The upper cenozoic evolution of the Duero and Ebro fluvial systems (N-Spain): part I. paleogeography; part II. geomorphology     

Daniel Mikeš 《Central European Journal of Geosciences》2010,2(3):420-432

Lack of age dates in the terrigenous Cenozoic sediments of the Duero and the Ebro sedimentary basins has complicated tecto-stratic correlation across the two basins. We tentatively synthesize a range of existing studies and new data to construct a rough general paleogeography throughout Upper Cenozoic times. The more extensive erosion of the Ebro has been previously attributed to the earlier moment of opening. We tentatively analyse lithostratic data to conclude that the lower knick-point and different lithologies have also contributed to the deeper erosion in the Ebro Basin. We conclude from lithostratic data and field evidence that the W half of the Rioja was part of the Duero in earlier times and that the escarpment retreated westward through the Rioja in four subsequent episodes of erosion. The tilt of the NW Duero is a consequence of isostatic rebound to this erosion.  相似文献   

A new pathway for Deep water exchange between the Natal Valley and Mozambique Basin?     

Errol Wiles  Andrew Green  Mike Watkeys  Wilfried Jokat  Ralf Krocker 《Geo-Marine Letters》2014,34(6):525-540

Although global thermohaline circulation pathways are fairly well known, the same cannot be said for local circulation pathways. Within the southwest Indian Ocean specifically there is little consensus regarding the finer point of thermohaline circulation. We present recently collected multibeam bathymetry and PARASOUND data from the northern Natal Valley and Mozambique Ridge, southwest Indian Ocean. These data show the Ariel Graben, a prominent feature in this region, creates a deep saddle across the Mozambique Ridge at ca. 28°S connecting the northern Natal Valley with the Mozambique Basin. Results show a west to east change in bathymetric and echo character across the northern flank of the Ariel Graben. Whereby eroded plastered sediment drifts in the west give way to aggrading plastered sediment drift in the midgraben, terminating in a field of seafloor undulations in the east. In contrast, the southern flank of the Ariel Graben exhibits an overall rugged character with sediments ponding in bathymetric depressions in between rugged sub/outcrop. It is postulated that this change in sea-floor character is the manifestation of deep water flow through the Ariel Graben. Current flow stripping, due to increased curvature of the graben axis, results in preferential deposition of suspended load in an area of limited accommodation space consequently developing an over-steepened plastered drift. These deposited sediments overcome the necessary shear stresses, resulting in soft sediment deformation in the form of down-slope growth faulting (creep) and generation of undulating sea-floor morphology. Contrary to previous views, our works suggests that water flows from west to east across the Mozambique Ridge via the Ariel Graben.  相似文献   

Is rainfall intensity significant in the rainfall–runoff process within tropical rainforests of northeast Queensland? The Hewlett regression analyses revisited     

Andrew J. Howard  Mike Bonell  Don Gilmour  David Cassells 《水文研究》2010,24(18):2520-2537

Following the statistical analyses of long‐term rainfall‐runoff records from research basins in humid temperate latitudes, Hewlett and co‐workers extended the global challenge to disprove their findings that rainfall intensity was non‐significant. This paper responds to Hewlett's challenge as no preceding analyses have involved forested basins in a tropical cyclone‐prone area. Based on a 7 year rainfall‐runoff record, quickflow (QF), peak flow (QP) and quickflow response ratios (QRR) were regressed as dependent variables against rainfall parameters (intensity, P_i, amount, P), storm duration, D and antecedent flow, I. These data sets were categorised into total streamflow (Q) classes and stratified into three seasons, (monsoon, post‐monsoon and dry) for forested and cleared catchments. Where rainfall variable collinearity met acceptable levels, the addition of P_i to regression models including P, D, I contributed up to 9% and 66% of the respective variations in quickflow and peak flow. For the highest Q storm classes (monsoon), P_i alone accounted for up to 67% and 91% of the variation in Q_F and Q_P respectively and was the dominant influence on Q_P for all seasons. The very high rainfall intensities experienced in the monsoon season is a causal factor why these results differ from those of other research drainage basins. Surprisingly, P_i continued to have a significant influence on Q_F for dry season classes when less‐intense rainfall occurs. Further the results were similar for both catchments across all seasons. P was the dominant independent variable affecting Q_F above a threshold Q of 50 mm (monsoon), as rainfall contributes directly to saturation overland flow and return flow under saturated conditions. Further although QRR increased with increasing Q for each season, the regression results for that parameter were poor possibly due to the non‐linearity of the rainfall‐runoff relationship. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Studies on the plankton and sediment diatoms in Xuanwu Lake,Nanjing, China     

Wang Ruping  Dickman M.D. 《中国海洋湖沼学报》1991,9(3):277-289

The sediment diatom data based on a 16 cm long sediment core removed from near the center of the lake indicated that nutrient pollution tolerant diatoms have replaced pollution intolerant taxa which were common near the base of the core (about 35 years before present). These observations support the hypothesis that there is progressive eutrophication in Xuanwu Lake. This conclusion is corroborated by direct comparisons of the present day phytoplankton and zooplankton species composition within the lake and published accounts of its species composition during the mid 1970s.  相似文献   

Equilibrium erosion of soft rock shores with a shallow or absent beach under increased sea level rise   总被引：1，自引：0，他引：1  

