The Origin of Oltu Stone (Turbostratic Carbon) from the Olur-Tortum Area: A Natural Composite Carbonaceous Material (Erzurum, Türkiye) Olur-Tortum Bölgesindeki Oltu Taşının (Turbostratik Karbon) Kökeni: Karbonlu Doğal Bir KompozitMalzeme, Erzurum, Türkiye

Creative Commons License

Helvaci C., HATİPOĞLU M., Passeri D., Konak N., Kinaci E. H.

TURKIYE JEOLOJI BULTENI-GEOLOGICAL BULLETIN OF TURKEY, cilt.68, ss.85-108, 2025 (ESCI, TRDizin)

Özet

This study focuses on geological, microstructural, oxygen isotopic, and thermogravimetric investigations of Oltu stone, which is the most important turbostratic carbonaceous material in Turkey. The results of our investigations indicate that the carbonaceous Oltu stone material (specific gravity of 1.317) is not an organic material, such as jet, derived from fossilized wood. Rather, it is composed of a carbonaceous phase intermediate between amorphous carbon and crystallized graphite (termed turbostratic carbon), that is intercalated with flysch and formed by the reduction of seeping magmatic carbon dioxide during the diagenesis of Upper Jurassic-Lower Cretaceous marine sediments. Oxygen isotope analyses (SMOW) (using EA-IRMS) of both Oltu stone (delta 18O = +37.2%oto +40.8%o) and the enclosing flysches (delta 18O = +10.3%o to +12.3%o) suggest that the nodules formed during diagenesis at a temperature of around 50 degrees C. However, they are enclosed in flysches whose grains are derived from rocks that formed at significantly higher temperatures, perhaps above 100 degrees C. The main industrial use of Oltu stone is as host material for diamond coating, as the sp3 bonds in the material can provide nucleation sites for diamond crystals and improve the nucleation rate at the early stage of diamond deposition on turbostratic carbon.