The paleoclimatic interpretation of clay minerals in sediments — a review

The application of paleoclimatic interpretation to clay minerals from continental and marine sediments is reviewed and the advantages of this method are indicated. Levels relatively rich in chlorite, illite, palygorskite and quartz are interpreted as corresponding to relatively dry periods, while more humid periods lead to more intensive weathering and consequently to the dominance of clay minerals more advanced in the relative stability scale, such as kaolinite. Smectite is taken to indicate a climate with contrasting seasons and a pronounced dry season.Using this and similar schemes, the paleoclimates of areas adjoining the Mediterranean Basin, North Sea, North Atlantic, Southern Arctic, Equatorial and North-West Pacific, and North Phillipine Sea are reconstructed.Clay minerals in sediments, particularly marine sediments, can be useful indicators of paleoclimatic conditions. While they do not produce direct indications of climatic parameters, they provide integrated records of overall climatic impact. Occasionally, they may be superior to the more conventional paleoclimatic methods, such as pollen or oxygen-isotope analysis.The limitations imposed on the paleoclimatic interpretation of clay minerals in sediments are discussed on the basis of examples. The distinction between authigenic and detrital clay minerals is shown to be problematic, particularly with regard to smectite. The relationship between climatic parameters and clay-mineral formation is complicated by the intervention of extra-climatic factors such as topography, geomorphology, lithology and time. Post-depositional diagenetic changes may not be recognized. Differentiation during transport, due to size sorting or differential flocculation may overlap climate-induced differentiation. The association of clay-mineral assemblages with specific source areas presents difficulties due to dispersal pathways that are affected by type of transport agency, i.e., water, ice or wind. Transport agencies are not constant with time. By an interdisciplinary approach, with the paleoclimatic information derived from clay minerals being correlated with that obtained from the analysis of microfossils and oxygen isotope data, many of these limitations can be overcome.     

Changes in mineralogy of loess-paleosol sections across the Chinese Loess Plateau

Quantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the Chinese Loess Plateau (CLP). Mineralogy, geochemistry, and single-particle petrography of loess and paleosols are relatively uniform over the CLP. However, in detail, there are mineralogical changes related to eolian process and chemical weathering. Particle-size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals. After deposition, detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite, dolomite, biotite, illite, chlorite, amphibole, and plagioclase. The weathering of biotite, chlorite, and illite resulted in a significant increase of expandable phyllosilicate contents. The sequential weathering of the minerals is reflected chemically in the decrease of Na and Mg and the increase of iron oxidation. Mineralogy of the Chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient, and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the CLP.     

灵台红粘土—黄土—古土壤序列频率磁化率的古气候意义

通过对甘肃灵台晚新生代红粘土－黄土－古土壤序列的磁化率测量和频率磁化率分析，发现红粘土及黄土－古土壤的磁化率和频率磁化率化率存有良好的正相关关系，表明两套沉积在成壤过程中由生物作用或化学作用而形成的超顺磁性矿物含量，对磁化率和频率磁化率增大有重要的贡献。相比化率而言，受影响因素较少的频率磁化率变化，反映了不同气候条件下形成的超顺磁粒级铁磁矿物的相对含量，能更真实、敏感地记录不同时间尺度的古气候波动。灵台红粘土－黄土－古土壤序列的频率磁化等在2．6MaBP前后不同的变率特征，揭示了大冰期来临前后黄土高原的冷暖、干湿反差产生了显著变化，而与此相关的冬、夏季风变迁则表现出不同的组合特征。     

西峰和西安黄土中盐碱化古土壤气候意义的初步探讨

对西峰和西安黄土剖面中古土壤的研究揭示出,作为重要气候地层标志的S₄和S₅古土壤竟有盐化和碱化现象。盐碱化特性直接关系到如何认识这些古土壤的气候意义。土壤化学、微形态及粘土矿物分析表明,上述古土壤以草原土特征为主,并在气候最宜期发育了森林植被。盐碱化特性并非产生于土壤被埋藏以后,而是古土壤发育末期的产物。该时期大气粉尘堆积似乎是可溶盐的来源。     

粘土矿物的环境意义

粘土矿物在沉积和埋藏作用过程中可发生转变。它的形成和转化与其所处的环境有密切关系 ,因此深入研究粘土矿物的组合与含量的变化、结构特点与转化规律以及粒度分布等特征 ,可以推测其形成区和来源区的风化作用类型和气候演变规律 ,有助于揭示全球性的环境演变规律。对粘土矿物的大量研究所揭示的古气候环境演变的信息 ,已被用于重建古气候和恢复大陆古环境。此外 ,由于粘土矿物具有较强的吸附性、离子交换性和膨胀性 ,对水体中各种类型的污染物有良好的吸附性能 ,并使土壤有一定的自净作用 ,所以在环境污染的防治中有广阔的应用前景。     

