Contribution à L’étude géologique des formations évaporitiques du bassin néogène de Guelma (NE d’Algérie)

Abstract

The Neogene basin of Guelma is located in the north eastern part of the great Constantinian Neogene basin. . It is an intramountaneous basin, located along a major accident, represented by the major E-W strike-slip of Debbagh in the north, and bounded by marginal faults. The basinage is Miocene; it contains evaporate formations like, limestone, sulphate, salt, which lie in discordance, on the reef limestones of the neocomian, on the Seneonian calcareous, clays and sandstones of the flysch, also on marl and marl- limestone.This basin is characterized by evaporative deposits which appear to be in connection with the Messenian salinity crisis of the Mediterranean. The petrographic study on vaporative formations in the study area shows the existence of different gypsum facies and rock salt; gypsum facies are: nodular gypsum, solid gypsum, crystalline gypsum, fibrous and microcrystalline gypsum (Alabastrite) also altered gypsum (white powder) and dissolved. These data were confirmed by XRF analysis, which also shows the existence of calcite and sulphur The evaporate formations of Guelma basin seem to be linked with the messeninian crisis, which led to the precipitation of ions of Ca++,SO-3,Na+ and Cl- resulting in the formation of salt and gypsum deposits.Another feature that is very important is the presence of the native sulphur, which is developed at Heliopolis. These native sulphur deposits associated with gypsum, limestone. The source of this native sulphur is the consequence of the reduction of gypsum sulphates by bacteria.The useful substances found in this basin are: gypsum, sulphur rock salt and currently the ORGM conduct prospecting and research on sulphur.