Geochemical studies in the Indian Pass and Picacho Peak Bureau of Land Management Wilderness study areas, imperial county, Southern California     

David B. Smith  Byron R. Berger  Richard M. Tosdal 《Journal of Geochemical Exploration》1987,28(1-3)

The U.S. Geological Survey has conducted geochemical studies in the Indian Pass (CDCA-355), 124 km², and Picacho Peak (CDCA-355A), 23 km², Wilderness Study Areas (WSA's) as part of a program to evaluate the mineral resource potential of designated areas in the California Desert Conservation Area. These two WSA's are of particular interest because they lie within a region which has intermittently produced significant quantities of Au since the mid-1800's, and is currently the site of much exploration activity for additional Au resources. Within a 15-km radius of the WSA's, there is one actively producing gold mine, a major deposit which began production in 1986, and one recently announced discovery. In the reconnaissance geochemical surveys of the two WSA's - 177 μm (-80 mesh) stream sediments, heavy-mineral concentrates from stream sediments, and rocks were prepared and analyzed.Four areas of possible exploration interest were identified within the WSA's. The first area is characterized by anomalous W and Bi in nonmagnetic heavy-mineral concentrates, and is underlain primarily by the Mesozoic Orocopia Schist which has been intruded by monzogranite of Oligocene age. Alteration and mineralization appear to be localized near the intrusive contact. The mineralized rock at the surface contains secondary Cu and Fe minerals where the monzogranite intrudes the metabasite horizons of the Orocopia Schist and scheelite where the monzogranite intrudes marble within the Orocopia Schist.The second area is characterized by anomalous As, Sb, Ba, B, and Sr in nonmagnetic heavy-mineral concentrates and by anomalous As in - 177 μm stream sediments. Geologically, this area is underlain by metasedimentary and metavolcanic rocks of Jurassic(?) age; a biotite monzogranite of Jurassic(?) age; and Tertiary volcanic and hypabyssal rocks composed of flows, domes, and tuffs of intermediate to silicic composition. All these rock types are cut by a set of north-south-striking normal faults. The anomalies in the heavy-mineral concentrates are believed to be related to silica-clay alteration observed in the vicinity of some of these faults.  相似文献   

Fundamental processes controlling the first stage of alteration of a basalt glass by seawater: an experimental study between 200° and 320°C     

Gilles Berger  Jacques Schott  Michel Loubet 《Earth and Planetary Science Letters》1987,84(4)

The first stage of alteration of a basalt glass by seawater has been studied experimentally between 200° and 320°C under vapor pressure, following both the chemical evolution of the reacting solutions during the experiments and the chemical and mineralogical transformations of the altered glass surface via microprobe, scanning transmission electron microscope and resonant nuclear reactions.The alteration is controlled by diffusion of dissolved species through an altered layer and not by surface chemical reaction. Selective removal of cations with respect to SiO₂ leads to the formation of a thick, porous protonated surface layer enriched in SiO₂. Aqueous diffusion of dissolved species from the reacting glass and from solution through the pores of this layer results in the formation of an amorphous silicate gel which is the precursor of normal crystalline clays (saponites) appearing in a later stage.Computer simulations of the alteration generated with the EQ3/6 computer software package account for the chemical composition of the rim and the sequence of secondary minerals found in the experiments.  相似文献   

Experimental determination of turbulent fluxes over the heterogeneous LITFASS area: Selected results from the LITFASS-98 experiment   总被引：1，自引：0，他引：1  

F. Beyrich  S. H. Richter  U. Weisensee  W. Kohsiek  H. Lohse  H. A. R. de Bruin  Th. Foken  M. Göckede  F. Berger  R. Vogt  E. Batchvarova 《Theoretical and Applied Climatology》2002,73(1-2):19-34

Summary ?During the LITFASS-98 experiment, local flux measurements were performed over five different types of underlying surface (grass, barley, triticale, pine forest, water) in a heterogeneous landscape using eddy covariance and profile techniques over a three week time period in June, 1998. Estimates of the area-integrated sensible heat flux during daytime were obtained from continuous measurements with a large aperture scintillometer (LAS) along a 4.7 km path. The calculation of a mean diurnal cycle of the fluxes during the experiment revealed significant differences between the main land use classes. A land-use weighted average of the sensible heat flux was found to be in good agreement with the LAS based estimate, which in turn was supported by other regionally integrated flux estimates from budget considerations and aircraft measurements for a few case studies. The profiles of turbulent quantities measured along a 99 m-tower significantly deviate from “idealised” profiles measured over homogeneous terrain. Peculiarities in the profile structure could be attributed to the heterogeneity of the terrain, namely to the differences in the surface characteristics of the footprint areas for the different tower levels. Received June 6, 2001; revised January 15, 2002; accepted April 4, 2002  相似文献   

