A study of global sand seas

TL;DR: In this paper, the authors identified the first time the occurrence of clay dunes in the Alashan Plateau, north China, and found that they are characterized by a relatively high content of silt and clay and are typically developed on the lee side margin of closed-basins in arid and semi-arid areas.

Abstract: Tropical deserts have existed sporodically on our planet from the Precambrian to the Present, and seem not to have been a permanent feature of its surface (Glennie 1987). Depending on their definition, tropical deserts and semi-deserts currently occupy between approximately one fifth and one third of the Earth’s land surface, of which only about 4% is covered by that popular concept of what a desert consists of—sand dunes. The remaining area comprises barren rock (both hill and plateau) with a variable cover of sediments transported by ephemeral streams (wadis, arroyos) to form the deposits at the terminal points of these streams. Varying with the ratio of water supply to the annual potential rate of evaporation, those terminal areas may be occupied by desert lakes that are generally of a temporary nature (permanent only if the water is provided from beyond the margins of the desert or is fed by groundwater), and become more saline as they become desiccated. The end product of such a situation is a salina or sabkha (area of sand, silt or clay, commonly encrusted with halite). There is no universally accepted definition of a desert. In its simplest form it can be defined as a barren tract of land over which rainfall is too limited or spasmodic to support vegetation adequately. Very few desert areas are completely devoid of vegetation, and many areas that fall within a desert in terms of average annual rainfall may have an even though sparse cover of plants that have adapted to the relatively arid environment in which they live. In this context, some writers define deserts as areas that have an average upper limit of 250 mm of annual rainfall, even though it may all fall in one storm and rainfall may not recur for several years. Perhaps more important than the rainfall itself is the ratio between it and the potential rate of evaporation—the aridity or desiccation factor. This is about 1:10 in some parts of the Australian Desert and up to 1:500 in areas of the Sahara (Cooke & Warren 1973). Tropical deserts exist either because the winds that cross their

TL;DR: Deserts are excellent geological, geomorphic, and archaeological museums as mentioned in this paper, and the very aridity to which they owe their existence has made them remarkable repositories of past depositional and erosional events.

TL;DR: In this article, Honglianghe River section of Qinghai-Tibet Railway and Danghe river section of Dunhuang-Golmud Railway were selected as the typical representatives of high and low-altitude sand hazard sections, respectively, to understand the sand hazard law of different altitude railway sections.

TL;DR: In this paper, a bar on the Brazos River near Calvert, Texas, has been analyzed in order to determine the geologic meaning of certain grain size parameters and to study the behavior of the size fractions with transport.

TL;DR: In this article, a detailed mapping of the sedimentary geology of Saudi Arabia by the Arabian-American Oil Co. (Aramco) began in 1933, and by 1959, exploration parties of one type or another had surveyed more than 1.3 million square kilometers (500,000 square miles).

TL;DR: In this article, the third moment (skewness) of a normal curve is used to distinguish between dune, beach, and river sand, and the difference between the two types of sand types can be numerically stated by computing the third moments of the distribution curve.