Late Devonian faunal events and sea level changes in east and central Iran: Correlation with global patterns of change

Abstract

Late Devonian sequences in east and central Iran display evidence of bioevents and sea level changes that can be aligned with those identified elsewhere. Remobilisation of sediments and hiatuses in early Frasnian sequences of the Shotori Range and in central Iran imply a change from terrestrial to shallow water marine conditions. Faunas of a pair of biostromes in the Shishtu Formation show the oldest horizons to be early Frasnian in age, no younger than the jamieae Zone. The paucity of fossils in these horizons suggests that shallow water, shoaling conditions prevailed at the base of the jamieae Zone. Diversification of the fauna, coinciding with a deepening event, indicates a change from nearshore to outer shelf or open marine conditions towards the end of the jamieae Zone, and on into the base of the linguiformis Zone. Depauperate faunas close to the Frasnian/Famennian boundary in the Shotori Range correspond to similar conditions in other parts of the world. The base of the Famennian in the Shotori Range exhibits shallow water and ironstone facies. Terrestrial to back‐reef conditions of the early Famennianin (triangularis Zone to the end of crepida Zone) in this area can be correlated with shallow, continental shelf environments of the same age in central Iran. The absence of palmatolepid conodonts is also indicative of a shallow, nearshore environment. The abundance of palmatolepids in the later rhomboidea to poster a zones points to open marine, deeper water conditions. Reducing conditions prevailed from the poster a Zone to the Famennian/Tournaisian boundary, with general shoaling interrupted briefly by a deeper water interval correlated with the Hangenberg extinction event.

Keywords:

• Iran
• Shotori Range
• Frasnian
• Famennian
• Ironstone facies
• Sea level
• Correlation