Fractures in mudrocks: Advances in constraining timing and understanding mechanisms

Recent advances in fracture-timing techniques have led to new insights about sequences and mechanisms of fracture formation in mudrocks. Methods to constrain fracture timing in mudrocks include: (i) field evidence, including crosscutting relationships and evidence of compaction; (ii) petrographic evidence, including signs of soft-sediment deformation and diagnostic mineral assemblages or textures; (iii) stable-isotopic evidence; (iv) thermometric dating using burial history modelling; and (v) radiometric age-dating. In this contribution, we briefly review each method with salient examples from the literature. Many documented examples of mudrock-hosted fractures formed during early burial, a non-intuitive finding that demands a re-assessment of our assumptions about what types of materials can develop opening-mode fractures. In general, the style and distribution of fractures varies dramatically based on fracture timing, highlighting the importance of constraining timing for predicting fracture patterns and interpreting their mechanisms, including the role of fluid flow.