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1.
张琛  孙顺才 《湖泊科学》1991,3(1):16-24
通过地质调查, 钻孔样品分析及历史资料对比, 得出:1.巢湖位于在中新生代形成的巢湖断陷盆地南部, 形成于更新世发育的河谷平原上, 由于全新世受气候及相应海平面变化和长江河道演变等三者共同影响而积水成湖。成湖历史大约2000年左右, 属河成型浅水湖。2.湖底沉积物平均中值粒径5-6ф, 并形成有三角洲沉积, 开阔湖沉积等五种沉积类型, 东、西、中三湖区的沉积物中分別为0.21, 0.37, 0.14cm/a, 全湖年淤积总量为93×l04t/a。3.湖泊污染加重起始于70年代, 磷除来自外源外, 内负荷引起的释放量达220.56t/a, 这对巢湖富营养化亦有着重要的影响。  相似文献   

2.
冲绳海槽年代地层与沉积速率   总被引：32，自引：1，他引：31  
采用AMS14 C ,常规14 C和ESR等方法 ,对冲绳海槽的 6个代表性岩芯进行了对比测年研究 .同时 ,对各岩芯连续性定向样品 ,进行了系统剩磁测量分析 .利用测年数据 ,特别是浮游有孔虫壳体的AMS14 C年龄 ,标定极性事件和极性漂移 ,并据此计算了各站及不同时代的沉积速率 .结果表明 ,槽底平原沉积速率高 ,不亚于东海陆架 ,一般在 1 0～ 30cm/ka之间 ,某些区域高于 40cm/ka ;同时代不同地貌部位或同地貌部位不同时代 ,沉积速率相差较大 ;冰后期沉积速率高于末次冰期沉积速率  相似文献   

3.
石梁河水库是江苏省最大的人工湖泊.开展水库沉积速率研究,对认识水库环境变化具有重要意义.本文对石梁河水库沉积物岩芯粒度组成特征进行了分析,表明沉积物以黏土质粉砂和粉砂质黏土为主,从底部向上呈明显的变细趋势,并记录了1970年的强降雨事件.采用137Cs同位素测年分析,得到1963年和1986年两个时标.通过石梁河水库的沉积年代序列,推算出平均沉积速率:1963 1970年为10.85 cm/a,1970 1986年为3.81 cm/a,1986 2005年为1.32 cm/a.对比粒度沉积特征和流域降水记录,粗颗粒物质和降雨量的变化趋势基本相同,沉积物粒度组成特点直接反映了沉积时的降水、水动力搬运强度等信息.在河川来水来沙、坝前水位变化和地形等条件下,石梁河水库表现为三角洲淤积,且沉积速率逐渐变缓,符合水库淤积的一般规律.此外,石梁河水库上游建设的众多大型水库,拦截了大量泥沙,也使得沉积速率呈现减小趋势.  相似文献   

4.
人类活动影响下的固城湖环境变迁   总被引：2，自引：1，他引：1  
2005年在江苏固城湖湖心采集了连续岩芯,进行了多环境代用指标(有机碳、氮、磷以及金属元素)的分析.210Pb CRS模式计算表明,1980s后沉积速率平均约0.067 cm/a,与137Cs 1986年时标得到的沉积速率吻合.而1920s至1980s,固城湖沉积速率变化较大,在0.056-0.167cm/a之间,其中1960s沉积速率最高,对应于该阶段固城湖强烈的人类围垦活动.元素Cu、Pb、Zn、Cr的含量在表层增长迅速,对比参考元素的变化,表明固城湖受到了一定程度的人为造成的重金属污染.岩芯0.5m到1.78m深度的AMS 14C的树轮校正年龄在8000-6500BC之间,光释光数据表明同等深度其绝对年龄在7-8ka之间,多环境代用指标在岩芯30cm深度左右出现了大的转折,表明近代存在沉积物缺失的可能。这也许与该区春秋末期以来的反复围垦活动有关,人类活动改变了湖泊沉积的模式.有资料表明,固城湖彻底与太湖隔绝是在公元1556年胥溪河河段下坝建成之后.若依此时间对应于岩芯30cm深度,得到的平均沉积速率为0.067cm/a,与1980s以来的沉积速率一致,有可能指示固城湖至下坝建成以来才出现沉积物的持续沉积.  相似文献   

