Albian-Cenomanian Zonation (Foraminifers and Calcareous Aglae) in the Northern Fars, Iran

Abstract

Problem statement: In the middle Cretaceous of Iran, fossil calcareous algae and zonation them with foraminifers are one of the less studied compared to others invertebrate groups such as foraminiferis, mollusks and others. Several stratigraphic units were analyzed in detail and a biostratigraphic zonation of the Albian-Cenomanian rocks of the Fars basin (Sw. Iran) is proposed. Approach: All stratigraphic units were studied for the determination calcareous algae accompanying with foraminifers. Identification of planktonic, benthic foraminifers and calcareous algae was made from thin slides. After the identification of the microfossils assemblages, benthic, planktonic microfossil and calcareous algae biostratigraphy was recognized and a possible correlation with the other zonations was established. Results: The stratigraphic distribution of 21 genus of calcareous algae and benthic and planktonic foraminifers is used to characterize 4 ass. zone that in ascending order are: Or. aperta-Cuneolina ass. zone, Or. conica-Hemicyclammina ass. zone, Dicyclina-Orbitolina ass. zone and Alveolinids ass. zone. The top of Or. aperta-Cuneolina ass. zone is marked at the last appearance of the marker fossil. The Or. conica-Hemicyclammina ass. zone was defined with the last appearance of Or. conica and represented by an assemblage characterized by Cuneolina pavonia-Hemicyclammina sigali-Pseudochrysalidina sp. together with calcareous algae such as: Trinocladus tripolitanus-Permocalcus irenae. Overmost of the area, the transition from shallow-marine limestones up into pelagic facies occurs within the R. appenninica-Radiolaria ass. Zone. The Orbitolina-Dicyclina ass. zone is recognized in the Sarvak Formation and is represented by an assemblage characterized by Nezzazata simplex-Neoiraqia convexa-Hemicyclammina sigali together with Permocalculus irenea. Toward the central and western part of the area in shallow marine facies, this zone is changed to the Alveolinids zone which corresponds to the last appearance of Simplalveolina. Conclusion/Recommendation: Therefore, calcareous algae can be an important source of introducing ass. zones.