A geoarchaeological perspective on the Holocene dynamics of Someșul Mic floodplain (Transylvanian Basin, Romania)

Someşul Mic River (105 km long, 20 mc/s) drains the western edge of the Transylvanian Basin ultimately joining the Danube, via the later’s Tisa tributary. The river developed and maintained a narrow sinuous channel during the Holocene, with local development of meanders and anabranches, in response to both climatic and geologic controlling factors. Its floodplain and lower terraces are home to the oldest (~8500 cal. BP) Neolithic settlement in Romania. Subsequently, the region has been continuously inhabited throughout the mid-to-late Holocene, with local populations moving through the landscape in response to social, climatic and environmental pressures. Consequently, a complex pattern of settlement and communication networks emerged that is partly imprinted (and preserved) on the surface morphology of the valley.

Here we combine Neolithic through modern constructions to constrain the position of the river’s channels during the past ~8000 years and, in combination with geophysical, geomorphological and sedimentological investigations, determine the style and rate of fluvial processes in the floodplain. The overall approach was as follows: 1) mapping of fixed (e.g., settlements, roads, buildings, cemeteries) points in the floodplain for different periods (Neolithic, Copper Age, Bronze Age, Iron Age, Roman, Medieval and Modern), 2) for each period, constrain the maximum potential area on which the river did not flow since, 3) identify areas of extensive lateral channel movement (meandering, anabranching, anastomosis) and/or fixed position, 4) geophysical (ERT) and sedimentological investigation of the floodplain and channel infills. Additionally, we have combined existing paleoclimatic and paleoenvironmental data to reconstruct Holocene climate and vegetation dynamics in the wider area as a backdrop for the fluvial dynamics. The geoarchaeological data allowed us to distinguish areas of long-term channel stability along the river, which we identified to be superimposed on small anticlines formed by salt diapirism, and of areas of active lateral channel movement (with removal of archaeological traces), induced by tectonic (e.g., slow tilting of the floodplain towards synclines), internal (i.e., river-specific) and climatic factors.

Summarizing, our aim is to show that geoarchaeological data can be used in a “reversed” approach, i.e., to reconstruct past fluvial dynamics, rather than to study the response of human societies to past environmental changes.