Weichselian sediments at Foss‐Eikeland,Jæren (southwest Norway): sea‐level changes and glaciation history

The Jæren area in southwestern Norway has experienced great changes in sea‐levels and sedimentary environments during the Weichselian, and some of these changes are recorded at Foss‐Eikeland. Four diamictons interbedded with glaciomarine and glaciofluvial sediments are exposed in a large gravel pit situated above the post‐glacial marine limit. The interpretation of these sediments has implications for the history of both the inland ice and the Norwegian Channel Ice Stream. During a Middle Weichselian interstadial, a large glaciofluvial delta prograded into a shallow marine environment along the coast of Jæren. A minor glacial advance deposited a gravelly diamicton, and a glaciomarine diamicton was deposited during a following marine transgression. This subsequently was reworked by grounded ice, forming a well‐defined boulder pavement. The boulder pavement is followed by glaciomarine clay with a lower, laminated part and an upper part of sandy clay. The laminated clay probably was deposited under sea‐ice, whereas more open glaciomarine conditions prevailed during deposition of the upper part. The clay is intersected by clastic dykes protruding from the overlying, late Weichselian till. Preconsolidation values from the marine clay suggest an ice thickness of at least 500 m during the last glacial phase. The large variations in sea‐level probably are a combined effect of eustasy and glacio‐isostatic changes caused by an inland ice sheet and an ice stream in the Norwegian Channel. Copyright © 2002 John Wiley & Sons, Ltd.     

Foraminifera from the Quaternary sequence in the Anholt boring, Denmark

The Quaternary sequence of a boring from the island of Anholt, Denmark, comprises both marine and non-marine sediments spanning a time interval from the Holocene to at least as far back as the Saalian. The oldest Quaternary sediments consist of a till and a glaciofluvial sand sequence. These are overlain by marine silty clays of Saalian to Eemian age. An interstadial (Flakket Interstadial) and a stadial (Kattegat Stadial) are identified in the late Saalian. This climatic fluctuation has been compared to the Allerød and Younger Dryas events at the Weichselian–Holocene transition. The Eemian sediments are followed by sand and non-marine, varved clay overlain by 2 m of marine clay, which is correlated with the Middle Weichselian of the Skærumhede series. The marine clay is covered by silty clay and a thick sand sequence of non-marine origin. The uppermost 2 m sediments may represent the Holocene coastal accretion on Anholt.     

Facies characteristics, morphology and depositional models of clay-slide deposits in terraced fjord valleys, Norway

Many bedrock-confined fjord valleys along the Norwegian coast contain thick accumulations of fine-grained sediments that were deposited during and after the last deglaciation. The deposits gradually emerged above sea level due to glacioisostatic uplift, and fjord marine sedimentation was gradually followed by shallow marine and fluvial processes. During emergence terraces and river-cut slopes were formed in the valleys. Subsequent leaching of salt ions from the pore water in the marine deposits by groundwater has led to the development of quick clay. The deposits are subject to river erosion and destructive landslides involving quick clay. Most slides are of prehistoric age. Others are known from modern observations as well as from historic records.Landforms such as distinct slide scars or the hummocky terrain of slide deposits may be strongly modified by secondary processes. In addition, deposits from the most liquid part of quick clay slides may have planar surfaces. Clay-slide deposits on a fluvial or deltaic terrace, therefore, are not always easily recognized from morphology, and only exposures may reveal their internal structures and allow them to be distinguished from overbank flood sediments. Detailed sedimentological work shows that slide deposits in such setting consist of distinct facies containing reworked marine sediments. We propose three facies successions of clay-slide deposits that form a continuum. The dominant components of these succession types are: slightly deformed blocks of laminated clay and silt (A), highly deformed clay and silt with gravel clasts (B) and massive to stratified clay and silt with scattered clasts (C). We suggest that in many cases a basal muddy diamicton is a characteristic, and possibly diagnostic feature. Processes and depositional models are interpreted from the different succession types. The results may be relevant for identifying clay-slide deposits elsewhere and may be useful during general mapping of fjord marine deposits and characterization of slide-prone areas as well as during identification of prehistoric slides.     

