Comparison of geomagnetic planetary reference fields over Italy     

F. Molina  A. Meloni  O. Battelli  A. De Santis 《Physics of the Earth and Planetary Interiors》1985,37(1):35-45

Geomagnetic field measurements on a network at 106 repeat stations (1/3000 km²), and a second order network at 2550 stations (1/100 km²), were completed in 1981. Total intensity and the horizontal and vertical component of the field were measured at all stations, and in addition declination was measured at the first order stations. Normal fields for each element were computed from the first order network measurements (using a second degree polynomial in latitude and longitude), and comparisons were made for total intensity with 3 planetary reference fields. The use of the polynomial normal normal field is suggested to draw anomaly maps.  相似文献   

Tectonic correlations of pre-Mesozoic crust from the northern termination of the Colombian Andes, Caribbean region     

Agustin Cardona Molina  Umberto G. Cordani  William D. MacDonald 《Journal of South American Earth Sciences》2006,21(4):337

Reconnaissance zircon U/Pb SHRIMP, Ar–Ar, and Sm–Nd geochronology, petrological, and geochemical data were obtained from selected localities of two pre-Mesozoic metamorphic belts from the northern termination of the Colombian Andes in the Caribbean region. The older Proterozoic belt, with protoliths formed in a rift- or backarc-related environment, was metamorphosed at 6–8 kb and 760–810 °C during Late Mesoproterozoic times. This belt correlates with other high-grade metamorphic domains of the Andean realm that formed a Grenvillian-related collisional belt linked to the formation of Rodinia. The younger belt was formed over a continental arc at <530–450 Ma in a Gondwanide position and metamorphosed at 5–8 kb and 500–550 °C, probably during the Late Paleozoic–Triassic, as part of the terranes that docked with northwestern South America during the formation of Pangea. A Mesozoic Ar–Ar tectonothermal evolution can be related to regional magmatic events, whereas Late Cretaceous–Paleocene structural trends are related to the accretion of the allocthonous Caribbean subduction metamorphic belts. Lithotectonic correlations with other circum-Caribbean and southern North American pre-Jurassic domains show the existence of different terrane dispersal patterns that can be related to Pangea’s breakup and Caribbean tectonics.  相似文献   

Spatial and seasonal patterns of European short-snouted seahorse Hippocampus hippocampus distribution in island coastal environments     

F Otero-Ferrer  R Herrera  VM Tuset  J Socorro  L Molina 《African Journal of Marine Science》2015,37(3):395-404

This study represents the first report on seahorses in the Macaronesian islands (North-East Atlantic), determining the spatial and seasonal abundance, population structure and physical appearance of European short-snouted seahorse Hippocampus hippocampus. Animals were surveyed off Gran Canaria Island in two bays, Melenara and Sardina del Norte, within three habitats: rocky bottom, artificial substrata and seagrass. Populations were monitored over a 5-year period (spring 2006–winter 2011) using 15-minute visual fast count (VFC) surveys. Seahorses were characterised by low abundances, small proportions of subadults and roughly equal sex ratios at each site. We aimed to determine whether environmental conditions and geographical position could explain differences in seahorse abundance and population structure between the study sites. Melenara Bay (mean sighting rate = 0.44 individuals VFC–¹; SD 0.72) offered protected environments where seahorse distribution varied with substratum type, irrespective of season. Strong hydrodynamic forces in winter affected abundance and size at exposed locations in Sardina del Norte Bay (mean sighting rate=0.21 individuals VFC^?1; SD 0.52). Our findings contribute to the scarce available knowledge about this Data Deficient species (IUCN Red List), helping to establish future conservation strategies and management recommendations for the preservation of H. hippocampus populations around Gran Canaria Island and other localities with similar coastal environments.  相似文献   

Biodiversity and environmental characteristics of the bycatch assemblages from the tropical tuna purse seine fisheries in the eastern Atlantic Ocean          下载免费PDF全文

Nerea Lezama‐Ochoa  Hilario Murua  Jon Ruiz  Pierre Chavance  Alicia Delgado de Molina  Ainhoa Caballero  Igor Sancristobal 《Marine Ecology》2018,39(3)

