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451.
Michael H. Robinson Clark R. Alexander Chester W. Jackson Christopher P. McCabe David Crass 《Geoarchaeology》2010,25(3):312-326
Archaeological sites in beach and estuarine environments are continually threatened by diverse natural marine processes. Shoreline erosion, bluff retreat, and sea level rise all present potential for site destruction. Using historic maps, aerial imagery, and field survey methods in a GIS, 21 potentially significant archaeological sites on Georgia barrier islands were selected for determination of site‐specific rates of shoreline change using a powerful, new, moving‐boundary GIS analysis tool. A prioritized list of sites, based on the order of site loss from erosion, was generated to assist coastal managers in identifying and documenting sites most at risk. From the original selection of 21 sites, 11 sites were eroding, 8 shorelines were stable, and 2 shorelines were accreting. The methodology outlined here produces critical information on archaeological site loss rates and provides a straightforward means of prioritizing sites for detailed documentation. © 2010 Wiley Periodicals, Inc. 相似文献
452.
C.M.O’D. Alexander S.D. Newsome L.R. Nittler G.D. Cody 《Geochimica et cosmochimica acta》2010,74(15):4417-7532
Here we report the elemental and isotopic compositions of the insoluble organic material (IOM) isolated from several previously unanalyzed meteorites, as well as the reanalyses of H isotopic compositions of some previously measured samples (Alexander et al., 2007). The IOM in ordinary chondrites (OCs) has very large D enrichments that increase with increasing metamorphism and decreasing H/C, the most extreme δD value measured being almost 12,000‰. We propose that such large isotopic fractionations could be produced in the OC parent bodies through the loss of isotopically very light H2 generated when Fe was oxidized by water at low temperatures (<200 °C). We suggest that similar isotopic fractionations were not generated in the IOM of CV and CO chondrites with similar metamorphic grades and IOM H/C ratios because proportionately less water was consumed during metamorphism, and the remaining water buffered the H isotopic composition of the IOM even a H was being lost from it.Hydrogen would also have been generated during the alteration of CI, CM and CR carbonaceous chondrites. The IOM in these meteorites exhibit a considerable range in isotopic compositions, but all are enriched in D, as well as 15N, relative to terrestrial values. We explore whether these enrichments could also have been produced by the loss of H2, but conclude that the most isotopically anomalous IOM compositions in meteorites from these groups are probably closest to their primordial values. The less isotopically anomalous IOM has probably been modified by parent body processes. The response of IOM to these processes was complex and varied, presumably reflecting differences in conditions within and between parent bodies.The D enrichments associated with H2 generation, along with exchange between D-rich IOM and water in the parent bodies, means that it is unlikely that any chondrites retain the primordial H isotopic composition of the water ice that they accreted. The H isotopic compositions of the most water-rich chondrites, the CMs and CIs, are probably the least modified and their compositions (δD ? −25‰) suggest that their water did not form at large radial distances from the Sun where ice is predicted to be very D-rich. Yet models to explain the O isotopic composition of inner Solar System bodies require that large amounts of ice were transported from the outer to the inner Solar System. 相似文献
453.
Andrey A. Gurenko Kaj A. Hoernle Alexander V. Sobolev Folkmar Hauff Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2010,159(5):689-702
The Canary Island primitive basaltic magmas are thought to be derived from an HIMU-type upwelling mantle containing isotopically
depleted (NMORB)-type component having interacted with an enriched (EM)-type component, the origin of which is still a subject
of debate. We studied the relationships between Ni, Mn and Ca concentrations in olivine phenocrysts (85.6–90.0 mol.% Fo, 1,722–3,915 ppm
Ni, 1,085–1,552 ppm Mn, 1,222–3,002 ppm Ca) from the most primitive subaerial and ODP Leg 157 high-silica (picritic to olivine
basaltic) lavas with their bulk rock Sr–Nd–Pb isotope compositions (87Sr/86Sr = 0.70315–0.70331, 143Nd/144Nd = 0.51288–0.51292, 206Pb/204Pb = 19.55–19.93, 207Pb/204Pb = 15.60–15.63, 208Pb/204Pb = 39.31–39.69). Our data point toward the presence of both a peridotitic and a pyroxenitic component in the magma source.
