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-Models for eolian aggradation. AD) Current model for eolian aggradation. A) Migration of dunes across a partially vegetated stabilized ''super'' surface (SS). This surface provides the primary surface from which dunes aggrade. B) Dunes aggrade through climb on first-order bounding surfaces. (1) C) Short-lived bypass surface (BP) cut by nonclimbing migration of dunes. These may interrupt climb and make difficult the recognition of first order surfaces. D) Aggradation of complex dunes through climb on first order surfaces. Stratigraphy is made more complex by downwinddipping surfaces. Reactivation surfaces (R) (third-order surfaces of Brookfield 1977) mark reworking of the slipface of the dune. Secondorder surfaces (2) mark superimposed barchanoid forms descending the slipface of the draa. E-G) New model for eolian aggradation. E) Growth and migration of draas (megadunes). Annotation is the same as above. Note the discontinuous first-order surfaces (1). F) Draa stabilization. Formation of a stabilization surface (ST) that drapes the draa. Sand sheets accumulate on both flanks of the stabilized megadune. G) Interdraa fills with strata separated by downwind-descending surfaces that mark accretion from the side of the draa (2).
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The dominant current model for the accumulation of eolian strata in the rock record emphasizes translation and climb of bedforms and the preservation of continuous beds. Studies of modern dune fields, however, show that, when large dunes form, they create a topographically irregular surface; later episodes of eolian activity commonly fill the low-l...
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... models for preservation of eolian cross-strata require migration of bedforms accompanied by base-level rise to create continuous beds . However, strata in the Permian Cedar Mesa Sandstone in southeastern Utah require a different model (Fig. 1). In this new model, large dunes form and grow downwind. The spaces between these dunes are filled by later eolian deposits formed in different conditions. Subsequent deposition is largely shaped by the preserved topographic remnants of the large dunes ( Fig. ...
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... in the Permian Cedar Mesa Sandstone in southeastern Utah require a different model (Fig. 1). In this new model, large dunes form and grow downwind. The spaces between these dunes are filled by later eolian deposits formed in different conditions. Subsequent deposition is largely shaped by the preserved topographic remnants of the large dunes ( Fig. ...
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... top of the draa has 25 m of relief, while SS 6 has only 8 m of relief. This is the result of partial filling of the interdraa lows as shown in Figures 1, 9 and 10. Imagery courtesy of Google Earth. ...
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... front of the northern draa may be traceable all the way to Squaw Butte, more than 5 km away along strike. Each draa was defined by dunes or sets of dunes separated by relatively steep (15 to 25 degrees) erosion surfaces that dipped subparallel to the foreset dip direction (Figs. 1, 6). These surfaces are second-order bounding surfaces in the terminology of Brookfield (1977), and mark the eroded tops of dunes migrating down the front of a larger dune or draa. ...
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... of these trough sets are only 0.5 to 1 m thick and are traceable laterally for less than 20 m, although plan-view exposures of these troughs were relatively rare. These sets are best described as down-climbing troughs because they are preserved through lateral migration of the draa as they climb down its front (''2s'' in Figures 1 and 6). ...
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... dune foresets intercalate with the down-climbing barcha- noid dunes. These typically built from an origin in the upper parts of the second order surfaces (Figs. 1, 6A). Six sets of transverse foresets were mapped. ...
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... downlap surface that defines the base of the draas is irregular (Fig. 1). In some locations, the barchans and planar foresets downlap onto a sand-sheet and pond deposit that must have existed in front of the dunes (Fig. 5B). However, in other places, the draa downlaps onto flood surface FS-3 (Fig. 5C). The maximum thickness of sand sheets measured beneath the draa was 4 m. The authors therefore infer that ...
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... of the draa were eroded. Wedge-shaped sand sheets (light pink) accumulated on the flanks of the draa (Fig. 8). 3. Sand sheets and ponds filled the interdraa area. Deposition occurred as en echelon sets from upwind to downwind. The prevalent wet eolian structures and ponds suggest a very different environment than that in which the draa formed (Figs. 9, 10). 4. The remaining interdraa was filled with trough cross-strata with foreset azimuths more eastward than the underlying strata that continued through deposition of the upper white unit. Up to 4 m of relief is evident at FS 4 at the base of the upper white unit. The barchans are interspersed with ponds, indicating a shallow water table ...
