A Middle Miocene carbonate embankment on an active volcanic slope: Ilhéu de Baixo,Madeira Archipelago,Eastern Atlantic     

B. Gudveig Baarli  Mrio Cacho  Carlos M. da Silva  Markes E. Johnson  Eduardo J. Mayoral  Ana Santos 《Geological Journal》2014,49(1):90-106

Carbonate factories on insular oceanic islands in active volcanic settings are poorly explored. This case study illuminates marginal limestone deposits on a steep volcanic flank and their recurring interruption by deposits linked to volcaniclastic processes. Historically known as Ilhéu da Cal (Lime Island), Ilhéu de Baixo was separated from Porto Santo, in the Madeira Archipelago, during the course of the Quaternary. Here, extensive mines were tunnelled in the Miocene carbonate strata for the production of slaked lime. Approximately 10 000 m³ of calcarenite (−1 to 1ø) was removed by hand labour from the Blandy Brothers mine at the south end of the islet. Investigations of two stratigraphic sections at opposite ends of the mine reveal that the quarried material represents an incipient carbonate ramp developed from east to west and embanked against the flank of a volcanic island. A petrographic analysis of limestones from the mine shows that coralline red algae from crushed rhodoliths account for 51% of all identifiable bioclasts. This material was transported shoreward and deposited on the ramp between normal wave base and storm wave base at moderate depths. The mine's roof rocks are formed by Surtseyan deposits from a subsequent volcanic eruption. Volcaniclastic density flows also are a prevalent factor interrupting renewed carbonate deposition. These flows arrived downslope from the north and gradually steepened the debris apron westwards. Slope instability is further shown by a coral rudstone density flow that followed from growth of a coral reef dominated by Pocillopora madreporacea (Lamarck), partial reef collapse, and transport from a more easterly direction into a fore‐reef setting. The uppermost facies represents a soft bottom at moderate depths in a quiet, but shore‐proximal setting. Application of this study to a broader understanding of the relationship between carbonate and volcaniclastic deposition on oceanic islands emphasizes the susceptibility of carbonates to dilution and complete removal by density flows of various kinds, in contrast to the potential for preservation beneath less‐disruptive Surtseyan deposits. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

High-resolution seismic stratigraphy of the late Neogene of the central sector of the Colombian Pacific continental shelf: A seismic expression of an active continental margin     

Jaime Orlando Martínez  Eduardo López Ramos 《Journal of South American Earth Sciences》2011,31(1):28-44

The sedimentary prism of the central Pacific continental shelf of Colombia was affected by regional folding and faulting, and probably later mud diapirism, from the Late Miocene to the Holocene. Interpretation of high-resolution seismic lines (2 s/dt) revealed that the prism consists of 13 high-resolution seismic units, that can be separated into 5 seismic groups.Deposition of the prism and the associated stacking pattern, are probably the response to variable uplift and subsidence in a fore-arc basin that underwent important tectonic events by the end of the Miocene. Throughout the Pliocene, the continental shelf sedimentation was affected by the growing of a dome structure probable due to mud diapirism. This fact caused peripheral faults both normal and reverse that controlled the distribution of some of the seismic units. During the Late Pleistocene (Wisconsin stage?) a eustatic sea level fall caused the shoreline to advance about 50 km westward of its present position. Because of this eustatic sea level change, a strong fluvial dissection took place and is interpreted as the probable extension of the San Juan River to the south of the present day river mouth. Within this framework it is believed that the Malaga and Buenaventura Bays were the passageways of branches of the old drainage system of the San Juan River. The inner branch circulated through the present Buenaventura Bay and runs southward leaving the mark of an apparent valley identified in the seismic information in the eastern sector of the study area. This old fluvial valley and its filling material located in the present day inner continental shelf front of Buenaventura are postulated as important targets to find placer minerals such as gold and platinum.  相似文献   

EXERCISE IN DOWNSCALING ON SEA SURFACE TEMPERATURE ALONG CHINESE COAST     

练树民  王凯  崔茂常  EduardoZorita 《中国海洋湖沼学报》2000,18(2)

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Putative Meteoritic Craters in Río Cuarto (Central Argentina) Interpreted as Eolian Structures     

