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1.
《Precambrian Research》1987,37(1):29-55
The Stella and Hauy Formations of the Archean Opemisca Group in the eastern Chapais Syncline feature numerous fluvial to shallow marine transitions throughout the stratigraphic sequence. During the first depositional phase (Stella Formation), relatively high gradient alluvial fans prograde into a shallow marine environment. The coarse clastic sediments reflect a Scott-type depositional environment. The initial depositional environment is envisaged to be a high-energy, wave- and storm (flood) -dominated coastline bordered by coastal alluvial fans. Shallow marine deposits consist of coarse- to very coarse-grained sandstones and intraclast and pebble to cobble conglomerates. The prevalent shallow marine sediments are related to storm and/or flood deposition.Terrigenous sediments of the Donjek-type depositional environment prevail during the second depositional phase (Hauy Formation). The shallow marine sediments, although still wave- and storm (flood) -dominated, are finergrained, and when correlated with the terrigenous sediments imply a lower gradient and a maturing of the coastline. Furthermore, contemporaneous volcanism of andesitic (shoshonitic) to basaltic composition, occurs during this evolutionary stage. The sedimentary basin gradually evolved during the two depositional phases.The repetition of terrigenous and shallow marine sediments throughout the stratigraphic sequence, coarsening- and fining-sequences in the conglomerates, and the alluvial fan setting strongly suggest a fault-bounded basin margin. Tectonic uplift of the hinterland initiates alluvial fan progradation onto the shelf, whereas quiescent periods are documented by marine transgression. The clast composition of the conglomerates and the alluvial fan environment suggest local derivation of clasts.The synvolcanic Chibougamau Pluton and the Lake Dore Complex acted as a stable basement during deposition of the Opemisca Group. The small landmass served as a stable platform for shallow marine deposition, even when tectonically influenced. A late phase intraplutonic (cratonic) development of an initial backarc basin system (internal zone of the Abitibi greenstone belt) is proposed as the overall depositional setting of the Chapais basin. 相似文献
2.
通过岩心观察,将克拉玛依油田三叠系克下组砾岩分为杂基支撑角砾岩(砾石成分同基岩)、弱胶结砾岩(严格意义上未胶结成岩)、泥质杂基支撑砾岩、砂砾质支撑砾岩和分选极好的细砾岩几种类型。通过岩心岩石特征与现代洪积扇沉积物特征对比,确定了每一类砾岩的形成环境。克下组沉积早期,气候干旱,洪积扇为干旱型,可与现代扎伊尔山山麓洪积扇(堆)沉积物特征相类比。克下组沉积后期气候变得潮湿,洪积扇类型逐渐转变为以河流作用为主,可与阜康市白杨河洪积扇沉积物特征相类比。克下组洪积扇在垂向上为向扎伊尔山后退的沉积序列。 相似文献
3.
Detrital sand grains from three beaches (Tecolutla, Nautla, and Veracruz) along the western Gulf of Mexico were studied by a scanning electron microscope, to investigate the depositional environment and paleoclimate. Totally, 24 microtextures are identified; among them, 13 are grouped as mechanical origin, 5 as mechanical and/or chemical origin, and 6 as chemical origin. These microtextures are nonuniformly distributed among the three beach areas. Concoidal fractures, straight and arcuate steps at Tecolutla and Veracruz beaches indicate that the sand grains were derived from the crystalline rocks. The abundance of angular outline grains at the Nautla beach supports for short transportation probably close to the source area. The domination of rounded sand grains in the Veracruz beach reveals that the sediments were derived by the aeolian mechanism. Chattermark trials at the Veracruz beach sands are indicating a wet tropical climate. Chemical features like silica globules, silica pellicle, and trapped diatoms in the Tecolutla and Veracruz beach sands suggest a silica saturated environment. Similarly, chemical etching and solution pits are common in the Veracruz beach sands, which are probably linked to the contaminated sea water. Desiccation crack at Veracruz beach sands is an indicator of temperature changes in the beach environment. Broken benthonic foraminifera Elphidium discoidale sp. present in the Veracruz beach indicates a high-energy littoral environment. 相似文献
4.
