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1.
Derek G. Turner Brent C. Ward Duane G. Froese Michel Lamothe Jeffrey D. Bond Nancy H. Bigelow 《Boreas: An International Journal of Quaternary Research》2016,45(3):521-536
At least five Middle to Late Pleistocene advances of the northern Cordilleran Ice Sheet are preserved at Silver Creek, on the northeastern edge of the St Elias Mountains in southwest Yukon, Canada. Silver Creek is located 100 km up‐ice of the Marine Isotope Stage (MIS) 2 McConnell glacial limit of the St Elias lobe. This site contains ~3 km of nearly continuous lateral exposure of glacial and non‐glacial sediments, including multiple tills separated by thick gravel, loess and tilted lake beds. Infrared‐stimulated luminescence (IRSL) and AMS radiocarbon dating constrain the glacial deposits to MIS 2, 4, either MIS 6 or mid‐MIS 7, and two older Middle Pleistocene advances. This chronology and the tilt of the lake beds suggest Pleistocene uplift rates of up to 1.9 mm a?1 along the Denali Fault since MIS 7. The non‐glacial sediment consists of sand, gravel, loess and organic beds from MIS 7, MIS 3 and the early Holocene. The MIS 3 deposits date to between 30–36 14C ka BP, making Silver Creek one of the few well‐constrained MIS 3‐aged sites in Yukon. This confirms that ice receded close to modern limits in MIS 3. Pollen and macrofossil analyses show that a meadow‐tundra to steppe‐tundra mosaic with abundant herbs and forbs and few shrubs or trees, dominated the environment at this time. The stratigraphy at Silver Creek provides a palaeoclimatic record since at least MIS 8 and comprises the oldest direct record of Pleistocene glaciation in southwest Yukon. 相似文献
2.
Grain-size distributions of fluvial, eolian and marine sediments were explicated decades ago. For lake sediments, however, there is still great uncertainty in explaining the genesis of grain-size components due to the inherent complexity of their polymodal distributions. In this study, the grain-size components of the surface sediments of Daihai Lake, Inner Mongolia, were partitioned using a lognormal distribution function and the relationship between the identity of each component and the specific sedimentary environment was investigated. The data indicate that the modern clastic sediments of Daihai Lake contain five distinct unimodal grain-size distributions representing five grain-size components. Each of the components retains its identity including modal size, manner of transportation and environment of deposition although the relative percentage varies with the hydraulic condition throughout the lake. These components are specified from fine to coarse modes as long-term suspension clay, offshore-suspension fine silt and medium-to-coarse silt, and nearshore-suspension fine sand and saltation medium sand. The percentage of the components interpreted as an indication of nearshore environments displays a negative correlation with water depth across the modern lakebed, suggesting a model for linking the nearshore components in sediment cores to the lake level status in the geological past. The model was applied to a sediment core from the lake where high percentages of the nearshore components in the core sediments were correlated with low regional precipitations reconstructed on the pollen profile of the same core. The coincidences between two independent proxies do not only demonstrate the validity of lognormal distribution function in partitioning polymodal sediments but also reveals the potential of the grain-size component–lake level status model for lake’s paleohydrological reconstruction. 相似文献
3.
通过对潘谢矿区新生界底部沉积物岩性特征、厚度分布、物质来源及沉积剖面等综合分析,得出该矿区古地形主要受构造、岩性以及风化作用等控制,在此基础上形成的底部砾石层与"红层"在整个空间分布呈非均匀性的特征,东部潘集矿区以砂砾层、砂层和含砾石粘土层为主,沉积厚度大,物源为就地风化和远处水流搬运物;西部张谢矿区以"红层"为主,成分混杂,厚度小,不连续,主要分布在山前低洼处,为山区"剥高填低、就地沉积"的沉积特征。底部松散沉积物主要有洪积环境、坡积环境以及河流环境下形成的沉积物,并依此推断了潘谢矿区底部松散层的沉积演化过程,洪积和河流冲刷作用对沉积物的形成及改造较为突出。研究成果为矿井在开采浅部煤层过程中,对于"底含"水的防治提供了重要的参考依据。 相似文献
4.
