Ichnological Analysis of the Miocene Marine Deposits of Makran (SE Iran): Implication for Paleoenvironmental Interpretations

The presence of trace fossils and their diversity in Miocene deposits of western Makran accretionary prism (SE Iran) was the center of this research. The trace fossil contents of Cheraghsuz and Sardasht (with Middle Miocene in age) and Gowharan (with Early Miocene in age) stratigraphic sections were analyzed. The recognized specimens of the Cheraghsuz section are Gordia isp., Helminthopsis hieroglyphica , Helminthopsis abeli , Helminthorhaphe flexsuosa , Paleodictyon maximum , and Spirorhaphe involuta . The Sardasht section is composed of Gordia isp., Helminthopsis hieroglyphica , Helminthopsis abeli , Helminthorhaphe flexsuosa , Paleodictyon maximum , Paleodictyon majus , Paleodictyon isp., Spirorhaphe involuta , Helicolithus isp., Helicorhaphe tortilis , and Neonereites isp.. In the Gowharan section, some gastropod trails, a giant and very well-preserved Archaeonassa -like ichnogenus, and ripple marks were observed. Majority of the recognized trace fossils are of the graphoglyptid group. The trace fossil contents of Cheraghsuz and Sardasht sections are compatible with Nereites ichnofacies; as graphoglyptids are thought to be indicative of oligotrophic conditions, the trace-producers are filter-feeder organisms that normally tend to take suspended nutrient materials in the water column, but due to lower sedimentation rate, the nutrient content is concentrated on the superficial part of the substrate; accordingly, the trace-makers prefer grazing and moving on the surface sediment to take their food. However, the exceptionally preserved trace fossils in Gowharan section should be formed in a tidal flat environment. In relation to the floor, it has recorded at least three shapes, including bi-lobed, uni-lobed and submerged forms. In addition, it could be observed that different trace fossils may be created by a single animal and different animals may create the same trace fossils.