Structure of the Multiphase Chalcolithic Tell Chiselet–Grădiștea Fundeanca (Romania) From SH-Wave Full-Waveform Inversion, Borehole Geophysics and Coring

Abstract

The emergence and development of settlement mounds, also called tells, is of major interest for the analysis of socio-economic transformations occurring in the lower Danube plain during the East European Chalcolithic period. In this context, the multiphase chronology and structural layout of tells are highly relevant indicators, but small-scale heterogeneities and pronounced topography constitute challenging conditions for noninvasive geophysical investigations. In this paper we demonstrate that essential stratigraphical and structural information can be obtained by combining areal magnetic prospection with two-dimensional seismic shear wave sounding evaluated with full waveform inversion (FWI). For the study, we performed measurements at the Chalcolithic tell Grădiștea Fundeanca near Chiselet village (Romania). Main objectives are the reconstruction of different settlement phases as well as the detection and verification of archaeological features, especially of buried house structures. For ground-truthing down-hole magnetic susceptibility measurements, dynamic testing (DynP) and geoarchaeological corings are integrated to our investigation. In our FWI tomograms, two zones of increased shear wave velocity are visible in the upper 5 m beneath the tell surface. Although postdepositional has altered and partly compacted the upper 1.5 m below the surface, we find that both zones originate from a dense accumulation of compacted house debris layers consisting of daub between surrounding looser filling material. We assume the zones are related to periods of settlement activity (around 4300 bc and 4500 bc). Comparing magnetic prospection and the seismic results, we found that house remains produce structural characteristic anomalies of 100% and more increased shear wave velocity in the FWI models independent of the degree of combustion. Based on criteria such as the shape, size, depth and arrangement of the seismic and magnetic anomalies, we evaluate the probability for the existence of house remains. So we were able to validate and improve the reconstruction of the youngest settlement layout.