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Assessment of widely used methods to derive depositional ages from detrital zircon populations

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geoscience Frontiers 2019年第4期10卷 1421-1435页

作者： Daniel S.Coutts William A.Matthews Stephen M.Hubbard Department of Geoscience University of Calgary

The calculation of a maximum depositional age(MDA)from a detrital zircon sample can provide insight into a variety of geological problems.However,the impact of sample size and calculation method on the accuracy of a resulting MDA has not been evaluated.We use large populations of synthetic zircon dates(N≈25,000)to analyze the impact of varying sample size(n),measurement uncertainty,and the abundance of neardepositional-age zircons on the accuracy and uncertainty of 9 commonly used MDA calculation methods.Furthermore,a new method,the youngest statistical population is tested.For each method,500 samples of n synthetic dates were drawn from the parent population and MDAs were calculated.The mean and standard deviation of each method ove r the 500 trials at each n-value(50-1000,in increments of 50)were compa red to the known depositional age of the synthetic population and used to compare the methods quantitatively in two simulation scenarios.The first simulation scenario varied the proportion of near-depositional-age grains in the synthetic population.The second scenario varied the uncertainty of the dates used to calculate the MDAs.Increasing sample size initially decreased the mean residual error and standard deviation calculated by each method.At higher n-values(>~300 grains),calculated MDAs changed more slowly and the mean resid ual error increased or decreased depending on the method used.Increasing the p roportion of near-depositional-age grains and lowering measurement uncertainty decreased the number of measurements required for the calculated MDAs to stabilize and decreased the standard deviation in calculated MDAs of the 500 samples.Results of the two simulation scenarios show that the most successful way to increase the accuracy of a calculated M DA is by acquiring a large number of low-uncertainty measurements(300300)approach is used if the calculation of accurate MDAs are key to research goals.Other acquisition method s,such as high-to moderate-precision measurement methods(e.g.,1%-5%,2σ)acquiring low-t

关键词： Detrital zircon Maximum depositional age Geochronology Basin chronology LA-ICP-MS

Delineation of spring capture zones in southern Great Basin,USA based on modeling results and geochemical data

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Water Science and Engineering 2022年第3期15卷 189-199页

作者： Anya Zhang Department of Geoscience University of NevadaLas VegasNV 89154-4010USA

The protection zones or capture zones of springs in desert environments can be hard to identify,but they are critical to spring protection.Most springs fed by regional aquifers are susceptible to contamination and groundwater development.The U.S.Environmental Protection Agency has established hydrogeologic mapping methods to delineate protection zones for springs.However,it is often difficult to determine a regional aquifer system's flow pattern with this technique alone,and the use of these methods is not conducive to efficient groundwater management.Particle tracking analysis using a well-conceptualized and calibrated numerical model for the three-dimensional groundwater flow domain feeding a given group of springs can help facilitate the identification of spring capture zone boundaries.Building upon this basis,a multifaceted approach was developed to define clear boundaries of the capture zones for the springs in the Furnace Creek,Ash Meadows,and the Muddy River areas in the southern Great Basin,USA.Capture zones were first delineated from inverse particle tracking and Hydrologic Unit 12 watersheds.Afterwards,they were adjusted based on water budgets,geology,and hydrologically significant faults.Finally,a geochemical analysis of the groundwater chemistry and isotopic data was conducted to verify the extent of each spring capture zone.This multifaceted approach adds confidence to the new delineations.

关键词： Spring capture zone Modeling Geochemical analysis Multivariate statistics Spatial analysis Southern Great Basin

Analysis of unlined pressure shafts and tunnels of selected Norwegian hydropower projects

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第3期10卷 486-512页

作者： Chhatra Bahadur Basnet Krishna Kanta Panthi Department of Geoscience and Petroleum Norwegian University of Science and Technology