黏土矿物古气候意义研究的现状与展望

系统地分析了利用海洋沉积物、古土壤、湖盆沉积物中黏土矿物进行古气候环境研究的现状、存在问题和发展趋势。海洋沉积物的物源范围广,影响因素复杂,其中的碎屑黏土矿物所指示的古气候参数只能用于解释母源区的气候变化,而只有自生黏土矿物才能指示沉积区的气候;古土壤形成于特定的地质背景条件下,尤其是发育于火山物质母岩之上的风化自生黏土矿物,可以准确地指示该区的古气候条件;湖盆沉积物的物源范围小,沉积物中的黏土矿物可以更有效地运用于古气候环境的分析。对于沉积物中黏土矿物来源的分析,可以借助晶体中cv空位和tv空位的精细结构特征进行判断;在风化改造的红土剖面研究中,因强烈的化学风化、淋滤和迁移,黏土矿物方法具有独特的优势。风化过程中形成的一些亚种或过渡性黏土矿物,以及同生沉积过程中形成的黏土矿物,对气候环境的变化更加敏感,应加强这方面的研究。此外,在造山带的气候环境演化研究中,自生黏土矿物稳定同位素可以更可靠地指示气候环境的变化。     

粘土矿物在黄河源区古气候研究中的应用

沉积物中粘土矿物的组成具有一定的古气候指示意义。利用沉积物中粘土矿物的组成探讨了黄河源区全新世的古气候变迁。通过X衍射方法分析了一个全新世地层剖面的粘土矿物类型和含量的变化,这些粘土矿物主要由伊利石、伊蒙混层矿物和少量的高岭石、绿泥石组成。对粘土矿物含量变化的分析和对比研究表明,黄河源区在全新世的气候寒冷干燥,即使在大暖期也显得温凉。全新世的气候演变可划分为3个阶段,即早全新世的干冷期、中全新世的温凉期(大暖期)和晚全新世的干冷期。在大暖期,在7 0kaB P 和5 0kaB P 前后发生了两次较强的降温事件。     

Controls on clay minerals assemblages in an early paleogene nonmarine succession: Implications for the volcanic and paleoclimatic record of extra-andean patagonia,Argentina

The distribution of the clay minerals of the Banco Negro Inferior-Río Chico Group succession (BNI-RC), a middle Danian–middle Eocene mainly continental epiclastic–pyroclastic succession exposed in the Golfo San Jorge Basin, extra-Andean Patagonia (∼46° LS), is assessed in order to determine the possible origin of clay and specific non-clay minerals using X-ray diffraction and scanning electron microscopy analyses. The control over the clay mineralogy of the sedimentary settings, contemporary volcanism, paleoclimate and weathering conditions is considered. A paleoclimatic reconstruction is provided and correlated with the main global warming events that occurred during the early Paleogene.Mineralogical analyses of BNI-RC demonstrate that smectite and kaolin minerals (kaolinite, halloysite and kaolinite/smectite mixed layers) are the main clay minerals, whereas silica polymorphs (volcanic glass and opal) are common non-clay minerals. Throughout the succession, smectite and kaolin minerals are arranged in different proportions in the three clay–mineral assemblages. These show a general vertical trend in which the smectite-dominated assemblage (S1) is replaced by the smectite-dominated assemblage associated with other clays (S2) and the kaolinite-dominated assemblage (K), and finally by S2 up-section. The detailed micromorphological analysis of the clay and non-clay minerals allows us to establish that the origins of these are by volcanic ash weathering, authigenic and pedogenic, and that different stages in the evolution of mineral transformations have occurred.The supply of labile pyroclastic material from an active volcanic area located to the northwest of the study area could have acted as precursor of the authigenic and volcanogenic minerals of the analyzed succession. Diverse fine-grained lithological facies (muddy and tuffaceous facies) and sedimentary settings (coastal swamp and transitional environments, and different fluvial systems) together with variable climate and weathering conditions controlled the mineralogical transformations and the arrangement of clay–mineral assemblages. The paleoclimatic reconstruction suggests a general warm and humid climate. However, the temporal trend of the clay–mineral assemblages, the ratios between smectite and kaolinite and the micromorphological analysis of clay minerals contrasted with evidence from sedimentological analyses suggest a warm and seasonal climate for the basal part of the unit, a warm and humid climate with a relatively more perennial rainfall regime in the middle part of the unit, and a warm and less humid, probably subhumid, climate up-section. Such a reconstruction makes it possible to establish a correlation with some of the hyperthermal events of the Early Paleogene Global Warming (EPGW) and, consequently, constitute one of the most complete time records of the EPGW in South America.     

