Characterization of fluvial terraces in the eastern segment of Adjara-Trialeti fold-thrust belt, Lesser Caucasus, Georgia

The Adjara-Trialeti fold-thrust belt (ATFTB) is an important and active structural system in the Caucasus region, which is the northernmost part of the Lesser Caucasus and is associated with Arabia-Eurasia convergency and extends over 300 km from the Black Sea to the east, where passing through Tbilisi, the capital of Georgia (population ~1.2 M). Geodetic data show the ATFTB is active, and absorbs 3-7 mm/ yr. of regional strain (northward motion), maximum strain is located in eastern segment. This area consists of deformed Paleogene to Neogene sedimentary and volcanic rocks. The Mtkvari/Kura is a major river of the Caucasus, it crosses along strike of eastern segment of ATFTB in area where the river flows through Tbilisi and Rustavi. Widespread upper Pliocene to Quaternary alluvial deposits along the course of the Mtkvari river unconformably overlie the deformed units of the ATFTB, thus providing a potentially valuable strain marker that can be used to quantify the magnitude and rate of neotectonic deformation within the ATFTB. We are investigating the formation and incision of these alluvial deposits using lidar data to determine their geometries and clast compositions and paleocurrent measurements to determine their provenance. The main geomorphic feature in the eastern segment of ATFTB are Quaternary(?) fluvial terraces of Mtkvari River. In this area we used airborne Lidar data to identify and map the river terraces, which we then checked using reconnaissance field observations. To date we have identified terraces in 13 different elevation bands at heights that range from 2 to 690 m above the Mtkvari and absolute elevations of 365 to 1090 m above sea level. To check that the platforms are of fluvial origin, we investigate the nature of the deposits that overlie them. To investigate the provenance of these deposits we are using pebble imbrication measurements to determine the paleocurrent directions, and the composition of clasts within the conglomerates. Paleoflow directions are generally NW to SE. Most clasts are composed of Neo-Paleogene sedimentary and volcanic rocks, and appear to be sourced from the Lesser Caucasus. Burial-dating using the 10Be&26Al isochron approach is in progress to determine the age of the deposits and thus the overall incision rate of the Mtkvari river where it crosses the ATFTB.