Blanket mire formation at the Cross Lochs, Sutherland, northern Scotland     

DANIEL J. CHARMAN 《Boreas: An International Journal of Quaternary Research》1992,21(1):53-72

A brief review of the genesis of blanket peats is presented, together with detailed analyses of basal peats from northern Scotland. Particular attention is paid to local factors affecting peat growth and the problems of sampling and interpretation arising from them. Macrofossil and loss-on-ignition analyses of four peat-mineral interfaces solve many of the terminological problems of such profiles and indicate that interpretations based on field stratigraphy alone are uncertain. Pollen analyses of two profiles from contrasting microtopographic situations show well-defined vegetational change associated with early peat development. Fully organic ombrotrophic peat is present from 6805 ± 50 BP at one site, following anthropogenic burning from c . 7500 BP and partial recovery of the open birch woodland. A change from birch woodland to Calluna heath occurs at approximately the same time on a more freely drained site with much later peat development, following further burning from 4890 ± 65 BP. Anthropogenic activity is clearly associated with changes in soil and vegetation preceding peat formation, and the role of climatic factors remains equivocal.  相似文献   

Truncated flame structures within a deposit of the Indian Ocean Tsunami: evidence of syn‐sedimentary deformation     

DAN MATSUMOTO  HAJIME NARUSE  SHIGEHIRO FUJINO  APICHART SURPHAWAJRUKSAKUL  THANAWAT JARUPONGSAKUL  NORIHIKO SAKAKURA  MASAFUMI MURAYAMA 《Sedimentology》2008,55(6):1559-1570

This study reveals the three‐dimensional morphology and syn‐sedimentary formation processes of a deformation structure termed ‘truncated flame structures’ which is found in a terrestrial tsunami deposit in southern Thailand that formed during the 2004 Indian Ocean Tsunami. The structure was found at the boundary between a lower fine‐grained layer and an upper coarse‐grained layer that are related to two runup events. In order to confirm the morphology of the structure, the authors excavated two trenches and an opencast pit. When viewed in a cross‐section oriented parallel to the direction of the runup current, the deformed boundary has an irregularly bulging profile, similar to that observed in flame structures. The protruding structures are inclined towards the downstream direction of the runup current, and are truncated horizontally along their upper surface by parallel laminations in the overlying layer. When viewed in a cross‐section oriented perpendicular to the current direction, it appears that parts of the upper layer descend into the lower layer as lobate masses. In places, these masses are completely detached from the main part of the upper layer, forming circular or elliptical shapes. The contact between the lower layer and the main part of the upper layer is a planar truncation surface. Opencast excavation of the contact surface revealed that the deformed structures have flat, sinuous horseshoe crests that open in a downstream direction. It is possible for the runup current to generate shear stress such that it deforms the boundary into a truncated flame structure. Moreover, the observations made in this study indicate the syn‐sedimentary development of the structure: deformation and truncation occurred simultaneously in association with the runup current that formed the upper layer. Truncated flame structures can be used as a criterion in identifying the syn‐sedimentary deformation of substrate: the structures are indicative of unidirectional flow with sufficiently high shear velocity to deform unconsolidated substrate. As in the present case, the truncated flame structures may be characteristic of tsunami events that involve strong unidirectional currents on land due to the extraordinarily long wave period of tsunamis, rather than other events such as storm surges or flooding.  相似文献   

鄂尔多斯盆地姬塬地区长6储层渗流特征     

张三  马文忠  马艳丽  李成  淡卫东 《地质通报》2016,35(203):433-439

对鄂尔多斯盆地姬塬地区长6储层特征、微观渗流特征及影响因素进行综合研究,为开发前期评价提供科学依据。以铸体薄片、扫描电镜等分析化验资料为基础,应用恒速压汞、核磁共振等储层评价新方法对岩石类型、孔隙结构进行分析。研究表明,该区长6储层物性较好,粒间孔发育,储层孔隙结构好,以小孔、微细喉为主,可动流体饱和度高,渗流能力强,有利于高效开发。储层孔隙结构、成岩相及储层润湿性是影响相渗特征的重要因素。  相似文献   

Melt Generation by Plumes: A Study of Hawaiian Volcanism   总被引：18，自引：9，他引：9  

WATSON  SARAH; McKENZIE  DAN 《Journal of Petrology》1991,32(3):501-537

The mantle plume underlying the Hawaiian Swell has been modellednumerically using a stationary steady axisymmetric plume undera solid conducting lid. A method of calculating the rate ofmelt production from the plume has been developed, and the totalmelt production rate, the residual depth anomaly and the geoidanomaly have been used to constrain the model. The plume hasa central potential temperature of 1558 ?C and the mechanicalboundary layer is 72 km thick. An average of 6?6% melting occursin a melt-producing region which has a vertical extent of 55km and a radial extent of 130 km to produce 0?16 km³/y of melt.A parameterization of melt composition has been developed thatis consistent with laboratory experiments, with models of MORBgeneration, and with primitive Hawaiian tholeiites containing 16% MgO. There is no evidence that the major and minor elementconcentrations in the source region of Hawaiian tholeiites differfrom those in the source region of MORB. The model is consistentwith the REE contents of Kilauean tholeiites if the source regionhas primitive REE contents. The viscosity of the low-viscositylayer is constrained to be 10¹⁶m²/s.  相似文献   

