Climate‐controlled aggradation and cyclicity of continental loessic siliciclastic sediments in Asselian–Sakmarian cyclothems,Permian, Hugoton embayment,USA     

ROBERT H. GOLDSTEIN  STEPHEN T. HASIOTIS 《Sedimentology》2012,59(6):1782-1816

Siliciclastic intervals in Lower Permian carbonate–siliciclastic cyclothems in western Kansas record climate control on facies progression, deposition and preservation. The 26 000 km² study area comprises seven marine‐continental (carbonate–siliciclastic) cyclothems caused by glacioeustasy. Core data and a three‐dimensional geological model provide a detailed view of the sub‐surface on a gently sloping ramp. Siliciclastic intervals in the cyclothems are fine‐grained red beds with extensive pedogenic features, indicating a continental origin. Bed geometry (sheet‐like deposits that thin to the east), lateral grading, grain size (very fine‐grained sand to silt) and grain angularity (sub‐angular to angular) suggest that the sediment is loess sourced from the west, probably the Ancestral Rocky Mountains. There is a repeated record of glacial‐cycle‐scale, climate‐controlled cyclicity within siliciclastic intervals that has not been recognized previously. Aeolian silt grain size coarsens upward towards the middle, then fines upward in each siliciclastic interval. When sea‐level was high (interglacial) and carbonate production flourished, aeolian sedimentation nearly ceased, suggesting increased vegetation and rainfall at the source. As sea‐level fell, fine‐grained siliciclastic sediments were deposited under relatively dry, but seasonally wet conditions on an exposed ramp. Laterally graded coarser grained siliciclastic sediments with diagnostic fabrics indicate drier conditions with seasonal rainfall during a continued relative fall in sea‐level. The coarsest siliciclastic sediments were deposited during the lowest sea‐level and driest conditions, but still with sufficient seasonal moisture to allow vegetative cover and bioturbation. Subsequent upward fining is correlated with sedimentological indications of wetter conditions during relative sea‐level rise. Unlike common sequence stratigraphic models that relate siliciclastic sediment accumulation to base‐level rise, continental deposits were preserved because plants and pedogenesis stabilized aeolian sediment. The aggradational landscape formed by this process had several metres of positive relief that reduced accommodation for overlying marine carbonate strata. Thus, this mechanism for continental siliciclastic aggradation has a significant effect on sequence stratigraphic architecture.  相似文献   

Risk analyses for a water supply system: Occoquan Reservoir,Fairfax and Prince William Counties,Virginia, USA / Des analyses aléatoires d'un système d'approvisionnement en eau: Occoquan Reservoir,Fairfax et Prince William Counties,Virginia, USA     

ROBERT M. HIRSCH 《水文科学杂志》2013,58(4):475-505

Abstract

This report demonstrates two techniques for evaluating risks in the operation of a water supply system. Both rely on reconstructed historical streamflow data to develop estimates of the probabilities of certain specific events occurring in the future. These techniques are applied to the Occoquan Reservoir which was experiencing an unprecedented low level of storage in the autumn of 1977. The two techniques are used respectively to evaluate the overall adequacy of the existing reservoir and to evaluate the risks in the 1977 crisis.

In the first technique, the general risk analysis model (GRAM), simulations of the reservoir's contents are carried out under a set of assumptions about withdrawal rates and emergency procedures. The results of the GRAM simulation for the Occoquan Reservoir are in the form of estimates of the probabilities that in any year contain emergency procedures will have to be invoked. These estimates are given for a range of rates of withdrawals and for four different stages of emergency actions. Also given are the estimated probabilities of entering emergency conditions in one year given that an emergency has occurred in the previous year. Due to the year-to-year persistence of low flows, these latter (conditional) probabilities are higher than the former (marginal) probabilities.