5.
137Cs质量平衡法测算青海湖现代沉积速率的尝试   总被引：4，自引：0，他引：4  
张信宝  曾奕  龙翼 《湖泊科学》2009,21(6):827-833
本文是~(137)Cs质量平衡法测算青海湖现代沉积速率的尝试.青海湖和其他低沉积速率湖泊沉积物剖面中,深度数cm处的~(137)Cs蓄积峰,也可能是沉降到底泥表面的~(137)Cs尘埃,以扩散和迁移的方式向下入渗形成.因此,将沉积剖面中的~(137)Cs蓄积峰解释为1963年的沉积,并据此计算沉积速率,未必合理.青海湖湖滨草地测得的2005年~(137)Cs本底值为1 17.7mBq/cm~2.湖泊中部海心山到东南部渔场一线的6个孔的~(137）Cs面积活度介于92.9-325.0mBq/cm~2,其中青海湖东南部两个孔的~(137)Cs面积活度较高,分别为本底值的155%和270%;湖泊中部4个孔的~(137)Cs面积活度略高于或低于本底值.显然,湖泊东南部有明显沉积发生,特别是位于江西沟冲积扇前缘水下部分的QHH02孔,沉积强烈,水深也最小;湖泊中部沉积轻微.根据表层底泥样品的~(137)Cs浓度,入湖河流泥沙的~(137)Cs浓度和流域内草地表层土壤~(137)Cs浓度的分析,初步确定C=30mBq/g,为1963年以来青海湖沉积泥沙的平均~(137)Cs浓度.利用~(137)Cs质量平衡模型求得的湖泊中部的平均沉积速率为0.020cm/a,和根据布哈河输沙模数求算出的青海湖平均沉积速率0.018cm/a吻合,远低于已报导的断代法测定的青海湖沉积速率.湖泊东南部的沉积速率大于湖泊中部,QHH02孔的沉积速率高达0.229cm/a,是已报导的青海湖沉积速率的两倍.  相似文献   

6.
辽东湾地区古近系层序地层格架与沉积体系分布   总被引：11，自引：0，他引：11  
充分利用地质和地球物理资料,依据层序界面特征,将辽东湾地区古近系孔店组-东营组划分为4个二级层序和10个三级层序.各三级层序可细分为低位体系域、湖侵体系域和高位体系域.低位体系域主要由进积准层序组构成,湖侵体系域主要由退积准层序组构成,而高位体系域则以进积式准层序组为主.沉积类型主要有滨浅湖、半深湖、深湖、三角洲、扇三角洲、辫状河三角洲和近岸水下扇.扇三角洲和辫状河三角洲沉积体系主要分布在早期的SEs4-Ek,SEs3和SEs1 2层序中,SEd3,SEd2和SEd1层序则以三角洲沉积为主,近岸水下扇沉积体系在各层序的凹陷边界断层下降盘发育.沉积体系在平面与纵向上的演化常受古构造与古地貌的控制.最后指出最有利的储集区位于辽西低凸起和辽中凹陷,辽西凹陷中部为较有利储集区.  相似文献   

7.
乌兰花凹陷位于二连盆地南部温都尔庙隆起上,是白垩纪开始形成的一个陆相湖盆,主要发育阿尔善组四段和腾格尔组一段.阿尔善组四段沉积时,凹陷断裂活动剧烈、沉降速率高,凹陷整体以深湖—半深湖环境为主,发育规模小、沉积时间短的扇三角洲、近岸水下扇和湖底扇.腾格尔组一段沉积时,断裂活动依然剧烈,但在凹陷南部陆源碎屑物质的供给率大于凹陷的沉降率,因此发育大面积的扇三角洲沉积;而在凹陷北部陆源碎屑物质供给仍然较少,为深湖—半深湖环境.通过对已有钻井的分析发现,在阿尔善组四段,砂体的展布主要受古地形的控制,有利储层主要为湖底扇的辨状水道砂体;而在腾格尔组一段,砂体的展布主要受沉积物供给和古地形的控制,有利储层主要为扇三角洲前缘水下分流河道砂体和席状砂砂体.  相似文献   