Ostracod stable isotope records from a deglacial isolation sequence in southern Sweden     

DAN HAMMARLUND 《Boreas: An International Journal of Quaternary Research》1999,28(4):564-574

A Late Weichselian sediment succession from the Kullen Peninsula, southern Sweden, was studied by means of stable carbon and oxygen isotope analyses of calcitic valves of selected ostracod taxa. The lower part of the record was deposited in a slightly brackish marginal sea close to the receding inland ice, whereas the upper part is lacustrine in origin as a result of glacio-isostatic rebound. The site was deglaciated at c. 17 200 cal BP (c. 14 500 ¹⁴C BP) within the earliest ice-free area of Sweden, and the isolation took place c. 1100 cal years later. As a result of extensive input of glacial meltwater to the near-shore, shallow basin, the isotopic records predating the isolation give no clear indications of marine conditions. However, the isolation of the lake from the marginal sea is reflected by a distinct depletion of ¹⁸O in ostracod calcite as a response to the changing isotope hydrology of the basin. The change towards a lacustrine environment also fostered a decrease in the input of minerogenic material and a related increase in organic carbon content of the sediments, which may explain a short-lasting depletion of ¹³C in dissolved inorganic carbon and ostracod calcite. During the period of c. 14 700-13 900 cal BP a pronounced warming occurred associated with the onset of the Late Weichselian interstadial complex (Greenland Interstadial 1). Based on a distinct enrichment of ¹⁸O in ostracod calcite and applying modern spatial relations between δ¹⁸O of precipitation and temperature, this climatic shift involved an increase in mean annual air temperature in southernmost Sweden of at least 7°C.  相似文献   

藏南隆子县模麓温泉群水文地球化学特征及成因机制研究          下载免费PDF全文

周鹏  孙明露  张云辉  荣峰  达娃  万忠焱  刘恭喜  彭清华  胡华山  旦增  刘振峰 《沉积与特提斯地质》2023,43(2):322-339

藏南地区地热资源丰富,是喜马拉雅地热带的重要组成部分,有望成为新的地热资源开发靶区。本文以藏南桑日-错那活动构造带内模麓温泉群为研究对象,以水化学和氢氧氚同位素为研究方法,分析模麓温泉群的水岩作用、热储温度、补给来源及径流时间,揭示了地热水的成因机制。模麓地热水pH在6.6～7.2之间,TDS为1 908mg/L～2 326 mg/L,水化学类型以HCO3·Cl-Na型和HCO3·Cl-Na·Ca型为主。地热水中主要阴阳离子来源于硅酸盐矿物的溶解和少量地球深部物质。利用硅-焓方程法和硅-焓图解法计算的初始热储温度为198℃～256℃,冷水混入比例为68%～85%。此外,对地热水中的Li、B、F等微量元素分析得出,研究区温泉水中微量组分除来自水-岩作用外,应该还与深部流体的混入有关,且该地区的氢氧同位素特征表明地下水补给主要来源于大气降水,补给高程为5 652m～5 664m,模麓地热水中的氚含量<0.5TU,表明其地热水为老水,有更长的径流时间,为水-岩作用提供了充足的时间,而宿麦郎曲河水为新水,补给径流时间短。研究区地热水与围岩遮拉组砂板岩发生水-岩作用,进行离子交换作用,在地...  相似文献   

上黑龙江盆地前哨林场黑云母二长花岗岩锆石U-Pb年龄、地球化学特征及地质意义     

巩鑫  张志博  杜蔺  蔡国盛  宋小军  曾凡祥  李光春  苏永虎  但仕生  赵元艺 《地球学报》2023,44(6):1017-1035

上黑龙江盆地前哨林场位于兴蒙造山带东段额尔古纳微地块北缘, 北与西伯利亚古陆以蒙古—鄂霍次克缝合带相隔, 东以塔源—喜桂图断裂与兴安地块相邻。本文通过对上黑龙江盆地前哨林场黑云母二长花岗岩进行锆石U-Pb年龄、主微量及同位素地球化学系统研究, 为探讨早古生代额尔古纳微地块与相邻地块的碰撞机制提供理论依据。利用LA-ICP-MS锆石U-Pb同位素测定技术, 获得研究区黑云母二长花岗岩结晶年龄为(458.4±2.4) Ma(MSWD=0.022), 确定了岩体形成时代为早古生代中—晚奥陶纪。岩石中锆石Hf同位素?Hf(t)值介于–4.64 ~ 1.84, 其测点大部分位于球粒陨石演化线之下, 两阶段模式年龄(tDM2)介于 715 ~ 1 126 Ma。地球化学显示岩石具有富硅、富铝、富碱等特征; 稀土配分曲线表现出轻稀土(LREE)相对富集, 重稀土(HREE)相对亏损的右倾特征, 且岩石相对富集大离子亲石元素Rb、K及高场强元素Th、U、Zr、Hf, 相对亏损大离子亲石元素Ba、Sr及高场强元素Nb、Ta、P、Ti。岩石成因类型判别图显示前哨林场黑云母二长花岗岩具A型花岗岩特征, 岩石Hf同位素及微量元素特征显示岩体岩浆来源于中—新元古代古老地壳的熔融, 且存在少许幔源物质及新增生地壳物质熔融的参与, 元素特征暗示岩石形成于额尔古纳地块与西伯利亚古陆碰撞后的伸展构造环境背景下。结合前人对额尔古纳地块早古生代花岗岩形成背景的研究, 认为额尔古纳地块北缘及东北缘早古生代花岗岩形成机制不同, 前者形成于额尔古纳地块与西伯利亚古陆及蒙古—图瓦地块碰撞、拼接后伸展背景下; 后者主要形成于额尔古纳与兴安地块碰撞伸展背景下。  相似文献   