Veena U. Joshi 《Journal of the Geological Society of India》2009,74(6):711-722
Quartz sand grains obtained from a deeply gullied topography along the banks of two tributaries of River Pravara in Godavari
Basin, Maharashtra have been examined with a scanning electron microscope (SEM) in order to make the environmental interpretations
of these deposits. The sediments reveal features resulting from mechanical grinding as well as from chemical alteration. Conchoidal
fractures, cleavage planes, grooves, v-shaped indentations etc are the mechanical features documented on the grains whereas
solution pits of varying sizes and intensity, precipitation surfaces, oriented v-pits, solution crevasses and etching are
the features of diagenetic origin. Few sand grains show the evidence of wind transported sediments. Several evidence indicate
that the samples have undergone digenetic changes. Few grains exhibit the features of intense chemical breakdown. The overall
assemblages of the grain surface features suggest that the samples have been subjected to subaqueous transport for a considerable
period of time. The chemical features such as etching, solution pits or semi circular arcuate steps that are found in abundance
in these grains are due to the dissolution of the sediments in a low energy fluviatile environment, such as in floodplain
region. 相似文献
5.
长江口区晚新生代沉积物粒度特征和沉积地貌环境演变 总被引：7，自引：0，他引：7
对长江河口区的三个晚新生代钻孔作了地层对比和粒度分析,据此探讨晚新生代长江河口的沉积地貌环境演变过程。结果表明,SG6和J18A孔上新世厚层含砾砂质沉积物粒度特征,反映了洪积扇和冲积扇相沉积环境,沉积物搬运距离短;而SG13孔缺失上新世沉积,反映古地势较高,以剥蚀为主。因此上新世长江三角洲地区古地势高差较大,侵蚀区和沉积区共存。早更新世,本区继承了上新世的冲、洪积扇沉积环境,但SG6孔泥质沉积明显变厚,J18A孔此时则以厚层含砾砂沉积为主,SG13孔也开始接受泥质沉积,反映在构造沉降作用下,冲、洪积扇体向西、南部迁移,沉积盆地范围扩大。中更新世,沉积物普遍变细且以悬浮沉积为主,显示了曲流河或曲流河冲积平原的沉积环境。晚更新世初,本区又发育含砾砂层,特别是SG13孔出现厚层含砾砂,但是粒径显著小于上新世和早更新世沉积物,反映本区再次发生显著构造沉积,河流地貌广泛发育。晚更新世中晚期和全新世沉积物以粘土和粉砂质粘土为主,悬浮沉积占优,说明本区已演变为滨、浅海沉积环境。因此在构造沉降、剥蚀和沉积的共同作用下,本区的地貌演变经历了自上新世至中更新世和自晚更新世至全新世的两次准平原化过程。 相似文献
6.
柴达木盆地处于古亚洲构造域和特提斯－喜马拉雅构造域的结合部，构造应力大而复杂，导致盆内地势起伏大，加上西南暖湿气流受喜马拉雅山系阻隔难以进入境内，盆内气候干旱，最终导致盆地内冲积扇极为发育。通过对大柴旦地区大头羊煤矿、鱼卡河、波门河和八里沟四个冲积扇的实地考察，共观测到3个亚相8个微相：扇根亚相沉积物最粗，分为古沟道、主水道和主水道间微相；扇中亚相沉积物偏细，成熟度增高，分为辫状水道、辫状水道间和纵坝微相；扇缘亚相沉积物最细，流体能量最低，分为水道径流和片流微相。不同沉积微相其沉积特征差异较大，认为古沟道、主水道和辫状水道微相具有较好的储集性能。勘探表明，冲积扇沉积与储层有着密切的关系，其内形成的油藏具有“自我保护”的能力；另外，冲积扇的形成很可能导致上覆地层形成扇背斜油藏，也可能导致下伏基岩形成基岩风化壳油藏。 相似文献
7.
The subtidal sediments of four coastal environments (beach, berm, surf zone and nearshore sea floor) of Kuala Terengganu have
been studied in terms of their textural characteristics and depositional process. Sampling and statistical analyses of the
grain size distributions of beach, surf zone and shallow sea-floor sediments at various locations along the coastline show
that they varied in their mean grain size as well as values of sorting and skewness. The statistical parameters of grain size
distributions thus allowed recognition of distinct sub-environments. The size distribution of such sediments suggests that
the various processes that are responsible for their transportation and deposition are wave, current and wind action. The
different energy conditions and the morphology of each coastal environment seem to be reflected in the characteristics of
the sediments in each environment. 相似文献
8.
Luke J. Wooldridge Richard H. Worden Joshua Griffiths James E. P. Utley 《Sedimentology》2019,66(3):1118-1138
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. 相似文献
9.
