Stratotype for the Mérida Glaciation at Pueblo Llano in the northern Venezuelan Andes     

W. C. Mahaney  M. W. Milner  J. Voros  V. Kalm  G. Hütt  M. Bezada  R. G. V. Hancock  S. Aufreiter   《Journal of South American Earth Sciences》2000,13(8):761

The Mérida Glaciation (cf. Wisconsinan, Weichselian) as proposed by Schubert (1974b) culminated at about 18 ka during the last glacial maximum (LGM) and ended at about 13 ka as indicated by ¹⁴C dating and correlation with the Cordillera Oriental of Colombia. Moraines of an early stade of Mérida Glaciation reached to 2800 m a.s.l. and were largely overrun or eradicated by the maximum Wisconsinan advance (LGM); where they outcrop, the older moraines are characterized by eroded, weathered glacial diamictons and outwash fans.At Pueblo Llano in the central Mérida Andes (Cordillera de Trujillo), older to younger beds of contorted glacitectonized diamict, overlying beds of bouldery till and indurated outwash, all belong to the early Mérida stade. Overlying the early Mérida stade, deposits of rhythmically bedded glaciolacustrine sediments are in turn overlain with contorted sand and silt beds capped with outwash. Above the outwash terrace a loop moraine of LGM age completely encircles the margins of the basin. A stream cut exposed by catastrophic (tectonic or surge?) release of meltwater displays a lithostratigraphic succession that is bereft of organic material for radiocarbon dating. Five optically-stimulated luminescence (OSL) dates place the maximum age of the lowest till at 81 ka.Particle size distributions allow clear distinctions between major lithic units. Heavy mineral analysis of the middle and lower coarse units in the section provide information on sediment sourcing and on major lithostratigraphic divisions. Trace element concentrations provide information on the relative homogeneity of the deposits. The HREE (heavy rare earth element) concentrations allow discrimination of the lower till from the rest of the section; the LREE (light rare earth element) concentrations highlight differences between the lower till, LGM till, and the rest of the section.  相似文献   

Natura 2000 sites and fisheries in German offshore waters     

Pedersen  Soren Anker; Fock  Heino; Krause  Jochen; Pusch  Christian; Sell  Anne L.; Bottcher  Uwe; Rogers  Stuart I.; Skold  Mattias; Skov  Henrik; Podolska  Magdalena; Piet  Gerjan J.; Rice  Jake C. 《ICES Journal of Marine Science》2009,66(1):155-169

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Radium and radon radioisotopes in regional groundwater, intertidal groundwater, and seawater in the Adelaide Coastal Waters Study area: Implications for the evaluation of submarine groundwater discharge     

Sbastien Lamontagne  Corinne Le Gal La Salle  Gary J. Hancock  Ian T. Webster  Craig T. Simmons  Andrew J. Love  Julianne James-Smith  Anthony J. Smith  Jochen Kmpf  Howard J. Fallowfield 《Marine Chemistry》2008,109(3-4):318

The input of groundwater-borne nutrients to Adelaide's (South Australia) coastal zone is not well known but could contribute to the ongoing decline of seagrass in the area. As a component of the Adelaide Coastal Waters Study (ACWS), the potential for using the radium quartet (²²³Ra, ²²⁴Ra, ²²⁶Ra and ²²⁸Ra) and ²²²Rn to evaluate submarine groundwater discharge (SGD) was evaluated. Potential isotopic signatures for SGD were assessed by sampling groundwater from three regional aquifers potentially contributing SGD to the ACWS area. In addition, intertidal groundwater was sampled at two sand beach sites. In general, the regional groundwaters were enriched in long-lived Ra isotopes (²²⁶Ra and ²²⁸Ra) and in ²²²Rn relative to intertidal groundwater. Radium activity (but not ²²²Rn activity) was positively correlated to salinity in groundwater from one of the regional aquifers and in intertidal groundwater. Radium isotope ratios (²²³Ra/²²⁶Ra, ²²⁴Ra/²²⁶Ra and ²²⁸Ra/²²⁶Ra) were less variable than individual Ra isotope activities within potential SGD sources. Recirculated seawater (estimated from the intertidal groundwater samples with seawater-like salinities) also had distinctly higher Ra isotope ratios than the regional groundwaters. The activities for all radioisotopes were relatively low in seawater. The activity of the short-lived ²²³Ra and ²²⁴Ra were highest at the shoreline and declined exponentially with distance offshore. In contrast, ²²⁸Ra and ²²⁶Ra activities had a weak linear declining trend with distance offshore. Rn-222 activity was at or near background in all seawater samples. The pattern of enrichment in short-lived Ra isotopes and the lack of ²²²Rn in seawater suggest that seawater recirculation is the main contributor to SGD in the ACWS area. Preliminary modeling of the offshore flux of ²²⁸Ra and ²²⁶Ra suggest that the SGD flux to the ACWS area ranges between 0.2 and 3 · 10^− 3 m³ (m of shoreline)^− 1 s^− 1.  相似文献   

Channel movement and erosion response to rainfall variability in southeast Australia     