Earth system models of intermediate complexity: closing the gap in the spectrum of climate system models   总被引：10，自引：7，他引：10  

M. Claussen  L. Mysak  A. Weaver  M. Crucifix  T. Fichefet  M.-F. Loutre  S. Weber  J. Alcamo  V. Alexeev  A. Berger  R. Calov  A. Ganopolski  H. Goosse  G. Lohmann  F. Lunkeit  I. Mokhov  V. Petoukhov  P. Stone  Z. Wang 《Climate Dynamics》2002,18(7):579-586

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The Origin and Distribution of Salts on Alluvial Fans in The Atacama Desert,Northern Chile     

I. A. Berger  R. U. Cooke 《地球表面变化过程与地形》1997,22(6):581-600

The Atacama Desert has been predominantly hyperarid since the middle Miocene. Combined ionic and X-ray diffraction analysis shows that calcium sulphate is prevalent on three similar alluvial fans in salar basins across a transect of different environments in Antofagasta Province, northern Chile. Differences between the fans were largely due to the effect of local factors on salt input, secondary redistribution and deposit preservation. Thus carbonate was notable in the High Andes (fan C) and Pre-Cordillera (fan B), whereas in the Central Valley (fan A) greater qualities of the more soluble salts (chlorides and nitrates) probably reflect the higher level of aridity and an oceanic source (the camanchaca). Calcium sulphate distribution on the alluvial fans and on adjacent hilltops indicates an aeolian origin. Evidence from the Pre-Cordillera (fan B), however, suggests that salt input may have been episodic, related to changes in conditions within the general aridity and possibly to stone pavement and soil development. Calcium sulphate sources range from an input in Andean precipitation and the camanchaca to abundant regional evaporite deposits. It is probable, however, that products of Andean volcanism constitute the dominant primary source of calcium sulphate, and that the salt has subsequently been distributed widely within the endoreic basins of the region by a combination of groundwater, surface flow and the wind. © 1997 John Wiley & Sons, Ltd.  相似文献   

The planet formation imager     

John D. Monnier  Stefan Kraus  Michael J. Ireland  Fabien Baron  Amelia Bayo  Jean-Philippe Berger  Michelle Creech-Eakman  Ruobing Dong  Gaspard Duchêne  Catherine Espaillat  Chris Haniff  Sebastian Hönig  Andrea Isella  Attila Juhasz  Lucas Labadie  Sylvestre Lacour  Stephanie Leifer  Antoine Merand  Ernest Michael  Stefano Minardi  Christoph Mordasini  David Mozurkewich  Johan Olofsson  Claudia Paladini  Romain Petrov  Jörg-Uwe Pott  Stephen Ridgway  Stephen Rinehart  Keivan Stassun  Jean Surdej  Theo ten Brummelaar  Neal Turner  Peter Tuthill  Kerry Vahala  Gerard van Belle  Gautam Vasisht  Ed Wishnow  John Young  Zhaohuan Zhu 《Experimental Astronomy》2018,46(3):517-529

The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H₂O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality.  相似文献   

Sediment deposition in the northern basins of the North Atlantic and characteristic variations in shelf sedimentation along the East Greenland margin   总被引：1，自引：0，他引：1  

Daniela Berger  Wilfried Jokat 《Marine and Petroleum Geology》2009,26(8):1321-1337

