Ichnology and sedimentology of a shallow marine Upper Cretaceous depositional system (Neyzar Formation, Kopet-Dagh, Iran): Palaeoceanographic influence on ichnodiversity

The trace fossil assemblages from the Upper Cretaceous Neyzar Formation are described for the first time from Kopet-Dagh, Iran, enhancing the record of this fossil group in the Cretaceous of the Middle East. Thirty-one ichnogenera have been identified in open marine successions: Agrichnium, Asteriacites, Asterosoma, Bergaueria, Chondrites, Cylindrichnus, Halopoa, Helminthopsis, Gordia, Gyrochorte, Laevicyclus, Lockeia, Megagrapton, Nereites, Neonereites, Ophioichnus, Ophiomorpha, Palaeophycus, Phycodes, Phycosiphon, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Scolicia, Sinusichnus, Skolithos, Spongeliomorpha, Taenidium, Teichichnus, and Thalassinoides. The Neyzar Formation accumulated on a gently dipping shelf dominated by storm- and fair weather-wave processes and includes shelf, lower offshore, upper offshore, lower shoreface-proximal offshore, middle-upper shoreface and foreshore deposits. Identification and interpretation of ichnological signatures and the spatial arrangement of sedimentary structures in the successions are used to further refine sedimentary interpretations of parameters such as wave energy, substrate properties, the nature of the available food supply, variability in sedimentation rates and proximal–distal trends of the wave-dominated shoreface–offshore complex. The prevalent palaeoceanographic situation during the deposition of the studied successions was ideal for tropical storms, thus promoting tempestite deposition and the occurrence of a tropical and subtropical trace fossil suite. According to this study, increasing mobility and infaunality with more complex trace systems or sophisticated feeding strategies, climax population strategies and the high diversity, associated with rapid increase in the abundance and depth of infaunal structures, indicate a major reorganization of the shallow-marine benthic communities that occurred in response to the Mesozoic marine revolution.