Geological review of a quarry section at Cosăuţi from Archean Eon

The review of a quarry section at Cosăuţi, the right bank of the Dniester Valley, through petrographical and sedimentological analyses, has allowed us new observations on the mineralogical composition (modal analysis) of the magmatic complex, microstructures and the textures of the associated rocks, but also a microscopic examination of the sedimentation sequence (Cosăuţi-Lower Ordovician). The polygenetic complex (G), magmato-metamorphic (Archaic-Proterozoic medium), with granitoids, gneiss, migmatite, xenolith is followed by a transition sequence (A) that appears to be an unevolved crust of alteration. Several genetic markers (quartz, potassic feldspar, triclinicity, myrmekites and perthites, restites, apatite and zircon) were identified. The three sedimentary units (B-C-D) considered the Lower Cryogenian age – medium. (Rifean, Geru, 1987) constitutes the beginning of the depositional sequence in the basin of the Dniester (with microconglomerate and coarse sandstones belonging to the Olcedaev member). The sequence reflects a shift from a LST regime to a transgressive TST regime, in which we have reconstituted sedimentation in shallow waters from the deltaic or coastal systems, with channel facies, levee and facies of the coastal or alluvial plains.