Geology of the Eski Gümüşhane and petrographic and geochemical investigation of sandstones in Şenköy formation (Early-Middle Jurassic)

This study contains geological analysis from H42-b2 unit and petrographic, and geochemical properties of sandstone in Early-Medium Jurassic aged Şenköy formation in Eski Gümüşhane area. Şenköy formation formed by conglomerate and silisified wood fragments at the bottom. In the study area, coal beraing sandstone levels are the main components of the Şenköy formation. The sandstones in Şenköy formation have the capability of saving substantial information on the geochemical and petrographical properties of the provenance. Rock fragments, feldspar and quartz are the main components of the sandstones. Rock fragments can also be divided into two sub-groups as acidic and basic fragments. These rock fragments might be derived from both previous basement volcanic rocks and basic arc volcanism in Jurassic time. Trace elements such as Th and U which represent the proportion of felsic components and Sc and Cr which measure the abundance of mafic components in clastic rocks display large variations in contents. This may suggest that the felsic rocks, as well as mafic rocks in significant proportions, in the source area might be found. Whole-rock geochemistry of these rocks defines more than one tectonic environment, e.g., island arc, active continental margin and passive margin, rather than a specific tectonic environment during their accumulation. Taking into account that the investigated sandstones were in a back arc position during the Early Jurassic, the clastic rocks accumulate in basins fed from either active volcanic arc and also from the continent. In the study area, sediments in Şenköy formation do not include finding of marine fossils and contains coal bearing levels, silisified wood fragments, conglomerate and sandstones. The conglomerate and sandstones are not continuously, and have abrupt facies change, almost angular component in silisic cement. The investigated sediments in Şenköy formation may accumulate in terrestrial environment.