Article

An example of liquefaction-induced interdune sedimentation from the early Jurassic Navajo Sandstone, USA

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  • Bryant Laboratories
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Abstract

Extensive outcrops of Navajo Sandstone in the southwestern United States expose eolian dune deposits that are subdivided in a complex array of foresets and bounding surfaces. In the Glen Canyon region, and other places, this architecture is frequently disrupted by large-scale, soft-sediment deformation features. These features have been attributed to episodic liquefaction events that affected saturated sand below the level of the interdune surface. Though erosional truncation of deformation features indicates that liquefaction often occurred in the uppermost levels of Navajo dune deposits, very few paleotopographic disruptions due to subsurface deformation have been documented.

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... Within Jurassic eolian deposits of the Colorado Plateau, including the Navajo Sandstone, many studies attributed SSD clastic pipes and contorted crossbedding to possible strong ground motion by earthquakes (Netoff and Shroba 2001;Netoff 2002;Huuse et al. 2005;Chan et al. 2007Chan et al. , 2019Bryant and Miall 2010;Hurst et al. 2011;Bryant et al. 2013Bryant et al. , 2016Loope et al. 2013;Ford 2015;Wheatley et al. 2016;Wheatley and Chan 2018). Other studies discuss conditions of dewatering in the groundwater system (Parrish and Falcon-Lang 2007), lake flooding (Eisenberg 2003), marine transgressions (Doe and Dott 1980), and monsoonal climates (Loope et al. 2001(Loope et al. , 2004. ...
... Although the thin eastern edge has been considered the Navajo erg margin, recent work by Parrish et al. (2019a) showed that the oldest part of the basin is likely in the area near Moab, Utah, close to the eastern terminus of the Navajo Sandstone. This eastern part of the Navajo Sandstone may, therefore, represent a small erg that would have been subject to groundwater fluctuations; however, SSD is also known in the younger, thick parts of the central erg (Marzolf 1983;Bryant et al. 2013). ...
... In most of the Navajo Sandstone deposits in the Moab area, there is evidence that surface water existed as carbonate lakes and springs (Parrish et al. , 2019b. In areas in between the study area and basin center of southwest Utah, there is still abundant and remarkable contorted crossbedding in the Navajo, even where the formation is thick (e.g., Bryant and Miall 2010;Bryant et al. 2013;Ford 2015;Bryant et al. 2016). ...
Article
Extensive soft-sediment deformation (SSD) of multiple expressions and scales record active and dynamic events and processes in erg deposits of the Lower Jurassic Navajo Sandstone near Moab, Utah. The erg deposits preserve depositional environments of eolian dune, interdune, fluvial, playa, lake, and spring. A large range of SSD features, from intact beds showing little deformation to pervasively disturbed beds, exist in many of these deposits. A simplified classification index captures the different scales of SSD in ascending order of deformation intensity: 1) mostly intact bedding with small-scale wavy or undulatory deformation structures within single beds; 2) dish and flame structures; 3) meter-scale, kinked, slumped, rolled, overturned, vertical, and detached contorted crossbedding, and associated centimeter- to meter-scale pipes; and 4) disruptive diapirs and laterally extensive massive sandstone. The SSD features of deformed crossbed sets, diapirs, and massive sandstone beds, are consistently juxtaposed, and are thus genetically linked. Although the Navajo Sandstone has been considered a classic example of an extensive dry eolian system, both individual and combinations of strata bounded SSD features exemplify dynamic deformation, liquefaction, and fluidization that took place at various times after deposition. The lowest degree of deformation, SSD 1, is largely attributed to autogenic––inherent to the eolian system––or local allogenic processes. Larger degrees of deformation, SSD 2–4, were more likely produced by allogenic, external-forcing processes from regional changes in climate and/or near-surface groundwater conditions originating from the Uncompahgre uplift, with the deformation triggered by some event(s). Possible significant ground motion could have led to large-scale disruption in the Navajo sand sea across kilometer-scale intervals. The Navajo example establishes valuable hierarchical relationships of processes and products for recognizing and interpreting SSD in other ancient and modern eolian systems. This has particular relevance to sedimentary discoveries on Mars, where SSD features are visible from remote sensing imagery and rover exploration.
... Here, the water table is shallow and water ponding can occur. In the Jurassic Navajo Sandstone, sand blows have been found in interdune depressions (Bryant et al., 2013;Chan and Bruhn, 2014). Bryant et al. (2013) concluded that sand blows formed in the interdune depressions as a consequence of subsidence related to massive outflow of fluidized sand (Figure 1.14). ...
... In the Jurassic Navajo Sandstone, sand blows have been found in interdune depressions (Bryant et al., 2013;Chan and Bruhn, 2014). Bryant et al. (2013) concluded that sand blows formed in the interdune depressions as a consequence of subsidence related to massive outflow of fluidized sand (Figure 1.14). Figure 1. 14 Liquefaction flows in the interdune deposits and pond formation as a consequence (Bryant et al., 2013), permission granted from Sedimentary Geology. ...
... Bryant et al. (2013) concluded that sand blows formed in the interdune depressions as a consequence of subsidence related to massive outflow of fluidized sand (Figure 1.14). Figure 1. 14 Liquefaction flows in the interdune deposits and pond formation as a consequence (Bryant et al., 2013), permission granted from Sedimentary Geology. ...
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Thesis
Liquefaction affects late Holocene, loose packed and water saturated sediment subjected to cyclical shear stress. Liquefaction features in the geological record are important off-fault markers that inform about the occurrence of moderate to large earthquakes (> 5 Mw). The study of contemporary liquefaction features provides a better understanding of where to find past (paleo) liquefaction features, which, if identified and dated, can provide information on the occurrence, magnitude and timing of past earthquakes. This is particularly important in areas with blind active faults. The extensive liquefaction caused by the 2010-2011 Canterbury Earthquake Sequence (CES) gave the geoscience community the opportunity to study the liquefaction process in different settings (alluvial, coastal and estuarine), investigating different aspects (e.g. geospatial correlation with landforms, thresholds for peak ground acceleration, resilience of infrastructures), and to collect a wealth geospatial dataset in the broad region of the Canterbury Plains. The research presented in this dissertation examines the sedimentary architecture of two environments, the alluvial and coastal settings, affected by liquefaction during the CES. The novel aim of this study is to investigate how landform and subsurface sedimentary architecture influence liquefaction and its surface manifestation, to provide knowledge for locating studies of paleoliquefaction in future. Two study cases documented in the alluvial setting showed that liquefaction features affected a crevasse splay and point bar ridges. However, the liquefaction source layer was linked to paleochannel floor deposits below the crevasse splay in the first case, and to the point bar deposits themselves in the second case. This research documents liquefaction features in the coastal dune system of the Canterbury Plains in detail for the first time. In the coastal dune setting the liquefiable layer is near the surface. The pore water pressure is vented easily because the coastal dune soil profile is entirely composed of non-cohesive, very well sorted sandy sediment that weakly resists disturbance from fluidised sediment under pressure. As a consequence, the liquefied flow does not need to find a specific crack through which the sediment is vented at the surface; instead, the liquefied sand finds many closely spaced conduits to vent its excess of pore water pressure. Therefore, in the coastal dune setting it is rare to observe discrete dikes (as they are defined in the alluvial setting), instead A horizon delamination (splitting) and blistering (near surface sills) are more common. The differences in styles of surface venting lead to contrasts in patterns of ejecta in the two environments. Whereas the alluvial environment is characterised by coalesced sand blows forming lineations, the coastal dune environment hosts apparently randomly distributed isolated sand blows often associated with collapse features. Amongst the techniques tested for the first time to investigate liquefaction features are: 3D GPR, which improved the accuracy of the trenching even six years after the liquefaction events; thin section analysis to investigate sediment fabric, which helped to discriminate liquefied sediment from its host sediment, and modern from paleoliquefaction features; a Random Forest classification based on the CES liquefaction map, which was used to test relationships between surface manifestation of liquefaction and topographic parameters. The results from this research will be used to target new study sites for future paleoliquefaction research and thus will improve the earthquake hazard assessment across New Zealand.
... Notably, shearing within DSS is cryptic, as it follows existing primary structures in DSS. For references to similar structures, see Plaziat et al. (2006) and Bryant et al. (2013). ...
... Wind ripple deposit are finer-grained and more tightly packed than grainfall or grainflow deposits (Hunter, 1977), they are less susceptible to liquefaction and often act as boundaries to fluid flow. During deformation, they generally respond by faulting and brecciating rather than by fluid deformation (for more examples, see Bryant and Miall, 2010;Bryant et al. 2013;Bryant et al. in this volume). Since such blocks of plinth material do not appear anywhere in the deformation complex, it may be that slope failure occurred along a portion of the dune with a strongly perpendicular orientation to the prevailing wind direction, which might be expected to host a poorly developed dune plinth (Hunter, 1977). ...