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。     

The high-level marine shell-bearing deposits of Clava, Inverness-shire, and their origin as glacial rafts

The enigmatic high-level, till-covered, cold water marine shell-bearing deposits at Clava, Inverness-shire, are described systematically in the light of new observations made at sites documented in the literature. The marine deposits, named here as the Clava Shelly Formation, include three members, the unfossiliferous Clava sand, the underlying Clava shelly clay and a shelly diamicton known as the Clava shelly till. The first two members form a conformable coarsening-upwards sequence containing a shallow water, high-boreal to low-Arctic fauna and flora. The Clava shelly till is essentially glacially re-sedimented glaciomarine clay containing a sparse fauna, but its stratigraphic relationship and age are not absolutely clear. The shelly clay is ascribed to a Mid-Devensian interstadial episode on the basis of amino-acid dating.It is concluded that the Clava shelly clay, and several discrete masses of Clava sand and shelly till, are glacially transported allochthons derived from the Great Glen. The rafts were probably detached as a result of high pore water pressure building up in laterally restricted aquifers beneath a confined glacier that flowed north-eastwards across the Loch Ness basin. This glacier was deflected eastwards and upwards towards Clava by ice flowing from the northern Highlands along the Beauly Firth during the build-up of the last Scottish ice-sheet. The rafts were stacked at the ice margin when the glacier entered the Nairn Valley before being overriden by the expanding ice-sheet.     

Clay‐coat diversity in marginal marine sediments

The specific mineralogy of clay grain coats controls the ability of the coat to inhibit quartz cementation in sandstones during prolonged burial and heating. How and why clay‐coat mineralogy varies across marginal marine systems is poorly understood, even though these eogenetic phenomena strongly influence subsequent mesodiagenesis and reservoir quality. The novel development of the ability to predict the distribution of clay‐coat mineralogy would represent an important development for sandstone reservoir quality prediction. In marginal marine sediments, clay minerals occur as grain‐coats, floccules, mud intraclasts, clay‐rich rock fragments or as dispersed material. However, the relationships between clay mineralogy, the amount of clay, and its distribution is poorly understood. This study focused on the Ravenglass Estuary, UK. The key aim was to develop and apply a novel methodology utilising scanning electron microscope – energy dispersive spectrometry, for the first time, on grain coats in modern sediments, to differentiate the clay‐coat mineral signature from that of the bulk sediment, and reveal the distribution of clay minerals across marginal marine sediments. The study showed that marginal marine sediments principally have their clay mineral assemblage present as clay‐coats on sand grains. These clay‐coats have a mixed clay mineralogy and are spatially heterogeneous across the range of marginal‐marine depositional environments. The study further showed that clay‐coat mineralogy is governed initially by the hydrologically‐controlled segregation of the clay minerals within inner estuarine depositional environments, and subsequently by the selective abrasive removal of specific clay mineral types during reworking and transport into the outer estuary and the marine environment. The highest relative abundance of grain‐coating chlorite was in sand‐flat and tidal‐bar depositional environments. The availability of an analogue data set, and an understanding of the controlling processes of clay‐coat mineralogy, offer crucial steps in building a predictive capability for clay‐coat derived elevated reservoir quality in deeply buried sandstones.     

海积软土前期固结压力与结构强度的关系及成因分析

通过对不同地区海积软土的大量试验，对原状土样和重塑土样的压缩曲线确定了海积软土前期固结压力和结构强度，并研究了海积软土前期固结压力及结构强度的关系。由于考虑了土的结构强度，对结构性土根据超固结比(OCR)对土的压密状态的判断与实际结果更加相符。为了定量地反映海积软土的结构强弱，首次引入反映海积软土结构性及其对扰动敏感程度的结构稳定系数，反映了海积软土结构性的稳定程度。初步分析了海积软土结构强度的成因。     

江苏省里下河(兴化-泰州)地区浅表沉积物特征及古地理环境演变

里下河地区浅部沉积物多为全新世中、晚期堆积,多数地区缺失全新世早期沉积。沉积物以淤泥质亚粘土、亚粘土、亚砂土,粉砂质淤泥、淤泥质粉砂、淤泥及泥炭为特征。沉积前的古地貌为四周高、中间低的碟形盆地。古气候经历了温湿—暖湿—温湿—温干的变化过程。区内曾有两次海侵,第一次海侵发生在全新世早中期,范围几乎遍及全区;第二次海侵发生在全新世晚期,规模小、范围窄、时间短,为海水沿江河倒灌、回溯形起。该区古环境自全新世以来经历了浅水海湾—古泻湖—湖沼地及平原的演变过程,最终形成现今河湖稠密的低凹平原。     

