Transient photoluminescence from highly disordered silica-rich natural phases with and without nanostructures   总被引：1，自引：0，他引：1  

E.?Fritsch  J.?Wéry  G.?Jonusauskas  E.?FaulquesEmail author 《Physics and Chemistry of Minerals》2003,30(7):393-400

The ultrafast transient photoluminescence of impact silica-rich glasses and nanostructured opals is investigated at the (sub)nanosecond time scale. Spectral and temporal data were acquired with a high-resolution streak camera under high-density energy laser excitation at 4.17 eV (297 nm). All samples reveal blue photoluminescence relaxing in less than 50 ns. Relaxation decays and luminescence energy vary strongly from opals to impact glasses. Opals are found to relax in less than 16 ns with a maximum emission at 2.6–2.8 eV (443–477 nm) while the high-silica glasses exhibit a much longer luminescence in the 50-ns time window, which is spectrally blueshifted towards 3.0–3.5 eV (354–413 nm). Results are interpreted in terms of the presence of nonbridging oxygen atoms, network modifiers, and nanostructures which produce emission from self-trapped excitons and from excitons recombining at surface defects. The short-lived emissions of opals are characteristic of intrinsic surface photoluminescence quenched after about 10 ns via nonradiative decay channels with an annihilation component, and involve recombination luminescence of self-trapped excitons.  相似文献   

洛川黄土剖面中蛋白石的发现及其意义          下载免费PDF全文

赵惠敏  袁宝印 《地质科学》1991,(4):399-402

洛川黄土剖面位于陕西省中部,洛川县城南5km 的坡头村附近。该剖面厚度大、地层发育较完整,系第四纪(Q₃—Q₁)风成堆积黄土中的典型剖面。前人从多方面进行过广泛深入研究。黄土的主要矿物成分为石英、长石和/或云母、方解石。在物质成分研究中提到过50多种矿物,但未涉及蛋白石。在黄土的风化成土作用研究中提到“植物蛋白岩偶见”(刘东生等,1985),但未作蛋白石矿物学工作。笔者这次发现的蛋白石,作了较多的矿物学研究。  相似文献   

Paleolimnological evidence of Holocene climatic changes in Lake Blanca, southern Uruguay     

L. del Puerto  F. García-Rodríguez  H. Inda  R. Bracco  C. Castiñeira  J. B. Adams 《Journal of Paleolimnology》2006,36(2):151-163

Paleolimnological data are presented on Holocene climatic changes in Lake Blanca, a small (0.6 km²), coastal fresh waterbody in southern Uruguay. Using a sediment core that extended to 7,300 year BP, analyses of pooid, panicoid and chloridoid phytoliths (Poaceae) allowed us to identify 16 Opal Phytoliths Association Zones (OPAZ). Both temperature and humidity indices were calculated from relative percentages of opal phytoliths and the climatic trends were inferred. During the early Holocene, prior to the first Holocene marine transgression (∼ ∼8,000–7,000 yr BP), cool-arid climatic conditions were inferred. After the first Holocene transgression, predominance of cool-humid conditions was registered until about 4,000 yr BP. A transition from cool-semiarid/arid to alternate warm-temperate and humid-very-humid conditions was detected for ∼∼4,000–1,000 yr BP. Increases in trophic state were observed because of such a climatic amelioration. After ∼ ∼1,000 yr BP, a shift from warm to temperate and cool temperatures was inferred. Such a cooling episode was assigned to a “LIA” which took place by the end of the 18th century and the beginning of the 19th century. A decrease in trophic state was observed during this climatic deterioration. After such a little ice age, present temperate humid conditions were established. The humidity indices calculated from relative percentages of opal phytoliths for the last ∼ ∼70 years were compared to annual rainfall data. Such a comparison showed that opal phytoliths are reliable indicators of humidity.  相似文献   

Particulate organic matter and ballast fluxes measured using time-series and settling velocity sediment traps in the northwestern Mediterranean Sea     

Cindy Lee  Michael L. Peterson  Stuart G. Wakeham  Robert A. Armstrong  J. Kirk Cochran  Juan Carlos Miquel  Scott W. Fowler  David Hirschberg  Aaron Beck  Jianhong Xue 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1420-1436

