Pleistocene radiolarian biostratigraphy in the South China Sea*   总被引：4，自引：0，他引：4  

Rujian Wang  Andrea Abelmann 《中国科学D辑(英文版)》1999,42(5):536-543

Based on a quantitative radiolarian analysis, 5 radiolarian zones (NR1-NR5) have been defined at Core. 17957-2 from the South China Sea, considering radiolarian zonations from low latitudes. The absolute age assignment of the radiolarian zones and the ranges of the six marker species is based on the direct correlation with the paleomagnetic and isotopic record, respectively. A comparison of the radiolarian stratigraphic data obtained from Core 17957-2 from the South China Sea with those from the equatorial Pacific and the tropical Indian Ocean shows a close similarity to the ages defined in the equatorial Pacific. The obtained biostratigraphic data provide an excellent tool for further dating of Pleistocene sediments in the China Sea. Project supported by the National Natural Science Foundation of China (Grant No. 49291100) and by the German Federal Ministry for Education, Science, Research and Technology (BMBF) as part of a GermadChinese scientific cooperation program. This is Alfred Wegener Contribution No. 1473.  相似文献   

A systematic analysis of the XMM-Newton background: III. Impact of the magnetospheric environment     

Simona Ghizzardi  Martino Marelli  David Salvetti  Fabio Gastaldello  Silvano Molendi  Andrea De Luca  Alberto Moretti  Mariachiara Rossetti  Andrea Tiengo 《Experimental Astronomy》2017,44(3):273-285

A detailed characterization of the particle induced background is fundamental for many of the scientific objectives of the Athena X-ray telescope, thus an adequate knowledge of the background that will be encountered by Athena is desirable. Current X-ray telescopes have shown that the intensity of the particle induced background can be highly variable. Different regions of the magnetosphere can have very different environmental conditions, which can, in principle, differently affect the particle induced background detected by the instruments. We present results concerning the influence of the magnetospheric environment on the background detected by EPIC instrument onboard XMM-Newton through the estimate of the variation of the in-Field-of-View background excess along the XMM-Newton orbit. An important contribution to the XMM background, which may affect the Athena background as well, comes from soft proton flares. Along with the flaring component a low-intensity component is also present. We find that both show modest variations in the different magnetozones and that the soft proton component shows a strong trend with the distance from Earth.  相似文献   

ASPHAA: A GIS‐Based Algorithm to Calculate Cell Area on a Latitude‐Longitude (Geographic) Regular Grid     

Monia Santini  Andrea Taramelli  Alessandro Sorichetta 《Transactions in GIS》2010,14(3):351-377

One characteristic of a Geographic Information System (GIS) is that it addresses the necessity to handle a large amount of data at multiple scales. Lands span over an area greater than 15 million km² all over the globe and information types are highly variable. In addition, multi‐scale analyses involve both spatial and temporal integration of datasets deriving from different sources. The currently worldwide used system of latitude and longitude coordinates could avoid limitations in data use due to biases and approximations. In this article a fast and reliable algorithm implemented in Arc Macro Language (AML) is presented to provide an automatic computation of the surface area of the cells in a regularly spaced longitude‐latitude (geographic) grid at different resolutions. The approach is based on the well‐known approximation of the spheroidal Earth's surface to the authalic (i.e. equal‐area) sphere. After verifying the algorithm's strength by comparison with a numerical solution for the reference spheroidal model, specific case studies are introduced to evaluate the differences when switching from geographic to projected coordinate systems. This is done at different resolutions and using different formulations to calculate cell areas. Even if the percentage differences are low, they become relevant when reported in absolute terms (hectares).  相似文献   

River of change: Prehistory of the Middle Little Colorado River Valley,Arizona     

Andrea K.L. Freeman 《Geoarchaeology》1999,14(1):90-92

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Systematically variable geometry and architecture of incised-valley fills controlled by orbital forcing: A conceptual model from the Pennsylvanian Breathitt Group (Kentucky,USA)     

Aymeric Le Cotonnec  Dario Ventra  Sam Hudson  Andrea Moscariello 《Sedimentology》2020,67(4):2149-2188

Incised-valley fills preserved within ancient coastal to shallow-marine successions represent important archives of environmental and sea-level change. Most current knowledge about the origin of incised valleys stems from Quaternary case studies; however, research on pre-Quaternary examples can shed light on valley formation and evolution across longer timespans. This article describes different types of incised-valley fills from Lower to Middle Pennsylvanian fluvio-deltaic successions of the Breathitt Group (eastern Kentucky), accumulated in the Central Appalachian Foreland under prevalent glacioeustatic forcing driven by Gondwanan glaciations. Based on well-established criteria for their recognition, numerous incised-valley fills were identified from outcrop and subsurface data through more than 300 m of clastic successions consisting of fourth-order stratigraphic sequences stacked into third-order composite sequences. Incised-valley fills were categorized into three archetypes based on lateral extent and aspect ratio (relatively wide versus narrow valley fills), nature of infill (fully continental versus mixed marine and continental facies associations) and relationships to underlying coal zones (truncating versus non-truncating). The systematic occurrence of each incised-valley fill type at specific stratigraphic positions within every third-order sequence suggests control by a periodic allogenic factor. Valley-fill archetypes are interpreted in terms of variable accommodation-supply ratios driven by variable duration of formative base-level cycles. For example, relatively wide incised-valley fills with alluvial infill evolved during long-lived cycles whose prolonged base-level drawdown maintained low accommodation/supply ratios. Deeper valleys with low aspect ratios and mixed marine-continental infills were generated by short-lived base-level drawdown that forced higher accommodation/supply ratios. Available chronological data for the studied successions consent to estimate base-level cycles spanning 10^4–5 years that were likely modulated by interference patterns of orbital parameters (obliquity and eccentricity) via global climate and glacioeustatic fluctuations. This conceptual model, relating incised-valley fill morphometry and internal architecture to orbital forcing patterns, provides a possible approach to predicting and interpreting incised-valley fill variability through successions accumulated during icehouse conditions.  相似文献   

