Figure 1 - Comparison of evolution of macroscopic and microstructural characteristics during burial of Shetland Group mudstones from the Northern North Sea basin. SEM images showed a change from a random arrangement of grains at shallow burial to a distinctly preferred orientation that occurred over the same depth interval as the change from smectite to illite (and compactional-loss of porosity). The inset figures give a quantitative measure of anisotropy from image analysis. TEM images revealed details of clay-grain packing with randomly aligned smectite crystals at shallow depths replaced by dominantly aligned illite crystals at great depths of burial.