沉积谷中衬砌隧道对SH波的散射

现实中衬砌隧道穿越沉积谷地十分常见,而国内外对其地震响应规律研究较少。基于MATLAB编程平台,采用间接边界积分方程法,就沉积谷地衬砌隧道对平面SH波的散射问题进行了初步探讨。研究了不同频率、隧道埋深与入射角度对地表位移和衬砌内外壁动应力集中因子的影响,并比较了沉积谷地中隧道与半空间隧道两种情况下的差别。结果表明:软土沉积中隧道衬砌动应力集中更为显著;高频波入射下,隧道埋深对沉积区域内位移分布、衬砌应力频谱特性和地表位移频谱特性均有较大影响。研究结论可为沉积谷地中衬砌隧道抗震设计与安全性评估提供定量依据。

半球形饱和土沉积谷场地对入射平面Rayleigh波的三维散射问题的解析解

用Biot饱和多孔介质动力学理论模拟半球形两相饱和土沉积谷,用单相介质弹性动力学理论模拟周围半空间场地.利用Fourier-Bessel级数展开法,在频域内给出了半空间中半球形饱和土沉积谷场地在平面Rayleigh波入射下三维散射问题的解析解.利用这一解析解计算分析了入射波频率、场地特征(包括孔隙比)对地表位移幅值的影响,并与已有的三维半球形沉积谷场地在单相介质中的散射问题进行了对比分析.

半球形沉积谷场地对入射平面Rayleigh波的三维散射解析解

把半球形沉积谷和周围半空间场地分别用具有不同弹性模量和不同半径的球坐标描述。利用Fourier-Bessel级数展开法,在频域内给出了半空间中半球形沉积谷场地在平面Rayleigh波入射下三维散射问题的解析解。利用这一解析解计算分析了入射波频率、场地软硬对场地内地表位移幅值的影响。

正交各向异性半圆形沉积谷对SH波的散射

采用波函数展开法给出了具有圆柱型正交各向异性半圆形沉积谷地形对SH波散射的解答,研究了入射波特性和沉积谷的各向异性对地面运动的影响。稳态SH波入射时,在圆柱型正交各向异性沉积谷中波函数的径向函数满足非整数阶的Bessel方程。数值结果表明:沉积谷地表位移的幅值大小与入射波的频率、入射方向、沉积谷介质的径向与环向剪切模量比及半空间与沉积谷剪切波速比和密度比密切相关,当沉积谷介质比半空间介质软时,沉积谷地表位移幅值明显增大,与各向同性介质的沉积谷地相比,沉积谷介质的各向异性对地面运动的影响非常显著。

饲料中添加谷胱甘肽对草鱼组织中谷胱甘肽沉积和抗氧化能力的影响

在基础饲料中分别添加还原型谷胱甘肽(GSH)至0mg/kg、100mg/kg、200mg/kg、300mg/kg、400mg/kg和500mg/kg,分别投喂草鱼(Ctenopharyngodon idella)幼鱼8周,草鱼幼鱼体质量(4.09±0.01)g,观察GSH在草鱼组织中沉积以及对草鱼抗氧化功能的影响。结果表明,饲料中添加外源GSH对草鱼生长影响不显著(P>0.05),实验组肌肉中GSH含量显著高于对照组(P<0.05),肝脏中GSH含量在GSH添加水平为200mg/kg时显著高于对照组(P<0.05),肝脏和肌肉中丙二醛(MDA)在GSH添加水平为300mg/kg组达到最低,显著低于对照组(P<0.05)。添加GSH对血清中GSH和MDA影响不显著(P>0.05)。草鱼肝脏中谷胱甘肽还原酶(GR)活力在400mg/kg组显著高于对照组(P<0.05),肌肉中GR活力有增高趋势但差异不显著(P>0.05);肝脏和肌肉中γ-谷氨酰转移酶(γ-GT)均高于对照组,分别在300mg/kg组和200mg/kg组达到显著水平(P<0.05);肝脏中谷胱甘肽过氧化物酶(GSH-PX)活力、总抗氧化能力(T-AOC)和超氧化物歧化酶(SOD)能力不同程度升高,均在200mg/kg组达到最高,显著高于对照组(P<0.05);血清GSH-PX活力和T-AOC有增高趋势但与对照组差异不显著(P>0.05);血清和肝脏中活性氧(ROS)含量分别在400mg/kg和300mg/kg组达到最低,显著低于对照组(P<0.05)。结果提示,饲料中添加GSH能够促进草鱼肝脏和肌肉中GSH的沉积,提高肝脏及肌肉中GR和γ-GT活力,以及肝脏中GSH-PX和SOD活力与总抗氧化能力,减少肝脏中MDA含量,降低肝脏及血清中ROS含量,因此GSH在水产饲料中具有广泛的应用前景。

