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D. Newsome 《Australian Journal of Earth Sciences》2013,60(4):695-706
Views on the origin of sandplains in Western Australia remain controversial with debate focusing around three different models of formation. These are in situ, aeolian and in situ formation with local remobilisation by wind or colluvial transport. The only recent work on the subject to date espouses a dominantly aeolian origin. New work from a detailed study on the Victoria Plateau is described and demonstrates the applicability of utilising a range of evidence in understanding the origin of sandplains in Western Australia. Field investigations show a strong association of sandplain with sandstone and an absence of sand on non‐arenaceous geology in similar and adjacent topographic settings. Grainsize, mineral magnetic analysis and heavy‐mineral spectra show the Victoria Plateau to be a heterogeneous body of sand. These findings coupled with a lack of internal sedimentary structures are not consistent with an aeolian origin for the sandplain. Furthermore, scanning electron microscopy, grainsize and heavy minerals also demonstrate a clear link between bedrock and overlying sandplain. These data support the hypothesis that Western Australian sandplains are mostly the product of in situ weathering. Such findings question whether the origin of sandplains can be satisfactorily deduced without such a range of data. 相似文献
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根据大亚湾的自然条件认为,大亚湾沉积物的物质来源是其周围集水区的岩石风化壳,并计算了其风化壳中重金属元素的平均丰度值;又根据沉积物的粒度和深层沉积物重金属元素的含量资料,列方程计算出湾内沉积物中重金属元素的平均含量,根据这两组数据,确定该区域内重金属元素的平均背景值。再通过粒度关系,计算得出大亚湾内各站沉积物中重金属元素的背景值。应用此结果和大亚湾沉积物重金属元素实测结果,计算了由人为影响带入沉积物中的重金属元素含量,了解其受污染的程度。 相似文献
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XU Jiongxin Professor Institute of Geography Chinese Academy of Sciences Beijing China 《国际泥沙研究》1997,(3)
LINTRODUCTIONThetributariesofmiddleYellowRiverarefamousintheworldforthehighestsuspendedsedimentconcentrationandsedimentyield.Forexample,atWenjiachuanstationofKuyeheRiverthemeasuredhighestsuspendedconcentrationis1700kg/m',andthemeanannualsedimentyieldis25000t/(kln'.a).Theformationofhyperconcentratedflowsandtheirinfluenceonerosionprocessesareofgreatimportancenotonlyfromatheoreticalpointofviewbutalsoforpracticalpurposes.Therefore,scientistsfromChinaandallovertheworldhavedrawntheirintensio… 相似文献
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青海湖湖东沙地典型剖面的AMS14C测年数据表明该剖面记录了当地约10 ka BP的风沙活动及环境变化。对沉积物的粒度组成特征、粒度参数、粒度环境敏感指标等分析,并结合沉积物磁化率和青海湖盆地相关研究中风成砂、黄土和弱发育古土壤、古土壤的OSL、AMS14C年代数据等,进行全新世以来的风沙活动及气候环境变化讨论。结果表明：（1）粗颗粒敏感组分（138~156μm）可以用来指示风沙活动的强弱,细颗粒敏感组分（2~5 μm）可以用来指示成壤作用。（2）10~9ka青海湖盆地气候状况较全新世之前略有好转,暖湿程度增加,部分区域开始发育古土壤,但总体上古土壤、弱发育古土壤、黄土、风成砂共存;9~4.2 ka青海湖盆地水热组合条件较好,风沙活动弱,大部分沙丘固定成壤,但9~8 ka和4.2 ka左右风沙活动较为频繁的特征可能指示了8.2 ka和4ka冷事件;4.2 ka之后特别是2 ka之后风沙活动显著增强,气候朝干冷化发展。 相似文献
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罗布泊地区红柳沙包纹层沙粒度特征与环境指示意义 总被引：3，自引：2，他引：3
通过对罗布泊西南缘一个红柳沙包的132个清晰沉积纹层沙物质特征分析表明:所有沉积纹层沙物质均以细砂为主,占42.54～91.82%,其中1871-1874年纹层砂粒最细,1903-1910年纹层砂粒最粗;沙物质粒径分布在0.044～0.283mm之间,平均值0.095mm,中值粒径0.083mm;所有纹层沙物质的分选性都很好,分选系数分布在0.04～0.06之间,平均值0.05;偏态值分布在0.14～0.35之间,平均值0.19;峰态值分布在1.03～1.17之间,平均值1.13;沙物质粒度分维值分布在1.39～2.88之间,平均值2.80。除沙层厚度外,粒级组成、粒度特征参数、粒级分布曲线以及粒度累计概率曲线等也有较明确的环境指示意义。 相似文献
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青土湖沉积物粒度特征及其古环境意义 总被引：18，自引：6，他引：18
青土湖沉积物的粒度特征反映了青土湖降水、水动力搬运强度以及湖面水位高低的变化。利用石羊河古终端湖泊青土湖剖面沉积物的粒度资料，分析了粒度组成、粒度参数等粒度特征，并探讨了古终端湖泊的沉积环境。结果表明青土湖从11000aBP年以来大致经历了4次极端干旱时期和4次温暖时期。通过对青土湖沉积物粒度频率曲线的分析，讨论了湖泊的几种可能沉积作用，区分出了湖相沉积、风成沉积浅湖相沉积以及水流和风力作用混合沉积，从而揭示了沉积时的古环境特征。青土湖全新世以来的环境演变，具有连续和沉积速率大的特点，不仅可以作为古环境与古气候变化的自然记录，而且为研究本区土地退化、荒漠化等问题提供了自然背景。 相似文献
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根据某些研究成果和实际经验,结合一些新资料,对固溶体的出溶结构、矿物晶体成因类型,尤其对矿物结晶粒度的概率统计特征、矿石中元素组合及其演化规律的定量分析,首次提出新见解。在实际应用上,这些新见识对矿床成因研究乃至矿床的评价将起积极的作用。 相似文献