沉积体的X光影像包含了沉积物密度、结构、构造等众多信息,对X光影像进行数字图像分析可快速提取这些信息,成为进行沉积记录和古环境演变研究的有力手段。基于长江水下三角洲沉积物岩芯的X光影像,利用Matlab软件平台把X光影像转换成数字灰度图像,进而提取了岩芯灰度值;结合该岩芯的粒度等沉积学属性,探讨了灰度图像的影响因素。结果表明:沉积物岩芯的X光图像灰度值是沉积物组成、结构和构造的综合反映,其中粒度对灰度值起到控制性的影响。平均粒径与灰度值之间为良好的线性关系;砂粒级、粉砂粒级含量与灰度之间存在较好的正相关,而黏土粒级含量与灰度存在很好的负相关。沉积物岩芯X光图像的灰度值可以作为该岩芯的粒度的良好替代性指标。 相似文献
5.
This study assesses spatial and temporal sedimentological trends in four mesohaline Chesapeake Bay submersed aquatic vegetation (SAV) habitats, two with persistent SAV beds and two with ephemeral SAV beds, to determine their relationship to current and historical sediment characteristics??grain size, organic content, and accumulation rates. In general, grain size is similar among all sites, and subsurface sediment differs from surficial sediment only at one site where a thin surficial sand layer (??2?C3?cm) is present. This thin sand layer is not completely preserved in the longer-term sedimentary record even though it is critical to determining whether the sediment is suitable for SAV. Evidence for nearshore fining, similar to that observed in the deeper waters of the Bay, is present at the site where the shoreline has been hardened suggesting that locations with hardened shorelines limit exchange of coarser (sandy) material between the shore and nearshore environments. Whether the fining trend will continue to a point at which the sediment will become unsuitable for SAV in the future or whether some new type of equilibrium will be reached cannot be addressed with our data. Instead, our data suggest that SAV presence/absence is related to changes in sedimentary characteristics??persistent beds have relatively steady sediment composition, while ephemeral beds have finer sediments due to reduced sand input. Additionally, sediment accumulation rates in the persistent beds are ??9?mm/year, whereas rates in the ephemeral beds are ??3?mm/year. Thus, the ephemeral sites highlight two potential sedimentary controls on SAV distribution: the presence of a sufficiently thick surficial sand layer as previously postulated by Wicks (2005) and accumulation rates high enough to bury seeds prior to germination and/or keep up with sea-level rise. 相似文献
6.
Hashem A. Madkour Abbas M. Mansour Abu El-Hagag N. Ahmed A. El-Taher 《Arabian Journal of Geosciences》2014,7(9):3427-3440
The textural and geochemical aspects of the sediments of subtropical mangrove ecosystem and surrounding areas have been studied and discussed. Forty sediment samples were collected from different areas of mangrove environment and surrounding areas along the Egyptian Red Sea coast. The sediments of each study areas are characterized by the abundance of sand with minor amounts of mud and gravel. The mean size of the sediments ranged from medium grained to fine grained at the study areas. Cluster analysis showed that the distribution of gravel, sand, and mud fractions is related to bottom facies and type of sediment source. Generally, sand fraction is the main category among the three constituents. Carbonate content recorded minor values in the study areas. The CaCo3 content of the sediments ranged from 4.7 % at Hamata area to 64.9 % at Erier area. Terrigenous and biogenic components are the factor controlling of the carbonate content of studies sediments. The organic carbon content ranged from 1.10 at Hamata area to 3.1 % at Sharm el-Qibli and Erier areas, which is controlled by particle size of the sediments. Phosphorus content in the different studied localities is related to the sources of phosphorus to the area. Our observations provide evidence that there are no significant differences in environmental texture and geochemistry of the sediments of subtropical mangrove ecosystem and surrounding areas of the Egyptian Red Sea coast. 相似文献
7.
Subaqueous sediment gravity flow deposits: practical criteria for their field description and classification 总被引：4，自引：0，他引：4
GUIDO GHIBAUDO 《Sedimentology》1992,39(3):423-454
8.
