Trace fossils of hybrid facies from Early-Middle Devonian strata in Longmenshan area, Sichuan Province

Abundant marine trace fossils are preserved in the Early-Middle Devonian strata of the Guixi-Shawozi section in Longmenshan area, Sichuan Province. According to the shapes, three types of trace fossils were identified that include Domichnia as Skolithos, Fodinichnia as Chondrites, Phycodes, Planolites, Rhizocorallium, Thalassinoides and Zoophycos; Food-seeking traces including Cylindrichnus and Palaeophycus; Repichnia as Cruziana and Monomorphichnus; Cubichnia as Asterichnus, Lockeia and Rusophycus. 14 kinds in total trace fossils can be identified clearly. The ichnocoenoses represent types of Domichnia, Fodinichnia, Food-seeking traces, Repichnia and Cubichnia. Four ichnocoenoses representing different sedimentary environments were recognized as follows:(1) Skolithos-Thalassinoides ichnocoenosis can be explained as Domichnia from higher-energy foreshore; (2) Rusophycus-Phycodes ichnocoenosis mainly consists of Cubichnia and Fodichnia generated in higher-energy nearshore; (3) Chondrites-Palaeophycus ichnocoenosis is from shallow shelf, which suggests sub-oxic and lower energy; (4) ZoophycosPalaeophycus ichnocoenosis is considered as Fodichnia from higher-energy shallow shelf between normal wave base to storm wave base. In terms of the ichnocoenoses, living environment and distribution pattern of trace fossils of hybrid facies were set up from Early-Middle Devonian strata in Longmen-shan area. Three kinds of Zoophycos fossils were observed, which were coexistent with concentrations of brachiopoda and shell, ripple marks, hummocky and swaley cross bedding, which reflects shallow environment sedimentary characteristics from Early to Middle Devonian in Longmenshan area and indicates that Zoophycos fossils were formed in a shallow environment.