The second technique used is position analysis. In this procedure probability distributions of future storages are estimated under existing storage conditions and an assumed rate of withdrawal from the reservoir. The position analysis which was initialized at the 1 October 1977 conditions indicates that the probability of entering a Stage III emergency (the prohibition of all uses of water non-essential to life, health, and safety) in the autumn of 1977 or winter of 1978 was 10 per cent at that time. With a reduction in water use by 8 million gallons per day, however, this probability would have fallen to 4 per cent.

If a long reconstructed historical streamflow record is available to a water supply agency, then the agency will have the capability to undertake its own risk analyses. It can carry out comparisons of alternative operating policies by using techniques such as GRAM. It can also evaluate the short-term risks of different plans of operation during crisis situations by using position analysis.  相似文献   

MOSCOW ON THE RISE: FROM PRIMATE CITY TO MEGAREGION*     

ROBERT ARGENBRIGHT 《Geographical review》2013,103(1):20-36

In this article I examine Moscow's role in the political‐economic space of the Russian Federation. A broad range of data supports the thesis that the capital has become a primate city, one that serves no longer as the command center of a closed system but as the primary node of interconnection between Russia and the rest of the world. The effort to create a larger, polycentric “New Moscow” next to the ancient capital is marked by a tightening of central control, in contrast to governance regimes of European megaregions. Nevertheless, expansion of the capital region very likely will further boost Moscow's dominance over the country.  相似文献   

Teaching generic GIS using commercial software     

ROBERT J. ROGERSON 《International journal of geographical information science》2013,27(4):321-331

Abstract

The debate between training and education in GIS in a university or college setting and whether or not commercial systems should be used in such institutions may be far from resolution, but an indication of the level of interest shown in hands-on, computer-based GIS education using a commercial system is the appearance and growth of the Institute for GIS in Education. The Curriculum Development Toolkit produced by the Institute has involved academic input and evaluation, and contains both generic GIS background information and system-specific computer-based learning materials, used in over 200 academic institutions world-wide.  相似文献   

Younger Dryas glacial advance in the southern Gulf of St. Lawrence,Canada: analogue for ice inception?     

RUDOLPH R. STEA  ROBERT J. MOTT 《Boreas: An International Journal of Quaternary Research》2005,34(3):345-362

In the summer of 1999, the Maritimes and Northeast Pipeline Company excavated a 3-m-deep trench across northern Nova Scotia exposing a continuous transect of surficial deposits along a 237-km corridor. A Lateglacial palaeosol with preserved A horizon (peat and wood) buried under 2-10 m of surface till consisted mainly of herbaceous plant material with few large wood fragments. Large pieces of wood from two sites yielded conventional radiocarbon ages of 10.9 ¹⁴C kyr BP (GSC-6435) and 10.8 ¹⁴C kyr BP (GSC-6419). Previous to these finds, only a few localities were known to reveal till overlying peat, so the extent of Younger Dryas (YD) glaciers could not be clearly established. Glacial flow lines indicated by fabric and fluting of the YD surface till sheet in northern Nova Scotia and ice-marginal deposits imply an ice cap centred over eastern P.E.I. and the southern Gulf of St. Lawrence. This glacier also dammed a series of glacial lakes against the highland-rimmed west coast of Cape Breton Island. Glaciers developed and advanced during the YD in the uplands and offshore shelf areas from small remnants of Late Wisconsinan ice. Renewed ice growth was enabled by increased precipitation and local cooling in the Gulf of St. Lawrence due to deflection of the jet stream and expanded sea-ice cover in the North Atlantic. The YD may provide an analogy to glacier development in Maritime Canada during the interglacial/glacial transition.  相似文献   

A first-order analysis of the potential rôle of CO₂ fertilization to affect the global carbon budget: a comparison of four terrestrial biosphere models     

