Morphometric analysis of slipface processes of an aeolian dune: Implications for grain‐flow dynamics

Cornwall, C.; Jackson, Derek W.T.; Bourke, M. C.; Cooper, J. Andrew G.

doi:10.1111/sed.12456

Cited by 16 publications

(29 citation statements)

References 39 publications

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“…5B). Although the relationship between grainflow deposit thickness and dune height may be modified by factors, especially wind speed (McDonald and Anderson 1995;Nickling et al 2002;Nield et al 2017;Cornwall et al 2018), these consistently thin grainflow strata are characteristic of small dunes. Moreover, the common presence of grainfall deposits between grainflow strata indicates small dunes where grainfall deposits of observable thickness extended to the base of the set (Hunter 1977;Kocurek and Dott 1981).…”

Section: Cross-strata Interpretationmentioning

confidence: 99%

Preservation of autogenic processes and allogenic forcings within set-scale aeolian architecture II: the scour-and-fill dominated Jurassic Page Sandstone, Arizona, USA

Cardenas¹,

Kocurek²,

Mohrig³

et al. 2018

Preprint

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The stratigraphic architecture of aeolian sandstones is thought to record signals originating from both autogenic dune behavior and allogenic environmental boundary conditions within which the dune field evolves. Mapping of outcrop-scale surfaces and sets of cross-strata between these surfaces for the Jurassic Page Sandstone near Page, Arizona, USA, demonstrates that the stratigraphic signature of autogenic behavior is captured by variable scour depths and subsequent fillings, whereas the dominant signatures of allogenic boundary conditions are associated with antecedent surface topography and variable water-table elevations. At the study area, the Page Sandstone is ~ 60 m thick and is separated from the underlying Navajo Sandstone by the J-2 regional unconformity with meters of relief. Thin, climbing sets of cross-strata of the basal Page representing early dune-field accumulations fill J-2 depressions. In contrast, the overlying lower and middle Page consist of cross-strata that are one to a few meters thick, and packaged between outcrop-scale bounding surfaces. These bounding surfaces have been previously correlated to high stand deposits of the adjacent Carmel sea and at this site possess meters of erosional relief produced by dune scour. Notably absent within packages of cross-strata bounded by these outcrop-scale surfaces are strata of early dune-field accumulations, any interdune deposits, and climbing-dune strata. Instead, these packages preserve a scour-and-fill architecture created by large migrating dunes migrating within a dry, mature, dune field undergoing negligible bed aggradation. Any record of early phases of dune-field construction for the lower and middle Page are interpreted to have been cannibalized by the deepest scours of later, large dunes. Interpretations are independently supported by the relatively large coefficients of variation in lower and middle Page set thicknesses, which are consistent with set production by successive deepest trough scours, and the relatively low coefficient of variation for the depression-filling basal Page sets consistent with a significant component of bed aggradation. Numerical modeling presented here and more completely in the companion paper demonstrates how this cannibalization of early-phase stratigraphy is an expected outcome of autogenic dune-growth processes, and that early-phase strata can be preserved within antecedent depressions. Relative rise of the inland water table from basin subsidence and Carmel sea level forced preservation of multiple stacked packages composed of scour-and-fill architecture. Without these allogenic forcings, the Page would be little more than an erosional surface.

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Section: Cross-strata Interpretationmentioning

confidence: 99%

Preservation of autogenic processes and allogenic forcings within set-scale aeolian architecture II: the scour-and-fill dominated Jurassic Page Sandstone, Arizona, USA

Cardenas¹,

Kocurek²,

Mohrig³

et al. 2018

Preprint

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“…The migration of stoss ripples may prolong grainflow beyond the spring and autumn seasons by creating localized over steepening on the slipface from sediment deposition. However, without grainfall, this mechanism for grainflow is likely short‐lived until higher magnitude winds can generate grainfall or redistribute sediment, restoring the slipface (e.g., Allen, ; Anderson, ; Bagnold, ; Cornwall, Jackson, et al, ; Hunter, ; Hunter, ; Kok et al, ; McDonald & Anderson, ). Some of the grainflows imaged by Curiosity during late autumn (Bridges et al, ), may be a product of such activity.…”

Section: Discussionmentioning

confidence: 99%

“…Curiosity Rover provided the first in situ observations and sediment analysis of Martian dunes while traversing the Bagnold Dune Field toward Aeolis Mons in Gale Crater (Figure S1). Images taken by Curiosity of the Namib dune slipface revealed a detailed record of grainflows, ripple formation, and tensional cracks (Cornwall, Bourke, et al, ; Ewing et al, ), similar to terrestrial dunes (Cornwall, Jackson, et al, ). The Bagnold dune field is active (Silvestro et al, ) but Curiosity visited the dunes during late autumn, a time of decreased eolian activity with little sediment movement (Bridges et al, ).…”

Section: Introductionmentioning

confidence: 99%

Seasonal Variations in Airflow Over the Namib Dune, Gale Crater, Mars: Implications for Dune Dynamics

