Hillslope coupled stream morphology,flow conditions,and their effects on detrital sedimentology in Garnet Canyon,Teton Range,Wyoming

Characterizing stream erosion in any steep mountain landscape is arduous, but the challenge level increases when the stream flows through a glaciated catchment frequently modified by hillslope debris.Glacial landforms and stochastic mass wasting in alpine systems may interfere with sediment delivery to downstream sites where detrital sediments are often collected to represent upstream bedrock sources.To use detrital sediments as indicators of erosion, we need to understand potential sediment accumulation in flat glaciated reaches or behind rockfall barriers. This study investigates the stream channel in Garnet Canyon, a glaciated catchment located in the central Teton Range, to describe hillslope coupled channel morphology and the subsequent effects on sediment transport throughout the catchment.Stream cross-section surveys and sediment size measurements of the surface bedload were collected in the field within a glacially flattened segment of Garnet Canyon. Calculations of shear stress conditions allowed evaluation of the importance of mineral densities on potential grain entrainment. The length of the Garnet Canyon stream observed in this study was coupled with hillslope deposits. Critical shear stresses were sufficient to move gravel-sized sediments through all sections when calculated with quartz mineral density and through most sections when applying apatite mineral density. These results verify the application of detrital sediments to evaluate erosion rates or spatial bedrock sources because snowmelt stream flow efficiently moves entrained sediment past glacially reduced slopes and potential talus barriers.     

琼东南盆地中央峡谷天然气成藏特征及其主控因素

基于地震、测井、岩芯、岩屑和天然气样品分析化验等资料,研究了中央峡谷天然气成藏特征,探讨了成藏主控因素与成藏模式。研究结果表明,晚中新世—早上新世沿琼东南盆地中央坳陷发育一条大型海底峡谷,称之为中央峡谷,峡谷内充填了多期相互叠置的浊积砂岩,平均孔隙度为15%~33%,渗透率为11×10-3~971.3×10-3μm2,为较好的储层;发育了岩性和构造-岩性复合两大类圈闭。峡谷的气源来自于崖城组的煤系地层,属于煤型气。烃源岩的有机质类型为Ⅱ2和Ⅲ型,以Ⅲ型为主;热演化程度处于成熟—高成熟阶段,晚中新世—上新世达到生烃高峰。琼东南盆地中央坳陷是一个高温高压的坳陷,实测地温梯度平均值高达4.2~4.6℃/100m,实测压力系数为1.20~2.15。在高温高压的环境下,盆地内孕育众多的底辟构造,而峡谷下伏的底辟构造与谷内相互叠置的复合砂体在空间上有效的配置构成了天然气垂向与侧向运移的输导体系,成为峡谷天然气成藏的关键因素。     

雅鲁藏布江大拐弯地区河流形态特征及其意义

为探讨雅鲁藏布江大拐弯地区区域隆升的特点,通过DEM(数字高程模型)和遥感影像提取雅鲁藏布江干流和帕隆藏布江的形态特征,引入Hack剖面、SL参数和Amos河宽理论模型进行分析。雅鲁藏布江干流在大渡卡以下河段的Hack剖面表现为上凸形态,SL参数升高、河流宽度减小,在藏布巴东瀑布-雅鲁藏布江大拐弯顶端段,SL参数达到最大值,河流宽度达到最小值;大拐弯顶端以下河段,SL参数减小,河流渐宽。帕隆藏布江古乡以下河段SL参数梯级增高,河流宽度总体收窄,大拐弯顶端附近达到最大值。综合2条河流的地貌特征和区域地质与地理背景,认为雅鲁藏布江大拐弯地区的隆升具有不均一性,雅鲁藏布江在大渡卡附近开始进入快速隆升区段,隆升最强烈的区段位于藏布巴东瀑布-大拐弯顶端段,大拐弯顶端之后雅鲁藏布江逐渐远离隆升中心区。     

台湾峡谷HD133柱状样中重力流、底流交互沉积的证据

在台湾峡谷水深3284 m处全长699 cm的HD133柱状样中共识别出1个厚沙层（厚127 cm）和8个薄沙层（单层厚度8-15 cm）,这些沙层中含大量浅水底栖有孔虫,反映其为来自浅水区的陆源物质以重力流方式形成的沉积物。然而,单用重力流无法对这些沙层的成因作出合理的解释：该样中的厚沙层以中沙为主,平均粒径范围1-2Φ,薄沙层以粉沙-细沙为主,平均粒径范围3-4Φ;沙层的分选系数小于2.5,局部接近于1,分选好-极好,长石/石英比值低,具有很高的结构成熟度和成分成熟度;在粒度特征上,其频率分布曲线为单峰,累积概率曲线为2-3段式,在C-M图上厚沙层的样点落在牵引流区域;特别是在垂向序列上,沙层顶底呈突变接触;以上特征均表现为明显的牵引流特征。此外,在柱状样中发现含有太平洋深层水所特有的底栖有孔虫Bulimina aculeata、Planulina wuellerstorfi、Eggerella bradyi种类,且大量生物壳呈棱角状破碎,表明该样在沉积过程中受到太平洋深层水的入侵,这些证据支持了前人关于研究区内可能发育活跃的底流作用的推断。综合分析认为HD133柱状样中的沙层是重力流和底流交互作用的产物。     