SUNG KWUN CHOUGH 《Sedimentology》2011,58(6):1530-1572
To understand the depositional processes and environmental changes during the initial flooding of the North China Platform, this study focuses on the Lower to Middle Cambrian Zhushadong and Mantou formations in Shandong Province, China. The succession in the Jinan and Laiwu areas comprises mixed carbonate and siliciclastic deposits composed of limestone, dolostone, stromatolite, thrombolite, purple and grey mudstone, and sandstone. A detailed sedimentary facies analysis of seven well‐exposed sections suggests that five facies associations are the result of an intercalation of carbonate and siliciclastic depositional environments, including local alluvial fans, shallowing‐upward carbonate–siliciclastic peritidal cycles, oolite dominant shoals, shoreface and lagoonal environments. These facies associations successively show a transition from an initially inundated tide‐dominated carbonate platform to a wave‐dominated shallow marine environment. In particular, the peritidal sediments were deposited during a large number of depositional cycles. These sediments consist of lime mudstone, dolomite, stromatolite and purple and grey mudstones. These shallowing‐upward cycles generally resulted from carbonate production in response to an increase of accommodation during rising sea‐level. The carbonate production was, however, interrupted by frequent siliciclastic input from the adjacent emergent archipelago. The depositional cycles thus formed under the influence of both autogenetic changes, including sediment supply from the archipelago, and allogenic control of relative sea‐level rise in the carbonate factory. A low‐relief archipelago with an active tidal regime allowed the development of tide‐dominated siliciclastic and carbonate environments on the vast platform. Siliciclastic input to these tidal environments terminated when most of the archipelago became submerged due to a rapid rise in sea‐level. This study provides insights on how a vast Cambrian carbonate platform maintained synchronous sedimentation under a tidal regime, forming distinct cycles of mixed carbonates and siliciclastics as the system kept up with rising relative sea‐level during the early stage of basin development in the North China Platform. 相似文献
10.
Alluvial fan is a depositional fluvial landform that is characterised by sediment flow and hydrological processes and is also controlled by tectonic activity. These extraordinary features have always attracted researchers since the past as they preserve the past records, but now, this study is focused on the formation meso-level fans with its spatio-temporal dynamic nature. These tributaries have formed secondary alluvial fans at their debouching points. The dynamics of the fans are controlled by the hydrological responses and tectonic base and also by the sedimentation processes. The origin of these tributaries and their respective fans are related to the last stage of Himalayan uplift. This is the region of Himalayan foreland basin which contains the main frontal thrust and makes the region tectonically very active. The region is drained by many large rivers and their numerous tributaries. The active tectonism, the configuration of the basin and also the deposition of the sediments carried by these rivers have formed alluvial fans where the channel debouches into the widened valley. In the present study, the meso-level alluvial fans formed by River Gish and the Rivers Neora and Murti have been studied. Both these fans are present in the piedmont region of the Himalayas, but they deliver different characteristics, and the nature of their deposition is also different. This is mainly because of the influence of the minor faults in the region which control the channel pattern and also have a great influence in the sediment delivery to the downstream section of the channels. Thus, in order to understand the influence of tectonics in the dynamics of these fans, some morphotectonic parameters have been taken into consideration. These include mountain front sinuosity index, valley floor width-to-depth ratio, and tectonic tilt. The calculated hypsometric integral also depicts that the two fans are at different stages of development. 相似文献
11.
白杨河冲积扇是由阵发性洪水期的碎屑流沉积物与间洪期辫状河沉积物组成的复合型冲积扇,其构型与碎屑流扇的构型和河流型扇的构型有很大的不同。本研究选取准噶尔盆地西北缘干旱气候下发育的现代白杨河冲积扇作为解剖实例,对103个天然剖面和9个人工大型探槽进行了详细测量,在沉积微相及不同级别的沉积构型的观测和分析的基础上,分析了阵发性洪水条件下间歇性辫状河型冲积扇体的地貌单元的演化过程和沉积构型特征,研究不同流态的阵发性洪水条件下各种建造和改造机制,明确受阵发性洪水控制的间歇性辫状河型冲积扇的沉积特征,建立了其沉积构型模式。认为: 在洪水期,阵发性洪流(碎屑流)形成席状化的片流(或片洪)沉积,在洪退期,随着洪水强度的减弱,又转变为辫流沉积,而在间洪期,仍有持续的辫状流体(牵引流)在限制性的水道中流动,并对洪水期的碎屑流沉积物进行改造,形成了限制性的(条带状的)辫状河道沉积,2个时期的沉积物在时空上频繁叠置,形成了一种更加复杂的沉积构型。该模式对油田地下冲积扇砂砾储集层的成因识别、预测及对比具有一定的参考价值。 相似文献
12.
