Quaternary alluvial-fan development, climate and morphologic dating of fault scarps in Laguna Salada, Baja California, Mexico

Late Quaternary slip across the Cañada David detachment has produced an extensive array of Quaternary scarps cutting alluvial-fans along nearly the entire length (~ 60 km) of the range-bounding detachment. Eight regional alluvial-fan surfaces (Q₁ [youngest] to Q₈ [oldest]) are defined and mapped along the entire Sierra el Mayor range-front. Terrestrial cosmogenic nuclide ¹⁰Be concentrations from individual boulders on alluvial-fan surfaces Q₄ and Q₇ yield surface exposure ages of 15.5 ± 2.2 ka and 204 ± 11 ka, respectively. Formation of the fans is probably tectonic, but their evolution is strongly moderated by climate, with surfaces developing as the hydrological conditions have changed in response to climate change on Milankovitch timescales. Systematic mapping reveals that the fault scarp array along active range-bounding faults in Sierras Cucapa and El Mayor can be divided into individual rupture zones, based on cross-cutting relationships with alluvial-fans. Quantitative morphological ages of the Laguna Salada fault-scarps, derived from linear diffusive degradation modeling, are consistent with the age of the scarps based on cross-cutting relationships. The weighted means of the maximum mass diffusivity constant for all scarps with offsets < 4 m is 0.051 and 0.066 m²/ka for the infinite and finite-slope solutions of the diffusion equation, respectively. This estimate is approximately an order of magnitude smaller than the lowest diffusivity constants documented in other regions and it probably reflects the extreme aridity and other microclimatic conditions that characterize the eastern margin of Laguna Salada.     

赣中良山钼矿床流体包裹体特征及其地质意义

良山钼矿是近年来赣中地区新发现的钼矿,浅部矿体主要赋存于南华系浅变质岩系的构造裂隙中,矿石类型以含辉钼矿石英脉为主。流体包裹体岩相学和显微测温结果表明：含辉钼矿石英脉中的流体包裹体主要呈星散状随机或成群分布,其形态多样,大小集中在2~15 μm,包裹体的类型主要有纯液相包裹体、富气相两相包裹体、富液相两相包裹体和含液体CO₂三相包裹体4类,其中以富液相两相包裹体最为发育;包裹体的均一温度为136~298 ℃,盐度为1.22%~10.11%NaCleqv,密度为0.78~0.99 g/cm3,成矿流体属中-低温、低盐度、较低密度流体;成矿压力估算为13~70 MPa,形成深度为0.5~2.6 km。流体包裹体激光拉曼光谱分析表明：包裹体中气液相成分以H₂O为主,气相中还有少量的CO₂和CO。H、O、S同位素组成显示：成矿流体的δD值介于-61‰~-57.9‰,δ¹⁸OH₂O值介于-3.32‰~-0.52‰,具有岩浆水和大气降水混合的特征;成矿热液中的δ³⁴S值介于-1.8‰~+1.9‰,具有岩浆硫的特征。综合成矿地质特征及相关分析,认为成矿流体可能与燕山期的岩浆活动有关,属于岩浆热液流体,混合作用及钾化作用是促进金属富集沉淀成矿的主要因素,推测矿床属于岩浆热液充填石英脉型钼矿。     

The potential of historic rock avalanches and man-made structures as chlorine-36 production rate calibration sites

Samples from three medieval rock avalanches from the French (Le Claps, Mont Granier) and Austrian Alps (Dobratsch) and a man-made structure, i.e. the Stephansdom in Vienna, have been analysed for in-situ produced ³⁶Cl by accelerator mass spectrometry (AMS). All four sampling sites of independently known exposure duration turned out to be not appropriate as calibration sites for the determination of the ³⁶Cl-production rate from Ca. Indeed, the determination of short exposure ages for dating rock avalanches and man-made structures by ³⁶Cl is hindered dramatically by inheritance, especially for samples characterized by high ^natCl-concentrations. Generally, there are hints that the theoretical calculation of ³⁶Cl-production from epithermal and thermal neutron-capture on ³⁵Cl is highly underestimated in all existing models, thus, asking for particular precaution if working on high-Cl samples for any project. Hence, this work evidences that potential high inheritance, even for samples reasonably shielded before exhumation, has to be considered especially when dealing with recently exposed surfaces such as glacially polished rocks, alluvial terraces, fault scarps etc.     

利用GRACE时变重力场探测2010年中国西南干旱陆地水储量变化

GRACE(Gravity Recovery And Climate Experiment)卫星计划为监测陆地水储量变化提供了有效技术手段.本文采用2003至2010年共计8年的GRACE月重力场模型反演中国西南区域陆地水储量变化,与GLDAS(Global Land Data Assimilation System)全球水文模型进行对比分析,其结果在时空分布上均符合较好,同时在2009年秋至2010年春该区域陆地水储量均呈现明显减少,与该时段云贵川三省的干旱事件相一致;比较分析了2009年秋至2010年春GRACE反演陆地水储量变化与TRMM(Tropical Rainfall Measuring Mission)合成数据计算的月降雨量的时空分布,两组结果均与西南干旱事件对应时段与区域十分吻合;对近8年的陆地水储量变化与月降雨量数据进行相关性分析,其结果表明陆地水储量变化与降雨量强相关,即降雨量是导致陆地水储量变化的主要因素;分析该区域地表温度变化,结果显示2009年9月至2010年3月地表温度均比历史同期高,地表温度的升高加剧了陆地水储量的减少.     