B.S. Daya Sagar,Qiuming Cheng and Frits Agterberg: Handbook of Mathematical Geosciences: Fifty Years of IAMG     

Kostyuchenko  Yuriy  Abioui  Mohamed  Di Cencio  Andrea 《Mathematical Geosciences》2020,52(5):725-729

Mathematical Geosciences -  相似文献   

The role of structural inheritance in continental break-up and exhumation of Alpine Tethyan mantle(Canavese Zone,Western Alps)     

Andrea Festa  Gianni Balestro  Alessandro Borghi  Sara De Caroli  Andrea Succo 《地学前缘(英文版)》2020,11(1):167-188

The Canavese Zone(CZ)in the Western Alps represents the remnant of the distal passive margin of the Adria microplate,which was stretched and thinned during the Jurassic opening of the Alpine Tethys.Through detailed geological mapping,stratigraphic and structural analyses,we document that the continental break-up of Pangea and tectonic dismemberment of the Adria distal margin,up to mantle rocks exhumation and oceanization,did not simply result from the syn-rift Jurassic extension but was strongly favored by older structu ral inheritances(the Proto-Canavese Shear Zone),which controlled earlier lithospheric weakness.Our findings allowed to redefine in detail(i)the tectono-stratigraphic setting of the Variscan metamorphic basement and the Late Carbonife rous to Early Cretaceous CZ succession,(ii)the role played by inherited Late Carboniferous to Early Triassic structures and(iii)the significance of the CZ in the geodynamic evolution of the Alpine Tethys.The large amount of extensional displacement and crustal thinning occurred during different pulses of Late Carbonife rous-Early Triassic strike-slip tectonics is wellconsistent with the role played by long-lived regional-scale wrench faults(e.g.,the East-Variscan Shear Zone),suggesting a re-discussion of models of mantle exhumation driven by low-angle detachment faults as unique efficient mechanism in stretching and thinning continental crust.  相似文献   

Perspectives of a visible instrument on the VLTI     

Florentin Millour  Denis Mourard  Julien Woillez  Philippe Berio  Andrea Chiavassa  Orlagh Creevey  Eric Lagadec  Marc-Antoine Martinod  Anthony Meilland  Nicolas Nardetto  Karine Perraut  Philippe Stee 《Experimental Astronomy》2018,46(3):497-509

In this paper we present the most promising science cases for a new generation visible instrument on the VLTI and the conceptual idea for the instrumental configuration. We also present a statistical study of the potential targets that may be accessible for the different classes of objects and for the required spectral resolutions.  相似文献   

Distribution and functional response of sublittoral soft bottom assemblages to sedimentary constraints   总被引：1，自引：0，他引：1  

Andrea Cosentino  Salvatore Giacobbe 《Estuarine, Coastal and Shelf Science》2008

Mollusc and annelid polychaete macrofaunal assemblages were studied in a sublittoral sandy bottom of 1.8 km² extension, along the western Calabrian coast (low Tyrrhenian Sea). The strict coupling of the local sedimentary dynamics with the benthic assemblages was investigated on a small spatial scale (patchiness), at the mesoscale depth-related gradients and at the level of functional/trophic habits. Non-metrical correlations (ρ), index of dispersion (Di) and dispersion weighted abundances, averaged per depth level highlighted the response of some characteristic species to the patchiness of sediments as well as to the predominant environmental gradients. Species habits and trophic guilds, that were assessed in terms of biomass (wet weight) and secondary “pseudo-production” (abundance × biomass), clarified the differential functional response of the assemblages at different depth levels. Polychaetes reached 84.86% abundance and showed a highly clumped distribution of sessile species (Ditrupa arietina, Aponuphis brementi, Chone acustica, Spiophanes kroyeri); to a lower extent the motile species (Hyalinoecia tubicola, Marphisa bellii, Phylo foetida) were present. Molluscs reached 15.14% abundance and only some bivalve taxa showed significant aggregated distributions (Corbula gibba, Tellina donacina, Tellina distorta), whereas gastropod species were more evenly distributed. Total biomasses were almost equal between the two taxonomic groups (46.41 g WW on average). Biotic–environmental rank matching highlighted depth, very fine sands (60–200 μm), sorting grade, skewness index and pH as being the most influential factors in the distributions of some species, followed secondarily by coarse silts (40–60 μm) and coarser sands (200–2000 μm). Within the local context of water/sediment oligotrophy, the adaptive strategies of macrofauna to a highly seasonal supply of autochthonous phytoplanktonic seston associated with imported macro debris and terrigenous components were emphasized. Evidence of such a differential nutrient supply was the clear functional differentiation of the shallower levels from the deeper ones, and the presence of an intermediate zone which was selectively dominated, in terms of abundance and biomass, by microphagous filter/suspension feeders. Moreover, the shortage of burrowing deposit feeders as well as the prevalence of motile macrophagous omnivores beyond 20 m depth may be considered as ecologically correlated aspects.  相似文献   

Chemical evidence of the changes of the Antarctic Bottom Water ventilation in the western Ross Sea between 1997 and 2003     

Paola Rivaro  Serena Massolo  Andrea Bergamasco  Pasquale Castagno  Giorgio Budillon 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(5):639-652

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