Stochastic Distance Based Geological Boundary Modeling with Curvilinear Features

Obtaining accurate geological boundaries and assessing the uncertainty in these limits are critical for effective ore resource and reserve estimation. The uncertainty in the extent of an ore body can be the largest source of uncertainty in ore resource estimation when drilling is sparse. These limits are traditionally interpreted deterministically and it can be difficult to quantify uncertainty in the boundary and its impact on ore tonnage. The proposed methodology is to consider stochastic modeling of the ore boundary with a distance function recoding of the available data. This technique is modified to incorporate non-stationarities in the form of a locally varying anisotropy field used in kriging and sequential Gaussian simulation. Implementing locally varying anisotropy kriging retains the geologically realistic features of a deterministic model while allowing for a stochastic assessment of uncertainty. A case study of a gold deposit in Northern Canada is used to demonstrate the methodology. The proposed technique generates realistic, curvilinear geological boundary models and allows for an assessment of the uncertainty in the model.     

Time–space continuity of daily maps of fractional snow cover and albedo from MODIS

Using reflectance values from the seven MODIS “land” bands with 250 or 500 m resolution, along with a corresponding cloud product, we estimate the fraction of each 500 m pixel that snow covers, along with the albedo of that snow. The daily products have data gaps and errors because of cloud cover and sensor viewing geometry. Rather than make users interpolate and filter these patchy daily maps without completely understanding the retrieval algorithm and instrument properties, we use the daily time series to improve the estimate of the measured snow properties for a particular day. We use a combination of noise filtering, snow/cloud discrimination, and interpolation and smoothing to produce our best estimate of the daily snow cover and albedo. We consider two modes: one is the “predictive” mode, whereby we estimate the snow-covered area and albedo on that day using only the data up to that day; the other is the “retrospective” mode, whereby we reconstruct the history of the snow properties for a previous period.     

Effect of fire on phytolith coloration

Dark‐colored phytoliths are often found preserved in paleosols and archaeological sediments. Some practitioners believe these darkened phytoliths provide evidence of fire histories, while others suggest alternative reasons for their occurrence. This study examines the effect of fire on phytolith appearance and discusses the extent to which color may be used as proxy evidence for fire. The results of this study demonstrate that under oxidative conditions of openair fire, the color of phytoliths can be altered, although dark‐colored phytoliths also occur naturally in some unburned plant species. Despite some overlap observed between burned and unburned color in phytoliths, clear differences are apparent in the way this color appears optically. In particular, transparent and opalescent qualities were found to occur in nature as opposed to a dull opaque appearance of charred phytoliths. Although fire‐induced color change is probably limited to a portion of the phytolith assemblage, phytolith color remains a tool that can be confidently used to indicate the presence of fire in various sedimentary contexts. © 2006 Wiley Periodicals, Inc.     

Separation of pedogenic and lithogenic components of magnetic susceptibility in the Chinese loess/palaeosol sequence as determined by the CBD procedure and a mixing analysis

Magnetic susceptibility variations in the Chinese loess/palaeosol sequences have been used extensively for palaeoclimatic interpretations. The magnetic signal of these sequences must be divided into lithogenic and pedogenic components because the palaeoclimatic record is primarily reflected in the pedogenic component. In this paper we compare two methods for separating the pedogenic and lithogenic components of the magnetic susceptibility signal: the citrate-bicarbonate-dithionite (CBD) extraction procedure, and a mixing analysis. Both methods yield good estimates of the pedogenic component, especially for the palaeosols. The CBD procedure underestimates the lithogenic component and overestimates the pedogenic component. The magnitude of this effect is moderately high in loess layers but almost negligible in palaeosols. The mixing model overestimates the lithogenic component and underestimates the pedogenic component. Both methods can be adjusted to yield better estimates of both components. The lithogenic susceptibility, as determined by either method, suggests that palaeoclimatic interpretations based only on total susceptibility will be in error and that a single estimate of the average lithogenic susceptibility is not an accurate basis for adjusting the total susceptibility. A long-term decline in lithogenic susceptibility with depth in the section suggests more intense or prolonged periods of weathering associated with the formation of the older palaeosols.
The CBD procedure provides the most comprehensive information on the magnitude of the components and magnetic mineralogy of loess and palaeosols. However, the mixing analysis provides a sensitive, rapid, and easily applied alternative to the CBD procedure. A combination of the two approaches provides the most powerful and perhaps the most accurate way of separating the magnetic susceptibility components.     

