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STRUCTURE AND EVOLUTION OF COLLAPSIBLE DEPOSITS EAST OF BUCHAREST OF THE MOSTISTEA PLAIN, ROMANIA

AL. Istrate, M. Frinculeasa

Abstract

Sedimentation of loess deposits in southern, southeastern and eastern Romanian Plain is a consequence of developments in Romanian Carpathian chain and the outer rigid platforms based on global climate changes, which have succeeded in the Quaternary period. The Loess deposition took place in at least two interglacial stages, the last one took place at the end of the upper Pleistocene, when is finalized, mostly the Romanian Plain relief. MostiЕџtea plain is situated at east of Bucharest; the area is bordered by rivers D\^amboviЕЈa, in southwest, and MostiЕџtea, in north-east, where is forming a tabularlooking field with inflexions of the surface, sometimes with high amplitude. The depression areas, where they were installed, often, lake systems, they are a reflection of the characteristics of the loess deposits to settle under their own weight in water load. From land investigation and laboratory analysis results vertical structure and evolution of loess deposits.Relatively uniform granular structure shows that the main factor is the eolian transport and sedimentation, the glacial deposits of the Carpathians being the sediment source. The sequence is separated vertically into two subareas with different behavior on the property of settlement by wetting. Thus, the surface retains the property to settle relatively suddenly the effect of vertical water infiltration, while the bottom subarea has lost this property. This results from the vertical distribution of calcium carbonate and the physical and mechanical properties determined by laboratory tests. From macroscopic observation the processes that are evident are calcium carbonate dissolution in their top and precipitation to bottom. This means, that in time, the subarea has evolved in a relatively constant intake of water which have reworked the carbonates towards the bottom and produced the settlement of loess deposits under its own weight. Perhaps this lower subarea evolved in wet weather conditions that keep excess moisture from the ground surface.

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