The microstructural analysis of muds and mudrocks requires very high-resolution measurement. Recent advances in electron microscopy have contributed significantly to the improved characterisation of mudrock microstructures and their consequent petrophysical properties. However, imaging through electron microscopy is limited to small areas of coverage such that upscaling of these properties is a great challenge. In this paper, we develop a new methodology for multiple large-area imaging using scanning electron microscopy through automated acquisition and stitching from polished thin-sections and ion-milled samples. The process is fast, efficient and minimises user-input and bias. It can provide reliable, quantifiable data on sediment grain size, grain orientation, pore size and porosity. Limitations include the time involved for individual runs and manual segmentation, the large amount of computer memory required, and instrument resolution at the nano-scale. This method is applied to selected samples of Quaternary muddy sediments from the Iberian margin at IODP Site 1385. The section comprises finegrained (very fine clayey silts), mixed-composition, biogenic-terrigenous hemipelagites, with a pronounced but non-regular colour cyclicity. There is a multi-tiered and diverse trace fossil assemblage of the deep-water Zoophycos ichnofacies. The sediment microstructures show small-scale heterogeneity in all properties, and an overall random fabric with secondary preferred grain-alignment. These results on the fabric differ, in part, from previous studies of hemipelagic muds. Further work is underway on their comparison with other deep-water sediment facies.
This research is part of Shereef Bankole’s PhD programme at Heriot-Watt University, Edinburgh, United Kingdom. He appreciates the sponsorship received from Petroleum Technology Development Fund, Nigeria. The authors are grateful to Mark Curtis of the University of Oklahoma, United States of America for preparing the ion-milled samples. We thank the International Ocean Discovery Program for giving access to the core samples and Shereef is grateful to IODP technical staff (Walter Hale and Alex Wülbers) for their guidance and co-operation during the core sampling at MARUM IODP repository, Bremen, Germany. The final publication is available at Springer via https://doi.org/10.1007/s12583-019-1210-4.