8.
青藏高原上分布着大量的大陆性冰川,其对区域及全球气候变化响应极其敏感.工业革命以来,随着全球升温速率加快(特别是北半球),青藏高原部分地区的冰川在近百年显著退缩.冰前湖沉积物是最直接的冰川变化记录载体之一,但其沉积速率如何响应冰川及气候变化,能否反演冰川进退过程却知之甚少.本文依据~(210)Pb和~(137)Cs限定藏南冰前湖枪勇错QY5沉积岩芯的年龄,计算出不同深度沉积物的沉积速率,且与前人(QY-3)的沉积速率进行对比,揭示了近百年来枪勇错流域冰川变化历史及其与气温之间的关系.结果表明,枪勇错QY5近百年来的平均沉积速率为0.21 cm/a,比湖心(QY-3)快2倍左右,但两者的变化基本同步,高沉积速率对应温度上升期,是冰川退缩的直接响应:(1)1900—1960年,枪勇错沉积速率整体增加且变幅较大,与1890—1950年之间西藏温度波动式升高相对应,反映枪勇冰川总体处于退缩状态;(2)1960—1985年,沉积速率低且变幅较小,同期气温下降,枪勇冰川退缩程度相对较低且保持平稳;(3)1985年以来,枪勇错沉积速率呈上升趋势,是全球增暖下冰川显著退缩的直接响应.在短时间尺度内冰前湖沉积速率所揭示的枪勇冰川变化主要受控于温度,降水量对冰川变化的影响较小,但冰川对温度变化的响应滞后5～10 a.由于全球变暖和冰川对温度响应的滞后,在未来几十年高原冰川的融化速率可能会加快,亚洲水塔将面临着新的挑战.  相似文献   

9.
呼伦湖晚第四纪湖相地层沉积学及湖面波动历史   总被引：2，自引：1，他引：2  
对内蒙古呼伦湖盆地扎赉诺尔地区晚第四纪湖泊沉积物进行了沉积学(沉积构造、结构、垂向层序等)和~(14)C年代地层学研究,并逐层识别出地层剖面的各种沉积相类型,包括开阔湖、近岸带、滨岸沙滩、滨岸沼泽和滨岸沙丘等不同类型沉积,依此恢复了30kaB.P.以来的湖泊演化和湖面波动历史。其中13～11kaB.P.是湖面最高时期,10.9～0.6kaB.P.的低湖面可能与新仙女木事件有关。  相似文献   

10.
C油田钻后揭示砂体横向变化快,需利用地震沉积学刻画储层平面展布,进一步落实储层.通过地震沉积学技术,识别了曲流河、辫状河、三角洲前缘及平原三类沉积体,理清了花上段垂向沉积演化规律.垂向上由三角洲平原演变为三角洲前缘、辫状河,最后演变为曲流河.研究区发育薄层、厚层及互层三类储层,不同类型的储层需采用不同策略去刻画.对于薄层,要小时窗提取属性,同时多属性融合刻画;对于厚层,要大时窗提取属性刻画;对于互层,要抓重点层合并刻画,反演地震和常规地震相结合分析.在落实储层的基础上,对C油田进行潜力搜索.H4层在C-A1井西侧储层上倾尖灭,具备发育岩性圈闭的条件,是下一步挖潜的主要方向.  相似文献   

