplay between young people’s past, present, and imagined futures. Within this emerging body of scholarship the role of the family and peer group in influencing young people’s orientations toward the future remain underexamined. Drawing on eleven months of ethnographic fieldwork, my research focuses on a first generation of college-going young women from socioeconomically marginalized backgrounds in India’s westernmost state of Gujarat. I draw on the “possible selves” theoretical construct in order to deploy a flexible conceptual framework that links imagined post-educational trajectories with motivation to act in the present. In tracing the physical movement of these young women as they navigate and complete college, my analysis highlights the ways in which particular kinds of spaces and spatial arrangements facilitate and limit intra- and inter-generational contact, and the extent to which this affects young women’s conceptions of the future. I conclude by considering the wider implications of my research for ongoing debates surrounding youth transitions, relational geographies of age, and education in the Global South. 相似文献
18.
The shape of sedimentary particles may carry important information on their history. Current approaches to shape classification
(e.g. the Zingg or the Sneed and Folk system) rely on shape indices derived from the measurement of the three principal axes
of the approximating tri-axial ellipsoid. While these systems have undoubtedly proved to be useful tools, their application
inevitably requires tedious and ambiguous measurements, also classification involves the introduction of arbitrarily chosen
constants. Here we propose an alternative classification system based on the (integer) number of static equilibria. The latter
are points of the surface where the pebble is at rest on a horizontal, frictionless support. As opposed to the Zingg system,
our method relies on counting rather than measuring. We show that equilibria typically exist on two well-separated (micro
and macro) scales. Equilibria can be readily counted by simple hand experiments, i.e. the new classification scheme is practically
applicable. Based on statistical results from two different locations we demonstrate that pebbles are well mixed with respect
to the new classes, i.e. the new classification is reliable and stable in that sense. We also show that the Zingg statistics
can be extracted from the new statistics; however, substantial additional information is also available. From the practical
point of view, E-classification is substantially faster than the Zingg method. 相似文献
19.
Hirokazu Fujimaki 《Contributions to Mineralogy and Petrology》1986,94(1):42-45
Concentration ratios of Hf, Zr, and REE between zircon, apatite, and liquid were determined for three igneous compositions: two andesites and a diorite. The concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient. Although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients, those for the apatite in the diorite may deviate from the partition coefficients. The HREE partition coefficients between zircon and liquid are very large (100 for Er to 500 for Lu), and the Hf partition coefficient is even larger. The REE partition coefficients between apatite and liquid are convex upward, and large (D=10–100), whereas the Hf and Zr partition coefficients are less than 1. The large differences between partition coefficients of Lu and Hf for zircon-liquid and for apatite-liquid are confirmed. These partition coefficients are useful for petrogenetic models involving zircon and apatite. 相似文献
20.
E. M. Prasolov S. A. Sergeev B. V. Belyatsky E. S. Bogomolov K. A. Gruzdov I. N. Kapitonov R. Sh. Krymsky V. O. Khalenev 《Geochemistry International》2018,56(1):46-64
This paper reports the first results of a study of 11 isotope systems (3He/4He, 40Ar/36Ar, 34S/32S, 65Cu/63Cu, 62Ni/60Ni, 87Sr/86Sr, 143Nd/144Nd, 206–208Pb/204Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others. 相似文献