Norwegian hydropower industry has more than 100 years of experiences in constructing more than4000 km-long unlined pressure shafts and tunnels with maximum static head of 1047 m（equivalent to almost 10.5 MPa） reached at unlined pressure tunnel of Nye Tyin project. Experiences gained from construction and operation of these unlined pressure shafts and tunnels were the foundation to develop design criteria and principles applied in Norway and some other countries. In addition to the confinement criteria, Norwegian state-of-the-art design principle for unlined pressure shaft and tunnel is that the minor principal stress at the location of unlined pressure shaft or tunnel should be more than the water pressure in the shaft or tunnel. This condition of the minor principal stress is prerequisite for the hydraulic jacking/splitting not to occur through joints and fractures in rock mass. Another common problem in unlined pressure shafts and tunnels is water leakage through hydraulically splitted joints or pre-existing open joints. This article reviews some of the first attempts of the use of unlined pressure shaft and tunnel concepts in Norway, highlights major failure cases and two successful cases of significance, applies Norwegian criteria to the cases and reviews and evaluates triggering factors for failure.This article further evaluates detailed engineering geology of failure cases and also assesses common geological features that could have aggravated the failure. The minor principal stress is investigated and quantified along unlined shaft and tunnel alignment of six selected project cases by using threedimensional numerical model. Furthermore, conditions of failure through pre-existing open joints by hydraulic jacking and leakage are assessed by using two-dimensional fluid flow analysis. Finally, both favorable and unfavorable ground conditions required for the applicability of Norwegian confinement criteria in locating the unlined pressure shafts and tunnels for geotectonic environment different from that of Nor

关键词： Hydropower projects Unlined pressure shafts and tunnels Minor principal stress Hydraulic jacking Water leakage

Is plate tectonics needed to evolve technological species on exoplanets?

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geoscience Frontiers 2016年第4期7卷 573-580页

作者： Robert J.Stern geoscience department University of Texas at Dallas

As we continue searching for exoplanets, we wonder if life and technological species capable of communicating with us exists on any of them. As geoscientists, we can also wonder how important is the presence or absence of plate tectonics for the evolution of technological species. This essay considers this question, focusing on tectonically active roclw （silicate） planets, like Earth, Venus, and Mars. The development of technological species on Earth provides key insights for understanding evolution on exoplanets, including the likely role that plate tectonics may play. An Earth-sized silicate planet is likely to experience several tectonic styles over its lifetime, as it cools and its lithosphere thickens, strengthens, and becomes denser. These include magma ocean, various styles of stagnant lid, and perhaps plate tectonics. Abundant liquid water favors both life and plate tectonics. Ocean is required for early evolution of diverse single-celled organisms, then colonies of cells which specialized further to form guts, ap- pendages, and sensory organisms up to the complexity of fish （central nervous system, appendages, eyes）. Large expanses of dry land also begin in the ocean, today produced above subduction zones in juvenile arcs and by their coalescence to form continents, although it is not clear that plate tectonics was required to create continental crust on Earth. Dry land of continents is required for further evolution of technological species, where modification of appendages for grasping and manipulating, and improve- ment of eyes and central nervous system could be perfected. These bioassets allowed intelligent crea- tures to examine the night sky and wonder, the beginning of abstract thinking, including religion and science. Technology arises from the exigencies of daily living such as tool-making, agriculture, clothing, and weapons, but the pace of innovation accelerates once it is allied with science. Finally, the importance of plate tectonics for developing a technological species is examined via a

关键词： Plate tectonics Exoplanets Planetary science Intelligent life

Petrophysical characterization and 3D seismic interpretation of reservoirs in the Baris Field,onshore Niger Delta Basin,Nigeria

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能源地球科学(英文)

能源地球科学(英文) 2023年第1期4卷 103-116页

作者： Boris B.Bate O.A.Boboye K.F.Fozao Edwin Ayuk Ndip Nancy O.Anene Petroleum geoscience Unit Department of GeoscienceInstitute of Life and Earth SciencePan African UniversityUniversity of IbadanIbadanNigeria department of Petroleum Engineering School of Engineering(NAHPI)University of BamendaCameroon department of Geology University of BueaCameroon

