Our study is focused on the structural geometry of the western part of Kura foreland fold-and-thrust belt (KFFTB) disposed in the central part of the Caucasus. Structural architecture of the Georgian part of the KFFTB has been interpreted using seismic reflection profile. Building of structures of the Kura foreland basin was formed by Greater Caucasus basement wedge propagation along detachment horizons within the cover-generating thinskinned structures represented by Neogene shallow marine and thick continental sediments. Based on the structural style of deformation, two seismicstructural complexes were identified in seismic profiles: an upper and a lower complex. Seismic reflection data reveal the presence of south-vergent thrusts, north-vergent backthrusts, and duplex. The deformations in the KFFTB structures were controlled by the multi-level detachments. The Didi Shiraki thrust-top basin has a bivergent geometry and is filled by Pliocene-Pleistocene syn-kinematic sediments.
Megagrapton Książkiewicz, 1968 is a characteristic deep-sea trace fossil belonging to the group of graphoglyptids and mostly preserved as a network of irregular meshes in hypichnial semirelief. So far, eleven ichnospecies have been distinguished under this ichnogenus, though commonly on weak evidence. The so-far poorly known ichnospecies Megagrapton aequale Seilacher, 1977 is described here on the basis of the numerous, newly discovered specimens from deep-sea siliciclastic deposits of the Bolevani Subsuite (lower Eocene) in the Lesser Caucasus of Georgia, together with other collections and published examples. A neotype of this ichnospecies is designated and the diagnosis emended. M. aequale occurs in lower Cambrian to upper Miocene deep-sea turbiditic deposits, mostly in the Paleogene. It is characterized by relatively small, variable meshes, which have mostly irregular sub-pentagonal, sub-hexagonal or sub-heptagonal shapes that are variable in size and are bordered by curved or straight semicircular ridges. It has been mistaken for Paleodictyon, which forms regular hexagonal nets. Paleodictyon imperfectum Seilacher, 1977 is included in M. aequale as the ichnosubspecies M. a. imperfectum, which is characterized by relatively thin bordering ridges. After critical analysis of all ichnospecies, only M. irregulare Książkiewicz, 1968, M. submontanum (Azpeitia Moros, 1933), and M. aequale are recommended for further use. These are distinguished on the basis of the prevailing morphology of the meshes, irrespective of large differences in morphometric parameters within the ichnospecies. Irredictyon chaos Vialov, 1972 is included in M. irregulare as the ichnosubspecies M. i. chaos, which is characterized by relatively thick bordering ridges. Megagrapton is interpreted as a cast of a subsurface open burrow network with a few connections to the sea floor. The burrows probably functioned as a trap for small organisms (ethological subcategory irretichnia).
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