Simple Dunes Research Articles

Holocene Eolian Sediments on the Southern Border of the Duero Basin (Spain): Origin and Development of an Eolian System in a Temperate Zone

ABSTRACT Holocene eolian sediments accumulated in the interior of the Iberian Peninsula, far from typical eolian environments (deserts, coasts, and periglacial arid belts). These eolian deposits are interpreted as a wet eolian system with dunes, interdune areas, and sand-sheet areas. Parabolic dunes predominate, indicating a dominant wind direction to the NE. Interdune areas may be either dry or wet. The eolian system is partly relict but also contains sporadically active dunes with visible slipfaces and partial vegetative cover. Several dunefields exist, having larger and more complex dunes at the center and downwind areas. Dunes originated from dome-shaped accumulations in the sand sheet, which became simple parabolic dunes and ramps. Larger, compound and complex parabolic dunes and ramps originated by merging and stacking of simple dunes. Finally, transverse dunes originated when the noses of parabolic dunes were stopped by water and the arms continued to move forward. The origin and development of the eolian system was related to abundant sand from underlying fluvial terraces, deposition in a depression with considerable relief and open to the wind, and changes in the water table, which controlled eolian accumulation. The presence of those eolian deposits in a temperate region suggests that, with the appropriate factors, eolian sedimentation is relatively independent of climate. The potential preservation of these sediments in temperate climates is problematic because they are vulnerable to erosion, mainly by water.

Geomorphology of sand dunes in the Northeast Taklimakan Desert

Three types of sand dunes exist in the Taklimakan Desert, namely compound/complex crescent dunes and crescent chains, compound dome dunes and compound/complex linear dunes. Besides these three compound/complex types, single simple dunes are also distributed throughout the sand sea. The compound/complex linear dunes are developed under acute bimodal wind regimes. Though the ratios of the resultant drift potential (RDP) and the drift potential (DP) are the same as that near the border and adjacent area of the sand sea, the compound/complex crescent and dome dunes are developed, respectively, because of divergence of the sand available, the stress of the sand-moving winds and the time scales of dune formation. The sand supply for the dunes is not from Lopo Nor in the east as previous studies suggested but mainly from local alluvial or lacustrine deposits. The grain size component does not correlate evidently to the morphology parameters of the sand dunes. Analyses of the DP and drift direction suggest that the northeast Taklimakan is an area of low wind energy and the resultant drift direction (RDD) coincides well with the distribution, morphology and scales of the dunes.

Barrier island to tidal shelf transition in the early Cambrian Eriboll Sandstone

Synopsis The Cambrian Eriboll Sandstone, 150–225 m of quartz arenites deposited on the western margin of the Iapetus Ocean, consists of a Lower Member (75–125 m thick) overlain by the Pipe Rock Member (75–100 m thick). The basal 10 m consists of tabular cross-bedded sands deposited within channels of a mesotidal barrier island system. These sands are truncated by an extensive ravinement surface overlain by thin cross-bedded and parallel-bedded shoreface sands with bimodal palaeocurrents. The ravinement surface reflects erosional retreat of the barrier foreshore and upper shoreface during transgression. Lower shoreface deposits were dominated by storm and tidal processes. Palaeocurrents in these were enhanced by superposition of northwards flowing geostrophic storm currents. Shoreface sands pass upwards into tidal shelf sands deposited as dunes and sandwaves. Sandwave cosets thicken upwards in the Lower Member indicating increased tidal current velocities. This may reflect resonant amplification of tides as the shelf became wider during sea level rise. As the transgression proceeded the bioturbated Pipe Rock was deposited. Proximal deposition was by large compound sandwaves, similar to those below, and grading offshore into small, simple dunes and sandwaves. Distal fades were storm dominated. Both were populated by suspension feeding animals which produced abundant Skolithos burrows.