四川邻水华蓥山大峡谷地质公园地质遗迹资源体系及地学意义

华蓥山大峡谷地质公园是以峡谷、构造和岩溶地貌为代表的风景地貌类地质公园。本文以华蓥山大峡谷地质公园地质遗迹景观资源为基础, 以川东褶皱带构造单元、川东平行岭谷地貌单元和上扬子地层分区的部分地层区域为研究视角, 构建华蓥山大峡谷地质公园地质遗迹资源体系——包括地质(体、层)剖面、古生物活动遗迹、地貌景观、水体景观以及环境地质遗迹5个大类、15个类共100多处地质遗迹景点; 通过对各类地质遗迹的特征进行分析, 对前人研究进行总结, 探讨了地质公园地质遗迹重要的地学意义。研究表明, 华蓥山大峡谷地质遗迹在地质构造、地层、岩溶学、水文地质学以及地貌学等领域具有重要的科学价值。     

The opening of the Plio-Quaternary Gibraltar Strait: assessing the size of a cataclysm

Abstract

The widespread Lago-Mare facies show that the Mediterranean was fully isolated from the World Ocean at the end of the Messinian salinity crisis (MSC): the Plio-Quaternary Gibraltar Strait has no geographical feature in common with the Miocene Portals, which were continentalised before the end of the MSC. A copy of a budget model has been modified to study the infilling of the Mediterranean. The yearly Atlantic water supply follows an exponential increase law. The level of the basins does not change significantly during the 26 early years, but the refill of the Mediterranean basins is completed within the next 10–11 years. The high velocity of the flow of Atlantic water can be reconfirmed by hydraulic calculations. The morphological study of the area suggests that the Gibraltar Strait originates from an eastwards flowing stream, which drained the eastern slope of an emergent Gibraltar Isthmus to the Mediterranean Basins at the end of the Messinian. Similar canyons are still found in the marine topography towards the Alboran Sea. The present Spartel and Camarinal Sills both originate from the coeval mass sliding of the northern bank of the strait. The strait of Gibraltar results from the work of a stream, which managed water-piracy from an Ocean. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.     

A proposed Laramide proto-Grand Canyon

The absence of “rim gravels” north of Grand Canyon and of “Canaan Peak-type” gravels south of Grand Canyon suggests that a paleocanyon, which intersected the transport of these gravels north and south, may have begun forming in the Laramide in approximately the same position as today's central Grand Canyon. This Laramide-age canyon is envisioned as having flowed generally from the SW to NE; from the Peach Springs Canyon area to Mile 197 where it was captured by karst; then along a N. 60°E joint system to the Kanab Point area where it converged with drainage coming off the west side of the Kaibab arch. From there it flowed north along the west flank of the Kaibab arch to Paleogene Lake Claron. The critical idea suggested by this proposed model is that the modern Colorado River utilized Laramide paleotopography in establishing its course through the central Grand Canyon, with younger sections of the canyon integrating with it later, in the middle to late Miocene. This paleocanyon route, in association with headward erosion from the Grand Wash Cliffs toward the Kaibab arch after 16–17 Ma, helps account for the total volume of rock eroded from Grand Canyon, which cannot be explained by present-day incision rates.     

圆弧状凹陷地形在平面SH波入射下的动力响应：高频解答

利用波函数的Fourier-Bessel级数展开法和外域型Graf加法公式,推导了圆弧状凹陷地形对平面SH波二维散射问题的解析解。与现有其他解析解不同的是,该解析解的获得无须求解线性方程组,从而避免了高频波入射下方程组系数矩阵可能出现的病态问题。因此,既使在入射波频率很高的情况下,该解析解也能够收敛。利用该解,在一个非常宽的频带范围内讨论了凹陷地形的几何形状对地面运动的影响。     

Tectonics and Seismicity of the Yarlung Tsangpo Grand Canyon Region

The Yarlung Tsangpo Grand Canyon region is located in the frontal zone of the eastern Himalayan syntaxis, where neo-tectonics and seismicity are intensive and closely related to each other. In the region, two sets of fault structures have developed, striking NNE-NE and NWW-NW, respectively. Investigation shows that they differ markedly in terms of scope, property, active times and intensity. The NWW-NW trending faults are large in size, and most are thrust and thrust strike-slip faults, formed in earlier times. The NEE-NE-strike faults are relatively small in size individually, with concentrated distribution, constituting the NNE-trending shear extensional fault zone, which is relatively younger with evident late Quaternary activities. Strong earthquakes occur mainly in the areas or zones of intensive differential movement of the Himalayas, e.g. along the deep and large fault zones around the crustal blocks. Most earthquakes of M≥7.0 are closely related to tectonics, where large-scale Holocene active faults are distributed with complicated fault geometry, or the faults of multiple directions intersect. Among them, earthquakes of M≥7.5 have occurred on the NW and NE-trending faults with a greater strike-slip component in the fault tectonic zones.