Rates of fluvial bedrock incision within an actively uplifting orogen: Central Karakoram Mountains, northern Pakistan     

Yeong Bae Seong  Lewis A. Owen  Michael P. Bishop  Andrew Bush  Penny Clendon  Luke Copland  Robert C. Finkel  Ulrich Kamp  John F. Shroder Jr. 《Geomorphology》2008,97(3-4):274-286

Terrestrial cosmogenic nuclide (TCN) ¹⁰Be surface exposure ages for strath terraces along the Braldu River in the Central Karakoram Mountains range from 0.8 to 11 ka. This indicates that strath terrace formation began to occur rapidly upon deglaciation of the Braldu valley at  11 ka. Fluvial incision rates for the Braldu River based on the TCN ages for strath terraces range from 2 to 29 mm/a. The fluvial incision rates for the central gorged section of the Braldu River are an order of magnitude greater than those for the upper and lower reaches. This difference is reflected in the modern stream gradient and valley morphology. The higher incision rates in the gorged central reach of the Braldu River likely reflect differential uplift above the Main Karakoram Thrust that has resulted in the presence of a knickpoint and more rapid fluvial incision. The postglacial fluvial incision rate (2–3 mm/a) for the upper and lower reaches are of the same order of magnitude as the exhumation rates estimated from previously published thermochronological data for the Baltoro granite in the upper catchment region and for the adjacent Himalayan regions.  相似文献   

Tropical climates at the Last Glacial Maximum: a new synthesis of terrestrial palaeoclimate data. I. Vegetation, lake-levels and geochemistry   总被引：1，自引：1，他引：0  

I. Farrera  S. P. Harrison  I. C. Prentice  G. Ramstein  J. Guiot  P. J. Bartlein  R. Bonnefille  M. Bush  W. Cramer  U. von Grafenstein  K. Holmgren  H. Hooghiemstra  G. Hope  D. Jolly  S.-E. Lauritzen  Y. Ono  S. Pinot  M. Stute  G. Yu 《Climate Dynamics》1999,15(11):823-856

 Palaeodata in synthesis form are needed as benchmarks for the Palaeoclimate Modelling Intercomparison Project (PMIP). Advances since the last synthesis of terrestrial palaeodata from the last glacial maximum (LGM) call for a new evaluation, especially of data from the tropics. Here pollen, plant-macrofossil, lake-level, noble gas (from groundwater) and δ¹⁸O (from speleothems) data are compiled for 18±2 ka (¹⁴C), 32 °N–33 °S. The reliability of the data was evaluated using explicit criteria and some types of data were re-analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month (MTCO), mean annual temperature (MAT), plant available moisture (PAM) and runoff (P-E). Cold-month temperature (MAT) anomalies from plant data range from −1 to −2 K near sea level in Indonesia and the S Pacific, through −6 to −8 K at many high-elevation sites to −8 to −15 K in S China and the SE USA. MAT anomalies from groundwater or speleothems seem more uniform (−4 to −6 K), but the data are as yet sparse; a clear divergence between MAT and cold-month estimates from the same region is seen only in the SE USA, where cold-air advection is expected to have enhanced cooling in winter. Regression of all cold-month anomalies against site elevation yielded an estimated average cooling of −2.5 to −3 K at modern sea level, increasing to ≈−6 K by 3000 m. However, Neotropical sites showed larger than the average sea-level cooling (−5 to −6 K) and a non-significant elevation effect, whereas W and S Pacific sites showed much less sea-level cooling (−1 K) and a stronger elevation effect. These findings support the inference that tropical sea-surface temperatures (SSTs) were lower than the CLIMAP estimates, but they limit the plausible average tropical sea-surface cooling, and they support the existence of CLIMAP-like geographic patterns in SST anomalies. Trends of PAM and lake levels indicate wet LGM conditions in the W USA, and at the highest elevations, with generally dry conditions elsewhere. These results suggest a colder-than-present ocean surface producing a weaker hydrological cycle, more arid continents, and arguably steeper-than-present terrestrial lapse rates. Such linkages are supported by recent observations on freezing-level height and tropical SSTs; moreover, simulations of “greenhouse” and LGM climates point to several possible feedback processes by which low-level temperature anomalies might be amplified aloft. Received: 7 September 1998 / Accepted: 18 March 1999  相似文献   

Paris Basin VSPs: case history establishing combinations of fine-layer (or lithologic) anisotropy and crack anisotropy from modelling shear wavefields near point singularities     

Iain Bush  Stuart Crampin 《Geophysical Journal International》1991,107(3):433-447

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Role of transverse strike-slip faults in the structure of the Karpinsky Ridge and their kinematics     