Prompted by recent data analyses suggesting that the flux of particulate organic carbon sinking into deep waters is determined by fluxes of mineral ballasts, we undertook a study of the relationships among organic matter (OM), calcium carbonate, opal, lithogenic material, and excess aluminum fluxes as part of the MedFlux project. We measured fluxes of particulate components during Spring and Summer of 2003, and Spring of 2005, using a swimmer-excluding sediment trap design capable of measuring fluxes both in a time-series (TS) mode and in a configuration for obtaining particle settling velocity (SV) profiles. On the basis of these studies, we suggest that distinct OM–ballast associations observed in particles sinking at a depth of 200 m imply that the mechanistic basis of the organic matter–ballast association is set in the upper water column above the Twilight Zone, and that the importance of different ballast types follows the seasonal succession of phytoplankton. As in other studies, carbonate appears to enhance the flux of organic matter over opal. Particles must be at least half organic matter before their settling velocity is affected by ballast concentration. This lack of change in ballast composition with SV in particles with <40% OM content suggests that particle SV reaches a maximum because of the increasing importance of inertial drag. Relative amounts of OM and opal decrease with depth due to decomposition and dissolution; carbonates and lithogenic material contribute about the same amount to total mass, or increase slightly, throughout the water column. The high proportion of excess Al cannot be explained by its incorporation into diatom opal or reverse weathering, so Al is most likely adsorbed to particulate oxides. On shorter time scales, dust appears to increase particle flux through its role in aggregation rather than by nutrient inputs enhancing productivity. We suggest that the role of dust as a catalyst in particle formation may be a central mechanism in flux formation in this region, particularly when zooplankton fecal pellet production is low.  相似文献   

Ba, Si, U, Al, Sc, La, Th, C and C/C in a sediment core in the western subarctic Pacific as proxies of past biological production     

Masahito Shigemitsu  Hisashi Narita  Yutaka W. Watanabe  Naomi Harada  Shizuo Tsunogai 《Marine Chemistry》2007,106(3-4):442-455

A sediment core covering the last 145 kyrs was collected in the western subarctic Pacific (WSAP), and analyzed for Ba, U, Al, Sc, La, Yb, Th, biogenic opal (Opal) and organic carbon (C_org) as well as its isotopic ratio (δ¹³C). This study examined the change of past biological production in WSAP with multiple proxies, together with understanding the relation between Loess from the Asian continent and the biological production. The Loess content was estimated from the metal components, Al, Sc, La, Yb and Th. In this high latitude core (50°N), the Loess content was generally high during the glacial periods, but it was also high even in some interglacial periods. The excess amount of Ba relative to the detrital material composition, Ba_ex, showed the best correlation with the Vostok δD (r = 0.72, p < 0.001), indicating that the biological production was lower in the glacial periods than in the interglacials. This corroborates the pervasive correlation between Ba_ex in the polar region, WSAP and the Antarctic Sea, and Antarctic temperature, combined with previous research. This correlation might be explained by the stratification caused by cooling. In addition, the time variations of Ba_ex in WSAP were similar to those of Ba_ex in the Okhotsk Sea and of other proxies (C_org and Opal) in both the Okhotsk and the Bering Sea, indicating the spatial homogeneity of Ba_ex in WSAP including proximal marginal seas. The Opal content was more weakly correlated with the Vostok δD (r = 0.46, p < 0.001) than Ba_ex, reflecting that Opal in WSAP including proximal marginal seas was spatially heterogeneous compared to Ba_ex. While both the C_org content and U_ex, the excess amount of U relative to the detritus composition, were not positively correlated with the Vostok δD, they behaved similarly in the sediments. The positive correlation between δ¹³C and the Vostok δD (r = 0.42, p < 0.001), between δ¹³C and Ba_ex (r = 0.60, p < 0.001) and between δ¹³C and Opal (r = 0.36, p < 0.01) indicates that δ¹³C in WSAP may give some information on the phytoplankton growth rate. There was not a significant correlation between the spatially homogeneous Ba_ex in WSAP and Loess (r = − 0.16, p > 0.01), suggesting that the increase of biological production with the increase of Loess supply during the glacial periods did not occur.  相似文献   

The hot spring and geyser sinters of El Tatio, Northern Chile     

J.L. Fernandez-Turiel  M. Garcia-Valles  D. Gimeno-Torrente  J. Saavedra-Alonso  S. Martinez-Manent 《Sedimentary Geology》2005,180(3-4):125-147

