Late Quaternary stratigraphy,sedimentology and geochemistry of an underfilled lake basin in the Puna plateau (northwest Argentina)     

Michael M. McGlue  Andrew S. Cohen  Geoffrey S. Ellis  Andrew L. Kowler 《Basin Research》2013,25(6):638-658

Depositional models of ancient lakes in thin‐skinned retroarc foreland basins rarely benefit from appropriate Quaternary analogues. To address this, we present new stratigraphic, sedimentological and geochemical analyses of four radiocarbon‐dated sediment cores from the Pozuelos Basin (PB; northwest Argentina) that capture the evolution of this low‐accommodation Puna basin over the past ca. 43 cal kyr. Strata from the PB are interpreted as accumulations of a highly variable, underfilled lake system represented by lake‐plain/littoral, profundal, palustrine, saline lake and playa facies associations. The vertical stacking of facies is asymmetric, with transgressive and thin organic‐rich highstand deposits underlying thicker, organic‐poor regressive deposits. The major controls on depositional architecture and basin palaeogeography are tectonics and climate. Accommodation space was derived from piggyback basin‐forming flexural subsidence and Miocene‐Quaternary normal faulting associated with incorporation of the basin into the Andean hinterland. Sediment and water supply was modulated by variability in the South American summer monsoon, and perennial lake deposits correlate in time with several well‐known late Pleistocene wet periods on the Altiplano/Puna plateau. Our results shed new light on lake expansion–contraction dynamics in the PB in particular and provide a deeper understanding of Puna basin lakes in general.  相似文献   

The potential for the use of Open Source Software and Open Specifications in creating Web‐based cross‐border health spatial information systems     

Rafael Moreno‐Sanchez  Geoffrey Anderson  Jesus Cruz  Mary Hayden 《International journal of geographical information science》2013,27(10):1135-1163

Globalization is contributing to the blurring of borders making irrelevant the distinctions between domestic and international health problems. Cross‐border and global health spatial information systems (CBHSIS) are required to address the new global health challenges. There is a need to build and document alternatives for addressing the technological, economic, and sociocultural–political challenges encountered in the creation and deployment of these systems. This paper documents the building of a prototype Web‐based multimedia GIS system for use in a public health context using Open Source Software and Open Specifications and its deployment across the US–Mexico border. These technologies offer advantages in addressing several of the challenges previously mentioned. We highlight the technological and sociocultural–political issues important in successful collaboration across borders and cultures and in the creation of interoperable CBHSIS.  相似文献   

The Punjab foreland basin of Pakistan: a reinterpretation of zircon fission‐track data in the light of Miocene hinterland dynamics     

Geoffrey Ruiz  Diane Seward 《地学学报》2006,18(4):248-256

Sedimentary basins represent an archive of tectonic events of the hinterland source regions. By determining the variation in sediment lagtime over time, events can be distinguished which may no longer be available as the source has been eroded. In regions characterized by rapid exhumation this is most often the case but the erosion products form a record of these events. Detrital zircon fission‐track ages from sediments of the Siwalik basin, Pakistan, originally presented by Cerveny et al. (New Perspectives in Basin Analysis, Springer‐Verlag, New York, 1988, p. 43), have been reinvestigated and reinterpreted using a revised methodological approach. Detrital age populations were determined from different stratigraphic levels and were correlated through time in order to assess the change in lag time over the stratigraphic section. This information was combined with the many new ages from the hinterland to further interpret events in the source region. The new investigation suggests that steady‐state evolution has not always existed. An overall trend of exhumation increasing by 0.1 mm Myr^?1 (from 0.9 to 2.65 mm yr^?1) from 18 Ma to the present is evident with a major exception of a net pulse between 11.7 and 10.9 Ma associated with an increase in sedimentation increasingly rich in hornblende. Earlier studies suggested that at this time the source of the sediments was the presently outcropping Kohistan Arc. We are able to demonstrate that this cannot be so but was rather the rapidly exhuming Nanga‐Parbat Haramosh syntaxis (> 2 mm yr^?1) coevally with transpressional displacement along the Main Karakorum Thrust, whereby the overlying Kohistan Arc sequences were removed. Furthermore, comparison of our detrital thermochronological data set with another one from the same basin and one from another foreland basin to the east, in NW India suggest that the Himalayan orogenesis was probably not synchronous for the late Early–Middle Miocene. Overall, regions that undergoes today's rapid uplift may be useless to reconstruct earlier phases of exhumation as the levels that may have yielded such info were eroded and deposited into the adjacent basin(s). Such scenario is reproducible in most orogens as in the Himalaya in NW Pakistan stressing the high potential of detrital thermochronological studies to trace hinterland dynamics. Terra Nova, 18, 248–256, 2006  相似文献   