G. R. Hancock  T. J. Coulthard 《水文研究》2012,26(5):663-673

Intrinsic and extrinsic forces on the catchment and stream channel network drive morphological change. Separating individual forcings is difficult given the complexity of such nonlinear systems. Here a modelling approach is used to investigate the sensitivity of channel position and movement under a series of realistic rainfall scenarios for a catchment in southeastern Australia. The results demonstrate the sensitivity of the catchment to different rainfall patterns and how relatively small changes in rainfall can lead to much larger sediment outputs revealing sensitivity to subtle changes in climate. Channel movement occurs as an avulsion. This is the first time such a process has been observed and modelled in an ephemeral stream environment and demonstrates fluvial geomorphic change at human time scales. Human intervention by rock lining channels was demonstrated to prevent the movement of the main channel. Overall the CAESAR landscape evolution and erosion model used in this study is able to replicate both erosion rates and the variation in past channel movement. The modelling suggests that any landscape change is based on both internal and external forcing and that landscape history also plays a significant role. Here, we demonstrate the potential to quantify many of the nonlinearities and thresholds in soil‐mantled catchments using a landscape evolution model. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Preface: hydrogeoecology, the interdisciplinary study of groundwater dependent ecosystems   总被引：1，自引：0，他引：1  

Peter J. Hancock  Randall J. Hunt  Andrew J. Boulton 《Hydrogeology Journal》2009,17(1):1-3

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Photometry and spectroscopy of the luminous red nova PSNJ14021678+5426205 in the galaxy M101     

V. P. Goranskij  E. A. Barsukova  O. I. Spiridonova  A. F. Valeev  T. A. Fatkhullin  A. S. Moskvitin  O. V. Vozyakova  D. V. Cheryasov  B. S. Safonov  A. V. Zharova  T. Hancock 《Astrophysical Bulletin》2016,71(1):82-94

We present the results of the study of a red nova from the observations carried out with the Russian 6-m telescope (BTA) along with other telescopes of SAO RAS and SAI MSU. To investigate the nova progenitor,we used the data from the Digital Sky Survey and amateur photos available on the Internet. In the period between April 1993 and July 2014, the brightness of the progenitor gradually increased by \(2_ \cdot ^m 2\) in the V-band. At the peak of the first outburst in mid-November 2014, the star reached an absolute visual magnitude of \(- 12_ \cdot ^m 75\) but was discovered later, in February 2015, in a repeated outburst at the magnitude of \(- 11_ \cdot ^m 65\). The amplitude of the outburst was minimum among the red novae, only \(5_ \cdot ^m 6\) in V-band. The Hα emission line and the background of a cool supergiant continuum with gradually decreasing surface temperature were observed in the spectra. Such process is typical for red novae, although the object under study showed extreme parameters: maximum luminosity, maximum outburst duration, minimum outburst amplitude, unusual shape of the light curve. This event is interpreted as a massive OB star system components’merging accompanied by formation of a common envelope and then the expansion of this envelope with minimal energy losses.  相似文献   

A Wind-Tunnel Artificially-Thickened Simulated Weakly Unstable Atmospheric Boundary Layer     

P. E. Hancock  S. Zhang  P. Hayden 《Boundary-Layer Meteorology》2013,149(3):355-380

A wind-tunnel simulation of an atmospheric boundary layer, artificially thickened as is often used in neutral flow wind-loading studies, has been investigated for weakly unstable stratification, including the effect of an overlying inversion. Rather than using a uniform inlet temperature profile, the inlet profile was adjusted iteratively by using measured downstream profiles. It was found that three cycles are sufficient for there to be no significant further change in profiles of temperature and other quantities. Development to nearly horizontally-homogeneous flow took a longer distance than in the neutral case because the simulated layer was deeper and therefore the length scales larger. Comparisons show first-order and second-order moments quantities are substantially larger than given by ‘standard forms’ in the mixed layer but are close in the surface layer. Modified functions, obtained by matching one to the other, are suggested that amount to an interpolation in the mixed layer between the strongly unstable and the weakly unstable cases.  相似文献   

Seeing the climate through the trees: observing climate and forestry impacts on streamflow using a 60‐year record          下载免费PDF全文

T. P. Burt  N. J. K. Howden  J. J. McDonnell  J. A. Jones  G. R. Hancock 《水文研究》2015,29(3):473-480

Paired watershed experiments involving the removal or manipulation of forest cover in one of the watersheds have been conducted for more than a century to quantify the impact of forestry operations on streamflow. Because climate variability is expected to be large, forestry treatment effects would be undetectable without the treatment–control comparison. New understanding of climate variability provides an opportunity to examine whether climate variability interacts with forestry treatments, in a predictable manner. Here, we use data from the H. J. Andrews Experimental Forest, Oregon, USA, to examine the impact of the El Niño‐Southern Oscillation on streamflow linked to forest harvesting. Our results show that the contrast between El Niño and La Niña events is so large that, whatever the state of the treated watershed in terms of regrowth of the forest canopy, extreme climatic variability related to El Niño‐Southern Oscillation remains the more dominant driver of streamflow response at this location. Improvements in forecasting interannual variation in climate might be used to minimize the impact of forestry treatments on streamflow by avoiding initial operations in La Niña years. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Geological atlas of Western and Central Europe: Ziegler, P. A. 1982. Elsevier (in collaboration with Shell International Petroleum). Amsterdam. 130 pp., 40 boxed enclosures. Price: US $68.00, DFL 160     

P.L. Hancock 《Journal of Structural Geology》1983,5(6):631-632

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Anomalous bedding-cleavage relationships in Silurian rocks at Marloes Sands,S.W. Dyfed (Pembrokeshire), Wales     

J.R. Graham  P.L. Hancock  D.M. Hobson 《Proceedings of the Geologists' Association. Geologists' Association》1977,88(3):179-181

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