Pleistocene volcanism and the geomorphological record of the Hrazdan valley, central Armenia: linking landscape dynamics and the Palaeolithic record

Abstract

The Southern Caucasus lies at the intersection of Africa, the Levant and Eurasia, and is thus a region of considerable interest in the study of Pleistocene hominin population dynamics and behaviour. While Palaeolithic archaeological sites in the region such as Dmanisi and Nor Geghi 1 attest to such palaeogeographic significance, a greater understanding of the chronology and nature of climatic and geomorphic changes in the region is needed to fully understand hominin settlement dynamics. The Hrazdan river valley, central Armenia, has the potential to offer such insights given its rich Palaeolithic record and complex history of Pleistocene infill as a result of alluvial, lacustrine, aeolian, and volcanic processes. We therefore present a stratigraphic framework for basin infill and hominin activity during the Pleistocene, based on extensive geomorphological and geological mapping, published chronometric results (40 Ar/ 39 Ar and K-Ar), and archaeological survey. We demonstrate that the onset of Pleistocene volcanism in the Gegham Range to the immediate east of the Hrazdan valley occurred around 700 ka BP, after which there were several phases of effusive eruption lasting until 200 ka. Interbedded with lava emplaced by these eruptions are alluvial and lacustrine sequences, some with evidence of pedogenesis and several of which have yielded Palaeolithic artefacts. Taken together these sequences suggest a cyclical model of infill whereby lava flow along the valley resulted in the blockage of the palaeo-Hrazdan river and lake formation in the lea of the lava dams. Breaching of these dams resulted in a shift to predominately fluvial deposition, and the consequent development of floodplain soils. Hominin populations exploited the floodplains at times when the last of these phases coincided with interglacial and interstadial climates, but they also occupied the surrounding valley sides during the same warm, humid phases.

Evidence for Middle Palaeolithic occupation and landscape change in central Armenia at the open-air site of Alapars-1

“…500 ka yr in the GVC (Lebedev et al, 2013, 2018). It is important to note, however, that ambiguities are associated with the chronological evidence from the volcanic deposits (Mitchell and Westaway, 1999; Sherriff et al, 2019). This is best exemplified by the previously published chronological evidence from the Fantan Dome, with K-Ar dates on extruded obsidian yielding an age of 480 ± 25 ka (Lebedev et al, 2011), whereas FT ages from the same obsidian extrusion have yielded ages of 320 ± 20 ka and 300 ± 20 ka (Badalian et al, 2001).…”

“…The timing of volcanic activity in the northwestern sector of the GVC is based principally on K-Ar and fission track (FT) ages of volcanic deposits (see Sherriff et al, 2019 for a full review). These ages indicate that the principal phase of volcanic activity associated with the formation of the GVC was ca.…”

“…6-m-thick sequence of alluvial and aeolian sediments containing three stratified soil complexes dated to MIS 5–3.

Figure 1.(color online) Location maps showing: (A) the topographical position of the Southern Caucasus; (B) the distribution of known Middle Palaeolithic sites in Armenia and Georgia; and (C) the Quaternary geology of the northwest sector of the Gegham volcanic massif and the Hrazdan River Valley (adapted from Karapetian et al, 2001 and Sherriff et al, 2019).

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Locally Thin Crust and High Crustal VP/VS Ratio Beneath the Armenian Volcanic Highland of the Lesser Caucasus: A Case for Recent Delamination

“…Most of the magmatism in the Armenian volcanic highland is dated to the Pliocene-Quaternary, generally less than 3.0-2.5 Ma, based on fissure-related lavas and central vent eruptions (IAEA, 2016;Karapetian et al, 2001;Meliksetian et al, 2014;Mitchell & Westaway, 1999;Neill et al, 2015;Nomade et al, 2016;Sherriff et al, 2019). The volcanoes are usually situated within the pull-apart structures of strike-slip fault systems, which parallels the SAS, and the neotectonic faults apparently act as an important control on volcanic activities and earthquakes (Avagyan et al, 2005;Karakhanian et al, 2002Karakhanian et al, , 2004.…”

“…Pleistocene-Holocene in Armenia (Karakhanian et al, 2003;Sherriff et al, 2019). We present detailed variations in the crustal structure constrained by receiver functions (RFs) in the Armenian Highland for the first time and discuss the possible control of delamination styles during continental collision.…”