Aeolian dune interactions and dune‐field pattern formation: White Sands Dune Field,New Mexico     

RYAN C. EWING  GARY A. KOCUREK 《Sedimentology》2010,57(5):1199-1219

Pattern formation is a fundamental aspect of self‐organization in fields of bedforms. Time‐series aerial photographs and airborne light detection and ranging show that fully developed, crescentic aeolian dunes at White Sands, New Mexico, interact and the dune pattern organizes in systematically similar ways as wind ripples and subaqueous dunes and ripples. Documented interactions include: (i) merging; (ii) lateral linking; (iii) defect repulsion; (iv) bedform repulsion; (v) off‐centre collision; (vi) defect creation; and (vii) dune splitting. Merging and lateral linking are constructive interactions that give rise to a more organized pattern. Defect creation and bedform splitting are regenerative interactions that push the system to a more disorganized state. Defect/bedform repulsion and off‐centre collision cause significant pattern change, but appear to be neutral in overall pattern development. Measurements of pattern parameters (number of dunes, crest length, defect density, crest spacing and dune height), dune migration rates, and the type and frequency of dune interactions within a 3500 m box transect from the upwind margin to the core of the dune field show that most pattern organization occurs within the upwind field. Upwind dominance by constructive interactions yields to neutral and regenerative interactions in the field centre. This spatial change reflects upwind line source and sediment availability boundary conditions arising from antecedent palaeo‐lake topography. Pattern evolution is most strongly coupled to the pattern parameters of dune spacing and defect density, such that spatially or temporally the frequency of bedform interactions decreases as the dunes become further apart and have fewer defects.  相似文献   

The development of a historical digital cadastral database†     

GARY J. HUNTER  IAN P. WILLIAMSON 《International journal of geographical information science》2013,27(2):169-179

With an ever-increasing number of land information systems being developed, there is a growing demand by users for systems which support the use of temporal data for time-based studies. System managers, however, may have difficulty responding to these calls because of the lack of available research to guide them in their task. This paper examines the simple method of storing and processing temporal graphical data by the addition of time-encoding attributes to data elements as required. To illustrate the technique, a historical digital cadastral database has been created which al lows users to display and report on the cadastral parcellation of a region at any time in the past. The method can also be widely applied to other data to assist a broad range of space/time-related studies.  相似文献   

A 1,800 MILLIVOLT SELF-POTENTIAL ANOMALY NEAR HUALGAYOC,PERU*     

S. PARKER GAY 《Geophysical Prospecting》1967,15(2):236-245

A large self-potential anomaly was outlined in 1963–64 at Tantahuatay near Hualgayoc in the Andes of northern Peru. Peak value recorded was–1842 millivolts–thus making it one of the strongest, or perhaps the strongest, SP anomaly ever measured. A lack of detailed geological data precludes the formulation of an adequate explanation for the Tantahuatay anomaly, but geological and mineralogical similarities with the well-documented Venencocha anomaly near Cerro de Pasco, Peru (Kruger and Lacy, 1949), suggest that the anomaly arises from sulfuric acid associated with the mineral alunite. The anomaly obviously cannot be explained by the half-cell mechanism of Sato and Mooney (1960), who place a limit of 700 millivolts on self-potential anomalies over sulfide bodies. Further study of the Tantahuatay anomaly would be of interest in understanding self-potential mechanisms in general.  相似文献   

Sedimentology and evolution of the Martinsburg Formation (Upper Ordovician) fine-grained turbidite depositional system, central Appalachians   总被引：1，自引：0，他引：1  

GARY G. LASH 《Sedimentology》1988,35(3):429-447

The Upper Ordovician Martinsburg Formation of eastern Pennsylvania consists of mudstone, siltstone, and sandstone turbidites that accumulated in a tectonically active foreland basin. The mudstone-rich Bushkill Member, the stratigraphically lowest unit of the Martinsburg in this area, grades upward into approximately equal proportions of mudstone, siltstone, and sandstone of the Ramseyburg Member. Many of the turbidites of these units are arranged in small-scale (1–9 m) fining-upward sequences that are interpreted as reflecting the influence of external or allocyclic controls such as variations in the local rate of sea-level rise and/or variations in the intensity of tectonic activity in shelf/nearshore or hinterland areas rather than more commonly cited autocyclic mechanisms. The thick (approximately 2000 m) Bushkill-Ramseyburg coarsening-upward sequence records progradation of a muddy turbidite depositional system along the axis of the foreland basin. Although this sequence accumulated during a Caradocian eustatic rise in sea-level, sedimentation rates landward of the shoreline were apparently great enough to allow for long-term seaward progradation of the shelf source. The paucity of depositional lobe-like facies (coarsening-upward sequences) in the Bushkill Member allows for tentative comparison of the progradational Bushkill-Ramseyburg system with the active fan lobe of the Mississippi Fan. Progradation of the Bushkill-Ramseyburg system ceased abruptly when mudstone turbidites and laminated black shale of the upper unit of the Martinsburg, the Pen Argyl Member, accumulated. The great thickness of some mudstone turbidite beds of the Pen Argyl Member is interpreted to record topographic confinement of the central Appalachian foreland basin, which may have helped to preclude continued progradation of the Bushkill-Ramseyburg turbidite system.  相似文献   

