Eolian Deposit

a deposit that forms as a result of the accumulation of wind-driven products of the weathering of solid bedrock or unconsolidated alluvial, lacustrine, marine, or other deposits.

Eolian deposits are found primarily in arid regions (sands, loesses), but they also occur in other natural zones. When moving in the wind-sand stream, grains of sand are bounced or rolled. In a suspended state, dust particles can be lifted by ascending air currents to 3,000–6,000 m and are transported hundreds or thousands of kilometers. When wind energy is not sufficient to transport sand and dust particles, they fall out of the air and accumulate, often in front of orographic barriers. When precipitating from the air, sometimes with rain droplets or snow, dust particles become mixed with marine and continental sediments of varying origin and in such cases do not form independent eolian accumulations. According to the findings of the Soviet geologist A. P. Lisitsyn, dust particles precipitated from the air constitute 20–75 percent of the oceanic bottom sediments; various salts (for example, carbonate and chloride salts) also precipitate from the air with them. Eolian sand deposits are found along seas and lakes and on river terraces, in addition to deserts. There are eolian sands confined to regions of former continental glaciation.

Eolian dust sediments, which in many cases have given rise to loesses and blanket loams, occur almost everywhere. Eolian deposits are usually formed from deposits of sand of marine, delta, alluvial, proluvial, lacustrine, or glaciofluvial origin. Compared to source sands, eolian deposits are usually better sorted, have fewer easily abraded minerals and more grains of solid and newly formed minerals, and are yellowish brown in color. Large and medium-size grains (more than 0.25 mm) of hard minerals are well rounded; angular to rounded grains predominate among the fine-grained fraction.

Prolonged eolian processing forms deposits of sand consisting of well-rounded, polished grains of the most stable minerals only, such as quartz, zircon, garnet, and, less frequently, magnetite and others. Some eolian deposits consist entirely of one component (for example, limestone, oolitic, coral, shell, and other sands). Eolian sandy deposits usually have diagonal-wavy or oblique-wedge stratification. Their thickness ranges from a few meters to a few dozen meters, occasionally reaching several hundred meters, corresponding to the height of major aggradational eolian landforms. Sandy deposits are subdivided into stationary (fixed) and migrating (drifting) sands on the basis of the degree and nature of eolian processing. The former are more common and have not lost their areal continuity with the underlying original sand. They are characterized by relatively large grains (1.0–0.25 mm), and they are richer than the original sand in heavy minerals, which sometimes leads to a concentration of minerals, as, for example, in the eolian placers of rare-metal minerals in the Sahara and Florida. Drifting sands do not have an areal continuity with the country rock and lie on a foreign substrate. They are characterized by fine-grained (0.25–0.1 mm) material and minerals of the light fractions.

The genetic classification proposed by the Soviet geologist A. V. Sidorenko, which considers the nature of the wind action, the source of the original material, and the degree of eolian differentiation, identifies the following types: (1) eolian deposits of regions where wind erosion predominates—wind-worked boulders, gravel, and pebble accumulations of the mountain, polar, and submontane flat deserts, with the wind faceting characteristic of them; (2) deposits of regions of wind erosion, drifting, and accumulation—eolian-eluvial deposits, which are the most widespread type and which form along river banks and, under arid conditions, in the vast river overflow regions; (3) eolian-delta deposits; (4) eolian-proluvial deposits; (5) eolian-coastal deposits; (6) eolian-lakeshore deposits; and (7) eolian-glaciofluvial deposits. Eolian deposits of regions of wind aggradation are accumulations of “warm” dust particles (dust blown up during the drifting of loose material in arid deserts) and “cold” dust particles (from wind dispersal of sand deposits in near-glacier zones during the age of continental glaciation).