LANDSCAPE CHANGE IN WESTERN AMAZONIA*     

SANTIAGO LÓPEZ  REBECCA BEARD  RODRIGO SIERRA 《Geographical review》2013,103(1):37-58

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Insights into the morphology of the Serra da Cangalha impact structure from geophysical modeling     

M. A. R. VASCONCELOS  K. WÜNNEMANN  A. P. CRÓSTA  E. C. MOLINA  W. U. REIMOLD  E. YOKOYAMA 《Meteoritics & planetary science》2012,47(10):1659-1670

Forward modeling is commonly applied to gravity field data of impact structures to determine the main gravity anomaly sources. In this context, we have developed 2.5‐D gravity models of the Serra da Cangalha impact structure for the purpose of investigating geological bodies/structures underneath the crater. Interpretation of the models was supported by ground magnetic data acquired along profiles, as well as by high resolution aeromagnetic data. Ground magnetic data reveal the presence of short‐wavelength anomalies probably related to shallow magnetic sources that could have been emplaced during the cratering process. Aeromagnetic data show that the basement underneath the crater occurs at an average depth of about 1.9 km, whereas in the region beneath the central uplift it is raised to 0.5–1 km below the current surface. These depths are also supported by 2.5‐D gravity models showing a gentle relief for the basement beneath the central uplift area. Geophysical data were used to provide further constraints for numeral modeling of crater formation that provided important information on the structural modification that affected the rocks underneath the crater, as well as on shock‐induced modifications of target rocks. The results showed that the morphology is consistent with the current observations of the crater and that Serra da Cangalha was formed by a meteorite of approximately 1.4 km diameter striking at 12 km s^?1.  相似文献   

Controls on marine–erg margin cycle variability: aeolian–marine interaction in the mid‐Cretaceous Iberian Desert System,Spain     

JUAN PEDRO RODRÍGUEZ‐LÓPEZ  NIEVES MELÉNDEZ  POPPE L. De BOER  ANA ROSA SORIA 《Sedimentology》2012,59(2):466-501

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Geological investigation and optical dating of Quaternary siliciclastic sediments near Apalachicola,North‐west Florida,USA     

WILLIAM J. RINK  GLORIA I. LÓPEZ  DAVID J. MALLINSON  PETER R. PARHAM  EDUARD G. REINHARDT 《Sedimentology》2012,59(6):1836-1849

Ground penetrating radar and single‐aliquot regenerative‐dose optically stimulated luminescence were used to determine the depositional environments and age of unconsolidated siliciclastic sediments near Apalachicola, Florida. Five direct‐push cores, five vibracores and 28 optically stimulated luminescence samples were collected, as well as 7 km of ground penetrating radar data. A new model of cosmic dose rate calculation, which removes the effect of a much younger aeolian cap, was utilized to calculate more representative optically stimulated luminescence ages. Five radar facies were identified based on reflector amplitude and orientation. The resulting data indicate that the Tertiary/Quaternary Shelly Sediments were deposited before marine isotope stage 6, the Quaternary Alluvium was deposited during marine isotope stage 6 and the Quaternary Beach Ridge and Dune was deposited during the marine isotope stage 5e sea‐level highstand, which peaked at approximately 2·5 m above present sea‐level in this area.  相似文献   

Karst subsidence as a control on the accumulation and preservation of aeolian deposits: A Pleistocene example from a proglacial outwash setting,Ebro Basin,Spain     

ARÁNZAZU LUZÓN  JUAN PEDRO RODRÍGUEZ‐LÓPEZ  ANTONIO PÉREZ  MARÍA ASUNCIÓN SORIANO  HÉCTOR GIL  ANDRÉS POCOVÍ 《Sedimentology》2012,59(7):2199-2225