东太平洋水合物海岭BSR以上沉积物粒度变化与气体水合物分布 总被引：10，自引：1，他引：10
文中对国际大洋钻探204航次在太平洋水合物海岭8 个站位BSR深度以上气体水合物稳定带的沉积物进行了粒度分析和对比研究。结果表明,该稳定带内沉积物总体粒径变化特征为:粉砂质量分数在60%~75%之间,为气体水合物稳定带内沉积组分的主体组分。粘土质量分数一般小于35%,砂质量分数小于5%。该结果获得的粒径变化范围,与204 航次中沉积学研究所确定的粘土质粉砂、粉砂质粘土夹含砂质粉砂、含砂质粘土岩性特征一致。各站位沉积粒径变化和代表气体水合物存在的岩心红外照相IR异常低温记录之间的初步对比说明,气体水合物主要富集在沉积组分较粗,相当于粉砂或者砂级质量分数较高的粒度层。统计学的相关性研究结果定量地揭示了各个站位沉积物粒径变粗与气体水合物的存在有不同的相关关系。归纳起来发现,不同构造部位沉积物中气体水合物赋存层段的粒径范围不同。坡后盆地由于当地总体沉积物颗粒细,气体水合物赋存在极细粉砂粒级(8~26μm)的沉积物中。水合物海岭南峰顶部附近站位气体水合物主要赋存在粗粉砂和细砂(50~148μm)之间。 相似文献
9.
Sediments exposed at low tide on the transgressive, hypertidal (>6 m tidal range) Waterside Beach, New Brunswick, Canada permit the scrutiny of sedimentary structures and textures that develop at water depths equivalent to the upper and lower shoreface. Waterside Beach sediments are grouped into eleven sedimentologically distinct deposits that represent three depositional environments: (1) sandy foreshore and shoreface; (2) tidal‐creek braid‐plain and delta; and, (3) wave‐formed gravel and sand bars, and associated deposits. The sandy foreshore and shoreface depositional environment encompasses the backshore; moderately dipping beachface; and a shallowly seaward‐dipping terrace of sandy middle and lower intertidal, and muddy sub‐tidal sediments. Intertidal sediments reworked and deposited by tidal creeks comprise the tidal‐creek braid plain and delta. Wave‐formed sand and gravel bars and associated deposits include: sediment sourced from low‐amplitude, unstable sand bars; gravel deposited from large (up to 5·5 m high, 800 m long), landward‐migrating gravel bars; and zones of mud deposition developed on the landward side of the gravel bars. The relationship between the gravel bars and mud deposits, and between mud‐laden sea water and beach gravels provides mechanisms for the deposition of mud beds, and muddy clast‐ and matrix‐supported conglomerates in ancient conglomeratic successions. Idealized sections are presented as analogues for ancient conglomerates deposited in transgressive systems. Where tidal creeks do not influence sedimentation on the beach, the preserved sequence consists of a gravel lag overlain by increasingly finer‐grained shoreface sediments. Conversely, where tidal creeks debouch onto the beach, erosion of the underlying salt marsh results in deposition of a thicker, more complex beach succession. The thickness of this package is controlled by tidal range, sedimentation rate, and rate of transgression. The tidal‐creek influenced succession comprises repeated sequences of: a thin mud bed overlain by muddy conglomerate, sandy conglomerate, a coarse lag, and capped by trough cross‐bedded sand and gravel. 相似文献
10.
