Abstract
A biostratigraphic study was carried out in the Lower Creaceous (Aptian-lower Albian) Zagros basin, northeastern Shiraz located at southwestern Iran, allowing the recognition of one lithostratigraphic unit. The Lower Cretaceous shallow-water limestones on the northeast of Shiraz contains abundant and diversified orbitolinid foraminifera. A biostratigraphy, based on the orbitolinid taxa and their distribution, is proposed for the Aptian and Albian deposits in the Lower Creaceous (Aptian-lower Albian) Zagros basin, northeastern Shiraz located at southwestern Iran, allowing the recognition of one lithostratigraphic unit. Three orbitolinid biozones have been recognized: 1) Palorbitolina lenticularis Assemblage Zone in the Lower Aptian; 2) Mesorbitolina parva Total Range Zone in the Late Aptian; 3) Orbitolina (Mesorbitolina) texana Assemblage Zone in the uppermost Aptian-lower Albian, the body of strata being characterized by a distinctive assemblage of Orbitolina (Mesorbitolina) texana and O. (M.) parva. The following taxa are the most abundant: Mesorbitolina texana, Mesorbitolina parva, Orbitolina sp., Pseudocyclammina lituus, Pseudochrysalidina conica, Pseudochrysalidina cf. arabica, Pseudocyclammina hedbergi, Praechrysalidina infracretacea, Cuneolina pavonia, Dictyocunus arabicus, Iraqia simplex, Vercosella laurentii, Protomarssonella trochus, Nautiloculina oolithica, and calcareous algae such as Salpingoporella dinarica, Trinocladus tripolitanus, Terquemella sp. and Lithocodium aggregatum-Bacinella irregularis.
Highlights
The Orbitolinidae are large benthic foraminifers with highest diversities in the Early to Mid-Cretaceous
A biostratigraphy, based on the orbitolinid taxa and their distribution, is proposed for the Aptian and Albian deposits in the Lower Creaceous (Aptian-lower Albian) Zagros basin, northeastern Shiraz located at southwestern Iran, allowing the recognition of one lithostratigraphic unit
This study aims to summarize the stratigraphic range of the assemblage zones and the species that occur in the Aptian-early Albian (Daryian Formation) and to compare these data with zonations that have been recorded for the Zagros Basin
Summary
The Orbitolinidae are large benthic foraminifers with highest diversities in the Early to Mid-Cretaceous. This family flourished in shallow marine carbonate facies deposited under subtropical to tropical conditions. The Daryian Formation is regionally significant as a petroleum reservoir and a source rock in the Zagros Basin [4]. James and Wynd [6] studied the stratigraphic relationships of the Daryian Formation at Gadun Mountain in the Zagros Foldbelt, but the age of the unit remains being poorly resolved. This study aims to document the foraminiferal fauna and calcareous algal flora in the formation in order to resolve the age of the unit and to clarify its depositional environment
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