... Although the material above the upper bounding surface (SDD) is clearly not affected by the gross deformation of the dune collapse process, there are small (cm scale) deformation features in these deposits that do not generally appear in Navajo dune deposits. This suggests that the slumped material continued to consolidate as subsequent dunes migrated across its surface (see comparable indications in Plaziat et al., 2006;Bryant et al., 2013). In at least one place, some source of stress has been accommodated through shearing along bedding planes in the otherwise undeformed dune (see Fig. 15). ...
Article
The Canyon Overlook Trail of Zion National Park follows an outcrop of Navajo Sandstone, which displays a uniquely well-exposed assemblage of features associated with failure of the lee face of a large eolian dune, and run-out over an expanse of interdune sediments downwind of that bedform. Exposed features include dramatic folds in the interdune succession and a stacked series of thrust sheets incorporating both interdune and overlying dune deposits. Thrust surfaces display consistent strikes, parallel to those of undeformed foresets, and incorporate zones of brittle failure and fluid deformation, including folds overturned in the direction of foreset dip. These features correspond to predictions made by a previous researcher's model of dune collapse, formulated from less fortuitously exposed architectures in the Navajo Sandstone. Unlike the previous model, however, this site preserves distinct indications that the bulk of deformed material accumulated above the level of the contemporary interdune surface, in an aggradational succession.
... Large masses of structureless sandstone are numerous in Navajo Sandstone outcrops exposed along the East Kaibab monocline in southern Utah and northern Arizona. The large percentage (by volume) of grain-flow strata in these outcrops helps to account for the abundance of structureless sandstone (Loope et al., 2012;Bryant et al., 2013): in shallow, water-saturated subsurface settings, unlithified grain flows are more easily liquefied by seismic shaking than the tighter-packed, wind-ripple deposits (Hunter, 1981). Although some of the structureless sandstone at Coyote Buttes is bioturbated (Loope and Rowe, 2003;Loope, 2006;Ekdale et al., 2007), contorted strata adjacent to and surrounding the structureless masses show that large volumes of originally stratified sand were homogenized during seismic shocks (Fig. 3;Bryant and Miall, 2010;Bryant et al., 2013). ...
... The large percentage (by volume) of grain-flow strata in these outcrops helps to account for the abundance of structureless sandstone (Loope et al., 2012;Bryant et al., 2013): in shallow, water-saturated subsurface settings, unlithified grain flows are more easily liquefied by seismic shaking than the tighter-packed, wind-ripple deposits (Hunter, 1981). Although some of the structureless sandstone at Coyote Buttes is bioturbated (Loope and Rowe, 2003;Loope, 2006;Ekdale et al., 2007), contorted strata adjacent to and surrounding the structureless masses show that large volumes of originally stratified sand were homogenized during seismic shocks (Fig. 3;Bryant and Miall, 2010;Bryant et al., 2013). Isolated, angular blocks of stratified sandstone are common within the bodies of structureless sandstone that were homogenized presumably during paleo-seismic shocks (Fig. 3B). ...
Article
Sheeting joints are ubiquitous in outcrops of the Navajo Sandstone on the west-central Colorado Plateau, USA. As in granitic terrains, these are opening- mode fractures and form parallel to land surfaces. In our study areas in south-central Utah, liquefaction during Jurassic seismic events destroyed stratification in large volumes of eolian sediment, and first-order sheeting joints are now preferentially forming in these structureless (isotropic) sandstones. Vertical cross-joints abut the land-surface-parallel sheeting joints, segmenting broad (tens of meters) rock sheets into equant, polygonal slabs ~5 m wide and 0.25 m thick. On steeper slopes, exposed polygonal slabs have domed surfaces; eroded slabs reveal an onion-like internal structure formed by 5-m-wide, second-order sheeting joints that terminate against the crossjoints, and may themselves be broken into polygons. In many structureless sandstone bodies, however, the lateral extent of first-order sheeting joints is severely limited by pre-existing, vertical tectonic joints. In this scenario, non-conjoined sheeting joints form extensive agglomerations of laterally contiguous, polygonal domes 3-6 m wide, exposing exhumed sheeting joints. These laterally confined sheeting joints are, in turn, segmented by short vertical cross-joints into numerous small (~0.5 m) polygonal rock masses. We hypothesize that the sheeting joints in the Navajo Sandstone form via contemporaneous, land-surface-parallel compressive stresses, and that vertical cross-joints that delineate polygonal masses (both large and small) form during compression-driven buckling of thin, convex-up rock slabs. Abrasion of friable sandstone during runoffevents widens vertical tectonic joints into gullies, enhancing land-surface convexity. Polygonal rock slabs described here provide a potential model for interpretation of similar-appearing patterns developed on the surface of Mars.
... The Lower Jurassic Navajo Ss (Pliensbachian-Toarcian) is well-studied owing to its extensive Several studies have examined aspects of wet SSD within the Jurassic Navajo Ss (Horowitz, 1982;Chan et al., 2007;Bryant & Miall, 2010;Bryant et al., 2013Bryant et al., , 2016Chan & Bruhn, 2014;Ford, 2015), but clastic pipes in the Navajo Ss have not been studied in detail and have had little mention in past published literature. Despite ample studies of clastic pipes in other Colorado Plateau units (see summaries in Chan et al., 2007;Hurst et al., 2011;Wheatley et al., 2016), the Navajo Ss examples of CANY show specific detailed internal pipe structures and associated ring faults that differ from most other Jurassic pipe or SSD examples. ...
... Other studies recognize similar convergence of conditions to produce pipes and spring pits in arenaceous deposits (Deynoux et al., 1990;Draganits & Janda, 2003;Draganits et al., , 2005. This combination of conditions meant that fluidized waters favoured the development of strong cylindrical features as opposed to the massive to contorted bedding types of SSD observed in elsewhere in the Navajo Ss (Bryant & Miall, 2010;Bryant et al., 2013Bryant et al., , 2016Chan & Bruhn, 2014;Ford, 2015). Many hypotheses for how individual clastic pipes might form have been published. ...
Article
Soft‐sediment deformation of contorted and massive sandstone is common throughout much of the siliciclastic record, but clastic pipes represent a distinctive class of pressurized synsedimentary features. Remarkable centimetre to metre‐scale clastic pipe exposures in the Jurassic Navajo Sandstone of Utah (USA) establish a range of pipe sizes, expressions and relationships to the host rock in an erg margin setting, traditionally thought to be just a dry desert system. In particular, the field and laboratory characterizations of cylindrical pipes show internal concentric, annular rings that imply water fluidization, with alignment of long grain axes due to shear flow along pipe margins. Central interior parts of decimetre‐scale pipes appear massive in plan view, but display weakly developed pseudobedding from post‐pressure release, gravitational settling in the cross‐sectional view. Deformation features of conjugate fractures, ring faults, hypotrochoid patterns (geometric arcs and circles) and breccia in the host material reflect both brittle and ductile behaviour in response to the fluidization and injection of the clastic pipes. The stratigraphic context of individual pipes and the stratabound intervals of pipe features imply dynamic deformation nearly coincident with deposition in this Early Jurassic aeolian system related to multiple factors of groundwater expulsion, timing and local host sediment properties that influenced pipe development. Although the pipe features might be easily overlooked as a smaller scale feature of soft‐sediment deformation in dune deposits, these are valuable environmental indications of disrupted fluid pathways within porous, reservoir quality sands, associated with periodic high water‐table conditions and significant, strong ground‐motion events. These pipe examples may be important analogues where exposures are not so clear, with applications to diverse modern and ancient clastic settings internationally on Earth as well as in planetary explorations such as Mars. This article is protected by copyright. All rights reserved.
... These studies were conducted within a research tradition that prioritized the identification of specific environmental indicators rather than the development of actualistic process/ response models, such as those that currently provide the basis for high-resolution genetic stratigraphies (Van Loon, 1987) and event interpretations. They culminated in a succinct model (Horowitz, 1982) that retains distinct value (See Ford et al., in press) and pervasive influence, even though more recent reports (Eschner and Kocurek, 1986;Netoff, 2002;Chan et al., 2007;Glennie and Hurst, 2007;Bryant and Miall, 2010;Bryant et al., 2013) have brought to light a much broader range of deformation styles in ancient eolianites than was considered during the initial phase of SSD analysis. Not only has the database of eolianite SSD expanded well beyond the reach of the Horowitz model, but a new wave of paleoclimatic interpretation (Loope et al., 2001(Loope et al., , 2004Loope and Rowe, 2003) has rendered obsolete certain paleohydrological assumptions that were incorporated into that Sedimentary Geology 344 (2016) 205-221 model. ...
... Within Navajo dune deposits, the only regular discontinuity in the homogenous lithology is the crossbedding, which dips in the preferred direction of deformation (downwind). The tendency for cryptic slippage along these surfaces, during a deformation event, has already been documented at other locations (Plaziat et al., 2006;Bryant et al., 2013;See also Ford et al., in press). ...