ESR/OSL ages of long-debated subtill fossil-bearing marine deposits from the southern Kola Peninsula: stratigraphic implications

The occurrence of sandy clay deposited in a warm marine environment just below the till of the last glaciation has created controversy about its age and stratigraphic position in the sedimentary basin of the Kola Peninsula. Data on marine microfauna, diatoms, malacofauna and pollen composition indicate that during the period when the sandy clay was deposited the climate was similar or even warmer than at present. According to ¹⁴ C dates, sedimentation of the sandy clay occurred around 40 ka BP. Based on these data, some researchers have attributed these marine deposits to the third Late Pleistocene Belomorian (sensu Lavrova 1960) interglacial transgression. At the same time there are geological indications suggesting re-deposition of these subtill sediments. To solve this problem we have reinvestigated the subtill interglacial marine deposits from the Varzuga section (∼66.4° N and 36.6° E). Four different marine shell species and enclosing sandy clay sediments taken from the subtill marine unit of the section were dated by the electron spin resonance (ESR) and optically-stimulated luminescence (OSL) methods at about 103 and 104 ka, respectively. The results indicate that the subtill marine deposits belong to the first Late Pleistocene Boreal transgression that, according to our previous studies of the marginal areas of the Eurasian North, has occurred in the time interval from approximately 145 to 70 ka BP.     

Sedimentary K-Ar signatures in clay fractions from Mesozoic marine shelf environments in Israel

The K-Ar system in clay fractions from shallow marine carbonate shelf environments was investigated on silicate fractions (clay minerals, feldspar) separated from 20 Lower Jurassic to Upper Cretaceous sedimentary rocks, deposited in the southern Tethys ocean. The range of lithologies investigated included dolomite and chalk [IR (insoluble residue)<10%], marl, shale (IR= 70–85%) and sandstone (IR>90%). The results show that K-bearing clay fractions often have K-Ar ages similar to the suggested age of deposition, which means either supply of land-derived authigenic K-bearing clays or synsedimentary diagenetic authigenesis, or both. This K-Ar synsedimentary signal is recorded in clay fractions from the whole range of studied lithologies and stratigraphic units. Among the clay minerals, the synsedimentary K-Ar signature was recorded and retained in illite/smectite of the <2-um and <0.2-um fractions. A prominent synsedimentary signature is found in K-feldspars, from shaly and especially from calcareous rocks, which is substantiated by their authigenic origin based on idiomorphic crystal morphology and their limited size distribution (4–10 um). Post-depositional closure of the K-Ar system is indicated by ages up to 15 Ma younger than the stratigraphic age in different lithologies from dispersed localities. A distinct late diagenetic (20–25 Ma younger) event is recorded in the formation of authigenic K-feldspar within Upper Cretaceous chalk and shale. In the IR and >10-um fractions the K-Ar ages reflect the contribution of detrital mica and feldspar which accompanies the kaolinite-dominated samples. The overall results differ considerably from K-Ar age patterns observed in deep-sea sediments, a difference which may be connected with the occurrence of brines in these shelf deposits. The findings indicate the potential in the K-Ar dating of fine IR fractions of marine shelf sediments in terms of geochronological-stratigraphic and palaeogeographical aspects as well as in the petrology of clay minerals themselves.     

Clay mineral distributions and source discrimination of upper Quaternary sediments,lower Chesapeake Bay,Virginia

Discriminant function analysis of clay mineral data from five cores of upper Quaternary sediment indicates that marine inputs are a significant source of fine-grained sediment near Thimble Shoal Channel, a major natural channel in lower Chesapeake Bay. Illite, of predominantly marine origin, is found to be enriched in clay fractions of three cores adjacent to the channel, relative to two cores near the mouth of the James River estuary. Thimble Shoal Channel is a significant repository and conduit for fine-grained sediment from the shelf. This result is analogous to previous results showing that the shelf is the dominant source of fine sand in the lower bay. Sediment in Thimble Shoal Channel reflects a shelf source even at the landward end, an area which was previously thought to be dominated by deposition from the James River.     