DAVID W. KICKLIGHTER  MICHELE BRUNO  SILKE DÖNGES  GERD ESSER  MARTIN HEIMANN  JOHN HELFRICH  FRANK IFT  FORTUNAT JOOS  JÖRG KADUK  GUNDOLF H. KOHLMAIER  A. DAVID McGUIRE  JERRY M. MELILLO  ROBERT MEYER  BERRIEN MOORE III  REAS NADLER  I. COLIN PRENTICE  WALTER SAUF  ANNETTE L. SCHLOSS  STEPHEN SITCH  UWE WITTENBERG  GUDRUN WÜRTH 《Tellus. Series B, Chemical and physical meteorology》1999,51(2):343-366

  相似文献   

Laboratory sustained turbidity currents form elongate ridges at channel mouths     

JAN ALEXANDER  STUART J. MCLELLAND†  THOMAS E. GRAY  CHRIS E. VINCENT  MIKE R. LEEDER  SUSANNA ELLETT 《Sedimentology》2008,55(4):845-868

The turbulent flow structure, suspended sediment dynamics and deposits of experimental sustained turbidity currents exiting a channel across a break in slope into a wide tank are documented. The data shed light on the flow evolution and deposit geometry of analogous natural channel‐fed submarine fans. Flows generated in a 0·3 m wide, sloping (0°, 6°, 9° or 20°) channel crossed an angular slope break and spread onto a horizontal tank floor. Flow development comprised: (i) channelized phase (unsteady channel flow developing into steady channel flow); (ii) initial lateral expansion phase (unsteady‐spreading wall jet phase); (iii) constant lateral expansion phase (steady‐spreading wall jet phase); and (iv) rapid waning phase. Phases (i) and (iv) are similar to laterally constrained turbidity currents, but phases (ii) and (iii) are considerably different from such two‐dimensional currents. Steeper channel slopes produced greater flow velocities and turbulence intensities, but these effects diminished markedly with distance from the channel mouth. Flow velocity vectors in the tank had similar patterns for all channel slopes, with a central core of faster velocity and narrow vector dispersion and slower flow with larger dispersion at the jet margins. Suspended sediment concentrations were higher within flow heads and dense basal layers in flow bodies. Time‐averaged acoustic backscatter data showed vertical concentration gradients, confirmed by siphon samples. The deposits comprised a thick central ridge, of similar order width to the channel mouth, with abrupt margins and a surrounding, very thin, fan‐like sheet. The ridge was coarser grained and better sorted than the original sediment, with grain‐size fining downstream, particularly over the fan‐like sheet. The formation of a central ridge suggests that, in the tank, vertical turbulent momentum exchange is more significant for sediment dynamics than spanwise momentum exchange due to lateral expansion. The streamwise elongate geometry of the ridge contrasts with conventional fan‐like geometry found with surge‐type turbidity flows, a result that has widespread stratigraphic and economic implications.  相似文献   

Exploring CO pollution episodes observed at Rishiri Island by chemical weather simulations and AIRS satellite measurements: long-range transport of burning plumes and implications for emissions inventories     

By HIROSHI TANIMOTO  KEIICHI SATO  TIM BUTLER  MARK G. LAWRENCE  JENNY A. FISHER  MONIKA KOPACZ  ROBERT M. YANTOSCA  YUGO KANAYA  SHUNGO KATO  TOMOAKI OKUDA  SHIGERU TANAKA  JIYE ZENG 《Tellus. Series B, Chemical and physical meteorology》2009,61(2):394-407

The summer of 2003 was an active forest fire season in Siberia. Several events of elevated carbon monoxide (CO) were observed at Rishiri Island in northern Japan during an intensive field campaign in September 2003. A simulation with a global chemistry-transport model is able to reproduce the general features of the baseline levels and variability in the observed CO, and a source attribution for CO in the model suggests that the contribution from North Asia dominated, accounting for approximately 50% on average, with contributions of 7% from North America and 8% from Europe and 30% from oxidation of hydrocarbons. With consideration of recent emission estimates for East Asian fossil fuel and Siberian biomass burning sources, the model captures the timing and magnitude of the CO enhancements in two pollution episodes well (17 and 24 September). However, it significantly underestimates the amplitude during another episode (11–13 September), requiring additional CO emissions for this event. Daily satellite images from AIRS reveal CO plumes transported from western Siberia toward northern Japan. These results suggest that CO emissions from biomass burning in western Siberia in 2003 are likely underestimated in the inventory and further highlight large uncertainties in estimating trace gas emissions from boreal fires.  相似文献   