Article
Many workers have noted the presence of contorted cross-strata in the Navajo Sandstone and other ancient eolianites, and have recognized their significance as indicators of sediment saturation during the accumulation history. Horowitz (1982) proposed a general model for the production of such features in ancient ergs by episodic, seismically induced liquefaction of accumulated sand. A key feature of that popular model is the prevalence of a flat water table, characteristic of a hyper-arid climatic regime, during deformation. Under arid climatic conditions, the water table is established by regional flow and liquefaction is limited to the saturated regions below the level of interdune troughs. However, various paleohydrological indicators from Navajo Sandstone outcrops point toward a broader range of water table configurations during the deformation history of that eolianite.
... Por otro lado, niveles de areniscas masivas, frecuentemente acumuladas en interdunas, fueron descriptos por Kamola y Chan (1988) e interpretados como el resultado de avalanchas de arena como consecuencia de desestabilizaciones de la cara de sotavento y de la cresta de las dunas. También han sido propuestos otros orígenes como bioturbación, retrabajo de interdunas durante inundaciones fluviales, procesos de licuefacción y degradaciones de dunas por precipitaciones extremas (Herries, 1993;Sweeny y Loope 2001, Simpson et al., 2002Bryant et al., 2013). En nuestro caso, las areniscas masivas aparecen preferentemente en facies de interdunas, sugiriendo que procesos de inundaciones fluviales, asociadas a estados de freáticas altas y fuertes precipitaciones podrían ser las responsables de la falta de laminación interna en los estratos de estas areniscas. ...
... Por el otro, la infiltración de agua de lluvias o crecientes que inunda la interduna, lo que favorece la redistribución de material coloidal y arcilloso dentro de las arenas eólicas y eventualmente promueve las estructuras de disipación (microfábrica 6). No se descarta además la presencia de procesos de licuefacción generados en arenas saturadas de interdunas (Bryant, 2013) como factor generador de niveles de areniscas masivas (microfábrica 5). ...
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Article
In this paper a study of microfabrics occurring in eolian Permian sandstones of the De La Cuesta Formation (Catamarca Province, northwest Argentina) is presented (Fig. 1). The middle part of the De La Cuesta Formation comprises thick and well exposed eolian sandstones, which were deposited in an erg environment during an arid Permian phase recognized in different parts of South America (Spalletti et al., 2011, Fig. 2). Following the scheme proposed by Spalletti et al. (2011) samples were collected from the following sedimentary facies: 1) cross-bedded fine-grained sandstones interpreted as crescent dunes, 2) wedge-shaped cross-bedded sandstones corresponding to longitudinal (seif) dunes, 3) horizontal-laminated or low-angle crosslaminated sandstones, in some cases showing inverse-grading, which would have been deposited in interdune and extradune (eolian sand-sheet) areas, and 4) fine- to very fine-grained sandstones formed in dry and wet interdunes (Figs. 2 and 3). On the basis of texture (grain size, sorting and asymmetry) and microstructures, six microfabrics were recognized (Table 1). Microfabric 1 comprises grainflow-foreset laminae found in large-scale cross-bedded sandstones; this type of microfabric is composed of medium-grained sandstones (less commonly coarse-grained sandstones) with mean values between 300 μ y 460 μ (Table 1). The sandstones are unimodal, moderately well sorted and the grain size distribution is slightly asymmetric (Fig. 5); they are composed of medium-grained sand (55%), fine-grained sand (21%) and coarse-grained sand (24%). Coarse-grained silt is almost entirely absent, and the intergranular space varies from 25% to 27%. This microfabric forms inclined laminae, 3 to 5 cm thick, commonly decreasing in thickness towards the base of the set. Microfabric 2 occurs closely associated with microfabric 1 forming large-scale cross-bedded sets. It corresponds to grainfall deposits and is mainly formed by fine-grained and less frequently by very finegrained sandstones (Table 1 and Fig. 5). Microfabric 2 is mainly composed of fine-grained sand (60%), very fine-grained sand (31%), medium-grained sand (7%) and coarse-grained silt (2%). The laminae are tabular, massive and their thickness range from 0.5 to 4 cm; the intergranular space is lower than microfabric 1 (17%-20%, Table 1 and Fig. 6). Microfabric 3 is made up by laminae of inverse graded sandstones, whose thickness vary from 10 mm to 30 mm, being the intergranular space between 10% and 15% (Figs. 5, 6 and 8). The particle size distributions are unimodal, moderately sorted with mean values in medium-grained sand (250 μ y 300 μ, Fig. 5). In almost all cases, the medium-grained sand prevails (42%), followed by fine-grained sand (38%), coarse-grained sand (13%) and very fine-grained sand (6%); coarse-grained silt is below 1% (Table 1, Fig. 6). This microfabric is interpreted as originated by the migration of eolian ripples that carried an appreciable amount of coarse- and medium-grained sand transported by creeping. Microfabric 4 is characterized by fine-grained unimodal, moderately well sorted sandstones with a slightly asymmetric distribution (Figs 5, 6 and 9). The average grain-size distribution is: fine-grained sand (50%), very fine-grained sand (28%), mediumgrained sand (20%) and coarse-grained sand (1.5%); the percentage of coarse-grained silt ranges from 1% to 8% (Table 1). Microfabric 4 is quite similar to microfabric 3, but it differs in the lack of graded lamination and in a higher proportion of fine-grained sand. As in the case of microfabric 3, this microfabric was probably formed by the migration of eolian ripples, but lacking enough amount of coarse- and medium-grained sand to promote graded structures. Massive very fine-grained and fine-grained sandstones showing adhesion ripples, bioturbation and centimeter-scale deformational structures, correspond to the microfabric 5. This microfabric dominates in dry interdune and extradune deposits. Sandstones are characterized by abundant carbonate (calcite) cement and high intergranular space (28%-30%). The particle size distribution is unimodal, moderately sorted, and dominated by very finegrained sand (44%) and fine-grained sand (39%), followed by discrete proportions of medium-grained sand (9%) and coarse-grained silt (7%); in all cases the amount of coarse-grained sand is lower than 1% (Table 1 and Fig. 6). Microfabric 6 exhibits the smallest grain-sizes and predominates in wet interdune and extradune deposits. It consists of well sorted, very fine-grained sand (media between 95 and 80 μ). The dominant very fine-grained sand population (72%) is accompanied by coarse-grained silt (17%) and fine-grained sand (10%, Table 1 and Fig. 6). The beds are massive, horizontally laminated or exhibit wavy lamination originated by post-depositional compaction. The mentioned microfabrics appear not randomly distributed, but they form specific associations among the different types of the dune, interdune and extradune deposits (Fig. 10). In the case of dune sandstones, the foresets of large-scale crossbedded units are mainly composed of alternated laminae of microfabrics 1 and 2, which represent the alternation of grainflow and grainfall processes. Less frequently, foresets comprise microfabrics 3 and 4, suggesting the development of lamination produced by migration of ripples on leeward side of dunes. A particular type of dune cross-bedded sets result from the stacking of laminae formed by microfabric 2, pointing out that grainfall of fine- and very fine-grained sand occurs without grainflow events or significant migration of ripples. In such circumstances, cross-laminated sets form pinstripe lamination, suggesting the development of lowangle leeward dune faces. Dry interdunes are chiefly composed of microfabrics 3 and 4, which show that ripple migration is the main mechanism of transport and deposition in this setting; scarce intercalations of microfabric 5 are interpreted as remobilized sand accumulations related to deflation and/or fluvial floods in interdune areas (Fig. 10). Deposits of wet interdunes comprise microfabrics 5 and 6 with minor contributions of microfabrics 3 and 4. Extradunes are formed by thick intervals (tens of meters) of horizontal laminated or low-angle crosslaminated sandstones. In these deposits microfabric analysis allows discriminating between dry and wet extradunes, since the former are characterized by microfabrics 3 and 4, whereas the second are essentially composed of microfabrics 5 and 6. Microfabric studies allow not only obtaining a more complete and precise information on the mechanism of transport and deposition in the eolian system, but also interpreting changes in the petrophysical features of the sandstones (permeability, porosity). Additionally, microfabric analysis can be employed as a useful tool in the description and interpretation of core wells.
... Por otro lado, niveles de areniscas masivas, frecuentemente acumuladas en interdunas, fueron descriptos por Kamola y Chan (1988) e interpretados como el resultado de avalanchas de arena como consecuencia de desestabilizaciones de la cara de sotavento y de la cresta de las dunas. También han sido propuestos otros orígenes como bioturbación, retrabajo de interdunas durante inundaciones fluviales, procesos de licuefacción y degradaciones de dunas por precipitaciones extremas (Herries, 1993;Sweeny y Loope 2001, Simpson et al., 2002Bryant et al., 2013). En nuestro caso, las areniscas masivas aparecen preferentemente en facies de interdunas, sugiriendo que procesos de inundaciones fluviales, asociadas a estados de freáticas altas y fuertes precipitaciones podrían ser las responsables de la falta de laminación interna en los estratos de estas areniscas. ...
