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1.
Pollen was collected from modern alluvium and from the atmosphere to document the nature and amount of paleoenvironmental information reflected by alluvial pollen chronologies. Results indicate that pollen in alluvium is a homogeneous mixture derived almost entirely from the floodplain itself. The few pollen grains derived from nonfloodplain plant communities and preserved in alluvial sediments are so well mixed that their frequencies no longer reflect the geographic distribution of the specific plant communities in which they originated. In contrast, the abundance of alluvial pollen grains, derived from the major floodplain taxa (Chenopodiineae, Ambrosia type), varies with summer and winter climate. This annual variation is preserved in alluvial pollen assemblages through a combination of processes within sedimentation basins involving discontinuous deposition events and mechanical pollen degradation. The high-frequency, wide-amplitude pollen variance in alluvial pollen assemblages contrasts with the low-frequency, narrow-amplitude pollen variance in sediments of lakes and ponds. The slight geographic variance in alluvial pollen assemblages, in contrast to the large variance in soil pollen, allows use of alluvial pollen to infer climate throughout the watershed in which pollen is sampled. 相似文献
2.
华北平原冲积物孢粉沉积相研究 总被引：8，自引：8，他引：8
华北平原孢粉沉积相研究表明，洪积扇和三角洲平原区沉积的花粉较多。花粉沉积浓度多在3000粒/g以上。冲积平原区沉积下来的花粉较少，花粉浓度多在1000粒/g以下。冲积物的花粉浓度可以作为划分不同地貌单元的指标。不同的沉积相存在着不同的孢粉组合。主流相一般沉积的花粉粒很少或不合花粉，花粉植物类型也较少。漫滩、心滩沉积的花粉较多，花粉植物类型也较丰富。边滩沉积的花粉较少，花粉浓度也低。自然堤和泛滥相以含有较多的松、卷柏孢子和当地花粉植物为特征。这些特征可以作为识别沉积相的指标。 相似文献
3.
Simulation experiment of sedimentary process and sedimentary architecture of alluvial fan under the control of normal faults 
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下载免费PDF全文 Normal fault structures are widely developed in basins and orogenic belts,which control the accommodation space and the distribution of sediments and thus affecting the morphology of alluvial fans. A flume tank experiment was carried to simulate and clarify the control of normal faults on the sedimentary process and internal architecture of alluvial fans.The results show that the large amount of sediments carried by debris flow tend to be unloaded near the hanging wall of faults and are subsequently reworked by traction current,which result in a triangular distributary gravel bar grows vertically on fault plane with the tip pointing to the source area. When the hydrodynamic force is strong,debris flow goes across distributary gravel bar and forms over-bar lobe at the tail of the distributary gravel bar. When the hydrodynamic force is weak,debris flow forms fault plane-dominated lobe along fault plane and is located on both sides of the distributary gravel bar. Under the control of normal faults and the barrier of distributary gravel bar,the unloading process of sediments varies greatly at different positions on the surface of alluvial fan. The particle size varies greatly among different facies,with coarsest grains developed on the fans of hanging wall,finer grained on over-bar lobe and finest sediments on fault plane-dominated lobe. The development process of alluvial fan can be divided into three stages,according to the sandbody thickness and fault throw of distributary gravel bar. The fault throw also affects the sedimentary architecture of alluvial fan,with larger the fault throw generating larger the accommodation space of hanging wall,longer development time of distributary gravel bar and more complex of the superposition pattern of the sand bodies inside the fan. The internal architecture of alluvial fan that is controlled by normal faults includes longitudinal sandbar,distributary gravel bar and debris flow lobe in the profile vertical perpendicular to the sediment source direction from the proximal to the distal end. Along sediment longitudinal section,composite channel,superimposed distributary gravel bar complex and superimposed bodies of multi-phased lobes are dominant facies. 相似文献
4.
