Mid-Cretaceous biostratigraphy (ammonites, inoceramid bivalves and foraminifers) at the eastern margin of the Anarak Metamorphic Complex (Central Iran)

Abstract Biostratigraphy of ammonite, inoceramid and orbitolinid foraminifer faunas from the mid-Cretaceous (Aptian–Turonian) succession at the eastern border of the Anarak Metamorphic Complex, a basement uplift in the north-western part of Central Iran, helped to understand complex lithostratigraphic patterns, to trace tectonic unconformities and to reconstruct the geodynamic significance of the succession. The basal continental Noqreh Formation can only be dated by stratigraphic superposition as pre-late early Aptian. An orbitolinid assemblage in the overlying shallow-marine Shah-Kuh Formation indicates a latest early Aptian age. The lower member of the overlying Bazyab Formation documents a considerable deepening in the early late Aptian (Epicheloniceras subnodosocostatum Zone). The boundary to the middle member of the Bazyab Formation is a conspicuous sedimentary unconformity, separating marly offshore strata below from shallow-marine, bioclastic sandstone above. The upper part of the middle member yielded ammonites of the upper lower Albian Douvilleiceras mammillatum Zone. In the upper member of the Bazyab Formation, ammonites of the upper Albian Mortoniceras rostratum Zone have been found. The base of the overlying Debarsu Formation is of earliest Cenomanian age (Mantelliceras mantelli Zone, Neostlingoceras carcitanense Subzone) and lower Cenomanian shallow-marine limestones range up to an intra-formational unconformity below the upper marl member of the formation, yielding early Turonian inoceramid bivalves and ammonites in the lower part. The Debarsu Formation is truncated along a major regional unconformity at the base of the Haftoman Formation. The erosional episode is correlated to a Coniacian tectonic event but further studies are needed to fully understand its geodynamic significance.