Provenance and distribution of tethyan pelagic and hemipelagic siliceous sediments,pindos mountains,Greece   总被引：2，自引：0，他引：2  

Miriam Baltuck 《Sedimentary Geology》1982,31(1):63-88

The broad range of time over which ribbon bedded cherts were deposited does not extend into the present marine environment, and no ribbon cherts have been recovered from the sea floor by the Deep Sea Drilling Project. The depositional environment of bedded cherts is difficult to determine, but extra-silicic impurities in the rock may offer clues about the provenance of the non-biogenic component. To test the usefulness of relative abundances of the extra silicic components in extracting information on the depositional environment of the chert, I analyzed the major element chemistry of chert samples from a broad range of environments including ophiolite-associated chert from the Franciscan Formation of California, deep-sea chert and porcellanite from the northwest Pacific (DSDP Leg 32), shallow pelagic shelf chert nodules from the Chalk of Britain, continental marginal basin chert from the Monterey Formation of California, and continental marginal basin chert from the Pindos Zone of Greece. The ratios FeO/A1₂O₃, TiO₂/A1₂O₃ and A1/A1+Fe+Mn were considered in detail. The interpretative logic is simple but empirically supported by observations of these ratio values at different depositional environments in the Pacific: A1 is concentrated most highly in continental material while Fe and Mn are more concentrated in pelagic sediments. FeO/A1₂O₃ can be used to differentiate between ophiolite associated chert and chert associated only with other sediments. TiO₂/A1₂O₃ is not a useful indicator, possibly because of the equalizing effect of widespread eolian transport. The A1/A1+Fe+Mn ratio was measured in detail in one stratigraphic section in central continental Greece. This ratio varied with the type of sediment admixture, decreasing in value after the influx of ophiolite debris-bearing sediments, even when their presence was undetectable in hand sample or under petrographic microscope.To help clarify the paleogeography of the main study area, the Pindos Zone, and to identify sources and dispersal patterns of extra-basinal materials, isopach maps of sedimentary facies of the Pindos were constructed. Superimposed directly upon the series of imbricated thrust slices that comprise the Pindos Zone, the maps are at best compressed pictures of the Pindos Sea Floor. Persistent regional variation of facies thicknesses over time suggests the existence of several smaller depressions surrounded by submarine highs in the Pindos Basin.  相似文献   

Evidence for extensive diagenesis,Madagascar Basin,Deep Sea Drilling Site 245     

Joris M. Gieskes  Miriam Kastner  Theodore B. Warner 《Geochimica et cosmochimica acta》1975,39(10):1385-1393

Deep Sea Drilling Hole 245 (31°32′S, 52° 18′E) in the southwest Indian Ocean shows pronounced linear concentration-depth gradients in interstitial dissolved Ca, Mg and Sr. Electrical conductivity tests enable us to make the estimate of a constant diffusion coefficient with depth of about 2 × 10^?6 cm²/sec. The shapes of the concentration-depth gradients suggest that the major reaction sites in this hole are situated in the basal sediments and/or underlying basalts. It is proposed that observed interstitial water concentration changes in Ca and Mg are related to alteration of basaltic material, whereas those in Sr are due to calcium carbonate recrystallization processes. Support for the basaltic material alteration hypothesis comes from petrochemical and mineralogical data. Geochemical data also indicate that the high contents in Fe and Mn of the basal sediments can be related to low temperature alteration of basaltic glass and not necessarily to ‘hydrothermal’ activity.  相似文献   

The magnetic effects of brecciation and shock in meteorites: I. The Ll-chondrites     

Aviva Brecher  Judy Stein  Miriam Fuhrman 《Earth, Moon, and Planets》1977,17(3):205-216

The complex brecciation and shock history of amphoterite (LL-) chondrites is well reflected in their diverse natural magnetic remanence (NRM) behavior: Most LL-chondrites have a multicomponent, undemagnetizable NRM, analogous to that of lunar breccias. Only one meteorite among those studied, namely Dhurmsala (LL6), meets the criteria of NRM stability and directional coherence with progressive AF cleaning, indicative of a useful paleoremanence. Ancient field paleointensity determinations for Dhurmsala (LL6) of 0.03 and 0.1 Oe, agree well with our earlier estimates of 0.01 and 0.08 Oe for the LL6 Jelica and Vavilovka, respectively. In light of their petrographic structure, cooling rates, radiometric ages and shock indicators, it appears likely that the NRM may have been thermally imprinted, during cooling following shock-metamorphism. The closely similar saturation remanence (IRM_s) behavior for LL-chondrites, in contrast to the intragroup scatter in NRM characteristics, implies that - although formed by similar process from the same starting material, - the LL-chondrites have suffered widely different degrees of shock/metamorphic reheating.  相似文献   

