Chromium Augite - A New Microprobe Reference Sample     

Eugene JAROSEWICH  Ron GOOLEY  John HUSLER 《Geostandards and Geoanalytical Research》1987,11(2):197-198

A microprobe reference sample was made from a portion of a large and homogeneous single crystal of augite which contains 0.85% of Cr₂O₃. The relatively high chromium content of this augite increases its usefulness as a microprobe reference sample.  相似文献   

Geothermal and other effects on amino acid racemization in selected Deep-Sea Drilling Project cores     

Barry J. Katz  Christopher G.A. Harrison  Eugene H. Man 《Organic Geochemistry》1983,5(3):151-156

Kinetic parameters for the epimerization of isoleucine in multispecific foraminiferal asemblages were used to establish the effects of burial depth and the geothermal gradient on the extent of reaction. It was observed that with a little as thirty meters of burial in a normal thermal regime there were differences between the extent of epimerization measured and that which would have been predicted for thermal equilibrium with bottom water temperatures. As would be expected, these differences are greatest when the heat flow (the geothermal gradient) and/or the sedimentation rates are highest. These effects were observed in most of the DSDP samples studied, and have been used to estimate the average heat flux since the time of sample deposition. Occasional anomalous effects were observed which could not be related to past or present heat flux. These were determined to be due to such geologic occurrences as slumping and reworking or to recent sample contamination. Other problems emerged related to bottom water temperatures including changes over geologic time which are unknown and could not be deduced. Thus, the presence of epimerization anomalies in DSDP cores as noted above limits the effectiveness of amino acid geochronology in such cores, unless these anomalies can be recognized as ab initio.  相似文献   

Use of Ground Water in Developing the Mekong Delta, Republic of Viet Nam     

Eugene D. Michael 《Ground water》1971,9(1):20-24

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Retrograde garnet zoning at low water pressure in metapelitic rocks from Kemiö, SW Finland     

Eugene J. L. Dietvorst 《Contributions to Mineralogy and Petrology》1982,79(1):37-45

The compositional zoning of almandine-spessartine garnet has been studied in pelitic gneisses from the Kemiö region, SW Finland. Garnets with inverse zoning (outward increase in Mn) abound in the low-grade musc+qz zone. Garnets with inverse zoning, normal zoning (outward decrease in Mn), and with a homogeneous composition occur in the higher-grade sill+ Kfs zone. The formation of garnet with inverse zoning is explained by continuous retrograde reactions in the model system K₂O-Al₂O₃-FeO-MnO-MgO-SiO₂-H₂O at strongly reduced partial water pressures.A comparison of temperatures based on critical metamorphic reactions and on garnet-biotite thermometry shows the usefulness of geothermometry in rocks with spessartine-rich garnet and Mn-bearing biotite.  相似文献   

Reminiscing my sixty year pursuit of the physics of the Sun and the Galaxy     

Eugene N.Parker 《天文和天体物理学研究(英文版)》2014,(1):1-14

Reminiscing begins with childhood and passes on to student days through graduate school and the first real contact with research.Then early academic positions and stumbling efforts to pursue my ideas.The first significant progress came as a research associate with Prof.W.M.Elsasser at the University of Utah,beginning with an introduction to magnetohydrodynamics and the generation of the geomagnetic field through induction in the liquid metal core of Earth.A move to the University of Chicago to work with Prof.J.A.Simpson,on the implications of cosmic ray variations and interplanetary magnetic fields,led to the theory of coronal expansion and the solar wind and then to exploring the dynamical effects of cosmic rays on the galactic magnetic field.Spontaneous current sheets and intrinsic rapid reconnection in interlaced magnetic field line topologies were the next big project,leading up to retirement.Finally,it is a pleasure to recall my many associates,whose fresh thinking helped stimulate the daily research activities.  相似文献   

Spatial and Temporal Variability of Ocean Temperature over the Labrador Shelf     

E.B. Colbourne  G. Mertz 《大气与海洋》2013,51(4):299-317

Abstract

The mid‐to‐bottom waters of the Labrador Shelf are shown to exhibit an anomalous along‐shelf temperature gradient, with warmer waters found in the north. This feature is present in summer and autumn but appears to reverse in December. Inadequate data are available during winter and spring to draw firm conclusions regarding this feature. A time averaged heat loss of the shelf waters to the atmosphere would result on average, in colder waters in the south (because of north‐south advection); however, it is shown that there is a net annual‐mean input of heat to the shelf waters. An examination of the seasonal temperature cycle at standard depths reveals that its phase is almost uniform below 30‐m depth on the northern banks of the Labrador Shelf. The limited phase variation suggests the influence of a plume of well mixed water originating near Hudson Strait. It thus appears that mixing at the entrance to Hudson Strait imparts a phase anomaly to the seasonal cycle in the north that contributes to the observed inversion of the expected latitudinal temperature gradient.  相似文献   

Depositional environment and OSL chronology of the Homeb silt deposits, Kuiseb River, Namibia     

Pradeep Srivastava  George A. Brook  Eugene Marais  P. Morthekai  Ashok K. Singhvi 《Quaternary Research》2006,65(3):478-491