Reconstruction of Eolian Sequences--A Function of Scale, Jurassic Page Sandstone, Arizona: ABSTRACT

Interpretation of sequences of ergs and bed forms that comprise an eolian unit is strongly dependent on the scale of mapping. A pentagon-shaped, three-dimensional outcrop of eolian Middle Jurassic Page sandstone near Page, Arizona, measuring 36 m high and nearly 1 km in perimeter, was mapped with the aid of an electronic tacheometer. The extent and orientation of bounding surfaces and sets of cross-strata were mapped in detail, foreset orientation were measured, and a general depiction was made of the lateral and vertical distribution of stratification types within sets and of features associated with the surfaces. The level of mapping is at a middle scale with respect to architectural elements and proved adequate for an interpretation of most bed forms in terms of shape (two or three dimensions, sinuosity, symmetry, and crestline-phase relationships), size (height and width), aerodynamics (overall primary and secondary airflow patterns), and migration behavior (degree of climb and recognition of cyclicity). These interpretations allow the determination of bed-form hierarchy (simple dunes or draas) and of the bed-form type according to the descriptive (crescentic, linear) and dynamic (transverse, oblique, longitudinal) classifications. In conjunction with this level of mapping, large-scale or regional mapping was used in order to identifymore » distinct, stacked, dune-field, and erg deposits that comprise the Page sandstone. Local mapping of the out-crop at a fine scale was necessary for refined interpretation of cyclicity, bed-form size, migration rate, and airflow pattern.« less

Eolian dune types preserved in the Tensleep Sandstone (Pennsylvanian-Permian), north-central Wyoming

The Tensleep Sandstone is one component of an erg system that prograded southward out of north-central Wyoming from Middle Pennsylvanian to Early Permian time. Each erg advance was temporarily interrupted by regional marine transgression. Interpretation of dune types deposited in these ergs is developed from an analysis of the relative proportions of eolian stratification types comprising foreset strata, geometry and relationships of bounding surfaces, and paleodispersal patterns. Two basic morphologic dune types are inferred: simple dunes and compound crescentic dunes. The simple dunes are dominant and are subdivided into 1–2 km wavelength and 1.0 km saddle-spacing slightly crescentic, and 0.1–0.2 km wavelength straight-crested subtypes based on their first-order bounding surface geometries. Foresets are composed of grainfall and wind-ripple strata; avalanche strata are rare. The compound crescentic dunes had wavelengths of 0.5–1 km and saddle spacings of 0.8 km. Foresets are dominated by avalanche and wind-ripple strata. A morphodynamic classification of the dune types is inferred from considerations deduced from paleodispersal patterns and comparison with paleocirculation models. The simple dunes were demonstrably oblique to some elements of the wind field and less oblique to others. The compound crescentic dunes had a predominantly transverse configuration.

Controls of eolian dune size and spacing

Research Article| November 01, 1988 Controls of eolian dune size and spacing N. Lancaster N. Lancaster 1Department of Geology, Arizona State University,Tempe, Arizona 85287-1404 Search for other works by this author on: GSW Google Scholar Author and Article Information N. Lancaster 1Department of Geology, Arizona State University,Tempe, Arizona 85287-1404 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (11): 972–975. https://doi.org/10.1130/0091-7613(1988)016<0972:COEDSA>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation N. Lancaster; Controls of eolian dune size and spacing. Geology 1988;; 16 (11): 972–975. doi: https://doi.org/10.1130/0091-7613(1988)016<0972:COEDSA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Data for the Namib and Gran Desierto sand seas suggest that the controls of dune size and spacing are complex. The relation between dune height and spacing varies with dune type and location and reflects both dune dynamics (vertical accretion vs. migration or extension) and availability of sand. There is no general relation between dune spacing and grain size. In the Namib sand sea the height of compound and complex dunes (draas) is inversely proportional to potential sand-transport rates, whereas the height of dunes superimposed on their flanks varies directly with potential sand-transport rates. These observations can be combined with data on dune spacing to demonstrate the existence of a hierarchy of eolian dunes, each element of which responds to variations in sand-transport rates at different temporal and spatial scales. Whereas the morphology of individual simple dunes and superimposed dunes on draas is related to contemporary rates and directions of sand transport, the morphology and development of draas reflects long-term and regional patterns of sand transport and deposition. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