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... where the gently dipping beds are truncated by erosion surfaces (Fig. 9). At the top of the main white sandstone, the wedges are truncated by FS 4. This gives the deposits an overall lenticular shape. They thicken as they dip into the interdraa (below FS 4) and then thin depositionally (enhanced by erosion to a pinchout within the interdraa) (Fig. ...
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... sand sheets may exhibit an abrupt, local facies transition into ponds at the toes of their depositional wedges (Figs. 9, 10). As with the sand-sheet wedges, stratigraphically higher pond deposits are displaced to the southeast, in a paleo-eolian transport direction (Fig. 10). The replacement of draa-barchan and transverse-dune deposits with pond and sand-sheet deposits suggests a wetter and more vegetated environ- ment than the one that built the ...
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... sand sheets may exhibit an abrupt, local facies transition into ponds at the toes of their depositional wedges (Figs. 9, 10). As with the sand-sheet wedges, stratigraphically higher pond deposits are displaced to the southeast, in a paleo-eolian transport direction (Fig. 10). The replacement of draa-barchan and transverse-dune deposits with pond and sand-sheet deposits suggests a wetter and more vegetated environ- ment than the one that built the ...
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... main white sandstone is constructed of two distinct deposits-a draa and interdraa-fill succession that formed in different settings at different times (Fig. 1). Three observations support this interpretation. First, the eroded downwind flank of the draa indicates reworking of the draa front. When combined with the absence of complex dune deposits beyond this eroded front, this indicates that the draa was eroded after deposition. Second, the weathering surface that covers the upwind top and ...
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... the weathering surface that covers the upwind top and downwind flanks of the draa suggests exposure of the eroded draa surface. Third, the preservation of sand-sheet deposits that lap onto the eroded upwind flank of the draas (Figs. 1, 7, 10) indicates that both flanks of the draa were stabilized prior to deposition of the interdraa fill. ...
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... sandstone (McKee and Moiola 1975;Brookfield 1977;Kocurek 1981;Rubin and Hunter 1982;Kocurek and Havholm 1993;Kocurek and Lancaster 1999;Mountney and Howell 2000;Mountney and Jagger 2004;Mountney 2006). Most of these studies stress the importance of bedform climb relative to a generally low-relief, subhorizontal underlying depositional surface (Fig. 1). Aggradation is assumed to occur through migration of generally similar-sized bedforms and preservation of the basal portion of the dune through climb during migration. This type of preservation likely occurs in many sandstones. Mountney and Jagger (2004) illustrate episodic bedform climb as a key FIG. 9.-Photo of stratigraphic ...
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... main white sandstone suggests an alternative mechanism for preservation of eolian sandstones that has been previously unrecog- nized-one in which the depositional surface is the upper surface of a draa or large dune form (Fig. 1). This irregular surface becomes the surface from which aggradation occurs and dunes aggrade laterally from the constructed topography of a large complex dune or draa. ...
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... complex dune or draa. A certain amount of bedform climb must have occurred relative to FS 3 during draa growth and migration. This is suggested by the sand-sheet deposits that underlie much of the preserved draas (Figs. 5, 6). The surfaces between these and the overlying draa deposits are likely first-order interdune-migration bounding surfaces (Fig. 1E). However, these first- order surfaces are discontinuous and both draa and interdraa deposits lap directly down onto flood surface FS 3. This indicates that bedform climb was either only a local phenomenon, where sand sheets aggraded in front of the draa, or was temporary (in which the interdraa sand sheet was episodically eroded during ...
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A depositional framework for late Pleistocene sediments in central British Columbia was developed from the composite stratigraphy of glacial sediments found in the Bulkley River region. Nonglacial deposits correlated to the Olympia Nonglacial Interval, are overlain in succession by sub-till, ice-advance sediments, Late Wisconsinan (Fraser Glaciatio...
Citations
... Moreover, high-relief topography and its related rain shadow effect also play an important role in the initiation, growth and maintenance of modern and ancient deserts (Guo et al., 2002;Spalletti et al., 2010;Zheng et al., 2015;Fan et al., 2020;Rodríguez-López et al., 2020;Wu et al., 2022). However, the role of topography and climate in the initial development and long-term construction of desert systems is a point of debate, with some arguing for a dominant control being exerted by topography (Langford et al., 2008;Rodríguez-López et al., 2014Ventra et al., 2017), while others emphasize the significance of climate factors (Talbot, 1985;Clemmensen et al., 1994). ...