Cornwall

Jackson

Bourke

et al. 2018

Geophysical Research Letters

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Dune length scale airflow modeling provides new insights on eolian bedform response and complex near-surface 3-D wind patterns not previously resolved by mesoscale models. At a 1-m surface resolution, Curiosity wind data are used to investigate the eolian environment of the Namib dune on Mars, providing improved seasonal constraints on grainfall, grainflow activity, and ripple migration. Based on satellite images, airflow patterns, and surface shear stress, enhanced eolian activity, and slipface advancement occurs during early springtime. Autumn and winter winds are also favorable to eolian activity, but minimal movement was detected in satellite images overlapping with wind data. During the summer, the migration of large stoss ripples on the Namib dune may augment sediment deposition on the slipface. These results provide a better understanding of the overall migration pattern of the Namib dune, which can be extrapolated to other dunes in the Bagnold Dune Field.Plain Language Summary At 1-m resolution, small-scale airflow modeling can provide new insights into sediment transport and dune migration on Mars. Coupled with wind data collected by the Curiosity rover, this study provides improved, realistic constraints on Martian sediment movement and illustrates how ripples seasonally form and migrate according to changing wind speeds and directions. The spring season with northerly winds is the most influential for dune migration based on modeling results and satellite monitoring, but the quieter summer and autumn seasons with southeasterly winds continue to facilitate ripple migration, which may help maintain slower rates of dune migration despite the opposing wind direction. Based on modeling results, the winter season with high-magnitude northerly winds should produce migration rates similar to spring, but according to satellite monitoring, dune migration stops. Small amounts of frost in between sand grains on the dune surface may be responsible for this halt in dune migration. These results can be applied to other dunes in the Bagnold Dune Field, which likely experience the same seasonal patterns in sediment transport.

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“…Modern aeolian grainflows typically exhibit a narrow, 'tongue-like' shape (Hunter, 1977;Sweet et al, 1988;Sweet, 1992;McDonald & Anderson, 1996;Pye & Tsoar, 2009), dip at angles near the angle of repose, and pinch out sharply at their bases (Hunter, 1977). Even though the tongueshaped morphology is common, Cornwall et al (2018) described relatively rare occurrences of 'slab' flows which may exhibit a wider lateral extent. The high dip angles and sharp 'pinch outs' are intrinsically linked to the gravity-driven nature of the grainflow process; Lowe (1976) suggested that grainflows 'freeze' on slopes below the angle of repose, and so their deposits should not be expected to extend into low-angle bottomsets.…”

Section: Sedimentological Criteria For Distinguishing Dune Stratificamentioning

confidence: 99%

Characterization of hard‐to‐differentiate dune stratification types in the Permian Coconino Sandstone (Arizona, USA)

2020

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Dune stratification types, which include grainfall, grainflow and ripple lamination, provide a record of the fine-scale processes that deposited sediment on palaeo-dune foresets. While these facies are relatively easy to distinguish in some cross-bedded sandstones, for otherslike the Permian Coconino Sandstone of northern and central Arizonadiscrete stratification styles are hard to recognize at the bedding scale. Furthermore, few attempts have been made to classify fine-scale processes in this sandstone, despite its renown as a classic aeolian dune deposit and Grand Canyon formation. To interpret depositional processes in the Coconino Sandstone, cross-bed facies were characterized using a suite of sedimentary textures and structures. Bedding parameters were described at multiple scales via a combination of field and laboratory methods, including annotated outcrop photomosaics, strike and dip measurements, sandstone disaggregation and laser-diffraction particle analysis, high-resolution scans of thin sections, and scanning electron microscopy. Cross-beds were observed to be laterally extensive along-strike, with most dip angles ranging from the mid-teens to mid-twenties. While some cross-bed sets are statistically coarser near their bases, others exhibit no significant vertical sorting trends. Both massive and laminated textures are visible in high-resolution scans of thin sections, but laminae contacts are commonly indistinct, making normal and reverse grading difficult to define. Diagenetic features, such as stylolite seams and large pores, are also present in some samples and might indicate alteration of original textures like detrital clay laminae and carbonate minerals. Observed textures and sedimentary structures suggest that the cross-beds may consist of grainflow and grainfall deposits, but these remain difficult to differentiate at outcrop and thin-section scales. This characterization of fine-scale processes will play a critical part in the development of depositional models for the Coconino Sandstone and elucidate interpretations for similar cross-bedded formations.

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Morphometric analysis of slipface processes of an aeolian dune: Implications for grain‐flow dynamics

Cited by 16 publications

References 39 publications

Preservation of autogenic processes and allogenic forcings within set-scale aeolian architecture II: the scour-and-fill dominated Jurassic Page Sandstone, Arizona, USA

Preservation of autogenic processes and allogenic forcings within set-scale aeolian architecture II: the scour-and-fill dominated Jurassic Page Sandstone, Arizona, USA

Seasonal Variations in Airflow Over the Namib Dune, Gale Crater, Mars: Implications for Dune Dynamics

Characterization of hard‐to‐differentiate dune stratification types in the Permian Coconino Sandstone (Arizona, USA)

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