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.
Source Potter, P. E., Maynard, J. B., & Depetris, P. J. (2005). “Mud and Mudstones: Introduction and Overview.” Springer.