Mud breccia is a sedimentary rock composed of angular fragments of mudstone or shale cemented together. It typically forms in tectonically active regions where mud is fractured and re-cemented due to faulting or other forms of deformation. Mud breccia provides insights into the geological history of deformation and sedimentation in an area.
Reference: Potter, P. E., Maynard, J. B., & Depetris, P. J. (2005). “Mud and Mudstones: Introduction and Overview.” Springer.