Late Neogene loess deposition in southern Tarim Basin: tectonic and palaeoenvironmental implications   总被引：2，自引：0，他引：2  

Hongbo Zheng  Chris McA Powell  Katherine Butcher  Junji Cao 《Tectonophysics》2003,375(1-4):49

Uplift of the Tibetan Plateau during the late Cainozoic resulted in a thick apron of molassic sediments along the northern piedmonts of the Kunlun and Altyn Mountains in the southern Tarim Basin. Early Neogene sediments are characterised by sandstone, siltstone and red mudstone, representing floodplain to distal alluvial fan environments. The Early Pliocene Artux Formation consists of medium-grained sandstone and sandy mudstone with thin layers of fine pebbly gritstone. The Late Pliocene to Early Pleistocene Xiyu Formation is dominated by pebble to boulder conglomerate typical of alluvial fan debris flow deposits. Sedimentological investigation, together with grain size and chemical analyses of siltstone bands intercalated with sandstone and conglomerate in the Xiyu and Artux Formations, point to an aeolian origin, suggesting desertic conditions in the Tarim Basin by the Early Pliocene. The onset of aeolian sedimentation in the southern Tarim Basin coincided with uplift of the northern Tibetan Plateau inferred from the lithofacies change from fine-grained mudstone and sandstone to coarse clasts. Tibetan Plateau uplift resulted in the shift of sedimentary environments northwards into the southern Tarim Basin, and could well have triggered the onset of full aridity in the Taklimakan region as a whole.  相似文献   

The chemical composition of fogs and intercepted clouds in the United States     

Jeffrey L. Collett  Jr.  Aaron Bator  D. Eli Sherman  Katharine F. Moore  Katherine J. Hoag  Belay B. Demoz  Xin Rao  Jill E. Reilly 《Atmospheric Research》2002,64(1-4)

Over the past decade, the chemical compositions of fogs and intercepted clouds have been investigated at more than a dozen locations across the United States. Sampling sites have been located in the northeast, southeast, Rocky Mountain, and west coast regions of the US. They include both pristine and heavily polluted locations. Frontal/orographic clouds (warm and supercooled), intercepted coastal stratiform clouds, and radiation fogs have all been examined. Sample pH values range from below 3 to above 7. Major ions also exhibit a wide concentration range, with clouds at some locations exhibiting high sea salt concentrations, while composition at other locations is dominated by ammonium and sulfate or nitrate.  相似文献   

Isotopic composition of carbon and oxygen in desert fauna: investigations into the effects of diet, physiology, and seasonality     

Katherine F. Smith  Zachary D. Sharp  James H. Brown 《Journal of Arid Environments》2002,52(4):419

Carbon and oxygen isotope ratios of bone apatite were measured in 14 endothermic and ectothermic vertebrates native to the Chihuahuan Desert and collected in June and July of 1999 and 2000. The δ⁸O values of most reptiles were very high, up to 44‰ (standard mean ocean water (SMOW), some of the highestδ¹⁸ O values ever measured for an animal. The δ¹⁸O values of rodents and birds were lower (32±5‰ vSMOW), and the earless lizard Holbrookia maculata were the lowest of all species analysed (25‰). Omnivorous grasshopper mice (Onychomys torridus) had lower δ¹⁸O values than granivorous rodents. Results from oxygen analysis likely reflect variation in diet and body water flux differences between endotherms and ectotherms. Carbon isotope analysis revealed a dramatic shift in diet from C₃ plants in 1999 to C₄ plants in 2000 in most rodents and birds. Kangaroo rats and reptiles did not change, having a constantδ¹³ C value indicative of a C₃-based diet in both years. This suggests reliance on winter annual plant seed caches for kangaroo rats, but not other rodents. The carbon isotope data can be explained in terms of seasonal differences within and between years in the timing and intensity of the seasonal rainfall events, and the productivity of summer and winter annual plants. This study illustrates that stable isotope analysis is a powerful method for tracking dietary change and feeding behavior in desert vertebrates.  相似文献   

