Geologic and Geomorphic Aspects of Deserts

Smith, H. T. U.

doi:10.1016/b978-1-4831-9868-2.50011-6

Cited by 40 publications

(2 citation statements)

References 70 publications

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“…Even with limited analytical tools, these workers were able to establish the essential elements of varnish films. Engel and Sharp (1958) were the first to quantify the enormous enrichment of manganese and to a lesser extent iron in varnish as compared to the 'heartrock', which many observers continue to cite as a probable source of varnish constituents (Peel, 1960;Opdyke, 1961;Marshall, 1962;Tricart and Cailleaux, 1964;Wilhelmy, 1964;Holmes, 1965;Wyckoff, 1966;Birot, 1968;Smith, 1968). Subsequently, Hooke et al (1969) analysed varnish with an electron microprobe, revealing layering within varnish and defining the relative quantities of elements at various depths within varnish films.…”

Section: Early Research On Rock Varnishmentioning

confidence: 96%

Rock varnish

Dorn¹,

Oberlander²

1982

Progress in Physical Geography: Earth and Environment

222

166

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Because of its wide distribution, the dark stain known as desert varnish, which covers rock surfaces in arid regions, has intriguing potential as a research tool in diverse fields of investigation. Dark coatings on rock surfaces can be seen in nearly all environments, but are most conspicuous in arid regions where coarse rock debris and solid rock outcrops dominate the landscape. The mode of origin of the coating and the enormous enhancement of manganese in it as compared with ambient levels have been topics of controversy for more than 100 years. More recently, there has been concern regarding the influence of desert varnish on the remote sensing of arid lands (e.g. Warner and El-Baz, 1978;Perry, 1979;Elvidge and Collet, 1981).Desert varnish is the arid phase of a wider phenomenon that we have termed 'rock varnish' (Dom and Oberlander, 1980;Dom, 1980). Rock varnish is usually 10 to 30 microns thick, but we have observed varnish depths ranging from under two to over 500 microns. The constituents of all rock varnishes are derived from sources external to the underlying rock. Varnish is composed of clay minerals, oxides and hydroxides of manganese and/or iron, detrital particles such as Si02 and CaC03 , and trace elements, among which Mg, Ca, K, Na, Ti, and Cu are most notable. The classic rock varnish, frequently described in the literature on arid landscapes, is a manganese-rich black coating on rocks, but orange to dusky-brown varnishes are also widespread. Iron and manganese are the distinctive elements of rock varnish. Weathering rinds and encrustations of calcium carbonate, sulphate, and other salts are regarded as distinct from the phenomenon of rock varnish.The degree of development of rock varnish has long been used by archaeologists to estimate the relative ages of stone artifacts and prehistoric rock inscriptions. Similarly, the relative development of varnish in arid regions has been used by geomorphologists to differentiate and correlate surface deposits of alluvium, talus, and eolian sand, as well as erosional features such as cliff faces and relict lake shorelines of varying ages. It has long been hoped that some characteristic of varnish might be used to establish absolute chronologies that could be used in both geomorphological and archaeological research. Wide variations in its chemical composition suggest that rock varnish could also be used as a geochemical prospecting tool. Finally, changes in chemical composition and micromorphology through the

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Section: Early Research On Rock Varnishmentioning

confidence: 96%

Rock varnish

Dorn¹,

Oberlander²

1982

Progress in Physical Geography: Earth and Environment

222

166

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“…Similar studies on interior dunes have been made by McKee and Tibbitts (1964), McKee (1966) and Tsoar (l983a). Characteristics of eolian environments in general have been described by Smith (1960Smith ( , 1968, Screiber (1968), and Bigarella (1972).…”

Section: Coastal Sand Dunes World Surveymentioning

confidence: 97%

Coastal Sedimentary Environments

Davis¹

1985

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Studies in fluviatile sedimentation: Implications of pedogenic carbonate units. Lower Old Red Sandstone, Anglo‐Welsh outcrop

Allen¹

1974

Geological Journal

164

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Carbonate units occur in varying numbers in the fine-grade members of the alluvial fining-upwards cyclothems present in the Lower Old Red Sandstone of the Anglo-Welsh outcrop. They closely resemble contemporary soilcarbonates (calcretes) and hence show that the local Siluro-Devonian climate was relatively hot with a comparatively low seasonal rainfall. Compared with contemporary calcretes, the units suggest that sites on the alluvial plains were denied river-borne sediments for periods each in the general order of 10' years. The pedogenic interpretation of the carbonate units, developed in the light of the behaviour of rivers today, leads to alternative models for the geomorphology of the Siluro-Devonian alluvial plains and for their gross subsurface structure. Geomorphologically, the plains at any instant presented depositionally active and inactive areas in juxtaposition. Under some circumstances the relief was provided only by alluvial ridges. Under others, relief was afforded by valley sides and perhaps river terraces, in addition to ridges. Knowledge of the character of the Lower Old Red Sandstone in vertical sequence leaves as plausible three alternative gross structures for the alluvial pile beneath the plains. They differ chiefly in the lateral variability and connectedness of the palaeosols and place hitherto unavailable limits on the threedimensional character ,OF the cyclothems.

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Geologic and Geomorphic Aspects of Deserts

Cited by 40 publications

References 70 publications

Rock varnish

Rock varnish

Coastal Sedimentary Environments

Studies in fluviatile sedimentation: Implications of pedogenic carbonate units. Lower Old Red Sandstone, Anglo‐Welsh outcrop

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