Large-Scale Exfoliation in Massive Sandstones of the Colorado Plateau

Bradley, William C.

doi:10.1130/0016-7606(1963)74[519:leimso]2.0.co;2

Cited by 64 publications

(46 citation statements)

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“…Stress-release joints weaken the rock mass and also form failure surfaces for mass movements. We do not support an ice-unloading origin for stressrelease joints for reasons given in the preceding section, but instead favour an alternative view that they form from erosion (Balk, 1939;Jahns, 1943;Lewis, 1954;Bradley, 1963;Wyrwoll, 1977;Lo, 1978). The fact that stress-release joints are also found in fluvial valleys (Matthes, 1936) adds significant support to this hypothesis.…”

Section: Stress-releasecontrasting

confidence: 66%

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Paraglacial rock-slope stability

2012

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Section: Stress-releasecontrasting

confidence: 66%

“…volcanic) material, the bedrock has high internal over-consolidation stresses (Bain, 1931;Farmin, 1937;Lo, 1978). Erosion causes the over-consolidated elastic rock mass to dilate and develop stress-release joints, often parallel to the erosion surface (Jahns, 1943;Bradley, 1963;Lo, 1978).…”

Section: Stress-releasementioning

confidence: 99%

Paraglacial rock-slope stability

2012

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“…3B). Bradley (1963) called attention to the near ubiquity of large-scale sheeting joints in the thick sandstones of the Colorado Plateau, described those joints as similar to those in crystalline rocks (especially in their parallelism to land surfaces), and argued that they play key roles in the origins of topographic domes and exfoliation "caves" or alcoves. He also noted that sheeting joints (in general) are scarce in heavily fractured rock, and that they are not controlled by rock textures or structures.…”

Section: Previous Studies Stratified and Structureless Navajo Sandstonementioning

confidence: 99%

“…Sheeting joints are prominent and well known from outcrops of homogenous granite, but they are also well developed in some stratified sandstones (Bradley, 1963;Bahat et al, 1995). Formation of these joints is not restricted to active plate boundaries; contemporaneous stresses are also forming them on cratons and passive margins (Twidale and Bourne, 2009).…”

Section: Introductionmentioning

confidence: 99%

Sheeting joints and polygonal patterns in the Navajo Sandstone, southern Utah: Controlled by rock fabric, tectonic joints, buckling, and gullying

Loope

Burberry

2018

Geosphere

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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 runoff events 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.

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“…Ubereinstimmend haben alle Autoren zum Thema Exfoliation das Verschwinden derselben in einer ungef/ihren Tiefe yon 50 m hinter der Oberfliiche mit Granit angegeben. Nach Bradley (1963) gehen die Exfoliationsers&einungen im Sandstein nicht so fief, sondern blof~ bis zu einer ungeffihren Tiefe yon 10 m.…”

Section: Quantitative Aussagen Zum Naturvorgangunclassified

Exfoliation

Brunner

Scheidegger

1973

Rock Mechanics

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Zusammenfassung --Summary --R&um~Ex/oliation. Es wird der Versuch unternommen, f/ir die weitverbreitere Naturers&einung der oberfliichenparaltelen Platten-und S&alenabl6sungen (Exfoliation) eine theoretische Entstehungserkl~irung zu geben. Zu diesem Zweck wird vorerst das gesamte Erscheinungsbild der Exfoliation geordnet aufgebreitet und die quantitativen Aussagen und Messungen zusammengestellt. Darauf aufbauend werden die bisherigen Entstehungserkliirungen vorgestellt und mit dem quantitativen Beobachtungsmaterial kritisch verglichen.Als Ex/oliation. Many attempts have been reported in the literature for setting up a theoretical model of the phenomenon of exfoliation which occurs very frequently in nature. Thus far, these attempts have been only very qualitative and no quantitative explanation of exfoliation has ever been proposed. In order to do this, it is first of all necessary to review the phenomenology of exfoliation in a systematic fashion. The latter encompasses features ranging from sheeting on domed granitic mountains of Australia, South America and Africa, to horizontal fissures in bedrock and to the splitting off of plates in sandstone.After the description of exfoliation, the quantitative observations are summarized so as to provide a basis for the critique of the explanations of exfoliation that have been proposed heretofore in the literature. The many investigations of exfoliation showed that the phenomenon is usually of preglacial age and that it is 44 F.K. Brunner und A.E. Scheidegger: independent of the primary structure of the rocks. Furthermore, the thickness of the plates increases with depth below the surface (cf. Fig. 1) and the ordered orientation of the exfoliation joints which is strictly parallel to the surface, loses itself completely at a depth of about 50 m (in granite).Then, a critical review is given of the attempts at explanations of the exfoliation (mechanical effects of fire, freezing and vegetation; chemical weathering, tectonic forces and stress relief by removal of a load). It is noted that a stress relief theory is presented in the literature as the most likely explanation of exfoliation. Therefore, a simple model corresponding to this type of theory is analysed mathematically: The stability against buckling of an elastic plate under horizontal compression (caused by a former overburden) is investigated. The critical dimensions of the plate as a function of the pressure are shown in Fig. 2 for various possible boundary conditions. It is shown that this model is rather unsuitable even if the tensional strength of the plates is neglected.However, if the exfoliation is considered as an analogon to the well known multiple axial tension fractures in compression-tests (the tensional stresses are induced stresses), then a model is found which has great possibilities for the explanation of exfoliation. Tensional stresses are induced in an uniaxial compression at the boundaries of the (Griffith) cracks; it can attain (depending on the shape of the cracks) similar absolute values as ...

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Large-Scale Exfoliation in Massive Sandstones of the Colorado Plateau

Cited by 64 publications

References 0 publications

Paraglacial rock-slope stability

Paraglacial rock-slope stability

Sheeting joints and polygonal patterns in the Navajo Sandstone, southern Utah: Controlled by rock fabric, tectonic joints, buckling, and gullying

Exfoliation

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