... Por el otro, la infiltración de agua de lluvias o crecientes que inunda la interduna, lo que favorece la redistribución de material coloidal y arcilloso dentro de las arenas eólicas y eventualmente promueve las estructuras de disipación (microfábrica 6). No se descarta además la presencia de procesos de licuefacción generados en arenas saturadas de interdunas (Bryant, 2013) como factor generador de niveles de areniscas masivas (microfábrica 5). ...
... Indeed, the application of SSDSs has greatly improved comprehension of the past allocyclic (e.g., palaeoseismicity) and autocyclic (e.g., flooding, or storm recurrence) processes (Montenat et al., 2007;Obermeier, 2009;Moretti et al., 2016) relative to different depositional environments on Earth, such as: fluvial (Rana et al., 2016;Rossetti et al., 2017), aeolian (Moretti, 2000;Bryant et al., 2013Bryant et al., , 2016, palustrine (Ezquerro et al., 2015), lacustrine (e.g., Törő and Pratt, 2016;Alsop et al., 2016), marine (e.g., Basilone et al., 2016) environments, and even on planet Mars Chan et al., 2019). Their occurrence requires (i) loss of strength (liquidization, sensu Allen, 1977) of a cohesionless water-saturated host bed (i.e., deformation mechanism, Obermeier, 2009;Moretti and Ronchi, 2011) or increase of stress field outside or inside until overcoming the strength of a cohesive material (Collinson, 1994;Pratt and Ponce, 2019), (ii) existence of a driving force system (sensu Owen, 1987), and (iii) a trigger mechanism for loss of strength (Owen, 1987;. ...
Article
Reverse-drags in extensional settings are emblematic structures that may provide imprints of (neo)tectonic pulses, and even evidence of palaeoseismic activity. The direct pieces of evidence of (neo)tectonic activity therein are mostly reported to be subsidiary grabens, synthetic and antithetic normal faults, and/or bed-parallel slip that brittlely deform newly deposited soft-sediments, therefor being classified as soft-sediment deformation structures (SSDSs). Liquidization-induced SSDSs are, reasonably, likely to occur in such tectonically active settings as well. Nonetheless, both SSDSs types have not gained enough interest from structural geologist and sedimentologist communities. We hereby address this gap by investigating brittle and liquidization-induced SSDSs from late Pleistocene-Holocene fluvio-lacustrine beds (Lake Ifrah, northern Morocco). Sedimentation and deformation occur upon a reverse-drag anticline connected to a master normal fault that borders a half-graben structure (Ifrah sub-basin) superimposed on a master basin (Ifrah Basin), itself connected to a major strike-slip fault (the Tizi n'Tretten Fault, TTF). Liquidization-induced SSDSs involve load structures and water-escape structures, whereas brittle deformations encompass shrinkage cracks, subsidiary grabens, neptunian dykes, and bed-parallel slip (BPS) and associated domino-style faults. The deformation mechanism for both SSDS types involves either loss of strength upon liquidization (load structures and water-escape structures) or an increase in applied (internal or external) shear (shrinkage cracks, faults). Facies analysis and conventional trigger assessment allowed deciphering endogenic from exogenic triggers for deformation. Liquidization has been inferred to be seismic-triggered whereby the deformed beds are considered seismites. While BPS deformed brittlely late Pleistocene deposits (probably Marine Isotope Stage 3, MIS-3) and subsidiary grabens and neptunian dykes involve Middle Holocene sediments, they are considered to be linked to two flexural-slip events of the reverse-drag during MIS-3? and the Middle Holocene, respectively. Scaling relationships between the structural entities of the hanging-wall-master fault-footwall system allowed estimation of the subsidence due to hanging-wall collapses, and thereby the initiation of the Ifrah sub-basin (at least since 260 kyr). The rhomboidal-shaped master basin was suggested to belong to a dilational quadrant of the associated strike-slip fault, the TTF, at a tip-damage region. Accordingly, we highlight structural isolation of a segment of the TTF that is synchronous with the Ifrah Basin initiation.
... Dune FA is interpreted to be deposits of the lee faces of migrating bedforms (Table 2). Highly contorted packages of Fgf are present within some cross-strata (Fig. 7B), interpreted as slumped blocks of once-cohesive cross-strata initiated by lee-face oversteepening, wind-direction fluctuations, or post-burial liquefaction or fluidization (McKee et al., 1971;Bryant et al., 2013;Wheatley et al., 2016). ...
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Aeolian deposits form noteworthy reservoirs (for example, Norphlet Formation and Rotliegend Group) in hydrocarbon extraction and carbon capture and storage contexts, but stratigraphic architecture imparts significant heterogeneity. Bounding surfaces result from autogenic and allogenic controls and can represent important changes in dune‐field dynamics. To further evaluate the impacts of facies heterogeneity and flow‐inhibiting bounding surfaces on reservoir performance and reconstruct ancient erg evolution, the stratigraphic architecture of aeolian systems must continue to be studied at multiple scales. This study pairs traditional methods (for example, measured stratigraphic sections) with advanced technologies (for example, drone‐derived outcrop models) to precisely resolve the metre to kilometre‐scale three‐dimensional stratigraphic architecture of wet aeolian Middle Jurassic Entrada Sandstone outcrops located at Rone Bailey Mesa near Moab, Utah, USA. Five facies are identified, primarily based on sedimentary fabrics, and are grouped into three associations named dune, sabkha and sand sheet. Statistical analyses of gamma‐ray spectrometer and automated mineralogy data indicate a distinct mineralogical difference between dune (quartz‐rich) and sabkha (more feldspathic) packages, suggesting that gamma‐ray logs may be used to better predict facies distribution in the subsurface. Seven modelled super bounding surfaces are planar to undulatory, with no perceived spatial trends. Five modelled interdune migration surfaces are undulatory but exhibit an average 0.09° angle of climb roughly parallel to the palaeocurrent direction. Two modelled superposition surfaces are linear to sinuous in plan‐view. Laterally discontinuous sabkha packages observed are interpreted to be remnants of closed, damp, interdune flats located between ca 8.5 to 17.0 m tall, sinuous, transverse bedforms or patches of such bedforms. Based on stratigraphic architecture interpretations, the Entrada Sandstone preserves signals of allogenic forcing and localized autogenic bedform cannibalization of the substrate. The findings of this study, some of which are not commonly recognized in wet aeolian facies models, enhance the understanding of erg evolution and can parameterize static models of aeolian reservoirs.
... Hexagonal patterns are present on many Navajo sandstone outcrops across southern Utah, and are especially well developed on homogeneous outcrops where bedding was obliterated during the Jurassic by burrowing or liquefaction (Loope and Rowe, 2003;Chan et al., 2008;Bryant et al., 2013;Loope and Burberry, 2018). The broad, planar hexagonal patterns displayed at Yellow Knolls, however, are highly unusual. ...
Article
Deep (> 5 m) sheeting fractures in the Navajo Sandstone are evident at numerous sites in southern Utah and derive from tectonic stresses. Strong diurnal thermal cycles are, however, the likely triggers for shallow (< 0.3 m) sheeting fractures. Data from subsurface thermal sensors reveal that large temperature differences between sensors at 2 and 15 cm depth on clear summer afternoons are as great as those that trigger sheeting fractures in exposed California granite. Extensive polygonal patterns in the Navajo are composed of surface‐perpendicular fractures and were produced by contractile stresses. Numerous studies have shown that porewater diminishes the tensile strength of sandstone. Based on our thermal records, we propose that cooling during monsoonal rainstorms triggers polygonal fracturing of temporarily weakened rock. On steep outcrops, polygonal patterns are rectilinear and orthogonal, with T‐vertices. Lower‐angle slopes host hexagonal patterns (defined by the dominance of Y‐vertices). Intermediate patterns with rectangles and hexagons of similar scale are common. We posit that outcropping fractures are advancing downward by iterative steps, and that hexagons on sandstone surfaces (like prismatic columns of basalt) have evolved from ancestral orthogonal polygons of similar scale. In lava flows, fractures elongate intermittently as they follow a steep thermal gradient (the source of stress) as it rapidly moves through the rock mass. In our model, a steep, surficial thermal gradient descends through unfractured sandstone, but at the slow pace of granular disintegration. Through time, as the friable rock on stable slopes erodes, iterative cracking advances into new space. Hexagonal patterns form as new fractures, imperfectly guided by the older ones, propagate in new directions, and vertices drift into a configuration that minimizes the ratio of fracture length to polygon area.
... The undulose to ripple-laminated facies (Smwb) represent the superimposition of ripple-scale bedforms onto dune-scale bedforms (Sharp, 1963;Fryberger & Schenk, 1988). Softsediment deformation of the cross-bedding indicates fluctuation of the water table at or shortly after the time of deposition, before the crossbedded sets were fully lithified (Mckee et al., 1971;Doe & Dott, 1980;Bryant et al., 2013Bryant et al., , 2016. ...