Cione  Alberto L.  Tonni  Eduardo P.  San Cristóbal  Jorge  Hernández  Pedro J.  Benítez  Adrián  Bordignon  Fernando  Perí  Jorge A. 《Earth, Moon, and Planets》2002,91(1):9-24

Ten oblong aligned depressions in the Río Cuarto area (provincia de Córdoba, Argentina) were supposed to be the result of very-low-angle Holocene meteoroid impacts. However, we consider that authors that studied the structures did not demonstrated their extraterrestrial origin. We suggest that an eolian origin for the structures of Río Cuarto is more likely. Actually, these landforms integrate large systems of similar deflation/accumulation geoforms aligned according to predominant winds during different periods.  相似文献   

The Cretaceous–Tertiary boundary in southern low-latitude regions: preliminary study in Pernambuco, northeastern Brazil     

Gilberto A. Albertão  Eduardo A.M. Koutsoukos  Marília P.S. Regali  Moses Attrep Jr  Paulo P. Martins Jr 《地学学报》1994,6(4):366-375

A preliminary integrated study of a Cretaceous-Tertiary (K/T) boundary section in Pernambuco, northeastern Brazil, provides evidence for an extraterrestrial bolide impact in the earliest Danian. A non-graded, nodular carbonate mudstone/wackestone bed is interpreted as a slump or a mud Flow deposit, induced by a tsunami event or by a gravity mass movement during a sea-level lowstand, the former possibly generated by the K/T boundary Yucatán impact. This bed overlies marlstones deposited in an upper bathyal environment and marks the top of the Cretaceous. Nearly all known latest Maastrichtian planktonic foraminifera are recovered from the Cretaceous strata. Iridium shows a marked peak in a thin hemipelagic claystone layer, about 75 cm above the K/T boundary, deposited in a middle to deep neritic environment. The claystone overlies alternating beds of finegrained limestones and marlstones and a 50 cm-thick graded bioclastic packstone, which rests upon a marly limestone breccia of the lowermost Danian. Abundant reworked Cretaceous and rare lowermost Danian microfossils (e.g. E. edita, E. eobulloides, E. fringa, G. irregularis, P. eugubina, P. cf. pseudobulloides, W. claytonensis and W. hornerstownensis ) have been recovered from these strata. These lowermost Danian beds record the sudden appearance of abundant shock-metamorphosed quartz grains, with several sets of intersecting deformation lamellae and microtektite-like microspherules. This suggests that these deposits were formed by an additional tsunami caused by a second impact event in the earliest Danian, near or at the boundary between the Palaeocene P α and P 1a foraminiferal zones. Impact-derived material has not been found in the uppermost Cretaceous beds.  相似文献   

Infrared light curves and absolute stellar parameters of the Algol system δ Librae: is δ Librae really an overmassive Algol binary?     

C. Lazaro  M. J. Arevalo  A. Claret 《Monthly notices of the Royal Astronomical Society》2002,334(3):542-552

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Clues to Substellar Formation: Rotation and the Low-Mass End of the Initial Mass Function     

María Rosa Zapatero Osorio  José Caballero  Eduardo L. Martín  Víctor J.S. Béjar  Rafael Rebolo 《Astrophysics and Space Science》2004,292(1-4):673-679

We have monitored S Ori 45, a young, low-mass (20 M _j up) brown dwarf of the σ Orionis cluster (～3 Myr, 352 pc), using optical and near-infrared filters. S Ori 45 (spectral type M8.5) is found to be multi-periodic with a dominant modulation at 2.5–3.5 h, and a short modulation at about 46 min. We ascribe the longer of these modulations to a rotation period. After comparing these results with observations of more massive cluster brown dwarfs and field brown dwarfs, we conclude that substellar objects present rotational and angular momentum evolution. We have also obtained intermediate-resolution near-infrared spectroscopy of S Ori 70, which is a T-class, free-floating planetary candidate member in the σ Orionis cluster. Its observed spectrum has been compared to data of field brown dwarfs of similar types and to theoretical spectra computed for different surface temperatures and gravities. We conclude that S Ori 70 has a significantly cool, low-gravity atmosphere. This supports the young age of this object and its membership in the cluster. From state-of-the-art evolutionary models, the mass of S Ori 70 is estimated at 3 times the Jovian mass (⁺⁵ _?2 M _j up), challenging current stellar/substellar formation models. S Ori 70 remains the lowest mass object so far identified in any open cluster.  相似文献   

shinyNORRRM: A Cross-Platform Software to Calculate the CIPW Norm     

González-Guzmán  Reneé  Elizondo-Pacheco  Luis Alejandro  González-Roque  Abraham  Sánchez-Torres  Carlos Eduardo  Cárdenas-Muñoz  Kevin Samuel 《Mathematical Geosciences》2023,55(4):563-577