Southern Ocean deglacial record supports global Younger Dryas     

Miriam S Andres  Stefano M Bernasconi  Ursula Röhl 《Earth and Planetary Science Letters》2003,216(4):515-524

In Northern Hemisphere deglaciation records, the transition from the last glacial to the Holocene indicates a rapid return to near-glacial conditions during the Younger Dryas, whereas their Southern Hemisphere ice core counterparts record two separate cooling events: the Antarctic Cold Reversal and the Oceanic Cold Reversal. Spatial distribution and relative timing of these events in both hemispheres are central for our understanding of causes and mechanisms of abrupt climate change. To date, no marine record from the southern mid-latitudes conclusively demonstrates that the Younger Dryas was a significant event in the Southern Ocean. Here, we present high-resolution oxygen isotope and iron content records of a radiocarbon-dated sedimentary sequence from the Great Australian Bight, which constrains oceanic and atmospheric changes during the last deglaciation. Oxygen isotopes from planktonic foraminifera indicate two rapid cold reversals (between 13.1 and 11.1 kyr BP) separated by a brief warming. The sedimentary iron content, interpreted as a proxy for wind strength, indicates a simultaneous change in atmospheric circulation pattern. Both records demonstrate the existence of cooling events in the Southern Hemisphere, which are synchronous with the Northern Hemisphere Younger Dryas cold reversal (between 12.9 and 11.5 kyr BP). Such evidence for the spatial distribution and timing of abrupt climatic fluctuations is essential data for groundtruthing results derived from global climate models.  相似文献   

Detection Capability of Selected Seismic Stations in Central Europe     

Kristeková  Miriam  Skáčiková  Iveta 《Studia Geophysica et Geodaetica》1997,41(2):149-163

The 50% and 90% P-wave detection thresholds of 3 Austrian, 2 Czech, 5 German, 1 Hungarian and 3 Slovak seismic stations have been determined for four intervals of epicentral distances by a direct method using the maximum-likelihood technique. The USGS-NEIC Earthquake Data Reports covering the period from January 1990 to November 1994 were used as the reference system. The seismic stations Kaperské Hory (KHC, Czech Republic) and Collmberg (CLL, Germany) are the stations with the best detection capabilities for all investigated intervals of epicentral distances.  相似文献   

Ontology‐supported Querying of Geographical Databases     

Miriam Baglioni  Emiliano Giovannetti  Maria Vittoria Masserotti  Chiara Renso  Laura Spinsanti 《Transactions in GIS》2008,12(Z1):31-44

Querying geographical information systems has been recognized as a difficult task for non‐expert users. Furthermore, user queries are often characterized by semantic aspects not directly managed by traditional spatial databases or GIS. Examples of such semantic geospatial queries are the use of implicit spatial relations between objects, or the reference of domain concepts not explicitly represented in data. To handle such queries, we envisage a system that translates natural language queries into spatial SQL statements on a database, thus improving standard GIS with new semantic capabilities. Within this general objective, the contribution of this article is to introduce a methodology to handle semantic geospatial queries issued over a spatial database. This approach captures semantics from an ontology built upon the spatial database and enriched by domain concepts and properties specifically defined to represent the localization of objects. Some examples of the use of the methodology in the urban domain are presented.  相似文献   

A case study of in situ oil contamination in a mangrove swamp (Rio De Janeiro, Brazil)     

Elcia M.S. Brito  Robert Duran  Marisol Goñi-Urriza  Miriam A.C. Crapez  Julio C.A. Wasserman 《Marine pollution bulletin》2009,58(3):418-423

