Review on the Permian–Triassic Boundary (PTB) in Abadeh (Iran), a Traveling Boundary

The Permian–Triassic transition along the South Cimmerian margin of the Neotethys in Abadeh (Iran) is built by four successive lithologies/events with apparently no gaps: (1) the stop of the skeletal carbonate factory of the Paratirolites limestone caused by the end-Permian mass extinction event (EPME); (2) replacement of carbonate deposits by the up to 0.3 m thick boundary clay, defining the base of the Elikah Formation; (3) sudden emergence of a sponge-microbial carbonate factory with buildups of ca. 1.6 m, called the microbial unit; (4) a thick succession of platy lime mudstone. Despite continued research for over 50 years, there still exists significant debate concerning the exact base of the Triassic. This is partially due to different proxies used for the identification of the Permian–Triassic boundary (PTB). Since the boundary was defined by the first appearance (FA) of the conodont Hindeodus parvus at the Global Stratotype Section and Point (GSSP), there is continued discussion concerning its earliest occurrence in Abadeh. Ongoing research shows the boundary at different stratigraphic levels: at the EPME horizon below the microbial unit, at its base, within the middle part, or at the base of the platy limestone beds directly above the microbial unit. We review the existing data, explain which level we regard as real PTB and recommend steps to achieve an agreement in the scientific community on the position of the PTB in Abadeh.