Distribution of Palygorskite in the Lingtai Profile of Chinese Loess Plateau: Its Paleoclimatic Implications

Palygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess-red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate. In this paper, field emission scanning electron microscope and high-resolution transmission electron microscope observations on the red clay-loess-paleosol of the Renjiapo profile at Lingtai, Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma, but no occurrence has been found in eolian sediments since 3.2 Ma. Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis, and transformed from iilite-montmorilionite under the pore water action. In the Lingtai profile, the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility, dust flux and depositional rate. The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon, when changes took place in the East Asia paleoclimate pattern, i.e. a high-frequency strong fluctuation alternative evolution of the environment. Therefore, palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time.     

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.     

A Terra Rossa-like paleosol complex from the Upper Jurassic of Portugal

The basal Upper Jurassic unconformity in the Lusitanian Basin of Portugal commonly exhibits an irregular palaeokarstic surface developed in underlying Middle Jurassic carbonates. In the Serra da Arrabida area south of Lisbon, wire cut quarry faces expose a thick Upper Jurassic paleosol complex overlying fissured and brecciated limestone veneered with a calcrete crust and associated with colluvial deposits. The paleosol complex is a red mudstone with calcrete stringers which superficially resembles present-day red Mediterranean Terra Rossa soils. A detailed micromorphological study indicates the absence of any clay illuviation in the paleosol unit, which suggests that it is not comparable to the true Terra Rossa Alfisols, but more closely resembles present-day Aridisols. This difference from true Terra Rossa soils probably reflects formation under a drier climate, which is confirmed by the occurrence elsewhere in Portugal of evaporitic lake deposits of the same age. The paper stresses the role of soil petrography (micromorphology) in interpreting pedogenesis in paleosols.     

Quaternary Stratigraphy and Paleogeography of the Galilee Coastal Plain, Israel

The Quaternary deposits in the Galilee coastal plain comprise alternating calcareous sandstone, red loam, dark clay, and uncemented sand. The calcareous sandstone in the lower part of the sequence represents a Pliocene to early Pleistocene marine transgression, and is covered unconformably by the late Quaternary sequence. The base of this sequence has an estimated age of 500,000 yr. It is covered unconformably by marine calcareous sandstone in the west, which represents the global high sea-level stand of isotope stage 7.1, and is known as one of the “Tyrrhenian” events in the Mediterranean area. The overlying members represent the low sea-level stand of stage 6, the first a red paleosol indicating a relatively wet phase and the second an eolianite unit representing a drier phase. The eolianite forms longitudinal, subparallel ridges that formed contemporaneously. The overlying marine sandstone, which contains one of the diagnostic fossils of the “Tyrrhenian” events, the gastropodStrombus buboniusLMK, accumulated during the global high stand of stage 5.5. The last glacial period left no sedimentary record. The Holocene is represented by a marine clay unit that is covered by sand. The present study establishes a complete and detailed chronostratigraphic sequence for an eastern Mediterranean beach, which contains the gastropodS. buboniusLMK.S. buboniuson the Galilee coast is attributed to stage 5.5 and, therefore, establishes an east–west Mediterranean correlation, which can be used for linking Mediterranean events to paleo-sea levels and global climate changes.     

Bedload transport of mud as pedogenic aggregates in modern and ancient rivers

Abundant sand-sized mud aggregates in the Cooper and Diamantina Rivers, Lake Eyre Basin, Australia are attributed to bedload transport of aggregates formed in deeply-cracked floodplain soils. The conditions required for formation of pedogenic mud aggregates are: (i) abundant clay containing at least minor swelling clay, and (ii) a climate with at least seasonally hot dry periods. The worldwide distribution of these soils (Vertisols) suggests that a significant amount of mud is transported as pedogenic aggregates by modern rivers. Ancient analogues in which mud aggregates and Vertisol profiles have been recognized are the Jurassic East Berlin Formation (Connecticut, USA) and the Carboniferous Maringouin Formation (New Brunswick and Nova Scotia, Canada). The dominant red mudstones of these formations are interpreted as mainly bedload sediments deposited by sheet floods in semi-arid palaeoclimates. The Triassic Hawkesbury Sandstone (NSW, Australia) also contains sand-sized mudstone aggregates, thought to be pedogenic, but its paleosol and other facies point to formation in a wetter palaeoclimate. The indications are that bedload transport of mud as pedogenic aggregates was as significant a process in ancient rivers as it is at present.     