11.
From 1998 to 2002 investigations were carried out to estimate both the quantity and quality (heavy metal contents) of suspended matter loads discharged into a floodplain area measuring approx. 5 km2 of the Central German river Weiße Elster, a tributary of the river Saale in the Elbe river basin. Flood sediments, suspended particulate matter, and floodplain soils were investigated especially for the main pollutants Cd, Zn, Cu, Pb, Cr, and Hg. Supplementary gamma spectroscopy examinations were performed to help to identify the age of deposits in order to estimate sedimentation rates for last decades. The recent flood sediments are contaminated by up to 33 times the geogenic background (Cd). Up to 55% of the total annual SPM load of the river Weiße Elster is relocated into the investigated retention area in the flood‐stricken year 2002. The sedimentation rates for the last 50 years vary between 0.5 mm/a and 1 mm/a in far away and rarely flooded parts and between 1 mm/a and 2 mm/a in the frequently flooded parts of the inflow of the retention area.  相似文献   

12.
The embanked floodplains of the lower River Rhine in the Netherlands contain large amounts of heavy metals, which is a result of many years deposition of contaminated overbank sediments. Depending on local sedimentation rates and changing pollution trends in the past, the metal pollution varies greatly between different floodplain sections as well as vertically within the floodplain soil profiles. Maximum metal concentrations in floodplain soils vary from 30 to 130 mg/kg for Cu, from 70 to 490 mg/kg for Pb and from 170 to 1450 mg/kg for Zn. In the present study these metals were used as a tracer to reconstruct sedimentation rates at 28 sites on the lower River Rhine floodplains. The temporal trend in pollution of the lower River Rhine over the past 150 years was reconstructed on the basis of metal concentrations in sediments from small ponds within the floodplain area. Using a one‐dimensional sedimentation model, average sedimentation rates over the past century were determined using an inverse modelling calibration procedure. The advantage of this method is that it uses information over an entire profile, it requires only a limited number of samples, it accounts for post‐depositional redistribution of the metals, and it provides quantitative estimates of the precision of the sedimentation rates obtained. Estimated sedimentation rates vary between about 0·2 mm/year and 15 mm/year. The lowest metal concentrations are found in the distal parts of floodplain sections with low flooding frequencies and where average sedimentation rates have been less than about 5 mm/year. The largest metal accumulations occur in low‐lying floodplain sections where average sedimentation rates have been more than 10 mm/year. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

13.
Paleomagnetic and/or micropaleontological studies have been carried out on approximately 28 sedimentary cores of latest Pleistocene age from the Gulf of Mexico. Sedimentation rates range from 9 cm to 20 cm/1000 yr. A distinct excursion in the earth's magnetic field occurs in the upper parts of 8 of 15 cores for which paleomagnetic studies were conducted and is independently correlated with planktonic foraminiferal zones. An inclination change to zero or negative inclination is often associated with a declination change. The age of the excursion was determined by extrapolation of sedimentation rates from the Z-Y paleontological boundary which is dated at 11,000 B.P. The magnetic excursion occurred between 12,500 and 17,000 yr ago within the upper part of zone Y. This falls within the age range of the Laschamp Event as originally defined.  相似文献   

14.
The GEF/UNDP/IMO/PEMSEA project identifies Manila Bay as among the marine pollution hot spots in the Seas of East Asia. 210Pb dating of its sediment can provide a historical perspective of its pollution loading. However, the validity of 210Pb dating in a complex dynamic coastal system of Manila Bay may come into question. Land-based sediment input can be high and physical and biological processes can possibly disturb the sediment layers. In this report, the 210Pb profiles of sediment cores from different parts of the bay are presented. The linear sedimentation rates are shown to be higher in the recent past and are also variable across the bay. The largest change in sedimentation rate, coincided with the occurrence of a volcanic eruption in 1991 and is shown by applying a variant of the CIC model in sedimentation rate calculations. The data suggest that 210Pb dating can be useful in estimating relative magnitudes of sedimentation rates, even in a complex dynamic coastal system like Manila Bay.  相似文献   