... Pedogenesis, interdune formation, and various stabilization surfaces have been directly tied to the saturated zone being at the surface (e.g., Kocurek 1988;Langford and Chan 1988;Mountney 2006Mountney , 2012Langford et al. 2008;Bristow and Mountney 2013;Lancaster and Mountney 2020). Soil-forming processes do not operate in water-saturated sediment that occurs at the surface (e.g., Brady and Weil 2002;Schaetzl and Anderson 2005;Hasiotis 2007;Hasiotis et al. 2007), but, instead, reflect vadose conditions with the phreatic zone below it. ...
... Paleosols, roots (Glennie and Evamy 1968;Anton 1983;Loope 1984Loope , 1985Talbot 1985;Kocurek 1991) Polygonal fractures (Kocurek and Hunter 1986) Punctuated, episodic accumulation (Blakey et al. 1996;Kocurek et al. 1991a) 1st order Interdune (relatively flat, horizontal) Stokes surfaces (Stokes 1968;Fryberger et al. 1988) Amalgamated interdune (Fryberger et al. 1988) Lag surfaces (Sweet et al. 1988) Flood surfaces (Langford and Chan 1988) Polygonal fractures (Kocurek and Hunter 1986) Stabilized surfaces (Talbot 1985;Fryberger et al.1988;Langford et al. 2008) vegetated Paleosols, roots (Glennie and Evamy 1968;Anton 1983;Loope 1984;Talbot 1985;Kocurek 1988) Event stratigraphy (Kocurek 1991) 2nd order Superposition (inclined, slope downwind) Superimposition (Mountney and Howell, 2000) May include stabilized surface, roots, and event stratigraphy 3rd order Reactivation or redefinition (periodic lee face erosion, within cosets) Mountains) in the east and thickens into the western part of the basin in southwestern Utah (Peterson and Pipiringos 1979;Blakey et al. 1988;Peterson 1994). In the study area (Fig. 1A, B), the Navajo Ss is underlain by and, in some places, interfingers with the Kayenta Formation (Fm) (Peterson and Pipiringos 1979;Hassan et al. 2018). ...
... The stratigraphic architecture captures the autogenic and allogenic processes that produced that unit. Composite units can interfinger and disappear within thicker, conterminous simple, compound, and/or cosets of eolian crossbedding, or can be truncated by higher rank surfaces (e.g., Kocurek et al. 1991a;Mountney 2006;Langford et al. 2008). Strata within composite units are genetically related in that they share similar a depositional history. ...
A model-independent, sequence stratigraphic approach is used to define bounding surfaces in the Navajo Sandstone in order to identify an architectural hierarchy of genetically related sedimentary packages and the surfaces that bound them across multiple scales of both eolian and non-eolian components of an erg system. Seven bounding surfaces and eight depositional units are defined, from small to large scale. A lamina-deviation surface bounds wedge- and tabular-shaped sets of laminae and/or laminasets, separating those that have different angle orientations on the dune slipface. A bed-deviation surface bounds a succession of beds (crossbeds) that lie at different angles or orientations to bedding above, below, or adjacent to it. A bedset-deviation surface is curved, inclined, and/or wavy and irregular that bounds bedsets and their internal stratification patterns; that is, bed-deviation surfaces, and lamina-deviation surfaces. A simple surface is gently inclined with or without small, concave or convex segments that bound beds and bedsets. A composite surface is horizontal with or without concave, curved, or irregular portions of that surface. A complex surface is laterally extensive (∼ 1–10+ km) that regionally bounds and truncates underlying conterminous and interfingered eolian and non-eolian strata. An amalgamated surface is a regionally extensive (∼ 10 to 100s km) mappable unconformity, merged unconformities, and their laterally equivalent conformable surface that can exhibit local to regional pedogenic modification, lags, and significant (meters to 10s m) paleotopographic relief. The genetically related sedimentary packages typically bounded by like or higher-rank surfaces are defined as laminae, laminasets, bed, bedsets, and simple, composite, complex, and amalgamated units. Field relationships of strata and surfaces are key to reconstructing the interactions between eolian and non-eolian deposits and the processes they represent at the local, regional, and basin scale. This classification scheme can be applied to erg-system strata to fully integrate changes in diverse facies within and between contiguous deposits.
... Dry aeolian systems are a class of depositional environment in which the water table (or its capillary fringe) does not influence the construction and accumulation of dune and interdune deposits (Kocurek and Havholm, 1993). In this system type, high sediment availability favours the construction of large dunes and/ or draas (megadunes), reducing the interdune flats to restricted topographic depressions (Kocurek et al., 1992;Langford et al., 2008). Dry interdune deposits are largely eroded during dune migration due to an (e.g., water or vegetation). ...
