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

作者：G.Shanmugam

摘要：Soft-sediment deformation structures(SSDS)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 sandegravel craters,clastic injections,crushed and deformed stromatolites,etc.)have been recognized in strata ranging in age from Paleoproterozoic to the present time.The 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(DSDP/ODP/IODP),published during a period between 1863and 2017,has yielded at least 31 different origins.Earthquakes have remained the single most dominant cause of SSDS because of the prevailing'seismite'mindset.Selected advances on SSDS research are:(1)an experimental study that revealed a quantitative similarity between raindrop-impact cratering and asteroid-impact cratering;(2)IODP Expedition 308 in the Gulf of Mexico that documented extensive lateral extent(>12 km)of mass-transport deposits(MTD)with SSDS that are unrelated to earthquakes;(3)contributions on documentation of pockmarks,on recognition of new structures,and on large-scale sediment deformation on Mars.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.,separ

发文机构：Department of Earth and Environmental Sciences

关键词：变形构造沉积学SSD起源定义分类案例IODPSoft-sediment deformation structures（SSDS） Prelithification deformation Liquidization Pockmarks Impact cratering Scientific drilling

分类号： P542.3[天文地球—构造地质学][天文地球—地质学]P512.2