Authigenic titanite in weathered basalts: Implications for paleoatmospheric reconstructions

The stability of titanite is sensitive to temperature and partial pressure of CO₂. The finding of authigenic titanite grains in weathering regolith formed on Paraná basalts, Brazil, under tropical climatic conditions, reveals the thermodynamically-driven conversion from calcite to titanite at elevated ambient temperatures. Being unusual nowadays, this phase transition provides important implications for the understanding of silicate weathering in earlier geological epochs.Two types of secondary titanites were identified in the weathering profile of the study area. The tiny grains of 10 ​μm are forming in the microscopic voids in the rock. Also, large fractures filled with Fe-rich clay minerals contain bigger specimens of up to 170 ​μm. The titanites of second type often coexist with chalcedony and barite. No carbonate minerals were found in the weathering profile. Weathering sphene can be discriminated from other titanite types by its strong positive Eu anomaly, increased Al₂O₃ content and low content of trace elements. Its specific chemical composition and reactive transport modeling link this secondary mineral with dissolution of plagioclase. The titanite precipitation is controlled by slow diffusion in poorly-aerated, highly-alkaline pore fluids.The subaerial weathering of basaltic rocks provides a significant reservoir for atmospheric CO₂. However, the deposition of carbonate minerals is thermodynamically avoided at the stability field of titanite. We demonstrate a complex feedback between CO₂ and soil carbonates. The rise in pCO₂ triggers the precipitation of calcite in the weathering regolith, but the greenhouse effect increasing the temperature can cease carbonate deposition. Secondary titanites were found in several paleosols and at least a part of them can be of weathering origin.     

Quantitative analysis of clay minerals and their admixtures

Clay minerals are of non uniform composition and particle size. Also their identification and nomenclature have given much confusion. Examples are given. Quantitative analysis of clay minerals from deposits and soils, by X-ray, thermo- and infrared analysis is treated. Examples are given of the large variability in the results; even for X-ray and electron microscope pure- and 85 to 90% chemical pure samples of kaolinite a well defined clay mineral. They are caused mainly by varying conditions of crystal growth from which result differences in isomorphous replacements, structure, ordering and strain. An amorphous weathering substance coating the mineral particles (Beilby layer) upsets in particular quantitative analyses of the finer kinds of clay minerals. Clay minerals from soils have, as compared to those from pure deposits, in particular formed by hydrothermal action, only poor characteristics of small intensity. Examples are given. Quantitative analyses are further hindered by specific characteristics for a certain mineral being masked by those of other minerals which usually occur in the same sample. Examples are given.     

北戴河红色风化壳地球化学特征及气候环境意义

风化壳地球化学特征具有环境指示意义。用X射线荧光光谱法(XRF)和X射线衍射法(XRD)分别测试了秦皇岛北戴河燕山大学北侧红色风化壳(简称燕大风化壳)主量元素和粘粒粘土矿物。结果表明:除Ca外,Si、Al、Fe、Na、K的含量在风化壳上均有不同程度的波动,其中Si、Na、K波动轨迹基本一致,Al、Fe则与其相反,相关性分析显示SiO2与Al2O3、TFe、Fe2O3,Al2O3与TFe、Fe2O3,Na2O与CaO具有较好相关性;粘土矿物组合为1·4nm过渡矿物(25%~45%)+伊利石(10%~20%)+伊蒙混层矿物(20%~35%)+高岭石(15%~30%),矿物演化系列是长石、黑云母→(蛭石→1·4nm过渡矿物)→(伊利石)→高岭石。与粘土矿物以1∶1型高岭石为主的富铝化南方红色风化壳相比,燕大风化壳Si淋失度,Fe、Al富集度,矿物演化程度都较低,属硅铝化风化壳。燕大风化壳是上新世暖温带到北亚热带过渡型气候的风化产物,与现代秦皇岛暖温带半湿润型气候不同,这反映第四纪以来该区气候干旱因子增多。CIA、S/A等指示的风化强度异常表明,燕大风化壳形成后至少遭受过两次构造抬升,为剥蚀型风化壳,反映该区新构造运动间歇式上升的特点。     