The Tayiba Red Beds: Transitional marine-continental deposits in the precursor Suez Rift,Sinai, Egypt

The Tayiba Red Beds, exposed in the Abu Zenima area, west-central Sinai, have been intensively studied for their clay mineralogy and charophytes assemblages. Three surface sections exposed at Wadi El-Tayiba and Wadi Nukhul were studied. The Tayiba Formation uncomformably overlies the Middle Eocene Khaboba Formation at Wadi Nukhul and the Late Eocene Tanka Formation at Wadi El-Tayiba and commonly underlies the Early Miocene Nukhul Formation with unconformable relationships. The Tayiba Formation at Wadi Nukhul consists predominantly of continental coarse clastic sediments represented by polymictic conglomerates, alternating with red to pinkish mudstone, ferruginous sandstone and varicoloured mottled siltstone with plant remains. At Wadi El-Tayiba, the Tayiba Formation is represented by marine, yellow mudstone and red siltstone, alternating with greyish and reddish-yellow argillaceous to sandy limestone, highly fossiliferous with reworked Nummulites spp. and molluscan shell fragments.The mineralogical composition of the studied clay size fraction showed that most samples are dominated by illite, together with smectite, kaolinite and illite/smectite mixed layers. The relative proportion of these constituents shows wide variation. Smectite is more abundant than other constituents at Wadi El-Tayiba. The high content of smectite is usually accompanied by a terrigenous influx in the form of kaolinite and illite, reflecting deposition in an inner neritic shallow marine environment. The sediments of Wadi Nukhul are characterised by an appreciable proportion of illite, together with an illite/smectite mixed layer and minor amounts of kaolinite, suggesting deposition in fluviatile environments.The detailed investigation of charophytes (green algae) in the investigated sections showed that Wadi El-Tayiba is nearly barren of these microflorae, except for some benthic foraminifera from a shallow marine environment. In contrast, Wadi Nukhul yielded a high frequency and great diversity of charophytes, where 15 species have been identified, described and illustrated for the first time. The utilisation of the ranges of these species allowed the subdivision of the section into three charophyte zones, which are correlated with other zones recorded in Europe, as well as the standard mammal levels in the world. These biozones strongly assign the Tayiba Formation to the Late Eocene to Late Oligocene (Late Priabonian to Chattian). A depositional model was suggested for the Tayiba Formation in west-central Sinai.     

Preliminary studies on the characterization of clay minerals in the Sundarban mangrove core sediments,West Bengal,India

Clay mineral found in rivers, estuaries, and marine sedimentary environments is an important group of minerals which is the by-product of chemical weathering. The main constituents of this fine-grained sediment include mudstones, clay stones, and shales. This is probably the first report of a Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) investigation on the clay minerals to characterize them in the Sundarban mangrove core sediments of Moipith Matla and Belamati Island. This study was carried out in the selected stretch for FTIR and SEM analyses. The study reveals the dominant association of kaolinite with subordinate amount of quartz, illite, and chlorite. The abundance of kaolinite, illite, chlorite, and clay with quartz helps in increasing the sediment in the island region. The geochemical and mineralogical evolution of mangrove sediment results in the interaction of biotic and abiotic parameters, whose balance is conditioned by the climate that governs the hydrologic regime, the sedimentation dynamics, and of the organic matter. This study on the characterization of clay provides substantial impact in the water-holding capacity, productivity, and mineralogical and chemical transformation in order to establish much more and intermediate equilibrium between marine influence and continental contribution, as a part of the estuarine environment.     

