The Upper Cretaceous sediments of the Gurun area (Sivas-Turkey) with particular reference to the diagenesis and environment of deposition and diagenesis of the carbonate rocks

Abstract

The work is primarily concerned with the study of the petrography, depositional environment and various aspects of diagenesis of the Upper Cretaceous carbonate rocks of the Gürün (SIVAS-TURKEY) area. At the same time the geologic evolution and geology of Anatolia has been reviewed. Over twenty complete sections of the Gürün carbonate rocks were sampled at various intervals for petrographic study. The environmental suite which can be delineated for the Upper Cretaceous rocks of the province is a typical carbonate platform sequence characterized by shallow-water cyclic carbonate sedimentation extending over large areas. This transgressive marine carbonate sequence is associated with regional Upper Cretaceous transgression. On the outer margins of the shelf knoll reef ramps were developed where rudists had played an important role. Deepwater sediments are characterized by calciturbidites. Ideal carbonate platform model and twenty-four Standar Microfacies Types proposed by WILSON (1975) have been found applicable to the Gürün carbonates and employed in the present account. Study of almost one thousand thin sections and more than one thousand and five hundred peels reveals that the original carbonate sediments have been modified by a number of diagenetic processes. Biologic diagenesis, formation of micritic envelopes and micritization were contemporaneous with deposition. Two phases of calcite cementation occurred in the grainstone facies. The origin of the limestone of the Gürün region involved the deposition of large quantities of carbonate mud over a long interval of geologic time and conversion of this carbonate mud to lithified micrite is the most important aspect of neomorphism. Two stages of dolomitization have been observed. Dolomitization of the Gürün sediments was caused by the mixing of seawater and ground water in the phreatic zone (Dorag dolomitization model). Dedolomitization is common in the NW of the area. Silicification is widespread in the calciturbidites. Where data permit, the author has attempted to draw conclusions regarding time relationships of the various diagenetic processes.