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1.
新疆塔城地区黄土沉积的磁学特征及其对古环境变化的指示 总被引：1，自引：0，他引：1
西风区黄土沉积序列的磁化率变化特征比较复杂,磁化率与成壤强度之间的相关性在不同的区域环境中具有一定的差异。选取塔城地区黄土剖面作为研究对象进行较为系统的磁学特征分析。结果显示,塔城剖面的磁性矿物主要为磁铁矿、磁赤铁矿等亚铁磁性矿物,同时含有一定量的反铁磁性矿物和顺磁性矿物,磁畴状态主要是多畴（MD）和假单畴（PSD）。成壤作用影响单畴（SD）颗粒磁性矿物的相对含量,而对超顺磁（SP）颗粒的贡献有限。影响地层磁学性质的因素比较复杂,粒度与磁学参数的变化与区域的气候波动具有一定的对应关系。古土壤中磁性矿物浓度的降低以及钙积现象可能反映了成壤时期温暖干燥的气候条件,磁性矿物浓度的变化在一定程度上或许是对区域相对湿度状况的反映。 相似文献
2.
黄土高原黄土来自于其北部或西北部的沙漠和戈壁被广泛认可。本文选取西北地区典型的沙漠、戈壁和黄土表土样品,进行系统的岩石磁学研究。结果显示：沙漠和戈壁磁学特征相似,以磁铁矿占绝对优势,磁颗粒为多畴和假单畴,几乎不含超顺磁颗粒,磁性矿物总体含量高于黄土表土。黄土表土以磁铁矿为主,同时含有磁赤铁矿,磁颗粒以成壤过程中形成的超顺磁和单畴颗粒为主。虽然沙漠和戈壁细粒中亚铁磁性矿物相对比例明显高于粗粒,但粗粒组分含量大,对磁性稀释作用显著,全样总体表现为粗粒磁性特征。影响沙漠、戈壁和黄土磁化率的主导因素不同,沙漠和戈壁为磁性矿物含量主导型,磁性矿物总含量高,黄土表土为磁性矿物粒度主导型,超顺磁对磁化率贡献占主导。合理区分风速论和成土论两种磁化率机制,需准确判断成壤程度和氧化还原状态。因此,不同环境条件下磁化率的环境意义及古气候重建,需首先准确区分影响磁化率的主导因素。 相似文献
3.
内蒙古嘎顺诺尔湖泊沉积物磁化率与粒度的古环境意义 总被引：3，自引：0，他引：3
湖泊沉积物磁化率和粒度已被广泛地应用于古环境和古气候研究,但在不同地区两者的关系不同,一般与磁性矿物来源、种类和赋存粒级有关。查明磁性矿物来源和赋存状态是利用粒度和磁化率恢复古环境的重要基础。通过测定干旱区嘎顺诺尔GXN剖面湖泊沉积物的磁化率与粒度及两者的相关关系,结合代表性样品的岩石磁学特征,揭示此类地区湖泊沉积物磁性矿物来源和赋存状态,探讨它们在干旱区湖泊沉积物中所反映的环境变化信息。结果显示,剖面下部（200~105 cm）和上部（36~0 cm）沉积物磁化率与粗砂含量呈正相关,中部（105~36 cm）与粉砂含量呈正相关,表明磁性矿物主要富集于粗颗粒和较粗颗粒组分中。剖面下部和中部沉积物以顺磁性矿物为主,含少量亚铁磁性矿物（如磁铁矿+磁赤铁矿）,含少量顺磁性矿物;剖面上部沉积物以亚铁磁性矿物为主（如磁赤铁矿+磁铁矿）,含少量顺磁性矿物。根据嘎顺诺尔晚全新世湖泊沉积物剖面的岩性、磁化率和粒度组合特征,可将其划分为河漫滩相沉积（200~105 cm）、浅湖相沉积（105~36 cm）和滨浅湖相沉积（36~0 cm）3个阶段。该湖粒度组分中<4 μm和4~64 μm颗粒主要反映了湖泊水动力的变化,受碎屑物来源和水动力条件的控制;而河漫滩相中>64 μm粗颗粒组分的峰值是风力作用的结果。河漫滩相及滨浅湖相的磁化率高值则指示了湖面较低,水动力较强,有较多的磁性矿物随粗颗粒入湖;浅湖相的磁化率低值则指示该时期湖面较高,水动力较弱,磁性矿物随入湖粗颗粒含量的减少而降低。 相似文献
4.