The roles of pedogenesis and diagenesis in clay mineral assemblages: Lower Cretaceous fluvial mudrocks,Nova Scotia,Canada

Clay mineral assemblages in alluvial mudrocks are important for paleoclimatic interpretation and for understanding burial diagenetic cementation in sandstones, but it is commonly difficult to unravel the relative importance of source weathering, pedogenesis and diagenesis in their origin. The clay mineral assemblages in fluvial overbank mudrocks from the Lower Cretaceous Chaswood Formation in central Nova Scotia, investigated by X-ray diffraction analysis of the < 2 µm fraction of 45 samples, include kaolinite, illite, vermiculite, and mixed layer kaolinite/expandable clay and mica/vermiculite. The assemblages vary with depositional facies. Wetland organic-rich mudrocks have large amounts of amorphous material and kaolinite is the dominant clay mineral. In the eastern part of the basin, where overbank mudrocks were episodically uplifted by syn-sedimentary strike-slip faulting, cumulate ultisol and alfisol paleosols are common. In the ultisols, hematite is enriched and kaolinite increases at the expense of illite in the B horizon. Alfisols contain more illite and vermiculite and the B horizon is enriched in goethite. In the western part of the basin, where thin sandstones with abundant diagenetic kaolinite cement are interbedded with the mudrocks, the distinctive clay mineral assemblage of mica/vermiculite mixed layer, vermiculite with 15.5 Å peak, and kaolinite/expandable mixed layer clay with a 17.7 Å peak is interpreted to result from bacterially-mediated oxidation of organic matter below the paleo-water table during early burial diagenesis. Deeper burial diagenesis may lead to slightly higher kaolinite crystallinity. Volcanic ash appears to alter to kaolinite/expandable mixed layer clay with a 7.9 Å peak. Comparison with the continuously subsiding and rapidly accumulated Wessex Formation of southern England, formed at a similar paleolatitude, shows the strong role of pedogenic processes and early diagenesis by meteoric water in development of clay mineral assemblages in the locally tectonically uplifted Chaswood Formation.     

Identification of paleosol types and their applicability for paleoclimatic reconstructions

Genetic diagnostics of paleosols are based on the morphology of soil profiles, on the combination of the stable properties of microstructure and on the mineral composition of soils (taking into account diagenetic transformations). As a result of spatial paleopedological reconstructions performed both at a level of the structure of soil cover (study of paleosols in the catena) and at the zonal-provincial level allowed to compile soil maps of Eastern Europe for the Mikulino Interglacial (125 ka BP), the Bryansk Interstadial (32 to 24 ka) and the Holocene climatic optimum (5.5 ka). These data can be used for paleoclimatic reconstructions.     

Mineral magnetic record of paleoclimate variation in loess and paleosol from the Buenos Aires formation (Buenos Aires, Argentina)

Environmental magnetic techniques were applied to a loess–paleosol sequence of the Chacopampean plain (Buenos Aires, Argentina). Mineral magnetic carriers and their grain size were identified in order to detect magnetic mineral fluctuations associated with climatic changes. Multidomain magnetite of detrital origin dominates the record. In paleosols, a high coercivity fraction was identified. Horizons with no visual evidence of pedogenesis, but showing magnetic behavior analogous to that of paleosols were observed and are thought to represent environmental conditions similar to those prevailing during paleosol formation.The results suggest that the magnetic signal yielded by paleosols in these South American loess deposits is different from that in the Chinese loess. This may be due to differences in parent materials, diagenetic processes and/or differences in paleoclimatic conditions in both regions.     

Climatic control on clay mineral formation: Evidence from weathering profiles developed on either side of the Western Ghats

Many physico-chemical variables like rock-type, climate, topography and exposure age affect weathering environments. In the present study, an attempt is made to understand how the nature of clay minerals formed due to weathering differs in tropical regions receiving high and low rainfall. Clay mineralogy of weathering profiles in west coast of India, which receives about 3 m rainfall through two monsoons and those from the inland rain-shadow zones (<200 cm rainfall) are studied using X-ray diffraction technique. In the west coast, 1:1 clays (kaolinite) and Fe—Al oxides (gibbsite/goethite) are dominant clay minerals in the weathering profiles while 2:1 clay minerals are absent or found only in trace amounts. Weathering profiles in the rain shadow region have more complex clay mineralogy and are dominated by 2:1 clays and kaolinite. Fe—Al oxides are either less or absent in clay fraction. The kaolinite—smectite interstratified mineral in Banasandra profiles are formed due to transformation of smectites to kaolinite, which is indicative of a humid paleoclimate. In tropical regions receiving high rainfall the clay mineral assemblage remains the same irrespective of the parent rock type. Rainfall and availability of water apart from temperature, are the most important factors that determine kinetics of chemical weathering. Mineral alteration reactions proceed through different pathways in water rich and water poor environments.     