正断层构造广泛发育于盆地内和造山带中,其对可容空间分配及沉积物分布具有明显的控制作用,从而影响了冲积扇形态。为进一步探究正断层构造对冲积扇沉积过程及其内部构型的控制作用,利用水槽实验对正断层构造发育背景下的冲积扇发育过程进行模拟再现。研究表明,携带大量沉积物的碎屑流优先在上盘近断层处泄载,后经牵引流的改造,形成沿断面垂向生长、尖端指向物源的三角形分水滩。水动力较强时碎屑流越过分水滩并在分水滩尾部发育越滩朵体,水动力较弱时碎屑流遇分水滩尖端分流后沿断面在分水滩两侧发育断面朵体。受控于断面及分水滩的阻挡,冲积扇表面不同位置的沉积物泄载过程差异较大,粒度差异明显,上盘扇体中分水滩沉积物偏粗,越滩朵体次之,断面朵体最细。冲积扇的发育过程依据分水滩砂体厚度和断距大小之间的差异,共分为3个阶段。断距大小还会影响冲积扇沉积构型,断距越大,上盘可容空间越大,分水滩发育时间越长,扇体内部砂体叠置样式越复杂。受控于正断层的冲积扇内部构型在垂直物源剖面上从近端至远端,分别发育纵向沙坝、分水滩及碎屑流朵体,在平行物源剖面上以复合水道主控、分水滩叠复体主控、多期朵体叠复体主控为主。 相似文献
5.
Xuanwei Formation is composed of mudstone, siltstone, and sandstone, with local conglomerate. However, its provenance and tectonic setting have been scarcely studied. In this paper, we use sedimentology, electron probe microanalysis(EPMA), and detrital zircon dating to investigate its source area and depositional tectonic setting. The facies assemblages indicate that it formed in alluvial fan and fluvial river sedimentary environments. The strata thicknesses and facies distribution indicate that the sediment supply was from the west. The results of EPMA show that chromian spinels within the sediments are characterized by high Cr# and varying Mg#. Discrimination plots suggest that these spinels were sourced from large igneous province(LIP) magmatic rocks. The laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) U–Pb chronology of detrital zircons suggests that the sediments were derived from intermediate–acid igneous rocks dating back to 251–260? Ma. We could, therefore, conclude that the provenance of the Xuanwei Formation is from Emeishan basalt and synchronous felsic igneous rocks, which is consistent with the composition of the detrital framework. The detrital zircon dates also suggest that felsic magmatism occurred during the Late Permian, not after the eruption of the Emeishan basalt. Based on the sedimentary successions and provenance analysis, the tectonic setting for Xuanwei Formation deposition was a volcanic rifted margin. 相似文献
6.
Andrei Matoshko Dmitry Bugai Lionel Dewiere Alexander Skalskyy 《Environmental Geology》2004,46(6-7):820-830
The approach, methods and results of a sedimentological study of a near-surface stratum of Late Pleistocene-Holocene deposits in the near-zone (5–10 km radius) of the Chernobyl Nuclear Power Plant are presented. Sedimentological analyses are carried out at three levels of detail: regional-, local- and object-scale. The unsaturated zone and unconfined aquifer at the site are composed of two main genetic types of deposits, aeolian and alluvial, including several dynamic facies. Consideration of lithological properties leads to following ranking of the main genetic sediments facies with respect to radionuclide migration retardation potential: aeolian <alluvial channel <alluvial overbank <alluvial abandoned channel. Based on sedimentological interpretations, the geological environment is schematised into a set of typical geological sections possessing different radionuclide retardation potential. 相似文献
7.
Pollen taphonomy in a canyon stream 总被引：1，自引：0，他引：1
Patricia L. Fall 《Quaternary Research》1987,28(3)
Surface soil samples from the forested Chuska Mountains to the arid steppe of the Chinle Valley, Northeastern Arizona, show close correlation between modern pollen rain and vegetation. In contrast, modern alluvium is dominated by Pinus pollen throughout the canyon; it reflects neither the surrounding floodplain nor plateau vegetation. Pollen in surface soils is deposited by wind; pollen grains in alluvium are deposited by a stream as sedimentary particles. Clay-size particles correlate significantly with Pinus, Quercus, and Populus pollen. These pollen types settle, as clay does, in slack water. Chenopodiaceae-Amaranthus, Artemisia, other Tubuliflorae, and indeterminate pollen types correlate with sand-size particles, and are deposited by more turbulent water. Fluctuating pollen frequencies in alluvial deposits are related to sedimentology and do not reflect the local or regional vegetation where the sediments were deposited. Alluvial pollen is unreliable for reconstruction of paleoenvironments. 相似文献
8.