In order to evaluate the petrophysical properties,characterize the structural framework and determine the hydrocarbon in place of potential reservoirs in the Baris Field,onshore Niger Delta Basin,Nigeria,3D seismic and well log data from the field were collected and interpreted using Geographix and Petrel software.Two reservoir zones B2 and B5 were identified having porosity ranging from 21%to 22%,permeability from 235 to 523 mD and water saturation from 16%to 28%.Petrophysical parameters show that the two zones are good reservoirs and highly petroliferous.Seismic interpretation revealed the presence of six listric faults,two major faults(F1 and F2 trending in the northwestesoutheast direction)and four minor faults(F3,F4,F5 and F6).Faults 3,4 and 5 trend in the same direction as the major faults,while fault 6 trends in the northeastesouthwest direction.Two major horizons were identified,and they correspond to the two reservoir tops(B2_top and B5_top).Roll-over anticlinal structures between the two major listric faults were identified.The depositional environment of the Reservoirs B2 and B5 have been deciphered to be of a barrier bar or crevasse play and the trapping mechanism in the Baris Field is a four-way structural closure.STOOIP and GIIP for the two zones have been estimated with the zone B5 more prolific with a STOOIP and GIIP of 7.98MMSTB and 12.77MMMSCF respectively.

关键词： Petrophysical properties Reservoir quality Listric faults GIIP STOOIP

Gardaneh Salavat porphyry copper system: Is it about metal endowment or fertility of the porphyritic intrusion?

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Acta Geochimica 2022年第3期41卷 496-514页

作者： Seyyed Reza Mashhadi Department of Geoscience Aarhus UniversityHøeghGuldbergs Gade 28000 Aarhus CDenmark

Gardaneh Salavat porphyry copper system is located in the northwest of Iran. It comprises a quartz diorite to diorite porphyritic intrusion that created extensive alteration haloes in the host rocks. Despite all technical considerations, the exploration activities did not yield to ore discovery. As the matter of fact, all of the geological,geophysical, and geochemical characteristics of a porphyry Cu-Au deposit exist but there is no economic mineralization. Detailed examinations suggest that the only reasonable explanation can be related to the infertility or low metal endowment of the porphyritic intrusion. The reasons include(1) anomalous ranges of Cu, Au, and Mo rather than economic ore grades,(2) weakly development of potassic alteration,(3) probably sulfur saturation of magma that occurred before intrusion emplacement in the host rocks, and(4) probably low metal endowment in the regional scale and the lack of known porphyry copper deposits in close neighborhoods. It is tried to test the proposed hypothesis with the introduced fertility indicators based on major and trace element geochemistry. However,current fertility indicators could not prove or reject the proposed hypothesis for Gardaneh Salavat porphyritic intrusion because of the high-K calc-alkaline to shoshonitic nature of the intrusive rocks together with the unavailability of relatively fresh/unaltered samples. This case study is notable to examine because(1) it shows that characterization of fertile from barren intrusions seems to be as important as vectoring towards concealed porphyry copper deposits, especially while dealing with deep exploration targets that are associated with high financial risks, and(2) it highlights the inefficiencies and uncertainties in introduced magma fertility indicators for porphyry copper intrusions. As a result, it is of high importance to conduct an overarching investigation on other possible fertility indicators as a fundamental need for the future of the exploration industry.

关键词： Porphyry Copper Fertility Metal endowment Barren intrusion

Deriving a minimum set of viewpoints for maximum coverage over any given digital elevation model data

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International Journal of Digital Earth 2016年第12期9卷 1153-1167页

作者： Xuan Shi Bowei Xue Department of Geoscience University of ArkansasFayettevilleARUSA

This paper introduces how to automatically derive a minimum set of viewpoints for maximum coverage over a large scale of digital terrain data.This is a typical data and computation-intensive research covering a series of geocomputation tasks that have not been implemented efficiently or optimally in prior works.This paper introduces a three-step computational solution to resolve the problem.For any given digital elevation model(DEM)data,automatic generation of control viewpoints is the first step through map algebra calculation and hydrological modeling approaches.For each viewpoint,the viewshed calculation then has to be implemented.The combined viewshed derived from the viewshed of all viewpoints establishes the maximum viewshed coverage of the given DEM.Finally,detecting the minimum set of viewpoints for the maximum coverage is a Non-deterministic Polynomial-time hard problem.The outcome of the computation has broader societal impacts since the research questions and solutions can be adapted into realworld application and decision-making practice,such as the distribution,optimization and management of telecommunication infrastructure and wildfire observation towers,and military tactics and operations dependent upon landscape and terrain features.