Mangroves are sensitive ecosystems of prominent ecological value that lamentably have lost much of their areas across the world. The vulnerability of mangroves grown in proximity to cities requires the development of new technologies for the remediation of acute oil spills and chronic contaminations. Studies on oil remediation are usually performed with in vitro microcosms whereas in situ experiments are rare. The aim of this work was to evaluate oil degradation on mangrove ecosystems using in situ microcosms seeded with an indigenous hydrocarbonoclastic bacterial consortium (HBC). Although the potential degradation of oil through HBC has been reported, their seeding directly on the sediment did not stimulate oil degradation during the experimental period. This is probably due to the availability of carbon sources that are easier to degrade than petroleum hydrocarbons. Our results emphasize the fragility of mangrove ecosystems during accidental oil spills and also the need for more efficient technologies for their remediation.  相似文献   

Deriving vulnerability curves using Italian earthquake damage data   总被引：3，自引：1，他引：2  

Miriam Colombi  Barbara Borzi  Helen Crowley  Mauro Onida  Fabrizio Meroni  Rui Pinho 《Bulletin of Earthquake Engineering》2008,6(3):485-504

The concerted effort to collect earthquake damage data in Italy over the past 30 years has led to the development of an extensive database from which vulnerability predictions for the Italian building stock can be derived. A methodology to derive empirical vulnerability curves with the aforementioned data is presented herein and the resulting curves have been directly compared with mechanics-based vulnerability curves. However, it has been found that a valid comparison between the empirical and analytical vulnerability curves is not possible mainly due to a number of shortcomings in the database of surveyed buildings. A detailed discussion of the difficulties in deriving vulnerability curves from the current observed damage database is thus also presented.  相似文献   

Effects of phenology and meteorological disturbance on litter rainfall interception for a Pinus elliottii stand in the Southeastern United States   总被引：1，自引：0，他引：1       下载免费PDF全文

John T. Van Stan II  Miriam Coenders‐Gerrits  Michael Dibble  Philine Bogeholz  Zachary Norman 《水文研究》2017,31(21):3719-3728

Litter layers develop across a diverse array of vegetated ecosystems and undergo significant temporal compositional changes due to canopy phenological phases and disturbances. Past research on temporal dynamics of litter interception has focused primarily on litter thickness and leaf fall, yet forest phenophases can change many more litter attributes (e.g., woody debris, bark shedding, and release of reproductive materials). In this study, weekly changes in litter composition over 1 year were used to estimate litter water storage dynamics and model event‐based litter interception. Litter interception substantially reduced throughfall (6–43%), and litter water storage capacity ranged from 1 to 3 mm, peaking when megastrobili release and liana leaf senescence occurred simultaneously during fall 2015. Tropical storm disturbances occurred during the sampling period, allowing evaluation of how meteorological disturbances altered litter interception. High wind speeds and intense rainfall from 2 tropical storms increased litter interception by introducing new woody debris, which, in this study, stored more water than the pre‐existing woody debris. After 2 extreme weather events, a third (Hurricane Hermine) did not increase woody debris (or litter interception), suggesting that the canopy pool of branches susceptible to breakage had been largely depleted. Needle and bark shedding had minor effects on litter interception. Results suggest that the release of reproductive materials and meteorological disturbances appear to be the major compositional drivers of litter interception beyond their obvious contribution to litter thickness.  相似文献   

Impact of acid sulfate soils on the geochemistry of rivers in south-western Finland   总被引：1，自引：0，他引：1  

Maria E. Nyberg  Peter Österholm  Miriam I. Nystrand 《Environmental Earth Sciences》2012,66(1):157-168

Large areas of acid sulfate (AS) soils are located along the coastal plains of Finland, and previous studies have shown that after reclamation they release extreme quantities of metals to watercourses in mid-western and northern Finland. In this study on streams of south-western Finland, where little information about AS soils is available, these soils were found to exhibit the same pattern of elevated metal- and sulfate concentrations as in the notorious AS soil landscapes of mid-western Finland. Meteorologically/hydrologically driven temporal variations of these elements were great in the most affected streams. There were also significant positive implications regarding future environmental work; AS soils in the highlighted region were found to cause sudden temporal influxes of acidic water only in the most affected streams, indicating that the overburden and soils of the area discharge well buffered water. Moreover, it was indicated that the high (less toxic) metal concentrations are largely caused by erosion of suspended phyllosilicates (<0.45 μm) from farmland rather than by AS soils.  相似文献