Pleistocene sediments,soils and landscape evolution at Stebbing,Essex

Pleistocene sediments and soils exposed at Stebbing in central Essex, England are described, analysed and interpreted. The sand and gravel units above Eocene London Clay and Upper Pliocene Red Crag are shown to be a high level member of the Kesgrave Formation, with a surface immediately beneath that of the Westland Green Gravels, which are tentatively assigned to the Pre-Pastonian ‘a’ Stage of the British Quaternary succession. The rubified, argillic soil developed in the surface of these fluvial deposits is a composite of the Valley Farm and Barham Soils and displays micromorphological evidence of several phases of clay illuviation, gleying and clay coating disruption. Originally truncated and buried beneath Anglian gelifluction deposits, cover sand and till, the soil has been exhumed in most places by subsequent erosion. The full succession, however, is preserved within large gulls that formed by periglacial cambering prior to this erosion. More recent loess incorporation and pedogenesis have modified the exhumed soil and the materials within the gulls.     

Geochemical compositional changes at the Pliocene–Pleistocene transition in fluviodeltaic deposits in the Tegelen-Reuver area (southeastern Netherlands)

2 O contents, which can be attributed to the Alpine source supplying fresh, sodic plagioclase-rich material instead of the local, strongly weathered sediments. Increasing K₂O/Al₂O₃ can be attributed to a similar decrease in degree of weathering. However, this trend is disturbed by the loss of K from clay minerals during weathering in organic-rich layers. Local high TiO₂ anomalies, caused by preferential sorting and concentration, are found in most Pliocene sections, but they are absent in the Upper Pliocene and Lower Pleistocene Alpine-derived deposits. This change is probably due to a change in the energy of the fluvial system. Finally, (pyrite-) S contents drop (siderite-) Fe contents rise. Micromorphological observations indicate that the Pliocene pyrite was formed when freshwater deposits were flooded with seawater during short-term events. The decrease in S, and the increase in siderite-Fe, can be attributed to decreasing marine influence, as a result of the marine regression at the Pliocene–Pleistocene transition. Received: 28 August 1999 / Accepted: 2 November 1999     

黄土高原红粘土与黄土古土壤粒度特征对比--红粘土风成成因的新证据

对黄土高原具有代表意义四个剖面的晚第三纪红粘土样品进行了粒度分析,并将结果与典型风成黄土古土壤样品的粒度特征进行详细对比,得到红粘土是风成成因的沉积学证据。结果表明,黄土高原红粘土与其上覆第四纪古土壤形成环境相似,红粘土是在相对于黄土堆积搬运风动力变幅小的条件下沉积的,在沉积之后受到较强的风化成壤改造作用。     

晋东南黄土

本文论述了晋东南榆社一带的各期黄土。这里是黄土自西而东分布的过渡地带,黄土的性状有共性也有各自的特性。晋东南的黄土分为早更新世老Ｒ红土、早至中更新世新Ｒ红土、中更新世上离石黄土、晚更新世马兰黄土和全新世黄土。古地磁年代学测试和剖面观察获得的各期黄土年龄为：老Ｒ红土形成于２．５－１．５ＭａＢ．Ｐ,新Ｒ红士形成于０．９—０．６ＭａＢ．Ｐ,离石黄土形成于０．６—０．１ＭａＢ．Ｐ。它们彼此之间都有不整合面相隔。自Ｒ红土开始出现,就意味着榆社古湖开始消失,气候环境向半干旱－半湿润方向发展。但比黄土高原略为湿润,夏季风的影响更强些。     

Textural studies on red sediments of Bhimunipatnam,Andhra Pradesh,east coast of India

