An improved sample preparation method for imaging microstructures of fine-grained marine sediment using microfocus X-ray computed tomography and scanning electron microscopy

Marine sediments are composed of various mineral species and are characterized by micro-scale grain fabric. The arrangements and interactions of component particles place critical constraints on the physical, chemical, and biological processes that occur in subseafloor environments. However, the observation of nearly intact microstructures is difficult, especially in soft, muddy sediments because of their high water content and the presence of organic molecules. In this study, a modified version of the resin-embedding method generally used for biological samples was applied to marine sediment sample preparation. The new method was compared with the conventional t-butyl alcohol freeze-drying method using microfocus X-ray computed tomography (mu XCT) and scanning electron microscopy (SEM). The mu XCT and SEM results showed that all t-butyl alcohol freeze-dried sediment samples contained microstructural disturbances (e.g., cracks). In contrast, no cracks were observed in the samples prepared using the new resin-embedding method, and the microstructural arrangement of the sediment particles were clearly visible. In addition, the porosity visible from SEM images of the resin-embedded samples was similar to that measured using the moisture and density method, providing additional evidence that the microstructures of the resin-embedded samples were well preserved. The resin-embedding method allowed observation of the limited contact of the fine particles in clayey sediments, the clay microaggregates throughout the continental margin to pelagic sediments, and the presence of organic materials in environmental sediments. This modified biological resin-embedding method is suitable for the detailed observation and characterization of fine-grained marine sediment microstructure.