... 30°) between the palaeocurrent of dunes cross-strata and the superimposition surface dip-azimuths supports this hypothesis, as proposed by the models for bedform reconstruction developed by Rubin and Hunter (1983). The variable thickness of the superimposed sets suggests an unstable climb angle for dunes of different sizes and morphologies during episodes of draa construction and migration (Dias and Scherer, 2008;Langford et al., 2008). This architectural framework shows similarities in relation to the depositional architecture originated by migration of compound transverse draa, such as proposed by computer simulations made by Rubin and Carter (2006, their Fig. ...
... Compound cross-bedded sets are also common in this succession. The architectural arrangement indicates the development of dry interdunes and transverse dunes fields with well-developed slipfaces, including draa-scale bedforms (e.g., Paim and Scherer, 2007;Langford et al., 2008). The regular spacing of dry-interdune deposits in this succession reveals the development of large and interconnected interdune corridors between the bedforms (cf., Jones et al., 2016). ...
It is currently not known whether the construction and accumulation of Precambrian aeolian interdunes occurred in the same way as for their Phanerozoic counterparts. To investigate this, a Mesoproterozoic aeolian succession, the Galho do Miguel Formation (SE Brazil), was studied using facies and architectural-element analyses. The sedimentary succession comprises deposits of simple dunes, draas (megadunes), and dry and wet interdunes. Dry and wet aeolian sub-environments were coeval and their development was likely controlled by local topographic relief that governed a hybrid dry-wet aeolian system. The dry sub-environment was composed of interconnected interdune corridors between large and well-developed bedforms (simple dunes and draas). The water table did not influence the construction of climbing dunes and dry interdunes, but this was fundamental for long-term aeolian accumulation. Due to the proximity of the water table to the depositional surface, the dry interdune flats were eroded only up to the groundwater level, where the wetness inhibited sand removal during dune migration. This condition enabled the accumulation of thick packages of dry interdune deposits (up to 3 m thick). The wet sub-environment is represented by extensive interdune flats, non-climbing dunes, and a continuously near-surface water table. In this context, the interdune deposits underwent only minimal reworking associated with dune migration. This setting allowed the progressive rise of the interdune substrate and the amalgamation of interdune deposits of different generations, thereby producing thick wet-interdune stratal packages (up to 8 m thick). The accumulation of thick packages of interdune strata in both sub-environments was generated by: (i) high rates of vertical accumulation of the interdune substrate due to high rates of sediment input for aeolian construction in Precambrian systems, and (ii) progressive relative rise of the water table. These conditions enabled the long-term accumulation and successive preservation of Precambrian aeolian systems, in which the stabilising effects of vegetation did not operate. Therefore, the aeolian architecture of the Galho do Miguel Formation suggests that: (i) Precambrian aeolian systems probably produced thicker dry and wet interdune deposits than their Phanerozoic counterparts, and (ii) hybrid dry-wet aeolian systems likely provided the most favourable conditions for long-term accumulation and successive preservation of these types of deposit in the Proterozoic.
... Due to the absence of geometries that can suggest higher morphological complexity, this architectural framework is related to a compound transverse draa . Similar features and interpretation have been described by in the Etjo Sandstone Formation and by and Langford et al. (2008) in Cedar Mesa Sandstone. The intersection line of two planes (the mean foresets plane of the superimposed small dunes and the plane of the superimposition surface) indicates that the trend of the sand drift direction ) presents values towards a 063º azimuth. ...
... 1.5 m) of simple and compound crossstrata sets suggests unvaried and low-to-moderate climbing angle, which implies high rates of bedform migration. These conditions, associated with the high sinuosity of bedforms, propose a sedimentation from a sand-saturated wind, which restricted interdune areas to small and isolated corridors along to the draa system ( Fig. 17A) (Kocurek, 1981b;Porter, 1986;Langford, et al., 2008). Due to these processes, the accumulation space is completely covered by dune/draa bedforms and small interdune corridors, which tend to be completely eroded by aeolian activity (Mountney, 2006a. ...
... indicating periods of negative dune climb and draa system retraction. In dry aeolian systems, scour features can be associated with periods of partial erg destruction (dune cannibalisation) due to changes in wind saturation, which generate shallow depressions inside the draa system Mountney, 2006a;Langford et al., 2008). The presence of erosional surfaces with small steps and concave-up depressions suggests that the limit of substrate cannibalisation was defined by the position of the water table (Fig. 16D) Mountney, 2006a;Kocurek and Day, 2018). ...
