Ichnofabrics and ichnofabric-forming trace fossils in Phanerozoic turbidites

Ichnology is commonly used in the palaeoenvironmental analysis and hydrocarbon reservoir characterization of bioturbated shallow marine facies, but is more rarely applied to deep marine and turbiditic successions. This work identifies the key trace fossils that are likely to be of use in ichnological analysis of drill cores, and in the application of ichnological data to the investigation of deep marine turbidite plays. The available data on trace fossil occurrences in turbidites have been analyzed for the whole of the Phanerozoic to identify the principal components of turbidite ichnofabrics at different times. It is found that a limited number of ichnofabric-forming ichnotaxa occur frequently in turbidite-bearing formations. In order of decreasing frequency of occurrence, the key ichnotaxa are Chondrites, Planolites, Scolicia, Zoophycos, Ophiomorpha, Phycosiphon, Thalassinoides and Nereites. Surprisingly, despite well-documented changes in deep marine benthic ecology through the Phanerozoic, ichnotaxonomic components of ichnofabrics show little behavioural change or evolution of new bioturbation styles. A number of ichnotaxa do show changes in their relative abundance through the Phanerozoic, possibly indicating ecological competition or niche replacement (e.g. Early Palaeozoic Dictyodora replaced by Mesozoic and Cenozoic Zoophycos). Ichnofabric-forming trace fossils need to be fully understood before they can be confidently applied to reservoir characterization of turbidite facies, but this study identifies the most important ichnotaxa in such settings and provides a framework for future research