The impact of human activities such as fishing has been identified as a main factor in diversity loss in the open ocean. This paper studies the diversity patterns and environmental characteristics of the bycatch assemblages in Fish Aggregating Devices (FADs) and Free School sets (sets made on schools of tuna) from the tropical tuna purse seine fishery in the eastern Atlantic Ocean (35°W–15°E and 20°N–15°S). Data were collected from scientific observer programmes carried out between 2003 and 2011 on board Spanish and French fleets. The results showed different structure and diversity patterns of the bycatch assemblages depending on the fishing mode, with higher number of species and diversity found in FAD sets than in Free School sets. Bycatch assemblages showed preferences for specific oceanographic characteristics of the Atlantic Ocean, such as the equatorial and seasonal coastal upwelling systems, the Cape Lopez front system and the Guinea dome. The type of set and sea surface temperature play an important role to describe the diversity patterns of these species. These results confirm the importance of integrating different methods to study the marine ecosystem towards the correct implementation of the Ecosystem Approach to Fishery Management (EAFM).  相似文献   

Palaeomagnetism and magnetostratigraphy of uppermost Permian strata, southeast New Mexico, USA: correlation of the Permian–Triassic boundary in non-marine environments     

Roberto S. Molina Garza  John W. Geissman  & Spencer G. Lucas 《Geophysical Journal International》2000,141(3):778-786

Continental red sandstone and siltstone rocks of the Dewey Lake (Quartermaster) Formation at Maroon Cliffs, near Carlsbad, New Mexico, are characterized by two components of magnetization with partially overlapping laboratory unblocking temperature spectra. Both magnetizations display high coercivities (>100 mT), probably residing in haematite. A north-directed magnetization with steep positive inclination unblocks between 100 and 650 °C, isolating a predominantly northwest-directed magnetization, with shallow inclination, of near uniform normal polarity and maximum unblocking temperatures of 680 °C.
We collected samples from 24 palaeomagnetic sites (i.e. individual beds) from a ~60 m thick section of flat-lying strata disconformably overlying carbonate and evaporite rocks of the Rustler Formation. The upper member of the Rustler Formation contains a Late Permian (early Changxingian) marine invertebrate and conodont fauna. Of the sampled sites, four yield only steep magnetizations, interpreted to be recent overprints. Eight sites did not yield well-grouped site means and were excluded from the final calculations. The formation mean (dec = 337.7°, inc = 9.2°; k = 31.6, α ₉₅ = 7.8°, N = 12 sites) defines a palaeomagnetic pole located at 55.2°N, 117.5°E, in good agreement with other Late Permian North American cratonic poles.
Correlation of the short polarity sequence of this section of Dewey Lake strata is unambiguous. Compared with the polarity stratigraphy of marine sections in Asia, and supported by isotopic age determinations on a widespread bentonite bed in Dewey Lake strata in west Texas (approximately 251 Ma) and fossil data for the underlying Rustler Formation, the magnetostratigraphy is consistent with deposition of the Dewey Lake Formation during the latest Changxingian (Late Permian) stage.  相似文献   

Quantification of fundamental frequency drop for unreinforced masonry buildings from dynamic tests     

C. Michel  B. Zapico  P. Lestuzzi  F. J. Molina  F. Weber 《地震工程与结构动力学》2011,40(11):1283-1296

The knowledge of fundamental frequency and damping ratio of structures is of uppermost importance in earthquake engineering, especially to estimate the seismic demand. However, elastic and plastic frequency drops and damping variations make their estimation complex. This study quantifies and models the relative frequency drop affecting low‐rise modern masonry buildings and discusses the damping variations based on two experimental data sets: Pseudo‐dynamic tests at ELSA laboratory in the frame of the ESECMaSE project and in situ forced vibration tests by EMPA and EPFL. The relative structural frequency drop is shown to depend mainly on shaking amplitude, whereas the damping ratio variations could not be explained by the shaking amplitude only. Therefore, the absolute frequency value depends mostly on the frequency at low amplitude level, the amplitude of shaking and the construction material. The decrease in shape does not vary significantly with increasing damage. Hence, this study makes a link between structural dynamic properties, either under ambient vibrations or under strong motions, for low‐rise modern masonry buildings. A value of 2/3 of the ambient vibration frequency is found to be relevant for the earthquake engineering assessment for this building type. However, the effect of soil–structure interaction that is shown to also affect these parameters has to be taken into account. Therefore, an analytical methodology is proposed to derive first the fixed‐base frequency before using these results. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Effects of sewage pollution and bacterial load on growth and oxidative balance in the freshwater mussel Diplodon chilensis     

Sebastián E. Sabatini  Iara Rocchetta  Carlos M. Luquet  Mariana I. Guido  María del Carmen Ríos de Molina 《Limnologica》2011,41(4):356-362

