The topology of geology 1: Topological analysis

Topology has been used to characterise and quantify the properties of complex systems in a diverse range of scientific domains. This study explores the concept and applications of topological analysis in geology. We have developed an automatic system for extracting first order 2D topological information from geological maps, and 3D topological information from models built with the Noddy kinematic modelling system, and equivalent analyses should be possible for other implicit modelling systems. A method is presented for describing the spatial and temporal topology of geological models using a set of adjacency relationships that can be expressed as a topology network, thematic adjacency matrix or hive diagram. We define three types of spatial topology (cellular, structural and lithological) that allow us to analyse different aspects of the geology, and then apply them to investigate the geology of the Hamersley Basin, Western Australia.     

The use of topology in fracture network characterization

In two-dimensions, a fracture network consist of a system of branches and nodes that can be used to define both geometrical features, such as length and orientation, and the relationship between elements of the network – topology. Branch lengths are preferred to trace lengths as they can be uniquely defined, have less censoring and are more clustered around a mean value. Many important properties of networks are more related to topology than geometry.The proportions of isolated (I), abutting (Y) and crossing (X) nodes provide a basis for describing the topology that can be easily applied, even with limited access to the network as a whole. Node counting also provides an unbiased estimate of frequency and can be used in conjunction with fracture intensity to estimate the characteristic length and dimensionless intensity of the fractures. The nodes can be used to classify branches into three types – those with two I-nodes, one I-node and no I-nodes (or two connected nodes). The average number of connections per branch provides a measure of connectivity that is almost completely independent of the topology. We briefly discuss the extension of topological concepts to 3-dimensions.     

Assessing the impact of conceptual mineral systems uncertainty on prospectivity predictions

The past two decades have seen a rapid adoption of artificial intelligence methods applied to mineral exploration. More recently, the easier acquisition of some types of data has inspired a broad literature that has examined many machine learning and modelling techniques that combine exploration criteria, or ‘features’, to generate predictions for mineral prospectivity. Central to the design of prospectivity models is a ‘mineral system’, a conceptual model describing the key geological elements that control the timing and location of economic mineralisation. The mineral systems model defines what constitutes a training set, which features represent geological evidence of mineralisation, how features are engineered and what modelling methods are used. Mineral systems are knowledge-driven conceptual models, thus all parameter choices are subject to human biases and opinion so alternative models are possible. However, the effect of alternative mineral systems models on prospectivity is rarely compared despite the potential to heavily influence final predictions. In this study, we focus on the effect of conceptual uncertainty on Fe ore prospectivity models in the Hamersley region, Western Australia. Four important considerations are tested. (1) Five different supergene and hypogene conceptual mineral systems models guide the inputs for five forest-based classification prospectivity models model. (2) To represent conceptual uncertainty, the predictions are then combined for prospectivity model comparison. (3) Representation of three-dimensional objects as two-dimensional features are tested to address commonly ignored thickness of geological units. (4) The training dataset is composed of known economic mineralisation sites (deposits) as ‘positive’ examples, and exploration drilling data providing ‘negative’ sampling locations. Each of the spatial predictions are assessed using independent performance metrics common to AI-based classification methods and subjected to geological plausibility testing. We find that different conceptual mineral systems produce significantly different spatial predictions, thus conceptual uncertainty must be recognised. A benefit to recognising and modelling different conceptual models is that robust and geologically plausible predictions can be made that may guide mineral discovery.     