山西太原至灵石一带石炭纪含煤地层中的粘土矿物

石炭纪含煤地层在山西省不仅含有重要价值的煤炭资源,而且也含有极为丰富的粘土。过去生产部门和科研机构曾从不同角度对含煤地层中的粘土进行过研究,并发表了数篇文章。笔者在参加研究华北地台沉积建造过程中,对太原西山七里沟剖面和灵石县城郊剖面进行了野外观察并系统地采集了标本。所有标本都进行了粘土提纯,去除碳酸盐、有机质,并分别作了差热、X射线衍射、红外吸收光谱和透射电镜的分析研究。本文试图从粘土矿物类型,纵向分布以及成因等方面进行探讨。     

Stratigraphy,sedimentology, age and palaeoenvironment of marine varved clay in the Middle Swedish end‐moraine zone

Johnson, M. D. & Ståhl, Y. 2009: Stratigraphy, sedimentology, age and palaeoenvironment of marine varved clay in the Middle Swedish end‐moraine zone. Boreas, 10.1111/j.1502‐3885.2009.00124.x. ISSN 0300‐9483 Deglaciation of the Middle Swedish end‐moraine zone and age of the sediment in and between the moraines have been discussed for about a hundred years. The goal of this project was to determine the stratigraphy and age of the sediment in and between the moraines. Inter‐moraine flats are underlain by clay, 10–25 m thick, overlying thin sand and gravel or till on bedrock. The clay is overlain by a few metres of sand and gravel. Much of the clay beneath the flats consists of rhythmites that grade from grey to red and are 2–74 cm thick. Our interpretation of these rhythmites as being varves is supported by grain size and mineralogical and elemental variations. Foraminifera and ostracods show that the clay was deposited in an arctic marine environment, while radiocarbon dating of the microfossils indicates that the clay was deposited 12 150 cal. ¹⁴C years ago, during the Younger Dryas chronozone (YD). Most of the optical stimulated luminescence dates on the clay are much older, containing quartz sand that was insufficiently bleached. The stratigraphy indicates that the moraines are composed of YD clay pushed into ridge forms during ice‐front oscillations. It is not possible to determine how far north the Scandinavian Ice Sheet retreated prior to the YD advance. We neither support nor reject the suggestion that the ice margin retreated to the northern edge of Mt. Billingen during the Allerød, causing the Baltic Ice Lake to drain.     

The Late Pleistocene Afton Lodge Clay Formation,Ayrshire, Scotland: evidence for Early to Middle Devensian climatic changes and Late Devensian onshore ice flow and rafting from the Firth of Clyde

An investigation into the late Pleistocene sediments exposed at Afton Lodge has helped to clarify the glacial history of western central Scotland. The sequence includes several allochthonous bodies of ‘shelly clay’ (Afton Lodge Clay Formation) associated with Late Devensian (Weichselian) age diamict. The shelly clay contains abundant marine macro- and microfauna, as well as palynomorphs consistent with its deposition within a shallow marine to estuarine environment. Faunal changes within the main body of marine clay record at least one, millennial-scale cycle of Arctic-Boreal, to Boreal, and back to Arctic-Boreal climatic conditions. A radiocarbon date of over 41 ka ¹⁴C BP obtained from the foraminifera indicates that the marine clays are older than the surrounding till. Afton Lodge is thus one of a suite of ‘high-level’ shelly clay occurrences around the Scottish coasts that are now considered to be glacially transported. Together with closely associated ‘shelly tills’, the rafts were emplaced during an early phase of the last glaciation by ice flowing from the western Grampian Highlands of Scotland through the topographically-confined Firth of Clyde basin. The blocks of marine sediment were detached subglacially, unfrozen, and carried at least 10 km by ice that splayed out onshore against reversed slopes favouring raft emplacement and the creation of closely associated ribbed moraine. Transport of the rafts was facilitated by water-lubricated décollement surfaces and their accretion was accompanied by dewatering. The shelly tills were formed mainly by the attenuation and crushing of rafts of shelly clay during their transport within the subglacial deforming bed.     

海相沉积软黏土的弹塑性本构模型研究

在深入探讨海相沉积原状软黏土压缩、变形等力学特性和详细分析加载屈服面随荷载情况变化的基础上,确认了海相沉积原状软黏土的强度、变形特性与结构屈服应力密切相关。即当固结压力小于结构屈服应力时,其力学特性与超固结重塑土的力学特性类似;当固结压力大于结构屈服应力时,其力学特性与正常固结重塑土的力学特性类似。为描述海相沉积原状软黏土的上述力学特性,将姚仰平等提出的超固结重塑土本构模型引入到海相沉积软黏土弹塑性本构模型的构建中。在本构模型构建过程中,考虑了海相沉积原状软黏土具有的抗拉强度及其演化规律,软黏土强度包线的特点及其进一步修正的表达式,使模型更符合海相原状软黏土的强度、变形特性。最后,将3种不同海相沉积软黏土固结排水剪切试验得到的应力-应变-体变曲线与模型预测结果进行对比。比较结果显示,本文提出的弹塑性本构模型能很好地描述海相沉积原状软黏土的剪缩硬化、剪胀软化以及变形的应力水平依存性等力学特性。     

