Geological structure of eastern part of Artvin-Bolnisi Block and Ichnological-sedimentological survey of upper cretaceous sediments

The study area is located within the Bolnisi zone of the Artvin-Bolnisi Block. According to lithostratigraphic features it is represented by the Khrami and Loki massifs, separated from each other by the Mamulo-Shikhilo sub-latitudinal reverse fault/thrust. The eastern part of the Artvin-Bolnisi block is made up by the Upper Cretaceous and Quaternary rock strata. The Upper Cretaceous is mainly represented by the marine dacite-rhyolite lavas, volcaniclastic and extrusive/volcanic rocks. They are intercalated by the alternation of regionally extended andesite-basalt formations and more or less continuous packages of sedimentary rocks. The Quaternary is represented by the basalt lava flows of the Akhalkalaki Formation and proluvian-alluvial sediments. Mesozoic-Cenozoic intrusive bodies represented by shallow-hypabyssal small porphyry veins, sheet/sills, dykes, necks and small or medium size stocks, demonstrate complete spatial, age, petrological and genetic relations with the volcanogenic-sedimentary rock formations. The main geological structure in the study area is the Mamulo-Shikhilo sub-latitudinal reverse fault/thrust which divides it into Loki and Khrami tectonic massifs (tectonic blocks). The major structure of the Senomanian-Danian structural stage is the gently dipping to the North monocline with weakly compressed folds. In some cases it is complicated by the local, low-amplitude reverse faults. Overall, trace fossils assemblage established in the upper Cretaceous sediments of the Artvin-Bolnisi Block: Bergaueria isp., Gyrolithes isp., Lockeia isp., Ophiomorpha annulata (Książkiewicz), Ophiomorpha rudis (Książkiewicz), Planolites isp., ?Skolithos isp., Thalassinoides isp. is atypical, but according to the ichnofacies distribution scheme, it resembles the shallow- marine (shelf) Skolithos and Cruziana ichnofacies Developed in the study area sedimentary structures are indicative of the shallow- marine depositional environment as well.