科尔沁沙地风沙沉积物磁学特征及其古环境意义初探 总被引：1，自引：0，他引：1
选取位于科尔沁沙地东北缘的六户屯剖面风沙沉积物为研究对象,进行系统的磁学特征和粒度分析。结果表明：六户屯剖面磁性矿物含量较少,磁学性质主要受亚铁磁性磁铁矿控制,并含有少量赤铁矿和针铁矿,磁性矿物粒度较细,以稳定单畴和超顺磁颗粒为主。沉积物中磁性矿物的粒度分布受风力大小与成壤强度的影响,单畴颗粒相对含量随风力的增强而增加,随土壤发育程度的增强而减少,χARM/χlf和χARM/SIRM可以指示冬夏季风的相对强弱。六户屯剖面磁性矿物粒度主要受冬季风强度及其动力分选作用的控制,磁性矿物粒度与沉积物总体粒度呈反相关;但在某些层位,夏季风影响下的成土过程对其改造作用不容忽视。成壤过程中形成的超顺磁颗粒是磁化率增强的主要因素,单畴颗粒对土壤发育适宜期磁化率的增加贡献相对较弱。 相似文献
5.
对于黄土-古土壤序列,磁化率增强机制已经被大家认可,并且磁化率被广泛作为古夏季风强弱变化的代用指标。红黏土伏于第四纪黄土之下,同为风成沉积物,对红黏土磁化率增强机制的研究程度不高,且对强发育红黏土获得比较低的磁化率值的原因不清楚。本文通过对佳县红黏土进行系统岩石磁学分析得出：(1) 红黏土磁性矿物种类以磁铁矿为主,同时含有一定量磁赤铁矿、赤铁矿;磁性矿物平均粒径为PSD颗粒;强发育层含有较多的软磁性矿物,弱发育层含有较多的硬磁性矿物。(2) χ、χfd和χARM两两之间表现出很好线性正相关关系,说明红黏土中含有大量SP和SD颗粒亚铁磁性矿物,这些细小磁颗粒是在成壤过程中产生,成壤作用导致古土壤层磁化率升高。(3) 红黏土χfd、χfd%值较高,说明经历较强的成壤过程,成壤环境与黄土高原黄土-古土壤序列类似,与阿拉斯加、西伯利亚黄土-古土壤明显不同。 相似文献
6.
中国帕米尔地区黄土磁化率特征及其影响因素 总被引：1，自引：0，他引：1
《干旱区地理》2016,(4)
通过对地处西风区的中国境内帕米尔剖面进行磁化率的研究,并与研究区剖面其他常用气候替代指标粒度、色度、Ca CO3(%)和TOC等进行对比分析,初步探讨了帕米尔黄土磁化率增强机制的差异性。研究表明:帕米尔黄土剖面磁化率的平均值低于黄土高原典型剖面。粒度组成以粉砂(4~63μm)为主,磁化率与细颗粒物质呈负相关,与粗颗粒物质呈正相关。色度a*,b*,L*及磁化率的关系表明该区由于所受控的物质种类不同,使磁化率同红度a*呈负相关,而与亮度L*呈正相关关系;碳酸钙和有机质对磁化率影响较小,贡献微弱;由于沉积环境、气候等多种因素对磁化率产生不同程度的影响,使该区磁化率增强机制存在着空间差异性。 相似文献
7.
8.