Turbiditic,clay‐rich event beds in fjord‐marine deposits caused by landslides in emerging clay deposits – palaeoenvironmental interpretation and role for submarine mass‐wasting

Distinct, clay‐rich beds are common in fjord‐marine deposits in Trondheimsfjorden near the outlet of the Nidelva River. Their characteristic light‐grey colour makes the beds easily distinguishable from the surrounding brownish, bioturbated, muddy fjord sediments. The clay‐rich beds commonly display a clear stratification in clay, silt and very fine sand. The beds are interpreted as originating primarily from large quick‐clay landslides upstream along the Nidelva River. Such events resulted in a sudden increase in the supply of fines to the fjord from disintegrating landslide debris and heavily loaded effluent plumes, possibly favouring hyperpycnal flow. Typical beds can be divided into a clay‐rich lower section, reflecting an initial surge with high concentrations of suspended mud, and a sandier upper section reflecting pulses of higher energy. This development can be explained, for example, by a lowering in the supply of mud, an increasing activity of deltaic sediment gravity flows due to a higher availability of sandy sediments in the landslide‐affected river, and by flooding and/or breaching of landslide dams. The typical, stratified beds are interpreted as the result of one quick‐clay landslide, whereas exceptionally thick, less organized, stratified beds are possibly the result of several large and/or complex landslides. Radiocarbon dating of mollusc shells has helped to establish a chronology for major terrestrial landslides in the area. The frequency of landslides increases towards the end of the Holocene. This is explained by a progressively deeper incision of rivers during glacioisostatic rebound, possibly combined with a change to a wetter climate. The marine core record displays deformation structures and hiati representing submarine mass‐wasting events, and supports the evidence that the clay‐rich beds are weak layers in the fjord‐marine stratigraphy. The inherent weakness of these layers may be explained by their composition, immature texture, loose fabric and contrasting permeabilities in the deposits. Slide‐prone layers similar to the clay‐rich beds described here may be found in other comparable fjord‐marginal settings and are considered to be of importance for geohazard assessments.     

粘土矿物保存海洋沉积有机质研究进展及其碳循环意义

海洋沉积物吸附有机质的量和有机质循环周期与粘土矿物类型和吸附方式密切相关,并在全球碳循环中扮演着不同的角色。粘土吸附有机质有物理吸附和化学吸附之分,前者主要存在于粘土的微孔隙中,参与年、十年或百年尺度的循环;后者主要存在于粘土矿物层间和外表面,稳定性较好,有机质易于保存,可参与百万年或更长时间的循环,这种不同时间尺度内的碳循环,将会改写海洋沉积物有机碳“源”、“汇”的关系。不同类型粘土矿物的性质存在差异,决定了吸附有机质量的多寡,蒙脱石的吸附量远大于伊利石的吸附量,这可能是造成全球不同海域中有机碳“源”、“汇”变化的原因。海洋沉积物处于水圈、生物圈和岩石圈的交汇地带,有机碳的差异和变化,都会对全球碳循环及气候变化产生重要的影响。     

湖北黄石、浙江长兴煤山二叠-三叠系界线处火山物质及粘土岩成因探讨

本文对湖北黄石、浙江长兴煤山剖面二叠-三叠系界线附近粘土岩层作了碎屑物的分析和测试,并计算了它们的百分含量。与火山活动有关的碎屑主要有石英(其中含六方双锥状的β石英)、锆石、磷灰石、玻璃圆球、铁质圆球及火山灰等。有些样品中还有电气石、石榴石及锐钛矿等。笔者认为粘土岩层的成因是火山物质在海水中沉积蚀变而成。火山喷出口不在工作区内,生物绝灭的主要原因不是火山活动引起的。