Petrographical and Geochemical Characteristics of Metacarbonates in the Bozdag Formation, Northwest Konya, Central Turkey

Abstract

Introduction The study area is located between Yiikselen-Osmancik and Kadinhani towns, about 40 km northwest of Konya. The area is included in the Afyon-Bolkardagi Zone (Okay, 1984), or in the Kiitahya-Bolkardag belt (Ozcan et al., 1988). Bozdag formation was first named by Dogan (1975) and its general field descriptions were reported by Eren (1993) and Kurt (1994). Bozdag formation, which can be observed as various shaped and isolated masses, include different grade metamorphosed limestone, dolomitic limestone and dolomite. The limestone is light grey, white in colour and generally massive to medium bedded (10-50 cm). The dolomite and dolomitic limestone are medium to thick bedded, black and dark grey in colour, which caused by very high contents of bituminous, and insoluble residue. They show very fine lamination and comprise widespread biostromes of Amphipora. When broken, all the dolomite and dolomitic limestone regardless of colour, give off a strong, petroliferous odour. The rocks of this formation, which metachert beds and chert lenses generally occurs in metacarbonate, are interfingering with each other laterally and vertically. The metacarbonate rocks contain corals, which are T h a m n o p o r a , S y r i n g o p o r a and C a n i n a , Stromatoporoid which is Amphipora, crinoids, fusulinide and algae. These fossils indicate a middle Devonian and early Carboniferous age for the formation. Otherwise the formation contains an abundant microfauna which is difficult to identify, due to metamorphism and recrystallization. These metacarbonates are cut by intrusive dykes and active volcanism and metasedimentary rocks also recorded in the surrounding area (Eren, 1993; Kurt, 1994). The aim of this research is to investigate the petrography and geochemistry of the metacarbonate rocks studied. Mineral identifications were made optically by X-ray diffraction methods. An analysis of major and trace elements was made by the X-ray fluorescence. Petrography The light coloured metacarbonate is composed of micrite cement, calcite, dolomite, biomicrite, coral and Fe-oxide. The calcite grain boundaries are sutured and are fragmented and set in a secondary calcite cement. Some coarse calcite crystals show deformation twinning, kinking and inclusion trails. The grain size distribution is unimodal. An abundance of such twinned lenses characterises as the twinning regime. Very small calcite grains are found mainly in the groundmass, but sometimes fill fossil cavities. Noncarbonate minerals accumulated along stylolites as insoluble residues, these residues also form the boundaries of veins, and this relationship indicates that some veins formed by void filling after formation of stylolite. Insoluble residues contain iron oxides, organic materials and sericite. The rocks show laminated zones and mosaic textures. Dark coloured, bituminous and partly dolomitized limestone consist of fine to medium crystalline sucrosic dolomite, biomicrites, pelmicrites, corals, with well developed crystalline microvuggy porosity. Dolomite has almost obliterated the original structure of the fossils. Very small calcite grains fill fossil cavities. The fine grained (0.1-1 mm) dolomite crystals are brownish and clearer rims. The texture is dominated largely elongation and characteristically have irregular and inter locking boundaries. Stylolitization occurs typically as a haphazard replacement of matrix and sparry calcite by irregular. Lithification after burial is partly supported by the preferred orientation of microfossil test and other grains (long axes are parallel with bedding) which is result of compaction and deformation. Geochemistry Two samples from dolomitized limestone were analysed for mineral compositions by XRD. Dolomitized limestone consist mainly dolomite (Fig. 1). 5 samples from limestone and 3 samples from dolomitized limestones were analysed for major and trace element composition by XRF method (Table 1).