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A pollen record from a sediment core drilled underneath the Acheulian site of Fontana Ranuccio provides new data on the vegetation characters in central Italy during the late Early Pleistocene, in a forest phase possibly corresponding to a substage of Marine Isotope Stage 21. A number of tree taxa nowadays extinct in Europe (Cathaya, Tsuga, Taxodium type, Carya and Pterocarya) are present at Fontana Ranuccio in a temperate phase characterised by dense forest conditions, dominated by Alnus and Pterocarya. The comparison of the Fontana Ranuccio record with other dated sites distributed along the Italian peninsula indicates that the floristic and vegetational characters of the Mid Pleistocene revolution present a rather distinct succession of biostratigraphic events. Compared to other Early Pleistocene pollen records from southern Europe, the Italian Peninsula shows greater floristic similarities with the Eastern Mediterranean regions than with the Iberian Peninsula. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Steven J. Ostro Lance A. M. Benner Christopher Magri Jon D. Giorgini Randy Rose Raymond F. Jurgens Donald K. Yeomans Alice A. Hine Michael C. Nolan Daniel J. Scheeres Stephen B. Broschart Mikko Kaasalainen Jean‐Luc Margot 《Meteoritics & planetary science》2005,40(11):1563-1574
Abstract— We present June 2004 radar images of asteroid 25143 Itokawa (1998 SF36) that improve upon the longitude‐latitude coverage of images obtained in 2001 by Ostro et al. (2004) and use the 2001–2004 data to refine that paper's constraints on Itokawa's shape. The 2004 images, the first of the asteroid's southern side, look distinctly different from the 2001 images, revealing leading edges that are much more curved and rugged than the nearly convex leading edges seen at northern latitudes in 2001. Itokawa is shaped like a slightly asymmetrical, bent, lumpy ellipsoid with dimensions along the principal axes within 10% of 594 times 320 times 288 m. To illustrate the uncertainty space associated with shape reconstruction from images with suboptimal orientational coverage, we present two alternative three‐dimensional models of the object. 相似文献
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Michael W. Busch Lance A.M. Benner Jon D. Giorgini Randy Rose Christopher Magri Michael C. Nolan 《Icarus》2008,195(2):614-621
During its close Earth approach in 2001, the E-class near-Earth Asteroid (33342) 1998 WT24 was the focus of extensive radar, optical, and thermal infrared observations. We present a physical model of this object, estimated from Arecibo and Goldstone radar images that cover multiple rotations and span over 100° of sky motion. The asteroid has an equivalent diameter of 415±40 m and a diffuse radar scattering law that is identical in both senses of circular polarization, implying a surface that is extremely rough on centimeter-to-decimeter scales. The shape is dominated by three large basins, which may be impact craters or a relic of past dynamical disruption of the object. Analysis of YORP perturbations on WT24's spin state predicts that the asteroid's spin rate is decreasing at a rate of . Simply extrapolating this rate suggests that the asteroid will despin over the next 150 kyr and was spinning at its surface disruption rate 75 kyr ago, but the rotational evolution of WT24 depends on the surface's thermal properties and probably is more complex than a simple spin-down. 相似文献
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Anatomy of shelf deltas at the edge of a prograding Eocene shelf margin, Spitsbergen 总被引：1，自引：0，他引：1
Abstract Although shelf‐edge deltas are well‐imaged seismic features of Holocene and Pleistocene shelf margins, documented outcrop analogues of these important sand‐prone reservoirs are rare. The facies and stratigraphic architecture of an outcropping shelf‐edge delta system in the Eocene Battfjellet Formation, Spitsbergen, is presented here, as well as the implications of this delta system for the generation of sand‐prone, shelf‐margin clinoforms. The shelf‐edge deltas of the Battfjellet Formation on Litledalsfjellet and Høgsnyta produced a 3–5 × 15 km, shelf edge‐attached, slope apron (70 m of sandstones proximally, tapering to zero on the lower slope). The slope apron consists of distributary channel and mouth‐bar deposits in its shelf‐edge reaches, passing downslope to slope channels/chutes that fed turbiditic lobes and spillover sheets. In the transgressive phase of the slope apron, estuaries developed at the shelf edge, and these also produced minor lobes on the slope. The short‐headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf, and the shelf‐edge position of the discharging deltas, made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin. The abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion. Evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane‐parallel laminae within turbidite beds in the slope channels, and thick spillover lobes with repetitive alternations of massive and flat‐laminated intervals. The examined shelf‐edge to slope system, now preserved mainly below the shelf break and dominated by sediment gravity‐flow deposits, has a threefold stratigraphic architecture: a lower, progradational part, in which the clinoforms have a slight downward‐directed trajectory; a thin aggradational zone; and an upper part in which clinoforms backstep up onto the shelf edge. A greatly increased density of erosional channels and chutes marks the regressive‐to‐transgressive turnaround within the slope apron, and this zone becomes an angular unconformity up near the shelf edge. This unconformity, with both subaerial and subaqueous components, is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level. The studied shelf‐margin clinoforms accreted mostly during falling stage (sea level below the shelf edge), but the outer shelf later became estuarine as sea level became re‐established above the shelf edge. 相似文献