Spitzer observations of M83 and the hot star, H ii region connection     

Robert H. Rubin  Janet P. Simpson  Sean W. J. Colgan  Reginald J. Dufour  Katherine L. Ray  Edwin F. Erickson  Michael R. Haas  Adalbert W. A. Pauldrach  Robert I. Citron 《Monthly notices of the Royal Astronomical Society》2007,377(4):1407-1418

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Lipids of marine Archaea: Patterns and provenance in the water-column and sediments   总被引：1，自引：0，他引：1  

Courtney Turich  Katherine H. Freeman  Maureen Conte  Stuart G. Wakeham 《Geochimica et cosmochimica acta》2007,71(13):3272-3291

We measured archaeal lipid distributions from globally distributed samples of freshwater, marine, and hypersaline suspended particulate matter. Cluster analysis of relative lipid distributions identified four distinct groups, including: (1) marine epipelagic (<100 m) waters, (2) marine mesopelagic (200-1500 m) and upwelling waters, (3) freshwater/estuarine waters, and (4) hypersaline waters. A pronounced difference in lipid composition patterns is the near absence of ring-containing glycerol dialkyl glycerol tetraethers (GDGTs) at high salinity. Different archaeal communities populate marine (mesophilic Crenarchaeota and Euryarchaeota), and hypersaline environments (halophilic Euryarchaeota) and community shifts can regulate differences in lipid patterns between marine and hypersaline waters. We propose that community changes within meosphilic marine Archaea also regulate the lipid patterns distinguishing epipelagic and mesopelagic/upwelling zones. Changes in the relative amounts of crenarchaeol and caldarchaeol and low relative abundances of ringed structures in surface waters differentiate lipids from the epipelagic and mesopelagic/upwelling waters. Patterns of lipids in mesopelagic (and upwelling) waters are similar to those expected of the ammonia-oxidizing Group I Crenarchaeota, with predominance of crenarchaeol and abundant cyclic GDGTs; non-metric multidimensional analysis (NMDS) shows this pattern is associated with high nitrate concentrations. In contrast, limited culture evidence indicates marine Group II Euryarchaeota may be capable of producing mainly caldarchaeol and some, but not all, of the ringed GDGTs and we suggest that these organisms, along with the Crenarchaeota, contribute to lipids in epipelagic marine waters. Calculated TEX₈₆ temperatures in mesopelagic samples (reported here and in published data sets) are always much warmer than measured in situ temperatures. We propose lipids used in the temperature proxy derive from both Euryarchaeaota and Crenarchaeota, and observed values of TEX₈₆ are subject to changes in their ecology as influenced by nutrient fluctuations or other perturbations. Applications of published core-top TEX₈₆-SST correlations require that (1) the surface waters are always composed of similar communities with the same temperature response and (2) that deeper water GDGT production is not transported to the sediments. Our lipid distribution patterns demonstrate both surface-water archaeal community differences (which accompany greater nutrient influxes, shoaling of mesopelagic Crenarchaeota during upwelling periods, and possibly due to an influx of terrestrial Archaea), and changes in organic matter transport through the water column can affect the distribution of lipids recorded in sediments. We therefore suggest that reported temperature shifts in ancient applications indicate TEX₈₆ lipids recorded not only temperature changes, but also changes in archaeal ecology, nutrient concentrations, and possibly oceanographic conditions.  相似文献   

Extremely red galaxy counterparts to 7C radio sources     

Chris J. Willott  Steve Rawlings  Katherine M. Blundell 《Monthly notices of the Royal Astronomical Society》2001,324(1):1-17

