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1.
This paper describes improvements for an inexpensive, lightweight percussion core sampling system and presents examples of recovered core. The system has proven most effective in remote settings where the weight of a coring system may be a constraint. Cores of up to 5.5 m in length have been recovered and the system has functioned successfully in water depths to 200 m. The system weighs approximately 25 kg and costs less than $450.00 (US).The percussion corer is designed for operation from a stable ice-pack surface. The core barrel assembly is lowered through the water column and driven into sediment with a weighted driver. A secondary line is used to raise and drop the driver. The driver is guided to the core barrel assembly by the main line. Cores are retrieved by a simple pulley system anchored to the ice pack.  相似文献   

2.
A monopod and piston coring apparatus for coring water-saturated sediment is described. The lightweight apparatus can be used from either an ice platform or the ground surface and can be transported by aircraft. Using a piston, core recovery is increased to better than 90%, and depending upon the monopod height, 7 m-long cores can be obtained. Tips for coring in freezing temperatures are also given.  相似文献   

3.
A lightweight, inexpensive jig for splitting 7.6 cm diameter vibracores is described. The advantage of the jig is its simplicity, low cost and portability to the coring site whether on land, ice or a boat. Core splitting at the coring site can guide additional coring activity, similar to other coring devices that extrude sediment as part of the coring process. The simple jig ensures straight and even cuts through the aluminum tube wall, leading to precise core splitting in the field or lab.  相似文献   

4.
We present a design for a piston corer that can take a sediment core up to 1 m long, with an undisturbed sediment–water interface. The coring device possesses a tripod unit and a core-tube unit, the latter comprised of a core tube, a piston with a wire, a drive weight in which the core tube is mounted and a steel rod. The tripod stands on the sediment surface during coring, stabilizing the system and serving as an anchor point for the piston wire. A ball clamp, the critical component of the design, is mounted on top of the tripod. The steel rod runs through the ball clamp and at its lower end, holds the drive weight and the core tube. The ball clamp allows the core tube to slide downward, while the piston is held in a fixed vertical position by the wire connected to the tripod. When the corer is lifted, however, the ball clamp locks. This makes it possible to operate the corer with a single cable, because the piston is not subject to any lifting force when the corer is retrieved. The piston remains in position in the core tube even if the collected sediment core is very short. The piston corer can be deployed from a raft or a boat.  相似文献   

5.
Lake Ohrid is considered to be of Pliocene origin and is the oldest extant lake in Europe. A 1,075-cm-long sediment core was recovered from the southeastern part of the lake, from a water depth of 105 m. The core was investigated using geophysical, granulometric, biogeochemical, diatom, ostracod, and pollen analyses. Tephrochronology and AMS radiocarbon dating of plant macrofossils reveals that the sediment sequence spans the past ca. 39,500 years and features a hiatus between ca. 14,600 and 9,400 cal. year BP. The Pleistocene sequence indicates relatively stable and cold conditions, with steppe vegetation in the catchment, at least partial winter ice-cover of the lake, and oxygenated bottom waters at the coring site. The Holocene sequence indicates that the catchment vegetation had changed to forest dominated by pine and summer-green oak. Several of the proxies suggest the impact of abrupt climate oscillations such as the 8.2 or 4.0 ka event. The observed changes, however, cannot be related clearly to a change in temperature or humidity. Human impact started about 5,000 cal. year BP and increased significantly during the past 2,400 years. Water column mixing conditions, inflow from subaquatic springs, and human impact are the most important parameters influencing internal lake processes, notably affecting the composition and characteristics of the sediments.  相似文献   

6.
The diatom record of V95-2P, a 7.6 m long sediment core collected from 67 m depth, is the first from the east central portion of Lake Victoria. A soil horizon developed at the coring site shortly before 12,400 14C yr BP due to a lakewide desiccation event. The radiocarbon chronology of the older half of this core is problematic, but if our estimated chronology is correct, then aridity and evaporative concentration of the lake are indicated by the presence of Thalassiosira rudolfi from > 12,400 BP to about 10,000 BP. Abundant Aulacoseira and generally rising biogenic silica concentrations may reflect enhanced water column mixing and rising precipitation:evaporation ratios ca. 10,000-8400 BP. A lakewide reorganization of diatom assemblages occurred around 7200 BP, when Aulacoseira nyassensis largely replaced A. granulata and after which rainfall and wind-driven mixing became more seasonally restricted. Pronounced reductions in offshore diatom deposition, from about 8300-5800 BP and after 3500 BP, may have been related to declines in the duration and/or intensity of wind-driven mixing. Increased aridity, and possibly deforestation in the lake basin, is indicated after 1400 BP.  相似文献   

