Влияние материнских пород на состав гипергенных продуктов кор выветривания в Южной Болгарии

T. Todorova, D. Stefanor. Influence of inirial rock s on the composition of supergenic products in the weathering crusts of South Bulgaria. Most of the so far known relics of ancient weathering crusts on the territory of Bulgaria occur in the southern parts of the country. They are exposed mainly in South Pirin, the Rhodopes and Strandža Mountain. Boreholes, drilled recently in some regions of Thracia, found in many places relics of ancient weathering crust below Paleogene sediments. The formation of the ancient weathering crust preserved until now in South Bulgaria began before the Paleogene, according to the available data during the Late Cretaceous and may be earlier. The growth of the thick crust terminated somewhere in the Miocene. The recent weathering is exposed mainly in the formation of grus and less commonly – in the origin of clay minerals.
   The crust are of sialitic type. They develop in rocks of different genetic and petrochemical types. Irrespective of the different age of the crusts the uniform sialitic character of the weathering processes enables to study in detail the intlerrelations between the composition of the initial rocks and their su pergcnic product which are well expressed in the lower zones of the weathering profiles. There is a tendency to form specific chromium- and nickel-bearing minerals after serpentinites, of smektites after amphibolites, actinolite schists and intermediate volcanic rocks, of minerals of the kaolinite group after gneisses, quartz-feldspar meta rocks, granites, pegmatites and acid tuffs. In the upper parts of the weathering profiles the in fluence of the in itial roks is not so well expressed but nevertheless mainly iron ochres form after serpentinites and kaoline clays of variable content of iron oxides and hydroxides – after the othe rrock types.