The study presents the textural characteristics of late Quaternary red sediments of Bhimunipatnam to understand the process of formation of these sediments. The red sediments are classified into (a) yellow sediments (b) reddish brown sediments (c) brick red sediments and (d) light yellow sediments sequence in the vertical litho section. The yellow sediments, rests on the khondalite basement, comprises of medium grained, moderate to poorly sorted and positively skewed. The rounded pebble beds with trough cross bedding indicate high energy turbulent conditions of deposition. The fining upward sequences indicate sediments were deposited under decreasing energy conditions under fluvial regime.The iron bearing minerals like garnets and pyriboles have undergone chemical weathering under high oxidizing environment resulting in addition of silt and clay to the reddish brown and brick red sediments and concretions were formed by carbonate precipitation. These processes caused changes in the mean grain size and sorting nature of these sediments which are originally aeolian in origin. The light yellow sediments were medium to fine grained, well sorted and similar to modern dune sands in terms of textural parameters. These sediments were deposited under low oxidation environmental conditions and acquired yellow colour due to Fe hydroxides.     

华北泥河湾盆地郝家台地区的沉积相组合特征：以台儿沟东剖面为例

泥河湾盆地东部郝家台地区的台儿沟东剖面主要出露地层为更新统和上新统,剖面顶部为厚9.4 m的马兰黄土和古土壤,剖面中部由更新统郝家台组和泥河湾组构成,剖面下部为上新统蔚县组。郝家台组和泥河湾组为三角洲平原、三角洲前缘和少量前三角洲亚相沉积组合,其中三角洲平原亚相可分为分支河道、分支间湾、天然堤、沼泽和淡水湖泊5个微相,由发育大型板状斜层理和底冲刷面构造的粗砂夹砾石透镜体,含钙质结核的透镜状黄褐色中 细砂以及富含炭屑的深色粘土等共同构成;三角洲前缘亚相则由水下分支河道、支流间湾、河口砂坝和末端砂坝构成,以发育底冲刷面构造并夹有细砾石透镜体的细中粒砂、小型板状斜层理细砂以及分选好且质纯的细砂等组合为特征;前三角洲亚相相对不发育,主要由浅灰色粘土以及灰绿色、灰黑色粘土夹钙质结核构成。蔚县组主要由滨湖亚相和浅湖亚相构成,其中前者为多种颜色的并发育泥裂和滑塌构造的粘土、粉砂组合,局部夹有透镜状砂砾层,底冲刷面发育;后者主要由粉砂、粘土组合构成,局部可见由砂泥交互构成的透镜状层理。古水流分析结果表明,上新统蔚县组沉积物源区位于泥河湾盆地NE侧,更新统泥河湾组和郝家台组碎屑沉积物主要来自于NE和NW方向,而泥河湾组底部约15 m厚沉积物除了来自NE方向外,还有部分沉积物来自SSW方向物源区。表明自上新世以来,泥河湾盆地周边具有北高南低古地理格局,从而为盆地提供丰富的碎屑沉积物。     

Distribution of Palygorskite in the Lingtai Profile of Chinese Loess Plateau： Its Paleoclimatic Implications

Palygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess-red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate.In this paper,field emission scanning electron microscope and high-resolution transmission electron microscope observations on the red clay-loess-paleosol of the Renjiapo profile at Lingtai,Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma,but no occurrence has been found in eolian sediments since 3.2 Ma.Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis,and transformed from illite-montmorillonite under the pore water action.In the Lingtai profile,the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility,dust flux and depositional rate.The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon,when changes took place in the East Asia paleoclimate pattern,i.e.a high-frequency strong fluctuation alternative evolution of the environment. Therefore,palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time.     

黄土高原风尘序列的碳酸盐成因及其风化过程

碳酸盐是黄土高原风尘序列的主要组成部分,其含量与原生碳酸盐溶解、再沉淀,以及含钙硅酸盐化学风化强度等密切相关。碳酸盐在表生环境下极易移动,且其迁移变化受大气降水、温度等古气候所制约,因此黄土次生碳酸盐记录了古气候的重要信息。甘肃西峰赵家川剖面碳酸盐含量、磁化率的系统测定和风尘序列地质特征研究表明,在整个剖面中,碳酸盐含量和磁化率曲线呈显著的负相关,并从剖面上部到红粘土底部,碳酸盐含量有增加趋势。黄土、古土壤和红粘土沉积分别处在不同风化阶段:黄土化学风化最弱,处于钙质残积阶段,古土壤处于强烈钙质淋溶阶段和硅铝残积阶段,红粘土化学风化最强烈,处于硅铝残积阶段或红土化阶段;不同的化学风化阶段古气候性质有别。     

