Magnetic susceptibility and electric conductivity of marine surficial sediments by benthic electromagnetic profiling, supplement to: Müller, H; von Dobeneck, Tilo; Hilgenfeldt, Christian; SanFelipo, Bill; Rey, Daniel; Rubio, Belen (2012): Mapping the magnetic susceptibility and electric conductivity of marine surficial sediments by benthic EM profiling. Geophysics, 77(1), E43-E56

DOI

Distribution, accumulation and diagenesis of surficial sediments in coastal and continental shelf systems follow complex chains of localized processes and form deposits of great spatial variability. Given the environmental and economic relevance of ocean margins, there is growing need for innovative geophysical exploration methods to characterize seafloor sediments by more than acoustic properties. A newly conceptualized benthic profiling and data processing approach based on controlled source electromagnetic (CSEM) imaging permits to coevally quantify the magnetic susceptibility and the electric conductivity of shallow marine deposits. The two physical properties differ fundamentally insofar as magnetic susceptibility mostly assesses solid particle characteristics such as terrigenous or iron mineral content, redox state and contamination level, while electric conductivity primarily relates to the fluid-filled pore space and detects salinity, porosity and grain-size variations. We develop and validate a layered half-space inversion algorithm for submarine multifrequency CSEM with concentric sensor configuration. Guided by results of modeling, we modified a commercial land CSEM sensor for submarine application, which was mounted into a nonconductive and nonmagnetic bottom-towed sled. This benthic EM profiler Neridis II achieves 25 soundings/second at 3-4 knots over continuous profiles of up to hundred kilometers. Magnetic susceptibility is determined from the 75 Hz in-phase response (90% signal originates from the top 50 cm), while electric conductivity is derived from the 5 kHz out-of-phase (quadrature) component (90% signal from the top 92 cm). Exemplary survey data from the north-west Iberian margin underline the excellent sensitivity, functionality and robustness of the system in littoral (~0-50 m) and neritic (~50-300 m) environments. Susceptibility vs. porosity cross-plots successfully identify known lithofacies units and their transitions. All presently available data indicate an eminent potential of CSEM profiling for assessing the complex distribution of shallow marine surficial sediments and for revealing climatic, hydrodynamic, diagenetic and anthropogenic factors governing their formation.

Identifier
DOI https://doi.org/10.1594/PANGAEA.776056
Related Identifier https://doi.org/10.1190/GEO2010-0129.1
Metadata Access https://ws.pangaea.de/oai/provider?verb=GetRecord&metadataPrefix=datacite4&identifier=oai:pangaea.de:doi:10.1594/PANGAEA.776056
Provenance
Creator Müller, H; von Dobeneck, Tilo; Hilgenfeldt, Christian; SanFelipo, Bill; Rey, Daniel; Rubio, Belen
Publisher PANGAEA - Data Publisher for Earth & Environmental Science
Publication Year 2012
Rights Creative Commons Attribution 3.0 Unported
OpenAccess true
Representation
Language English
Resource Type Supplementary Collection of Datasets
Format application/zip
Size 15 datasets
Discipline Earth System Research
Spatial Coverage (-9.374W, 41.965S, -8.975E, 42.167N)
Temporal Coverage Begin 2008-06-05T00:00:00Z
Temporal Coverage End 2008-06-17T00:00:00Z