陕西府谷高岭土矿沉积环境与成矿关系研究

通过对高岭土矿及含矿沉积环境分析,认为府谷地区沉积型硬质高岭土矿分别形成于海岸后受淡水控制的湖泊、三角洲分流间湖泊、三角洲平原湖泊和曲流河岸后湖泊等。不同沉积环境其矿体特征、矿石类型及工业用途不同。海岸后受淡水控制的湖泊、三角洲分流间湖泊型沉积高岭土矿规模巨大,分布范围广,但高岭石含量低,杂质含量高,质量较差,工业用途受限用于制瓷业。而三角洲平原湖泊和曲流河岸后湖泊型矿床规模较前者小些,但高岭石含量高,杂质含量低,质量好,用于造纸、涂布原料及分子筛等。该项研究成果对高岭土矿勘查及其工业利用有所帮助。

半球形凹陷谷场地对Rayleigh波的三维散射

利用半空间场地用单相介质动力学理论模拟,并略去阻尼项的影响,首次推导出了三维半球形凹陷谷场地在平面Rayleigh波入射下散射问题的解析解。确定局部场地的三维波场分布,给出半球形沉积谷场地地表位移分量,分析了入射波频率对场地震动的影响,并进一步与单相弹性介质情况下的地表运动进行了对比。

Extreme Flood Events over the Past 300 Years Inferred from Lake Sedimentary Grain Sizes in the Altay Mountains,Northwestern China

Understanding the temporal variations of extreme floods that occur in response to climate change is essential to anticipate the trends in flood magnitude and frequency in the context of global warming. However, long-term records of paleofloods in arid regions are scarce, thus preventing a thorough understanding of such events. In this study, a reconstruction of paleofloods over the past 300 years was conducted through an analysis of grain sizes from the sediments of Kanas Lake in the Altay Mountains of northwestern China. Results showed that grain parameters and frequency distributions can be used to infer possible abrupt environmental events within the lake sedimentary sequence, and two extreme flood events corresponding to ca. 1736–1765 AD and ca. 1890 AD were further identified based on canonical discriminant analysis(CDA) and coarse percentile versus median grain size(C-M) pattern analysis, both of which occurred during warmer and wetter climate conditions by referring to tree-ring records. These two flood events are also evidenced by lake sedimentary records in the Altay and Tianshan mountains. Furthermore, through a comparison with other records, the flood event from ca. 1736–1765 AD in the study region seems to have occurred in both the arid central Asia and the Alps in Europe, and thus may have been associated with changes in the North Atlantic Oscillation(NAO) index.

Application of Grain Size Analysis to Study Sedimentary Environment of Sand Dune in the Vicinity of Tumen River

The average size of the sand of dune in the vicinity of Tumen River is 0.12～0.30 mm, its standard deviation is 0.45～0.99 φ and the frequency cumulative distribution curve is divided into the single peak and the double peak. The Ski of the single peak is negative and the double peak is positive. There are two different areas in the plot of the Ski versus σi* It is shown that the sedimentary environment of the dunes is neritic deposit by the expressions of the grain-size parameters. All of the characters show that the sand dunes in Estuary of Tumen River may be the dunes of sea facies which were changed again by weathering and fluvialaction.

New findings concerning the Pleistocene Glaciation of the Leh Basin,Ladakh(34°03'N/77°38'E)

Like for most parts of High Asia,researches concerning the Pleistocene landscape evolution of the Leh Basin(34°03' N/77°38' E) have also left contradictions.To push this topic,three up to now unexplored Ladakh Range tributaries of the Leh Basin(Stagmo-,Arzu-and Nang-Valley) have been investigated.U-shaped profiles,transfluence passes,moraine mantled and glacially rounded peaks and ridges,roches moutonnées,glacial flank polishings and ground moraines document the former glaciation of the study area.The ice fillings of these tributaries reached a minimum thickness up to 540 m.Even at the valley outlets and on the orographic right side of the Leh Basin,the glaciation was more than 350 m thick.Based on these empirically extracted results,theoretical snow line considerations lead to the conclusion that the whole Leh Basin was filled up by a former Indus-Valley glacier.An ice injection limited to the nourishment areas of the Ladakh Range valleys could not have caused the reconstructed ice cover(down to 3236 m a.s.l.),which is proved by extended ground moraine complexes.Only an Indus ice stream network(most likely during the LGP),nourished by inflowing glaciers of the Ladakh-and Stok Range,explains the widespread existence of the glacial sediments at the outlets of the investigated valleys.