Electrical resistivity ground imaging (ERGI): a new tool for mapping the lithology and geometry of channel-belts and valley-fills 总被引：1，自引：0，他引：1
Dave Baines Derald G. Smith Duane G. Froese Paul Bauman† Grant Nimeck† 《Sedimentology》2002,49(3):441-449
Efforts to map the lithology and geometry of sand and gravel channel‐belts and valley‐fills are limited by an inability to easily obtain information about the shallow subsurface. Until recently, boreholes were the only method available to obtain this information; however, borehole programmes are costly, time consuming and always leave in doubt the stratigraphic connection between and beyond the boreholes. Although standard shallow geophysical techniques such as ground‐penetrating radar (GPR) and shallow seismic can rapidly obtain subsurface data with high horizontal resolution, they only function well under select conditions. Electrical resistivity ground imaging (ERGI) is a recently developed shallow geophysical technique that rapidly produces high‐resolution profiles of the shallow subsurface under most field conditions. ERGI uses measurements of the ground's resistance to an electrical current to develop a two‐dimensional model of the shallow subsurface (<200 m) called an ERGI profile. ERGI measurements work equally well in resistive sediments (‘clean’ sand and gravel) and in conductive sediments (silt and clay). This paper tests the effectiveness of ERGI in mapping the lithology and geometry of buried fluvial deposits. ERGI surveys are presented from two channel‐fills and two valley‐fills. ERGI profiles are compared with lithostratigraphic profiles from borehole logs, sediment cores, wireline logs or GPR. Depth, width and lithology of sand and gravel channel‐fills and adjacent sediments can be accurately detected and delineated from the ERGI profiles, even when buried beneath 1–20 m of silt/clay. 相似文献
11.
利用粒度资料进行沉积物的粒度结构分析, 能有效地判定沉积物搬运方式、判别水动力条件、区分沉积环境类型, 研究沉积物的成因机制。本文通过大量粒度频率曲线、概率累计曲线和粒级-标准偏差曲线等图件的分析, 详细研究了沉积物所包含的粒度组分及各自特征, 并提取出对沉积环境变化敏感的粒度组分, 确定了各自组分所对应的沉积水动力类型, 结合沉积相和构造背景研究, 探讨了东营凹陷辛176块沙四上亚段纯上5砂组砂体的成因, 认为辛176块王斜583、辛176斜1井砂体是广饶凸起的碎屑物质在南斜坡形成三角洲后被入湖河流继续搬运、沉积并被波浪改造形成的滩坝砂体; 牛114斜1、王587井砂体为青坨子凸起的碎屑物质以重力流方式搬运并与广饶凸起的物质混合、沉积, 后又被波浪改造而形成; 王58井砂体为来自青坨子凸起的重力流入湖后发生卸载形成的沟道砂体。 相似文献
12.
13.
根据2016年伶仃洋128个表层沉积物粒度参数以及前人对伶仃洋表层沉积物的研究成果,结合Flemming沉积动力判别图解和粒径趋势分析模型（GSTA）,分析伶仃洋40年来的沉积格局演变特征,并探讨了人类活动在伶仃洋沉积格局演变中的作用。结果显示:1）2016年,伶仃洋表层沉积物中粉砂组分含量最多（56.67%）,黏土组分含量其次（26.08%）,砂含量最少（17.23%）,湾内表层沉积物总体较细,主要有砂、砂—粉砂—黏土、砂质粉砂、粉砂质砂和黏土质粉砂5种类型,各类型沉积物呈现斑块状分布。2）近40年来,伶仃洋表层沉积物的平均粒径、粒级组分的空间格局发生了显著变化,从之前的条带状分布变为斑块状分布,但沉积格局的剧烈演变主要集中于2004—2016年这十多年间,Flemming三角图分区变化显示出40年来伶仃洋沉积环境整体表现出动力增强的趋势。3）受人类大规模采砂影响,中滩区域原有的完整沉积中心被分散,分别向北和向南形成“两格局、三中心”的新型沉积模式,从而改变伶仃洋的沉积物源—汇过程。4）伶仃洋沉积物空间分布、沉积动力环境、运移趋势等特征的变化与采砂、航道浚深等人类活动有着密切的联系,反映出人类工程活动已成为影响伶仃洋沉积格局演变的重要因素。 相似文献
14.
