(20) An improved sample preparation method for imaging microstructures of fine-grained marine sediment using microfocus X-ray CT and SEM

From Stratodynamics


Go-Ichiro Uramoto1, Yuki Morono1, Katsuyuki Uematsu2, and Fumio Inagaki1

1Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) 2Marine Works Japan

E-mail: uramotog@jamstec.go.jp


Marine sediments composed of various mineral species, and micro-scale interactions and arrangements of component particles place critical constraints on the physical, chemical, and biological processes occurring in subseafloor environments. However, the observation of nearly intact microstructures has been difficult especially soft muddy sediments because it’s high content of water and organic molecules. In this study, we examined the biologically used resin-embedding method for marine sediments, and compared it with the t-butyl alcohol freeze-drying method by observations using microfocus X-ray computed tomography (μXCT) and scanning electron microscopy (SEM). In all t-butyl alcohol freeze-dried sediment samples, μXCT and SEM observations showed the occurrence of structural disturbances (e.g., cracks) during the sample preparation, which has significantly changed the sediment microstructure and physical properties. In marked contrast, no cracks were observed in the samples prepared using our resin-embedding method, and the microstructure of the sediment particles were clearly visible. To binarize the pore and particle-occupied spaces, we calculated sample porosities from the SEM images of the flattened surfaces of the resin-embedded samples. The measured porosities were overall similar to those obtained using the moisture and density method, providing another indication that the microstructures of the resin-embedded samples are well preserved. Additionally, we observed that numerous particles in high-porosity surficial clayey sediments are "loosely-packed" in the sectioned surface, clay microaggregates throughout continental margin to pelagic sediments, and presence of organic materials in environmental sediments. The modified biological resin-embedding method is suitable for the detailed observation and characterization of fine-grained sediment microstructure.