Late Younger Dryas and early Holocene palaeoenvironments in the Skagerrak,eastern North Atlantic: a multiproxy study     

DORTHE RENG ERBS‐HANSEN  KAREN LUISE KNUDSEN  ANTHONY CAVEDO GARY  EYSTEIN JANSEN  RICHARD GYLLENCREUTZ  VINCENT SCAO  KURT LAMBECK 《Boreas: An International Journal of Quaternary Research》2011,40(4):660-680

Erbs‐Hansen, D. R., Knudsen, K. L., Gary, A. C., Jansen, E., Gyllencreutz, R., Scao, V. & Lambeck, K. 2011: Late Younger Dryas and early Holocene palaeoenvironments in the Skagerrak, eastern North Atlantic: a multiproxy study. Boreas, 10.1111/j.1502‐3885.2011.00205.x. ISSN 0300‐9843 A high‐resolution study of palaeoenvironmental changes through the late Younger Dryas and early Holocene in the Skagerrak, the eastern North Atlantic, is based on multiproxy analyses of core MD99‐2286 combined with palaeowater depth modelling for the area. The late Younger Dryas was characterized by a cold ice‐distal benthic foraminiferal fauna. After the transition to the Preboreal (c. 11 650 cal. a BP) this fauna was replaced by a Cassidulina neoteretis‐dominated fauna, indicating the influence of chilled Atlantic Water at the sea floor. Persisting relatively cold bottom‐water conditions until c. 10 300 cal. a BP are presumably a result of an outflow of glacial meltwater from the Baltic area across south‐central Sweden, which led to a strong stratification of the water column at MD99‐2286, as also indicated by C. neoteretis. A short‐term peak in the C/N ratio at c. 10 200 cal. a BP is suggested to indicate input of terrestrial material, which may represent the drainage of an ice‐dammed lake in southern Norway, the Glomma event. After the last drainage route across south‐central Sweden closed, c. 10 300 cal. a BP, the meltwater influence diminished, and the Skagerrak resembled a fjord with a stable inflow of waters from the North Atlantic through the Norwegian Trench and a gradual increase in boreal species. Full interglacial conditions were established at the sea floor from c. 9250 cal. a BP. Subsequent warm stable conditions were interrupted by a short‐term cooling around 8300–8200 cal. a BP, representing the 8.2 ka event.  相似文献   

OPTIMAL MANAGEMENT OF THE SUBSURFACE ENVIRONMENT / L'aménagement optimal de l'environnement souterrain     

ROBERT WILLIS 《水文科学杂志》2013,58(2):333-344

Abstract

A mathematical model for the optimal, conjunctive management of a groundwater basin's quality and quantity resources is presented. The quality resource, the assimilative waste capacity, is the ability of the aquifer to degrade certain non-conservative constituents through the actions of molecular diffusion, hydrodynamic dispersion, adsorption, biochemical reactions and convective mass transport. The model is applicable to saturated, isothermal, porous media. The Galerkin method is used to express the spatial and temporal variations in hydraulic head and constituent concentrations as a function of possible recharge, pumping, and treatment decisions. The Galerkin procedure ensures that the constraint equations actually model the response characteristics (flow and mass transport) of the groundwater basin. In each planning period, the groundwater basin is required to meet an exogenous water demand while maintaining adequate water quality levels throughout the aquifer. The model, structured as a mathematical program, minimizes the sum of waste water treatment and pumping and recharge costs. The results indicate (1) the feasibility of conjunctive management of an aquifer's quality and quantity resources, and (2) that the assimilative waste capacity can function as a form of secondary or advanced waste water treatment.  相似文献