Coast and Shelf
Sediment dynamics in coastal and shelf areas
Scientists: Firoz Badesab, Tobias Kulgemeyer, Benjamin Baasch, Wei Leng, Tilo von Dobeneck
Methods: Enviromagnetics, Electromagnetics, Hydroacoustics, Sedimentology
Projects: MARUM Sediment Dynamics projects SD1, SD2, INTERCOAST projects IC8 IIC8 II

Topics: Large spatial variations in magnetic and heavy mineral content are typical for sublittoral sediment facies. These patterns reflect modern sediment dynamics driven by waves, tides and currents as well as relict structures of past sea-level change, glacial activity, tectonics or human impact. With electro- and enviromagnetic methods we can map these structures to reveal provenance areas, sediment facies, transport pathways and fractionation mechanisms.

Magnetite layers and ripples at Orokawa Beach, NZ

Deglacial outburst flood deposits and history of the Laurentian Channel Ice Stream
Scientists: Wei Leng, Tilo von Dobeneck, Janna Just, Fenna Bergmann, David Piper
Projects: IRTG ArcTrain, Chinese Scholarship Council

Summary: The reddish-brown plumite layers deposited on the levees of the Laurentian Fan valleys appear to have recorded multiple Laurential Channel subglacial outburst floods between deglacial Heinrich events 2 and 1. Five event layers have been consistently recorded in three new gravity cores retrieved on the SW Grand Banks slope. The apparently huge extent of these outburst plumes around the Laurentian Fan as well as their causes and consequences are investigated using physical properties, rock magnetic and grain-size analyses, together with seismoacoustic profiling. We provide the first detailed 14C ages of the outburst event sequence and discuss their recurrence intervals in the context of regional ice retreat. Event layers show systematic changes in their rock-magnetic properties; hematite contents increase over time and proximally while magnetite grain sizes fine upwards and spatially away from the fan. We argue that these plumites were formed by recurrent erosion of glacial mud deposits in the Laurentian Channel by meltwater outbursts and evaluate alternative event scenarios including outburst from pro- or subglacial lakes driven by ice bulging or meltwater injection. In a joint provenance and transport study, we compare major element and magnetic mineral contents of these event beds with a new collection of 80 source reference samples for the Gulf of St. Lawrence area. Element ratios suggest a steady compositional change from older to younger outburst event beds, while element-specific offsets from reference sample compositions indicate grain-size and mineral partitioning during suspension transport. Their magnetic properties place event beds on the source mixing trend of four reference samples groups where two represent a magnetite-rich source (Canadian Shield and/or Southern Newfoundland) and two a hematite-rich source (Appalachian red beds). The overproportional Ca contents suggest that a third, calcareous source must have contributed, possibly from the lower Paleozoic Anticosti Island limestones of the former Appalachian Foreland.
Selected Publications:

Leng W., von Dobeneck T., Bergmann F., Just J., Mulitza S., Chiessi C., St-Onge G., Piper D. (2018)
Sedimentary and rock magnetic signatures and event scenarios of deglacial outburst floods from the Laurentian Channel Ice Stream
Quaternary Science Reviews, 186, 27 - 46
doi: 10.1016/j.quascirev.2018.01.016

Magnetic minerals as markers of coastal zone evolution in the Bay of Plenty, NZ
Scientists: Firoz Badesab, Tobias Kulgemeyer, Hendik M├╝ller, Karin Bryan, Tilo von Dobeneck
Projects: International Research Training Group INTERCOAST Projects IC8 I, IC8 II

Summary: Magnetic iron minerals are widespread and indicative sediment constituents in estuarine, coastal and shelf systems. A combination of geophysical (in particular environmental magnetic and electromagnetic), sedimentological and numerical methods is used to identify magnetite-enriched placer-like zones in a complex coastal system and delineate their formation mechanisms.
Selected Publications:

Badesab F., von Dobeneck T., Bryan K., M├╝ller H., Briggs R., Frederichs T., Kwoll E. (2012)
Formation of magnetite-enriched zones in and offshore of a mesotidal estuarine lagoon: An environmental magnetic study of Tauranga Harbour and Bay of Plenty, New Zealand
Geochemistry Geophysics Geosystems, 13
doi: 10.1029/2012GC004125

Badesab F., von Dobeneck T., Briggs R., Bryan K., Just J., M├╝ller H. (2017)
Sediment dynamics of an artificially deepened mesotidal coastal lagoon: An environmental magnetic investigation of Tauranga Harbour, New Zealand
Estuarine, Coastal and Shelf Science, 149, 240 - 251
doi: 10.1016/j.ecss.2017.06.017