山陰の海岸砂丘

Most of the San' in sand dunes are those of‘dune ridge’(dune on the beach ridge) type which was proposed in the essay of D.W. JOHNSON (1919). So called‘old dunes’are not the simple dunes but old dunes on the old beach ridge and beach berm which formed at +25m former sea level. These old sand deposits were covered with brown soil and dissected and excavated by the wind and stream. The old sand dunes were formed on these marine deposits and brown soil and then covered with red soil, grey clay and Daisen middle volcanic ashes. New sand dunes which formed in Holocene are well developed everywhere along sandy coast. In Kyuhin penninsula three curved beach ridge groups are clearly recognised on which three new sand dunes were developed. These new dune ridges are widespread and their zonal or linear pattern are useful for analyzing dune formation history. New dune Ia and Ib are discovered under the black sand a and b respectively along inland part of the dune pattern. The New dune IIa, IIb and IIc are found near the present shoreline. These new dunes seem to have been formed after Jomon, Heian and very recent transgressions, respectively.

Depositional and Dispersal Dynamics of Intertidal Sand Bars

ABSTRACT The intertidal sand bars of the Minas Basin, Nova Scotia, are asymmetrical in cross-section and linear in plan. They are formed and reworked by tidal currents which are characterized by an asymmetric time-velocity profile. A causal connection between time-velocity asymmetry of tidal currents and bar topography is demonstrated. Average bottom ebb current velocities (90 cm/sec) were found to exceed average bottom flood current velocities (65 cm/sec) over gently-sloping (2 to 3 degree) bar surfaces, whereas over steep-sloping (8 degree) bar surfaces, average bottom flood current velocities (90 cm/sec) were found to exceed average bottom ebb current velocities (65 cm/sec). Both bar topography and zones of flood- or ebb-dominated bottom tidal currents control the distribution of sediment texture and sedimentary structures. On steeper bar slopes, the sediment is fine-grained sand and is characterized by airholes, planar lamination, and surface dunes and ripples. On the gentler bar slopes, the texture of the sediment is medium-grained and coarse-grained sand which has been fashioned into current ripples, simple dunes, complex dunes, simple sand waves and complex sand waves. The internal organization of some dunes and sand waves is extremely complex, inasmuch as thickness of internal sets of cross-stratification is considerably less than dune and sand wave height. A total of 14 sedimentary bar facies are defined from combinations of texture, internal cross-stratification and surface bedforms. Both topography and zones of ebb- and flood-dominated bottom tidal currents control the orientation of directional current structures. Over steep faces of bars, the slip faces of sand waves are oriented in the same direction as flow directions of bottom flood tidal currents, although they do show evidence of reworking by ebb currents. Over gently sloping bar surfaces, slip faces of both dunes and sandwaves are oriented parallel to the direction of flow of bottom ebb current systems. Because dunes and sand waves migrate only during a single phase (ebb or flood) of a tidal cycle, their orientation is generally unimodal. Current ripples are formed in depths of water less than 0.6 meters, during late-stage sheet-like runoff that is controlled by local slope changes on the bar. Indi idual tracer grains are dispersed in a radial-elliptical pattern form a point source. The size of directional properties is hierarchically sensitive to dispersal history. Tracer grains (modeling mineral indicator grains) are dispersed in a radial-elliptical pattern from a point source. Trimodal, highly variant, current ripple slip face orientation develops during late stage sheet runoff at low water depths; this flow is controlled by local bar slope. Unimodal, low variant dune slip faces, sand wave slip faces and associated maximum dip direction of cross-stratification are aligned parallel to tidal current flow and basinal topographic trend. The sand bars are aligned parallel to basinal topographic trend and in turn segregate zones of flood- and ebb-dominated bottom current systems. The tidal sand bars of the Minas Basin are equilibrium forms. Sand is dispersed alternately around the bar through zones of ebb- and flood-dominated bottom tidal currents. As a consequence, the sedimentary facies distribution on the bars has remained essentially unchanged since 1938. Comparison of low-tide airphotos taken in 1938, 1947 and 1963 in one of the study areas shows a slight erosional regime. This erosional regime controls the extreme reworking of sediments, and the formation of an erosional sand wave bedform by wave processes. Physical criteria characteristic of tide-dominated sand bodies include: sharp erosional contacts between sets of cross-stratification; rounded upper set boundaries of cross-stratification; unimodal and bimodal distributions of orientation of cross-stratification; bimodal distributions of set thickness and dip angles of cross-stratification; orientation of dunes, sand waves and cross-stratification in the dominant direction of flood or ebb tidal flow, basinal topographic trend and sand body axis; trimodal orientation of current ripples; oblique or 90° superposition of smaller current ripples on larger current ripples; double-crested current ripples; superposition of current ripples at 90° or 180° on slip faces and crests of dunes and sand waves; complex organization of inte nal cross-stratification in sand waves; etch marks on slip faces of dunes and sand waves; and alignment of the long axis of sand bodies parallel to tidal current flow, basinal topographic trend and basin axis.