Meltwater flows emanating from the Pyrenees during the Pleistocene constructed a braided outwash plain in the Ebro Basin and led to the karstification of the Neogene gypsum bedrock. Synsedimentary evaporite dissolution locally increased subsidence rates and generated dolines and collapses that enabled the accumulation and preservation of outwash gravels and associated windblown deposits that were protected from erosion by later meltwater flows. In these localized depocentres, maximum rates of wind deceleration resulted from airflow expansion, enabling the accumulation of cross‐stratified sets of aeolian strata climbing at steep angles and thereby preserving up to 5 m thick sets. The outwash plain was characterized by longitudinal and transverse fluvial gravel bars, channels and windblown facies organized into aeolian sand sheets, transverse and complex aeolian dunes, and loess accumulations. Flat‐lying aeolian deposits merge laterally to partly deformed aeolian deposits encased in dolines and collapses. Synsedimentary evaporite dissolution caused gravels and aeolian sand deposits to subside, such that formerly near‐horizontal strata became inclined and generated multiple internal angular unconformities. During episodes when the wind was undersaturated with respect to its potential sand transporting capacity, deflation occurred over the outwash plain and coarse‐grained lags with ventifacts developed. Subsequent high‐energy flows episodically reached the aeolian dune field, leading to dune destruction and the generation of hyperconcentrated flow deposits composed in part of reworked aeolian sands. Lacustrine deposits in the distal part of the outwash plain preserve rhythmically laminated lutites and associated Gilbert‐type gravel deltas, which developed when fluvial streams reached proglacial lakes. This study documents the first evidence of an extensive Pleistocene proglacial aeolian dune field located in the Ebro Basin (41˙50° N), south of what has hitherto been considered to be the southern boundary of Pleistocene aeolian deposits in Europe. A non‐conventional mechanism (evaporite karst‐related subsidence) for the preservation of aeolian sands in the stratigraphic record is proposed.  相似文献   

Late Quaternary Iceberg Rafting along the Antarctic Peninsula Continental Rise and in the Weddell and Scotia Seas     

Colm Cofaigh  Julian A Dowdeswell  Carol J Pudsey 《Quaternary Research》2001,56(3)

Sediment cores from the continental rise west of the Antarctic Peninsula and the northern Weddell and Scotia Seas were investigated for their ice-rafted debris (IRD) content by lithofacies logging and counting of particles >0.2 cm from core x-radiographs. The objective of the study was to determine if there are iceberg-rafted units similar to the Heinrich layers of the North Atlantic that might record periodic, widespread catastrophic collapse of basins within the Antarctic Ice Sheet during the Quaternary. Cores from the Antarctic Peninsula margin contain prominent IRD-rich units, with maximum IRD concentrations in oxygen isotope stages 1, 5, and 7. However, the greater concentration of IRD in interglacial stages is the result of low sedimentation rates and current winnowing, rather than regional-scale episodes of increased iceberg rafting. This is also supported by markedly lower mass accumulation rates (MAR) during interglacial periods versus glacial periods. Furthermore, thinner IRD layers within isotope stages 2–4 and 6 cannot be correlated between individual cores along the margin. This implies that the ice sheet over the Antarctic Peninsula did not undergo widespread catastrophic collapse along its western margin during the late Quaternary (isotope stages 1–7). Sediment cores from the Weddell and Scotia Seas are characterized by low IRD concentrations throughout, and the IRD signal generally appears to be of limited regional significance with few strong peaks that can be correlated between cores. Tentatively, this argues against pervasive, rapid ice-sheet collapse around the Weddell embayment over the last few glacial cycles.  相似文献   

Fluorine in basalts from Iceland     

Gudmundur E. Sigvaldason  Níels Óskarsson 《Contributions to Mineralogy and Petrology》1986,94(3):263-271

The fluorine content of Icelandic tholeiitic and alkaline basalts matches values found in similar rocks from other areas. Covariation between fluorine and incompatible minor elements such as potassium or phosphorus is found in evolved tholeiites and alkali basalts. Lack of such covariation in primitive olivine tholeiites indicates that fluorine and other incompatible minor and trace elements are not controlled by minerals such as amphibole, mica or apatite in the mantle residue, and that the covariation between these elements in the evolved basalts cannot be inherited from the mantle. Model calculations on rocks from the Langjökull area show that olivine tholeiite suites are, if derived by simple fractional crystallization, enriched in incompatible elements much in excess of the increase due to crystal removal. These observations are taken to indicate that the well documented covariation between fluorine and other incompatible elements is not established until evolution of the basaltic magma has started in crustal holding chambers. The constancy of element ratios and enrichment in excess of what can be accounted for by crystal fractionation or incremental addition of new batches of primitive magmas does indicate (1) mineral control involving amphibole, mica or apatite and (2) addition of fluorine, potassium and phosphorous from an external source. It is argued that this source is the crustal envelope of the holding chamber.  相似文献   

