Ichnofossils and Their Environmental Significance in Storm Deposit from the Middle Devonian Yangmaba Formation in Longmenshan Area

Key words: 
• Longmenshan area /
• Devonian /
• trace fossils /
• paleoenvironment

Abstract: Abundant marine trace fossils are preserved in Devonian strata in the Longmenshan area. Geological investigation of the Shigouli outcrop in the Jiangyou area found trace fossils preserved in tempestite from the upper Yangmaba Formation,and are systematically described. A total of five ichnogenera were identified:Chondrites, Changchengia,Rhizocorallium,Skolithos and Zoophycos. Of these,Chondrites-Zoophycos ichnofacies reflect a shallow shelf environment affected by storm action. The order in which the trace fossils appeared was identified from the cross-cutting relationship between the traces and their positions:Chondrites,Zoophycos,Rhizocorallium, Changchengia and Skolithos. The Chondrites and Zoophycos ichnofossils in the tempestite had the distinctive features of opportunistic species,and are important indicators of the sedimentary environment. Numerous thick branched Chondrite burrows reflect the oxygen content of the water at that time. This not only controlled the burrow diameter,it may also imply a link between burrow diameter and the severity of the living environment. The Zoophycos in the tempestite revealed that its trace maker was living in shallow shelf deposits in the Devonian.