Shale fissility: relation to bioturbation

Fissility in shales appears directly related to the parallel orientation of mineral grains in the rock fabric. In two shale sequences examined, fissility increases along a gradient of decreasing bioturbation. Normal marine mudrocks should be characterized by lack of fissility due to the randomized fabric produced by bioturbation, while azoic marine mudrocks should exhibit good fissility due to the lack of biogenic reworking and the preservation of an originally horizontal particle arrangement.