Diagenesis and Paleogeographic Development of Oligocene Evaporites of the Germik Formation (Kurtalan, Sw Siirt), Turkey

Abstract

This study deals with the Oligocene evaporites of Germik Formation near Kurtalan to the SWof Siirt. The diagenetic phases (early-late) and processes (compaction, cementation, hydration and substitution) of evaporites were determined and paleogeography of the region was revealed. According to stratigraphic and sedimentological rocks and constituent studies, evaporitic minerals were investigated together with their textures, lithologies and sedimentary structures and a lithofacies classification is proposed. The lateral and vertical continuity of lithofacies with regards to each other was interpreted considering stratigraphic sections and the variation of gypsum and anhydrite formation in various climatic and tectonic conditions was introduced. Besides field studies, the petrographic and minerologic properties of evaporites were also investigated and the primary fabric and sedimentary structures (such as lamination, stromatolitic, nodular and chicken-wire structures) of evaporite types were determined. Eventually, it was identified that the evaporites in the region were generally altered by diagenesis and are secondary in origin. The evaporites of Germik Formation were formed during early diagenesis (primary anhydrite, formation of anhydrite nodules) and late diagenesis (burial-exhumation: anhydrite-gypsum transformation, calcite, dolomite and celestite crystallization and formation of secondary gypsum such as alabastrine, porphyroblastic and satin spar by the interaction of anhydrite with soil or ground water) processes in an environment changing from coastal sabkha to shallow sea. In the region, a deepening sea environment from NW to SE during Oligocene period was revealed according to the correlations of the W-E and N-S trending measured stratigraphic sections taken from the Germik Formation.