Mike Walkden  Mark Dickson   《Marine Geology》2008,251(1-2):75-84

A process-based numerical model was used to explore the response of soft rock shores with low volume beaches to variable rates of sea level rise. Equilibrium recession rates were simulated for ranges of wave height and period, tidal amplitude, rock strength, beach volume and rate of sea level rise. Equilibrium shore profiles were found to be steeper with higher rates of sea level rise. Beaches were represented as protective surfaces yet were found to cause no significant reduction in equilibrium recession rate when their volumes were below a critical threshold. Reduced equilibrium recession rates were found with beaches that extended sufficiently far below low tide level. The model results imply that, given several constraints, a very simple relationship exists between increased rates of sea level rise and the response of eroding composite soft rock/low volume beach shores.  相似文献   

The 6dF Galaxy Survey: samples, observational techniques and the first data release     

D. Heath Jones  Will Saunders  Matthew Colless  Mike A. Read  Quentin A. Parker  Fred G. Watson  Lachlan A. Campbell  Daniel Burkey  Thomas Mauch  Lesa Moore  Malcolm Hartley  Paul Cass  Dionne James  Ken Russell  Kristin Fiegert  John Dawe  John Huchra  Tom Jarrett  Ofer Lahav  John Lucey  Gary A. Mamon  Dominique Proust  Elaine M. Sadler  Ken-ichi Wakamatsu 《Monthly notices of the Royal Astronomical Society》2004,355(3):747-763

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The effect of drawdown on suspended solids and phosphorus export from Columbia Lake,Waterloo, Canada     

Mike Shantz  Elizabeth Dowsett  Emma Canham  Guillaume Tavernier  Mike Stone  Jonathan Price 《水文研究》2004,18(5):865-878

This study examines the effect of drawdown on the timing and magnitude of suspended solids and associated phosphorus export from a 12 ha reservoir located in an urbanized watershed in southern Ontario, Canada. Water level in Columbia Lake was lowered by 1·15 m over a 2‐week period in November 2001. The total phosphorus (TP) concentrations ranged from 63 to 486 µg L^?1 in Columbia Lake and 71 to 373 µg L^?1 at its outflow. All samples exceeded the Provincial Water Quality Objective of 30 µg TP L^?1. Outflow concentrations of suspended solids and TP increased significantly with decreasing lake level and were attributed to the resuspension of cohesive bottom sediments that occurred at a critical threshold lake level (0·65 m below summer level). Suspended solids at the outflow consisted of flocculated cohesive materials with a median diameter (D₅₀) of c. 5 µm. Particulate organic carbon accounted for 8·5% of the suspended solids export by mass. A total mass of 18·5 t of suspended solids and 62·6 kg TP was exported from Columbia Lake, which represents a significant pulse of sediment‐associated P to downstream environments each autumn during drawdown. The downstream impacts of this release can be minimized if the water level in Columbia Lake is lowered no more than 0·5 m below summer levels. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Science into policy: global lessons from Antarctica by Paul Arthur Berkman,Academic Press,San Diego, 2002. Number of pages: 252 (with CD‐ROM,Antarctic Treaty Searchable Database: 1959–1999). ISBN 0 120 91560 X.     

Mike Bentley 《地球表面变化过程与地形》2002,27(9):1027-1027

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Detection and rapid recovery of the Sutter's Mill meteorite fall as a model for future recoveries worldwide     

Marc Fries  Lucille Le Corre  Mike Hankey  Jeff Fries  Robert Matson  Jake Schaefer  Vishnu Reddy 《Meteoritics & planetary science》2014,49(11):1989-1996

The Sutter's Mill C‐type meteorite fall occurred on 22 April 2012 in and around the town of Coloma, California. The exact location of the meteorite fall was determined within hours of the event using a combination of eyewitness reports, weather radar imagery, and seismometry data. Recovery of the first meteorites occurred within 2 days and continued for months afterward. The recovery effort included local citizens, scientists, and meteorite hunters, and featured coordination efforts by local scientific institutions. Scientific analysis of the collected meteorites revealed characteristics that were available for study only because the rapid collection of samples had minimized terrestrial contamination/alteration. This combination of factors—rapid and accurate location of the event, participation in the meteorite search by the public, and coordinated scientific investigation of recovered samples—is a model that was widely beneficial and should be emulated in future meteorite falls. The tools necessary to recreate the Sutter's Mill recovery are available, but are currently underutilized in much of the world. Weather radar networks, scientific institutions with interest in meteoritics, and the interested public are available globally. Therefore, it is possible to repeat the Sutter's Mill recovery model for future meteorite falls around the world, each for relatively little cost with a dedicated researcher. Doing so will significantly increase the number of fresh meteorite falls available for study, provide meteorite material that can serve as the nuclei of new meteorite collections, and will improve the public visibility of meteoritics research.  相似文献   

The Shear Testing Programme – I. Weak lensing analysis of simulated ground-based observations     

Catherine Heymans  Ludovic Van Waerbeke  David Bacon  Joel Berge  Gary Bernstein  Emmanuel Bertin  Sarah Bridle  Michael L. Brown  Douglas Clowe  Håkon Dahle  Thomas Erben  Meghan Gray  Marco Hetterscheidt  Henk Hoekstra  Patrick Hudelot  Mike Jarvis  Konrad Kuijken  Vera Margoniner  Richard Massey  Yannick Mellier  Reiko Nakajima  Alexandre Refregier  Jason Rhodes  Tim Schrabback  David Wittman 《Monthly notices of the Royal Astronomical Society》2006,368(3):1323-1339

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