Suspended sediment dynamics in the meltwater of Chhota Shigri glacier, Chandra basin, Lahaul-Spiti valley, India

Present study shows suspended sediment dynamics in the meltwater of Chhota Shigri glacier,Himachal Pradesh,India for different melt seasons during the period 2011-2014.Maximum suspended sediment concentration in the meltwater was found during the month of July 2011,2012 and 2014 constituting to 55.2%,48.3% and 46.9%,respectively.Whereas in 2013,maximum suspended sediment concentration was observed in August accounting for46.1% of the total.On the other hand,maximum suspended sediment load was monitored in the month of July 2011,2012 and 2014 constituting 59.5%,63% and 55.7% of the total,respectively.Whereas in2013,maximum suspended sediment load was observed in the month of August accounting for 49.8% of the total suspended sediment load.Annual distribution of suspended sediment concentration(SSC)and suspended sediment load(SSL)in the Chhota Shigri glacier shows higher value of SSC and SSL during the study period 2012 and 2013,which may be due to the presence of high glacial runoff and negative mass balance of the studied area during these time periods.Marked diurnal variation has been observed in the SSC of meltwater.Strong correlation was observed between SSC and SSL with discharge.On the other hand,SSC and SSL also showed strong exponential correlation with air temperature of the studied area.Sediment yield from the catchment of Chhota Shigri glacier is high during the peak melt season(July and August)and low during the late melt season(September and October).The average value of erosion rate for Chhota Shigri glacier basin during the study period 2011-2014 was calculated to be 1.1mm/yr,which is lower than the average erosion rate of other Himalayan glaciers such as Rakiot,Chorabari and Gangotri glaciers,which may be caused by its geological setting containing high erosion resistant rocks such as granite,granite gneiss and porphyritic granite.

Oxygen and hydrogen isotope ratios of chert from the Sixtymile Formation in Grand Canyon National Park,USA：a warm palaeoclimate,freshwater deposit

New oxygen and hydrogen isotope ratios of chert from middle, intraformational breccias, and upper breccia members of the Sixtymile Formation（SMF） in eastern Grand Canyon National Park（AZ） yield palaeoclimate estimates between 27 and 33℃. The isotopic compositions of cherts define a domain approximately parallel to the meteoric water line when plotted on a δD–δ-（18）O diagram; these data indicate that meteoric water was involved during formation of the chert. In thin section, the absence of interlocking mega quartz（〉35 lm） and silicafilled fractures and veins, along with preserved micromorphological silica fabrics, suggest that the chert has not been permeated by later hydrothermal fluids. Petrographic observations in thin section such as cyclic silica precipitation phases and glaebular micromorphologic fabrics lend support to the interpretation that meteoric waters were involved during chert precipitation. The post 742 Ma SMF has been correlated with diamictite（transition） beds of the Kingston Peak Formation（CA）, which in turn have been interpreted to have been deposited during the Sturtian Ice Age（-750–700 Ma）. Absence of facetted and striated clasts and other diagnostic glaciogenic features in the SMF,an unconformable contact with the stratigraphically older Chuar Group, coupled with warm palaeotemperature data inferred from stable isotope values of chert, tentatively suggest that deposition of sediment in the SMF likely did not take place during the Sturtian Ice Age.

Origin of Taiwan Canyon and its effects on deepwater sediment

The continental slope of the Taiwan Shoal, which has cultivated numerous submarine canyons, is located in a passive conti- nental margin environment. However, the trend of the Taiwan Canyon, with its 45° intersection angle, is obviously different from that of the erosion valley downward along the continental slope. A distinct break is present in the lower segment of the Taiwan Canyon, which then extends from west to east parallel to the continental slope until finally joining the Manila Trench. By utilizing multiple-beam water depth data, high-resolution seismic data, and sediment cores, this study describes the topo- graphic characteristics of the Taiwan Canyon and provides a preliminary discussion on the origin of the Taiwan Canyon and its effect on deepwater sediment. The terrain, landform, and sediment of the Taiwan Canyon exhibit segmentation characteristics. The upper segment is characterized primarily by erosion, downward cutting with a V shape, and wide development of sliding, slumping, and other gravity flow types. The middle segment is characterized mostly by U-shaped erosion-sedimentation transi- tion and development of an inner levee. The lower segment is characterized primarily by sedimentation and development of a sediment wave. The bottom current has a significant reworking effect on the interior sediments of the canyon and forms re- worked sands. The formation and evolution of the Taiwan Canyon is closely related to sediment supply, gravity sliding （slumping）, faulting activities, and submarine impaling. Given the sufficient terrigenous clastic supply, the sediments along the continental shelf edge continuously proceed seaward; gliding and slumping in the front edge provide driving forces for the formation of the canyon. Faulting activities result in stratum crushing, and the gravity flow takes priority in eroding the relatively fragile stratum. Thus, the direction of the extension of the canyon crosses the surrounding erosion valley obliquely. Seamounts are formed through submarine impaling. Owing to seamount blocking, the lower segment of the canyon is turned toward the east-west direction. Large amounts of sediments overflow at the turning, formin~ sediment waves.

