Chapter 9 - Soft-sediment deformation structures

Abstract

Soft-sediment deformation structures (SSDS), commonly associated with deep-water deposits, have been the focus of attention for over 150 years. Existing unconstrained definitions allow one to classify a wide range of features under the umbrella phrase “SSDS.” As a consequence, a plethora of at least 120 different types of SSDS (e.g., convolute bedding, slump folds, load casts, dish-and-pillar structures, pockmarks, raindrop imprints, explosive sand-gravel craters, clastic injections, crushed and deformed stromatolites, etc.) have been recognized in strata ranging in age from Paleoproterozoic to the present time. Two factors that control the origin of SSDS are prelithification deformation and liquidization. A sedimentological compendium of 140 case studies of SSDS worldwide, which include 30 case studies of scientific drilling at sea (Deep Sea Drilling Project/Ocean Drilling Program/Integrated Ocean Drilling Program), published during a period between 1863 and 2017, has yielded at least 31 different origins. Earthquakes have remained the single most dominant cause of SSDS because of the prevailing “seismite” mindset. This chapter provides a detailed account of documented case studies worldwide and related problems. The remaining unresolved issue is in distinguishing SSDS formed from mass transport from those that formed by tectonics.