Paleontology and paleoecology of coralline algal assemblages from the Early–Middle Miocene deposits in NW of the Zagros basin, Iran

Abstract

The paleontology and paleoecology of coralline red algal assemblages of Asmari carbonate platform in north-west Zagros basin (Lurestan province) are described. The Asmari Formation was deposited during the Burdigalian to Langhian interval. This Formation unconformably overlies Eocene dolomites of Shahbazan Formation and is conformably underlain by Gachsaran Formation. The thin section analysis of carbonate facies from Asmari Formation yielded a rich assemblage of coralline red algae that deposited on a carbonate ramp environment. These associations were predominant on inner and middle ramp settings. The coralline red algal assemblage comprises both geniculate and non-geniculate forms. Encrusting, encrusting to layered, arborescent and lumpy were the growth forms. The distribution of them across the ramp profile is related to the paleobathymetric position. Thin section analysis shows that Lithothamnion and Mesophyllum are the most abundant, whereas Lithoporella, Neogoniolithon, Sporolithon and Spongites are less abundant and Phymatholithon together with Corallina are rare. Neogoniolithon, Lithothamnion and Lithoporella were predominant in calm waters of euphotic-mesophotic inner ramp. Spongites and Corallina together with fragments of reworked melobesioids constituted the high energy parts of euphotic zone. Neogoniolithon is present in the shallower parts of a middle ramp. Deep and calm waters of the oligophotic zone in middle ramp characterized by the dominance of Mesophyllum and Lithothamnion. The presence of Lithoporella, Spongites and Sporolithon among the red algal assemblage indicates that carbonate production took place in warm waters of the tropical to subtropical zone.