Early-Middle Pleistocene environmental and biotic transition in NW Armenia, southern Caucasus

Abstract

Quaternary biota of north-western Armenia is studied from several localities in the Ani and Arapi fluvial formations of the Shirak and Upper Akhuryan sedimentary basins. Palynology of lacustrine deposits of the Ani Formation indicates cyclic alternation of forest-steppe and steppe coenoses in the Shirak Depression. The patchy pollen record from the sections of the Arapi Formation indicates forest-steppe coenoses. Aquatic molluscs from the Ani Formation are dominated by gastropods and dreissenid bivalves. Molluscs of the Arapi Formation are characterised by limnophilic freshwater species with mostly extant forms. The Arapi deposits yielded remains of fishes, amphibians, and small mammals. The freshwater fish assemblage comprises cyprinid species that derived from the earlier Plio-Pleistocene fish communities of Armenia. The assemblage indicates lacustrine and river habitats with rocky bottoms and the presence of water plants overgrowth. The herpetofauna from the Arapi Formation includes remains of anuran amphibians that indicate aquatic habitats. Small mammals include Sorex cf. runtonensis, Neomys cf. hintoni, Ochotona sp., Mimomys intermedius, Terricola sp., Microtus gr. nutiensis, Prolagurus pannonicus transylvanicus,and Ellobius pomeli. This fauna characterises the Leninakan (Gyumri) faunal assemblage correlated to the late Biharian of the European land mammal biochronology, Tiraspol faunal complex of Eastern Europe, and the Cromerian of NW Europe. The studied record has an important biogeographic significance for the southern rim of the Ponto-Caspian region. It shows the complex history of the biotic exchanges and polygenous origin of the terrestrial communities in the southern Caucasus. Radiometric, paleomagnetic, and biotic control make it possible to date the Ani deposits to late Early and earliest Middle Pleistocene. The age of the Arapi formation is early Middle Pleistocene older than 0.6 Ma. The main trend of landscape evolution in the region between ca. 1.5-0.7 Ma is a transition from forest-steppe to steppe conditions.