This study consists of the investigation of lithological and mineralogical properties of Lower Miocene aged Kapıkaya Formation that outcrops in Siirt-Kapıkaya region located in Southeastern Anatolia Autochthon (SEAA) representing the north of Arabian Platform. Kapıkaya formation consists of gypsum, limestone and tuff interbedded red-brown and gray mudstone, siltstone and sandstone alternation. Quartz, calcite, feldspar, phyllosilicates, dolomite, analcime, gypsum and pyroxene minerals were determined at Kapıkaya Formation volcaniclastic, clastic and sulfate rocks. The abundance of minerals are respectively phyllosilicates, feldspar, quartz, gypsum, calcite, analcime, dolomite and pyroxene minerals according to the overall average value. Illite, smectite and chlorite represents phyllosilicates minerals belonging to the formation. The mineral forms listed as chlorite, illite and smectite according to the presence frequency are listed as illite, chlorite and smectite according to the overall average abundance minerals. Calcite + quartz + feldspar + phyllosilicate assemblages are commonly observed at clastic rocks (shale, siltstone). In tuffite, volcanogenic origin analcime minerals are added to calcite + quartz + feldspar + phyllosilicate assemblages.Besides the existance of gypsum mineral in sulfate rocks, it was determined that calcite and quartz accompany to these minerals. Illite + chlorite + smectite, illite + chlorite and smectite + chlorite association compose common phyllosilicates assemblage at Kapıkaya formation. Besides that the unit represent the marine sediments, it was interpreted that volcaniclastic levels Lower Miocene age unit that accompany to these rocks is fed from Miocene old volcanism that is active in the area and analcime and smectite minerals compose with the interaction of especially volcanic glass + seawater.
Key words: Arabian plate, Analcime, Clay, XRD, Volcanoclastic