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The Lower Murrumbidgee alluvial fan at the eastern edge of the Murray Basin is comprised of high‐yielding coarse‐grained aquifers and interlayered fine‐grained deposits that exert an important control on recharge and vertical leakage of contaminants such as salt. Concerns over increasingly saline shallow groundwater, particularly in irrigation areas, has focused investigations on the depositional origin and spatial distribution of these fine‐grained deposits (aquitard units), which may constitute both a source of leachable salt and a barrier to leakage. Detailed laboratory analysis of a minimally disturbed core to 83m depth, obtained from a drillhole adjacent to an irrigation bore, was augmented with geophysical investigations from this and other boreholes near the apex of the alluvial fan. Previously mapped clay units (aquitards) are redefined as clayey silts based on clay content variation between 10% and 30%. Mineralogical and lithostratigraphic evidence for three clayey silt units is presented: a lower unit (75–83m), a middle unit (45–64m) and an upper unit (0–16m). Electrical image surveys indicate that the upper unit is discontinuous, interrupted by large palaeodrainage features probably containing sands and gravels. These palaeodrainage channels are buried beneath a veneer of clay and significantly increase recharge and leakage. Some evidence suggests an aeolian component near the surface and within the middle clayey silt unit. However, mixing with fluvial deposits and subsequent weathering has also occurred. The clayey silt units are extensively weathered and oxidised, with the degree of oxidation increasing towards the surface and adjacent to aquifers saturated with oxygenated groundwater. Post‐depositional weathering of the middle and lower units may also have been associated with leaching of salts. No salt remains in the middle and lower units, but 10.2kg/m2 is stored within 15m of the surface at the Tubbo site. The upper clayey silt unit is a significant source of leachable salt, which is associated with increasing shallow groundwater salinity at some sites. 相似文献
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The tephra fallout from the 12–15 August 1991 explosive eruption of Hudson volcano (Cordillera de los Andes, 45°54 S-72°58 W; Chile) was dispersed on a narrow, elongated ESE sector of Patagonia, covering an area (on land) of more than 100 000 km2. The elongated shape of the deposit, together with the relatively coarse mean and median values of the particles at a considerable distance from the vent, were the result of strong winds blowing to the southeast during the eruption. The thickness of the fall deposit decreases up to 250 km ESE from Hudson volcano, where it begins to thicken again. Secondary maxima are well developed at approximately 500 km from the vent. Secondary maxima, together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation. The fallout deposit is well stratified, with alternating fine-grained and coarsegrained layers, which is probably a result of strong eruptive pulses followed by relatively calm periods and/or changes in the eruptive style from plinian to phreatoplinian. The tephra is mostly composed of juvenile material: the coarse mode (mostly pumice) shifts to finer sizes with distance from the volcano; the fine mode (mostly glass shards) is always about 5/6 phi. Glass shards and pumice are mostly light gray to colorless. However, considerable amounts of dark, poorly vesiculated, blocky shards, suggest a hydromagmatic component in the eruption. A land-based tephra volume of 4.35 km3 was estimated, and a total volume of 7.6 km3 arose from an extrapolation, which took into account the probable volume sedimented in the sea. Bulk density ranges from 0.9 to 1.10 gr/cm3 (beyond 110 km from the vent). Rather uniform density values measured in crushed samples (2.45–2.50 gr/cm3 at all distances from the vent) reveal a relatively homogeneous composition. Mean and median sizes decrease rapidly up to 270 km from the vent; beyond that point they are more or less constant, whereas the maximum size (1 phi) shows a steady decrease up to 550 km. A concomitant improvement in sorting is observed. This is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent. The Hudson tephra fallout shares some strikingly similar features with the Mount St. Helens (18 May 1980) and Quizapu (1932) eruptions. 相似文献