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Ephemeral fluvial systems are commonly associated with arid to semi‐arid climates. Although their complex sedimentology and depositional settings have been described in much detail, depositional models depicting detailed lateral and vertical relationships, and interactions with coeval depositional environments, are lacking compared to well‐recognized meandering and braided fluvial systems. This study critically evaluates the applicability of current models for ephemeral fluvial systems to an ancient arid fluvial example of the Lower Jurassic Kayenta Formation of the Colorado Plateau, USA. The study employs detailed sedimentary logging, palaeocurrent analysis and photogrammetric panels across the regional extent of the Kayenta. A generic model that accounts for the detailed sedimentology of a sandy arid ephemeral fluvial system (drawing upon both ancient and geomorphological studies) is developed, along with analysis of the spatial and temporal interactions with the aeolian setting. Results show that the ephemeral system is dominated by laterally and vertically amalgamated, poorly channelized to sheet‐like elements, with abundant upper flow regime flat beds and high sediment load structures formed between periods of lower flow regime conditions. Through interaction with a coeval aeolian system, most of the fluvial deposits are dominated by sand‐grade sediment, unlike many modern ephemeral fluvial systems that contain a high proportion of conglomeratic and/or finer grained mudstone and siltstone deposits. During dominantly fluvial deposition, high width to thickness ratios are observed for channelized and sheet‐like elements. However, with increasing aridity, the aeolian environment becomes dominant and fluvial deposition is restricted to interdune corridors, resulting in lower width to thickness ratio channels dominated by flash‐flood and debris‐flow facies. The data presented here, coupled with modern examples of ephemeral systems and flood regimes, suggest that ephemeral flow produces and preserves distinctive sedimentological traits that can not only be recognized in outcrops, but also within core.
... Wheeler (2002) recommended abandoning the term because other researchers have expanded the meaning to include any and all geologic records of seismic activity. Characteristics of the disturbed facies preserved in the Navajo Sandstone at Stop 5 are similar in form and scale to those described in the eolian Navajo Sandstone at other locations in southern Utah by Doe and Dott (1980), Horowitz (1982), Loope et al. (2001Loope et al. ( , 2013, Loope and Rowe (2003), Bryant and Miall (2010), and Bryant et al. (2013Bryant et al. ( , 2016. In those reports, the authors ascribed the deformities in eolian strata to earthquake shaking of water-saturated eolian sand prior to burial and lithification. ...
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Two sites in Kane County, south-central Utah were selected for this 2-day field trip. Stunning outcrop examples of the internal structure of eolian, wadi, and microbialite beds are accessible in the Middle Jurassic Carmel Formation at White House camp along the Paria River, and outcrop details of deformed bedding are accessible in the Lower Jurassic Navajo Sandstone on Wire Pass/Coyote Wash trail. Respective facies are described and interpreted within a theme of “back to basics in sedimentology” and within a landscape framework of the Grand Staircase and the East Kaibab monocline. A tan cross-bedded facies of coastal eolian origin and a red lenticular facies of wadi origin in the Thousand Pockets Member, Carmel Formation were coeval with a wavy laminated facies of organo-sedimentary origin in the Judd Hollow Tongue of the Carmel Formation. Grainflow, wind-ripple, and grainfall processes conspired on Jurassic dunes to deposit a cross-bed array of eolian sandflow, wind-ripple, and grainfall foreset strata, and wind-ripple and possibly grainfall toeset strata in the tan cross-bedded facies. Episodes of wadi flooding are preserved in the red lenticular facies as cyclical, upward-fining sandstones-mudstones punctuated by exposure and mudcrack fills. They locally and temporarily interrupted eolian sedimentation before being overrun and buried by eolian dunes. Ripples and microbes built-up the wavy laminated facies at a supratidal marine shoreline of the Middle Jurassic seaway. Ground-shaking from an earthquake or extraterrestrial impact triggered severe deformation of eolian dune sand in the disturbed facies of the Navajo Sandstone.
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The recognition of seismically-induced soft-sediment deformation structures (SSDS) in sedimentary successions characterized by different facies, and hence by different rheology, is challenging. This is the case for high porosity and high permeability aeolian facies interbedded with muddy wet interdune deposits and alluvial conglomerates and sandstones that present. Several types of SSDS have been studied in two exposures of the Upper Pliocene (2.9 to 2.6 Ma) sediments of a fault-bounded intracontinental aeolian dune field in the Teruel Basin (Iberian Chain, eastern Spain). Among SSDS, load and fluid-escape structures, apart from several animal tracks, have been recognized. Those structures show an irregular distribution through the studied stratigraphic sections, being scarce in homogenous aeolian sands and frequent in water-related facies. A detailed study of the distribution and geometry of SSDS and their relationships with respect to the stratigraphic architecture and facies has allowed a critical discrimination of trigger mechanisms, i.e. biological or physical overloading vs. earthquakes. The seismically-induced structures are concentrated into seven deformed beds, showing an uneven lateral distribution and geometry closely controlled by the hosting sedimentary facies and their rheology. These seismites resulted from liquefaction during moderate earthquakes (estimated magnitude from 5.0 to 6.8). The most probable seismogenic source was the Sierra del Pobo normal fault zone, located 2 km to the East. Results show how an appropriate recognition of sedimentary facies is crucial to understand the lateral variability of seismites in sedimentary environments characterized by sharp facies changes.
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Glen Canyon National Recreation Area contains some of the best examples of the spectacular and unique geology that the Colorado Plateau has to offer. The recreation area is located in southeastern Utah and in a small part of northern Arizona. It includes the shores of Lake Powell—the reservoir behind Glen Canyon Dam—and parts of other main drainages of the Colorado River including the Green, Dirty Devil, Escalante, and San Juan Rivers. The canyons in the recreation area formed within the past 5 million years (much within the last one million years) by vigorous downcutting of the Colorado River and its tributaries to expose more than 10,000 feet of bedrock that spans about 300 million years. The recreation area is dominated by sparsely vegetated, spectacularly exposed layers of classic Colorado Plateau rocks. The bedrock units range in age from Late Pennsylvanian (300 million years ago) to Late Cretaceous (about 85 million years ago), and record a fascinating history of deposition in shallow seas, tidal flats, sabkhas, vast alluvial plains, and enormous sand dune-covered deserts dotted with oases. Glen Canyon National Recreation Area also contains a surprising variety of unconsolidated surficial deposits that provide clues to the age of the canyons. Active surficial processes continue to shape the recreation area, such as large landslides and rock falls involving the Triassic Chinle Formation and Triassic-Jurassic Wingate Sandstone. The recreation area has literally had its “ups and downs.” The tectonic history of the area is recorded in the stratigraphy and consists of several episodes of subsidence and deposition alternating with periods of uplift and erosion. Recent uplift to its present high-desert elevation has caused aggressive incision by the Colorado and Green Rivers and their many tributaries, forming a unique combination of beauty, isolation, and geologic history.
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The Navajo Sandstone of the American Southwest was deposited at approximately 190 Ma in a giant, subtropical dune field near the western margin of Pangea. From this unit, we report thick intervals of dune cross-strata that were churned by insects and trampled by reptiles. Although dunes continued to migrate freely, the distribution of trace fossils shows that plant life in wet interdune areas sustained high levels of animal activity on the dunes for many thousands of years. We interpret this suite of structures as the record of a pluvial episode climatologically similar to the period of “greening” in the Sahara 4000–10,000 yr ago. A high percentage of the rainfall on the Navajo erg recharged the water table and led to the development of highly dilute, local groundwater flow systems that discharged into interdune areas.
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The occurrence of two large earthquakes (M>7.5) in the Kachchh basin within a short span of ˜200 years is quite unusual for an intracratonic region (Figure l). What factors could possibly make this region different from other, mid-plate settings? Could some of these factors be responsible for the relatively shorter recurrence times? Does the tectonic history provide us with any clues about the uniqueness of this intraplate region?
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A descriptive classification of sandstones (exclusive of carbonate and volcaniclastic sandstones) based on the composition of framework grains is proposed that can be used equally well in the field and laboratory. The framework grains are grouped into (1) quartz plus chert and quartzite, (2) feldspar, and (3) rock fragments which constitute the end-members of the quartzarenite, arkose, and litharenite clans respectively. The clans are subdivided to make eight major rock types. Graywacke is defined on the basis of both texture and framework composition and is treated as a special rock type instead of as a clan or subclan type. Because the texture of a sandstone is as important an attribute as framework composition, a polynomial system of sandstone nomenclature should be used in which at least grain size and clan name are cited (i.e., muddy coarse arkose).
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Three orders of aeolian bounding surface are arranged in a hierarchy based on their extent and regularity.First order surfaces are the most extensive. They are flat-lying bedding planes cutting across all other aeolian structures and are attributed to the passage of the largest aeolian bedforms—draas—across an area. First order surfaces cut across second order surfaces, which are gentle to moderately dipping surfaces bounding sets of cross-strata. Second order surfaces are attributed to the passage of dunes across draas, or to longitudinal dunes migrating across the lower ice slopes of draas. Third order surfaces bound bundles of laminae within coscts of cross laminae and are due either to local fluctuations in wind direction and velocity or to changes in airflow patterns caused by configurational changes in dune patterns. All these bounding surfaces could be explained by wind variations and dune migration, but the rates of dune migration relative to probable sediment deposition rates are incompatible with this general explanation of the form and spacing of the bounding surfaces. The concept of climbing bedforms of different hierarchical order together with subsidence provides a better explanation. Analogous bounding surfaces in aqueous bedforms have already been attributed to climbing bedforms of differing hierarchical order.