Direct georeferencing of airborne LiDAR data in national coordinates

The topographic mapping products of airborne light detection and ranging (LiDAR) are usually required in the national coordinates (i.e., using the national datum and a conformal map projection). Since the spatial scale of the national datum is usually slightly different from the World Geodetic System 1984 (WGS 84) datum, and the map projection frame is not Cartesian, the georeferencing process in the national coordinates is inevitably affected by various geometric distortions. In this paper, all the major direct georeferencing distortion factors in the national coordinates, including one 3D scale distortion (the datum scale factor distortion), one height distortion (the earth curvature distortion), two length distortions (the horizontal-to-geodesic length distortion and the geodesic-to-projected length distortion), and three angle distortions (the skew-normal distortion, the normal-section-to-geodesic distortion, and the arc-to-chord distortion) are identified and demonstrated in detail; and high-precision map projection correction formulas are provided for the direct georeferencing of the airborne LiDAR data. Given the high computational complexity of the high-precision map projection correction approach, some more approximate correction formulas are also derived for the practical calculations. The simulated experiments show that the magnitude of the datum scale distortion can reach several centimeters to decimeters for the low (e.g., 500 m) and high (e.g., 8000 m) flying heights, and therefore it always needs to be corrected. Our proposed practical map projection correction approach has better accuracy than Legat’s approach,¹ but it needs 25% more computational cost. As the correction accuracy of Legat’s approach can meet the requirements of airborne LiDAR data with low and medium flight height (up to 3000 m above ground), our practical correction approach is more suitable to the high-altitude aerial imagery. The residuals of our proposed high-precision map projection correction approach are trivial even for the high flight height of 8000 m. It can be used for the theoretical applications such as the accurate evaluation of different GPS/INS attitude transformation methods to the national coordinates.     

An automated algorithm for extracting road edges from terrestrial mobile LiDAR data

Terrestrial mobile laser scanning systems provide rapid and cost effective 3D point cloud data which can be used for extracting features such as the road edge along a route corridor. This information can assist road authorities in carrying out safety risk assessment studies along road networks. The knowledge of the road edge is also a prerequisite for the automatic estimation of most other road features. In this paper, we present an algorithm which has been developed for extracting left and right road edges from terrestrial mobile LiDAR data. The algorithm is based on a novel combination of two modified versions of the parametric active contour or snake model. The parameters involved in the algorithm are selected empirically and are fixed for all the road sections. We have developed a novel way of initialising the snake model based on the navigation information obtained from the mobile mapping vehicle. We tested our algorithm on different types of road sections representing rural, urban and national primary road sections. The successful extraction of road edges from these multiple road section environments validates our algorithm. These findings and knowledge provide valuable insights as well as a prototype road edge extraction tool-set, for both national road authorities and survey companies.     

Faunal and palaeoenvironmental changes in the Çal Basin,SW Anatolia: Implications for regional stratigraphic correlation of late Cenozoic basins

The Çal Basin formed in the late Miocene as an orogen-top rift hosting terrestrial sedimentation. The initial array of alluvial fans in a half-graben basin was replaced by an axial meandering-river system during the late Tortonian. Palaeomammal taxa indicate a mid-Turolian age of the deposits and a grass-dominated steppe ecosystem. Isotopic data from pedogenic carbonates indicate a warm, semiarid to arid climate. Subhumid to humid climatic conditions prevailed in the Pliocene, with a palustrine environment and savannah-type open ecosystem, recording a regional response to the marine flooding that terminated the Messinian ‘salinity crisis’ in the Mediterranean. Pleistocene saw re-establishment of a fluvial system in the basin with the development of an open steppe ecosystem in warm, semiarid to arid climatic conditions. The sedimentary facies analysis of the basin-fill succession, combined with biostratigraphic data, render the basin a regional reference and help to refine the Neogene tectono-climatic history of SW Anatolia.     

Terrestrial laser scanning to estimate plot-level forest canopy fuel properties

This paper evaluates the potential of a terrestrial laser scanner (TLS) to characterize forest canopy fuel characteristics at plot level. Several canopy properties, namely canopy height, canopy cover, canopy base height and fuel strata gap were estimated. Different approaches were tested to avoid the effect of canopy shadowing on canopy height estimation caused by deployment of the TLS below the canopy. Estimation of canopy height using a grid approach provided a coefficient of determination of R² = 0.81 and an RMSE of 2.47 m. A similar RMSE was obtained using the 99th percentile of the height distribution of the highest points, representing the 1% of the data, although the coefficient of determination was lower (R² = 0.70). Canopy cover (CC) was estimated as a function of the occupied cells of a grid superimposed upon the TLS point clouds. It was found that CC estimates were dependent on the cell size selected, with 3 cm being the optimum resolution for this study. The effect of the zenith view angle on CC estimates was also analyzed. A simple method was developed to estimate canopy base height from the vegetation vertical profiles derived from an occupied/non-occupied voxels approach. Canopy base height was estimated with an RMSE of 3.09 m and an R² = 0.86. Terrestrial laser scanning also provides a unique opportunity to estimate the fuel strata gap (FSG), which has not been previously derived from remotely sensed data. The FSG was also derived from the vegetation vertical profile with an RMSE of 1.53 m and an R² = 0.87.     

基于地面三维激光技术的建筑物变形监测研究

地面三维激光雷达测量系统是最近几年刚刚新生的一个测量技术,本文提出一种研究建筑物变形的方法即用三维激光扫描仪对建筑物或者构筑物进行三维扫描并获得建筑物的三维点云模型,然后通过前后两次建筑物的三维点云数据的比对、分析,可以对建筑物进行平面位移监测、沉降监测、倾斜分析、整体形变监测。