Wyniki wyszukiwania - BazTech

Ograniczanie wyników

Znaleziono wyników: 3

Liczba wyników na stronie

Wyniki wyszukiwania

Sortuj według:

Ogranicz wyniki do:

Geodynamics of the Eurasian and Africa–Arabian collision zone as exemplified by the Black Sea–Caspian Sea region

Adamia Shota, Sadradze Nino, Chabukiani Alexander, Lebanidze Zurab, Aphkhazava Maia, Sadradze Guga

Geotourism / Geoturystyka

2023

nr 1-2 (72-73)

9--10

The lithosphere structure and geological evolution of the Caucasus and adjacent areas is determined by its position in the continental collision zone between the Eurasian and African-Arabian lithosphere plates, where convergence is still on-going at average rate of movement 10–30 mm/per year. The region located in the central part of the collision zone represents the lithosphere fragments collage of the Tethys Ocean and its continental margins. Within this area the system of island arcs, intra- and back arc bsins existed during Neoproterozoic–Early Cenozoic. Supra-subduction, midocean ridges and within plate magmatic activity took place during Paleozoic–Early Cenozoic. In Late Cenozoic closure of the oceanic and backarc basins took place followed by the continent-continent collision, topography inversion and formation of modern structures in the region (Adamia et al., 1981, 2017; Dercourt et al., 1986). During the pre-collision stage there were not two, but three Tethys branches. The third of them is Van-Khoi oceanic branch. Number of palaeo-subduction zones (two or three?) is still debatable within the academic community. One research group (e.g. Sosson et al., 2010; Barrier et al., 2018) admits existence of two subduction zones: Peri-Arabian and Ankara-Erzincan-Sevan-Zangezur zones, whilst another group including the abstract authors refer to the presence of three subduction zones and aside from abovementioned zones consider the presence of the Khoy Ocean and third subduction zone related to one of the Neotethys branches (Adamia et al., 1981, 2017; Dercour et al., 1986; Stampfli, 2001). According to Adamia et al. (1981, 2017), Dercourt et al. (1986), Daralogöz-South Armenian block and Nakhchevan (SAB) in the Late Paleozoic–Mesozoic–Early Cenozoic represent the part of the Iranian but not the Anatolian Microcontinent.

Revision of the trace fossil Megagrapton Książkiewicz, 1968 with focus on Megagrapton aequale Seilacher, 1977 from the lower Eocene of the Lesser Caucasus in Georgia

Uchman Alfred, Lebanidze Zurab, Beridze Tamar, Kobakhidze Nino, Lobzhanidze Koba, Khutsishvili Sophio, Chagelishvili Rusudan, Makadze Davit, Koiava Kakha, Khundadze Nino

Geological Quarterly

2022

Vol. 66, No. 1

art. no. 8

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).

Unusual echinoid resting trace records change in the position of the redox boundary (Palaeogene of the Lesser Caucasus in Georgia)

Uchman Alfred, Lebanidze Zurab, Kobakhidze Nino, Beridze Tamar, Makadze Davit, Lobzhanidze Koba, Khutsishvili Sophio, Chagelishvili Rusudan, Koiava Kakha, Khundadze Nino

Acta Geologica Polonica

2022

Vol. 72, no. 3

317--330

The first recognition of a tracemaker responding to a temporary shift in the redox boundary is recognized. This is recorded by a new trace fossil, Sursumichnus orbicularis igen. et isp. nov., which is established for mound-like structures on the upper surfaces of sandstone beds from the Borjomi Flysch (upper Paleocene–lower Eocene) in the Lesser Caucasus (Georgia). It is connected with the spatangoid echinoid burrow Scolicia de Quatrefages, 1849 and interpreted as a resting trace of the same tracemaker produced after moving up from a deeper position within the sediment. The resting is caused by an episode of unfavourable conditions related to shallowing of the redox boundary. The trace fossil is a component of the Nereites ichnofacies.