Sedimentology

Large-scale sedimentary structures on the seafloor are visualized together with the “Geophysics” section using sediment echography, such as the Parasound system aboard research vessels. Smaller sediment structures such as stratification, bioturbation or the content of ice-rafted debris (IRD, > 2 mm) are either examined on X-radiographs that are made during the documentation of the sediment cores or visualized with computed tomography (CT). Physical sediment parameters such as the sound velocity, wet density and magnetic susceptibility are measured both with the multi-sensor core logger (MSCL) on the entire core and on discrete samples to calibrate and determine the water content and grain densities. For this purpose, the samples are freeze-dried, divided and ground up for analysis. It is important to determine the salt content of the freeze-dried sample (2-10%) so that the weights or concentrations can be corrected (Kuhn, 2013). An essential task of the sedimentology group is the identification of sediment dynamics and thus the determination and separation of the sediment into grain size fractions such as gravel (> 2 mm), sand (2-0.063 mm), silt (63-2 µm) and clay (<2 µm) . Each of these fractions can be further subdivided and the composition analyzed separately in order to obtain information about the sediment origin (provenance) and transport processes. The sand and gravel fractions (coarse fraction) are separated by sieving. The silt and clay fraction (fine fraction) is separated by sedimentation in standing cylinders using the Atterberg method. The grain size analysis of the fine fractions is also carried out via sediment settling according to Stokes' equation with two sedigraphs. It is also possible to determine grain size distributions with laser or Coulter analyzers at the AWI stations in Potsdam and Sylt.

Grain shapes and the chemical element composition of individual smaller particles are determined with the scanning electron microscope (SEM) and combined energy-dispersive X-ray fluorescence analysis (EDX). We investigate the mineralogical composition of a sample with an X-ray diffractometer (XRD) both on the ground total sample (bulk) and on filter-cake texture preparations of the clay fraction. The concentrations of the clay minerals chlorite, illite, smectite and kaolinite are determined using the Biscaye (1965) method. The proportions of these clay minerals can not only provide information about sediment origin, but also about the weathering conditions at the source.