Sistemas eólicos são abundantes no registro geológico após 1.8 Ga e, apesar da aplicação dos modelos atualísticos para os estudos desses sistemas, as condições sedimentares que os controlavam na Terra Proterozoica foram diferentes em comparação ao Fanerozoico. Portanto, é razoável supor que os padrões de construção, acumulação e preservação eólica entre esses Éons também tenham sido distintos. A presente Tese de Doutorado oferece um estudo acerca da dinâmica eólica presente no Mesoproterozoico a partir da análise sedimentológica e arquitetural da Formação Galho do Miguel (Supergrupo Espinhaço, 1.2-1.0 Ga), unidade de natureza eólica depositada sobre o Cráton do São Francisco. Durante o processo de construção, os depósitos demonstraram um sistema composto por um alto suprimento sedimentar e pelo amplo desenvolvimento de dunas sobrepostas (draas). O sistema estudado é caracterizado por uma grande variedade de morfologias e tamanhos de formas de leito, que contrastam com a maioria das reconstruções paleoambientais em exemplos correlatos. Esse contraste se justifica pela ação coeva entre o lençol freático e a subsidência na preservação do substrato acumulado, previamente depositados em condições secas. Contudo, as características genéticas observadas propõem que a presença de um lençol freático próximo à superfície foi fundamental para a preservação eólica, principalmente em áreas topograficamente elevadas. Os sistemas eólicos úmidos nesta sucessão são interpretados como o produto de taxas contínuas e proporcionais entre a elevação do lençol freático e o suprimento de areia ao longo do tempo. Nesse contexto, a ausência de depósitos fluviais e grandes superfícies erosivas indicam que os depósitos se originaram em condições áridas/semiáridas e em uma contínua taxa de acumulação. Logo, é possível que as mudanças climáticas nem sempre sejam o principal fator de controle sobre a posição do lençol freático em sistemas eólicos úmidos antigos. Caso contrário, os sedimentos acumulados seriam retrabalhados pelo desenvolvimento das planícies fluviais. Estas características levam a considerar que um lençol freático alto durante o avanço das dunas é atribuído a um ambiente costeiro, cujo aumento da continentalidade é acompanhado pelo desenvolvimento de campos de dunas mais secas. A Formação Galho do Miguel representa um extenso erg costeiro desenvolvido em condições híbridas (secas e úmidas). A presença de água desempenhou um papel duplo e ambíguo nesses sistemas que, por um lado, acumulou e preservou os depósitos eólicos e, por outro, limitou sua construção. Esta dualidade justifica (i) uma sucessão eólica seca com uma espessura incomum (~ 1000 m), (ii) os diferentes estilos de acumulação lateralmente coeva e (iii) a grande complexidade arquitetural dos depósitos preservados. Em contrapartida, em um cenário de baixa influência do lençol freático sobre as paleosuperfícies deposicionais, os sistemas eólicos possuíam um baixo potencial de preservação, uma vez que a ausência de agentes fixadores (cobertura vegetal) não proporcionaria a retenção dos sedimentos acumulados na bacia.
... Multiple episodes of dune-field construction, accumulation and stabilization can lead to the generation of complex stratigraphic sequences, whereby stabilized relic topography acts to control local geomorphic accommodation space by encouraging later episodes of accumulation to preferentially infill topographic interdune depressions left by older, stabilized sequences. Quaternary examples include parts of the Sahara (Kocurek et al., 1991;Swezey, 2001;Swezey et al., 1999), whereas part of the Permian Cedar Mesa Sandstone represents an example from the ancient geologic record (Langford et al., 2008). ...
Eolian strata include wind ripple lamination, airfall lamination, eolian plane-bed laminae as well as grainflow (avalanche) cross-strata. These small-scale sedimentary structures and their bounding surfaces can be used to reconstruct original dune morphology and style of accumulation. Dunes respond rapidly to changes in wind conditions and the resulting changes in dune morphology are represented by bounding surfaces that are common in eolian sandstones. Using theses sedimentary structures it is possible to reconstruct wind directions and with measurements from regional outcrops global circulation patterns. The preservation of eolian strata within sedimentary systems in a sequence stratigraphic framework is discussed.