阿西克剖面记录的西天山地区黄土磁学性质及古气候意义初探 总被引：1，自引：0，他引：1
选取阿西克剖面作为研究对象,对伊犁地区末次间冰期以来的沉积的黄土地层的磁学特征进行分析。结果发现,伊犁地区黄土地层的磁性矿物有磁铁矿、磁赤铁矿、赤铁矿、针铁矿,磁学性质受亚铁磁性的磁铁矿（和磁赤铁矿）控制;MD和PSD是地层中亚铁磁性矿物的主要磁畤状态,随着成壤强度增加,地层中的SP和SD颗粒相对含量逐渐增加;亚铁磁性矿物含量与地层并不完全对应。对磁学参数控制机制的分析表明,本剖面磁学性质受控因素比较复杂,磁性矿物含量主要受控于物源的磁学性质,成壤作用对地层中细粒磁性矿物含量具有很大影响,还原作用可能对底部古土壤层的磁学性质造成一定影响,但对整个剖面的磁学性质影响相对较小。 相似文献
9.
选取云南不同气候区发育于弱磁性砂岩的土壤剖面,分析磁性差异及其对气候变化的响应,探讨赤铁矿和针铁矿与气候因素的关系。结果表明：1）位于热带亚热带地区的峨山（EF）、普洱（PF）和景洪（F）土壤中亚铁磁性矿物主要为磁赤铁矿和磁铁矿,不完全反铁磁性矿物为针铁矿和赤铁矿。EF土壤中亚铁磁性矿物含量相对较高,PF和F土壤中针铁矿和赤铁矿的含量相对较高;3个研究区均含大量的细粒（超顺磁、单畴等）磁性矿物。2）土壤磁化率与温度和降水无显著相关性,难以作为该区域的气候代用指标。3）赤铁矿和针铁矿比值Hm/Gt和Hm/（Hm+Gt）与温度有良好的对应关系,在指示温度方面有应用潜力。 相似文献
10.
南方第四纪红土是记录南方古环境信息的良好载体和第四纪古气候环境研究的重要内容。本文对采自福建北部闽江流域大横第四纪红土剖面的样品进行磁化率、等温剩磁、饱和等温剩磁和代表样品的κ-T曲线等多磁学参数的详细测量和分析,研究结果表明:大横剖面的磁化率范围为8.87~35×10-8m3·kg-1,饱和等温剩磁范围为51.77×10~(-5)~294.51×10-5Am~2·kg~(-1),总体偏低,说明大横剖面的磁性矿物含量较低,可能是福建北部化学风化作用强烈且温暖湿润的环境导致的;频率磁化率、非磁滞磁化率及χARM/SIRM比值说明剖面自上而下,磁性矿物颗粒大小总体上呈现变粗趋势,由SP+SD颗粒到SD+MD颗粒的转变,剖面磁性矿物以磁铁矿为主,并含有磁赤铁矿、赤铁矿和纤铁矿等。本文探讨了红土剖面的不同沉积层磁学特征变化及对环境的指示意义,对认识该地区第四纪红土的风化特征及发育环境有一定借鉴意义。 相似文献
11.
对居延海G36钻孔进行了系统磁性特征分析,并结合总有机碳含量和粒度等环境代用指标,在精确测年的基础上,探讨了居延海地区全新世时期以来的环境变化。结果显示,居延海岩芯磁性矿物主要存在于粗颗粒的沉积物中,载磁矿物为颗粒较粗的多畴磁铁矿;磁化率变化机制比较复杂,与干湿环境变化没有简单正（反）关系。根据G36沉积物环境代用指标的变化,大致可以将其分为4个干湿交替时期:6 700~4 600 a BP干旱时期,4 600~3 100 a BP湿润时期,3 100~2 500 a BP干旱时期以及1 800 a BP以来湖泊干涸。在这4个时期中,磁学参数记录了两次显著湿润事件和两次显著干旱事件。 相似文献
12.
