Kura (Mtkvari) River terraces record fluvial response to the collision of the Greater and Lesser Caucasus thrust belts, Georgia

Abstract

Near Tbilisi, Georgia, the Kura (Mtkvari) River flows across the junction between seismically active thrust belts in the Greater and Lesser Caucasus Mountains, near the locus of modern contractional strain within this sector of the Arabia-Eurasia collision. Here we describe and use a suite of fluvial terraces to explore the regional paleogeography, landscape evolution, and neotectonic development of the east end of the Adjara-Trialeti fold-thrust within the Lesser Caucasus. Specifically, we identified and mapped a suite of fluvial terraces within and around Tbilisi by integrating analyses of airborne LiDAR data with provenance observations from clast compositions and paleoflow directions from clast imbrication data. These data reveal three distinct types of fluvial strath terraces in the region: a main set from the Kura River and two secondary sets sourced from tributaries on its western (right) and eastern (left) banks. There are seventeen different elevation levels, with heights ranging from 10 to 690 m above the current river level of the Kura River. We infer that the Kura terraces are formed by local surface uplift above actively growing folds because they mainly occur in areas underlain by anticlines, therefore we find evidence of localized folding and faulting of terrace deposits. However, we are unable to determine if individual generations of terraces are folded, as this requires detailed terrace correlations that go beyond the initial mapping and dating, we report here. Based on our regional mapping and paleocurrent data, we conclude that the Kura River migrated over time from the northeast to the southwest. This migration is inferred to result from differential uplift in this part of the Adjara-Trialeti fold-thrust belt, with active collision between the Greater and Lesser Caucasus in the northeast causing enhanced surface uplift, pushing the river towards the southwest.