... Due to the absence of geometries that can suggest higher morphological complexity, this architectural framework is related to a compound transverse draa (McKee, 1979). Similar features and interpretation have been described by Mountney et al. (1999) in the Etjo Sandstone Formation and by Mountney and Jagger (2004) and Langford et al. (2008) in Cedar Mesa Sandstone. The intersection line of two planes (the mean foresets plane of the superimposed small dunes and the plane of the superimposition surface) indicates that the trend of the sand drift direction (Havholm and Kocurek, 1988) presents values towards a 063°azimuth. ...
... 1.5 m) of simple and compound cross-strata sets suggests unvaried and low-to-moderate climbing angle, which implies high rates of bedform migration. These conditions, associated with the high sinuosity of bedforms, propose a sedimentation from a sand-saturated wind, which restricted interdune areas to small and isolated corridors along to the draa system (Fig. 17A) (Kocurek, 1981b;Porter, 1986;Chakraborty, 1991;Langford et al., 2008). Due to these processes, the accumulation space is completely covered by dune/draa bedforms and small interdune corridors, which tend to be completely eroded by aeolian activity (Mountney, 2006a(Mountney, , 2012. ...
... Accumulation rates during the second depositional stage were unsteady, as suggested by the common presence of scour surfaces at the bottom of a few compound sets (Fig. 16C), indicating periods of negative dune climb and draa system retraction. In dry aeolian systems, scour features can be associated with periods of partial erg destruction (dune cannibalisation) due to changes in wind saturation, which generate shallow depressions inside the draa system (Mountney et al., 1999;Mountney, 2006a;Langford et al., 2008). The presence of erosional surfaces with small steps and concave-up depressions suggests that the limit of substrate cannibalisation was defined by the position of the water table (Fig. 16D) (Mountney and Thompson, 2002;Mountney, 2006a;Kocurek and Day, 2018). ...
Proterozoic aeolian successions tend to exhibit a low complexity in the architectural organisation, generally related to simple dunes with low morphological diversity. Although most palaeoenvironmental reconstructions of ancient ergs confirm this scenario, the general conditions in the Precambrian landmass should have allowed the construction of larger and more complex sedimentary aeolian systems than those recorded in the Phanerozoic successions. To address this paradigm, the present work proposes to discuss the development and morphodynamics of ancient draa-scale bedforms and to understand which controlling factors produced the apparent absence of draa architecture in the Precambrian sedimentary record. For this purpose, this study examines an interval of c. 80 m of the Galho do Miguel Formation, which is a Mesoproterozoic aeolian succession composed of metasandstones showing well-preserved primary sedimentary structures and geometries with excellent vertical and horizontal exposures. A detailed sedimentological analysis allowed the recognition of six main architectural elements: (i) simple transverse dune, (ii) simple linear dune; (iii) compound transverse draa; (iv) complex linear draa, (v) dry interdune and (vi) sand sheet. The lateral and vertical relationships between these architectural elements support the evidence of coeval spatial coexistence of distinct aeolian morphologies (transverse and linear bedforms), probably controlled by lateral variations in sand saturation and in circulation pattern of the palaeowind. The stratigraphic organisation indicates different intervals of draa construction and destruction, which appear to be associated with different sedimentary pulses. The intervals of draa construction represent the vertical succession between simple and compound dunes of similar morphologies, representing temporal variation in sedimentary availability and changes in angle of dune climbing. The erosional and irregular surface at the bottom of compound sets of cross-strata can represent periods of irregular accumulation, associated with partial draa destruction (dune cannibalisation), probably due to seasonal variations in sedimentary availability throughout construction stages. Evidence of a near-surface water table level, as small wave ripples, indicates that the position of the water table was directly linked to the sedimentation pattern throughout these intervals. This relationship implies that ground water was the main controlling factor on sand availability and wind saturation during aeolian morphodynamics, as well as on accumulation and preservation processes. Moreover, in conditions of high rates of subsidence, the thickness accumulated and preserved via water table fluctuation is incorporated in the sedimentary record; otherwise, these deposits would have eroded due to aeolian deflation or fluvial reworking. Apparently, the absence of large and complex aeolian systems in the Precambrian record can be related to the absence of continuous near-surface water table during the draa development, directly decreasing their preservation potential.
... Thus, the observed barchan dune height and migration velocity have decreased simultaneously during the recent decades (Text S3 and Figure S2), which can exclusively be explained by decreasing wind-driven sand transport (Figure 4). Although the underlying topography can cause spatial changes in dune height and volume through its influence on surface winds (Iversen and Rasmussen, 1999) and sediment availability (Langford et al., 2008), it cannot explain lowering of the dune height over the time in our study area. These evidences support that main controlling factor to affect the dune height in the Mu Us Desert is the decreasing wind velocity, not sediment availability and underlying topography. ...