Application of physical modelling of debris flow triggering to field conditions: Limitations posed by boundary conditions

Debris flows are often triggered by Hortonian overland flow during high-intensity rainstorms. Data derived from debris flow trigger zones in the southern French Alps were fed into a physical model of debris flow triggering based on Takahashi. Using a Monte Carlo approach with 1000 runs, the results show a wide distribution of safety factor values, indicating that physical modelling based on actual field measurements may not always be practical.As all safety factor values obtained are well below 1 even though debris flows only occur during very high-intensity rainstorms, the model used must be inappropriate. Apparently, the composition of the overland flow plays an important role: during high-intensity rainstorms it usually has a very high sediment content and contains stones. This prevents it from flowing through the pores of coarse debris accumulations in the central gully of a trigger zone; it will rather run over the debris. This situation is more stable than with the fluid flowing through the pores. The behaviour switch of the fluid above a certain sediment and stone content thus drastically changes the triggering conditions for debris flows and it is concluded that debris flow triggering in the area requires the occurrence of both overland flow and landsliding.     

Inverse method applied to a sand wedge: Estimation of friction parameters and uncertainty analysis

We examine the fundamental mechanism of frontal accretion in a sand wedge from the occurrence of a forward thrust ramp evolving into a fault-bend fold to the jump of deformation to a new frontal ramp ahead. We use inverse problem theory to extract quantitative information on friction parameters from the systematic comparison of experimental observations and theoretical predictions. The observables are locations, dips and lifetime of thrust ramps, hinge and associated compression. The experimental values (observed data) are cast into statistical models describing the error bars. The theory of limit analysis provides calculated data, requiring five parameters : material density, friction coefficient of the décollement plane, friction coefficient of the bulk material, and the variation of friction with slip on the ramp as well as the distance for this variation. The misfit between observed data and calculated data is determined for all physically admissible values of the parameters. Values yielding a small misfit are interpreted as highly probable. The mean misfit per observable is within their error bars and therefore application of the theory reproduces the observables. Bulk and décollement friction coefficient values with high probability are compared to independent measurements. The inversion also reveals systematic discrepancies: the frictional weakening on the ramps is overestimated, while the force is underestimated, the calculated thrust sheet is longer than observed and the calculated jump to a second ramp occurs earlier than observed. These conclusions allow us to identify necessary improvements for the experimental set-up and of the theoretical assumptions.     

关于当前我国城市地质研究的认识

进入21世纪，保护和合理利用资源环境已成为我国的一个重大战略问题。城市地质以调查研究和解决与城市建设及发展有关的各种资源、环境等地质问题为其基本任务。随时代发展和国家需要，它的侧重点也有所不同。当前我国处于城市化高速发展的历史阶段，城市地质主要任务更是要强调环境问题，即城市地质着重解决城市环境岩土工程和地质灾害问题，或者说是解决城市安全特别是城市土工安全问题，为城市防灾减灾与城市生态建设和城市可持续发展服务。     

A statistical assessment of the uncertainty in a 3-D geological framework model

Three-dimensional framework models are the state of the art to present geologists’ understanding of a region in a form that can be used to support planning and decision making. However, there is little information on the uncertainty of such framework models. This paper reports an experiment in which five geologists each produced a framework model of a single region in the east of England. Each modeller was provided with a unique set of borehole observations from which to make their model. Each set was made by withholding five unique validation boreholes from the set of all available boreholes. The models could then be compared with the validation observations. There was no significant between-modeller source of variation in framework model error. There was no evidence of systematic bias in the modelled depth for any unit, and a statistically significant but small tendency for the mean error to increase with depth below the surface. The confidence interval for the predicted height of a surface at a point ranged from ±5.6 m to ±6.4 m. There was some evidence that the variance of the model error increased with depth, but no evidence that it differed between modellers or varied with the number of close-neighbouring boreholes or distance to the outcrop. These results are specific to the area that has been modelled, with relatively simple geology, and reflect the relatively dense set of boreholes available for modelling. The method should be applied under a range of conditions to derive more general conclusions.     

