Ichnofossils and Ichnofacies of Pabdeh Formation in NW Ilam, West Iran

Pabdeh Formation in Ivan- Gharb area comprises alternation of thin to thick limestones (mudstone, wackestone and packstone) and dark to light gray planktonic foraminifera bearing shale beds. Five ichnogenera, which classified in two ichnoassemblages, were recognized. The first ichnoassemblage with relatively high ichnodiversity (Arenicolites, Chonderites, Planolites and Neonerites) occurs in wackestone, mudstone and packstone facies. This assemblage of ichnofauna represents the Cruziana ichnofacies, formed in a relatively high energy condition. The second ichnoassemblage with lower ichnodiversity (Zoophycos and Chondrites) is found in shale, wackestone, mudstone and packstone facies and represents the Zoophycos ichnofacies which were formed in a low energy and deeper condition. Presence of horizons rich in organic matter (TOC>2%) in the middle and lower units of Pabdeh Formation containing Zoophycos ichnofacies, indicate an environment with low oxygen level.