Echelle spectroscopy of Ca ii HK activity in Southern Hemisphere planet search targets     

C. G. Tinney  Chris McCarthy  Hugh R. A. Jones  R. Paul Butler  Brad D. Carter  Geoffrey W. Marcy  Alan J. Penny 《Monthly notices of the Royal Astronomical Society》2002,332(3):759-763

We present the results of ultraviolet echelle spectroscopy of a sample of 59 F, G, K and M stars from the Anglo-Australian Planet Search target list. Ca  ii activity indices, which are essential in the interpretation of planet detection claims, have been determined for these stars and placed on the Mount Wilson R '_HK system.  相似文献   

Linear and Circular Polarization from Sagittarius A* and M81*     

Geoffrey C. Bower 《Astrophysics and Space Science》2003,288(1-2):69-76

We describe recent results for Sgr A*, M81* and other low luminosity active galactic nuclei. We have conducted linear and circular polarimetry over a frequency range of 1.4 to 230 GHz and detected a variety of phenomena. The polarization properties of the studied sources are substantially different from higher powered AGN. In the case of Sgr A*, we are able to eliminate ADAFs and Bondi-Hoyle flows as possible models based on mm λ polarimetry. Our success with Sgr A* demonstrates that we can learn about the nature of accretion and outflow in these sources with unprecedented detail. We may also develop probes of general relativity in the strong-field limit.  相似文献   

George Morton, Henry Beasley and Triassic footprint classification     

Geoffrey Tresise 《Proceedings of the Geologists' Association. Geologists' Association》2003,114(2):129-138

  相似文献   

Mass-transfer bursts and the superhumps in cataclysmic variables     

Geoffrey T. Bath 《Monthly notices of the Royal Astronomical Society》2004,349(4):1505-1508

  相似文献   

The H i opacity of the intergalactic medium at redshifts 1.6 < z < 3.2     

David Kirkman †  David Tytler †  Nao Suzuki †  Carl Melis  Susan Hollywood  Kory James  Geoffrey So  Dan Lubin †  Tridivesh Jena    Michael L. Norman  Pascal Paschos 《Monthly notices of the Royal Astronomical Society》2005,360(4):1373-1380

We use high-quality echelle spectra of 24 quasi-stellar objects to provide a calibrated measurement of the total amount of Lyα forest absorption (DA) over the redshift range  2.2 < z < 3.2  . Our measurement of DA excludes absorption from metal lines or the Lyα lines of Lyman-limit systems and damped Lyα systems. We use artificial spectra with realistic flux calibration errors to show that we are able to place continuum levels that are accurate to better than 1 per cent. When we combine our results with our previous results between  1.6 < z < 2.2  , we find that the redshift evolution of DA is well described over  1.6 < z < 3.2  as   A (1 + z )^γ  , where   A = 0.0062  and  γ= 2.75  . We detect no significant deviations from a smooth power-law evolution over the redshift range studied. We find less H  i absorption than expected at   z = 3  , implying that the ultraviolet background is  ∼40  per cent higher than expected. Our data appears to be consistent with an H  i ionization rate of  Γ∼ 1.4 × 10⁻¹² s⁻¹  .  相似文献   

Enceladus' south polar sea     

Geoffrey C. Collins  Jason C. Goodman 《Icarus》2007,189(1):72-82

Recent observations of the south pole of Saturn's moon Enceladus by the Cassini spacecraft have revealed an active world, powered by internal heat. In this paper, we propose that localized subsurface melting on Enceladus has produced an internal south polar sea. Evidence for this localized sea comes from the shape of Enceladus, which does not match a differentiated body at its current orbital position. We show that melting induced by the observed heat flow at the south pole produces a large enough pit to match the shape of Enceladus with a differentiated rock and ice interior. Numerical modeling of melting and ice flow shows that the sea produced beneath the south pole is stable against inflow of ductile ice from its surroundings for the duration of the heating. The shape modification due to melting also produces a negative degree-two gravity anomaly, which can reorient the spin axis of Enceladus in order to place the sea at the pole.  相似文献   

An exoplanet in orbit around τ¹ Gruis     

Hugh R. A. Jones  R. Paul Butler  C. G. Tinney  Geoffrey W. Marcy  Alan J. Penny  Chris McCarthy  Brad D. Carter 《Monthly notices of the Royal Astronomical Society》2003,341(3):948-952

  相似文献