Post-rift volcanism and high heat-flow at the ocean-continent transition of the eastern Gulf of Aden     

Francis Lucazeau  Sylvie Leroy  Julia Autin  Alain Bonneville  Bruno Goutorbe  Louise Watremez  Elia d'Acremont  Doga Düsünur  Frédérique Rolandone  Philippe Huchon  Nicolas Bellahsen  Patrick Tuchais 《地学学报》2009,21(4):285-292

A high heat-flow (∼900 mW m⁻²) has been observed over a volcanic structure at the Ocean-Continent Transition in the Eastern Gulf of Aden (Oman margin). The anomaly is superposed to a progressive increase of heat-flow across the margin and can be interpreted either by (1) heat refraction, (2) fluid discharge or (3) cooling magma. The two first explanations cannot be ruled out definitely by modelling analysis, but require unlikely thermal conductivity or permeability values. The third one implies that the latest activity of the volcano was about 100 000 years old and therefore continued c. 18 Ma after the break-up of Africa and Arabia. This potential mechanism is consistent with other lines of evidence of post-rifting activity in the Gulf of Aden and could invalidate the conventional assumption that rifted-margins become passive after the break-up of continents.  相似文献   

The observed concentration–mass relation for galaxy clusters     

Julia M. Comerford  Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》2007,379(1):190-200

The properties of clusters of galaxies offer key insights into the assembly process of structure in the universe. Numerical simulations of cosmic structure formation in a hierarchical, dark matter dominated universe suggest that galaxy cluster concentrations, which are a measure of a halo's central density, decrease gradually with virial mass. However, cluster observations have yet to confirm this correlation. The slopes of the run of measured concentrations with virial mass are often either steeper or flatter than that predicted by simulations. In this work, we present the most complete sample of observed cluster concentrations and masses yet assembled, including new measurements for 10 strong-lensing clusters, thereby more than doubling the existing number of strong-lensing concentration estimates. We fit a power law to the observed concentrations as a function of virial mass, and find that the slope is consistent with the slopes found in simulations, though our normalization factor is higher. Observed lensing concentrations appear to be systematically larger than X-ray concentrations, a more pronounced effect than that found in simulations. We also find that at a fixed mass, the bulk of observed cluster concentrations are distributed lognormally, with the exception of a few anomalously high concentration clusters. We examine the physical processes likely responsible for the discrepancy between lensing and X-ray concentrations, and for the anomalously high concentrations in particular. The forthcoming Millennium simulation results will offer the most comprehensive comparison set to our findings of an observed concentration–mass power law relation.  相似文献   

Influence of the sample history and the moisture status on the thermal behavior of soil organic matter     

Julia Hurrass 《Geochimica et cosmochimica acta》2007,71(3):691-702

Recent studies indicate that glassiness represents a characteristic feature of soil organic matter (SOM). It is however unknown, to which extent the transitions detected in humic substances and whole soil samples correspond to common models of synthetic polymers providing the theoretical basis for explaining their glass transition characteristics. Physical aging associated with structural relaxation of amorphous substances below their glass temperature is one fundamental basis for the glass transition behavior of synthetic polymers. According to the results of this study, aging processes also occur in SOM. In whole soil samples, this process can be observed by the shift of glass transition-like step transitions to higher temperatures within the time scale of years. Not only the structural relaxation of the macromolecular organic substances, but also interactions with water molecules, which may exhibit both plasticizing and antiplasticizing properties, influence the aging process of SOM. Especially under moistening or drying conditions, a differentiation between the effects of water and of alterations of the SOM structure in the course of time on the rigidity of the macromolecular network is difficult.  相似文献   

Stable carbon and oxygen isotopic evidence for late Pleistocene to middle Holocene climatic fluctuations in the interior of southern Africa     

Jeannette M. Smith  Julia A. Lee‐Thorp  Judith C. Sealy 《第四纪科学杂志》2002,17(7):683-695

Stable carbon and oxygen isotope analyses of ungulate grazers from four archaeological sites located in different environs within the Caledon River Valley have provided a relatively well‐dated proxy palaeoenvironmental and palaeoclimatic sequence for the period between 16 000 and 6000 calendar (cal.) yr BP. Within the overall trend towards hot mid‐Holocene temperatures and a summer rainfall pattern, stable carbon isotope results show that there were three periods when growth season temperatures were cool enough for C₃ grasses to be present: 16 000–14 000; 10 200–9600, and 8400–8000 cal. yr BP. Similar trends were recorded in stable oxygen isotope values, reflecting shifts in either temperature or available moisture. Although having a similar pattern to that of the lower altitude site, sites situated in foothills and montane portions of the valley consistently maintained lower temperatures until the mid‐Holocene altithermal. At this time growth season temperatures warmed sufficiently for a 100% C₄ grassland to expand in altitude from the warmer low lying localities. In relation to present understanding of synoptic and global climatic patterning, these findings suggest that the early to middle Holocene transition was not a gradual warming trend, but rather it was marked by a series of climatic fluctuations. Of particular note is the possible global, rather than regional, occurrence of the 8200 cal. yr BP ‘event’. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Vertical and lateral organization of a carbonate deep-water slope marginal to a submarine fan system, Miocene, southern Turkey     