A preliminary study of the dynamics of a modern draa, Algodones, southeastern California, USA   总被引：2，自引：0，他引：2  

KAREN G. HAVHOLM  GARY KOCUREK 《Sedimentology》1988,35(4):649-669

A transverse crescentic draa in the Algodones dune field, California, was monitored for a year using surface process mapping, aerial photography and supplemental wind measurement. The draa is oriented by the long-term resultant wind, whereas its superimposed features are in equilibrium with the bedform-modified secondary airflow. Surface airflow and the movement of superimposed bedforms is typically oblique or parallel to the draa brinkline, particularly on the lee slope. Comparison of measurements of draa movement and sand deposition on the lee slope, with expected rates calculated from wind data and draa size, confirm that there is a significant component of sand flow parallel to the draa brinkline. The internal structure being generated at the base of the draa lee slope is inferred from the surface processes active there. Within the space of a kilometer two types of compound cross-strata, separated by an area of simple cross-strata, are being produced. This has significant implications for interpretations of ancient aeolian strata. Variations in internal structure types found in lateral sequence may be generated by one complex bedform, and these cross-strata may be simple or compound. Second-order bounding surface orientations indicate resultant primary palaeowind directions; compound cross-strata dip directions indicate secondary flow conditions. The existence of cross-strata dip directions oblique or perpendicular to the second-order surface indicates longitudinal secondary flow on the lee face, but not necessarily a longitudinal or oblique draa. Without further detailed knowledge about various draa configurations and behaviour, stratification attributed to draas can be used only to interpret activity on the lower draa lee face.  相似文献   

Longitudinal petrographic variations in a Middle Ordovician trench deposit, Central Appalachian orogen     

GARY G. LASH 《Sedimentology》1987,34(2):227-235

Petrographic analysis of Middle Ordovician turbidite sandstones of the Greenwich slice of the Hamburg klippe (eastern Pennsylvania), inferred to be part of a fossil subduction complex, define three coeval petrofacies. The Jonestown petrofacies was derived from felsic plutonic and less abundant metasedimentary rocks, whereas the Windsor Township, the most extensive petrofacies, and Werleys Corner petrofacies were derived from sources characterized by various proportions of sedimentary/metasedimentary, plutonic, and volcanic rocks. The presence of minor but conspicuous extrabasinal carbonate and microlitic volcanic lithic fragments together with higher percentages of polycrystalline quartz, serve to distinguish the Werleys Corner from the Windsor Township petrofacies. It is conceivable that sandstones of the Greenwich slice were derived from microplates inferred to have existed to the southeast of the proto-North American plate in Early Palaeozoic time. The variations in sandstone composition along the length of the Greenwich slice may be explained by post-accretion tectonic juxtaposition of petrofacies derived from various sources. An equally plausible explanation involves transverse infilling of a channelized longitudinal transport system (Windsor Township petrofacies) by sediment derived from compositionally diverse source terranes orthogonal to the trench (Jonestown and Werleys Corner petrofacies).  相似文献   

Conditions favourable for the formation of warm-climate aeolian sand sheets   总被引：1，自引：0，他引：1  

GARY KOCUREK  JAMIE NIELSON 《Sedimentology》1986,33(6):795-816

Aeolian sand sheets are areas of aeolian sand where dunes with slipfaces are generally absent. Sand sheets are ubiquitous to modern, warm-climate sand seas, generally occurring marginal to dune fields, although they may exist within the interior of a sand sea or independent of a dune field. Sand-sheet deposits are recognized in ancient aeolian sequences, where they may account for significant accumulations of low-angle aeolian stratification. We suggest that the occurrence of sand sheets instead of dunes indicates that conditions are outside the range within which dunes form or that one or more factors interfere with dune development while also favouring the accumulation of sand sheets. A study of six modern sand sheets in North America (located at Great Sand Dunes, Gran Desierto, Dumont, Algodones, Padre Island, and Colorado River delta) indicates that the factors favourable for sand-sheet development are: (1) a high water table, (2) surface cementation or binding, (3) periodic flooding, (4) a significant coarse-grained sediment population, and (5) vegetation. These factors are reflected in the nature of stratification and the accessory features of sand-sheet accumulations within the areas of modern sand sheets as well as in their ancient counterparts in the Triassic Dolores and Pennsylvanian-Permian Rico formations.  相似文献   

