Quantification of the relation between surface morphodynamics and subsurface sedimentological product in sandy braided rivers     

Natalie O. Parker  Gregory H. Sambrook Smith  Philip J. Ashworth  James L. Best  Stuart N. Lane  Ian A. Lunt  Christopher J. Simpson  Roberte. Thomas 《Sedimentology》2013,60(3):820-839

This study uses digital elevation models and ground‐penetrating radar to quantify the relation between the surface morphodynamics and subsurface sedimentology in the sandy braided South Saskatchewan River, Canada. A unique aspect of the methodology is that both digital elevation model and ground‐penetrating radar data were collected from the same locations in 2004, 2005, 2006 and 2007, thus enabling the surface morphodynamics to be tied explicitly to the associated evolving depositional product. The occurrence of a large flood in 2005 also allowed the influence of discharge to be assessed with respect to the process–product relationship. The data demonstrate that the morphology of the study reach evolved even during modest discharges, but more extensive erosion was caused by the large flood. In addition, the study reach was dominated by compound bars before the flood, but switched to being dominated by unit bars during and after the flood. The extent to which the subsurface deposits (the ‘product’) were modified by the surface morphodynamics (the ‘process’) was quantified using the changes in radar‐facies recorded in sequential ground‐penetrating radar surveys. These surveys reveal that during the large flood there was an increase in the proportion of facies associated with bar margin accretion and larger dunes. In subsequent years, these facies became truncated and replaced with facies associated with smaller dune sets. This analysis shows that unit bars generally become truncated more laterally than vertically and, thus, they lose the high‐angle bar margin deposits and smaller scale bar‐top deposits. In general, the only fragments that remain of the unit bars are dune sets, thus making identification of the original unit barform problematic. This novel data set has implications for what may ultimately become preserved in the rock record.  相似文献   

Tungsten Mineralization Processes at the Sisson Brook W-Mo-Cu deposit, Central New Brunswick: the Role of Formation of Titaniferous Phases at Reaction Fronts     

BUSTARD Aaron  ZHANG Wei  MCFARLANE Christopher R.M.  LENTZ David 《《地质学报》英文版》2013,87(Z1):672-675

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Using Mg Isotopes to Trace Cyanobacterially Mediated Magnesium Carbonate Precipitation in Alkaline Lakes   总被引：1，自引：0，他引：1  

Liudmila S. Shirokova  Vasileios Mavromatis  Irina A. Bundeleva  Oleg S. Pokrovsky  Pascale B��n��zeth  Emmanuelle G��rard  Christopher R. Pearce  Eric H. Oelkers 《Aquatic Geochemistry》2013,19(1):1-24

This study assesses the potential use of Mg isotopes to trace Mg carbonate precipitation in natural waters. Salda Lake (SW Turkey) was chosen for this study because it is one of the few modern environments where hydrous Mg carbonates are the dominant precipitating minerals. Stromatolites, consisting mainly of hydromagnesite, are abundant in this lake. The Mg isotope composition of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments were measured. Because Salda Lake is located in a closed basin, mass balance requires that the Mg isotopic offset between Lake Salda water and precipitated hydromagnesite be comparable to the corresponding offset between Salda Lake and its water inputs. This is consistent with observations; a ??²⁶Mg offset of 0.8?C1.4??? is observed between Salda Lake water and it is the incoming streams and groundwaters, and precipitated hydromagnesite has a ??²⁶Mg 0.9?C1.1??? more negative than its corresponding fluid phase. This isotopic offset also matches closely that measured in the laboratory during both biotic and abiotic hydrous Mg carbonate precipitation by cyanobacteria (Mavromatis, V., Pearce, C., Shirokova, L. S., Bundeleva, I. A., Pokrovsky, O. S., Benezeth, P. and Oelkers, E.H.: Magnesium isotope fractionation during inorganic and cyanobacteria-induced hydrous magnesium carbonate precipitation, Geochim. Cosmochim. Acta, 2012a. 76, 161?C174). Batch reactor experiments performed in the presence of Salda Lake cyanobacteria and stromatolites resulted in the precipitation of dypingite (Mg₅(CO₃)₄(OH)₂·5(H₂O)) and hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O) with morphological features similar to those of natural samples. Concurrent abiotic control experiments did not exhibit carbonate precipitation demonstrating the critical role of cyanobacteria in the precipitation process.  相似文献   

