Sub-wavebase cross-bedded grainstones on a distally steepened carbonate ramp, Upper Miocene, Menorca, Spain   总被引：1，自引：0，他引：1  

Luis Pomar  Antonio Obrador†  & Hildegard Westphal‡ 《Sedimentology》2002,49(1):139-169

Cross‐bedded grainstones on carbonate ramps and shelves are commonly related to the locus of major wave energy absorption such as shorelines, shoals or shelf breaks. In contrast, on the Early Tortonian carbonate platform of Menorca (Balearic Islands), coarse‐grained, cross‐bedded grainstones are found at a distance from the palaeoshoreline where they were deposited below the wavebase. Excellent exposures along continuous outcrops on the sea cliffs of Menorca reveal the depositional profile and three‐dimensional distribution of the different facies belts of the Tortonian ramp depositional system. Basinward from the palaeoshoreline, fan deltas and beach deposits pass into 5‐km‐wide gently dipping bioturbated dolopackstone (inner and middle ramp), then into 12–20°‐dipping dolograinstone/rudstone clinobeds (ramp slope) and, finally, into subhorizontal fine‐grained basinal dolowackestone to dolopackstone (outer ramp). In this Miocene example, coarse‐grained grainstones exist in five different settings other than beach deposits: (1) on the middle ramp, where cross‐bedded grainstones were deposited by currents roughly parallel to the shoreline at 40–70 m estimated water depth and are interbedded with gently dipping bioturbated dolomitized packstones; (2) on the upper slope, where clinobeds are composed mostly of in situ rhodoliths and red‐algae fragments; (3) on the lower slope, as small‐scale bedforms (small three‐dimensional subaqueous dunes) migrating parallel to the slope; (4) at the transition between the lower slope and the outer ramp, where mollusc‐rich and rhodolithic rudstones and grainstones, interbedded in dolomitized laminated wackestones containing abundant planktonic foraminifera, infill slide/slump scars as upslope‐backstepping bodies (backsets); (5) at the toe of the slope, where coarse skeletal grainstones indicate bedform migration parallel to the platform margin, induced by currents at more than 150 m estimated water depth. This Late Miocene example also illustrates how changes in intrabasinal environmental conditions (nutrients and/or temperature) may produce changes in stratal patterns and facies architecture if they affect the biological system. Two depositional sequences compose the Miocene platform on Menorca, where a reef‐rimmed platform prograded onto an earlier distally steepened ramp. The transition from the ramp to the reef‐rimmed platform was effected by an increase in accommodation space caused by ecological changes, promoting a shift from a grain‐ to a framework‐producing biota.  相似文献   

Ray tracing in elliptical anisotropic media using the linear traveltime interpolation (LTI) method applied to traveltime seismic tomography   总被引：3，自引：0，他引：3  

Ettore Cardarelli  Antonio Cerreto 《Geophysical Prospecting》2002,50(1):55-72

The linear traveltime interpolation (LTI) method is a suitable ray‐tracing technique for modelling first‐arrival times in isotropic media. LTI is extended to elliptical anisotropic media and applied to a tomographic inversion procedure. A theoretical formulation is first derived and then LTI implementation is discussed in terms of source–receiver arrays and cell size. The method is then combined with the tomographic inversion procedure adopted. The matching of the ray tracing with inversion in elliptical anisotropic media posed a double non‐linear problem. Thus two assumptions were made: the velocity in each cell is uniform and the main directions of anisotropy are known. To take into account the geometrical characteristics of the area under investigation (depth and velocity of the weathering, and thickness of the inner media), cells of varying size were considered. No hypothesis was made on anisotropy weakness.
The algorithm was first tested on synthetic models and then applied to a field survey. On comparing the results of the synthetic models and the field survey with those obtained with a linear raypath approximation, it was found that there were fewer data misfits.  相似文献   

δO of carbonate, quartz and phosphate from belemnite guards: implications for the isotopic record of old fossils and the isotopic composition of ancient seawater     

Antonio Longinelli  Paola IacuminMichele Ramigni 《Earth and Planetary Science Letters》2002,203(1):445-459