Mohsen Henchiri Walid Ben Ahmed Andrea Brogi Mehmet Cihat Alçiçek Ramdhane Benassi 《Geodinamica Acta》2017,29(1):20-41
The Quaternary stratigraphic record of Jebel El Mida, composed of continental deposits, is a useful example of concomitant travertines and alluvial deposition in an extensional setting. Travertine deposition occurred in a faulted Pleistocene alluvial fan giving rise to seven (recognised) facies interfingering with five other alluvial ones. The travertine depositional events indicate a tectonically driven evolution from terraced slope (facies group FC1–FC6) to a travertine fissure ridge-type depositing phase (facies group of FC1–FC7). Interfingering between travertine and alluvial facies indicates the co-existence of adjacent and time-equivalent depositional environments. The travertine deposition resulted from deep origin hydrothermal fluids channelled along damaged rocks volumes associated to a regional fault system, named as the Gafsa Fault (GF). The travertine–terrigenous succession in Jebel El Mida highlights the major role played by the GF in controlling: (i) the hydrothermal fluid flow, still active as also indicated by the numerous thermal springs aligned along the fault zone; (ii) paleoflow directions, discharge locations, volume, rate and fluctuations of the water supply. The paleoclimatic correlation with adjacent localities reveals that, at that time, humid episodes could have contributed to the recharge of the hydrothermal system and to the deposition of alluvial sediments. 相似文献
9.
羌塘盆地地处藏北高原,其南、北边界分别为班公错一怒江缝合带与拉竹龙一金沙江缝合带,盆地面积约18×104km2,可进一步分为羌北坳陷、中央隆起带和羌南坳陷3个二级构造单元.双湖托纳木地区地处羌北坳陷南部,与中央隆起带毗连,广泛发育上侏罗统雪山组沉积,垂向上由3个沉积旋回组合构成,总体显示为一个向上变粗的充填序列.雪山组发育扇三角洲相和冲积扇相,其中雪山组一段为前扇三角洲亚相沉积;二段为扇三角洲前缘亚相和扇三角洲平原亚相沉积,扇三角洲前缘亚相分为水下分流河道、河口坝和远砂坝沉积,扇三角洲平原亚相发育天然堤和分流河道沉积;三段为冲积扇相沉积,包括扇端和扇中沉积.雪山组沉积的物源来自西南部的中央隆起带. 相似文献
10.
沉积环境对孢粉组合影响的探讨--以石羊河流域为例 总被引：7，自引：0，他引：7
西部干旱区小型内陆流域 (石羊河流域 )内三个地点孢粉分析显示不同地点全新世孢粉组合差异极大。三角域剖面孢粉组合完全以针叶树为主;洪水河剖面孢粉组合下部以旱生草本为主,上部以针叶树为主;终闾区表土孢粉组合中 90 %为旱生草本、灌木。其差异已远远超出气候环境变化所导致的差异。结合沉积相、沉积环境、孢粉在不同沉积环境中的传播、扩散特性的综合分析,笔者认为这种差异是沉积环境、搬运介质差异造成的。三角城剖面处于半封闭环境,接纳储存来自上游的所有沉积物的信息,孢粉组合反映的是流域上游祁连山上的植被状况。洪水河剖面下部冲积地层发育时,剖面处于开放环境,孢粉组合反映当地植被;上部湖相层发育时,剖面处于半封闭环境,孢粉组合的环境指示意义与三角城剖面一致。终闾区表土孢粉组合反映现代风媒环境终闾区植被状况。古环境重建不能仅从孢粉组合出发,必须结合沉积环境综合分析,否则,古环境重建的结果是不可靠的. 相似文献
11.
比重是物质的重要物性之一,是物质成分和结构的反映。不同矿物的比重可以相差若干倍,因而用以鉴定矿物的种类。在河流动力学有关基本原理和计算公式中,比重是一种重要的因素,在沉积岩石学中被视为沉积物的沉积三要素(粒度、比重和形状)之一。我们对滹沱河现代沉积物进行沉积构造、粒度、矿物成分和扫描电镜等项分析的同时,对沉积物的比重作了一些分析,探讨了沉积物的比重在河流沉积体系中的变化情况。 相似文献
12.
