Geological structure of the middle part of the river Aragvi valley and trace fossils of upper Cretaceous sediments

The study area is located within the Zhinvali-Gombori and Shovi-Fasanauri sub-zones (structural-morphological units) of the Mestia-Tianeti zone of the Greater Caucasus fold-and-thrust belt. The oldest formations of the Aragvi River valley midstream are upper Jurassic-lower Cretaceous sediments, which, depending on the composition and source of the material, are characterized by all the common to flysch features. Together with upper Cretaceous-Paleogene formations they represent the entire carbonate-clastic/calciclastic flysch formation of the eastern part of the Greater Caucasus backarc basin (the eastern Chiauri-Dibrari Flysch basin). According to geological-structural features, the study area can be divided into two Ananuri-Zemo Mleta and Zemo Mleta-Kobi segments. The first one is characterized by the development of structures of different morphologies and sizes, complicated by mainly north- and rarely south-dipping steep (60-85°) faults (reverse faults and steep thrusts) with different amplitudes. The characteristic feature of the second fold structure is the development of the first order plicative dislocations which are similar in shape, but differ in size and the almost complete absence of disjunctive dislocations, which do not break the unity of folds. Trace fossils within the study area have been found in the small Jakha-quarry and Tsikhisdziri cross-sections. Rocks of the Campanian "Jorchi" and Maastrichtian "Sabue" formations host ichnofauna. The identified in the upper Cretaceous sediments of the Aragvi river ichnocomplex: Chondrites intricatus (Brongniart), Ch. targionii (Brongniart), Ch. affinis (Brongniart), Halopoa imbricata Torell, Helminthopsis isp., Megagrapton aequale Seilacher, Nereites irregularis (Schafh.), Nereites isp., Ophiomorpha annulata (Książkiewicz), Oph. rudis (Książkiewicz), Phycosiphon incertum Fischer-Ooster, Planolites isp., Protopaleodictyon isp., Scolicia strozzii (Savi & Meneghini), Spirorhaphe isp.,Thalassinoides isp., Trichichnus linearis Frey, Zoophycos isp. - indicates to the Nereites ichnosubfacies of the deep-sea Nereites ichnofacies. According to the paleogeographic map of Santonian-Maastrichtian time (Tsagareli, 1954, Fig. 33), the study area was a deep marine basin of turbidite sedimentation, which is confirmed by the paleoichnological data.