Reconstruction of the Holocene climate of Transbaikalia: Evidence from the oxygen isotope analysis of fossil diatoms from Kotokel Lake     

S. S. Kostrova  H. Meyer  B. Chapligin  E. V. Bezrukova  P. E. Tarasov  M. I. Kuz’min 《Doklady Earth Sciences》2013,451(1):732-736

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Cobble cam: grain‐size measurements of sand to boulder from digital photographs and autocorrelation analyses     

Jonathan A. Warrick  David M. Rubin  Peter Ruggiero  Jodi N. Harney  Amy E. Draut  Daniel Buscombe 《地球表面变化过程与地形》2009,34(13):1811-1821

A new application of the autocorrelation grain size analysis technique for mixed to coarse sediment settings has been investigated. Photographs of sand‐ to boulder‐sized sediment along the Elwha River delta beach were taken from approximately 1·2 m above the ground surface, and detailed grain size measurements were made from 32 of these sites for calibration and validation. Digital photographs were found to provide accurate estimates of the long and intermediate axes of the surface sediment (r² > 0·98), but poor estimates of the short axes (r² = 0·68), suggesting that these short axes were naturally oriented in the vertical dimension. The autocorrelation method was successfully applied resulting in total irreducible error of 14% over a range of mean grain sizes of 1 to 200 mm. Compared with reported edge and object‐detection results, it is noted that the autocorrelation method presented here has lower error and can be applied to a much broader range of mean grain sizes without altering the physical set‐up of the camera (～200‐fold versus ～6‐fold). The approach is considerably less sensitive to lighting conditions than object‐detection methods, although autocorrelation estimates do improve when measures are taken to shade sediments from direct sunlight. The effects of wet and dry conditions are also evaluated and discussed. The technique provides an estimate of grain size sorting from the easily calculated autocorrelation standard error, which is correlated with the graphical standard deviation at an r² of 0·69. The technique is transferable to other sites when calibrated with linear corrections based on photo‐based measurements, as shown by excellent grain‐size analysis results (r² = 0·97, irreducible error = 16%) from samples from the mixed grain size beaches of Kachemak Bay, Alaska. Thus, a method has been developed to measure mean grain size and sorting properties of coarse sediments. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Reconstruction of paleocoastlines for the northwestern South China Sea since the Last Glacial Maximum   总被引：1，自引：0，他引：1  

YanTao Yao  Jan Harff  Michael Meyer  WenHuan Zhan 《中国科学D辑(英文版)》2009,52(8):1127-1136

The range of relative sea level rise in the northwestern South China Sea since the Last Glacial Maximum was over 100 m. As a result, lowland regions including the Northeast Vietnam coast, Beibu Gulf, and South China coast experienced an evolution from land to sea. Based on the principle of reconstructing paleogeography and using recent digital elevation model, relative sea level curves, and sediment accumulation data, this paper presents a series of paleogeographic scenarios back to 20 cal. ka BP for the northwestern South China Sea. The scenarios demonstrate the entire process of coastline changes for the area of interest. During the late glacial period from 20 to 15 cal. ka BP, coastline slowly retreated, causing a land loss of only 1×10⁴ km², and thus the land-sea distribution remained nearly unchanged. Later in 15–10 cal. ka BP coastline rapidly retreated and area of land loss was up to 24×10⁴km², causing lowlands around Northeast Vietnam and South China soon to be underwater. Coastline retreat continued quite rapidly during the early Holocene. From 10 to 6 cal. ka BP land area had decreased by 9×10⁴km², and during that process the Qiongzhou Strait completely opened up. Since the mid Holocene, main controls on coastline change are from vertical crustal movements and sedimentation. Transgression was surpassed by regression, resulting in a land accretion of about 10×10⁴km². Supported by Key Laboratory of Marginal Sea Geology, Chinese Academy of Sciences (Grant No. MSGL0711), the Guangdong Natural Science Foundation (Grant No. 04001309) and Open Fund of the Key Laboratory of Marine Geology and Environment, Chinese Academy of Sciences (Grant No. MGE2007KG04)  相似文献   