鄂尔多斯盆地白垩纪沙漠石英沙颗粒表面特征 总被引：12，自引：0，他引：12
沉积环境的判别是沉积盆地分析、古地理、古气候研究和储层评价的重要手段。石英具有较大的硬度和较高的化学稳定性,因而其沉积物颗粒表面特征能很好地反映沉积环境,而通过扫描电镜研究石英颗粒表面微细特征是分析沉积环境行之有效的方法。尽管鄂尔多斯盆地早白垩纪志丹群存在沙漠沉积已被广为接受,但石英颗粒表面微细特征分析还比较薄弱。对采自鄂尔多斯盆地白垩纪志丹群洛河组 (K1l)和罗汉洞组 (K1lh)的沙丘沙进行石英颗粒表面微细特征分析的结果表明,其石英沙颗粒表面特征具有明显的风成特征,及易与水成特征相区别。因此,本研究从石英沙颗粒表面特征方面进一步肯定了鄂尔多斯盆地白垩纪古沙漠的存在 相似文献
13.
A consistent pattern for the silica sources, depositional environments and timing of chertification was observed in a diverse suite of five Late Mesozoic and Middle Palaeozoic carbonate sequences; the (1) Upper Greensand (Cretaceous) and (2) Portland Limestone (Jurassic) of southern England, (3) the Ramp Creek Formation (Mississippian) of southern Indiana, and the (4) lower Helderberg Group (Devonian) and (5) Onondaga Limestone (Devonian) of New York State. Nodular chert formation in all five limestone sequences occurred in sediments that were largely uncemented. Ghosts of pre-chertification carbonate cements are present in some chert nodules but are volumetrically minor. In every limestone sequence except the Upper Greensand, chertification occurred after burial to a depth sufficient for intergranular pressure solution and mechanical grain deformation of carbonate sand. Nodular chert is most abundant in subtidal, normal marine wackestones and mudstones that were deposited at or below fair-weather wave base, and is absent or rare in supratidal, intertidal and high-energy subtidal limestones and dolomites. An intraformational sponge spicule silica source for chert nodules is suggested by direct evidence, such as calcitized sponge spicules in the host limestone, and circumstantial evidence, such as ghosts of sponge spicules in chert nodules and a correlation of chert abundance with depositional environment. Most molds of siliceous sponge spicules were apparently obliterated by post-chertification intergranular compaction. We propose that these general trends for the depositional environments, silica sources and timing of chertification are representative of most Mesozoic to Middle Palaeozoic platform limestones. 相似文献
14.
玛湖凹陷是准噶尔盆地最具规模的油气聚集带与勘探区,发育以砾岩为主、具有较强非均质性的粗粒沉积复杂地层。对粗粒沉积体的精细刻画有助于研究沉积体内部的非均质性特征。应用储层构型分析法,结合研究区岩心、测井、录井资料,对玛湖凹陷夏子街扇区三叠系百口泉组沉积体内部9个级次构型要素的几何形态、大小、方向以及相互之间的叠置关系进行了表征,识别出12种岩石相类型以及10种由岩石相组合而成的沉积微相类型。通过分析沉积微相在垂向、平面上的不同组合特征,扇体的类型受沉积环境影响发生变化,逐渐由冲积扇、河流扇转换为扇三角洲,整体反映了湖平面上升或沉积物供给量逐渐减小的沉积背景。分析夏子街扇区各期次的扇体特征,包括长轴、短轴距离、长轴短轴比、扇根与扇缘厚度变化、扇体坡度变化、扇体最大粒径变化等,认为扇体顺物源方向有以下变化趋势: 沉积物粒径大小随河道搬运逐渐减小,减小的幅度受扇体坡度影响,坡度越陡沉积物粒径减小的越快;河道数量减少,流量降低;河道沉积物在横向和纵向上的连通性逐渐降低;砂岩、砾岩厚度逐渐减小,泥岩厚度逐渐增加,湖相沉积变得较为发育。总结玛湖凹陷百口泉组的各期次扇体共可归纳出6种扇体模式: 冲积扇、冲积—河流扇、河流—末梢扇、河流扇—扇三角洲、扇三角洲、大型河流扇。 相似文献
15.
