Ichnostratigraphy

Trace fossils can provide biostratigraphic data, particularly in siliciclastic strata where other fossil age control may be limited or lacking. In continental environments, tetrapod trackways have been used to delineate several global time intervals. The biostratigraphic application of marginal-marine trace fossils seems to be limited, although a few ichnotaxa (e.g., Heimdallia, Climactichnites) may be stratigraphically restricted. In shallow-marine deposits, trace fossils constrain the position of the Ediacaran–Cambrian boundary (based on the appearance of Treptichnus pedum) and the dating of adjacent strata, and also provide relative ages for Cambrian to Devonian siliciclastic strata based on ichnospecies of Cruziana and Rusophycus (Cruziana stratigraphy) or such ornamented burrows as Arthrophycus. Ichnostratigraphy has not been explored in deep-marine strata to the same degree as in shallow-marine counterparts. The paucity of body fossils in many lower Paleozoic deep-marine successions hampers relative dating, and so trace-fossil data can be highly useful, as in the long-standing use of Oldhamia as a Cambrian index fossil. A few graphoglyptid ichnotaxa also have narrow stratigraphic ranges in younger deep-marine deposits.