The evolution of barchan‐to‐parabolic dunes can be driven by vegetation establishment, which may be linked to climate change and/or human activity. However, little is known of the impact of changes in wind strength on vegetation development and the resulting impacts on the evolution of dune morphology and sedimentological characteristics. To address this issue, we studied the morphology and grain‐size characteristics of barchan, barchan‐to‐parabolic and parabolic dunes in the Mu Us Desert in North China, which was combined with an analysis of changes in normalized difference vegetation index (NDVI) and climatic variables during 1982‐2018. The results reveal a trend of increasing growing‐season NDVI which was related to a significant decrease in drift potential (DP). Therefore, we suggest that the initiation of dune transformation was caused by the reduced wind strength which favored the establishment and development of vegetation. To reveal the response of sedimentological reorganization during the processes of dune transformation, grain‐size characteristics along the longitudinal profile of the three different types of dunes were examined. The decreasing wind strength led to the transport of fine sands on the upper part of the windward face of the dunes, resulting in a progressive coarsening of the grain‐size distribution (GSD) and a reduction in dune height at the crest area. No distinct trend in sorting and mean grain‐size was observed on the windward slope of the barchan‐to‐parabolic dune, indicating that the sand in transit had little influence on the GSD. Conversely, progressive sorting and coarsening of the sand occurred towards the crest of the parabolic dune. This indicates that vegetation development limited the transport of sand from upwind of the dune, and affected a shift in the dune source material to the underlying source deposits, or to reworked pre‐existing aeolian deposits, and resulted in the trapping of sand in the crest area.
... Interdunal pond deposits have been previously described by Stanesco & Campbell (1989), Duncan (2006), and Langford et al., (2008); however, Massad (2013) rejects this interpretation due to the lateral extent (up to 4 km) of the lacustrine facies. The lack of microfossils and fossil fragments, a smooth upper and lower surface compared to the rough surface seen in pond deposits, and the lack of confinement to interdune areas form the basis of this facies interpretation (Massad, 2013). ...
... Freshwater to brackish interdunal pond deposits fed by streams entering the dune field have been described by Stanesco & Campbell (1989), Duncan (2006), and Pettigrew, R.P. (October 2019) Sedimentological characterisation of continental sabkhas: an example from the cedar mesa sandstone of the Paradox Basin, Utah, USA Langford et al., (2008). These deposits occur as randomly-distributed lenses of limestone, chert and sandstone, with a thin thickness (0.30-0.60 m).They have irregular upper and lower contacts and a distinct rough and bumpy appearance (Massad, 2013), also showing ostracod microfacies, dolomite cementation and intense rooting at the margins. ...
Continental sabkhas are present within many arid sedimentary basins, however they are often overlooked compared to coeval aeolian and fluvial deposits, despite their potential to record and preserve sedimentary signatures relating to basin formation and fill.
The relationships between evaporitic sabkha deposits and genetically-related coeval clastic sediments are strongly influenced by complex processes between autocyclic and allocyclic controls, including climate, however within arid continental settings these signatures are often difficult to detect within the preserved sediments.
This thesis presents results from the margin of the Cedar Mesa erg of the Paradox Basin, Utah, USA, which preserves complex interactions of clastic and evaporitic sediments. Studies are based upon extensive regional fieldwork examining the sedimentology, geometries, and interactions, complemented with outcrop gamma ray data and microfacies analysis. The sedimentology shows large variations spatially and temporally which grade through aeolian, sabkha and lacustrine settings with complex interactions occurring where these sediments transition.
This work details the facies present in a continental sabkha allowing for identification and interpretation of these complex interbedded relationships over a regional scale. The results have been developed into idealised models and recognisable log signatures which characterise and assess their impact on reservoir quality. Cyclic climatic trends, on various orders of magnitude, have been identified in relation to distinct spatial facies changes. Identification of these allows for basin-wide correlation and prediction of where facies will occur in space and time.
... Thicknesses of bounding zones remains relatively constant, and no apparent microtopography on the basal surface of the bounding zones was observed. Additionally, the bounding zones do not show a bimodal grain-size distribution (Fig. 6A) observed in some interdraa deposits (Clemmensen, 1989;Langford et al., 2008). These observations bolster the interpretation that the bounding zones in the study area are SBZ, rather than first-order surfaces. ...
