Abstract: Three ichnocoenoses have been distinguished in turbidity current,storm and flood event deposits.
(1)Nereites ichnocoenose in turbidity current deposits(turbidites)contains as many as 100 genera and 297 species of trace fossils among which the common ichnogenera are:Nereites,Neonereites, Scolicia,Helminthopsis,Cosmorhaphe,Paleomeandron,Urohelminthoida,Paleodictyon,Megagrapton,Zoophycos, Glockeria,Lorenzinia,Chondrites,Granularia and Thalassinoides and so on.Laterally,they may be subdivided into three different assemblages,including:1)the Thalassinoides—Rhizocorallium—Scolicia assemblage in the inner fan zone;2)the Zoophycos—Glockeria—Paleodictyon assemblage in the middle fan zone,and 3)Nereites—Cosmorhaphe—Paleodictyon assemblage in the outer fan zone.
(2)Cruziana ichnocoenose in storm deposits(tempestites)consists mainly of Cruziana,Zoophycos, Rhizocorallium,Kechia,Muensteria,Teichicknus,Rosselia,Chondrites,Planolites,Paleophycus,Scolicia,Asteriacites,Cochlichnus,Thalassinoides,Ophiomorpha and Fugichnia.Laterally,they tend to be controlled by water depths,and may be subdivided,from the depth to the shallow,into:1)the large-scale Zoophycos—Planolites assemblage generally near or below storm wave base;2)the small-scale Zoophycos—Rhizocorallium Prevailingly above storm wave base;3)the Rhizocorallium—Diplocraterion assemblage usually below fair-weather wave base,and 4)Skolithos-type burrows scattered near or above fair-weather wave base.
(3)Scoyenia ichnocoenose in flood event deposits(inundites)or flood plain deposits comprises the animal trace fossils such as Scoyenia,Ancorichnus,Steinichnus,Muensteria,Edaphichnium,Scaphichnium, Planolites,Skolithos,Cochlichnus,Ophiomorpha,Rusophycus and Rhizoliths,including root mats which are developed in areas along the shore zone of perennial lakes or streams,horizontal roots which occur dominantly in the nearshore zone or areas where thephreatic water is shallow,and vertical and diagonal roots which generally indicate the terrestrial environments with ephemeral surflcial water sources.