The evolution of the terrestrial-terminating Irish Sea glacier during the last glaciation     

Richard Christopher Chiverrell  Geoff Stephen Powell Thomas  Matthew Burke  Alicia Medialdea  Rachel Smedley  Mark Bateman  Chris Clark  Geoffrey A. T. Duller  Derek Fabel  Geraint Jenkins  Xianjiao Ou  Helen Marie Roberts  James Scourse 《第四纪科学杂志》2021,36(5):752-779

Here we reconstruct the last advance to maximum limits and retreat of the Irish Sea Glacier (ISG), the only land-terminating ice lobe of the western British Irish Ice Sheet. A series of reverse bedrock slopes rendered proglacial lakes endemic, forming time-transgressive moraine- and bedrock-dammed basins that evolved with ice marginal retreat. Combining, for the first time on glacial sediments, optically stimulated luminescence (OSL) bleaching profiles for cobbles with single grain and small aliquot OSL measurements on sands, has produced a coherent chronology from these heterogeneously bleached samples. This chronology constrains what is globally an early build-up of ice during late Marine Isotope Stage 3 and Greenland Stadial (GS) 5, with ice margins reaching south Lancashire by 30 ± 1.2 ka, followed by a 120-km advance at 28.3 ± 1.4 ka reaching its 26.5 ± 1.1 ka maximum extent during GS-3. Early retreat during GS-3 reflects piracy of ice sources shared with the Irish-Sea Ice Stream (ISIS), starving the ISG. With ISG retreat, an opportunistic readvance of Welsh ice during GS-2 rode over the ISG moraines occupying the space vacated, with ice margins oscillating within a substantial glacial over-deepening. Our geomorphological chronosequence shows a glacial system forced by climate but mediated by piracy of ice sources shared with the ISIS, changing flow regimes and fronting environments.  相似文献   

Metasomatism and the formation of greisen in Grainsgill,Cumbria, England     

D. E. Roberts 《Geological Journal》1983,18(1):43-52

A section of hornfelsed Skiddaw Slate adjacent to the margin of the Grainsgill Greisen is described and chemical analyses of the various rock types presented. The results confirm that hydrothermal fluids liberated K and Na from the granite to produce the greisen. This gave rise to K metasomatism of the adjacent hornfels and to retrogressive metamorphism over a radius of 200m from the intrusion. Na leached from the hornfels near the intrusion and that liberated during the formation of the greisen are probably the sources of the Na in the brines recorded in fluid inclusions within the nearby quartz-tungsten veins.  相似文献   

The boyndie syncline,a D1 structure in the Dalradian of Scotland     

J. E. Treagus  J. L. Roberts 《Geological Journal》1981,16(2):125-135

The structure of the Dalradian rocks of the Banffshire coast has been re-examined. It is shown that D₁ structures face upwards along the entire section and the major Boyndie Syncline (Sutton and Watson 1956) must also be of D₁, age and not D₃ as proposed by Johnson (1962). D₂ structures are developed in the west, most strongly in the Portsoy Group and Cowhythe Gneiss where they may be related to the Portsoy Thrust (Elles 1931). East of the Cowhythe Gneiss D₂ structures are not developed but D₃ structures are of local importance. Porphyroblast growth is considered to be post-D₁, pre-D₃ related to the ‘active’ D₂ deformation in the west (Barrovian) and to the ‘static’ D₂ interval in the east (Buchan). The wider implications of these conclusions for Dalradian structure are briefly considered.  相似文献   

Predicting suitable habitat for the cold-water coral Lophelia pertusa (Scleractinia)     

Andrew J. Davies  Max Wisshak  James C. Orr  J. Murray Roberts   《Deep Sea Research Part I: Oceanographic Research Papers》2008,55(8):1048-1062

Ecological-niche factor analysis (ENFA) was applied to the reef framework-forming cold-water coral Lophelia pertusa. The environmental tolerances of this species were assessed using readily available oceanographic data, including physical, chemical, and biological variables. L. pertusa was found at mean depths of 468 and 480 m on the regional and global scales and occupied a niche that included higher than average current speed and productivity, supporting the theory that their limited food supply is locally enhanced by currents. Most records occurred in areas with a salinity of 35, mean temperatures of 6.2–6.7  °C and dissolved oxygen levels of 6.0–6.2 ml l⁻¹. The majority of records were found in areas that were saturated with aragonite but had low concentration of nutrients (silicate, phosphate, and nitrate). Suitable habitat for L. pertusa was predicted using ENFA on a global and a regional scale that incorporated the north-east Atlantic Ocean. Regional prediction was reliable due to numerous presence points throughout the area, whereas global prediction was less reliable due to the paucity of presence data outside of the north-east Atlantic. However, the species niche was supported at each spatial scale. Predicted maps at the global scale reinforced the general consensus that the North Atlantic Ocean is a key region in the worldwide distribution of L. pertusa. Predictive modelling is an approach that can be applied to cold-water coral species to locate areas of suitable habitat for further study. It may also prove a useful tool to assist spatial planning of offshore marine protected areas. However, issues with eco-geographical datasets, including their coarse resolution and limited geographical coverage, currently restrict the scope of this approach.  相似文献   

Bandpass calibration of a wideband spectrometer using coherent pulse injection     

Nipanjana Patra  Justin D. Bray  Paul Roberts  Ron D. Ekers 《Experimental Astronomy》2017,43(2):119-129

