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

Abstract

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 (µXCT) and scanning electron microscopy (SEM). The µXCT 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.

A comparison of micro-CT and thin section analysis of Lateglacial glaciolacustrine varves from Glen Roy, Scotland

“…Palmer et al, 2008a). This study demonstrates that sediment disturbance in Quaternary sediments caused by thin section production by scanning before and after impregnation can be recognised, reaching similar findings to that of Uramato et al (2014), albeit the latter study examined much Fig. 9.…”

“…Finally, under cross-polarised light, the fine component displays a distinctive masepic fabric (cf. Carr, 2004;van der Meer and Menzies, 2011). These structures are typical of distal glaciolacustrine varves (cf.…”

“…When viewed under cross-polarised light in thin section the latter structures are evident as intraclasts of very fine silt or clay with distinctive masepic fabrics (cf. van der Meer and Menzies, 2011).…”

“…Menzies and Maltman, 1992;van der Meer, 1993van der Meer, , 1997Phillips and Auton, 2000;Carr and Rose, 2003;van der Meer et al, 2003;Heimstra et al, 2005;Larsen et al, 2006;Menzies et al, 2006;Hart, 2007;Phillips et al, 2007Phillips et al, , 2011Lee and Phillips, 2008) and lacustrine environments. For palaeolimnologists, micromorphological techniques have developed in line with recognition that lacustrine sediments may store environmental information on an annual and even sub-annual basis, in the form of discrete laminations and sublaminations (e.g.…”

Low-Temperature Clay Mineral Dehydration Contributes to Porewater Dilution in Bering Sea Slope Subseafloor

“…The samples were embedded in LR White epoxy resin (hard grade) as described by Kim et al (1995) and Uramoto et al (2014). A previous problem in TEM investigation of I/S mixed-layer minerals was the collapse of expandable interlayers under high vacuum, making the discrimination of smectite and illite layers very difficult.…”