胶北粉子山群石榴云母片岩的三叠纪独居石年龄及其地质意义

胶北地块粉子山群石榴云母片岩中石榴石变斑晶内包裹物迹线明显,保留了岩石形成过程中的多期变质变形信息。电子探针成分面扫描图显示石榴石成分环带明显,可分为核部、幔部和边部。石榴石中MgO、FeO、MnO和CaO含量变化特征表明其核部到边部温度先升高后降低,对应进变质及退变质过程。根据原位独居石Y元素成分面扫描图显示,部分独居石颗粒由核部到边部Y含量呈现逐渐降低趋势,说明测得的232.6±1.1Ma~229.5±3.7Ma的独居石U-Pb年龄,对应石榴石的进变质生长过程。结合1869±72Ma的锆石U-Pb年龄数据,可推断粉子山群石榴云母片岩至少经历了古元古代及三叠纪两期变质事件的改造。粉子山群石榴云母片岩卷入了苏鲁超高压变质带的俯冲碰撞造山事件。电子探针成分分析结果表明粉子山群石榴云母片岩中的石榴石属于铁铝榴石,反映出经受中级区域变质作用的特征。说明粉子山群石榴云母片岩虽然参与了三叠纪苏鲁超高压变质带的俯冲碰撞造山过程,但俯冲深度较浅。这可用大陆俯冲过程中上盘的俯冲剥蚀来解释,并可为陆-陆碰撞俯冲剥蚀模式提出的扬子板片在240~220Ma的深俯冲作用过程中拽动胶北地块向下俯冲又折返的运动过程提供佐证,但胶北地块是否经历了深俯冲超高压变质作用,还需要进一步验证。     

Comparing the transitional behaviour of kaolinite and bentonite suspension flows

Past research has demonstrated the dramatic effects that variations in suspended clay can have on the properties of flow by producing a range of transitional flows between turbulent and laminar states, depending on clay concentration and fluid shear. Past studies have been restricted to kaolinite flows, a clay mineral that has relatively weak cohesive properties. This paper extends these studies to suspension flows of bentonite, a clay mineral that attains higher viscosities at far lower volumetric concentrations within a flow. The results show that the types of transitional flow behaviour recognized in past studies can also be found in bentonite suspension flows, but at lower suspended sediment concentrations, thus demonstrating an even more dramatic effect on flow properties, and potentially on sediment transport and resulting bed morphology, than kaolinite flows. The paper proposes new stability diagrams for the phase space of bentonite flows and compares these to past work on kaolinite suspension flows. These new data suggest that the transitional‐flow Reynolds number can be used to delineate the types of transitional flow across different clay types and assess modern and ancient clay‐suspension flows. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Heterogeneous effects of warming and drought on selected wheat variety yields

Climate change is likely to significantly impact agricultural production in the Great Plains region of the Central United States. This study estimated the impact of changes in temperature and precipitation on wheat (triticum aestivum) variety yield distributions using the moment-based maximum entropy (MBME) model. This approach allows for quantification of potential weather impacts on the yield distribution, and allows these effects to vary across varieties. The unique data set matches wheat variety trial data for 1985 to 2011 with weather data from the exact trial site for 11 locations throughout Kansas. Ten widely-planted varieties with a range of biotic and abiotic characteristics were included for comparison. Weather scenarios were simulated for baseline, increased temperature (one-degree Celsius warming), decreased precipitation (tenth-percentile rainfall outcome), and a combination warming and drought scenario. Warming resulted in an 11 % yield reduction, drought a 22 % reduction, and warming and drought a cumulative 33 % reduction. These effects vary across varieties. Alternative measures of yield risk (e.g. yield variance and coefficient of variation) were also constructed under each scenario and a similar pattern of heterogeneous impacts emerges. The key findings are that (i) exposure to warming and drought lead to mean yield reductions coupled with increased yield risk for all varieties, and (ii) newer (post 2005) seed varieties have a yield advantage over older varieties, however this advantage is reduced under warming and drought conditions.