A Tentative Classification of Sand Dunes Its Application to Dune History in the Southern High Plains

Part I. Existing sand dunes fall naturally into two groups-complex and simple, the former being much the more common. Variable factors, such as wind direction, depth of sand, irregularity of vegetal growth, etc., are responsible for the rarity of the simple dunes. It is only by first studying simple forms, however, that one can discern the origin and history of surfaces of complex form. Following is a basic classification of simple dunes which is at the same time genetic and naturalistic. It is based on the assumption that the sand-moving wind blows with unvarying direction. Simple Dunes A. Bare Surfaces or Loose Sand I. The barcan dune. An isolated bare-sand hill on a nonsandy base II. The transverse dune series. Formed on bare, loose sand of "unlimited" surface area and "unlimited" depth III. The isolated transverse dune ridge. Formed (frequently with human aid) from bare, loose sand of unlimited surface area, but shallow depth IV. Lee dunes 1. Wind-shadow dunes ("umbracer" dunes). Longitudinal dunes. Formed from a continuing (unlimited) sand supply in the lee of a bedrock obstacle 2. Shrub-coppice dunes (see p. 124) 3. Source-bordering lee dunes ("umbrafon" dunes, lee-source dunes). Formed from a continuing (unlimited) sand supply leeward from a source of sand of limited area (e.g., stream flood plain) B. Formed by Wind in Conflict with Vegetation I. Shrub-coppice dune cluster. Formed in and to leeward from bunch or clump vegetation, such as mesquite bush, on an unlimited and smooth surface of very shallow sand II. (a) Blowout or parabolic dunes; (b) elongate-blowout dunes; and (c) windrift dunes. Formed by gentle, moderate, and strong winds, respectively, on deep sand with shrub- or grass-covered surface Under the heading "Complex Dune Forms" is considered the ideal simple case of two equally effective sand-moving winds blowing at right angles. It is pointed out that even this degree of complexity is much simpler than that of many of the well-known sand-dune areas. PART II. A study of dunes in the southern High Plains by means of vertical aerial photographs reveals: 1. Up to the decade from 1920 to 1930, active sand dunes were insignificant in number and total area, compared to the anchored dunes of Recent or post-Pleistocene age. 2. There has been a systematic shift in the direction of the prevailing sand-moving wind during the last 15,000 years (estimate), such that winds which formerly blew toward S. 70° E. have been replaced gradually by modern winds blowing N. 20° E. in most of the region. For convenience in description these dunes are divided into three series: I, II, and III, from youngest to oldest. 3. An unusual series of large parallel windrift dunes, indicating strong persistent winds, was formed around 15,000 years ago. Sand dunes of this type (Series III) are apparently not forming at present to any noteworthy degree, either in the interior of North America or along the coasts.