Akademik Veri Yönetim Sistemi
CANADIAN MINERALOGIST, cilt.40, ss.1091-1102, 2002 (SCI-Expanded)
The Middle to Upper Miocene volcano-sedimentary units in the Mihaliccik-Eskisehir area of Turkey consist mainly of altered tuff and claystone, with thin layers of dolomite and silica nodules and horizons. Ripple marks and desiccation cracks are common in the siliceous tuff and dolomite units. Green to yellowish green claystone exhibits either hard layered or friable features. Sepiolite and loughlinite are dominant in the claystone of the study area. These minerals are generally associated with opal-CT, analcime, feldspar, dolomite and calcite. At Mihaliccik, loughlinite and sepiolite are identified by d(110) reflections at 12.9 and 12.3 Angstrom, respectively. Loughlinite and sepiolite occur as fibers in dissolution voids and along the sides of dissolved volcanic glass particles and casts of silicic nodules. The area is represented by a lacustrine environment of variable depth and salinity, controlled by synsedimentary step-faulting in and and semi-arid climatic conditions. Under these conditions, volcanic glass as well as dolomite release Si and Mg, which are used for the formation of sepiolite. Increasing evaporation causes the dominance of Mg with Na and K in the depression zone in the Killik area, favoring the formation of loughlinite under alkaline conditions. Field observations and mineralogical determinations indicate that sepiolite and loughlinite are both formed authigenically and independently in different physicochemical environments rather than being the product of a transformation of one to the other.