7.
We present a design for a large diameter piston corer, deployed from a raft that is suitable for use in shallow lakes. The piston corer, known as Big Ben, consists of a core tube, a piston on a rope and a corer head, to which rods are attached to drive the tube into the sediment. A core catcher, which aids the support of the core tube when full of sediment, has been incorporated into the design. To extrude the sediment, a framework has been designed to keep the core tube upright and stationary and a modified bottle jack is used to push the piston upwards during the extrusion process. The practical operation of the Big Ben coring system from setting up a coring platform to collecting and safely extruding a core is detailed. Finally we summarise recent experiences of deploying the corer and highlight its potential uses in the developing field of multi-proxy palaeolimnology.  相似文献   

8.
Sub-bottom profiling and coring were undertaken at eight sub-basins along the lower French River and at five small lakes near North Bay, Ontario, to collect stratigraphical and chronological evidence to investigate whether lakes occupying the Huron–Georgian basins during the early- to mid-Holocene became hydrologically closed. All of the coring sites are located within the route of the North Bay outlet that carried outflow from the upper Great Lakes during this period. Sand beds containing organic detritus are present within five cores from Muskrat, Crombie and Deep bays that otherwise are composed of glaciolacustrine rhythmites or fine-grained lacustrine deposits. These sand beds are interpreted to represent intervals when water levels within the sub-basins were lower than present, based on chronology, sediment texture, and macrofossil assemblages. It is inferred that the water surface in the Huron–Georgian basins fell below the level of the Dalles Rapids sill isolating the lower French River sub-basins from the large lake. A core from Depensier Lake, North Bay, contains an organic-rich sand interval within a thicker sand unit barren of organic materials. Macrofossils within this organic-rich interval are interpreted to be evidence of substantially diminished flow through the North Bay outlet channel. Radiocarbon dates of terrestrial macrofossils provide correlation of the sand beds between the French River cores as well as with the organic-rich sand in the Depensier Lake core. The possibility that the sand beds in the French River cores represent flood deposits rather than evidence of hydrologically closed conditions is considered, but rejected, based on the occurrence of multiple peaty layers and the record of shallow water conditions inferred from macrofossils within the upper sand bed of core MUS1, Muskrat Bay, in combination with the evidence of quiescent depositional conditions from similarly aged macrofossils in the core from Depensier Lake. Eight radiocarbon dates from the French River cores are incorporated into an elevation-age plot of paleo-indicators of water levels in the Huron–Georgian basins, using additional data from the literature. This plot and stratigraphic evidence from the Muskrat Bay cores indicates that separate closed-basin intervals occurred between 9.0 and 8.4, and 9.5 and 9.3 ka cal BP (~ 8.1 and 7.6, and ~ 8.5 and 8.3 ka BP). The occurrence of these two closed-basin intervals between 9.6 and 8.4 ka cal BP (~ 8.7 and 7.6 ka BP) implies that run-off derived exclusively from precipitation within the non-glaciated portions of the upper Great Lakes drainage basins was likely insufficient at this time to support an open-basin lake hydrology during the contemporary climate, which was colder and drier than present, without being supplemented from glacial Lake Agassiz overflow and/or Laurentide Ice Sheet meltwater.  相似文献   

9.
Lacustrine sediment sampling equipment, such as lightweight gravity corers, are limited in operation to relatively shallow water environments (less than 50 m). This is because the ability to control such equipment becomes difficult with increasing water depth. In addition, adverse weather conditions, wind and waves etc. can further limit the success of such operations. The deep water equipment is designed to attach to gravity corers of the Kajak Brinkhurst type, and extend the operating depth by eliminating the need for direct control from the surface. The equipment stabilizes the corer on entry into the sediment and automatically closes the top of the core tube after driving is completed. No changes are required to be made to the corer whose mechanical operation remains the same.  相似文献   

10.
对南极沿海伯尔顿盐湖浮游桡足类双刺镰状水蚤(Drepanopus bispinosus)种群生态进行了全年连续观察和研究,结果表明,该水蚤为一年一代,其个体发育周期,雄性约为10～12个月,雌性约为12～18个月。种群密度随季节不同而差异较大,其成体高密度期约在6～9月份,幼体高密度期大约在11～12月份,主要为无节幼体,桡足幼体Ⅰ期的高密度期出现在1月份。该水蚤繁殖期大约从6月至翌年1月,期间出现两次生殖高峰,7～8月为前一高峰期,所出现的无节幼体受环境因子主要是湖中食物和含氧量不足的影响而不能继续发育至桡足幼体Ⅰ期以上的阶段,后一高峰大约在10～12月,所出期的无节幼体能继续发育至桡足幼体各期直至成体。伯尔顿湖双刺镰状水蚤种群生态特征及其出现两次生殖高峰的现象,可能与该湖环境的季节变化有关。  相似文献   

