Paleoenvironmental analyses of coralline red algal assemblages in Lower Miocene carbonate deposits of Central Iran

Abstract

ABSTRACT This work is based on coralline red algal flora-dominated Lower Miocene carbonates of the Qom Formation from Central Iran Basin. Five assemblages, including corallinoid, lithophylloid, mastophoroid, melobesioid and sporolithoid corresponding to 11 genera of geniculate and non-geniculate, were identified. Also, growth forms and taphonomic characteristics of coralline-algal grains were assessed. The arborescent, layered to foliose lamellae, fruticose, lumpy, warty and encrusting growth forms of studied taxa are observed and five taphonomic traits belonging to both mechanical [abrasion, disarticulation, fragmentation] and biological [encrustation, bioerosion] processes were recognised. The relative abundance of assemblages, growth forms, and taphonomy of red algae visualised at thin-section scale were calculated. Our quantitative analysis highlights mechanical (abrasion > fragmentation) and biological (bioerosion> encrustation) processes. Moreover, layered to foliose and fruticose abundance peaks reveal higher than others. This kind of algal distribution in the examined region indicates that the Qom Formation was deposited on a marine carbonate shelf, which is a deepening depositional system in tropical and subtropical zone. This approach expresses more abundance of red algal assemblages on the deep part of inner and proximal to distal middle shelf settings along with a regime of moderately high towards low hydrodynamic energy and mesophotic – oligophotic conditions.