On the role of grain topology in dynamic grain growth — 2D microstructural modeling

Microstructural modification processes like dynamic recrystallization and grain growth can have a major effect on the transient and (semi-)steady state flow behaviour of deforming materials. Work on metals and ceramics suggests that deformation-enhanced changes in grain topology and the corresponding increase in fraction of non-hexagonal grains, called cellular defect fraction, can promote grain growth during deformation. The present study tests this hypothesis, by investigating the evolution of the cellular defect fraction during deformation, accompanied by grain growth, of aggregates with distributed grain sizes. For this purpose, we made use of the ELLE 2D microstructural modeling package. We simulated and quantified microstructural evolution under conditions where both surface energy driven grain boundary migration (GBM) and homogeneous deformation or grain size sensitive (GSS) straining were allowed to occur. The simulations show that contemporaneous GBM and simple geometrical straining of grain aggregates with distributed grain size and coordination number lead to extra grain neighbor switching, an increase in defect fraction, and enhanced grain growth. An increase in defect fraction was also found in a selected set of natural calcite mylonites that, with increasing temperature, show an increase in grain size and contribution of GSS creep. Analysis of defect fraction thus appears to be a good microstructural tool to establish whether or not a material has experienced normal static (defect fraction  0.7) or dynamic grain growth (defect fraction  0.8).     

Geostatistical modeling of the geological uncertainty in an iron ore deposit

This paper addresses the problem of quantifying the joint uncertainty in the grades of elements of interest (iron, silica, manganese, phosphorus and alumina), loss on ignition, granulometry and rock types in an iron ore deposit. Sampling information is available from a set of exploration drill holes. The methodology considers the construction of multiple rock type outcomes by plurigaussian simulation, then outcomes of the quantitative variables (grades, loss on ignition and granulometry) are constructed by multigaussian joint simulation, accounting for geological domains specific to each quantitative variable as well as for a stoichiometric closure formula linking these variables. The outcomes are validated by checking the reproduction of the data distributions and of the data values at the drill hole locations, and their ability to measure the uncertainty at unsampled locations is assessed by leave-one-out cross validation.Both the plurigaussian and multigaussian models offer much flexibility to the practitioner to face up to the complexity of the variables being modeled, in particular: (1) the contact relationships between rock types, (2) the geological controls exerted by the rock types over the quantitative variables, and (3) the cross-correlations and stoichiometric closure linking the quantitative variables. In addition to this flexibility, the use of efficient simulation algorithms turns out to be essential for a successful application, due to the high number of variables, data and locations targeted for simulation.     

中国地质学的产生与发展——写在地质调查所创建100周年之际

中国的地质学非我国自有,而是在传播和引入西方近代科学文化的过程中逐渐形成的,是"西学东渐"的结果。在欧美等西方国家,至19世纪中叶,便建立并完善了近代地质学的理论和方法体系,完成了学科体制化建设,比中国至少早一个世纪。从16世纪后半叶的"西学东渐",西方近代地学传入中国进行第一次启蒙,到引进、消化、吸收和本土化,最后建立中国地质学理论和方法体系,完成学科建制,中国地质事业历经了长达三个半世纪艰辛曲折并充满坎坷的历史进程。创建于1913年的地质调查所是中国近代第一个科研机构,在章鸿钊、丁文江、翁文灏等第一代地质学家的领导下,筚路蓝缕、艰苦奋斗,在短短的二、三十年里,全面开创和奠定了中国近代地质事业,培养了一大批早期地质学家,取得了举世瞩目的成果,赢得国内外学术界的广泛赞誉。地质调查所的成功及其所取得的成就远远超出了地质学,对我国古生物学、地理学、地震学、地球物理学、土壤学、考古、古人类学、燃料和地图等诸多学科领域都产生了深远影响。     

The universal applicability of logistic curve in simulating ecosystem carbon dynamic

As an S-shaped curve, the logistic curve has both high and low limit, which provides advantages in modelling the influences of environmental factors on biogeological processes. However, although the logistic curve and its transformations have drawn much attention in theoretical modelling, it is often used as a classification method to determine a true or false condition, and is less often applied in simulating the real data set. Starting from the basic theory of the logistic curve, with observed data sets, this paper explored the new application scenarios such as modelling the time series of environmental factors, modelling the influence of environmental factors on biogeological processes and modelling the theoretical curve in ecology area. By comparing the performance of traditional model and the logistic model, the results indicated that logistic modelling worked as well as traditional equations. Under certain conditions, such as modelling the influence of temperature on ecosystem respiration, the logistic model is more realistic than the widely applied Lloyd-Taylor formulation under extreme conditions. These cases confirmed that the logistic curve was capable of simulating nonlinear influences of multiple factors on biogeological processes such as carbon dynamic.     

