Classification of and Criteria for Recognition of Slumps, Slides and Water Escape Features in Subaqueous Settings

Ole J. Martinsen

Soft-sediment deformation occurs in virtually every modern and ancient subaqueous depositional environment. Understanding of the genesis and occurrence of such deformational features gives vital input to depositional and paleogeographic models.

Slumps and slides classify within a range of mass movements from creep to debris falls. Slumps are downslope movements of sediment above a basal shear plane with substantial internal deformation, while slides also move downslope above a basal shear surface but with little internal deformation. Individual types of slumps and slides are classified by grain size and whether the movement above the basal shear plane is translational or rotational. In contrast, water-escape is largely vertical movement of escaping pore water and surrounding sediment and creates a number of phenomena including diapirs, sediment volcanoes and injections.

Analysis of the structural style makes distinction and recognition of deformational features possible. Slides have a family of listric, extensional faults in the head region and an undeformed central part. The toe region is either open-ended (with no evidence of contraction) or has a family of listric thrust faults. Slumps have a scar in the head region, and is dominated by internal simple shear folds and plastic deformation. The toe zone is open-ended or has a contractional fault family. Water-escape features are recognized by external shape (e.g., sediment volcanoes). Convoluted zones are differentiated from slumps based on an unsystematic fold style.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California