The effect of chronic exposure to Escherichia coli on morphometrical parameters, different antioxidant defenses, lipid peroxidation and protein oxidation has been studied in digestive gland of the freshwater mussel Diplodon chilensis in the laboratory during 6 weeks. In, a parallel field study, we evaluated morphometrical and oxidative stress parameters in digestive glands of mussels collected from a sewage polluted area (SMA) and from a pristine area (control). Both sites were characterized by analyzing bacteriological and physic-chemical parameters. In the laboratory D. chilensis was able to filter bacteria at high concentrations with a clearing rate of 0.510 ± 0.036 L/h per gram of dry soft tissue mass. The digestive gland mass to shell length ratio (DGM/SL), reduced glutathione (GSH), lipid peroxidation, as concentration of thiobartituric acid reactive substances (TBARS), and glutathione-S-transferase (GST) activity of mussels fed with bacteria were significantly higher than those of control mussels after the fourth week. Fecal bacteria in lake water samples were undetectable in the control, and higher than 24,000 MPN (most probable number)/100 mL in SMA. DGM/SL was higher in SMA. No differences between sites were observed in total lipid and protein content, neither in superoxide dismutase activity. GSH content was higher in SMA, with no difference in the oxidized form. GST activity and MDA were significantly higher in SMA but protein oxidation was not affected.  相似文献   

Energy balance in urban Mexico City: observation and parameterization during the MILAGRO/MCMA-2006 field campaign     

Erik Velasco  Shelley Pressley  Rasa Grivicke  Eugene Allwine  Luisa T. Molina  Brian Lamb 《Theoretical and Applied Climatology》2011,103(3-4):501-517

The parameterization of the energy balance from a residential and commercial neighborhood of Mexico City was investigated using direct measurements of radiative and heat fluxes carried out during the MILAGRO/MCMA-2006 field campaign as a reference. The measured fluxes were used to evaluate different models of the energy balance based on parameterizations that require standard meteorological observations: ambient temperature, relative humidity, atmospheric pressure and cloudiness. It was found that these models reproduce with reasonable accuracy the diurnal features of the radiative and heat fluxes. The largest differences between modeled and observed fluxes correspond to the incoming longwave radiation, mainly due to errors in the cloudiness data. This paper contributes to the understanding of the energy partitioning in (sub)tropical urban environments, particularly in the developing world, where energy balance models have not been evaluated.  相似文献   

Importance of porosity and transfer of matter in the rock weathering processes: two examples in central Spain     

E. Molina Ballesteros  J. García Talegón  A. C. I?igo I?igo  M. González Sánchez  H. Herrero Fernández 《Environmental Earth Sciences》2011,64(7):1741-1754

Some physical properties (bulk and free porosity, pore size distribution), and the chemical composition and mass balance of two deeply weathered profiles one developed on Hercynian granodiorite and the other on pre-Cambrian slates were studied. Hydric and mercury porosimetry, nitrogen adsorption techniques, chemical analyses and XRD techniques were used. On granodiorite, weathering has created increased porosity with a pore diameter <5 μm, whereas on slates the weathering has produced of ca. 1 μm in diameter. These pore sizes have played an important role in the weathering processes. Assuming that weathering preserves volumes, except in the uppermost part of the profiles, it brought about a loss of matter of more than 12% (~300 kg/m³) on granodiorite and ca. 30% (~800 kg/m³) on slates. These changes are related to shifts in the mineralogical evolution, with the appearance of new 2:1 and 1:1 phyllosilicates and Fe oxy-hydroxides as the main authigenic minerals. The release of matter, at least since the upper Neogene until the present, has led to the lowering of relief in a more or less homogeneous way, giving rise to gentle hillsides and flat surfaces below which the current river networks are incised. Porosity studies have the potential to explain several specific landforms as well as affecting landscape development in general.  相似文献   

Soft-sediment deformation structures induced by cyclic stress of storm waves in tempestites (Miocene, Guadalquivir Basin, Spain)   总被引：1，自引：0，他引：1  

Molina  Alfaro  Moretti  & Soria 《地学学报》1998,10(3):145-150

The identification of triggering agents for soft-sedimentation structures is an enigmatic geological problem. Mainly seismic-induced soft-sediment structures have been recognized in ancient sediments, rather than those resulting from storm waves. We analyse soft-sediment deformation structures in Upper Miocene calcarenitic tempestites of the Guadalquivir Basin (Southern Spain). The most common structures are load-casts which vary in height and width from 10 centimetres to several metres. The structures are always restricted to a small part of the stratigraphic sections, in exclusive association with tempestites. The analysed soft-deformation structures are interpreted to be the result of liquidization processes. Chiefly from their inferred depositional environment, and subordinately from the deformation style, we have devised basic criteria to identify the trigger mechanism. In these soft-sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves.  相似文献