The origin of fluids and nature of fluid–rock interaction in mid-crustal auriferous mylonites of the Renco mine, southern Zimbabwe     

J. Kolb  A. F. M. Kisters  S. Hoernes  F. M. Meyer 《Mineralium Deposita》2000,35(2-3):109-125

Geothermometric constraints on auriferous shear zones of the Renco mine in the Northern Marginal Zone of the late-Archaean, granulite-facies Limpopo Belt in southern Zimbabwe indicate that deformation and associated mineralization occurred at temperatures of at least 600 °C up to more likely 700 °C. Mid- to upper-amphibolite facies conditions during mineralization correspond to the regional-scale retrogression of granulite facies wall rocks during the late-Archaean thrusting of high-grade metamorphic rocks of the Northern Marginal Zone onto low- to medium-grade granite-greenstone terrains of the Zimbabwe craton. Mineral assemblages indicate that the ore fluid was moderately oxidized with log f_O2 values between 10⁻¹⁷ and 10⁻¹⁸ bars with high H₂S activities of 0.25–0.75. Elements enriched in the shear zones include Au, S, Fe, Cu, Mo, Bi, Te, Ni, Co, and H₂O, Au and Cu being the most enriched. Geochemically, Au correlates with Cu but not with S, which, together with the fact that gold is only rarely intergrown or in direct contact with sulfides, possibly indicates a transport of gold as a chloride complex. The siting of gold along fractures or within implosion breccias suggests that gold was precipitated due to fluid immiscibility induced by catastrophic fluid pressure drops during seismic slip events. Fluid inclusions are predominantly CO₂ (±CH₄ ± N₂)-rich, but petrographic work indicates that fluid inclusions have undergone extensive post-entrapment modifications due to the pervasive recrystallization of mineral textures in the high-temperature shear zones. The mineralized shear zones are enriched in ¹⁸O compared to wall-rock enderbites, which is interpreted to represent an influx of externally derived fluids of probably metamorphic origin. Based on temporal and spatial relationships between mineralization, late-Archaean overthrusting of the Northern Marginal Zone onto the Zimbabwe craton, and coeval amphibolite-facies hydration of granulites, we suggest that the Renco mineralization formed in a mid-crustal environment from metamorphic fluids that were generated from dehydration of subcreted greenstone terrains of the Zimbabwe craton. Received: 27 October 1998 / Accepted: 13 August 1999  相似文献   

Structural controls of lode-gold mineralization by mafic dykes in late-Paleozoic granitoids of the Kochkar district, southern Urals, Russia   总被引：2，自引：0，他引：2  

A. F. M. Kisters  F. M. Meyer  S. E. Znamensky  I. B. Seravkin  R. G. W. Ertl  A. M. Kosarev 《Mineralium Deposita》2000,35(2-3):157-168

The Kochkar gold district in the East Uralian Zone of the southern Urals is located in late-Paleozoic granite gneisses of the Plast massif. Gold mineralization is associated with tabular quartz lodes that are preferentially developed along the margins of easterly trending mafic dykes. Fabric development indicates that dykes had a profound influence on the development of shear zones in granitoids. ENE- and SE-trending dykes have been reactivated as dextral and sinistral oblique strike-slip shear zones, respectively, forming a set of approximately conjugate shear zones related to the Permian, regional-scale E-W directed shortening. Dyke-shear zone relationships in the Plast massif are the result of strain refraction due to the presence of biotite-rich, incompetent dykes in more competent granite-gneisses. Deformation and the formation of associated gold-quartz lodes occurred close to peak-metamorphic, upper-greenschist to lower-amphibolite facies conditions. Strain refraction has resulted in partitioning of the bulk strain into a component of non-coaxial mainly ductile shear in mafic dykes, and a component of layer-normal pure shear in surrounding granitoids where deformation was brittle-ductile. Brittle fracturing in granitoids has resulted in the formation of fracture permeabilities adjacent to sheared dykes, that together with the layer-normal dilational component, promoted the access of mineralizing fluids. Both ore-controlling dykes and gold-quartz lodes were subsequently overprinted by lower greenschist-facies, mainly brittle fault zones and associated hydrothermal alteration that post-date gold mineralization. Received: 15 October 1998 / Accepted: 18 August 1999  相似文献   