15.
Understanding sedimentation patterns in small coastal watersheds due to landscape perturbations is critical for connecting hillslope and fluvial processes, in addition to managing aquatic habitats for anadromous fish and other aquatic species in the Oregon Coast Range (OCR). Changes in sedimentation patterns spanning the last 250 years are preserved in two landslide-dammed lakes in small watersheds (< 10 km2) underlain by the Tyee Formation in the central OCR. Dendrochronology of drowned Douglas-fir stumps in both lakes provided precise timing of the damming and formation of the lakes, with Klickitat Lake forming in winter ad 1751/52 and Wasson Lake in winter ad 1819/20. Perturbations from wildfires, logging and road development, and previously underappreciated snow events affect sedimentation rates in the lakes to different degrees, and are identified in the sediment record using cesium-137 (137Cs), high-resolution charcoal stratigraphy, local fire records, and aerial photography. Each lake has variable sedimentation accumulation rates (0.05–4.4 cm yr−1) and mass accumulation rates (0.02–1.42 g cm−2 yr−1). Sedimentation rates remained low from the landslide-damming events until the mid-19th century, when they increased following stand-replacing wildfires. Aside from a sediment remobilization triggered by human modification of the landslide dam at Klickitat Lake around 1960, the largest peaks in mass accumulation rates in the mid-20th century at both lakes in the early 1950s precede major road construction and logging activity in the watersheds. Subsequent sedimentation rates are lower, but variable, and possible effects of logging and road development might be exacerbated by abnormal precipitation and heavy snow events. A comparison of previous studies of landslide-dammed lakes in larger watershed of the OCR are consistent with our findings of increased sedimentation in the mid-20th century, as well as higher sedimentation rates in the debris-flow dominated southern Tyee Formation than in the lower-relief northern Tyee Formation.  相似文献   

16.
Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land-use changes and climatic variability are hindering the actions needed to future-proof Tanzanian land-use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20-fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land-use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land-use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality.  相似文献   

17.
Sediment geochemical techniques were used to assess how the sediment record reflects the loading and land use history of Laajalahti Bay, a semi-enclosed bay adjacent to the city of Helsinki, Finland. A dated sediment core was analysed for concentrations of Al, Ca, K, Mg, Na, Fe, Mn, Cu and Zn and total concentrations of C, N and P together with P fractions and biogenic silica (BSi) at intervals of 1 cm to a depth of 88 cm. Furthermore, five phases of development were identified in the sediment record by using principal components analysis and cluster analysis. The lithology of the core indicates sharp changes in the sedimentation environment in the earlier history of the embayment that are most likely due to isostatic uplift and changes in salinity. The most prominent recent trends were the increasing sedimentation rates and nutrient concentrations towards present. In addition, significant increases were observed in the concentrations of anthropogenic indicators Cu and Zn. In spite of decreased nutrient loading to Laajalahti Bay no significant signs of improvement were observed in the sediment record yet.  相似文献   

18.
This paper focuses on one aspect of riparian zone change associated with channel incision. It presents information on sedimentation within the riparian zone of the River Garonne, France, derived from both historical and contemporary sources. The riparian zone investigated is morphologically complex, containing a remnant island and cut‐off channel. Information drawn from historical and contemporary sources permits the reconstruction of channel planform and cross‐profile change, as well as an assessment of changes in riparian zone sedimentation rates and patterns. Very significant changes are identified over the last 50 years: a change from a multiple thread to single thread channel planform; high rates of riparian zone sedimentation of the order of 0·5 to 2·5 cm a−1; clear spatial patterns in over‐bank sedimentation, reflecting topographic and vegetational variations and flood event magnitude; and a reduction in morphological and vegetational diversity through the period, which is expected to continue as the zone is transformed into an increasingly homogeneous sediment sink. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

19.
Palaeomagnetic measurements on three cores from the Tyrrhenian Sea abyssal plain appear to provide evidence of short-period geomagnetic secular variation during historical times. Using these patterns of variation a method is proposed to determine the relative sedimentation rates between cores.Tentative correlation with dated secular variation curves from Lake Windermere, England (R. Thompson, 1973) gives absolute sedimentation rates for the Tyrrhenian cores in the range 65–130 cm/1000 years.  相似文献   

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