Late Triassic age of moshevani suite of the Loki massif (Georgia, the Caucasus)

Abstract

The Loki massif is located near the southern border of Georgia and is represented by large anticline structure of E-W oriented extension. The most ancient formations of the massif are crystalline schists outcropping along western, northern and southern peripheries of the massif. Crystalline schists are penetrated by granites and divided in two age complexes, Paleozoic and Middle Jurassic. Almost around all perimeter crystalline basement and granites are transgressively overlaid by series of strata of conglomerates and quartz sandstones, desribed as Moshevani suite and its age has so far been given as Hettangian. A section located at the western periphery of the Loki massif, to the N-E of v. Gora, in the gorge of the r. Gorastskali, right tributary of r. Moshevani, was studied in these sediments. Slides were prepared from the selected samples using decantation method (separation of fraction 3―30 µm). The samples were placed into a 45 mm water column, where the heavy fraction was allowed to settle for 3 minutes, while the fine-fraction was saved for slide preparation after 45 minutes. All slides were studied with a Carl Zeiss microscope «Amplival» at 1200x magnification. Despite the lacking of nannofossils in these deposits, a complex association of calcareous nannofossils including Crucirhabdus minutes Jafar 1983; C. primulus Rood, Hay & Barnard 1973; Prinsiosphaera triassica Jafar 1983; Tetralithus cassianus Jafar 1983; T. pseudotrifidus Jafar 1983; Hayococcus floralis Jafar 1983; known from Norian-Rhaetian stage. Due to this complex the presence of Upper Triassic deposits has been found for the first time within the limits of Loki-Karabakhian structural facial zone. Therefore, taking into consideration the above mentioned data a new corrected lithostratigraphic column and a map of the area were composed.