The evolution and geography of Jurassic ammonoids     

Kevin N. Page 《Proceedings of the Geologists' Association. Geologists' Association》2008,119(1):35-57

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A carbon and oxygen isotopic analysis of molluscan faunas from the Callovian-Oxfordian boundary at Redcliff Point, Weymouth, Dorset: implications for belemnite behaviour     

Gregory D. Price  Kevin N. Page 《Proceedings of the Geologists' Association. Geologists' Association》2008,119(2):153-160

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Population growth and its spatial distribution as factors in the deforestation of Nang Rong, Thailand     

Barbara Entwisle  Ronald R. Rindfuss  Philip H. Page 《Geoforum》2008,39(2):879-897

Frontiers constitute a major source of global land cover change hot spots, with forests and grasslands being converted into agricultural uses. As such, frontiers provide an opportunity to see how people manipulate the land and their lives in the context of social, cultural and environmental constraints. This paper examines frontier settlement and land cover change in Nang Rong district, Northeast Thailand for the last half century. It uses a Cellular Automata (CA) model to explore the land cover consequences of alternative patterns of settlement in a setting where people establish dwelling units in nucleated villages and work agricultural plots that surround villages. Forested land around the center of a village is converted into agricultural uses in an inverse relationship to the distance from the village center, but frequently modified by biophysical conditions. Land at the center of the village may be reforested after the village is established as a source of shade as well as fruit and other products. Model variation in land cover change is more sensitive to the spatial reach of village households than their temporal reach, suggesting the important role that technology plays in how villagers travel to their fields (walking versus motorized transit).  相似文献   

Clustering of X-ray selected active galactic nuclei     

F. J. Carrera  X. Barcons  A. C. Fabian  G. Hasinger  K. O. Mason  R. G. McMahon  J. P. D. Mittaz  & M. J. Page 《Monthly notices of the Royal Astronomical Society》1998,299(1):229-236

A total of 235 active galactic nuclei (AGN) from two different soft X-ray surveys [the ROSAT Deep Survey (DRS) and the ROSAT International X-ray Optical Survey (RIXOS)] with redshifts between 0 and 3.5 are used to study the clustering of X-ray selected AGN and its evolution. A 2σ significant detection of clustering of such objects is found on scales < 40–80 h ⁻¹ Mpc in the RIXOS sample, while no clustering is detected on any scales in the DRS sample. Assuming a single power-law model for the spatial correlation function (SCF), quantitative limits on the AGN clustering have been obtained: a comoving correlation length 1.5 ≲  r ₀ ≲ 3.3  h ⁻¹ Mpc is implied for comoving evolution, while 1.9 ≲  r ₀ ≲ 4.8 for stable clustering and 2.2 ≲  r ₀ ≲ 5.5 for linear evolution. These values are consistent with the correlation lengths and evolutions obtained for galaxy samples, but imply smaller amplitude or faster evolution than recent ultraviolet and optically selected AGN samples. We also constrain the ratio of bias parameters between X-ray selected AGN and IRAS galaxies to be ≲ 1.7 on scales ≲ 10  h ⁻¹ Mpc, a somewhat smaller value than is inferred from local large-scale dynamical studies.  相似文献   

Continuing effects of the Exxon Valdez oil spill     

Boehm PD  Neff JM  Page DS 《Marine environmental research》2003,55(5):459-61; author reply 463-8

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Ignimbrites of the Cerro Galan caldera, NW Argentina     

R.S.J. Sparks  P.W. Francis  R.D. Hamer  R.J. Pankhurst  L.O. O'Callaghan  R.S. Thorpe  R. Page 《Journal of Volcanology and Geothermal Research》1985,24(3-4)

The 35 × 20 km Cerro Galán resurgent caldera is the largest post-Miocene caldera so far identified in the Andes. The Cerro Galán complex developed on a late pre-Cambrian to late Palaeozoic basement of gneisses, amphibolites, mica schists and deformed phyllites and quartzites. The basement was uplifted in the early Miocene along large north-south reverse faults, producing a horst-and-graben topography. Volcanism began in the area prior to 15 Ma with the formation of several andesite to dacite composite volcanoes. The Cerro Galán complex developed along two prominent north-south regional faults about 20 km apart. Dacitic to rhyodacitic magma ascended along these faults and caused at least nine ignimbrite eruptions in the period 7-4 Ma (K-Ar determinations). These ignimbrites are named the Toconquis Ignimbrite Formation. They are characterised by the presence of basal plinian deposits, many individual flow units and proximal co-ignimbrite lag breccias. The ignimbrites also have moderate to high macroscopic pumice and lithic contents and moderate to low crystal contents. Compositionally banded pumice occurs near the top of some units. Many of the Toconquis eruptions occurred from vents along a north-south line on the western rim of the young caldera. However, two of the ignimbrites erupted from vents on the eastern margin. Lava extrusions occurred contemporaneously along these north-south lines. The total D.R.E. volume of Toconquis ignimbrite exceeds 500 km³.Following a 2-Ma dormant period a single major eruption of rhyodacitic magma formed the 1000-km³ Cerro Galán ignimbrite and the caldera. The ignimbrite (age 2.1 Ma on Rb-Sr determination) forms a 30–200-m-thick outflow sheet extending up to 100 km in all directions from the caldera rim. At least 1.4 km of welded intracaldera ignimbrite also accumulated. The ignimbrite is a pumice-poor, crystal-rich deposit which contains few lithic clasts. No basal plinian deposit has been identified and proximal lag breccias are absent. The composition of pumice clasts is a very uniform rhyodacite which has a higher SiO₂ content but a lower K₂O content than the Toconquis ignimbrites. Preliminary data indicate no evidence for compositional zonation in the magma chamber. The eruption is considered to have been caused by the catastrophic foundering of a cauldron block into the magma chamber.Post-caldera extrusions occurred shortly after eruption along both the northern extension of the eastern boundary fault and the western caldera margin. Resurgence also occurred, doming up the intracaldera ignimbrite and sedimentary fill to form the central mountain range. Resurgent doming was centred along the eastern fault and resulted in radial tilting of the ignimbrite and overlying lake sediments.  相似文献   