11.
Paleohydrologists sometimes use macrofossils of aquatic vascular plants as one of several independent lines of evidence to infer changes in past lake-levels. Typically, this usage relies on an assumption that the seeds of aquatic species are not dispersed far from the source plants. The water depth over the coring site at the time the seeds were deposited is inferred from the water depth at which the species generally grows today. We determined the water depths at which particular plant-remain types are deposited, and tested whether they can be used successfully as proxy evidence for lake level. The results should aid the interpretation of fossil seeds in paleohydrological studies. A total of 189 surface sediment samples from 13 lakes in Maine and Massachusetts were examined for plant remains, and vegetation was surveyed in the immediate vicinity of each sediment sampling-site. The seeds of some taxa were found in sediment from water-depth ranges much broader than those in which living plants occur. However, in combination, even plant-remain types with broad depth ranges can be used effectively to reconstruct water depth. Presence of plant-remain types can be used to infer water depth regardless of abundance. Test samples indicate that inferring water depth from plant remains works well for shallow, alkaline lakes in New England.  相似文献   

12.
深部盐矿勘探钻井液研究与应用   总被引：2，自引：0，他引：2       下载免费PDF全文
ZK001井钻遇地层为大段泥岩,部分地层为页岩、含盐泥岩、盐膏层。在泥页岩地层进行大口径全面钻进,钻速较快,固控设备能力有限,引起钻屑中粘土颗粒重复性膨胀、软化及裂解分散,最终可能造成粘土侵,对井内安全造成威胁。深部岩膏层易溶于水,从而导致盐层蠕变、井径扩大、井壁失稳等问题。以ZK001井为例,通过优化钻井液体系及现场施工工艺,解决了地层强造浆、盐层失稳等问题。通过岩石力学测试、阳离子交换容量测试、钻井液体系优选及性能测试,确定了上部地层采用聚合物钻井液体系,下部含盐层取芯钻进转换为饱和盐水钻井液体系。通过选用合适的钻井液密度、粘度、切力量、滤失量、含盐量等指标,可以有效控制上部泥岩井壁稳定、含盐层蠕变、井径扩大的问题。钻进过程中钻井液性能稳定且易于维护,从而保证了钻进工作安全、高效、顺利的进行。  相似文献   

13.
A new freeze corer is described that is specifically designed for operation in warm tropical lakes. It combines the standard wedge-shaped freeze-on container with a 20-liter thermos from which pellets of solid CO2 descend into the wedge to replace those that have sublimated. This extends the duration of effective freezing from ~20 to ~45 min, sufficient to form an adequate thickness of frozen crust in warm (> 22 °C) lakes and prevent its premature melting during retrieval through the water column. The instrument contains no electrical components, which simplifies construction, operation, and maintenance. The front and back surfaces of the freeze wedge are fitted length-wise with serrated ridges to facilitate removal of the crust as four rectangular sediment slabs. The feasibility of freeze coring studies in tropical regions is mainly determined by the local availability of a large-volume dry ice producer.  相似文献   

14.
In order to compare two widely used piston-coring techniques, parallel cores were taken with both a Kullenberg and a Livingstone corer in the deepest part of Soppensee (25 m), a small eutrophic Swiss lake containing varved sediments. The cores were taken within a horizontal distance of 3 m and yield comparable stratigraphic records. Differences in millimetre-scale microstructure are attributed to primary sedimentation processes at the water/sediment interface. Sediment thin-sections, as well as sediment x-radiograph investigations, reveal no difference in microstructure that could unequivocally be attributed to one of the coring methods used. The differences in deposition are therefore thought to reflect the inherent variability of lacustrine sedimentation in Soppensee.Major differences in overall core recovery do occur, however, in organic-rich, highly porous sediments. These variations are primarily attributed to differential gas expansion. Actual sediment-accumulation rates can therefore only be correctly estimated if the sedimentary record can be constrained within a high-resolution temporal framework, e.g. by annual laminations.  相似文献   

15.
A sub-bottom acoustic survey of Devil Lake on the Canadian Shield in southern Ontario reveals three acoustic facies: (I) a moderately acoustically transparent, laminated sequence interpreted as a glacilacustrine deposit in glacial Lake Iroquois or a subsequent phase in water depths up to 200 m greater than at present, (II) a transitional more transparent, less layered facies interpreted as being deposited in a more distal glacial lake from erosion of sediment in the watershed exposed by the failure of the ice dam and lowering of the glacial lake before stabilization by the development of forests, and (III) an acoustically transparent facies with similar transmissivity to the water column, interpreted as Holocene gyttja. Each is spatially variable in extent and thickness in response to those processes. There is only a very weak relation between sediment thickness and the water depth in which it was deposited. Wave processes prevent deposition in water depths less than about 6 m and evidence of erosion to the greatest depths of the lake (>40 m) is pervasive. The data demonstrate the value of acoustic survey in assessing lacustrine processes and the history of lakes, and the significance of such documentation in planning a coring program and in interpreting the results.  相似文献   

