Photo: A 20m thick sequence of river sediment and buried soils beneath basalt south of the village of Solak. The gravels accumulated in the former channel of the River Hrazdan, the fine-grained sediments on its floodplain while the soils represent drier intervals. The Hrazdan has cut down over 50m since these deposits accumulated (photograph by Monika Knul).
We are now two thirds of the way through this first fieldwork campaign.
Indeed two of us have returned to the UK, meaning that I am writing this second post from Winchester. With its temperate climate, I can truly feel the 3800 km distance and 10o of latitude that separate it from Yerevan, where temperatures soared to 40oC+ degrees in my final week. The rest of the PAGES team remains in Armenia and for them the fieldwork continues into August.
I thought that we would be able to cover around half of our Hrazdan study area this July and August, and – somewhat to my surprise – we have almost achieved that goal already.
We have walked between the village of Ptghni, just beyond the northern outskirts of Yerevan, and Arzakan, 21 km north. As we traversed the area we mapped basalt units outcropping in the valley sides, each of which represents a separate lava flow. To date we have recorded approximately 20 basalts, three of which we think have their origin in the Arailer volcano to the west and the rest in the Gegham range to the east.
Previous work by Vladimir Lebedev and colleagues suggests that Arailer had an eruptive history lasting until around one million years ago, while the Hattis, Gutansar and Mensakar volcanoes of the Gegham range formed after 700 thousand years before present (BP). Our mapping so far suggests that the Arailer basalts have been eroded by the Hrazdan to leave a distinct step in the landscape west of the river. Beyond are the Arailer basalts, which are separated from one another by pyroclastic debris and lake deposits, all presumably dating to the Early Pleistocene (2.5 million to 780 thousand years BP).
To the east are the Gegham basalts, which in turn are of two types. Firstly, flows forming aprons around the base of the volcanoes, some of which have also been trimmed by the Hrazdan, and secondly, lavas that flowed down the course of the Hrazdan valley. We presently only have a broad idea of the age of these basalts, namely that the latest flow is c.198 thousand years old, on the basis of 40Ar/39Ar dating that we have previously published (in Science) for the archaeological site of Nor Geghi 1.
As we carry out more 40Ar/39Ar dating over the next couple of years we will gain a much better understanding of the chronology of eruption.
Basalts have not been the only focus of our work this month, and indeed from an archaeological point of view it is the layers between the volcanic deposits that are of importance.
It is therefore encouraging that we have found so many outcrops of lake (termed 'lacustrine' in geological parlance) sediment, which we think date from both the Middle (780-120 thousand years BP) and Early Pleistocene. We have spent a considerable amount of time recording and sampling these deposits as the chemical signatures and included biological remains will tell us about the environments and climates in which the lakes formed. We have not so far found new archaeological sites, but at the same time as we have been walking the Hrazdan valley, teams led by Dan Adler, and Ariel Malinsky-Buller and Phil Glauberman, have been excavating Palaeolithic sites at Nor Geghi and Alapars respectively. We will report on PAGES work on those sites in future blogs.
While the fieldwork so far has been both interesting and fun – the latter in part thanks to the very friendly inhabitants who have frequently invited us into their homes for coffee and apricots – there have been problems that we could not have foreseen when we set up the project.
BREXIT, for example, has had an impact even in Armenia as 14% of the fieldwork budget disappeared with the rapid fall of the UK Pound against the Armenian Dram, while the majority of Armenian currency exchanges no longer take Sterling. Being British, particularly English, is consequently to be the butt of jokes from international colleagues at the moment…
The next couple of posts will come from other members of the PAGES team still in the field and will consider different perspectives of the work and being in Armenia.
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About the author
Dr Keith Wilkinson is Reader in Environmental Archaeology at the University of Winchester and Principal Investigator of the PAGES project.
Posted 28 July 2016