Studies of magnetic properties enable reconstruction of environmental conditions that affected magnetic minerals incorporated in sediments from Upper Klamath Lake. Analyses of stream sediment samples from throughout the catchment of Upper Klamath Lake show that alteration of Fe-oxide minerals during subaerial chemical weathering of basic volcanic rocks has significantly changed magnetic properties of surficial deposits. Titanomagnetite, which is abundant both as phenocrysts and as microcrystals in fresh volcanic rocks, is progressively destroyed during weathering. Because fine-grained magnetite is readily altered due to large surface-to-volume ratios, weathering causes an increase in average magnetic grain size as well as reduction in the quantity of titanomagnetite both absolutely and relative to hematite. Hydrodynamic mineralogical sorting also produces differences in magnetic properties among rock and mineral grains of differing sizes. Importantly, removal of coarse silicate and Fe-oxide grains by sorting concentrated extremely fine-grained magnetite in the resulting sediment. The effects of weathering and sorting of minerals cannot be completely separated. These processes combine to produce the magnetic properties of a non-glacial lithic component of Upper Klamath Lake sediments, which is characterized by relatively low magnetite content and coarse magnetic grain size. Hydrodynamic sorting alone causes significant differences between the magnetic properties of glacial flour in lake sediments and of fresh volcanic rocks in the catchment. In comparison to source volcanic rocks, glacial flour in the lake sediment is highly enriched in extremely fine-grained magnetite. 相似文献
13.
蓬莱黄土剖面光释光年代学及其沉积特征研究 总被引：1，自引：1，他引：0
对山东半岛北部蓬莱林格庄黄土剖面进行了系统的野外考察,并进行了光释光测年以及粒度、磁化率指标分析。研究表明,磁化率的变化与不同粒级的百分含量具有一定的相关性,频率磁化率与粗颗粒含量基本呈一定的负相关。结合野外地层划分与光释光年代学测试可以将该剖面划分为3个黄土层和3个古土壤层,该剖面记录了末次间冰期以来该区气候和环境变化的历史。 相似文献
14.
The Holocene magnetic signature due to environmental change has been investigated in sediments from Sägistalsee, a small alpine lake in the Bernese Alps, Switzerland. The environmental signal in the mineral magnetic parameters of the sediments was compared with palynological and geochemical data. The types of magnetic minerals and their grain size reflect changes in the lake catchment, vegetation, and degree of erosional input. The concentration of the magnetic minerals, as expressed by isothermal and anhysteretic remanent magnetizations also reflect changes in vegetation, but may also be related to redox conditions during sedimentation. Climate influence on the mineral magnetic record has been recognized and interpreted as a consequence of the production of an authigenic mineral with particularly uniform magnetic properties during warmer stages and the influx of heterogeneous detrital magnetic mineral during cooler stages and under increased human activity. 相似文献
15.
山东长岛黄土沉积物的磁性与碳酸盐特征及其环境意义初探 总被引：1，自引：0，他引：1
通过对长岛沉积物采样和磁性测试,分析和讨论了长岛黄土沉积物的磁性特征:该剖面磁性矿物的含量并不是很高,且以亚铁磁性矿物为主,磁性矿物的粒度主要以细粒为主,亚铁磁性矿物的变化在沉积物磁性变化中占主导地位.通过对沉积物磁性特征和碳酸盐特征的对比发现:该剖面沉积物磁化率和碳酸盐具有很好的对应关系,并且明显表现出4个阶段的主要变化,对应了暖湿和冷干的气候旋回.根据沉积物的磁化率与古气候环境的内在联系,结合碳酸盐含量变化情况,对该地区风成沉积物的物源变迁及环境演变也进行了初步探讨和分析. 相似文献
16.
南昌厚田沙地沉积物的粒度特征及其影响因素 总被引：2，自引：1，他引：1
厚田沙地是亚热带湿润地区的典型风沙化土地,分析不同地貌部位沉积物的粒度特征,有助于探讨其分布规律与影响因素。结果表明：厚田沙地沉积物主要由中沙和粗沙组成,平均粒径为1.28 Ф,分选性较差,呈正偏和窄峰态分布,整体表现为距赣江越远,细颗粒含量增多,粗颗粒含量减少,平均粒径逐渐变细。不同地貌部位沉积物的粒度特征存在较大差异：迎风坡风力作用强劲,侵蚀强烈,导致细颗粒较少、平均粒径较粗,表层相对20 cm深度更粗;背风坡由于风力涡旋而沉积较多细颗粒,平均粒径较细,表层相对20 cm深度更细;前丘顶与平沙地不仅受到风力侵蚀,也是人工活动强烈区,导致平均粒径变化较大,但大部分表层比20 cm深度更粗。 相似文献
17.
