Combined Electrical Resistivity Tomography (ERT), Direct‐Push Electrical Conductivity (DP‐EC) Logging and Coring – A New Methodological Approach in Geoarchaeological Research

Abstract

Non-invasive geophysical methods have been increasingly applied in geoarchaeological research commonly showing the need of data calibration based on stratigraphical information deduced from outcrops or sediment cores. In this contribution, a methodological approach combining two-dimensional (2D) electrical resistivity tomography (ERT) and stratigraphical data based on coring and, for the first time in geoarchaeological research, direct-push electrical conductivity (DP-EC) logging is presented and discussed. The approach yields high resolution data based on studies of two different types of archives, the Holsterburg site in central Germany located in a fluvio-terrestrial zone and the Corfu City site in Greece located in a near-coastal zone. It is shown that DP-EC logs trace fluctuations over grain size in high resolution which reflect changes of depositional conditions in the course of time. In addition, constraints from DP-EC logs in the form of layer interfaces and electrical resistivities were incorporated into the ERT inversion process minimizing the ambiguity of inversion results. It is shown that incorporating regions with certain starting resistivities based on DP-EC logs exceed the advantage of using layer interfaces alone. It is concluded that in future geoarchaeological and geomorphological studies a combined application of coring, DP-EC logging and ERT measurements should be considered as a standard approach towards a more comprehensive stratigraphical characterization of the shallow subsurface.

River channel evolution and tsunami impacts recorded in local sedimentary archives – the ‘Fiume Morto’ at Ostia Antica (Tiber River, Italy)

“…For further reading and application of DP–EC logging within geoarchaeology, see Fischer et al . (), Finkler et al . () and Wunderlich et al .…”

“…The latter has four electrodes in a linear Wenner arrangement (Schulmeister et al, 2003). For further reading and application of DP-EC logging within geoarchaeology, see Fischer et al (2016 and Wunderlich et al (2018b).…”

“…In cases where groundwater is dominated by brackish or saltwater conditions, this relation is reversed due to the increased influence of pore-filling saltwater in coarse-grained deposits (see e.g. Schulmeister et al, 2003;Fischer et al, 2016;Hausmann et al, 2018;Wunderlich et al, 2018b). Strong decreases in DP-EC values for depths higher than ca 0Á5 m a.s.l.…”

Tracing tsunami signatures of the ad 551 and ad 1303 tsunamis at the Gulf of Kyparissia (Peloponnese, Greece) using direct push in situ sensing techniques combined with geophysical studies

“…Usually, low EC values are related to coarser sediments, such as sand and gravel. In contrast, high EC values represent fine‐grained sediments, such as clay and silt (Wunderlich et al ., ; Fischer et al ., ). Contrary to the HPT, EC is also dependent on chemical and mineralogical factors and, therefore, HPT logs show changes in sedimentary characteristics below the ground water surface more reliably (Geoprobe, ).…”

“…Because these techniques allow the differentiation of sediment properties such as composition, grain size and material consolidation, they are increasingly being applied in hydrogeological and geotechnical investigations. However, the DP techniques have been used very little in geomorphological studies (Schmelzbach et al ., ; Fischer et al ., ; Wunderlich et al ., ). So far, DP measurements have not been used within the framework of palaeotsunami research.…”