通过对冀北坳陷中新元古界下马岭组进行剖面实测,对下马岭组底部的沥青砂岩进行室内薄片鉴定和扫描电镜分析,观察与分析了下马岭组沥青砂岩的出露分布特征,镜下研究了此砂岩的碎屑颗粒和填隙物的组分特征和磨圆、分选、粒度等结构特征,依据岩石学特征、粒度分析系列参数等研究了沥青砂岩的沉积环境。结果表明此砂岩为成分与结构成熟度均高的纯石英砂岩和石英砂岩,硅质与沥青质填隙、沥青含量达5%~15%,细粒为主,分选好到极好。粒度分析是本段松散状沥青砂有效环境判别标志。综合分析认为下马岭沥青砂岩形成于无障壁海岸体系的滨浅海环境,形成于前滨到临滨的海相高能环境,可能的沉积位置是前滨下部到中上临滨;此砂岩主要来自临滨潮下高能带的沉积物、含部分前滨下部沉积物、也夹少量潮汐水道沉积物。不同剖面位置所处的沉积环境不同,凌源地区和平泉地区为临滨带的中上部的水下高能带沉积为主,宽城地区为临滨带上部沉积和前滨下部沉积,凌源地区和宽城地区也包含少量的潮汐水道沉积。 相似文献
16.
通过现场实地踏勘、拍照、开挖探槽、利用卫星图解译等方法,对乌伦古湖环布伦托海区域和吉力湖北部乌伦古河现代三角洲地区的湖泊滨岸沉积环境和沉积体系进行了现代沉积调查。研究表明乌伦古湖滨岸沉积环境可以划分为基岩型湖岸、砾质湖岸、砂质湖岸、泥质湖岸等4种类型,发育山前基岩型湖岸、侵蚀基岩型湖岸、砾质冲积扇-扇三角洲、砾质辫状河三角洲、砾质滩坝、砂质滩坝、砂质三角洲、风成沙丘和泥质沼泽等9种滨岸沉积体系。山前基岩湖岸分布在布伦托海的北部,主要发育小型塌积扇、倒石锥和狭窄的湖滩。侵蚀型基岩湖岸位于布伦托海西岸和东北角地区,发育湖滩宽20~40 m。砾质冲积扇-扇三角洲沉积体系分布在布伦托海西北部25.8 km狭长区域,表现为一系列冲积扇-扇三角洲体系在山前形成裙边状展布的辫状平原,顺流向长5~15 km。砾质辫状河三角洲体系发育在布伦托海西部,砾质滩坝发育在砾质三角洲前缘,沉积物一般为中砾和粗砾,泥质含量低。现代乌伦古河三角洲位于吉力湖北部,沙丘广泛分布在布伦托海东部的三角洲平原。砂质滩坝发育在布伦托海东岸南部地区,滩坝带宽30~100 m,发育大量障碍痕、冰划痕。泥质沼泽占据湖岸总长度29.22 km,沼泽地带植物繁茂,水动力微弱,泥质和有机质含量高。根据卫星照片推测乌伦古湖水位可能发生过3次较大的下降,现代乌伦古河三角洲可能经过了4个发育阶段,但目前缺乏地质年代学证据。构造格局控制了湖泊边界的地形地貌特征,平行构造线走向容易形成规模较大的沉积体系,垂直构造走向形成的沉积体系规模较小。寒旱地区湖泊周缘入湖河流较少,具有季节性和暂时性特点,洪水泥石流、塌积扇等重力沉积体系比较发育。湖泊封冻是寒旱区湖泊区别于温暖地区湖泊的重要特征。在相同气候背景下,源汇地区的高差和河流的流程、流量决定了沉积物的供给总量和沉积体系的特征。湖盆边界形态影响沿岸流的发育,也影响湖泊风动力方向和强度。乌伦古湖滨岸沉积体系的多样性对研究古代湖泊滨岸沉积体系具有重要的启发,开展湖泊滨岸沉积环境和沉积体系调查对完善陆相湖盆沉积体系模式,对发现新的储层类型,对重建湖泊古地理环境具有重要的意义。 相似文献
17.
