Global case studies of soft-sediment deformation structures (SSDS): Definitions, classifications, advances, origins, and problems

Problems that hinder our understanding of SSDS still remain. They are: (1) vague definitions of the phrase “soft-sediment deformation”; (2) complex factors that govern the origin of SSDS; (3) omission of vital empirical data in documenting vertical changes in facies using measured sedimentological logs; (4) difficulties in distinguishing depositional processes from tectonic events; (5) a model-driven interpretation of SSDS (i.e., earthquake being the singular cause); (6) routine application of the genetic term “seismites” to the “SSDS”, thus undermining the basic tenet of process sedimentology (i.e., separation of interpretation from observation); (7) the absence of objective criteria to differentiate 21 triggering mechanisms of liquefaction and related SSDS; (8) application of the process concept “high-density turbidity currents”, a process that has never been documented in modern oceans; (9) application of the process concept “sediment creep” with a velocity connotation that cannot be inferred from the ancient record; (10) classification of pockmarks, which are hollow spaces (i.e., without sediments) as SSDS, with their problematic origins by fluid expulsion, sediment degassing, fish activity, etc.; (11) application of the Earth's climate-change model; and most importantly, (12) an arbitrary distinction between depositional process and sediment deformation. Despite a profusion of literature on SSDS, our understanding of their origin remains muddled. A solution to the chronic SSDS problem is to utilize the robust core dataset from scientific drilling at sea (DSDP/ODP/IODP) with a constrained definition of SSDS.