JASPER KNIGHT 《Boreas: An International Journal of Quaternary Research》2011,40(2):289-302
Knight, J. 2010: Subglacial processes and drumlin formation in a confined bedrock valley, northwest Ireland. Boreas, 10.1111/j.1502‐3885.2010.00182.x. ISSN 0300‐9483. Subglacial processes beneath the Late Weichselian ice sheet in northwest Ireland are deduced from sediments and structures within drumlins in a bedrock valley at Loughros Beg, County Donegal. Here, a glacially smoothed bedrock surface underlies the drumlins, which are composed on their up‐ice side of stacked, angular rafts of local bedrock. Overlying and down‐ice from these rafts are down‐ice‐dipping beds of massive to bedded diamicton that contain sand and gravel interbeds. In a down‐ice direction the diamicton matrix coarsens and the beds become laterally transitional to water‐sorted gravels. The down‐ice end of one drumlin shows a concentrically bedded stratified gravel core aligned parallel to ice flow and resembling the internal structure of an esker. With distance away from this core, the gravels become more poorly sorted with an increase in matrix content, and are transitional to massive to stratified diamicton. A four‐stage model describes the formation of drumlins in this sediment‐poor setting. The sediments that are located directly above the bedrock represent deposition in a semi‐enclosed subglacial cavity. A trigger for this process was the formation of subglacial relief by the thrusting up of bedrock rafts, which created the leeside cavity. Subsequent sediment deposition into this cavity represents a form of feedback (self‐regulation), which may be a typical characteristic of subglacial processes in sediment‐poor settings. 相似文献
15.
Some observations from radiometric ‘8 bit’ data of sediment thin sections based on alternative petrographic image analysis method 总被引：1，自引：0，他引：1
Sudip Dey Suvendu Ghosh Chandrani Debbarma Prasamita Sarkar Mhu Aris Marfai Sabyasachi Maiti 《Journal of Earth System Science》2009,118(2):163-173
This paper deals with the experiment of sediment microstructure analysis especially microfabric mapping by digital imaging.
For that purpose the greyscale images (Red band from RGB combination) of the thin sections have been prepared from the selected
12 samples. The basis of this mapping is the reflectance capacity of different sediments which is influenced by the physical
parameters like grain size and colour. The reflectances of different sediments are represented in digital format by different
DN values from 0–255 within the radiometric ranges of ‘8 bit’ data. Density slicing has been chosen as the method of microstructure
mapping in this research. This study shows that lower DN values normally present dark coloured coarser sand and clay while
higher DN values present light coloured finer sediment samples. In the selected samples for this study the maximum DN value
has been found from micaceous materials. Another remarkable thing observed from the microfabric mapping is that the presence
of coarser sediments forms complex microfabric pattern than the finer sediments in the study area. Though this method have
some demerits, still its simple technique can be very useful for accurate microstructure analysis. 相似文献
16.
《Applied Geochemistry》1999,14(6):807-816
A rapid procedure is described to evaluate the significance of inorganic and organic pollutants in fine-grained sediments. The air- (<30°C) or freeze-dried samples are screened within 30 min. in stainless steel sieves (<0.04 mm) prior to chemical analysis. This procedure is also suitable for analysis of such elements as Hg and many non-volatile organic pollutants. The sediment size fraction of <0.04 mm was chosen in order to separate the smallest grain-size obtainable by rapid dry-screening techniques; this is representative of the grain-size of suspended matter transported at low and medium river discharge (0.1–0.7 m/s). The screened fraction (<0.04 mm) of aquatic sediments is more homogeneous in grain-size and distribution, and the fine particles are more capable of adsorbing pollutants than coarser fractions. However, large differences are observed in grain-size distribution and adsorbable phases from one sample to another, even in the smallest size fractions (<0.04, <0.02, <0.002 mm). Clay minerals, Fe- and Mn-(oxy)hydrates, amorphous silica and humic substances all adsorb water at normal humidity. In order to estimate and standardise the adsorption capacity of the surface of these screened sediment fractions, the weight loss after heating at 105°C is used, instead of tedious quantification of all the above mentioned sediment phases. In addition, this procedure allows the rejection of sediment samples, unsuitable for monitoring purposes, which have very low adsorption capacities. In order to correct for the variable adsorption capacity of different sediment samples or size fractions, the weight loss (WL) at 105°C can be inserted in the widely used GeoIndex formula (Igeo105°=log2 (Cmeasured/Cbackground1WL105°C). This improves the evaluation of pollution in aquatic environments. 相似文献
17.