南海沉积物中的黏土矿物:指示东亚季风演化历史?

黏土矿物以其示踪洋流变化和揭示物源区同时期气候变化的能力,近年来在南海沉积古环境研究中的地位日益显现。但是,南海黏土矿物能否用于直接指示东亚季风演化历史的研究仍然颇为争议。本研究认为,南海黏土矿物主要受控于物源区供给和洋流搬运作用,黏土矿物本身不具同时期气候条件特征。以南海北部为例,珠江、台湾和吕宋岛这三个主要物源区无论是冰期还是间冰期都提供相同的黏土矿物组合,这些黏土矿物在输入到南海后分别受到不同洋流的搬运。因此,南海晚第四纪黏土矿物组合用于指示东亚季风演化历史的应用是通过洋流的搬运作用来实现的,在不同海区的应用效果不同。     

Paleoenvironment of geomorphic surfaces of an alluvial fan in the eastern Isfahan,Iran, in the light of micromorphology and clay mineralogy

Alluvial fans are one of the most important landforms in geomorphological and paloenvironmental studies. The objective of this study was the application of clay mineral assemblages and micromorphological properties of the studied paleosols in the geomorphic surfaces of an alluvial fan in the eastern Isfahan as proxies for paleoenvironmental and paleoclimatic changes. Micromorphology, X-ray diffraction, and scanning electron microscopy approaches were used to study the representative pedons. The results indicated that the illuviation process in the calcareous soils of the arid regions of the eastern Isfahan was probably in response to Quaternary moist conditions. There was no significant difference between clay coating properties of the studied relict and buried paleosols. Clay mineralogical study suggested that kaolinite and illite were inherited from the parent materials, while smectite and palygorskite were formed in the soil environment. Paleoargillic horizon was characterized by smectite and calcic (especially the calcrete) horizons were dominated by palygorskite. Palygorskite was accumulated by both neoformation and illuviation processes. High clay content, high intensity of smectite peak, and activity of the illuviation process in paleoargillic horizon demonstrated the seasonality of climate (rainfall) even in the moist periods of Quaternary in Central Iran. Clay mineralogical assemblages suggested a trend of increasing environmental aridity in the study area. This study, therefore, highlighted the role of clay mineralogical investigations in arid lands’ geomorphological and paleoenvironmental researches.     

中国黄土中古土壤的发生学研究

应用形态学、微形态学、化学和矿物学研究了中国黄土中古土壤的发生学性状和成土过程。离石黄土(中更新世)中古土壤为发育程度(碳酸盐淋溶和粘化)不同的褐土型土壤。马兰黄土(晚更新世)中为生草过程强和粘化过程稍弱的灰褐土型土壤。全新世黄土中为碳酸盐淋溶和粘化过程均弱的弱度发育的碳酸盐灰褐土型土壤。午城黄土(早更新世)中可能是棕褐土。本文还探讨了黄土中古土壤在时间和空间上的演替和分类问题。     

江西龙南花岗岩稀土风化壳中粘土矿物的研究

本区燕山早期花岗岩发育的风化壳中的粘土矿物以高岭石和埃洛石(7Å)为主;蒙脱石、三水铝石及其它为新查明矿物。据粘土矿物组合特征,自风化剖面深部到地表分为三个带:含蒙脱石带,高岭石和埃洛石(7Å)带,含三水铝石带。本文探讨了矿物在风化过程中的生成演化顺序,并进行了热力学的解释。据各带粘土物质的阳离子交换量与稀土含量变化的不一致关系认为,稀土在C带中的富集是化学风化的结果,与粘土矿物组合无关。     

干旱绿洲区运积物发育土壤的地球化学特征—以新疆焉耆盆地为例

土壤的矿物及其地球化学特征是指示其风化特征的重要依据.为理解干旱绿洲区土壤发育特征,本文选取新疆焉耆盆地两个土壤剖面对其粒度、矿物、元素地球化学特征进行分析,结果表明:两剖面沉积物的粒度主要以黏粒、粉粒为主,矿物主要为石英、长石和黏土矿物,石英/长石多数小于1,长石以斜长石类为主,化学风化作用极弱.两剖面的化学蚀变指数...