Using the model (Sobolev et al. in: Science 316:412–417, 2007) in which the reaction of Si-rich melts originated during partial
melting of eclogite (a high pressure product of subducted oceanic crust) with ambient peridotitic mantle forms olivine-free
reaction pyroxenite, we obtain an end member composition for peridotite with 87Sr/86Sr = 0.70337, 143Nd/144Nd = 0.51291, 206Pb/204Pb = 19.36, 207Pb/204Pb = 15.61 and 208Pb/204Pb = 39.07 (EM-type end member), and pyroxenite with 87Sr/86Sr = 0.70309, 143Nd/144Nd = 0.51289, 206Pb/204Pb = 20.03, 207Pb/204Pb = 15.62 and 208Pb/204Pb = 39.84 (HIMU-type end member). Mixing of melts from these end members in proportions ranging from 70% peridotite and 30%
pyroxenite to 28% peridotite and 72% pyroxenite derived melt fractions can generate the compositions of the most primitive
Gran Canaria shield stage lavas. Combining our results with those from the low-silica rocks from the western Canary Islands
(Gurenko et al. EPSL 277:514–524, 2009), at least four distinct components are required. We propose that they are (1) HIMU-type
pyroxenitic component (representing recycled ocean crust of intermediate age) from the plume center, (2) HIMU-type peridotitic
component (ancient recycled ocean crust stirred into the ambient mantle) from the plume margin, (3) depleted, MORB-type pyroxenitic
component (young recycled oceanic crust) in the upper mantle entrained by the plume, and (4) EM-type peridotitic component
from the asthenosphere or lithosphere above the plume center. 相似文献
454.
Alexander Krohe Evripidis Mposkos Anastasios Diamantopoulos Georgios Kaouras 《Earth》2010,98(1-2):81-104
In seismically active regions, active low-angle detachment faults are probably more frequent as is commonly thought and may play an important but still underestimated role in the evolution of landforms and basins. We investigate the tectonically active region of Attica (Greece) in the Aegean back arc as a model region to show how basins and mountain ranges commonly thought to be formed by movements on high-angle normal faults in fact reflect the surface expression of displacements on yet undetected, deep-seated, active low-angle normal detachment faults. Inferences are made based on an integrated study of Attica linking the petrology of clastic sediments with geomorphology and structures, and including few new palynological data. From the Miocene to Recent, three sets of normal detachment fault systems were successively active. Shear zones of the 1st (Early Miocene) stage emplaced rocks of the Attic Cycladic high-P metamorphic belt (AC-HP-belt) from depth corresponding to greeschist facies conditions in the brittle, upper crust. In the 2nd stage the WNW dipping Attica low-angle normal detachment fault system between the AC-HP-belt and the un- or weakly metamorphosed rocks of the sub-Pelagonian Zone (SPZ) was active. Clastic sedimentation started in the Late Miocene, during the 2nd stage. Late Miocene and Early Pliocene clastic sediments reveal that during the 2nd stage many areas that presently expose the AC-HP-belt were still covered by the overlying SPZ. Also, now uplifted areas such as the Parnitha mountain range that currently undergo strong erosion were then the sites of sedimentary sinks. The 3rd stage (Late Pliocene through Recent) is associated with dramatic changes in the morphology and recurring steepening of the relief. Reversal of the Parnitha area from the site of deposition into the site of erosion is associated with deposition of coarse conglomerates to the SE of the Parnitha Mt. and S of the Penteli Mt. Sediments of the 3rd stage reflect activity of the here newly described, SSE-dipping Penteli—Athens low-angle detachment fault (PADF) system formed at a high angle to the Attica detachment fault. The outcome of this study is that the present-day geomorphology is to a high degree related to the operation of the PADF system. Steep fault bounding the Athens and Mesogea basins as well as the mountain ranges (Parnitha, Penteli, Hymittos mounts) belongs to its breakaway zone or root into the PADF. Ongoing tectonic movements related to this fault system were responsible for the 1999 Athens (Mw = 6.0) earthquake. We particularly discuss how the PADF may continue into greater depth, the translation magnitude, and how the PADF fits into the wider kinematic framework of the Aegean region. 相似文献
455.
