浊流、风暴和洪水事件沉积及其伴生的痕迹群落

浊流、风暴和洪水事件沉积中的痕迹化石研究开始于七十年代,迄今已有不少重要著作相继发表(如Crimes,1970、1973、1976;Seilacher,1977、1982;杨式溥,1982、1983、1986;吴贤涛,1982、1985等)。前人工作表明,结合痕迹学研究对判别上述各事件沉积的类型、追踪其形成过程和古环境再造,以及盆地分析和盆地内地层对比等均具重要潜在价值。

Turbidity Current,Storm and Flood Event Deposits and Their Concomitant Ichnocoenoses

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.