Chapter
This chapter describes the processes and controls on the intertonguing of the Kayenta and Navajo formations in northern Arizona. The Kayenta comprises a heterogeneous assemblage of coarse- to fine-grained clastics that crop out in western Colorado, southwestern Utah, and northern Arizona. The sandy facies is best developed near the type locality at Kayenta, Arizona, where it consists of reddish brown, lenticular, lithic, and feldspathic sandstone interbedded with subordinate amounts of gray to red mudstone. The sandstone units typically have channeled bases and contain small- to medium-scale trough and horizontal stratification. The Navajo is composed largely of fine-grained, well sorted, and subrounded quartz-rich sand. Large-scale features include Nedge–planar and tabular–planar cross-bedding, contorted bedding, horizontally bedded sandstone and siltstone, and cherty limestone. Six facies are recognized within the intertonguing interval of the Navajo and Kayenta formations. Facies were erected based on combinations of lithology, sedimentary structures, and unit geometries. The association with the brecciated zones suggests that deformation occurred at the air-water interface. It is found that moist conditions were relatively common during the early stages of Navajo erg development.
Chapter
Diversity of pelagic biotas varies with a rhythm of about 32 million years. “Polytaxic” times of maximal diversity coincide with higher and more uniform oceanic temperatures, with continuous pelagic deposition and with widespread marine anaerobism, eustatic sea-level rises, and heavier carbon isotope values in marine calcareous organisms and organic matter. Pelagic communities reach maximal complexity, expressed in numbers of taxa and in predator size. “Oligotaxic” episodes are characterized by lower marine temperatures and sharper latitudinal and vertical temperature gradients, by interruptions of submarine sedimentation caused by intensified current systems, by marine regression, by a lack of anaerobic marine sedimentation, and by lighter carbon isotope values in marine carbonate skeletons and organic compounds. Degradation of pelagic communities is reflected by loss of large predators and lowered diversity; blooms of opportunistic species occur during these intervals. The fluctuation from oligotaxic to polytaxic conditions is attributed to changes in rates of oceanic circulation as a direct result of climatic variation: during polytaxic times warm, globally equable climates result in reduced oceanic convection rates, causing expansion and intensification of the oxygen minimum layer. Colder climatic intervals lead to increased circulation rates, more efficient oxygenation of ocean waters, and oligotaxy. The climate changes in response to either fluctuations in receipt of solar energy, or to internal causes such as rhythms in mantle convection and associated processes: rates of plate motions, volcanism and orogeny. These cycles directly influence the accumulation patterns of petroleum source rocks, major phosphorite deposits, deep-sea carbonates and biogenic silica.
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Where bedforms migrate during deposition, they move upward (climb) with respect to the generalized sediment surface. Sediment deposited on each lee slope and not eroded during the passage of a following trough is left behind as a cross-stratified bed. Where sediment is transported solely by downcurrent migration of two-dimensional bedforms the thickness of cross-stratified beds is equal to the decrease in bedform cross-sectional area divided by the migration distance over which that size decrease occurs; where bedforms migrate more than one spacing while depositing cross-strata, bed thickness is only a fraction of bedform height. Equations that describe this depositional process are used to explain observations on actual dunes and to predict dune sizes for ancient sandstones. -from Authors
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Large-scale deformational features that disrupt the cross-bedded strata of some ancient wind-blown dune sand deposits (Jurassic Aztec and Navajo Sandstones, U.S.A.) can be traced laterally for at least tens of metres. Information from four exposures leads to an idealized deformation style. An hypothesis involving earthquake-induced liquefaction and collapse of the dunes is proposed. -from Author
Article
Types of deformation affecting cross bedded sands include sandflow-deformed, parabolically overturned and complexly contorted, and brecciated and/or faulted. Sandflows are due to oversteepening of lee faces of both subaerial and subaqueous dunes. Brecciated and faulted sands form on subaerial dunes due to gravity failure of lee faces moistened with capillary water. Parabolic overturning generally forms at a subaqueous depositional interface due to current shear and scour of a partially liquefied sand bed. More intensely contorted cross laminae also can form either at the depositional interface or after burial due to liquefaction of saturated sand. Most of the cross bedded sandstones of both formations display features characteristic of eolian deposition yet also display contorted zones indicative of failure in a saturated condition.- from Authors
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The behaviour of the depositional surface over time is described by the sediment conservation equation, and is a function of the downwind sediment transport rate amd the concentration of sediment in transport over time, the latter measured largely by average dune height. The depositional surface rises over time, where the sediment budget is positive or influx exceeds outflux, and the balance is stored as the accumulation. A change from a positive sediment budget, where an accumulation forms, to one that is neutral (influx = outflux) or negative (influx < outflux) results in a bypass or erosional super-bounding surface, respectively. The super surface, therefore, bounds the accumulation, and accumulations and their capping super surfaces are the basic building blocks of eolian sequence stratigraphy. -from Authors
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Liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the Holocene. These features include dikes, craters, vented sand, sills, and laterally spreading landslides. The relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo-earthquakes. This state-of-the-art summary for using liquefaction-induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives.
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Boiling (motion, not temperature) sand springs fed by ground water moving upward along distinct conduits occur along the Dismal River in the Nebraska Sand Hills. The cylindrical conduits are developed in alluvium and are as large as 10 m in diameter and 44 m deep. Sides of the spring conduits are firm. Boiling sand is overlain in several places by a clear layer of water in the spring. Time-varying wave patterns and boils can be observed along the interface between these layers. Sediment within the conduits is generally well sorted, although some debris is present. Because of their large size, firm sides, and persistence in time, the conduits have the potential for preservation as vertical cylindrical structures comparable to those reported in sedimentary rocks of several ages. The discovery of preserved structures is evidence of paleo-ground-water discharge, and therefore the structures are a useful mapping tool for determining position in landscape evolution.
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The requirement of long-term accommodation space for preservation in the geological record is particularly acute in the case of thick wind-blown deposits that accumulate to heights well above the regional elevation. The Mesozoic of the western United States contains a number of well-developed erg systems. The clue to their formation and preservation is the combination of a positive sand budget and the generation of shortening events in the early Mesozoic continental margin arc of the U.S. Cordillera, which flexed the continental interior downward. The combination of the creation of a wide topographic depression representing a retro-foreland basin, sheltered behind a mountain belt exerting a rain shadow effect, and a background dynamic subsidence, produced optimum conditions for the preservation of thick eolian deposits during the Jurassic. The onset of flexural subsidence in Utah is thought to have been as early as Early Jurassic on the basis of the characteristic signature of the subsidence profiles, which is in agreement with the recent documentation of Early Jurassic igneous and structural activity west of the Luning-Fencemaker thrust belt in Nevada.
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The high coastal cliffs of Sidi Moussa reveal a complex, reliably dated coastal series of Late Pleistocene age. The lagoon, beach and dunes sequence shows repeated seismically induced deformation. These seismites range from the classic hydroplastic load-casts and convolute laminations to a new type of seismite, which corresponds to an oblique fracturation with respect to the horizontal substratum, parallel to the leeside bedding (avalanche foresets) of the overlying dune sequence. Three major earthquakes are thus identified in two high sea-level deposits (lagoonal and paleocliff foot beach), both related to Eemian sea-level peaks (Marine Isotope Stages, MIS 5.53; 5.51), associated with shoreline dune complexes (MIS 5.52; 5.54). The most destructive historical earthquake to affect this Moroccan coast is the so-called Lisbon, 1755 megaseism , the 350 km eastward Atlantic origin of which must be excluded because stratigraphic analysis locally demonstrates repeated co-seismic subsidence. Rather, the tectonic history of the Gharb foreland basin (basement faults reactivation) accounts for the location of major seismicity changing from the Neogene to Pleistocene to the recent times activity. This example of paleo-earthquake reconstruction demonstrates the need for precise chronology and environmental interpretation of the host sedimentary sequence. The discovery of a new structure-type also exemplifies the unbounded diversity of syn-diagenetic seismites, including those found in early lithified eolianites.