The geology and structure of the Rustenburg Layered Suite in the Potgietersrus/Mokopane area of the Bushveld Complex,South Africa

A new geological map of the Rustenburg Layered Suite south of the Ysterberg–Planknek fault of the northern/Potgietersrus limb of the Bushveld Complex is presented, displaying features that were not available for publication in the past and are considered contributing to the complexity of this region. The northern limb is known for the Platreef, atypical mafic lithologies in sections of the layered sequence and the unusual development of the ultramafic Lower Zone as satellite bodies or offshoots at the base of the intrusion. The outcrop and suboutcrop pattern of Lower Zone Grasvally body and its relation to the surrounding geology of Main Zone, Critical Zone, and floor rocks is described. The extent of the base metal sulfide (BMS) and platinum-group element (PGE)-mineralized cyclic unit 11 of the Drummonlea harzburgite–chromitite sub zone is shown. Only that which is considered to be the equivalents of the mafic Upper Critical Zone has thus far been traced south of Potgietersrus/Mokopane. The Platreef is traced from the farm Townlands and further northwards. The presence of Platreef proper south of Potgietersrus/Mokopane appears to be speculative. However, Merensky Reef, UG 2, and equivalent layers outcrop or were intersected to the south of the town. The Kleinmeid Syncline comprising Main Zone/Critical Zone layers and its structure is discussed. The lateral lithological transfomation of the Merensky Reef/UG 2 and equivalent layers south of the Ysterberg–Planknek fault to Platreef north of this fault is recorded. Attenuation of both the Main Zone and Upper Zone is observed from the northwest towards the town and resulted in only the lower units being developed. The lateral change of Main Zone and Upper Zone lithologies from the northwest towards the town is described. The PGE and BMS economic potential south of the town are briefly tabulated.     

Establishment of an assessment method for site-scale suitability of CO2 geological storage

Geological storage of CO2 (known as geological sequestration) is increasingly seen as a viable strategy to reduce the release of greenhouse gases into the atmosphere. China has become one of the largest emitters of CO2 in the world. Therefore, alongside other emissions reductions measures, the deployment of geological storage projects to capture CO2 in China is essential. This paper focuses on the establishment of qualitative and quantitative assessment methods for site-scale suitability of CO2 geological storage in deep saline formation systems. This is based on numerical modelling prior to the development a specific geological storage project, providing a more accurate selection of preferential sites from a list of potential storage locations. However, the detailed design of specific geological storage projects was not con?sidered.     

全球地质学复兴：我们正进入“人类幻”——第32届国际地质大会环境地质述评

概要介绍了第32届国际地质大会的议题概况。7个大会报告中与环境地质问题相关的竟有6个,反映以人类与地球相互作用为中心的研究已成为地质学家们不得不关注的主题。重点介绍了环境地质方面的几个重要议题：气候与地质环境、地质灾害风险评估、城市化与城市地质、地下水资源与环境、地质环境标识。阐明了关于全球地质学复兴的几点思考：人类活动已成为一种地质营力、地质工作者应成为管理地球的主力军、重在预测人类的未来、地质环境与地球环境、地球系统与地球问题。     