Ancient eolian deposits are effective records of environmental conditions and commonly exhibit cyclicity. Accordingly, these deposits can reveal information that allows assessment of the earth system drivers controlling that cyclicity. Here, we assess those drivers in the lower Permian Ingleside Formation exposed near Manitou Springs, Colorado. The unit is characterized by two major eolian depositional intervals, exposed as topographic ridges, and punctuated by alluvial facies, exposed as a valley between the two ridges. Eolian facies are moderately sorted, sub-rounded, fine-grained, sub-arkosic sandstone. Sets of cross strata are up to 10.5 meters thick, and foresets exhibit internal laminae. Eolian cosets are regularly truncated by parallel to sub-parallel bounding zones composed of laterally continuous massive to planar laminated muddy sandstone. Rhizoliths are locally present in these zones. Thin section petrography demonstrates that clay and carbonate cement are abundant in these zones when compared to eolian cosets. Bounding zone thicknesses range from surfaces (with no thickness) to 1.7 m. The bounding zones cut across all other surfaces within the eolian stratigraphy, and are inferred to be super bounding zones (SBZ). Based on similar relationships to interior erg deposits of the coeval Cedar Mesa Sandstone and in the context of late Paleozoic glacioeustasy, we propose the following model for creation of the SBZ. Dry eolian dunes mobilized and climbed during regression when abundant sand was available. During transgression, the encroaching shoreline trapped sediment resulting in deflation due to the loss of sediment flux. Relative sea level rise also raised the water table and when deflation reached a depth near the capillary fringe of the water table, the deflationary surface stabilized resulting in the SBZ. Three levels of cyclicity are observed in the Ingleside Formation that are inferred to reflect changes in local and global paleoenvironmental conditions. The first is the long-term gradation from the predominantly fluvial upper part of the Fountain Formation to the predominantly eolian Ingleside Formation. This trend is inferred to be the result of long-term aridification of the Pangaean interior. The second scale of cyclicity is denoted by punctuation of the two eolian ridges by alluvial facies comprising the intervening valley. We propose that this dry—wet—dry environmental change is driven by relative global ice volume during the early Permian. Higher volumes of global ice, occurring as Gondwanan ice sheets, appear to correlate to the eolian intervals, whereas, the alluvial interval may be coeval with feckless or complete loss of Gondwanan ice sheets. The third scale of cyclicity is indicated by the SBZ-coset couplets and is inferred to be the result of glacioeustatic variations in sea level resulting from the waxing and waning of relatively large Gondwanan ice sheets.
... However, there are several alternative mechanisms for the accumulation and preservation of sets of aeolian strata of the type observed in the Auk Formation, including the infilling of localised accommodation space present between existing bedforms (e.g. Langford et al., 2008;Luzón et al., 2012), accumulation around relic aeolian topography (e.g. Fryberger, 1986), and exceptional bedform preservation following rapid inundation by water or other fluids (e.g. ...
A series of well logs and cores penetrating the predominantly aeolian Auk Formation, Permian Rotliegend Group, Central North Sea, UK, have been evaluated to determine the morphology and style of migratory behaviour of the original dune bedforms, the overall depositional environment, and to assess implications for reservoir heterogeneity. This has been achieved by detailed facies analysis of subsurface datasets and by comparison of the observed sedimentary styles of accumulation to analogous modern aeolian dune fields. Aeolian bedform type, morphology, detailed migratory behaviour, and the nature of the accumulation surface have been interpreted. Analysis of the facies architecture of preserved cross-bedded sets and cosets indicates accumulation on a dry substrate via the migration and climb of large linear bedforms that possessed low-angle inclined lower plinths, up to 15 m thick. Dune plinth elements are dominated by wind-ripple and reworked wind-ripple strata, and were preferentially preserved as successive bedforms migrated over one another at low angles. Packages of grainflow-dominated strata representative of accumulation on the higher part of the bedform lee slope are less common and tend to be preserved mostly in the upper parts of large cosets of strata (∼30 m thick). Large linear bedforms were separated by dry interdune areas. Although the primary direction of sand transport was along the elongated crests of the bedforms, a secondary component of transverse motion enabled the lateral migration and preferential preservation of lee-slope deposits that arose from a minor oblique component of bedform migration. In places, the architecture records the preservation of small barchanoid dune deposits, either within interdune depressions or superimposed on the lower flanks of the large linear bedforms. The preserved aeolian facies types exert a primary control on reservoir quality. Few previous studies have documented linear dunes in ancient successions; these findings represent a valuable case example.