The life marker chip (LMC) is being designed to test for the chemical signature of life in the soil and rocks of Mars. It will use an antibody array as part of its detection and characterisation system and aims to detect both polar and non-polar molecules at the sub-ppm to tens of ppb level. It is necessary to use a solvent to transfer organic compounds from the Martian samples to the LMC itself, but organic solvents such as dichloromethane or hexane, commonly used to dissolve non-polar molecules, are incompatible with the LMC antibodies. Hence, an aqueous-based solvent capable of dissolving the biomarkers that might exist in the soil or rocks of Mars is required. Solvent extractions of a Martian soil analogue, JSC Mars-1, spiked with a range of standards show that a 20:80 (vol:vol) mixture of methanol and water is incapable of extracting compounds insoluble in water. However, addition of 1.5 mg ml−1 of the surfactant polysorbate 80 produces extraction efficiencies of the aliphatic standards, hexadecane and phytane, equal to 25-30% of those produced by the common organic solvent mixture 93:7 (vol:vol) dichloromethane:methanol. Extraction of squalene and stigmasterol using the polysorbate solution is less efficient but still successful, at 5-10% of the efficiency of 93:7 dichloromethane:methanol. Such aliphatic compounds with occasional functional groups represent the compound classes to which most fossil organic biomarkers belong. The polysorbate solution did not extract the aromatic compounds pyrene and anthracene with great efficiency. A solvent of 20:80 methanol:water with 1.5 mg ml−1 polysorbate 80 is therefore capable of selectively extracting aliphatic biomarkers from Martian samples and transferring them to the antibody sites on the life marker chip. 相似文献
456.
Ohne Zusammenfassung 相似文献
457.
David Beresford-Jones Sean Taylor Clea Paine Alexander Pryor Jiří Svoboda Martin Jones 《Quaternary Science Reviews》2011,30(15-16):1948-1964
Precisely how Upper Palaeolithic human ecology was shaped by changing climate during the Pleniglacial remains a matter of debate, for while this generally cold period is now understood to include complex and often rapid flux in climate, there are still considerable difficulties in resolving climatic variations at particular times and places — derived from various lines of proxy evidence — with the high-resolution proxy record of temperature changes from oxygen isotope analysis of the Greenland ice-cores.In this paper we apply the methodology of large-scale flotation to newly excavated contexts from the Upper Palaeolithic (Gravettian) site of Dolní V?stonice II, Czech Republic, to explore the potential of charcoal — as a natural archive of environmental information — to offer information on environmental change towards the end of the middle pleniglacial during Oxygen Isotope Stage 3, between c. 32,500 and 31,200 Cal yr BP. The results of an analysis of ring widths and other anatomical features — interpreted alongside micromorphological data — indicate that this charcoal may capture a higher-resolution record of the changing climatic conditions during which humans were first expanding into these hitherto marginal ecologies and, consequently, shed new light upon the complexity of the lifeways that enabled them to do so. 相似文献
458.
Len R. Garces Michael D. Pido Robert S. Pomeroy Sonny Koeshendrajana Budi Iskandar Prisantoso Nurul Ahmad Fatan Dedi Adhuri T. Raiful Syamsul Rizal Alexander Tewfik Madan Dey 《Ocean & Coastal Management》2010,53(2):69-79
This paper describes the application of the methodology called Rapid Appraisal of Fisheries Management System (RAFMS) to assess quickly the situation in tsunami-affected coastal fisheries in Aceh Province, Indonesia. As a diagnostic tool, the RAFMS is introduced in terms of its conceptual framework and procedures. The RAFMS was used to appraise the status of the fisheries sector in selected 15 villages. Information generated concerning level of fishing effort, marketing patterns and community perspectives on livelihood options are used as three illustrative examples. The paper also provides some insights in applying the RAFMS methodology in the context of disasters and in the broader context of tropical fisheries management. 相似文献
459.
460.