Fred T. Mackenzie: Gentleman,Scholar, Mountaineer and Model Colleague     

Eric Heinen De Carlo  Rolf S. Arvidson  Lei Chou  Christopher L. Sabine  George W. Luther 《Aquatic Geochemistry》2013,19(5-6):347-351

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Khatyrka,a new CV3 find from the Koryak Mountains,Eastern Russia     

Glenn J. MacPherson  Christopher L. Andronicos  Luca Bindi  Vadim V. Distler  Michael P. Eddy  John M. Eiler  Yunbin Guan  Lincoln S. Hollister  Alexander Kostin  Valery Kryachko  William M. Steinhardt  Marina Yudovskaya  Paul J. Steinhardt 《Meteoritics & planetary science》2013,48(8):1499-1514

A new meteorite find, named Khatyrka, was recovered from eastern Siberia as a result of a search for naturally occurring quasicrystals. The meteorite occurs as clastic grains within postglacial clay‐rich layers along the banks of a small stream in the Koryak Mountains, Chukotka Autonomous Okrug of far eastern Russia. Some of the grains are clearly chondritic and contain Type IA porphyritic olivine chondrules enclosed in matrices that have the characteristic platy olivine texture, matrix olivine composition, and mineralogy (olivine, pentlandite, nickel‐rich iron‐nickel metal, nepheline, and calcic pyroxene [diopside‐hedenbergite solid solution]) of oxidized‐subgroup CV3 chondrites. A few grains are fine‐grained spinel‐rich calcium‐aluminum‐rich inclusions with mineral oxygen isotopic compositions again typical of such objects in CV3 chondrites. The chondritic and CAI grains contain small fragments of metallic copper‐aluminum‐iron alloys that include the quasicrystalline phase icosahedrite. One grain is an achondritic intergrowth of Cu‐Al metal alloys and forsteritic olivine ± diopsidic pyroxene, both of which have meteoritic (CV3‐like) oxygen isotopic compositions. Finally, some grains consist almost entirely of metallic alloys of aluminum + copper ± iron. The Cu‐Al‐Fe metal alloys and the alloy‐bearing achondrite clast are interpreted to be an accretionary component of what otherwise is a fairly normal CV3 (oxidized) chondrite. This association of CV3 chondritic grains with metallic copper‐aluminum alloys makes Khatyrka a unique meteorite, perhaps best described as a complex CV3 (ox) breccia.  相似文献   

Neutron absorption constraints on the composition of 4 Vesta     

Thomas H. Prettyman  David W. Mittlefehldt  Naoyuki Yamashita  Andrew W. Beck  William C. Feldman  John S. Hendricks  David J. Lawrence  Timothy J. McCoy  Harry Y. McSween  Patrick N. Peplowski  Robert C. Reedy  Michael J. Toplis  Lucille Le Corre  Hugau Mizzon  Vishnu Reddy  Timothy N. Titus  Carol A. Raymond  Christopher T. Russell 《Meteoritics & planetary science》2013,48(11):2211-2236

Global maps of the macroscopic thermal neutron absorption cross section of Vesta's regolith by the Gamma Ray and Neutron Detector (GRaND) on board the NASA Dawn spacecraft provide constraints on the abundance and distribution of Fe, Ca, Al, Mg, and other rock‐forming elements. From a circular, polar low‐altitude mapping orbit, GRaND sampled the regolith to decimeter depths with a spatial resolution of about 300 km. At this spatial scale, the variation in neutron absorption is about seven times lower than that of the Moon. The observed variation is consistent with the range of absorption for howardite whole‐rock compositions, which further supports the connection between Vesta and the howardite, eucrite, and diogenite meteorites. We find a strong correlation between neutron absorption and the percentage of eucritic materials in howardites and polymict breccias, which enables petrologic mapping of Vesta's surface. The distribution of basaltic eucrite and diogenite determined from neutron absorption measurements is qualitatively similar to that indicated by visible and near infrared spectroscopy. The Rheasilvia basin and ejecta blanket has relatively low absorption, consistent with Mg‐rich orthopyroxene. Based on a combination of Fe and neutron absorption measurements, olivine‐rich lithologies are not detected on the spatial scales sampled by GRaND. The sensitivity of GRaND to the presence of mantle material is described and implications for the absence of an olivine signature are discussed. High absorption values found in Vesta's “dark” hemisphere, where exogenic hydrogen has accumulated, indicate that this region is richer in basaltic eucrite, representative of Vesta's ancient upper crust.  相似文献   

