Traits Particuliers Minéralogiques-Géochimiques de L'assise Terrigène du Carbonifère Inférieur Dans La Région Ouralienne-Volgienne

Abstract

On the basis of the content of syngenetic iron-minerals in the clayey and clayey–silty deposits of the terrigenous layer, two series of mineralogical–geochemical facies have been established: those where the zones of oxidation and reduction have undergone small scale fluctuations, and those where these zones had a constant position. The first ones typically contain sulfide–siderite, siderite, etc., while in the second facies the syngenetic iron-minerals are represented only by sulfides in presence of benthos. The sediments of Radaev and Bobrikov age (Lower Vistan) in the Ural–Volga region best demonstrate the analyses of littoral–marine intertidal and deltaic sediments. During the Radaev stage (characterized by dominantly regressive conditions) a narrow sea strait existed in the area of the Kama–Kinel depression, which opened at the northeastern and southern endsinto marine basins. The marine deposits here show a development of the sulfide–siderite facies. Locally, along this strait mangroves were present during Radaev times. West of the Kouibychev area as well as in Tataria, beyond the Kama, lacustrine to marshy deposits were formed, which show a facies analogous to the siderite–sulfide facies. During the Bobrikov stage delta sediments were accumulated in the Perm area, while in the Kama–Kine depression two river valleys were formed, separated from each other by a saddle. In these valleys two types of sedimentation took place: one mainly limited to the river bed itself, the other limited to the flood plain. The Bobrikov deposits show chiefly a facies analogous to the siderite–sulfide facies.