Microtextural Characteristics and Origin of Dolomites in the Tepearasi Formation, SW of Beysehir‐Konya, Turkey

Abstract

Abstract The Tepearasi Formation of the autochthonous Geyikdagi Group in the Central Tauride Belt, SE of Beysehir, is Dogger in age and consists dominantly of massive limestones and greyish dolomites occurring within the middle to upper sections. The total thickness of the dolomitic levels ranges from 100–300 m and laterally extends 500–700 m. Three types of dolomite were distinguished through petrographic analyses: homogeneous, mottled (saddle‐crystalline) and joint‐filling dolomite, which were interpreted to have formed in two different stages, early diagenetic and late diagenetic. The homogeneous dolomite of the early diagenetic stage is light‐coloured and monotonous‐textured and shows the form of a dolosparite mosaic. The mottled dolomite formed in the late diagenetic stage is light‐ to dark‐coloured and coarsely granular idiomorphic. The other type of late diagenetic dolomite, described as the joint‐filling type, presents a crystal growth pattern from the joint walls towards the centre of the joint space. It is associated with coarse calcite crystals as well as primary dolomite crystal clasts which were formed in the early diagenetic stage. In addition to these characteristics, cataclastic texture indicating the influence of tectonism is also observed. Microtexture‐oriented scanning electron microscopy (SEM) studies indicate that mottled dolomites show zonal structures and contain secondary dissolution vugs. SEM studies also revealed the existence of some remains (calcite, clay etc.) in joint‐filling dolomites. Analyses by energy dispersive spectrometry (EDS) indicate the existence of clay minerals (likely to be illite) in the pores of dolomite. Isotope studies conducted to shed light onto the origin of the dolomites of the Tepearasi Formation yielded the results of δ18O=‐2.48 to −3.87%‰ and δ13C=0.93 to 1.12%‰ for the early diagenetic homogeneous dolomites. Mottled and joint‐filling type dolomites of the late diagenetic stage, on the other hand, gave the results of δ18O = −5.42 to −7.12%‰, and δ13C=‐2.29 and −5.70 respectively. X‐Ray diffractometry (XRD) and energy dispersive analysis X‐Ray (EDAX), atomic absorption spectrometry (AAS) analyses, results of petrographic data, and δ18O and δ13C values suggest that the early diagenetic dolomitization in the Tepearasi Formation occurred under the control of hypersaline (rich in Mg) and fresh water mixing zone. The late diagenetic dolomites partly developed under the control of tectonic thrusting.