Development of spatially diverse and complex dune-field patterns: Gran Desierto Dune Field, Sonora, Mexico   总被引：5，自引：0，他引：5  

CARRIE BEVERIDGE  GARY KOCUREK  RYAN C. EWING  NICHOLAS LANCASTER†  P. MORTHEKAI‡  ASHOK K. SINGHVI‡  SHANNON A. MAHAN§ 《Sedimentology》2006,53(6):1391-1409

The pattern of dunes within the Gran Desierto of Sonora, Mexico, is both spatially diverse and complex. Identification of the pattern components from remote‐sensing images, combined with statistical analysis of their measured parameters demonstrate that the composite pattern consists of separate populations of simple dune patterns. Age‐bracketing by optically stimulated luminescence (OSL) indicates that the simple patterns represent relatively short‐lived aeolian constructional events since ～25 ka. The simple dune patterns consist of: (i) late Pleistocene relict linear dunes; (ii) degraded crescentic dunes formed at ～12 ka; (iii) early Holocene western crescentic dunes; (iv) eastern crescentic dunes emplaced at ～7 ka; and (v) star dunes formed during the last 3 ka. Recognition of the simple patterns and their ages allows for the geomorphic backstripping of the composite pattern. Palaeowind reconstructions, based upon the rule of gross bedform‐normal transport, are largely in agreement with regional proxy data. The sediment state over time for the Gran Desierto is one in which the sediment supply for aeolian constructional events is derived from previously stored sediment (Ancestral Colorado River sediment), and contemporaneous influx from the lower Colorado River valley and coastal influx from the Bahia del Adair inlet. Aeolian constructional events are triggered by climatic shifts to greater aridity, changes in the wind regime, and the development of a sediment supply. The rate of geomorphic change within the Gran Desierto is significantly greater than the rate of subsidence and burial of the accumulation surface upon which it rests.  相似文献   

CAUSES OF THE FETCH EFFECT IN WIND EROSION     

DALE A. GILLETTE  GARY HERBERT  PAUL H. STOCKTON  P. R. OWEN 《地球表面变化过程与地形》1996,21(7):641-659

The increase of soil mass flux with distance downwind, the fetch effect for wind erosion, has been observed and reported on since 1939. This model incorporates the following three mechanisms. (1) The ‘avalanching’ mechanism in which one particle moving downwind would dislodge one or more particles upon impact with the surface. The result of a chain of such events is an increase of mass flux with distance. (2) The ‘aerodynamic feedback’ effect, suggested by P. R. Owen, in which the aerodynamic roughness height is increased by saltation of particles; the resulting increased momentum flux increases saltation. These increases define a positive feedback loop with respect to distance downwind. (3) The ‘soil resistance’ mechanism, which is largely an expression of the change with distance of threshold velocity. Change of threshold velocities may be caused by inhomogeneities of the soil or progressive destruction of aggregates and crust in the direction of saltation fetch. An experiment was run in March 1993 at Owens Lake to test this model. Detailed measurements of wind profiles and mass fluxes were taken on a line parallel to the wind direction. These data support the proposed three-mechanism model.  相似文献   

Coastal Change in Ras Al Khaimah (United Arab Emirates): a Cartographic Analysis   总被引：2，自引：0，他引：2  

A.S. GOUDIE  A.G. PARKER  A. AL-FARRAJ 《The Geographical journal》2000,166(1):14-25

The coastline of Ras Al Khaimah, United Arab Emirates, has three main constructional complexes: Jazirat al Hamra, Julfah, and Jazirat Hulaylah. Archival information, air photographs and maps dating back to 1819, enable the history of coastal change to be reconstructed. Jazirat al Hamra has been much affected by recent reclamation and harbour works, but appears to have been relatively stable. Jazirat Hulaylah also appears to have changed relatively little. However, the Julfah complex, which includes the harbour mouth for Ras Al Khaimah city, has shown very considerable change as a result of coastal breaching and spit growth and decay.  相似文献