Belemnite guards of Cretaceous and Jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum. The oxygen isotopic composition of coexisting carbonate, quartz and phosphate from the same rostrum was measured according to well-established techniques. None of these compounds showed isotopic values in equilibrium with one another. Assuming δ¹⁸O values of the diagenetic water within the range of meteoric waters, the δ¹⁸O(SiO₂) yield temperatures in agreement with the apparent secondary origin of this phase. The δ¹⁸O(CO₃²⁻) range, with a certain continuity, between −10.8 and +0.97 PDB-1 with most of the intermediate values being within the range of the carbonate isotopic values of Mesozoic fossils. The most positive isotopic results obtained from phosphate are close to +23/+24‰ (V-SMOW). They can hardly be related to a secondary origin of the phosphate, or to the presence of diagenetic effects, since these results are among the most positive ever measured on phosphate. As far as we know there is no widespread diagenetic process determining an ¹⁸O enrichment of phosphate. The very low concentration of phosphate did not allow the determination of its mineralogical composition. All the available δ¹⁸O(PO₄³⁻) values from belemnite and non-belemnite fossils of marine origin of Tertiary and Mesozoic age are reported along with the newly measured belemnites. The following conclusions may be drawn from the data reported: (1) the pristine oxygen isotope composition of fossil marine organisms (either carbonate or phosphate) may easily undergo fairly large changes because of oxygen isotope exchange processes with diagenetic water; this process is apparent even in the case of geologically recent fossils; (2) the δ¹⁸O(PO₄³⁻) of belemnite rostra seems to be, at least in the case of the most positive results, in isotopic equilibrium with environmental water because of the similarity between the results from Cretaceous belemnites and the results from Cretaceous and Lower Tertiary pelecypods and fish teeth; 3) if so, the only feasible interpretation that can be suggested for the ¹⁸O enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from Jurassic to recent time.  相似文献   

Morphology of the ovotestis of Serranus atricauda (Teleostei,Serranidae)     

María Mercedes García-Díaz  María José Lorente  José Antonio González  Víctor Manuel Tuset 《Aquatic Sciences - Research Across Boundaries》2002,64(1):87-96

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Upper Oligocene-Lower Miocene shallowing-upwardlacustrine sequences controlled by periodic and non-periodic processes(Ebro Basin, northeastern Spain)     

Arantxa Luzón  Angel González  Arsenio Muñoz  Belén Sánchez-Valverde 《Journal of Paleolimnology》2002,28(4):441-456

The lacustrine facies from two sections (Candasnos and Fraga) ofthe Oligocene-Miocene Torrente de Cinca lithostratigraphic Unit in thecentral part of the Ebro Basin (Spain) have been analysed to determine theinfluence of orbital parameters in lacustrine sedimentation. The unit ispredominantly composed of limestones and marls, and represents a shallowlacustrine freshwater system. The sedimentological features of the faciesstudied demonstrate that the lower part of the Candasnos section representsoffshore lacustrine subenvironments whereas the upper part, and the whole ofthe Fraga section, characterise marginal lacustrine areas. Series of stratalthickness variations of limestone, marl, and limestone/marl couplets fromboth sections have been analysed using spectral analysis. This shows thatinformation corresponding to periodic cycles only appears in the offshorefacies, that is to say, in the lower part of Candasnos section, and disappearsin the marginal facies where non-periodic cycles exist. Furthermore, thespectral analysis of the offshore facies highlights the existence of a peak inthe power spectrum with a period of around 7 (6.8 to 7.8) that can berecognised in the field as shallowing-upward lacustrine sequences.Magnetostratigraphic data from the Candasnos section allow us to establish atime span of 2,808 years for the limestone/marl couplet from the lower partof this section, and between 19,000 and 22,000 years for the periodic cycleidentified, thus representing the climatic precession cycle. Shallowingsequences from marginal areas do not correspond with any periodiccycle.  相似文献   

Sea cliffs resulting from late Miocene extensional tectonics: the Serra Gelada case study (Betic Cordillera, Spain)     

Alfonso Ybenes  Pedro Alfaro  Jos Delgado  Antonio Estvez  Jesús M. Soria 《Geomorphology》2002,42(3-4)

The Serra Gelada sea cliffs are carved in Mesozoic carbonate rocks belonging to the External Zones of the eastern Betic Cordillera (Alicante, SE Spain). Several normal faults with vertical slips of more than a hundred metres have played an important role in the origin of this coastline. Some previous studies propose that the present cliff morphology was mainly originated by Quaternary fault activity. However, the integration of geomorphological features, stratigraphical and sedimentological data, together with the results of the tectonic analysis of fractures occurring in Serra Gelada, and a detailed study of seismic reflection profiles carried out in the adjacent continental shelf, indicate that these normal faults were active mainly during the late Miocene. Therefore, the Serra Gelada sea cliffs represent a tectonically controlled long-term landscape. Thus, normal faults have not significantly modified the Serra Gelada relief since then. Furthermore, the northern part of the Serra Gelada cliff may be considered as an inherited pre-Quaternary relict palaeocliff since it has only undergone very little erosive recession.  相似文献   