The siliceous sinter deposits of El Tatio geothermal field in northern Chile have been examined petrographically and mineralogically. These sinters consist of amorphous silica (opal-A) deposited around hot springs and geysers from nearly neutral, silica-saturated, sodium chloride waters. Water cooling and evaporation to dryness are the main processes that control the opal-A deposition in both subaqueous and subaerial settings, in close spatial relation to microbial communities. All fingerprints of organisms observed in the studied sinter samples represent microbes and suggest that the microbial community is moderately diverse (cyanobacteria, green bacteria, and diatoms). The most important ecological parameter is the temperature gradient, which is closely related to the observed depositional settings: 1) Geyser setting: water temperature = 70–86 °C (boiling point at El Tatio: 4200 m a.s.l.); coarse laminated sinter macrostructure with rapid local variations; biota comprises non-photosynthetic hyperthermophilic bacteria. 2) Splash areas around geysers: water temperature = 60–75 °C; laminated spicule and column macrostructure, locally forming cupolas (< 30 cm); predominant Synechococcus-like cyanobacteria. 3) Hot spring setting: water temperature = 40–60 °C; laminated spicules and columns and subspherical oncoids characterize the sinter macrostructure; filamentous cyanobacteria Phormidium and diatoms (e.g., Synedra sp.) are the most characteristic microbes. 4) Discharge environments: water temperature = 20–40 °C; sinter composed of laminated spicules and oncoids of varied shape; cyanobacterial mats of Phormidium and Calothrix and diatoms (e.g., Synedra sp.) are abundant. El Tatio is a natural laboratory of great interest because the sedimentary macrostructures and microtextures reflect the geological and biological processes involved in the primary deposition and early diagenesis of siliceous sinters.  相似文献   

Relationships between Trophic State, Paleosalinity and Climatic Changes during the First Holocene Marine Transgression in Rocha Lagoon, Southern Uruguay     

H. Inda  F. García-Rodríguez  L. del Puerto  V. Acevedo  D. Metzeltin  C. Castiñeira  R. Bracco  J. B. Adams 《Journal of Paleolimnology》2006,35(4):699-713

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Rocha Lagoon, a 72 km² coastal lagoon in southern Uruguay. Using a sediment core that extended from 7000 to about 3700 yr BP, analyses of organic matter, carbonate, diatoms and chrysophyte cysts were used to track the early Holocene paleolimnological conditions of Rocha Lagoon. Opal phytoliths were also counted and identified, both temperature and humidity indices were calculated, and Opal Phytolith Association Zones (OPAZ) were identified by performing Principal Coordinates Analysis (PCO). Diatom Association Zones (DAZ) corresponding to marine/brackish and brackish/freshwater episodes were closely related to changes in trophic state. Those DAZ representing marine/brackish stages exhibited a lower trophic state than those DAZ dominated by brackish and freshwater diatoms. This highlights that during the first Holocene marine transgression, Rocha Lagoon did not continuously exhibit marine/brackish conditions as reported in previous papers. Instead, three brackish/freshwater episodes related to sea level variation and changes in humidity were identified. The first episode, by ~6000 yr BP, was related to sea level change as no significant changes in either temperature or humidity indices were observed. The second episode, between 5000 and 4400 yr BP, was related to both a sea level decrease and an increase in humidity, as a transition from humid to very humid climate was inferred. Concomitant decreases in salinity and increases in trophic state were also observed. The third episode, after ~4000 yr BP, was related to the end of the first Holocene regressive phase when sea level was slightly below present levels. Further decreases in salinity and increases in trophic state were detected. The paleoclimatic trends inferred in this study were in close agreement with other regional studies on climatic change, as cool temperatures were inferred. However, major changes in humidity were also detected. A humid to very humid climate was inferred for ~7000–4500 yr BP, but the occurrence of a semiarid/arid climate was inferred for ~4500–3700 yr BP. Our data suggest that during transgressive and regressive events there might be higher frequency and lower amplitude sea level oscillations that might lead to changes in salinity and trophic state of coastal aquatic systems. Such oscillations could only be tracked by high resolution analyses of sedimentary records and could be best interpreted with complementary data on paleoclimate. In addition, microfossils such as diatoms and opal phytoliths were shown to be very sensitive to such paleoenvironmental changes.  相似文献