关键词： Minimum set maximum coverage viewshed digital terrain optimization

Principles of rockbolting design

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第3期9卷 14-32页

作者： Charlie C. Li Department of Geoscience and Petroleum The Norwegian University of Science and Technology Norway

This article introduces the principles of underground rockbolting design.The items discussed include underground loading conditions,natural pressure zone around an underground opening,design methodologies,selection of rockbolt types,determination of bolt length and spacing,factor of safety,and compatibility between support elements.Different types of rockbolting used in engineering practise are also presented.The traditional principle of selecting strong rockbolts is valid only in conditions of low in situ stresses in the rock mass.Energy-absorbing rockbolts are preferred in the case of high in situ stresses.A natural pressure arch is formed in the rock at a certain distance behind the tunnel wall.Rockbolts should be long enough to reach the natural pressure arch when the failure zone is small.The bolt length should be at least 1 m beyond the failure zone.In the case of a vast failure zone,tightly spaced short rockbolts are installed to establish an artificial pressure arch within the failure zone and long cables are anchored on the natural pressure arch.In this case,the rockbolts are usually less than 3 m long in mine drifts,but can be up to 7 m in large-scale rock caverns.Bolt spacing is more important than bolt length in the case of establishing an artificial pressure arch.In addition to the factor of safety,the maximum allowable displacement in the tunnel and the ultimate displacement capacity of rockbolts must be also taken into account in the design.Finally,rockbolts should be compatible with other support elements in the same support system in terms of displacement and energy absorption capacities.

关键词： Rockbolting design Pressure arch Bolt length Bolt spacing Factor of safety

Determination of total organic carbon content using Passey's method in coals of the central Kalahari Karoo Basin,Botswana

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Petroleum Research 2023年第2期8卷 192-204页

作者： Mamphedi Sylvia Mabitje Mimonitu Opuwari Petroleum geoscience Research Group Department of Earth SciencesUniversity of the Western CapeCape TownSouth Africa

This paper focuses on determining total organic carbon(TOC)from boreholes in the Kalahari Basin,Botswana,using Passey's method.The Kalahari Karoo basin is one of several basins in southern Africa filled with Late Carboniferous to Jurassic sedimentary strata that host Permian age coal seams.Nine exploration boreholes(wells)drilled in the central Kalahari Karoo basin are used to determine the Total Organic Carbon potential.Vitrinite reflectance(Ro),proximate and ultimate analyses were conducted on cored coal intervals.Passey's DLogR method applied in this study employs resistivity and porosity logs to identify and quantify potential source rocks.Results of Passey's method compared with laboratorymeasured carbon showed that Passey's method effectively identifies coal intervals.In terms of TOC calculations,the method works poorly in coal metamorphosed by dolerite intrusions.The heat affected coal samples had Ro from 0.77% to 5.53% and increased in maturity from primarily maceral controlled to high volatile bituminous and anthracite coal.Results from proximate analysis showed compositional changes in the coal were controlled by proximity to sill intrusion,with a decrease in Fixed Carbon and an increase in ash yield in the contact metamorphism zone(2-12 m from sill).For the unaltered coal that has undergone burial maturation displaying Ro of 0.44%-0.65%,the method works well.In unintruded boreholes,correlations between Carbon and calculated TOC indicate strong relationships.Passey's DLogR method proved to be a suitable method of estimating TOC on coal that has undergone burial maturation.This study has demonstrated that TOC calculated from the sonic log is more reliable in coal not affected by contact metamorphism than TOC calculated from the density log.

关键词： Passey's method Vitrinite reflectance Total organic carbon Coal Ultimate analysis Central Kalahari Karoo basin