Place Systems and Social Resilience: A Framework for Understanding Place in Social Adaptation,Resilience, and Transformation   总被引：1，自引：0，他引：1  

Christopher Lyon 《社会与自然资源》2014,27(10):1009-1023

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A Test of Central Place Theory Using Shuttle Imaging Radar (SIR‐A) of China's North Central Plain     

Christopher Shane Davies  Robert K. Holz  David Robertus 《国际地球制图》2013,28(1):14-23

Abstract

This study utilizes radar imagery to test the application of Walter Christaller's central‐place theory on China's North Central Plain. Examination of the spatial order and layout of settlements reveal that central place theory's transportation principle, k=4 exists. The study distinguishes four hierarchical settlement sizes and shows how effective rural societies are in evolving settlement structures whose spatial order and regularity avoids spatial inefficiencies. The advent of space based imaging systems such as SIR‐A radar imagery has permitted tests of new sites where the restrictive conditions of central place theory exist. These studies allow parallels to be drawn between the postulates of this theory of settlement structure and whether the theory is matched in reality.

This work is needed because of such scarcities. It allows the theory to undergo further subjections, a scrutiny needed for the validation, or otherwise of its postulates. The work adds to a large body of literature on this topic whose limitation has been the scarcity of actual test sites where theory and reality can be compared. The study presents positive indications that central place theory exists in reality, a compliment to the remarkable perceptions of Walter Christaller.  相似文献   

Temporal Uncertainty in a Small Area Open Geodemographic Classification     

Christopher G. Gale  Paul A. Longley 《Transactions in GIS》2013,17(4):563-588

The 2001 Output Area Classification (2001 OAC) is an open source geodemographic classification of the UK built exclusively from 2001 UK Census data. There has been considerable user interest in its applicability to subsequent time periods, particularly given the potential propensity of characteristics and attributes in some areas to change during inter‐censual periods. Users often purchase commercial geodemographic classification products in the belief that purely census‐based classifications such as the 2001 OAC are uniformly unreliable because there is no temporal updating of input data. Yet there is evidence to suggest that whilst some UK neighborhoods are prone to sudden changes, many others change very little over protracted time periods. Using measures that are available at the small area level, temporal uncertainty indicators can be constructed to identify those areas that are less stable. Using mid‐year population estimates and dwelling stock data, this article develops three temporal uncertainty indicators. These provide a reliable means of gauging the stability or otherwise of neighborhood conditions. The conclusion from this is that while a large number of small areas in the UK do experience change over time, this change is not uniform in either degree or distribution, or by geodemographic type.  相似文献   

Developing and testing the Automated Post-Event Earthquake Loss Estimation and Visualisation (APE-ELEV) technique     

Anthony Astoul  Christopher Filliter  Eric Mason  Andrew Rau-Chaplin  Kunal Shridhar  Blesson Varghese  Naman Varshney 《Bulletin of Earthquake Engineering》2013,11(6):1973-2005

An automated, real-time, multiple sensor data source relying and globally applicable earthquake loss model and visualiser is desirable for post-event earthquake analysis. To achieve this there is a need to support rapid data ingestion, loss estimation and integration of data from multiple data sources and rapid visualisation at multiple geographic levels. In this paper, the design and development of the Automated Post-Event Earthquake Loss Estimation and Visualisation (APE-ELEV) system for real-time estimation and visualisation of insured losses incurred due to earthquakes is presented. A model for estimating ground up and net of facultative losses due to earthquakes in near real-time is implemented. Since post-event data is often available immediately from multiple disparate sources, a geo-browser is employed to facilitate the visualisation and integration of earthquake hazard, exposure and loss data. The feasibility of APE-ELEV is demonstrated using a test case earthquake that occurred in Tohoku, Japan (2011). The APE-ELEV model is further validated for ten global earthquakes using industry loss data.  相似文献