Holocene human-environmental interactions and seismic activity in a Late Bronze to Early Iron Age settlement center in the southeastern Caucasus

Long-term human-environmental interactions in naturally fragile drylands are an actual topic of geomorphological and geoarchaeological research. Furthermore, many prehistoric societies in drylands were also affected by seismic activity. The semi-arid Shiraki Plain in the tectonically active southeastern Caucasus is currently covered by steppes and largely devoid of settlements. However, numerous Late Bronze to Early Iron Age city-type fortified settlements suggest early state formation between ca. 3.2 – 2.5 ka that abruptly ended after that time. A paleolake was suggested for the lowest plain, and nearby pollen records suggest forest clearcutting of the upper altitudes under a more humid climate during the Late Bronze/Early Iron Ages. Furthermore, also an impact of earthquakes on regional Early Iron Age settlements was suggested. However, regional paleoenvironmental changes and paleoseismicity were not systematically studied so far. We combined geomorphological, sedimentological, chronological, paleoecological and hydrological modelling data to reconstruct regional Holocene paleoenvironmental changes in the Shiraki Plain, and identify possible natural and anthropogenic causes as well as possible seismic events during the Late Bronze/Early Iron Ages. Our results show a balanced to negative Early to Mid-Holocene water balance probably caused by forested upper slopes. Hence, no lake but an incipient Chernozem developed in the lowest plain. Following, Late Bronze/Early Iron Age forest clear-cutting obviously caused lake formation and the deposition of lacustrine sediments derived from intensive soil erosion. Subsequently, regional aridification obviously caused slow lake desiccation. Remains of freshwater fishes indicate that the lake potentially offered valuable ecosystem services for regional prehistoric societies even during the desiccation period. Finally, colluvial coverage of the lake sediments during the last centuries could have been linked with hydrological extremes during the Little Ice Age. Our study demonstrates that the Holocene hydrological balance of the Shiraki Plain was and is situated near a major hydrological threshold, making the landscape very sensitive to also small-scale human or natural influences with serious consequences for local societies. Furthermore, seismites in the studied sediments do not indicate an influence of earthquakes on the main and late phases of Late Bronze/Early Iron Age settlement. Altogether, our study underlines the high value of multi-disciplinary approaches to investigate long-term human-environmental interactions and paleoseismicity in drylands on millennial to centennial time scales.