柴北缘牦牛山地区牦牛山组沉积相组合特征 总被引：5，自引：0，他引：5
柴达木盆地北缘牦牛山地区出露的牦牛山组是一套由冲积扇和扇三角洲相共同构成的陆相沉积组合,冲积扇相砾岩-粗砂岩组合主要分布于研究区SE侧,扇三角洲相砂岩-泥岩组合主要分布于研究区NW侧。古水流分析表明牦牛山组沉积物主要来自其SE侧古隆起,但后期扇三角洲相包含少量来自NW和NE向的沉积物。该套沉积组合序列特征与区域上分布在牦牛山西侧同时期形成的湖泊相、滨浅海相沉积共同表明,柴达木盆地北缘在晚志留-早泥盆世时期存在一NW向倾斜的古斜坡,且晚期北侧发生抬升。砾岩和砂岩碎屑组成与区域岩石组合类型对比表明,牦牛山组沉积碎屑物主要来自于滩间山群。沉积组合序列特征、碎屑组成和区域构造背景综合研究表明,牦牛山组可能为柴达木板块向北俯冲过程中形成的局部断陷盆地的充填物。 相似文献
13.
内蒙古平庄盆地黑水地区上白垩统孙家湾组上段沉积相为冲积扇相,宏观上分为近端砾质辫状平原、远端砂质辫状平原及扇前洪泛平原3个亚相,进一步细分为泥石流、砾质辫状河道、砾质坝、砂质辫状河道、砂质坝、洪泛细粒、泥炭沼泽等微相。孙家湾组上段可划分为3个亚段,第一亚段为干旱_潮湿过渡气候下形成的退积型序列的旱地扇沉积;第二亚段为潮湿气候下形成的退积型序列的湿地扇沉积;第三亚段为潮湿气候下形成的进积型序列的湿地扇沉积。黑水地区的孙家湾组上段经历了早期退积型旱地扇—中期退积型湿地扇—晚期进积型湿地扇的过程。沉积相对该区铀成矿具有控制作用,铀矿化主要以不连续、局部富集的形式赋存于远端砂质辫状平原前缘的砂质辫状河砂体中,泥炭沼泽和泥质含量少的泥石流沉积中有少量存在。泥炭沼泽沉积所形成的泥岩及泥质含量高的泥石流沉积充当了局部隔水层,但由于泥炭沼泽沉积较薄,以及泥石流沉积的不均一性,致使铀矿（化）不连续、不稳定。 相似文献
14.
为揭示北票(金-羊)盆地内北票组层序地层特征及沉积体系分布规律,应用层序地层学及沉积学理论和方法,综合利用野外露头、剖面等资料,建立了北票(金-羊)盆地北票组的层序地层格架,确定研究区的沉积相类型及分布规律。研究结果表明,北票(金-羊)盆地北票组可划分为2个三级层序,其内部可进一步划分为7个准层序组。在层序内识别出冲积扇、辫状河三角洲、湖泊3个沉积相。明确了沉积相的分布规律,向上形成由冲积扇到辫状河三角洲,再到湖相,最后是辫状河三角洲的沉积体系;平面上呈近北西—南东向展布的沉积体系,整体构成2个水进、水退的沉积体系。古地貌影响了底部冲积扇相沉积物的沉积特征。气候不仅影响了沉积物类型,且和湖平面变化共同控制了沉积物的演化规律。 相似文献
15.
兰州-民和盆地下白垩统河口群沉积序列及沉积相研究 总被引：2，自引：0，他引：2
兰州—民和盆地下白垩统河口群是一套厚度巨大的陆相碎屑岩沉积，根据岩性组合和沉积旋回，自下而上将河口群划分为8个非正式的组级单位。通过对河口群基本层序的分析和沉积序列及沉积相的研究，可以识别出冲积扇相、三角洲相和滨浅湖相3类相环境，细分为13种微相。沉积相的演变从整体上反映了整个盆地的演化过程。河口群的沉积环境由冲积扇相→三角洲相→滨浅湖相→三角洲平原相演变，形成了一个完整的序列，反映了盆地从开裂→扩张→萎缩→消亡的不同发展阶段。 相似文献
16.