Climate-Vegetation Interannual Variability in a Coupled Atmosphere-Ocean-Land Model   总被引：1，自引：0，他引：1  

ZHI Hai  WANG Panxing  DAN Li  YU Yongqiang  XU Yongfu  ZHENG Weipeng 《大气科学进展》2009,26(3):599-612

The coupled models of both the Global Ocean-Atmosphere-Land System (GOALS) and the Atmosphere-Vegetation Interaction Model (GOALS-AVIM) are used to study the main characteristics of interannual variations. The simulated results are also used to investigate some significant interannual variability and correlation analysis of the atmospheric circulation and terrestrial ecosystem. By comparing the simulations of the climate model GOALS-AVIM and GOALS, it is known that the simulated results of the interannual variations of the spatial and temporal distributions of the surface air temperatures and precipitation are generally improved by using AVIM in GOALS-AVIM. The interannual variation displays some distinct characteristics of the geographical distribution. Both the Net Primary Production (NPP) and the Leap Area Index (LAI) have quasi 1-2-year cycles. Meanwhile, precipitation and the surface temperatures have 2--4-year cycles. Conditions when the spectrum density values of GOALS are less than those of GOALS-AVIM, tell us that the model coupled with AVIM enhances the simulative capability for interannual variability and makes the annual cycle variability more apparent. Using Singular Value Decomposition (SVD) analysis, the relationship between the ecosystem and the atmospheric circulation in East Asia is explored. The result shows that the strengthening and weakening of the East Asian monsoon, characterized by the geopotential heights at 500 hPa and the wind fields at 850 hPa, correspond to the spatiotemporal pattern of the NPP. The correlation between NPP and the air temperature, precipitation and solar radiation are different in interannual variability because of the variation in vegetation types.  相似文献   

On the relationship between flow and suspended sediment transport over the crest of a sand dune, Río Paraná, Argentina     

DAN H. SHUGAR  RAY KOSTASCHUK  JAMES L. BEST†  DANIEL R. PARSONS‡  STUART N. LANE§  OSCAR ORFEO¶  RICHARD J. HARDY§ 《Sedimentology》2010,57(1):252-272

The links between large‐scale turbulence and the suspension of sediment over alluvial bedforms have generated considerable interest in the last few decades, with past studies illustrating the origin of such turbulence and its influence on flow resistance, sediment transport and bedform morphology. In this study of turbulence and sediment suspension over large sand dunes in the Río Paraná, Argentina, time series of three‐dimensional velocity, and at‐a‐point suspended sediment concentration and particle‐size, were measured with an acoustic Doppler current profiler and laser in situ scattering transmissometer, respectively. These time series were decomposed using wavelet analysis to investigate the scales of covariation of flow velocity and suspended sediment. The analysis reveals an inverse relationship between streamwise and vertical velocities over the dune crest, where streamwise flow deceleration is linked to the vertical flux of fluid towards the water surface in the form of large turbulent fluid ejections. Regions of high suspended sediment concentration are found to correlate well with such events. The frequencies of these turbulent events have been assessed from wavelet analysis and found to concentrate in two zones that closely match predictions from empirical equations. Such a finding suggests that a combination and interaction of vortex shedding and wake flapping/changing length of the lee‐side separation zone are the principal contributors to the turbulent flow field associated with such large alluvial sand dunes. Wavelet analysis provides insight upon the temporal and spatial evolution of these coherent flow structures, including information on the topology of dune‐related turbulent flow structures. At the flow stage investigated, the turbulent flow events, and their associated high suspended sediment concentrations, are seen to grow with height above the bed until a threshold height (ca 0·45 flow depth) is reached, above which they begin to decay and dissipate.  相似文献   

2010年度大气科学领域项目评审与研究成果分析   总被引：2，自引：2，他引：0  

张朝林  丹利  罗斯琼 《地球科学进展》2010,25(12)

1 2010年项目申请、送审与资助情况2010年地球科学五处共受理各类项目863项,比2009年(768项)增加了95项。面上项目、青年基金和地区基金3类项目共791项。天气与气候  相似文献