Concave-bank benches and associated floodplain formation     

Kenneth Page  Gerald Nanson 《地球表面变化过程与地形》1982,7(6):529-543

This paper describes the morphology, sequential development and general sedimentology of concave-bank benches on the Murrumbidgee River of southeastern Australia, and also notes their important role in floodplain formation on certain meandering rivers in western Canada. Benches form against the concave bank (cut-bank) of abruptly curving bends immediately upstream of the point of maximum curvature. As a result of flow deflection against the upstream limb of the convex bank, the channel widens here and produces a zone of expanded flow facilitating flow separation near the upstream limb of the concave bank. Sedimentation within this zone starts with a longitudinal-shaped bar of medium sand forming a platform isolated even at low flow by a narrow secondary channel against the concave bank. Aggradation of the longitudinal-shaped bar with fine sand, mud and organic matter permits the establishment of trees. Further sedimentation, particularly around the young trees, results in the formation of a fully developed bench isolated by the secondary channel from the remainder of the floodplain only during high flows. Observations on confined meandering rivers in western Canada provide evidence of substantial floodplain formation by concave-bank bench accretion, a process distinctly different in character to the more familiar mechanism of lateral point-bar accretion. Furthermore, the preservation of abundant organic debris means that extensive bench deposits may be a source of locally useful natural gas from within floodplain sediments.  相似文献   

Strontium isotope ratios of quaternary volcanic rocks from Papua New Guinea     

R.W Page  R.W Johnson 《Lithos》1974,7(2):91-100

Strontium isotope data for Quaternary volcanic rocks from six separate areas in Papua New Guinea suggest a subdivision into two broad groups. One group consists of island volcanoes that have lower Sr³⁷/Sr³⁸ ratios (0.7034–0.7043) and show isotopic homogeneity within each area sampled. Except for the St. Andrew Strait samples, it is considered that these rocks were produced from relatively homogeneous source regions in the upper mantle. Volcanoes of the second group (on the Papua New Guinea mainland) have generally a higher and wider range of Sr³⁷/Sr³⁶ ratios, compared to those of the first group. It is thought that the magmas of these mainland volcanoes were affected by different degrees of sialic crustal contamination, or were derived from heterogeneous sources in the upper mantle.  相似文献   

Meso-scale surface wind changes associated with the passage of cold fronts along the eastern side of the Southern Alps,New Zealand     

Dr. A. P. Sturman  R. K. Smith  M. A. Page  R. N. Ridley  J. T. Steiner 《Meteorology and Atmospheric Physics》1990,42(2):133-143

Summary The movement of cold fronts along the eastern side of the Southern Alps has been studied in detail during the Southerly Change Experiment (SOUCHEX). An enhanced network of surface wind monitoring stations was established in the Canterbury region of the South Island to allow detailed study of meso-scale wind fields during the passage of fronts. Fivesoutherly changes occurred during the experiment, one of which failed to produce a clear wind change over much of the area. The often erratic movement of these fronts along the eastern side of the mountains is illustrated by isochrone maps of the onset of the wind change. Other general characteristics of these events include their shallowness (1000–1500 m deep) and in most cases their abrupt onset. Detailed analysis of anemograph data collected during SOUCHEX indicates great variability in the surface wind field associated with passage of the fronts. Maps of the meso-scale wind field plotted for the first southerly change of the 14 January 1988 illustrate the complexity of the wind changes experienced over the eastern South Island in particular. The arrival of the cold fronts at individual sites provided features of air mass interaction which appear to relate to time of day, and regional and local site factors. Variations, in wind, temperature and relative humidity provide clear examples of both single and double air mass changes. However, nocturnal changes seem to be less distinct due to lower ambient temperatures and increased boundary layer stability.With 9 Figures  相似文献   

Nonlinear western boundary current flow near a corner     

Michael A. Page  E. R. Johnson 《Dynamics of Atmospheres and Oceans》1991,15(6)

This paper analyses a western boundary current striking a solid boundary. Interest is concentrated on the case where inertial effects are sufficient to modify the flow from its ‘Stommel-layer’ form with Ekman friction relatively unimportant in the interior. It is shown that, beyond a critical inflow speed, a complicated system of four asymptotic regions forms near the corner, turning some of the flow along the blocking boundary and then returning it westwards to rejoin the western boundary current. A comparison with the results of a simple ocean model shows that many of the features in that flow can be explained through the asymptotic theory.  相似文献