Daniel W. J. Bosence 《Geological Journal》1980,15(2):91-111
Five sedimentary facies are described from SCUBA diving examination and sampling of Mannin Bay, Ireland. A Bank facies is built up by the unattached coralline algae Lithothamnium corallioides and Phymatolithon calcareum. This autochthonous facies occurs in shallow sheltered environments. In exposed areas a rippled Clean Algal Gravel facies is found composed of coralline and molluscan debris. In intermediate energy areas a Muddy Algal Gravel facies is found with small amounts of live corallines. Sheltered creeks have a Mud facies which is partly carbonate and partly terrigenous. The shallow water coralline algal sediments are overlapped by a Fine Sand facies of mixed biogenic composition. Each facies is characterized by particular phenotypic growth forms of the unattached corallines. Rates of organic calcium carbonate production are obtained which are found to be similar to rates from shallow tropical non-reef environments. The carbonate sediments of Mannin Bay are compared with similar sediments from Kilkerrin Bay. Ireland, from Brittany and from Falmouth Harbour. From these comparisons, facies models are proposed for these carbonate sediments. The major factor controlling facies distribution is coastal morphology. The present day shelf is considered to be too exposed to preserve complete sequences of the shallow water sediments. 相似文献
17.
S. G. Lewis D. Maddy C. Buckingham G. R. Coope M. H. Field D. H. Keen A. W. G. Pike D. A. Roe R. G. Scaife K. Scott 《第四纪科学杂志》2006,21(2):181-205
Pleistocene fluvial sediments of the Northmoor Member of the Upper Thames Formation exposed at Latton, Wiltshire, record episodic deposition close to the Churn–Thames confluence possibly spanning the interval from Marine Isotope Stages (MIS) 7 to 2. The sequence is dominated by gravel facies, indicating deposition by a high‐energy, gravel‐bed river. A number of fine‐grained organic sediment bodies within the sequence have yielded palaeoenvironmental and biostratigraphical data from Mollusca, Coleoptera, vertebrates, pollen and plant macrofossils. The basal deposit (Facies Association A) contains faunal material indicating temperate conditions. Most of the palaeontological evidence including a distinctive small form of mammoth (Mammuthus cf. trogontherii), together with the U‐series age estimate of >147.4 ± 20 kyr suggest correlation with MIS 7. The overlying deposits (Facies Associations B and C) represent deposition under a range of climatic conditions. Two fine‐grained organic deposits occurred within Association B; one (Association Ba) in the northern part of the pit as a channel fill and the other (Association Bb) in its southern part as a scour‐fill deposit. The coleopteran assemblages from Ba, indicate that it accumulated under temperate oceanic conditions, while Bb, which also yielded a radiocarbon age estimate of 39 560 ± 780 14C yr BP, was formed under much colder and more continental climatic conditions. The sequence is considered to represent deposition within an alluvial fan formed at the Churn–Thames confluence; a depositional scenario which may account for the juxtaposition of sediments and fossils of widely differing age within the same altitudinal range. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
18.
新疆乌恰萨热克含铜盆地上侏罗统库孜贡苏组复合型冲积扇沉积相研究 总被引：1，自引：0，他引：1
新疆萨热克含铜盆地库孜贡苏组是复合型冲积扇沉积相,是重要的赋矿层。利用研究区24个钻孔和10个露头剖面资料,运用高分辨率层序地层学原理进行单孔沉积相、连孔沉积相、平面沉积相分析,对新疆萨热克含铜盆地库孜贡苏组(J3k)复合型冲积扇内部垂向和3个中期旋回期间沉积相亚相的平面分布特征进行了研究。研究表明,该区库孜贡苏组垂向分布大体可分为3个中期基准面旋回和若干短期基准面旋回,据此建立了高分辨率层序地层对比格架。3个中期旋回期间,沉积亚相平面发育模式差异大。铜矿(化)体垂向、平面分布特征明显。 相似文献
19.
合肥盆地是与大别山造山带有密切关系的山前前陆盆地，盆地中、新生界沉积物主要来自南面大别山区以及盆地东部、北部剥蚀区。通过野外实际踏勘、室内岩石薄片显微分析，认为合肥盆地中、新生界发育的沉积相主要有冲积扇相、河流相和湖泊相，其中以河流相最为发育。该盆地中、新生界油气源条件比较丰富，储盖条件良好，生储盖组合形式多样，存在多种油气圈闭类型，是一个油气勘探潜力较大的陆相沉积盆地。 相似文献
20.
Sedimentological study of the digitated lobes of gravel and associated sediments in the north of Durgapur results in identification
of five major facies. Facies analysis indicates the sediments were deposited from an alluvial fan that has prograded in to
an inferred shallow body of water. The analysis also suggests debris flow deposits dominate proximal part, modified grain
flow and turbidity current the middle part and current generated channel and non-channel deposits in the distal part of the
alluvial fan — fan-delta sequence. 相似文献