V. G. Kaz’min  V. A. Bush  L. I. Lobkovsky 《Geotectonics》2008,42(3):176-185

The segmented structure of the Karpinsky Ridge is determined by NE-trending transverse strikeslip faults with offsets of approximately 30–40 km. The newly recognized Pribrezhny Fault and the well-known Agrakhan Fault are the largest. A new correlation scheme for structural elements of the ridge’s eastern segment and its underwater continuation is proposed with account of offset along the Pribrezhny Fault. According to this scheme, the Semenovsky Trough rather than the Dzhanai Trough is an onshore continuation of the underwater Zyudevsky Trough. The uplift located south of the Zyudevsky Trough is correlated with the Promyslovy-Tsubuk Swell offset along the Pribrezhny Fault. In turn, this uplift is displaced along the right-lateral strike-slip fault that coincides with the Agrakhan Fault. The transverse faults were formed during the Early Permian collision related to the closure of the basin, which was presumably underlain by the oceanic crust. The faults were active during the Early Triassic rifting and Late Triassic inversion. Judging from the map of the surface of the Maikop sediments, the Agrakhan Fault does not cross the Terek-Caspian Trough. Bending arcwise, the fault joins a system of right-lateral strike-slip faults that border the Daghestan Wedge in the east. A system of rightlateral strike-slip faults may also be traced along the western coast of the Caspian Sea. The Agrakhan Fault as a northern element of this system functioned mostly in the Late Paleozoic-Early Mesozoic in connection with the formation of the fold-thrust structure of the Karpinsky Ridge. In the east the faults of the southern segment bound the Caucasus syntaxis of the Alpine Belt; they have retained their activity to the present day.  相似文献   

A simple and inexpensive chromium-reducible sulfur method for acid-sulfate soils   总被引：2，自引：0，他引：2  

Edward D. Burton  Leigh A. SullivanRichard T. Bush  Scott G. JohnstonAnnabelle F. Keene 《Applied Geochemistry》2008

A new chromium-reducible sulfur (CRS) method suitable for the quantification of reduced inorganic S (RIS) in acid-sulfate soils is presented. The new method utilises the reduction of RIS by an acidic Cr(II) solution within a sealed reaction chamber and diffusion of the produced H₂S_(g) into an alkaline Zn solution. It offers rapid sample processing times, without the need for large volumes of high-purity N_2(g) or for specialized, expensive glassware. Examination of pyrite-talc mixtures containing up to 11.8% pyrite, revealed that the method achieves 95–98% recovery of RIS. A comparison between CRS measured by the new diffusion-based method and that measured by a standard purge-and-trap method for 25 pyritic soil samples shows a very strong (r² = 0.996) linear relationship with a slope of 0.995. The ability of the new diffusion-based CRS method to achieve accurate and precise quantification of RIS in acid-sulfate soils is demonstrated.  相似文献   

Ecological aspects of plant colonisation of the Krakatau Islands     

R. J. Whittaker Dr.  M. B. Bush Dr.  T. Partomihardjo  N. M. Asquith  K. Richards 《GeoJournal》1992,28(2):201-211

Species assemblage data from the Krakatau Islands, Indonesia, are presented for the period 1883 to 1989 (including previously unpublished data from the 1989 survey). Since 1934, 16 additional families of higher plants have colonised. Recent arrivals at the family level are mostly of zoochorous species of forest tree, indicating (subject to the effects of disturbance) a continuing increase in potential niche space within the island interiors. The data for Rakata (an uninterrupted prisere) conform to a successional explanation in which identifiable ecological groups of plants exhibit differing colonization and turnover patterns. Animal-dispersed canopy tree species and species which are widespread within the group, exhibit a very low probability of extinction once they have colonized successfully. There are, however, several constraints on the rapid spread of species within the group, in particular those connected to local dispersal (eg lack of large terrestrial mammals). In respect of dispersal to the group, partial survey data for the island of Sebesi from 1921 (revised) and 1989 provides the basis for comment as to the changing biogeographical circumstances of the Sunda Straits and the role of Sebesi as a stepping stone island.The varied data discussed in the paper indicates that with the exception of the strand-line, no component of the Krakatau flora or vegetation has yet approached a stable composition. Both floral and faunal diversification are argued to be proximally controlled not only by dispersal opportunities but also by the dynamics of the dominant life-forms of the system, ie, the forest trees. Such hierarchical links, across trophic boundaries, should receive greater recognition in the construction of island biogeographical theory.  相似文献   

Changes in Canada's Climate: Trends in Indices Based on Daily Temperature and Precipitation Data   总被引：1，自引：0，他引：1  

