Alluvial features

One of the characteristic features of Reg soils is the vesicular nature of the uppermost soil horizon. The size distribution of the vesicles is up to a few mm in diameter. Similar vesicular structures were also observed in lithosols and takyr-like alluvial soils and were always associated with the presence of stones or thin, hard crusts that sealed the soil surface. It forms mostly through accumulation of aeolian dust (McFadden et al., 1998). 

The Danube underwater canyon system is crowned by a thick alluvial fan. The relative height of this topographic feature reaches 500 m at a width changing from 40 km in its upper part to 60 km at its base. The alluvial fan is advanced by 100 km in the southeastern direction into the western depression of the sea. At the center of the fan, one observes an underwater valley rimmed by high (up to 300-400 m) near-channel bars [11]. 

The northwestern region is characterized by large provenance areas, from which alluvial matter is supplied via the deltas of the Danube, Dniester, and Dnieper rivers. The Danube River, which features a wide delta with numerous channels and branches provides the greatest solid runoff to the shelf zone. The delta is composed of terrigenous sediments and is advanced toward the sea by 7-10 km. 

Unit C at Nekhen is clearly different from the sediments above and below it. Comparing all features (including the location of its occurrences), it is clear that Unit C is material washed from the wadi and deposited in a small alluvial fan during the period from 3200 to 2500 B.C. At this time, Nile flooding must not have reached the site, but there were substantial amounts of water to wash sediments from the wadi. This evidence supports other paleoclimatic studies that suggest periods of moist conditions on the Egyptian desert (18). 

Figure 2.9 Characteristics of groundwater calcretes. (A) Generalised macroscopic features based on various sources. Some workers, such as Carlisle (1980), identify two zones in the massive phreatic unit an upper earthy zone with remnant soil and alluvium, and a lower, dense porcellaneous zone with abundant cracks and cavities. Phreatophytic plants may also produce features such as rhizocretions and laminar rhi-zolite crusts (Seminiukand Meagher, 1981). (B) Generalised model for the evolution of groundwaters and their precipitates in semi-arid to arid alluvial systems based on Arakel (1986).

Figure 10.4 Playa depositional/evaporative facies arranged parallel to, and potentially concentrically in plan around the shorelines of an evaporating lake (from Eugster Hardie, 1978 with additional information from Kendall, 1992 Warren, 2006). The figure shows the relationship with other geomorphological and hydrological features such as alluvial fans, dunes, spring tufa, and the sources and movement of water.

This is a zone of poorly drained alluvial-lacustrine plains, where features of continental salt accumulation are clearly expressed. Broad-Leafed Aspen Forest and Meadow Steppe ecosystems on Phaeozems and Chernozems with association with meadow-bog soils and Solods are characteristic of this region. 

Geomorphic features Surface ruptures Colluvial aprons Titled surfaces Tectonic alluvial terraces... 

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