An 11 m long sediment core ftorn Lama Lake, Northern Siberia, has been subjected to intense sedimentological, geochemical and rock magnetic analyses. According to a palynologic investigation the recovered sediments cover the whole Holocene and the late Pleistocene reaching back to about 17 ka. IRM acquisition experiments, hysteresis loop and back field as well as thermomagnetic measurements revealed magnetite in the pseudo-single domain range as the only remanence carrier. Sharp rock magnetic boundaries occur at 20 and 745 cm sub-bottom depth that are clearly linked to shifts in the median grain size of the magnetite. These boundaries are close to the present boundaries that bracket an anoxic zone between the subrecent and a late Pleistocene oxic section of the sediments. Within the anoxic section, magnetites are characterized by significantly larger median grain sizes but within a very narrow grain size range. The shift from fine grained magnetite within the oxic sediments to coarse grained magnetite is interpreted as the result of dissolution of the finest magnetite grains within the anoxic sediments. A significant shift of the Ti/Fe-ratio of the bulk sediment at a sub-bottom depth of 735 cm does not correspond to thermomagnetic properties, i.e. Curie-temperatures do not follow the variable Ti-content of the sediment. 相似文献
18.
Sedimentology,clay mineralogy and grain-size as indicators of 65 ka of climate change from El’gygytgyn Crater Lake,Northeastern Siberia 总被引：2，自引：0，他引：2
Celeste A. Asikainen Pierre Francus Julie Brigham-Grette 《Journal of Paleolimnology》2007,37(1):105-122
El’gygytgyn Crater Lake, NE Siberia was investigated for sedimentological proxies for regional climate change with a focus
on the past 65 ka. Sedimentological parameters assessed relative to magnetic susceptibility include stratigraphy, grain size,
clay mineralogy and crystallinity. Earlier work suggests that intervals of high susceptibility in these sediments are coincident
with warmer (interglacial-like) conditions and well-mixed oxygenated bottom waters. In contrast, low susceptibility intervals
correlate with cold (glacial-like) conditions when perennial ice-cover resulted in anoxia and the dissolution of magnetic
carrier minerals.
The core stratigraphy contains both well-laminated to non-laminated sequences. Reduced oxygen and lack of water column mixing
preserved laminated sequences in the core. A bioturbation index based upon these laminated and non- laminated sequences co-varies
with total organic carbon (TOC) and magnetic susceptibility.
Clay mineral assemblages include illite, highly inter-stratified illite/smectite, and chlorite. Under warm or hydrolyzing
conditions on the landscape around the lake, chlorite weathers easily and illite/smectite abundance increase, which produces
an inverse relationship in the relative abundance of these clays. Trends in relative abundance show distinct down-core changes
that correlate with shifts in susceptibility. The mean grain-size (6.92 μm) is in the silt-size fraction, with few grains
larger than 65 μm. Terrigenous input to the lake comes from over 50 streams that are filtered through storm berms, which limits
clastic deposition into the lake system. The sedimentation rate and terrigenous input grain-size is reduced during glacial
intervals. Measurements of particle-size distribution indicate that the magnetic susceptibility fluctuations are not related
to grain size.
Lake El’gygytgyn’s magnetic susceptibility and clay mineralogy preserves regional shifts in climate including many globally
recognized␣events like the Younger Dryas and Bolling/Allerod. The sedimentary deposits reflect the climatic transitions starting
with MIS4 through the Holocene transition. This work represents the first extensive sedimentological study of limnic sediment
proxies of this age from Chukotka (Fig. 1).
This is the tenth in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and
its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献