Türkiye Jeoloji Bülteni

Sedimanter Petrographic Properties of Eocene Sandstones and an Approach to Provenance According to Plate Tectonics in the Gümüşhane Region

Abstract: This study aims at determining the sedimentological and sedimanter petrographic features of, and thecorrelation between, Eocene aged volcanoclastic and siliciclastic characterized sandstones in theGümüşhane region.The thickness of the volcanoclastic sequence is 195 m. around Eski Gümüşhane and thethickness of the siliciclastic sequence is 280 m. around Ünlüpınar (Kelkit). The volcanoclastic sequenceis a composite of grey colored and medium, thick bedded limestone, grey, brown colored and thin,medium, thick bedded sandstone, green, grey, brown colored and thin, medium bedded marl-claystoneand tuff. The siliciclastic sequence is a composite of grey, yellowish brown colored and thin to thickbedded sandstone, and green, greenish grey, brown colored and thin, medium bedded marl. There isfrequently observed locally interbedded light grey, thin, medium bedded limestone, conglomarete andtuff.Sandstones of the Eski Gümüşhane sequence are median grained, well to moderately sorted andnear symmetrical to fine skewed. Sandstones of the Ünlüpınar sequence are medium to fine grained,very well sorted to poorly sorted and coarse skewed to fine skewed.The composite of the Eski Gümüşhane sequence’s sandstones comprises Quartzes(monocrytalline and polycrystalline quartzs), feldspars (alkali feldspars and plagioclases), lithicfragments (volcanic rock fragments), accessory minerals (olivine, epidote, biotite, chlorite), opaqueminerals, matrices and cements. According to the mineral ratios in the rock, sandstones belonging to thevolcanoclastic sequence are identified as arkose and lithic arkose.The composite of the Ünlüpınar sequence’s sandstones mainly comprises Quartzes(monocrytalline and polycrystalline quartzs), feldspars (alkali feldspars and plagioclases), lithicfragments, sedimentary rock fragments, (volcanic rock fragments), opaque minerals and cements.According to the mineral ratios in the rock, sandstones belonging tothe siliciclastic sequence areidentified as litarenite.Both of the sequences are either compositionally immature or texturally immature.The main provenances of the volcanoclastic and siliciclastic sandstones are generally magmaticarc, recycled orogen region and back arc subduction complex.