Late Miocene Tectonic Uplift and Sediment Routing in the Caucasian Foredeep: Insights from Provenance Analysis and Stratigraphic Architecture

Abstract

The spatial distribution of sediment source areas and paleodrainage evolution of the Ciscaucasian Foredeep's Neogene-Quaternary deposits have remained contentious. Here, we resolve this debate through systematic analysis of the Upper Miocene Lysogorskaya Formation's alluvial facies, which constrain provenance terranes via integrated paleocurrent direction (PCD) compositional data and stratigraphic position. Comprehensive representative paleocurrent datasets (n = 70) were acquired from the formation's spectacular exposures in two deeply incised river valleys of two biggest Terek's tributaries: The Baksan River section near village Islamey and the Cherek River section near village Aushiger (Kabardino-Balkarian Republic). These continuous, vertically-oriented outcrops display the complete stratigraphic architecture, featuring five main conglomerate units separated by minor erosional remnants of floodplain deposits. Systematic evaluation of six distinct sedimentary structure types within the formation demonstrates a predominant northeastward paleocurrent direction during alluvial deposition. This directional trend unequivocally identifies the sediment source area as the southwestern, axial zone of the Central Caucasus, directly opposing the paleoflow. The conglomerates' composition, featuring crystalline rock fragments intermingled with sedimentary lithologies and granitoid clasts, provides definitive evidence for syn-depositional exposure of the Central Caucasus crystalline core through orogenic uplift during this period. The observed unconformities, with their north-east-directed dips, record tectonic uplift along the south-west margin of the depositional basin during the Miocene-Quaternary. That uplifted zone simultaneously acted as a sediment source for the basin, as indicated by angular discordances between the Lysogorskaya Formation and the underlying/overlying sedimentary units. These findings collectively with polymictic contain and pebble-boulder dimension of alluvium establish the crystalline highlands of Central Caucasus in the south-west as the principal sediment provenance while documenting active tectonic uplift in the Late Miocene foredeep setting.