MANAGEMENT AND SUBSURFACE EFFECTS ON RUNOFF AND SEDIMENT YIELD FROM SMALL WATERSHEDS     

Dabney  S. M.  L. D. Meyer  C. E. Murphree 《国际泥沙研究》2000,(2)

lINTR0DUCTIONSoiler0si0ncanbeaseriousproblemonsl0pinguplands0fthes0uthemUnitedStatesthatareintensivelycr0pped.Conservati0nprovisionsofthel985U.S.FarmBillmandateddevelopmentofaconservati0nplanonhighlyer0diblelands.Researchwasinitiatedinl9870na28-haareaattheA-E.Nels0nFarrninn0rthernMississippit0determineiftheconservati0nprovisionscouldbeachievedwhileprofitablygr0wingrowcropsincludingcott0n(GosSyPiumhirsutumL.),soybean(GlyciDemax(L.)Merr.),sorghum(SOrghumbicolor(L.)Moench),c0rn(Zeam…  相似文献   

Author'Reply     

Solomon A. Isiorho  John H. Meyer 《Ground water》2000,38(3):327-328

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Evolution and observational signature of diffused antiworld     

M. Yu. Khlopov  R. V. Konoplich  R. Mignani  S. G. Rubin  A. S. Sakharov   《Astroparticle Physics》2000,12(4):367-372

The existence of macroscopic regions with antibaryon excess in the baryon asymmetric Universe with general baryon excess is the possible consequence of practically all models of baryosynthesis. Diffusion of matter and antimatter to the border of antimatter domains defines the minimal scale of the antimatter domains surviving to the present time. A model of diffused antiworld is considered, in which the density within the surviving antimatter domains is too low to form gravitationally bound objects. The possibility to test this model by measurements of cosmic gamma ray fluxes is discussed. The expected gamma ray flux is found to be acceptable for modern cosmic gamma ray detectors and for those planned for the near future.  相似文献   

A novel sampling technique for image sharpening in infrared array cameras     

G. Finger  P. Biereichel  M. Meyer  A. F. M. Moorwood 《Experimental Astronomy》1994,3(1-4):185-187

A new nondestructive readout scheme of the array will be presented which allows first order wavefront corrections of images degraded by atmospheric seeing. During the stare time the integration ramp of the detector signal is sampled every 100 msec. A regressional fit of the sampled data points yields the slope of the integration ramp which is proportional to the flux received by a detector pixel. To this readout mode which is commonly used for IR arrays a small software module can be added to compensate the image motion of the observed object by shifting the nondestructively sampled images. This has the same effect as a tip tilt correction by an active optical element - but without the extra complexity of such a device. First results obtained at the telescope are presented.  相似文献   

Heavy-element abundances from a neutron burst that produces Xe-H     

W. Michael Howard  Bradley S. Meyer  Donald D. Clayton 《Meteoritics & planetary science》1992,27(4):404-412

Abstract— We examine quantitatively the suggestion that the heavy anomalous isotopes of Xe-HL found in meteoritic diamonds were produced by a short intense neutron burst and then implanted into the diamonds. Using a large nuclear reaction network we establish one (out of many) neutron irradiation histories that successfully reproduces the heavy isotopes of Xe-HL, and then evaluate what that same history would produce in every heavy element. This has become more relevant following recent measurement of anomalous Ba and Sr in those same diamond samples. Therefore we offer these calculations as a guide to the anomalies to be expected in all elements if this scenario is correct. We also discuss several other aspects of the problem, especially the established contradictions for Ba, the observed Kr pattern, the near normalcy of ¹²⁹Xe, and some related astrophysical ideas. In particular we argue from p-process theory that the observed deficit of ⁷⁸Kr in correlation with ^124–126Xe excess implicates Type II supernovae as the diamond sources. However, our more complete astrophysical conclusions will be published elsewhere. This present work is offered as computational expectation for this class of models and as a guide to considerations that may accelerate the digestion of new experimental results in the diamonds.  相似文献