Morphotectonics of the Iberian Peninsula   总被引：1，自引：0，他引：1  

M. O. Cotilla Rodríguez  D. CÓrdoba Barba 《Pure and Applied Geophysics》2004,161(4):755-815

A morphotectonic interpretation of the relief of the Iberian Peninsula (IP) is presented based on an analysis of its gross forms. Several geological–geophysical and geomorphological methods were used in order to build up a morphostructural sketch. Three main categories were established using the approach of Rantsman (1979): Territorial Units (1-megablock, 9-macroblocks, 34-mesoblocks, 1.374-blocks and 2.523-microblocks); Morphostructural Alignments (2-first, 8-second, 20-third and 1-fourth rank; and 43 knots between Morphostructural Alignments (second-fourth rank). The main seismic activity is concentrated on the first- and second-rank lineaments, and some important epicenters are located near the lineament intersections. The origin of the earthquakes in the vicinity of such knots can be explained by the forcing/pushing of macroblocks westwards. The existence of earthquakes along the lineaments may be explained by tension. From the present study it appears that earthquake occurrence in the IP is due principally to stress concentrations around morphotectonic zones. A seismotectonic interpretation of the IP is also presented. On this map three zones are distinguished (A, B, C), each of them with a different active level and dimensions.Received: 25 November 2000  相似文献   

Maximum extent and readvance dynamics of the Irish Sea Ice Stream and Irish Sea Glacier since the Last Glacial Maximum     

J. D. Scourse  R. C. Chiverrell  R. K. Smedley  D. Small  M. J. Burke  M. Saher  K. J. J. Van Landeghem  G. A. T. Duller  C. Ó Cofaigh  M. D. Bateman  S. Benetti  S. Bradley  L. Callard  D. J. A. Evans  D. Fabel  G. T. H. Jenkins  S. McCarron  A. Medialdea  S. Moreton  X. Ou  D. Praeg  D. H. Roberts  H. M. Roberts  C. D. Clark 《第四纪科学杂志》2021,36(5):780-804

The BRITICE-CHRONO Project has generated a suite of recently published radiocarbon ages from deglacial sequences offshore in the Celtic and Irish seas and terrestrial cosmogenic nuclide and optically stimulated luminescence ages from adjacent onshore sites. All published data are integrated here with new geochronological data from Wales in a revised Bayesian analysis that enables reconstruction of ice retreat dynamics across the basin. Patterns and changes in the pace of deglaciation are conditioned more by topographic constraints and internal ice dynamics than by external controls. The data indicate a major but rapid and very short-lived extensive thin ice advance of the Irish Sea Ice Stream (ISIS) more than 300 km south of St George's Channel to a marine calving margin at the shelf break at 25.5 ka; this may have been preceded by extensive ice accumulation plugging the constriction of St George's Channel. The release event between 25 and 26 ka is interpreted to have stimulated fast ice streaming and diverted ice to the west in the northern Irish Sea into the main axis of the marine ISIS away from terrestrial ice terminating in the English Midlands, a process initiating ice stagnation and the formation of an extensive dead ice landscape in the Midlands.  相似文献   

Energy-intensive manufacturing sectors in China: policy priorities for achieving climate mitigation and energy conservation targets     

Li Li  Brian Ó Gallachóir  Hua Cai  Jian Zhang 《Climate Policy》2019,19(5):598-610

In this study, a long-range energy alternative planning (LEAP) model was built to evaluate the relative priority of three kinds of policies expected to be implemented for the energy-intensive manufacturing sectors (EIMS) in China to achieve CO₂ mitigation and energy conservation targets. These policies encourage (1) the use of more electricity instead of coal; (2) the continuous improvement of energy efficiency; and (3) a shift to other less energy-demanding sectors. The results indicate that the policy of shifting economic activity from the EIMS to other sectors is most helpful for China to achieve its targets of mitigating CO₂ emissions and conserving energy. Encouraging the EIMS to use more electricity can help China to achieve a higher proportion of non-fossil-fuel based energy in its overall primary energy consumption. No single policy will allow China to achieve all the targets, emphasizing the need for an integrated policy design that combines all types of policies.

Key policy insights

• The policy of encouraging a shift to less energy intensive industries should receive the highest priority in aiming to peak China's energy-related CO₂ emissions as early as possible, and lower overall CO₂ emissions, coal consumption and primary energy consumption in the long run.

• Encouraging a shift to electricity should go hand-in-hand with greater energy efficiency, otherwise such a policy cannot help China significantly reduce energy-related CO₂ emissions.

• Encouraging the EIMS to use more electricity should receive the highest priority in helping China achieve a higher proportion of non-fossil-fuel based energy in its overall primary energy consumption.

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