中国第四纪地层

本文综述了中国第四纪沉积类型及第四系的划分,并与国际第四系划分进行了对比。指出中国第四纪沉积物分布广泛,种类繁多,以陆相沉积为主。按其成因主要有风成黄土堆积、河一湖相沉积、冲一洪积堆积、冰川沉积、洞穴堆积、风化壳残积（红土）、火山堆积和海相沉积等。各种沉积物都有很好的剖面,尤其是黄土和河一湖相沉积更为连续完整。按中国第四纪地层发育的实际情况,第四系的底界应置于松山一高斯极性转换界线（Ｍ／Ｇ,２．６ＭａＢ,Ｐ,）;第四系内部划分为更新统（Ｑ_ｐ）和１４新统（Ｑ_ｈ）,界线在１１０００ａＢ,Ｐ,。更新统进一步划分为下、中和上３个阶(Ｑ_ｐ１, Ｑ_ｐ２, Ｑ_ｐ３), Ｑ_ｐ２／Ｑ_ｐ１的界线为布容一松山极性转换界线（Ｂ／Ｍ; ０．７８ＭａＢ,Ｐ,）;Ｑ₍ｐ３_／Ｑ_ｐ２的界线为本次间冰期的起始时间（０．１２８ＭａＢ,Ｐ,）。     

中国北方上新世晚期-更新世早期风成沉积物磁化率各向异性初探

前人对中国黄土高原晚更新世黄土沉积物的磁化率各向异性的研究表明,磁化率椭球体最大轴(Kmax)偏角的方向能够指示黄土沉积时期的搬运动力方向,即古风向,并可以通过这种途径进行古季风的重建.本研究试图通过对中国黄土高原晚上新世-早更新世转折时期的风成沉积磁化率各向异性研究进一步检验其在古风向重建方面的应用潜力.选择分别地处黄土高原中部、南部和东部地区的灵台、渭南和保德3个剖面,对红粘土向黄土过渡时期4个不同地层单元古土壤层(S32)、黄土层(L33)、过渡层(TU)以及红粘土沉积(RC)的样品进行了磁化率各向异性测量,结果表明磁线理L值很小,而磁面理F较为发育,这与前人对晚更新世黄土沉积磁化率各向异性的研究结果一致;同时,4个不同地层单元的磁面理F、各向异性度P和形状因子T在3个剖面上均表现出随土壤发育程度增强而减小的变化趋势,说明后期的成壤作用能够不同程度地降低磁面理、磁化率各向异性度以及形状因子的大小.与前人对于晚更新世黄土沉积磁化率各向异性的研究结果不同的是3个剖面的S32,L33,TU以及RC的Kmax的偏角似乎并不能反映出当时的搬运动力方向,即古风向,而长期的压实作用以及不同程度的后期土壤化作用是造成这一时期黄土和红粘土沉积物磁化率各向异性最大轴偏角方向未能反映出当时搬运动力方向(古风向)的原因之一.     

中国南方红土与第四纪环境变迁的初步研究

本文简述了我国南方红土的形成时期，讨论了安徽省宣城剖面的特征及其成因，并对此剖面进行了ＥＳＲ年代学的研究，建立了此剖面的时间坐标。作者在此基础上，根据土壤地层学、磁化率、全氧化铁含量及有机质的含量分析和碳同位素测定等手段，将中更新世以来的沉积物──红土(古土壤)划分为８个沉积旋回，代表了８个大的气候旋回，并与我国北方黄土—古土壤系列具有明显的可比性。     

Grain-size analysis of the Neogene red clay formation in the Pannonian Basin

The red clay is a significant deposit underlying the Pleistocene loess-paleosols sequence in the Pannonian Basin. The sedimentary processes involved and the origin of the materials remain controversial. In order to determine the depositional processes of the Pliocene red clay formation we studied many red clay sections in Hungary. Here, we present results of grain-size analyses of the red clay from representative sites. In particular their grain-size distribution is compared with that of typical Pleistocene eolian loess-paleosols, as well as lacustrine and fluvial sediments. It appears from the sedimentological data that the majority of the red clay is of a wind-blown origin. The red clay might be transported by weak westerly winds and has been modified by post-depositional alteration.     

