Demirözü (Bayburt) permo-carboniferous: Petrographical and geochemical investigation of clastic sedimentary rocks

In this study, the clastic sedimentary rocks in the Demirözü (Bayburt) area have been investigated in terms of their petrographical and geochemical compositions. As it is known, clastic sedimentary rocks form a single rock group having capability to give information on the disappeared parts of orogenic belts. In this contex, Permo-Carboniferous clastic rocks were measured in two locations near the Çatalçeşme as well as in one location near the Çamdere, and sampled especially in terms of their clastic rocks.Çatalçeşme formation is composed of sequential alternations of pebblestone, sandstone, shale and limestone. Hardişi formation, lies conformably over the Çatalçeşme, starts with pebblestone at the bottom and passes upward into the transgressive type sandstone, siltstone and shale. Sandstones of the Çatalçeşme formation were well-rounded and matured. They are largely of sublitarenite, and less subarkose and quartz arenite in composition. However, sandstones of the Hardişi formation are moderately rounded and arkosic arenite in compositipon. On the other hand, Çamdere ophiolitic mélange, which lies further east, appears to be equivalent of Hardişi formation in terms of time of occurrence. Limestones and sandstones in it generally carry the paleontological and sedimentological features similar to those of the Çatalçeşme. But, apart from the Çatalçeşme, it comprises blocks of meta-tuff, dolerite, basalt and meta-basalt surrounded by thin-bedded slate.Çatalçeşme sandstones have SiO2 contents > 85 wt %. SiO2 content of the clastic rocks of the Hardişi formation, stratigraphically above the Çatalçeşme, is in between 66-81 wt%. Once compared to each other, the Çatalçesme sandstones display more depleted trace and rare earth element (REE) concentrations than those of the Hardişi formation. On the other hand, the rocks of the Çamdere ophiolitic mélange exhibit a large compositional range (SiO2 = 47-92 wt %).A felsic provenance for the rocks of both the Çatalçeşme and Hardişi formations is inferred from their major and trace element geochemistry. REE profiles that are similar to those of the granites point to granitic or rhyolitic rocks in their source areas. Rocks with the moderate composition in the provenance are indicated by major and trace element geochemistry of the slates from the Çamdere ophiolitic mélange. Chemical Index of Alteration (CIA) values vary in between 75-81 for the Çatalçeşme sandstones while in between 58-65 for the rocks of the Hardişi formation. These CIA values point out an intensive and a moderate chemical alteration, respectively, in the source areas of the rocks from the Çatalçeşme and Hardişi formations. The CIA values of 67-79 of the slates from the Çamdere ophiolitic mélange imply climatic conditions in their source area similar to those of the Çatalçeşme sandstones. The major and trace element geochemistry of Çatalçeşme sandstones are typical of passive margin setting that is characterized by recycling and maturation of earlier sediments, whereas the rocks of the Hardişi formation carry the geochemical features of subduction related settings such as active continental margin, continental arc and oceanic island arc. On the other hand, although the clastic rocks of the Çamdere ophiolitic mélange seem to offer a large interval of tectonic setting, if rocks are considered separately, sandstones and slates in turn define same tectonic settings as those of the Çatalçeşme sandstone and Hardişi clastic rocks.