The BEAM-project: prediction and assessment of mixture toxicities in the aquatic environment     

Thomas Backhaus  Rolf Altenburger  sa Arrhenius  Hans Blanck  Michael Faust  Antonio Finizio  Paola Gramatica  Matthias Grote  Marion Junghans  Wiebke Meyer  Manuela Pavan  Tobias Porsbring  Martin Scholze  Roberto Todeschini  Marco Vighi  Helge Walter  L. Horst Grimme 《Continental Shelf Research》2003,23(17-19):1757

Freshwater and marine ecosystems are exposed to various multi-component mixtures of pollutants. Nevertheless, most ecotoxicological research and chemicals regulation focus on hazard and exposure assessment of individual substances only, the problem of chemical mixtures in the environment is ignored to a large extent. In contrast, the assessment of combination effects has a long tradition in pharmacology, where mixtures of chemicals are specifically designed to develop new products, e.g. human and veterinary drugs or agricultural and non-agricultural pesticides. In this area, two concepts are frequently used and are thought to describe fundamental relationships between single substance and mixture effects: Independent Action (Response Addition) and Concentration Addition. The question, to what extent these concepts may also be applied in an ecotoxicological and regulatory context may be considered a research topic of major importance, as the concepts would allow to make use of already existing single substance toxicity data for the predictive assessment of mixture toxicities. Two critical knowledge gaps are identified: (a) There is a lack of environmental realism, as a huge part of our current knowledge about the applicability of the concepts is restricted to artificial situations with respect to mixture composition or biological effect assessment. (b) The knowledge on what exactly is needed for using the concepts as tools for the predictive mixture toxicity assessment is insufficient. Both gaps seriously hamper the necessary, scientifically sound consideration of mixture toxicities in a regulatory context.In this paper, the two concepts will be briefly introduced, the necessity of considering the toxicities of chemical mixtures in the environment will be demonstrated and the applicability of Independent Action and Concentration Addition as tools for the prediction and assessment of mixture toxicities will be discussed. An overview of the specific aims and approaches of the BEAM project to fill in the identified knowledge gaps is given and first results are outlined.  相似文献   

Is Prediction of Future Landslides Possible with a GIS?   总被引：5，自引：0，他引：5  

Fabbri  Andrea G.  Chung  Chang-Jo F.  Cendrero  Antonio  Remondo  Juan 《Natural Hazards》2003,30(3):487-503

This contribution explores a strategy for landslide hazard zonation inwhich layers of spatial data are used to represent typical settings inwhich given dynamic types of landslides are likely to occur. Theconcepts of assessment and prediction are defined to focus on therepresentation of future hazardous events and in particular on themyths that often provide obstacles in the application of quantitativemethods. The prediction rate curves for different applications describethe support provided by the different data layers in experiments inwhich the typical setting of hazardous events is approximated bystatistically integrating the spatial information.  相似文献   

Structural setting of the Bay of Naples (Italy) seismic reflection data: implications for Campanian volcanism: [Tectonophysics 372 (2003) 193–213]     

Pier Paolo G. Bruno  Antonio Rapolla  Vincenzo Di Fiore 《Tectonophysics》2003,376(3-4)

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Validation of Landslide Susceptibility Maps; Examples and Applications from a Case Study in Northern Spain   总被引：9，自引：3，他引：9  

Remondo  Juan  González  Alberto  De Terán  José Ramón Díaz  Cendrero  Antonio  Fabbri  Andrea  Chung  Chang-Jo F. 《Natural Hazards》2003,30(3):437-449

A procedure for validating landslide susceptibility maps wasapplied in a study area in northern Spain and the results obtained compared. Validationwas used to carry out sensitivity analysis for individual variables and combinationsof variables. The validity of different map-making methods was tested, as well as theutility of different types of Favourability Functions. The results obtained show thatvalidation is essential to determine the predictive value of susceptibility maps. Italso helps to better select the most suitable function and significant variables, thus improving the efficiency of the mapping process. Validation based on a temporal strategy makes it possible to derive hazard maps from susceptibility maps.  相似文献