New seismic data off East Greenland were acquired in the summer of 2002, between 77°N and 81°N, north of the Greenland Fracture zone. The data were combined with results from the Greenland Basin and ODP site 909, and indicate a pronounced middle Miocene unconformity within the deep sea basins between 72°N and 81°N. Seismic unit NA-1 consists of sediments older than middle Miocene age and unit NA-2 contains sediments younger than the middle Miocene. Classification of a thinly bedded succession in the Molloy Basin resulted in a subdivision into four units (unit I, unit II, unit IIIA and unit IIIB). A comparison of volume estimations and sediment thickness maps between 72°N and 81°N indicates differences in sediment accumulation in the Greenland, Boreas and Molloy basins. Important controls on the variation of accumulation included different opening times of the basins, as well as tectonic conditions and varying sources of sediment transport.Due to prominent basement structures and the varying reflection character of the sediments along the entire East Greenland margin, we defined an age model of shelf sediments on the basis of similar sediment deposit geometry and known results from other regions. The seismic sequences on the shelf up to an age of middle Miocene are divided into three sub-units along the East Greenland margin: middle Miocene–middle late Miocene (SU-3), middle late Miocene–Pleistocene (SU-2), Pleistocene (SU-1). The differences in the geometry of the sequences show more ice stream related sedimentation between 72°N and 77°N and more ice sheet related sedimentation north of 78°N. The region south of 68°N is dominated by more aggradational sedimentary strata so that a glacio-fluvial drainage seems the main transport mechanism. Due to the Greenland Inland–ice borderlines, we assume the glaciers between the Scoresby Sund and 68°N did not reach the shelf break. A first comparison of the sediment structure of the Northeast Greenland margin with the Southeast Greenland margin made it possible to demonstrate significant differences in sedimentation along this margin.  相似文献   

IUGS and Geological Society of London begin a publishing partnership     

Dr.AntonyR.Berger 《《幕》》2003,26(2):133-133

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News from the IUGS Geoindicator Initiative     

AntonyR.Berger 《《幕》》2004,27(1):55-56

As evidence for abrupt environmental change grows, the task of assessing the effects of rapid geological processes is becoming more important. Increasing interest in tracking and reporting landscape changes that take place within a normal human lifetime is, thus, not surprising. IUGS continues to emphasize the importance of tracking rapid geological change in State of  相似文献   

EMIC Intercomparison Project (EMIP–CO2): comparative analysis of EMIC simulations of climate, and of equilibrium and transient responses to atmospheric CO2 doubling     

V. Petoukhov  M. Claussen  A. Berger  M. Crucifix  M. Eby  A. V. Eliseev  T. Fichefet  A. Ganopolski  H. Goosse  I. Kamenkovich  I. I. Mokhov  M. Montoya  L. A. Mysak  A. Sokolov  P. Stone  Z. Wang  A. J. Weaver 《Climate Dynamics》2005,25(4):363-385

An intercomparison of eight EMICs (Earth system Models of Intermediate Complexity) is carried out to investigate the variation and scatter in the results of simulating (1) the climate characteristics at the prescribed 280 ppm atmosphere CO₂ concentration, and (2) the equilibrium and transient responses to CO₂ doubling in the atmosphere. The results of the first part of this intercomparison suggest that EMICs are in reasonable agreement with the present-day observational data. The dispersion of the EMIC results by and large falls within the range of results of General Circulation Models (GCMs), which took part in the Atmospheric Model Intercomparison Project (AMIP) and Coupled Model Intercomparison Project, phase 1 (CMIP1). Probable reasons for the observed discrepancies among the EMIC simulations of climate characteristics are analysed. A scenario with gradual increase in CO₂ concentration in the atmosphere (1% per year compounded) during the first 70 years followed by a stabilisation at the 560 ppm level during a period longer than 1,500 years is chosen for the second part of this intercomparison. It appears that the EMIC results for the equilibrium and transient responses to CO₂ doubling are within the range of the corresponding results of GCMs, which participated in the atmosphere-slab ocean model intercomparison project and Coupled Model Intercomparison Project, phase 2 (CMIP2). In particular EMICs show similar temperature and precipitation changes with comparable magnitudes and scatter across the models as found in the GCMs. The largest scatter in the simulated response of precipitation to CO₂ change occurs in the subtropics. Significant differences also appear in the magnitude of sea ice cover reduction. Each of the EMICs participating in the intercomparison exhibits a reduction of the strength of the thermohaline circulation in the North Atlantic under CO₂ doubling, with the maximum decrease occurring between 100 and 300 years after the beginning of the transient experiment. After this transient reduction, whose minimum notably varies from model to model, the strength of the thermohaline circulation increases again in each model, slowly rising back to a new equilibrium.  相似文献