The genesis and environmental context of hypogene-sourced terrestrial carbonates of the middle Pleistocene in Vedi, Ararat Depression

Abstract

The Ararat Depression (Armenia), situated between the southern Caucasus and northern Mesopotamia, holds substantial archaeological Middle Paleolithic sites. However, as paleoclimate archives are scarce in the region, the climatic history is not well constrained. To reconstruct the local paleoclimatic conditions in the past, we studied a ∼30 m-thick sequence of carbonates deposited in the Vedi Valley, a tributary of the Ararat Valley. We applied field mapping, petrography, geochemistry, stable isotope analysis, and U–Th dating to investigate the genesis and evolution of these carbonates. Two main facies are identified: (1) a micritic-peloidal microbial facies formed in low-energy palustrine settings, and (2) a sparitic calcite facies formed via CO₂ degassing from deeply sourced hypogene fluids. δ¹³C and δ¹⁸O values, together with elemental proxies, indicate early closed-system degassing of hydrothermal solutions interacting with marine carbonates of the Yerakh Anticline, followed by increased meteoric influence and detrital input in the upper portion of the sequence.

Three distinct detrital units coincide with heavier δ¹⁸O and lighter δ¹³C values and likely reflect wetter intervals during interglacial phases. Isochron U–Th dating constrains deposition to occur between 319 ± 84 and 198 ± 14 ka, corresponding to Marine Isotope Stages (MIS) 9–7. The results indicate that the Vedi Valley carbonates constitute a Middle Pleistocene sequence formed under the combined influence of active tectonics, volcanism, and climatic shifts. As such, they provide a rare archive of landscape evolution in a region critical for understanding past environmental variability and human dispersal pathways.