We present a relatively simple time domain method for determining the bandpass response of a system by injecting a nanosecond pulse and capturing the system voltage output. A pulse of sub-nanosecond duration contains all frequency components with nearly constant amplitude up to 1 GHz. Hence, this method can accurately determine the system bandpass response to a broadband signal. In a novel variation on this impulse response method, a train of pulses is coherently accumulated providing precision calibration with a simple system. The basic concept is demonstrated using a pulse generator-accumulator setup realised in a Bedlam board which is a high speed digital signal processing unit. The same system was used at the Parkes radio telescope between 2–13 October 2013 and we demonstrate its powerful diagnostic capability. We also present some initial test data from this experiment.  相似文献   

An analytical description of three-dimensional heliocentric solar sail orbits     

Brian Stewart  Phil Palmer  Mark Roberts 《Celestial Mechanics and Dynamical Astronomy》2017,128(1):61-74

  相似文献   

How U.S. ocean policy and market power can reform the coral reef wildlife trade     

Brian N. Tissot  Barbara A. Best  Eric H. Borneman  Andrew W. Bruckner  Cara H. Cooper  Heather D’Agnes  Timothy P. Fitzgerald  Amanda Leland  Susan Lieberman  Amy Mathews Amos  Rashid Sumaila  Teresa M. Telecky  Frazer McGilvray  Brian J. Plankis  Andrew L. Rhyne  Glynnis G. Roberts  Benjamin Starkhouse  Todd C. Stevenson 《Marine Policy》2010

As the world’s largest importer of marine ornamental species for the aquaria, curio, home décor, and jewelry industries, the United States has an opportunity to leverage its considerable market power to promote more sustainable trade and reduce the effects of ornamental trade stress on coral reefs worldwide. Evidence indicates that collection of some coral reef animals for these trades has caused virtual elimination of local populations, major changes in age structure, and promotion of collection practices that destroy reef habitats. Management and enforcement of collection activities in major source countries such as Indonesia and the Philippines remain weak. Strengthening US trade laws and enforcement capabilities combined with increasing consumer and industry demand for responsible conservation can create strong incentives for improving management in source countries. This is particularly important in light of the March 2010 failure of the parties to the Convention on International Trade in Endangered Species (CITES) to take action on key groups of corals.  相似文献   

A geochronological and petrological study of anatectic paragneiss and associated granite dykes from the Day Nui Con Voi metamorphic core complex,North Vietnam: constraints on the timing of metamorphism within the Red River shear zone     

R. M. Palin  M. P. Searle  D. J. Waters  R. R. Parrish  N. M. W. Roberts  M. S. A. Horstwood  M.‐W. Yeh  S.‐L. Chung  T. T. Anh 《Journal of Metamorphic Geology》2013,31(4):359-387

The Red River shear zone (RRSZ) is a major left‐lateral strike‐slip shear zone, containing a ductilely deformed metamorphic core bounded by brittle strike‐slip and normal faults, which stretches for >1000 km from Tibet through Yunnan and North Vietnam to the South China Sea. The RRSZ exposes four high‐grade metamorphic core complexes along its length. Various lithologies from the southernmost core complex, the Day Nui Con Voi (DNCV), North Vietnam, provide new constraints on the tectonic and metamorphic evolution of this region prior to and following the initial India–Asia collision. Analysis of a weakly deformed anatectic paragneiss using P–T pseudosections constructed in the MnO–Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O (MnNCKFMASHTO) system provides prograde, peak and retrograde metamorphic conditions, and in situ U–Th–Pb geochronology of metamorphic monazite yields texturally controlled age constraints. Tertiary metamorphism and deformation, overprinting earlier Triassic metamorphism associated with the Indosinian orogeny and possible Cretaceous metamorphism, are characterized by peak metamorphic conditions of ~805 °C and ~8.5 kbar between c. 38 and 34 Ma. Exhumation occurred along a steep retrograde P–T path with final melt crystallizing at the solidus at ≥~5.5 kbar at ~790 °C. Further exhumation at ~640–700 °C and ~4–5 kbar at c. 31 Ma occurred at subsolidus conditions. U–Pb geochronological analysis of monazite from a strongly deformed pre‐kinematic granite dyke from the flank of the DNCV provides further evidence for exhumation at this time. Magmatic grains suggest initial emplacement at 66.0 ± 1.0 Ma prior to the India–Asia collision, whereas grains with metamorphic characteristics indicate later growth at 30.6 ± 0.4 Ma. Monazite grains from a cross‐cutting post‐kinematic dyke within the core of the DNCV antiform provide a minimum age constraint of 25.2 ± 1.4 Ma for the termination of fabric development. A separate and significant episode of monazite growth at c. 83–69 Ma is suggested to be the result of fluid‐assisted recrystallization following the emplacement of magmatic units.  相似文献   

Editorial announcement     

P. H. Roberts 《地球物理与天体物理流体动力学》2013,107(1)

  相似文献   

Utilising borehole image logs to interpret delta to estuarine system: A case study of the subsurface Lower Jurassic Cook Formation in the Norwegian northern North Sea     

Atle Folkestad  Zbynek Veselovsky  Paul Roberts 《Marine and Petroleum Geology》2012,29(1):255-275

  相似文献