Previous studies suggest that the Homeb silts of the Kuiseb valley, Namibia (i) accumulated in a dune-dammed lake, (ii) are end-point deposits, (iii) represent an aggrading river bed, and (iv) are slackwater deposits. Thus, they have been used alternatively as evidence of past drier conditions or past wetter conditions. Lithostratigraphic analysis of two sediment sequences at Homeb indicates sedimentation by aggradation of the Kuiseb River triggered by a transition from an arid to humid climate. OSL ages for the sequences were obtained by the SAR protocol on aliquots of 9.6-mm and 4.0-mm diameter and on single grains. Four-millimeter aliquot minimum ages closely approximate the single-grain minimum ages and are younger than 9.6-mm aliquot minimum and central ages. Based on these results, the small-aliquot (4-mm) approach appears to provide ages comparable to those obtained by the more laborious and time-consuming single-grain method. Minimum ages indicate rapid deposition of the Homeb Silts in at least two episodes centered at 15 ka and 6 ka during climate transitions from arid to humid. Flash floods eroded the valley fills during slightly more arid conditions.  相似文献   

A simple method to model the reduced environment of lake bottom sapropel formation     

Gaskova  Olga L.  Strakhovenko  Vera D.  Ermolaeva  Nadezhda I.  Zarubina  Eugene Yu.  Ovdina  Ekaterina A. 《中国海洋湖沼学报》2017,35(4):956-966

The Kambala and Barchin brackish lakes(Baraba steppe,southern West Siberia) contain an organic-rich sapropel layer that was formed in oxygen-depleted waters.We measured the bulk sediment elemental composition,the water chemistry and determined the mineralogical composition and predominant biota species(Diatoms and Cyanobacteria in phytoplankton community respectively) in the lakes.The result indicates that the first lake has a siliceous type of sapropel and the second a carbonaceous one.A computer thermodynamic model was developed for chemical interaction in water-bottom sediment systems of the Kambala and Barchin Lakes.The surface sodium bicarbonate waters are supersaturated with respect to calcite,magnesite(or low Mg-calcite),quartz and chlorite with minor strontianite,apatite and goethite(pH8.9-9.3,Eh 0.3 V).Nevertheless,it is shown that during sapropel deposition,deep silt waters should be anoxic(Eh0 V).The virtual component CH_2O has been used to create an anoxic environment suitable for pyrite formation due to the biotic community impact and abiotic reduction.Thermodynamic calculation has shown that silt water is not necessarily euxinic(anoxic and sulfidic).Depending on Eh,sulfate sulfur can dominate in solution,causing the formation of gypsum together with pyrite.An attempt was made to find a reason for solution supersaturation with respect to Ca and Mg ions due to their complexation with humic acids.  相似文献   

GPS揭示的贝加尔湖地区现今地壳形变特征   总被引：2，自引：0，他引：2  

孟国杰  申旭辉  伍吉仓  任金卫 《大地测量与地球动力学》2006,26(1):15-20

利用贝加尔湖地区GPS监测网测站坐标,根据边长尽量相等的原则,形成了11个Delaunay三角形,计算了各三角形的形状因子,结果表明有9个三角形的形状因子大于0.1。利用3期GPS观测结果,通过对位移速率和应变分量的分析,初步得到以下基本认识贝加尔湖地区目前整体上处于拉张状态,拉张速度约为4.5±1.2mm/a,拉张方向为NW-SE方向;地壳应变是不均匀的,应变分量存在区域上的差异性。东部和西部主张应变均为NW向,但主压应变方向表现不一致,监测网东西两端的应变大于中部地区,最大应变为5.4×10-8,最小应变为-2.6×10-8。贝加尔湖东南部地壳处于压缩状态,压缩方向为NNW向和NNE向;东西部剪切应变比中部大,东西部剪切应变方向基本一致,表现为近南北向;7个三角形的面应变计算结果显示地壳为膨胀状态,2个三角形显示为压缩状态。大地转动结果表明,东北部表现为顺时针的旋转,而西部地区和中部显示为逆时针的旋转。GPS揭示的应变结果与地质和地震学结果基本一致。  相似文献   

Use of archaeology to date liquefaction features and seismic events in the New Madrid seismic zone,Central United States     

Martitia P. Tuttle  Robert H. Lafferty  Margaret J. Guccione  Eugene S. Schweig  Neal Lopinot  Robert F. Cande  Kathleen Dyer-Williams  Marion Haynes 《Geoarchaeology》1996,11(6):451-480

Prehistoric earthquake-induced liquefaction features occur in association with Native American occupation horizons in the New Madrid seismic zone. Age control of these liquefaction features, including sand-blow deposits, sand-blow craters, and sand dikes, can be accomplished by extensive sampling and flotation processing of datable materials as well as archaeobotanical analysis of associated archaeological horizons and pits. This approach increases both the amount of carbon for radiocarbon dating and the precision dating of artifact assemblages. Using this approach, we dated liquefaction features at four sites northwest of Blytheville, Arkansas, and found that at least one significant earthquake occurred in the New Madrid seismic zone between A.D. 1180 and 1400, probably about A.D. 1300 ± 100 yr. In addition, we found three buried sand blows that formed between 3340 B.C. and A.D. 780. In this region where very large to great earthquakes appear to be closely timed, archaeology is helping to develop a paleoearthquake chronology for the New Madrid seismic zone. © 1996 John Wiley & Sons, Inc.  相似文献