Since Plio-Pleistocene time, southward migration of shortening in the eastern part of the Greater Caucasus into the Kura foreland basin has progressively formed the Kura fold–thrust belt and Alazani piggyback basin, which separates the Kura fold–thrust belt from the Greater Caucasus. Previous work argued for an eastward propagation of the Kura fold–thrust belt, but this hypothesis was based on coarse geological maps and speculative ages for units within the Kura fold–thrust belt. Here we investigate the initiation of deformation within the Gombori range in the western Kura fold–thrust belt and evaluate this eastward propagation hypothesis. Sediments exposed in the Gombori range have a Greater Caucasus source, despite the modern drainage network in the NE Gombori range, which is dominated by NE-flowing rivers. Palaeocurrent analyses of the oldest and youngest syntectonic units indicate a switch happened between ~2.7 Ma and 1 Ma from dominantly SW-directed flow to palaeocurrents more similar to the modern drainage network. A single successful 26Al–10Be burial date indicates the youngest syntectonic sediments are 1.0 ± 1.0 Ma, which, while not a precise age, is consistent with original mapping suggesting these sediments are of Akchagylian–Apsheronian (2.7–0.88 Ma) age. These results, along with recent updated dating of thrust initiation in the eastern Kura fold–thrust belt, suggest that deformation within the Kura fold–thrust belt initiated synchronously or nearly synchronously along-strike. We additionally use topographic analyses to show that the Gombori range continues to be a zone of active deformation.

<p>Since the Plio-Pleistocene, southward migration of shortening in the Eastern part of the Greater Caucasus (GC) into the Kura foreland basin has formed the Kura fold–thrust belt (KFTB) and Alazani piggyback basin between the GC and KFTB, modifying the drainage network within the southern foreland. <span>The northern, eastern and south-eastern flanks of the Western KFTB (Gombori range) expose the predominantly alluvial Alazani series, w</span><span>hile the central (highest) part of the range is covered by Tsivi suite</span><span>.</span> The base of the Alazani series is estimated to be 2.7-2.5 Ma and deposition spanned the Akchagyl and Apsheronian regional stages. The KFTB likely initiated during the Akchagyl-Apsheronian period, and thus the paleocurrents of the alluvial Alazani series sediments represent potential archives for tracking resulting drainage reorganization within the foreland. Previous measurements of paleocurrents from the Alazani series revealed a reversal from south to north flow directions, but the measurements were limited to the northern flank of the Gombori range. Here we present new observations from the central and southern flanks of the Gombori. Results from the eastern and southeastern regions are consistent with the currents from the northern flank, but paleocurrents from the Tsivi suite are more complex and raises additional questions regarding its depositional context and age. The new results help to build a more complete picture of fluvial dynamics driven by Quaternary tectonic deformations within the GC foreland.</p>

Since the Plio-Pleistocene, southward migration of shortening in the eastern part of the Greater Caucasus (GC) into the Kura foreland basin has progressively formed the Kura-Fold Thrust belt (KFTB) and Alazani piggyback basin, which separates the KFTB from the GC. Previous work argued for an eastward propagation of the KFTB, implying that the western portion in Georgia is the oldest, but this hypothesis was based on coarse geologic maps and speculative ages for units within the KFTB. Here we investigate this hypothesis and focus on the Gombori Range (GR), which defines NW edge of the belt. Previous work divided the sediments of northern flank of the range into three facies. The rock types in the older and middle facies suggest a GC source provenance, despite the modern drainage network in the NE GR, which is dominated by NE flowing rivers.Paleocurrent analyses of the alluvial conglomerates of the oldest and youngest syntectonic units indicate a switch from dominantly SW directed paleocurrents in the oldest unit to paleocurrents more similar to the modern drainage network in the youngest unit. A single successful 26Al-10Be burial date indicates these syntectonic sediments are 1±1 Ma, which while not a precise age, is consistent with original mapping suggesting these sediments are Akchagyl-Apsheron (2.7-0.88 Ma) age. Tectonic geomorphologic analyses indicate that western GR is the most active. Given its close proximity to the capital city of Tbilisi, this suggests that active structures within the Gombori range pose seismic hazard to this city of 1.2 million people.