Sediment distribution on the NW Iberian Shelf (completed)
Scientists: Benjamin Baasch, Vera Bender, Hendrik M├╝ller, Thomas Frederichs, Tilo von Dobeneck
Projects: MARUM Sediment Dynamics SD1, SD2, EUROPROX Project 12b

Summary: The NW Iberian continental shelf is a high energy, low accumulation nonglaciated shelf of narrow width (25 to 50 km) and large variety of sediment types and patterns. Extensive EM cross-shelf profiling in this area on a 2008 RV Poseidon and 2010 RV Meteor cruise had the objective to classify the facies and textures of the four major surficial sediment types of the entire Galician shelf and to map their distribution at meter-scale spatial resolution with a special focus on transitions: (1) mud facies of fine-grained, mostly muddy Holocene high-stand sediments from the Duero and Mi├▒o rivers deposited in two successive coast-parallel mud belts, (2) mixed sand facies consisting of relict and reworked siliciclastic and carbonatic sands deposited at moderate regimes, (3) glaucony facies of mostly relict late Miocene sands indicative of slow to arrested sediment accumulation on the outer shelf, and (4) gravel facies dominated by bioclasts and siliciclasts representing low-stand shoreface and storm deposits. All facies could be easily discriminated by EM-based crossplots of sediment and matrix susceptibility against porosity, demonstrating the potential of EM-based sediment classification. Transitional environments between the sediment units cover several hundreds of meters within the profiles linking facies end-members in the crossplots. Large bedforms and seabed undulations clearly correlate with porosity and susceptibility profiles, indicating mud deposition in troughs and glauconite or magnetite enrichment on bottom-current exposed ridge crests.
Selected Publications:

Baasch B., M├╝ller H., von Dobeneck T., Oberle F. (2017)
Determination of grain-size characteristics from electromagnetic seabed mapping data: A NW Iberian shelf study
Continental Shelf Research, 140, 75 - 83
doi: 10.1016/j.csr.2017.04.005

Baasch B., M├╝ller H., von Dobeneck T. (2018)
Predictive modelling of grain size distributions from marine electromagnetic profiling data using end-member analysis and a radial basis function network
Geophysical Journal International, ggy152 - ggy152

doi: 10.1093/gji/ggy152

Baasch B., M├╝ller H., Oberle F., von Dobeneck T. (2014)
Inversion of marine multifrequency electromagnetic profiling data: a new approach to resolve surficial sediment stratification
Geophysical Journal International, 200, 438 - 451
doi: 10.1093/gji/ggu406

CSEM mapping of submarine freshwater seepage at Eckernf├Ârde Bay (completed)
Scientists: Hendrik M├╝ller, Kai Hamer, Wiebke Nehmiz, Tilo von Dobeneck
Project: RCOM/MARUM Sedimentation Processes Project C1

Summary: Submarine groundwater discharge in coastal settings can massively modify the hydraulic and geochemical conditions of the seafloor. Controlled source electromagnetic imaging offers an innovative dual approach to seep characterization by its ability to detect pore-water electrical conductivity, hence salinity, as well as sediment magnetic susceptibility, hence preservation or diagenetic alteration of iron oxides. The newly developed electromagnetic (EM) profiler Neridis II successfully realized this concept for the first time with a high-resolution survey of freshwater seeps in Eckernf├Ârde Bay (SW Baltic Sea). EM profiling creates a crisp and revealing fingerprint image of freshwater seepage and related reductive alteration of near-surface sediments. Our findings imply that (1) freshwater penetrates the pore space of Holocene mud sediments by both diffuse and focused advection, (2) pockmarks are marked by focused freshwater seepage, underlying sand highs, reduced mud thickness, higher porosity, fining of grain size, and anoxic conditions, (3) depletion of Fe oxides, especially magnetite, is more pervasive within pockmarks due to higher concentrations of organic and sulfidic reaction partners, and (4) freshwater advection reduces sediment magnetic susceptibility by a combination of pore-water injection (dilution) and magnetite reduction (depletion). The conductivity vs. susceptibility biplot resolves subtle lateral litho- and hydrofacies variations.

Processes at submarine freshwater seeps

M├╝ller H., von Dobeneck T., Nehmiz W., Hamer K. (2011)
Near-surface electromagnetic, rock magnetic, and geochemical fingerprinting of submarine freshwater seepage at Eckernf├Ârde Bay (SW Baltic Sea).
Geo-Marine Letters, 31(2), 123-140
doi: 10.1007/s00367-010-0220-0






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University of Bremen Research group Marine Geophysics
Faculty of Geosciences | FB5