We present RIJHK imaging of seven radio galaxies from the 7C Redshift Survey (7CRS) which lack strong emission lines and we use these data to investigate their spectral energy distributions (SEDs) with models that constrain their redshifts. Six of these seven galaxies have extremely red colours ( R − K >5.5) and we find that almost all of them lie in the redshift range 1< z <2. We also present near-infrared spectroscopy of these galaxies which demonstrate that their SEDs are not dominated by emission lines, although tentative lines, consistent with H α at z =1.45 and z =1.61, are found in two objects. Although the red colours of the 7CRS galaxies can formally be explained by stellar populations that are either very old or young and heavily reddened, independent evidence favours the former hypothesis. At z ∼1.5 at least 1/4 of powerful radio jets are triggered in massive (> L *) galaxies, which formed the bulk of their stars several Gyr earlier, that is at epochs corresponding to redshifts z ≳5. If a similar fraction of all z ∼1.5 radio galaxies are old, then extrapolation of the radio luminosity function shows that, depending on the radio source lifetimes, between 10 and 100 per cent of the near-IR selected extremely red object (ERO) population undergo a radio outburst at epochs corresponding to 1< z <2. An ERO found serendipitously in the field of one of the 7CRS radio sources appears to be a radio-quiet analogue of the 7CRS EROs with an emission line likely to be [O  ii ] at z =1.20. The implication is that some of the most massive elliptical galaxies formed the bulk of their stars at z ≳5 and these objects probably undergo at least two periods of active galactic nucleus activity: one at high redshift during which the black hole forms and another one at an epoch corresponding to z ∼1.5.  相似文献   

Six-color observations of the Eclipsing binary AR Cas     

Katherine C. Gordon  Gerald E. Kron 《Astrophysics and Space Science》1973,23(2):403-416

Depths and phases of both minima of AR Cas in six colors in 1959 are presented. Analysis leads to a color distribution for the secondary component which corresponds to spectral type A5–A7.  相似文献   

Black Sea chemocline oscillations during the Holocene: molecular and isotopic studies of marginal sediments     

Yongsong Huang  Katherine H. Freeman  Richard T. Wilkin  Michael A. Arthur  A. Daniel Jones 《Organic Geochemistry》2000,31(12):642

We measured δ¹³C values of free and sulfur-bound lipids and framboidal pyrite-size distributions in three sediment cores from the southern margins of the Black Sea. The margin cores show a marked difference in the occurrence of biomarkers from green sulfur bacteria compared with the deep-basin cores, as a result of deepening of the chemocline resulting from enhanced mixing and/or decreased light-penetration as a consequence of high turbidity and productivity in shelf waters. Quantitation of biomarkers suggests that photic-zone anoxia along the shelf margin was generally absent during the deposition of unit I, although occurred during the deposition of Unit IIb at two sites.  相似文献   

Magnetic study of serpentinized harzburgites from the Islas Orcadas Fracture Zone     

Nazarova  Katherine A.  Wasilewski  Peter J.  Dick  Henry J.B. 《Marine Geophysical Researches》2000,21(5):475-488

Magnetic properties and bulk densities of 27 serpentinized harzburgite samples from the Islas Orcadas Fracture Zone, located in the vicinity of the Bouvet Triple Junction, have been measured and analyzed. Polished sections were examined using reflected light and scanning electron microscopy to characterize the size and geometric arrangement of opaque minerals. The relationship between the saturation magnetization (I_S) and remanent coercive force (H_R) is considered in terms of the amount of ferrimagnetic material and maghemitization. A suite of continental serpentinites from Canada is offered as contrast, to consider the role of weathering and maghemitization. Magnetite in the Islas Orcadas serpentinites is variably maghemitized, whereas continental serpentinites do not appear to contain maghemitized oxides. We verify this with optical microscopy, thermomagnetic analyses and cryogenic temperature cycling of saturation remanence. Maghemitization serves to reduce initial magnetic susceptibility, and introduce error in the use of I_S to evaluate the magnetic mode of magnetite. The presence of maghemite and the existence of a three dimensional vein network for magnetite geometry would suggest that magnetic hysteresis parameters can not reliably indicate grain size. Magnetic hysteresis ratios fall in a restricted range regardless of coercivity. The apparent grain size configured in a three dimensional vein network plus maghemitization might be responsible for this observation. Maghemitization does not affect thermal magnetic stability and enhances the geophysical importance of remanence in serpentinites. Paleomagnetic data suggest that important information about the geologic circumstances for oceanic rock serpentinization is embodied in the paleomagnetic records. This observation may be very important for generation of long wavelength aeromagnetic and possibly even satellite magnetic anomalies.  相似文献   

Global climate,energy, and economic implications of international energy offsets programs     

Katherine Calvin  Steven Rose  Marshall Wise  Haewon McJeon  Leon Clarke  Jae Edmonds 《Climatic change》2015,133(4):583-596

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