Provenance of Central Canyon in Qiongdongnan Basin as evidenced by detrital zircon U-Pb study of Upper Miocene sandstones

Deep-water canyon systems can provide important sandstone reservoirs for deep-water oil and gas exploration in the South China Sea;however,the sedimentary provenance of the Central Canyon in the Qiongdongnan Basin remains controversial.In this work,detrital zircon grains from three drilling sandstones in the Upper Miocene Huangliu Formation in the western part of the Central Canyon were analysed by LA-ICP-MS for U-Pb ages,in order to constrain their provenance.One hundred and ninety-one zircon grains yield concordant U-Pb ages ranging from 28.6 to 3285 Ma.Most of them show oscillatory or linear zoning in CL-images and high Th/U ratios(>0.1),suggesting that they are magmatic zircons.Three major age clusters at about30 Ma(N=6),220–270 Ma(N=29),and 420–440 Ma(N=13),and five minor age clusters at 70–110 Ma(N=7),150–170 Ma(N=4),800–850 Ma(N=11),1800–2000 Ma(N=16),and 2400–2600 Ma(N=7),can be identified in the age spectrum,which are very similar to those of the Upper Miocene sandstones and modern river sands in the Red River area,but different from those of other nearby regions(e.g.,Hainan Island,the Pearl River area,and the Mekong River area)in Southeast Asia.The major age peak at about 30 Ma in our samples is consistent with the timing of tectonothermal events in the Red River Fault Zone.Therefore,we suggest that the provenance of the western part of the Central Canyon,in the Qiongdongnan Basin,was fed dominantly by the Paleo-Red River system during the Late Miocene.

Sedimentary erosive processes and sediment dispersal in Kaoping submarine canyon

The Kaoping submarine canyon, connected to the Kaoping River in the coastal plain in SW Taiwan, continues the dispersal path of modern Kaoping River sediments, from an active small mountainous drain basin to the receiving basin of the South China Sea. Using seismic reflection sections, Chirp sonar profiles, and bathymetric mapping, we reveal characteristic erosive processes responsible for multiple cut-and-fill features, deeply entrenched thalweg, and sediment dispersal that are closely related to turbidity currents in the canyon. The river-canyon connection setting, along with extreme climatic conditions and active tectonism, is favorable for generation of turbidity currents at the canyon head. The upper reach of the Kaoping Canyon is distinguished into three distinct morpho/sedimentary features. The canyon head is characterized by V-shaped axial thalweg erosion. The sinuous segment of the upper reach is dominated by a deeply incised canyon pathway with trough-like morphol- ogy. Relatively small-scaled features of cut-and-fill associated with the dominant incision process are commonly along the canyon floor, resulting in a flat-floored pathway. Sliding and slumping dominated the steep canyon walls, producing and transporting sediments to canyon floor and partially filling up canyon thalweg. The meandering segment is characterized by erosive features where deeply down-cutting occurs in the outer bend of the major sea valley, forming V-shaped entrenched thalweg. The recurrences of turbidity currents have allowed continuous incision of the canyon head and have kept the connec- tion between the canyon head and the river mouth during Holocene highstand of sea level. The upper reach of the Kaoping Canyon is linked to drainage area and maintains as a conduit and/or sink for terrigenous and shallow marine material. Sediment-laden river plume operates in the Kaoping River-Canyon system, with turbidity currents flushing fiver sediments into the canyon head where the canyon thalweg is the most erosive. Presently, the upper reach of the Kaoping Canyon can be considered as a temporal sediment sink.

Sediment storage and morphology of the Yalu Tsangpo valley due to uneven uplift of the Himalaya

The fluvial process of the Yalu Tsangpo River occurs concurrently with the uplift of the Qinghai-Tibet Plateau.Therefore,the river exhibits unique features in morphology and sediment deposition.Field investigations were performed from 2009–2011and the depth of the interface between the sediment deposits and bed rock was detected with an electromagnetic imaging system(EH4)at 29 cross sections.Sediment deposits were sampled along the Yalu Tsangpo valley from Xietongmen to the Yalu Tsangpo Canyon.The results show that a huge amount of sediment has been deposited in four wide valley sections because the uplift rate in these sections was lower than that in the downstream gorge sections over the past million years.About 518 billion m3of gravel and sand have been stored in the high mountain river valleys,which has changed the V-shaped mountain river valley into a U-shaped wide river valley in the four sections.In the sections with high uplift rates the river bed is incised and has formed gorges and the Yalu Tsangpo Canyon.