Application of uncertainty analysis to groundwater pollution modeling

Prediction and evaluation of pollution of the subsurface environment and planning remedial actions at existing sites may be useful for siting and designing new land-based waste treatment or disposal facilities. Most models used to make such predictions assume that the system behaves deterministically. A variety of factors, however, introduce uncertainty into the model predictions. The factors include model and pollution transport parameters and geometric uncertainty. The Monte Carlo technique is applied to evaluate the uncertainty, as illustrated by applying three analytical groundwater pollution transport models. The uncertainty analysis provides estimates of statistical reliability in model outputs of pollution concentration and arrival time. Examples are provided that demonstrate: (a) confidence limits around predicted values of concentration and arrival time can be obtained, (b) the selection of probability distributions for input parameters affects the output variables, and (c) the probability distribution of the output variables can be different from that of the input variables, even when all input parameters have the same probability distribution     

Reducing geological uncertainty by conditioning on boreholes: the coupled Markov chain approach

The CMC (coupled Markov chain) model, which is based on the extension of Markov chains in two-dimensions, is used in the reduction of uncertainty in geological structures when conditioned (i.e., honours the data and their location) on a number of boreholes. The model has been applied to an unconsolidated aquifer deposit located in the central Rhine-Meuse delta (the Gorkum study area) in the Netherlands. A comparison is also made between the CMC and the SIS (sequential indicator simulation) model, which is based on Kriging and co-Kriging theories on the same deposit. The results show the potential applicability of the CMC model in reducing the uncertainty in geological configurations when a sufficient number of boreholes is available. Reproduction of the global geological features requires relatively few boreholes (in this case study, nine boreholes with 30-m spacing over a distance of 240 m). However, reproduction of the proportion of each state requires a relatively large number of boreholes (in this case study 31 boreholes with 8-m spacing over a distance of 240 m). It has been shown that variograms can be deceptive in modeling the spatial pattern and that they reflect only part of the complete spatial structure in the field. The use of transition probabilities via the CMC model provides a better alternative approach, because it uses multiple point information. Amro M. M. Elfeki on leave from Department of Irrigation and Hydraulics, Faculty of Engineering, Mansoura University, Mansoura, Egypt     

地下水数值模拟不确定性分析研究进展

地下水数值模拟不确定性分析旨在提高研究区域地下水流的模拟精度。学者们将地下水数值模拟不确定性分析分为:模型的不确定性、参数的不确定性以及资料的不确定性三类,其中参数的不确定性分析在研究中是最为重要的。同时,对模型、参数、资料不确定性分析的研究进展和成果进行归纳总结,补充关于参数不确定性分析过程中的替代模型的一些研究成果以及模型不确定性分析的多模型分析;强调在地下水数值模拟的过程中,重视模型、资料的不确定性分析;展望未来,随着地下水数值模拟不确定性分析研究的深入,方法和应用会更加多样化。     

The geology of Goa Group: Revisited

The supracrustals that constitute the Goa Group of Gokul et al. (1985) can be divided into two lithostratigraphic sequences namely the Barcem Group and the Ponda Group. The former comprises predominantly greenstones (metabasalts) and rests on a basement of the 3300–3400 Ma Anmode Ghat trodhjemite gneiss with a crudely developed quartz-pebble conglomerate at the base, and shows lithological similarities with the lower part of the Bababudan Group. The younger sequence is dominated by clastics, and is assigned to a new stratigraphic group formally termed the Ponda Group which is equivalent to the Chitradurga Group of the Dharwar Supergroup. This group rests on a basement of the 2700–2900 Ma Chandranath granite gneiss with a distinct unconformity marked by a polymict, granite-clast metaconglomerate. The conglomerate displays many similarities with the Talya conglomerate that occurs at the base of the Chitradurga Group. It is overlain by a psamolitic sequence which is followed in ascending order by the chemogenic sediments that host the BIF and by the deep water turbidite sequence (argillite-graywacke association) with intercalations of mafic volcanics. The supracrustal sequence is intruded by the Bondla layered mafic-ultramafic complex along a major shear zone (NW-SE) that largely controls the course of the northwesterly flowing tributary of River Mandovi. The late intrusive, Canacona potassic granite marks the culmination of the sedimentation in the Shimoga-Goa basin.