Discovery of trilobite trace fossils from the Early to Middle Cambrian, Tabas Block, Central Iran

Early to Middle Cambrian successions exposed at the Shirgesht area, Tabas Block of central Iran has yielded a high diversity and abundant ichnofossils with arthropod trackways. These trace fossils contain diverse ethological patterns, including furrowing or crawling (Cruziana), resting (Rusophycus), walking (Diplichnites), sideways grazing (Dimorphichnus) and swimming grazing (Monomorphichnus). The assemblage of trace fossils reported from the Early to Middle Cambrian of the Tabas Block, has a significant stratigraphic importance as they provide evidence regarding the developmental patterns during the early phase of life on earth. Stratigraphically, trace fossils studies is significant for defining the age of the unfossiliferous Cambrian successions of the Tabas Block from Central Iran where typical diagnostic trilobite fauna is absent. According to Cruziana ichnostratigraphy and comparsion the Lalun ichnofauna with other examples from similar age, the present assemblage could represent the late Early to Middle Cambrian. The distribution of trace fossils in the Early to Middle Cambrian successions reflects the paleoecological conditions including the availability of oxygen and nutrient influx. Hwever, the diversity and abundance of infauna, smaller trace fossil size, sporadic distributions of burrowing and lower intensities of bioturbation of trace fossil suite and the presences of evidence of predominance of trilobite trace fossils with morphologically simple represents a stressed expression of the ichnofacies and ichnologically stressed environment during deposition such as estuary.