冲积扇是发育于盆地边缘的一种重要的沉积相类型。近20年来,在冲积扇分布的控制作用、内部构型及储集层特征研究等方面取得了很大的进展:(1)深化了断层活动、物源岩性条件及不同级次基准面旋回对冲积扇沉积构型的控制作用机理;(2)建立了碎屑流主控、碎屑流与河流主控、河流主控的冲积扇以及末端扇的沉积构型模式;(3)分析了冲积扇沉积机制及沉积构型对储集层质量的控制作用。今后有必要充分应用水槽模拟实验、沉积数值模拟和探地雷达等先进技术,对冲积扇沉积过程、内部构型及储集层非均质性进行更为深入的研究。 相似文献
18.
塔里木盆地西南缘中生代沉积古环境恢复 总被引：1，自引：0，他引：1
对塔里木盆地西南缘中生代沉积相和沉积环境的研究,不仅可以了解晚三叠世—晚白垩世塔里木板块南缘活动大陆边缘的历次碰撞事件,也为研究新生代中亚地区强烈的陆内变形活动提供了重要信息。本文利用野外地质调查结果和地球物理资料,在沉积相和地震相分析基础上,重建中生代沉积体系和沉积环境。结果表明:塔里木盆地西南缘中生界的原始分布受晚三叠世弧后前陆冲带冲断作用和造山后伸展作用形成的古地形控制。早侏罗世发育了一系列独立分割的小断陷,以巨厚的冲积扇、辫状河三角洲沉积为特征,其受控于NWW—SEE走向的正断层,而非NW—SE走向的古塔拉斯-费尔干纳右旋走滑断裂;早侏罗世晚期—中侏罗世广泛发育滨浅湖和河流-沼泽相沉积,可能存在一个连通了塔里木盆地南缘、吐拉以及柴达木盆地西缘的统一沉积坳陷;至晚侏罗世,冲积环境再次出现,发育的粗粒碎屑岩为早白垩世湖盆扩张前的产物;早白垩世,丰富的陆源碎屑在古昆仑山前形成多个相互叠置的冲积扇—扇三角洲—扇三角洲平原沉积体;晚白垩世,随着海水自西向东侵入,塔里木盆地西南缘陆相碎屑沉积向东逐渐退却,海相沉积占有优势。 相似文献
19.
沉积物岩心记录着沉积环境的演变过程,其中生物硅(BSi)记录能反映硅质生物的生产力时间和空间变化,2012年5月在下辽河平原西南缘得到了ZK2钻孔柱状样,通过对其沉积物原位密度、生物硅、碳埋藏、粒度、AMS~(14)C和OSL测年、有孔虫鉴定、孢粉鉴定,将ZK2孔的沉积环境主要划分为上三角洲平原相沉积、海洋主导的沉积、湖相沉积、河道沉积4个沉积单元,其相应的生物硅(BSiO_2)浓度分布依次为(2.85±0.23)%、(1.55±0.10)%、(1.96±0.10)%、(0.92±0.05)%,并且生物硅的波动与颗粒有机碳浓度的波动同步。特别是在17~25 cal ka BP冰期形成的湖沼沉积出现较大的颗粒无机碳(PIC)浓度的波动,推测与当时干冷气候条件下CaCO_3过饱和从湖水中沉淀析出有关。钻孔沉积物生物硅浓度记录对格陵兰冰芯~(18)O同位素值的响应存在大约300 a的滞后现象。 相似文献
20.
A depositional model of the lower Pliocene Hagul formation, which is exposed in the East Cairo district (Egypt), is proposed with more than 10 depositional cycles recognized. Field occurrence, detailed petrographic investigation and geochemical analysis revealed that the sediments within each cycle are the result of three sequential sedimentological processes: (1) alluvial sedimentation, (2) calcretization, and (3) precipitation of palustrine carbonate. It was concluded that Hagul formation has been deposited within the distal part of an alluvial plain during three successive climatic conditions: a humid climate during which alluvial sediments were deposited, a semi-arid climate with episodic precipitation which was favorable for pedogenic calcrete development, and a sub-humid climate during which groundwater level was gradually elevated and groundwater calcrete accumulated. Rising groundwater level continued until shallow wetlands covered the area and palustrine limestone was precipitated. Variations in the thickness and the nature of the host sediment, calcrete and palustrine limestone cycle suggest that each of the sedimentation processes varied from cycle to cycle. 相似文献