Article
The eolian Pennsylvanian-Permian Weber Sandstone, predominantly a 300m-thick, cross-bedded quartz arenite, contains carbonate lenses deposited in interdune ponds. The carbonates are thin (- 60 cm), laterally impersistent (100-1000m) and consist chiefly of unfossiliferous, fenestral dolomitic mudstone. An interdune pond origin is supported by: 1) lenticular, three-dimensional geometry, 2) exclusive occurrence along first-order bounding surfaces, 3) lateral intertonguing with dry and damp interdune sandstone facies, 4) lack of marine fossils, and %) megascopic features indicative of extremely shallow to emergent, hypersaline to brackish conditions. Weber interdune ponds were probably fed by spring seeps and ground waters derived from deeper aquifers.-from Author
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The Upper Minnelusa Formation comprises a parasequence set of at least four parasequences. Each parasequence boundary was formed by marine transgression over an aeolian dunefield. The entire sequence is bounded by unconformities at the top and base. Most oil exploration takes place within the individual parasequences. The most important form of bounding surface control on reservior quality that can confidently be identified is fabric-selective cementation along primary bounding surfaces and strata. -from Author
Article
At Capitol Reef National Park, Utah, 5-m-high stromatolites are present locally on interdune carbonate lenses in the Early Jurassic Navajo Sandstone. The stromatolites display both finely laminated and fenestral internal fabrics, and grew along south-facing interdune margins. These stromatolites formed during a high-water-table episode engendered by a dune-dammed paleodrainage in a stabilized Navajo erg. These stromatolites, and the thick interdune section associated with them, suggest a hiatus in erg accumulation and the presence of a super bounding surface.
Article
Superscoops are large concave-up features associated with rocks deposited by eolian depositional systems. They can be tens of metres deep and several kilometres wide and are common in Pennsylvanian through Jurassic eolian sandstones of the Colorado Plateau. They are formed by wind deflation or water scouring and are filled with eolian or aqueous sediments. They are associated with entirely eolian sequences to mixed eolian and noneolian sequences. Formation of superscoops requires a pause in deposition followed by erosion. The surfaces are subsequently filled and preserved in the stratigraphic sequence. The preserved fill may contrast with enclosing deposits, thus providing information about ancient depositional systems not represented in enclosing deposits.
Article
New road cut and mass-grading excavations in the north coastal area of San Diego County, California expose heretofore generally unrecognized, probable late Holocene tsunami deposits and paleoseismically deformed sediments. Remnant tsunami deposits occur up to 100 + m in elevation around the margins of modern coastal lagoons and estuaries and, combined with local mima mounds of possible sand blow origin, provide indirect but compelling evidence for the late Quaternary activity of onshore and offshore faults in the immediate study area. Probable paleoliquefaction features are regionally widespread and range from fissures filled with sediments derived from overlying marine terrace sand and soil, to the more traditional sand-filled injection dikes and sills, lateral spreads, and filled craterlets. The source of most liquefied sediment is underlying Tertiary “bedrock sand” and local, Quaternary marine-terrace deposits. A paleoseismic liquefaction origin rather than soft-sediment loading is deduced for these features based on morphology, internal stratigraphy, field setting, and near proximity to known seismogenic sources.
Article
Outliers of Navajo Sandstone (Lower Jurassic Glen Canyon Group) form low paleohills east of the main body of the Formation in the Salt Anticline region of southwestern Colorado. The paleohills consist of interdune deposits which developed topographic inversion during erosion of the Jurassic J-2 unconformity owing to a tough shell of early cemented sandstones and cherty limestones.The interdune deposits accumulated over playa mudstones of the Kayenta Formation which formed in a structural low between the Uncompahgre Uplift and the Paradox Valley salt anticline. Open-framework textures indicate the early formation of quartz or chert cement in sandstone beds immediately above the impermeable playa mudstones. The mudstones enhanced the subsequent formation of wet interdune deposits keeping groundwater near the surface. Microcrystalline quartz cements and fresh feldspars suggest that groundwater was alkaline. A source of alkalinity may have been eolian dust carried from emergent Pennsylvanian evaporite intrusions upwind of the playa deposits. The high specific surface of siliceous and evaporite dusts combined with shallow groundwater and high evaporation rates resulted in the rapid formation of quartzitic silcrete crusts above the playa mudstone aquacludes.As these early silcretes were buried, the impermeable mudstone foundations beneath them continued to serve as aquacludes. The inclined potentiometric surface of perched water tables above the isolated aquacludes intersected the land surface at progressively higher levels as the mudstone lenses were buried. Groundwater moving laterally from above the aquacludes carried dissolved material towards the inclined water tables at their margins. This mobilized material was redeposited as early cement where the capillary fringe intersected the land surface. As the land surface aggraded vertically, the zone of cement formation migrated laterally in response of a change of the relative positions of the land surface and an inclined perched water table.The final products of this process were topographic remnants of Navajo Sandstone with a resistant rind of cemented material enclosing a core of leached, compacted and friable sandstones. Erosion of the J-2 unconformity left the cemented rind in relief while removing all material around it. The resulting hills survived the onlap of the Middle Jurassic Entrada Formation, leaving considerable relief beneath the unconformity.
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It is shown that the design engineer has two basic choices if he considers it appropriate to neglect the possible effects of drainage occurring during the period of cyclic stress applications: (1)To calculate the stresses induced in the ground by the design earthquake, and to compare these stresses with those required to cause cyclic mobility or liquefaction of representative samples in the laboratory. The main problem in this approach lies in correctly assessing the characteristics of the in-situ deposit from laboratory tests performed on even good quality undisturbed samples. (2)to be guided by the known field performance of sand deposits correlated with some measure of in-situ characteristics, such as the standard penetration test. In some cases it is desirable to evaluate the possible effects of pore pressure dissipation in different layers of a deposit during and following earthquake shaking. Methods of accomplishing this are reviewed and described.
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Land subsidence, lowering of the land surface by mass movement, has been caused by human activities in many countries all over the world. The full economic impact of man-induced subsidence is large, yet difficult to estimate. Groundwater withdrawal is one of the most important causes of land subsidence that has caused extremely expensive damages to buildings, walls, roads, railroads, pipelines, and casings of the water wells. A necessary step to perform a proper analysis of land subsidence is to obtain accurate measurements of actual subsidence at certain intervals. The objective of this paper is to evaluate land subsidence using global positioning system (GPS) technique. One example of subsiding areas is the Rafsanjan plain, which has had the most subsidence in Iran. First, the latest situation of land subsidence in the Rafsanjan plain as well as the geological, hydrogeological conditions and groundwater utilization are explained. Next, the monitoring program and engineering works for its implementation are discussed. Finally, the results of two successive measurements carried out recently as the first attempt in Iran to monitor land subsidence by using GPS are presented and interpreted. Based on the results obtained, it was found that the relationship between the decline of groundwater level and land subsidence is not exactly or necessarily linear at every point. Also, the response of different points of the soil body within the plain would not be the same due to the groundwater withdrawal and the change in groundwater level. The ground behavior is influenced by many other factors such as the thickness of aquifer, soil structure, and interlaying manner of sublayers.Key words: land subsidence, groundwater, monitoring, GPS, Iran.
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Interprets sand dune deposits and sequences from a sedimentary structure point of view. An introductory section is followed by a description of the components of sand dune deposits and the interpretation of sand dune deposits. -A.W.Hall
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This chapter describes the changing wind and hydrologic regimes during deposition of the Navajo and Aztec sandstones. The Navajo and Aztec sandstones form a wedge of predominantly crossbedded sandstone that thickens westward from its zero edge in western Colorado and northeastern Arizona to over 650 m in exposures along the eastern edge of the foreland fold and thrust belt in southern Nevada. The Navajo Sandstone is a feldspathic quartz arenite to quartz-rich subarkose composed of rounded to well-rounded quartz sand and containing large to very large-scale trough, tabular–planar, and wedge–planar cross-stratification. It is found that although cross-stratified sandstone is the most conspicuous and most common sedimentary structure, other sedimentary features which are important to the interpretation of the depositional environment of the Navajo Sandstone are volumetrically significant. Noncrossbedded features are distributed throughout five of the six sections measured in the Navajo Sandstone in southeastern Utah. Noncrossbedded lithologies average 32% of the total thickness of the measured sections with a range of 15 to 50%. Horizontally stratified sandstone is most common near the base of the Navajo Sandstone, whereas limestone lenses, contorted stratification, structureless sandstone, and dessiccation-cracked erosion surfaces are more common.
