Understanding Wetlands Stratigraphy: Geophysics and Soil Parameters for Investigating Ancient Basin Development at Lake Duvensee

Erica Corradini, Stefan Dreibrodt, Ercan Erkul, Daniel Gross, Harald Lübke, Diana Pannig, Natalie Pickartz, Martin Thorwart, Andreas Vött, Timo Willershäuser, Dennis Wilken, Tina Wunderlich, Marco Zanon, Wolfgang Rabbel

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We present a case study of a bog showing how an integrated approach of multi-method
geophysical sounding and local soil sampling can be used to identify, dierentiate, and map organic
sediments. Our study is based on ground-penetrating radar (GPR), electrical resistivity tomography
(ERT) and shear-wave seismic (SH seismic) profiling applied to sediments of the former Lake
Duvensee (northern Germany), nowadays a bog. This is a well-known locality for remains from the
Mesolithic hunter-gatherers’ occupation that has been attracting archaeological and geoarchaeological
research for100 years. The bog is embedded in low conductive glacial sand and is characterized
by layers of dierent gyttja sediments (detritus and calcareous). The present study was conducted
in order to identify the bog morphology and the thickness of the peat body and lake sediments,
in order to understand the basin evolution. To validate the geophysical results, derived from surface
measurements, drilling, soil analyses as well as borehole guided wave analysis of electromagnetic
waves and Direct-Push (DP-EC) have been carried out and used for comparison. It turned out that
each method can distinguish between sediments that dier in grain size, particularly between peat,
lake sediments (gyttjas and mud) and basal glacial sand deposits. GPR is even able to separate
between strongly and weakly decomposed peat layers, which is also clear considering resistivity
variations in the ERT computation. From the association between geophysical properties and sediment
analysis (e.g., water content and organic matter) dierent gyttjas were distinguished (coarse and fine)
and seismic velocity was correlated to bulk density. Moreover, GPR and SH-wave seismics present
dierent resolutions, confirming that the latter allows measurements, which are more focused on
determining the extension of basal sand deposits, the depth of which is dicult to reach with GPR.
Representative values of electrical resistivity, dielectric permittivity, and shear wave velocity have
been determined for each sediment type and are therefore available to complete the investigation
of wetland environments. Fine grained lake sediments were dicult to dierentiate by the applied
methods. This could be a result of high ionic concentration within the permanent groundwater body,
partly masking the sediment properties.
Udgave nummer8
Sider (fra-til)1-35
Antal sider35
StatusUdgivet - 2020