In this paper, a novelty-free software to assess an efficient CIPW Norm (± 0.006 wt.% in differences between input and output data) is presented. The package is available in the official repository for user-contributed R packages (CRAN: Comprehensive R Archive Network). The software is able to handle big data sets and considers minor and trace element compositions. The algorithm can calculate odd minerals in igneous rocks, such as cancrinite and calcite, adjust the Fe⁺³/Fe⁺² ratio in different standard approaches, and recalculate the compositions of the rocks in an anhydrous basis (100 ± 0.003 wt.% volatile-free adjusted). Furthermore, the package calculates several petrological parameters, and the graphical outputs are displayed following IUGS scheme standards. The prime aspect of shinyNORRRM is the symbiosis of native R functions with the R package’s shiny (Web Application Framework for R) to run the norm in a user-friendly interface. shinyNORRRM can be executed in any operating system and requires no previous programming knowledge, thus promising to be the universal computational program in this matter. The output data are printed in the standard comma-separated values (*.csv) format, which is highly compatible with general spreadsheet editors. In this work, the algorithm of our program is validated using already compiled whole-rock geochemical databases.

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Characterization of the Frictional Behavior of Steel-Polymer Interfaces with Pronounced Stick-Slip Effect for Use in Seismic Isolation     

Messina  Armando  Miranda  Eduardo 《Bulletin of Earthquake Engineering》2022,20(11):6307-6326

Bulletin of Earthquake Engineering - The frictional behavior of steel-PTFE interfaces for use in seismic isolation has been studied extensively in the past. However, alternative polymers, such as...  相似文献   

A multi-physics ensemble of present-day climate regional simulations over the Iberian Peninsula     

Sonia Jerez  Juan Pedro Montavez  Pedro Jimenez-Guerrero  Juan Jose Gomez-Navarro  Raquel Lorente-Plazas  Eduardo Zorita 《Climate Dynamics》2013,40(11-12):3023-3046

This work assesses the influence of the model physics in present-day regional climate simulations. It is based on a multi-phyiscs ensemble of 30-year long MM5 hindcasted simulations performed over a complex and climatically heterogeneous domain as the Iberian Peninsula. The ensemble consists of eight members that results from combining different parametrization schemes for modeling the Planetary Boundary Layer, the cumulus and the microphysics processes. The analysis is made at the seasonal time scale and focuses on mean values and interannual variability of temperature and precipitation. The objectives are (1) to evaluate and characterize differences among the simulations attributable to changes in the physical options of the regional model, and (2) to identify the most suitable parametrization schemes and understand the underlying mechanisms causing that some schemes perform better than others. The results confirm the paramount importance of the model physics, showing that the spread among the various simulations is of comparable magnitude to the spread obtained in similar multi-model ensembles. This suggests that most of the spread obtained in multi-model ensembles could be attributable to the different physical configurations employed in the various models. Second, we obtain that no single ensemble member outperforms the others in every situation. Nevertheless, some particular schemes display a better performance. On the one hand, the non-local MRF PBL scheme reduces the cold bias of the simulations throughout the year compared to the local Eta model. The reason is that the former simulates deeper mixing layers. On the other hand, the Grell parametrization scheme for cumulus produces smaller amount of precipitation in the summer season compared to the more complex Kain-Fritsch scheme by reducing the overestimation in the simulated frequency of the convective precipitation events. Consequently, the interannual variability of precipitation (temperature) diminishes (increases), which implies a better agreement with the observations in both cases. Although these features improve in general the accuracy of the simulations, controversial nuances are also highlighted.  相似文献