Bryan T. Cronin  Kemal GÜrbÜz  rew Hurst  & Nick Satur 《Sedimentology》2000,47(4):801-824

Organization is recognized in the forereef–deep water slope–submarine fan system of the Burdigalian-Langhian Kaplankaya Formation. A basinwards transition from a prograding shelfal reef complex, through forereef talus, deep-water slope and laterally encroaching bypass deep-water clastic system is described, although the deep-water slope makes up the bulk of the succession. Considerable thickness variations occur between the reef and deep-water clastic complexes; these are controlled by sea-floor topography, carbonate foreslope gradient and degree of mass wasting off the platform and foreslope. The vertical and lateral heterogeneity of the Kaplankaya deep-water slope system is described from a number of localities along a 40-km-long and up to 3-km-wide exposed section of the northern margin of the Miocene Adana Basin, a foreland basin setting resulting from thrust sheet loading from the north during the Tauride Orogeny. Detailed field mapping is supplemented with vertical sedimentary logs, photomosaics, palaeontological and petrological data to investigate stratal variation, diagnostic architectural elements, controls on slope progradation, differential timing of basinward encroachment of the reefal complex and lateral onlap of the deep-water clastic system onto the slope. Three-dimensional models are presented showing the vertical and lateral facies associations in different parts of the deep-water slope system, and provide a basis for architectural prediction of geometry and relative position in such environments.  相似文献   

IRAS 12311−3509: a carbon star with SiC₂ emission     

T. Lloyd Evans  M. E. Hurst  P. J. Sarre 《Monthly notices of the Royal Astronomical Society》2000,319(1):111-120

The optical spectrum of the carbon star IRAS 12311−3509 is dominated by the Merrill–Sanford emission bands of SiC₂, by absorption and emission in the Swan system of C₂, and by resonance emission lines of neutral metals. The infrared energy distribution is flat from 1 to 60 μm. These observations are interpreted as arising from a star with a cool dusty disc which is edge-on to the observer and obscures direct starlight. The infrared continuum is caused predominantly by absorption of stellar light by dust in the disc and re-emission at longer wavelengths. The optical stellar spectrum is seen by reflection off dusty material which lies out of the plane of the disc, and the molecular and atomic emission arises in the same geometry through resonance fluorescence. The object has similarities to the J-silicate stars, but may have a carbon-rich rather than oxygen-rich disc. A full spectroscopic assignment and discussion of the SiC₂ bands and their intensities are given. Modelling of the rotational contours of the     band yields a rotational temperature of 250 K, indicating very cool gas.  相似文献   

Petroleum geoscience by Jon Gluyas & Richard Swarbrick,Blackwell Publishing, 2003. No. of pages: 359. ISBN: 0 632 03767 9.     

Andrew Hurst 《Geological Journal》2005,40(2):247-248

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Stable isotope evidence of late MIS 3 to middle Holocene palaeoenvironments from Sehonghong Rockshelter,eastern Lesotho          下载免费PDF全文

Emma Loftus  Brian A. Stewart  Genevieve Dewar  Julia Lee‐Thorp 《第四纪科学杂志》2015,30(8):805-816

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Hydrological principles for sustainable management of forest ecosystems     

Irena F. Creed  Gabor Z. Sass  Jim M. Buttle  Julia A. Jones 《水文研究》2011,25(13):2152-2160

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Fifty years of runoff response to conversion of old-growth forest to planted forest in the H. J. Andrews Forest,Oregon, USA     

Emily A. Crampe  Catalina Segura  Julia A. Jones 《水文研究》2021,35(5):e14168

Long-term watershed experiments provide the opportunity to understand forest hydrology responses to past logging, road construction, forest regrowth, and their interactions with climate and geomorphic processes such as road-related landslides. We examined a 50-year record from paired-watershed experiments in the H. J. Andrews Experimental Forest, Oregon, USA in which 125 to 450-year-old conifer forests were harvested in the 1960s and 1970s and converted to planted conifer forests. We evaluated how quickflow and delayed flow for 1222 events in treated and reference watersheds changed by season after clearcutting and road construction, including 50 years of growth of planted forest, major floods, and multi-decade reductions in snowpack. Quickflow runoff early in the water year (fall) increased by up to +99% in the first decade, declining to below pre-harvest levels (−1% to −15%) by the third to fifth decade after clearcutting. Fall delayed flow responded more dramatically than quickflow and fell below pre-treatment levels in all watersheds by the fifth decade, consistent with increased transpiration in the planted forests. Quickflow increased less (+12% to 70%) during the winter and spring but remained higher than pre-treatment levels throughout the fourth or fifth decade, potentially impacted by post-harvest burning, roads, and landslides. Quickflow remained high throughout the 50-year period of study, and much higher than delayed flow in the last two decades in a watershed in which road-related changes in flow routing and debris flows after the flood of record increased network connectivity. A long-term decline in regional snowpack was not clearly associated with responses of treated vs. reference watersheds. Hydrologic processes altered by harvest of old-growth conifer forest more than 50 years ago (transpiration, interception, snowmelt, and flow routing) continued to modify streamflow, with no clear evidence of hydrologic recovery. These findings underscore the importance of continued long-term watershed experiments.  相似文献