Sediment grain size effect on benthic microalgal biomass in shallow aquatic ecosystems 总被引：1，自引：0，他引：1
Benthic microalgal biomass is an important fraction of the primary producer community in shallow water ecosystems, and the factors controlling benthic microalgal biomass are complex. One possible controlling factor is sediment grain-size distribution. Benthic microalgal biomass was sampled in sediments collected from two sets of North Carolina estuaries Massachusetts and Cape Cod bays, and Manukau Harbour in New Zealand. Comparisons of benthic microalgal biomass and sediment grain-size distributions in these coastal and estuarine ecosystems frequently showed a negative relationship between the proportion of fine-grained sediments and benthic microalgal biomass measured as chlorophylla. The highest sedimentary chlorophylla levels generally occurred in sediments with lower percentages of fine particles (diameter <125 mm). A negative relationship between the proportion of fine sediments and benthic microalgal biomass suggests anthropogenic loadings of fine sediment may reduce the biological productivity of shallow-water ecosystems. 相似文献
18.
Naohisa Nishida Taku Ajioka Ken Ikehara Rei Nakashima Hajime Katayama Tomoyuki Sato Seishiro Furuyama Toru Tamura 《Sedimentology》2020,67(1):559-575
Sandy shelf sediments are important elements of clastic sedimentary systems because of their wide distribution in the geological record and their significance as hydrocarbon reservoirs. Although many studies have investigated shelf sediments influenced by waves or tidal currents, little is known about shelf sediments influenced by oceanic currents, particularly their lithofacies characteristics and stratigraphic evolution. This study investigated the stratigraphic evolution of shelf sediments off the Kujukuri strandplain facing the Pacific Ocean, which is influenced by the strong Kuroshio Current. Sediment cores were obtained from six locations on the Kujukuri shelf (34 to 124 m water depth) using a vibrocorer. The dominant lithofacies is mud-free sand with low-angle cross-lamination associated with alternating beds of finer and coarser sand with cross-lamination. These display depositional processes influenced by storm waves and the Kuroshio Current, respectively. This finding is consistent with the previously presented modern and historical observations of the Kuroshio Current and estimates of the storm-wave base. Radiocarbon dates show that the sediment succession formed during the last transgressive and highstand stages after 13·1 ka. The depositional processes during the stages represent a transition from storm waves with abundant sediment supply to both storm waves and the Kuroshio Current with sediment starvation mainly due to its trapping in the strandplain. Comparison to other Holocene–Modern shelf systems suggests that the sandy shelf successions are strongly influenced by oceanic currents under conditions of limited riverine input and open coastal geometry. The resultant sand-dominated succession is characterized by reversal of the proximal to distal grain-size trend compared to the fining for most other recognized wave/storm-dominated shelf successions. This is because of seaward increase in the influence of the Kuroshio Current. Thus, shelf deposits are naturally complex, and these may be further complicated by the additional influence of oceanic currents above the usual wave-dominated and tide-dominated end members. 相似文献
19.
海南岛北部浅海海砂资源丰富,以砂砾质沉积为主,集中于琼州海峡东口潮流沙脊区、河口三角洲和沿岸水下岸坡等海域。本文通过对海南岛北部海域的地形地貌、地层、底质类型等方面的调查,分东、西两个区域研究了海砂资源的分布、范围、规模和类型等地质特征,并估算了海砂资源量,结合沉积环境,评价了各区域海砂的资源潜力。研究区海砂分布广泛,但东、西区特征和规模具有较大差异,西区海砂以砂质砾和泥质砂为主,厚度5~10 m;东区海砂以砂、砾质砂和砂质砾为主,厚度10~50 m,规模远超西区。研究区共圈定出9处资源潜力区,资源量为91.4亿m3,其余区域为远景区,其资源量为71.5亿m3。根据地形地貌、水动力和沉积环境等因素,研究区海砂可分为潮流沙脊堆积体系、河口水下三角洲堆积体系、岬湾海岸水下岸坡堆积体系和侵蚀残留体系几种类型。其中位于琼州海峡东口浅滩区的潮流沙脊堆积体系海砂连续分布面积达328 km2,平均厚度超过25 m,资源量83.9亿m3,最具潜力。 相似文献