MICROMORPHOLOGICAL INVESTIGATION OF VESICULAR SOIL HORIZONS AND DESERT VARNISH IN THE MOJAVE (USA) AND TRANS-ALTAI GOBI (MONGOLIA) DESERTS

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgem.org, SGEM2017 Conference Proceedings, ISBN 978-619-7408-05-8 / ISSN 1314-2704, 29 June - 5 July, 2017, Vol. 17, Issue 32, 381-388 pp, DOI: 10.5593/sgem2017/32/S13.050

ABSTRACT

Due to the global problem of desertification, the demand in the diagnostics of the soil forming in the desert conditions is increased. The desert varnish and the vesicular (porous) crust horizon are distinctive morphological features of desert landscapes and, at the same time, generally recognized features of desert soil formation, being commonly referred to as the yermic horizons in different sub-groups within reference groups of desert soils. The objects of the present study were the surface horizons of vesicular crust and desert pavement in extremely arid soils of the Mojave (USA) and Trans-Altai Gobi (Mongolia) Deserts. The study methods included tomographic c analyses (using a Bruker SkyScan 1172 microtomograph), micromorphological analyses (using an Olympus BХ51 polarizing microscope equipped with an Olympus DP26 digital camera) and submicromorphological analyses (using a JEOL JSM-6610LV scanning electron microscope with an INCA Energy X-Ray analyser) with determination of the elemental composition of pedofeatures and minerals in different parts of desert varnish cross-sections. Our research on the surface horizons of extremely arid soils developed within the ancient piedmont plains has revealed a large complex of similar elements of microfabrics. The microchemical composition of the darkest and thickest varnish from deserts of different continents is similar and does not depend on the bedrock composition. Thin varnish films have deferent composition depending on the microrelief of rock fragment surface. Combining the data of micromorphological and microchemical analyses of numerous samples has allowed us to suggest that desert varnish development is a polygenetic and polychronic process. We believe that the formation of desert varnish as well as light-coloured vesicular porous surface crust horizons of desert soils can be interconnected and predetermined by hydrophysical-biochemical processes with a leading role of water movements within moisture films and an explosive character of microbiological activity
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Keywords: desert soils, micro-submorphological analyses