L.A. Vincent  X. Zhang  É. Mekis  H. Wan  E.J. Bush 《大气与海洋》2013,51(5):332-349

ABSTRACT

Trends in indices based on daily temperature and precipitation are examined for two periods: 1948–2016 for all stations in Canada and 1900–2016 for stations in the south of Canada. These indices, a number of which reflect extreme events, are considered to be impact relevant. The results show changes consistent with warming, with larger trends associated with cold temperatures. The number of summer days (when daily maximum temperature >25°C) has increased at most locations south of 65°N, and the number of hot days (daily maximum temperature >30°C) and hot nights (daily minimum temperature >22°C) have increased at a few stations in the most southerly regions. Very warm temperatures in both summer and winter (represented by the 95th percentile of their daily maximum and minimum temperatures, respectively) have increased across the country, with stronger trends in winter. Warming is more pronounced for cold temperatures. The frost-free season has become longer with fewer frost days, consecutive frost days, and ice days. Very cold temperatures in both winter and summer (represented by the 5th percentile of their daily maximum and minimum temperatures, respectively) have increased substantially across the country, again with stronger trends in the winter. Changes in other temperature indices are consistent with warming. The growing season is now longer, and the number of growing degree-days has increased. The number of heating degree-days has decreased across the country, while the number of cooling degree-days has increased at many stations south of 55°N. The frequency of annual and spring freeze–thaw days shows an increase in the interior provinces and a decrease in the remainder of the country. Changes in precipitation indices are less spatially coherent. An increase in the number of days with rainfall and heavy rainfall is found at several locations in the south. A decrease in the number of days with snowfall and heavy snowfall is observed in the western provinces, while an increase is found in the north. There is no evidence of significant changes in the annual highest 1-day rainfall and 1-day snowfall. The maximum number of consecutive dry days has decreased, mainly in the south.  相似文献   

Conjugate zone between the northern termination of the Baikal-Patom Foldbelt and the Siberian Craton: Structure of the crystalline basement     

V. A. Bush 《Geotectonics》2011,45(6):469-480

New data on the deep structure of the crystalline basement in the conjugate zone between the northern termination of the Baikal-Patom Foldbelt and the Siberian Craton are discussed. Digital processing of the data of a high-precision airborne geophysical (magnetic, gravity, radiometric) surveys on a scale of 1: 50000 allows us to construct 3D models of the petrophysical properties of the rocks and to ascertain the main features of the deep structure of the pre-Riphean crystalline basement overlapped by a thick sedimentary cover. The Archean and Paleoproterozoic metamorphic and plutonic petrophysical complexes are identified, and their vertical and horizontal relationships are outlined. Horizontal tectonic movements and overthrusting for many tens of kilometers are interpreted in the internal structure of the crystalline basement. The tectonic overriding of the marginal part of the Siberian Craton by nappes of the Baikal-Patom Foldbelt is proved. In particular, the completely detached, allochthonous position of the Kotuikan Zone along which the Magan and Daldyn terranes cojugate with the Aldan Province in the south of the craton is established. This compels us to consider a re-evaluation of the currently accepted concept concerning the structure and formation history of the basement of the ancient Siberian Craton.  相似文献   

Iron geochemical zonation in a tidally inundated acid sulfate soil wetland     

Scott G. Johnston  Annabelle F. Keene  Richard T. Bush  Edward D. Burton  Leigh A. Sullivan  Lloyd Isaacson  Angus E. McElnea  Col R. Ahern  C. Douglas Smith  Bernard Powell 《Chemical Geology》2011,280(3-4):257-270

Tidal inundation is a new technique for remediating coastal acid sulfate soils (CASS). Here, we examine the effects of this technique on the geochemical zonation and cycling of Fe across a tidally inundated CASS toposequence, by investigating toposequence hydrology, in situ porewater geochemistry, solid-phase Fe fractions and Fe mineralogy. Interactions between topography and tides exerted a fundamental hydrological control on the geochemical zonation, redistribution and subsequent mineralogical transformations of Fe within the landscape. Reductive dissolution of Fe(III) minerals, including jarosite (KFe₃(SO₄)₂(OH)₆), resulted in elevated concentrations of porewater Fe²⁺ (> 30 mmol L^?1) in former sulfuric horizons in the upper-intertidal zone. Tidal forcing generated oscillating hydraulic gradients, driving upward advection of this Fe²⁺-enriched porewater along the intertidal slope. Subsequent oxidation of Fe²⁺ led to substantial accumulation of reactive Fe(III) fractions (up to 8000 μmol g^?1) in redox-interfacial, tidal zone sediments. These Fe(III)-precipitates were poorly crystalline and displayed a distinct mineralisation sequence related to tidal zonation. Schwertmannite (Fe₈O₈(OH)₆SO₄) was the dominant Fe mineral phase in the upper-intertidal zone at mainly low pH (3–4). This was followed by increasing lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) at circumneutral pH within lower-intertidal and subtidal zones. Relationships were evident between Fe fractions and topography. There was increasing precipitation of Fe-sulfide minerals and non-sulfidic solid-phase Fe(II) in the lower intertidal and subtidal zones. Precipitation of Fe-sulfide minerals was spatially co-incident with decreases in porewater Fe²⁺. A conceptual model is presented to explain the observed landscape-scale patterns of Fe mineralisation and hydro-geochemical zonation. This study provides valuable insights into the hydro-geochemical processes caused by saline tidal inundation of low lying CASS landscapes, regardless of whether inundation is an intentional strategy or due to sea-level rise.  相似文献   

The Effect of the Solar Eclipse of March 29, 2006 on Atmospheric Pressure Fluctuations and Surface Temperature Profiles     

Bush  G. A.  Elansky  N. F.  Kadygrov  E. N.  Kulichkov  S. N.  Chunchuzov  I. P.  Prokosheva  N. S. 《Izvestiya Atmospheric and Oceanic Physics》2022,58(4):346-352

Izvestiya, Atmospheric and Oceanic Physics - The data of measurements of atmospheric pressure fluctuations together with measurements of air temperature profiles in the surface layer of the...  相似文献