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Bounding surfaces and interdune deposits provide keys for detailed interpretations of aeolian bedforms, as well as overall sand sea conditions. Two perpendicular traverses of Jurassic Entrada Sandstone, Utah, reveal relations among cross-strata, first-order bounding surfaces, and horizontal strata. These field relations seem explicable only as the deposits of downwind-migrating, climbing, enclosed interdune basins (horizontal strata) and dune bodies consisting of superimposed smaller crescentic dunes (cross-stratified deposits). A traverse perpendicular to the paleowind direction provides a view at an instant in geological time. Hierarchies of bounding surfaces reflect bedform development. The presence of three orders of bounding surfaces indicates dune bodies consisting of smaller, superimposed dunes. The presence of only two orders of bounding surfaces indicates simple dunes. Modern interdune deposits show a wide variety of types and are the best indicators of overall erg conditions.-from Author
Article
The Navajo Sandstone of the Colorado Plateau, USA, displays a wide range of soft-sediment deformation (SSD) features, including decametre-scale features that have not been found in any modern desert environment. Laboratory simulations and partial analogues from other depositional environments suggest that these features derived from episodic liquefaction and fluidization of unconsolidated dune deposits. Outcrop details at many locations preserve the effects of fluid-escape dynamics through porous, permeable, well-sorted sand, which was partitioned by subtle textural changes at depositional boundaries between successive dune deposits and, less commonly, by distinct lithofacies changes marking the interface between wet and dry depositional environments. Extreme deformation and turbulent sediment flow have effaced primary structures in some zones of deformation; but other sites preserve the ductile modification of primary structures. Some outcrops preserve evidence of dramatic alterations in topography and sedimentation patterns due to localized compaction and large, subsurface, sediment displacements. Particularly notable among these extraordinary features are those representing the foundering of active dunes, sediment eruptions, and the subsidence of interdune surfaces in the ancient erg. The distinctive patterns of deformation in the Navajo Sandstone, interpreted in the context of its primary sedimentary architecture, provide unique insights into environmental conditions in the region during the Early Jurassic. Widespread ductile deformation in the Navajo indicates extraordinarily wet conditions for an active dune environment. The truncation of successive deformation features by deflation surfaces establishes the episodic nature of deformation in the unit and also suggests climatic variability. The widespread, episodic occurrence of SSD features, viewed within the seismic context provided by palaeotectonic reconstructions, strongly suggests that earthquake triggering of localized liquefaction controlled the distribution of deformation in this unit.
Article
The Permian Cedar Mesa Sandstone represents the product of at least 12 separate aeolian erg sequences, each bounded by regionally extensive deflationary supersurfaces. Facies analysis of strata in the White Canyon area of southern Utah indicates that the preserved sequences represent erg-centre accumulations of mostly dry, though occasionally water table-influenced aeolian systems. Each sequence records a systematic sedimentary evolution, enabling phases of aeolian sand sea construction, accumulation, deflation and destruction to be discerned and related to a series of underlying controls. Sand sea construction is signalled by a transition from damp sandsheet, ephemeral lake and palaeosol deposition, through a phase of dry sandsheet deposition, to the development of thin, chaotically arranged aeolian dune sets. The onset of the main phase of sand sea accumulation is reflected by an upward transition to larger-scale, ordered sets which represent the preserved product of climbing trains of sinuous-crested transverse dunes with original downwind wavelengths of 300–400 m. Regularly spaced reactivation surfaces indicate periodic shifts in wind direction, which probably occurred seasonally. Compound co-sets of cross strata record the oblique migration of superimposed slipfaced dunes over larger, slipfaceless draa. Each aeolian sequence is capped by a regionally extensive supersurface characterized by abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode whereby the accumulation surface was lowered close to the level of the water table as the sand sea was progressively cannibalized by winds that were undersaturated with respect to their potential carrying capacity.
Article
Experiments demonstrate that fluid escape structures can be produced as a result of unstable fluidization behaviour where a lower base layer of granular material is inhibited from fluidizing by the presence of an overlying non-fluidizing top layer. Before the base layer can fluidize the weight of the overlying material must be balanced, and this is accomplished by base layer material pressing against the bottom surface of the confining top layer forming a static layer. This static layer allows the top layer to lift away from the base layer which is then free to fluidize. -from Authors
Article
Large-scale deformational features that disrupt the cross-bedded strata of some ancient wind-blown dune sand deposits (Jurassic Aztec and Navajo Sandstones, U.S.A.) can betraced laterally for at least tens of metres. Information from four exposures leads to an idealized deformation style characterized by (1) a ‘head’ portion marked by collapse features, (2) a middle portion marked by a thrust ramp or a large recumbent fold, and (3) a ‘toe’ portion marked by a planar shear zone with small recumbent folds, drag folds, and possibly small horizontal shear faults. An hypothesis involving earthquake-induced liquefaction and collapse of the dunes is proposed. Sands liquefied during earthquakes cannot support an unequal surface load, resulting in the collapse of surface dunes above the liquefied substrate. Compensatory lateral squeezing of liquefied sand and buried strata produces the shear zone in the ‘toe’ portion. Engineering studies suggest that buried strata underlying interdunal lows, where over-burden stress is least, will be most susceptible to liquefaction. Other considerations suggest that it will be the steeper lee sides of advancing surface dunes that collapse, squeezing liquefied sand forward or downwind, i.e. away from the lee slope of surface dunes. If the liquefied condition persists, load structures can be formed when unliquefied layers founder into the liquefied substrate.
Article
Three processes of water escape characterize the consolidation of silt-, sand-and gravel-sized sediments. Seepage involves the slow upward movement of pore fluids within existing voids or rapid flow within compact and confined sediments. Liquefaction is marked by the sudden breakdown of a metastable, loosely packed grain framework, the grains becoming temporarily suspended in the pore fluid and settling rapidly through the fluid until a grain-supported structure is re-established. Fluidization occurs when the drag exerted by moving pore fluids exceeds the effective weight of the grains; the particles are lifted, the grain framework destroyed, and the sediment strength reduced to nearly zero. Diagenetic sedimentary structures formed in direct response to processes of fluid escape are here termed water escape structures.
Article
Deformations formed in unconsolidated sediments are known as soft-sediment deformation structures. Their nature, the time of their genesis, and the state in which the sediments occured during the formation of soft-sediment deforma-tion structures are responsible for controversies regarding the character of these deformations. A defi nition for soft-sediment deformation structures in siliciclastic sediments is therefore proposed. A wide variety of soft-sediment deformations in sediments, with emphasis on deformations in siliciclastic sediments studied by the present author, are described. Their genesis can be understood only if their sedimentary context is con-sidered, so that attention is also paid to the various deformational processes, which are subdivided here into (1) endo-genic processes resulting in endoturbations; (2) gravity-dominated processes resulting in graviturbations, which can be subdivided further into (2a) astroturbations, (2b) praecipiturbations, (2c) instabiloturbations, (2d) compagoturbations and (2e) inclinaturbations; and (3) exogenic processes resulting in exoturbations, which can be further subdivided into (3a) bioturbations – with subcategories (3a') phytoturbations, (3a'') zooturbations and (3a''') anthropoturbations – (3b) glaciturbations, (3c) thermoturbations, (3d) hydroturbations, (3e) chemoturbations, and (3f) eoloturbations. This sub-division forms the basis for a new approach towards their classifi cation. It is found that detailed analysis of soft-sediment deformations can increase the insight into aspects that are of im-portance for applied earth-scientifi c research, and that many more underlying data of purely scientifi c interest can, in specifi c cases, be derived from them than previously assumed. A fi rst assessment of aspects that make soft-sediment deformation structures in clastic sediments relevant for the earth sciences, is therefore provided.
Article
Abstract New and previously published models of wet aeolian system evolution form a spectrum of types that may be explained in terms of aeolian dune dynamics, rate of water table rise and/or periodicity of interdune flooding. This is illustrated with an example from the Mid-Triassic (Anisian) Helsby Sandstone Formation, Cheshire, UK. Lenses of damp and wet interdune strata exhibit an intertonguing, transitional relationship with the toe-sets of overlying aeolian dune units. This signifies dune migration that was contemporaneous with water table-controlled accumulation in adjacent interdunes. Downwind changes in the geometry and facies of the interdune units indicate periodic expansion and contraction of the interdunes in response to changes in the elevation of the groundwater table and episodic flooding, during which accumulation of dune strata continued relatively uninterrupted. This contrasts with other models for accumulation in wet aeolian systems where interdune flooding is associated with a cessation in aeolian bedform climbing and the formation of a bypass or erosional supersurface. Architectural panels document the detailed stratigraphy in orientations both parallel and perpendicular to aeolian transport direction, enabling a quantitative three-dimensional reconstruction of genetically related aeolian dune and interdune elements. Sets of aeolian dune strata are composed of grainflow and translatent wind-ripple strata and are divided by a hierarchy of bounding surfaces originating from oblique migration of superimposed dunes over slipfaceless, sinuous-crested parent bedforms, together with lee-slope reactivation under non-equilibrium flow conditions. Silty-mudstone and sandstone interdune units are characterized by wind ripple-, wavy- and subaqueous wave ripple-laminae, desiccation cracks, mud flakes, raindrop imprints, load casts, flutes, intraformational rip-up clasts and vertebrate and invertebrate footprint impressions and trackways. These units result from accumulation on a substrate that varied from dry- through damp- to wet-surface conditions. Interdune ponds were flooded by either fluvial incursions or rises in groundwater table and were periodically subject to gradual desiccation and reflooding. Red silty-mudstone beds of subaqueous origin pass laterally into horizontally laminated wind-ripple beds indicating a progressive transition from wet- through damp- to dry-surface conditions within a single interdune.
Article
A descriptive classification of cross-stratified units is proposed based on six objective criteria, and diagnoses are given for fifteen distinct kinds of cross-stratified unit recognised with their aid. The origin of each kind is discussed in the light of existing observational, experimental, and theoretical studies. A three-fold genetic classification of cross-stratified units is tentatively outlined in which apparent origin and physical properties are closely correlated.