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Tino Rödiger Fabien Magri Stefan Geyer Shehan Tharaka Morandage H. E. Ali Subah Marwan Alraggad Christian Siebert 《Hydrogeology Journal》2017,25(7):2139-2149
Both increasing aridity and population growth strongly stress freshwater resources in semi-arid areas such as Jordan. The country’s second largest governorate, Irbid, with over 1 million inhabitants, is already suffering from an annual water deficit of 25 million cubic meters (MCM). The population is expected to double within the next 20 years. Even without the large number of refugees from Syria, the deficit will likely increase to more then 50 MCM per year by 2035 The Governorate’s exclusive resource is groundwater, abstracted by the extensive Al Arab and Kufr Asad well fields. This study presents the first three-dimensional transient regional groundwater flow model of the entire Wadi al Arab to answer important questions regarding the dynamic quality and availability of water within the catchment. Emphasis is given to the calculation and validation of the dynamic groundwater recharge, derived from a multi-proxy approach, including (1) a hydrological model covering a 30-years dataset, (2) groundwater level measurements and (3) information about springs. The model enables evaluation of the impact of abstraction on the flow regime and the groundwater budget of the resource. Sensitivity analyses of controlling parameters indicate that intense abstraction in the southern part of the Wadi al Arab system can result in critical water-level drops of 10 m at a distance of 16 km from the production wells. Moreover, modelling results suggest that observed head fluctuations are strongly controlled by anthropogenic abstraction rather than variable recharge rates due to climate changes. 相似文献
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Hechmi Garnit Salah Bouhlel Donatella Barca Chaker Chtara 《Chemie der Erde / Geochemistry》2012,72(2):127-139
Laser ablation ICP-MS was used to determine trace (TE) and rare earth element (REE) contents of sedimentary phosphatic pellets and coprolites collected from late Paleocene-early Eocene phosphorite deposits in Tunisia. TE and REE contents in the investigated deposits exhibit a close relationship with grain types and paleogeography. Phosphatic pellets seem to concentrate more TE and REE than co-existing coprolites. Both particle types display modern oxic-suboxic seawater patterns. In most coprolites, ∑REE, Y, Cr, Ni, Th, and V show an increase from core to rim, whereas Ba, Cd, Cu, and U abundances decrease from core to rim, reflecting adsorption processes during early diagenesis consistent with changing redox and productivity conditions.The northern basins (Sra Ouertane) within open marine and platform settings tended to be more oxic-suboxic with relative high organic matter flux, while the eastern basins (Jebel Jebs) and Gafsa-Metlaoui basin are characterized by semi-restricted situation associated with suboxic-oxic conditions. This result is consistent with previous reconstructions which suggest that phosphorites of northern basins had a more direct connection to the open ocean than those to the south and east of the emerged area.This study highlights the potential for using laser ablation ICP-MS as a tool to reconstruct phosphorite depositional paleoenvironments. 相似文献
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Combined analyses of pollen, seeds, woods, micro-charcoal and non-pollen palynomorphs from Stagno di Maccarese, an artificially
dried out coastal basin north of the Tiber delta now occupied by the Fiumicino Airport (Rome, Italy), document marked vegetation
and environmental changes during the last 8300 years. Between 8300 and 5400 cal. a BP dense mixed deciduous and evergreen
forests surrounded a eutrophic freshwater basin. An abrupt change around 5400 cal. a BP marks the transition to a marshy environment,
due to a lowering of the water table. An increase of cereals and micro-charcoals matches the presence of a nearby Eneolithic
settlement. Between 5100 and 2900 cal. a BP there is a remarkable expansion of riparian trees, indicating an increase of the
water level. Between 2900 and 2000 cal. a BP, a new development of marshlands points to a progressive lowering of the lake.
After 2000 cal. a BP, during the Roman exploitation of the area, an expansion of arboreal vegetation is recorded, characterized
by evergreen and deciduous oak-dominated forests, while an extensive chenopods marshland matches the presence of saltworks.
On the whole, the Stagno di Maccarese area appears very unstable, due to changes in lake level, introgression of marine water,
eutrophic phases, flood events, desiccations and openings of the forest vegetation. 相似文献