16.
The tephrochronology of the last 3000 years has been investigated in soil sections in north Iceland and in a marine sediment core from the north Icelandic shelf, 50 km offshore. Tephra markers, identified with major element geochemical analysis of volcanic glass shards, serve to correlate the marine and terrestrial records. Hekla 3, the largest Holocene tephra marker from the volcano Hekla, in south Iceland, dated to 2980 years BP, is used as the basal unit in the tephra stratigraphy. AMS 14C dating of molluscs in the sediment core shows variable deviation from the tephrochronological age model, indicating that the reservoir age of the seawater mass at the coring site has varied with time. A standard marine reservoir correction of 400 14C years appears to be reasonable at the present day in the coastal and shelf waters around Iceland, which are dominated by the Irminger Current. However, values over 500 years are observed during the last 3000 years. We suggest that the intervals with increased and variable marine reservoir correction reflect incursions of Arctic water masses derived from the East Greenland Current to the area north of Iceland.  相似文献   

17.
自1988年11月至1989年3月,对南极乔治王岛的长城湾沿岸水域中的海洋生物和环境因子进行了调查,1988年11月20日在2号站采得的冰芯中部有一层约5cm的棕色层,而1988年11月17日、20日和26日在5号站采得的冰芯样中有二层棕色层。固定冰中叶绿素a浓度范围在2.55～56.8mg/m~3之间,而且大部分含量集中在海冰的中间层中,而不象其它海区如昭和、戴维斯、凯西和麦克默多等站,大部分叶绿素a集中在海冰的底部,造成这种差别的原因、可能是由于海冰的结构和形成过程不同所致。  相似文献   

18.
冰芯钻取后，样品截取原则和环境记录的初步解释要求对年代－深度剖面有一初步了解，即要求建立冰体随深度变化的时间尺度。根据柯林斯冰帽一年多野外实测资料所揭示的小冰穹运动状况、温度分布、物质平衡和动力学特征，本文采用Ｄａｎｓｇａｒｒｄ－Ｊｏｈｎｓｅｎ模型和等温冰体流动模型（ｎ＝３），分别对一支８０．２ｍ冰芯的时间尺度进行初步估算。结果表明两种模型断代结果非常接近，在距冰床１０ｍ深度处，两模型分别给出１８９７年和１８５４年的冰龄。对比指出两种模型计算出的冰帽各深度冰龄最大误差不大于２％。与冰芯中上部含深褐色火山灰冰层的历史记录年代相比误差小于３％。  相似文献   

19.
珠穆朗玛峰北坡东绒布冰川成冰作用的新认识   总被引：7，自引：3，他引：4  
冰川成冰作用的研究对于选择冰芯钻取点具有重要的科学意义。前人对珠穆朗玛峰北坡冰川成冰作用的研究,由于缺少高海拔区域的实测资料而具有一定的局限性。文章通过1998年东绒布冰川垭口处(6 500 m a. s. l.)11 m冰芯和海拔6 450 m处20 m冰芯剖面的成冰作用过程研究,认识到由于水、热条件的逐年波动,冰川成冰作用也处于变化之中。珠穆朗玛峰北坡东绒布冰川高海拔区域,在一定的水、热条件下(如气温较低和降水量较大等),再冻结-重结晶作用依然占主导地位,该成冰作用至少在垭口部位是有分布的。而一般在气温较高或降水量较少等条件下,冰川的成冰作用则以冷渗浸-重结晶作用为主。  相似文献   

20.
Analysis of siliceous microfossils of a 79 cm long peat sediment core from Highlands Hammock State Park, Florida, revealed distinct changes in the local hydrology during the past 2,500 years. The coring site is a seasonally inundated forest where water availability is directly influenced by precipitation. Diatoms, chrysophyte statospores, sponge remains and phytoliths were counted in 25 samples throughout the core. Based on the relative abundance of diatom species, the record was subdivided into four diatom assemblage zones, which mainly reflect the hydrological state of the study site. An age-depth relationship based on radiocarbon measurements of eight samples reveals a basal age of the core of approximately 2,500 cal. yrs. BP. Two significant changes of diatom assemblage composition were found that could be linked to both, natural and anthropogenic influences. At 700 cal. yrs. BP, the diatom record documents a shift from tychoplanktonic Aulacoseira species to epiphytic Eunotia species, indicating a shortening of the hydroperiod, i.e. the time period during which a wetland is covered by water. This transition was interpreted as being triggered by natural climate change. In the middle of the twentieth century a second major turnover took place, at that time however, as a result of human impact on the park hydrology through the construction of dams and canals close to the study site.  相似文献   

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