SEDIMENTOLOGY OF CALICHE (CALCRETE) OCCURRENCES OF THE KIRŞEHİR REGION

ABSTRACT.- Study was conducted in the Kırşehir region. Carbonate occurrences within the upper Miocene-Pliocene deposits forming the subsidence basins surrounded by the Kırşehir massive, are described as caliche. These caliche deposits in the alluvial fan-meandering river and lacustrine environments are found in three different zones. In the measured, sections, conglomerate comprises the basement and is overlain by a transition zone made of sandy mudstone (Zone I). Above them is the rarely nodular carbonaceous zone with horizontal and vertical positions in the reddish mudstone-siltstone (Zone II). Finally, laminated caliche (calcrite) comprises the upper most part (Zone III). Carbonates in the basement, country rocks, and in the soil are dissolved in the acidic environment and become a solution saturated with calcium bicarbonate. This solution is transported to the sediments and capillary rises through the sediments during arid-semi arid seasons. Carbondioxide in the Ca and HCO3-bearing solution is removed from the system and as a result, calcium carbonate nodules and laminated caliche are formed. These stromatolite-like laminated caliche occurrences show a criptoalgal structure under polarized microscope and scanning electron microscope (SEM), and they contain microerosional surfaces and caliche pisolites that are formed by dissolution. Caliche occurrences are believed to be source of camotite, thorium, vanadium, sepiolite, huntite, dolomite, and magnesite