中太平洋海盆表层沉积物及其与锰结核的关系

通过对中太平洋海盆表层沉积物与相伴生的锰结核的研究表面,丰度、品位等有明显的差异,在深海粘土中锰结核干度最度,钙质软泥多,锰结核的发现聚集与沉积物类型,沉积速率、孔隙度、金属含量及形成时的氧化还原条件,水深、底层流等的影响.锰结核的形成,发育与富集是受多种因素所控制,是一个模式内的约制。     

Lithology, Biostratigraphy, and Magneto stratigraphy of Gas Hydrate-Bearing Sediments in the Eastern Nankai Trough

Abstract: Stratigraphic controls on the formation and distribution of gas hydrates were examined for sediments from a BH-1 well drilled in the landward slope of the Nankai Trough, approximately 60 km off Omaezaki, Japan. Three lithologic units were recognized in the 250 m-thick sequence of sediments: Unit 1 (0–70 mbsf) consists of calcareous silt and clay with thin volcanic ash layers, Unit 2 (70–150 mbsf) consists of calcareous silt and clay with volcanic ash and thin sand layers, and Unit 3 (150–250 mbsf) consists of weakly consolidated calcareous silt and clay with thick and frequent sand layers. Soupy structures and gas bubbles in the sediments indicate the presence of two hydrate zones between 40 and 130 mbsf and below 195 mbsf. Nannofossil biostratigraphy and magnetostratigraphy indicate that the sequence recovered at the BH-1 well is mostly continuous and represents sediments deposited from 0 to 1.5 Ma. Calculation of the sedimentation rate reveals a condensed section between 65 and 90 mbsf. The inferred distribution of gas hydrates in the BH-1 well appears to be strongly controlled by the stratigraphy and lithology of the sediments. Thick, gently inclined sand layers in Unit 3 provide a conduit for the migration of gases from deeper regions, and are considered responsible for the formation of the hydrate zone below 195 mbsf. At shallower levels, thin, gently inclined sand layers are also considered to allow for the migration of gases, leading to the formation of the upper hydrate zone between 40 and 130 mbsf. The overlying sub-horizontal silt and clay of the condensed section, truncating the underlying gently inclined sand and silt/clay layers, may provide an effective trap for gases supplied through the sand layers, further contributing to hydrate formation in the upper hydrate zone.     

The peterson limestone — early cretaceous lacustrine carbonate deposition in western wyoming and southeastern idaho

The lacustrine Peterson Limestone of western Wyoming and southeastern Idaho comprises six lithofacies throughout its 20,000 km² aerial extent. These are: (1) calcareous sandstone and shale, (2) red nodular limestone, (3) pink sandy micrite, (4) biomicrite, (5) graded silty micrite, and (6) limestone conglomerate. The first two represent floodplain deposition and paleosols, whereas the remaining are shallow nearshore and deeper lacustrine sediments.This sequence was developed in a large fresh, hardwater lake surrounded by fluvial systems and associated flood plains in a warm temperate climate. Well-oxidized sandy terrigenous rocks, together with calcareous paleosol nodules, indicate that flood-plain deposition both preceded and was concurrent with lacustrine carbonate deposition. Micrite and biomicrite formed in deeper parts of the basin while sandy and silty carbonate accumulated in shallower lake-margin areas. Less-calcareous shale units which are interbedded with deeper-water carbonate were deposited either during rapid basin subsidence and deepening of the lake center or during periods of slower carbonate precipitation. Turbidity currents and subaqueous debris flows generated along steeper lake margins, resulted in the deposition of rhythmic layers of graded silty micrite and diamictic limestone conglomerate in the deepest part of the basin. The carbonate-rich sediments comprising these two lithofacies were originally deposited on shallow lake-margin benches and subsequently were transported downslope toward the lake center.Comparison with other carbonate-precipitating lacustrine systems indicates that this lake was not like modern playas. Although no known modern lacustrine system is precisely like Lake Peterson, the flora, fauna, composition, and distribution of facies within modern temperate-region lakes most closely resemble those of the Peterson Limestone.