New planktonic foraminiferal record across the Aptian–Albian transition in Interior Fars, Zagros Basin, SW Iran: Implication for latest Aptian paleogeography along the southern shallower Neo-Tethys

Abstract

The Aptian–Albian (A–A) transition encompassed a critical timing in the evolution of Fars Platform (Zagros Basin, SW Iran), such that a number of previous studies on its proximal part (called “Coastal Fars”) illustrated platform recovery after sustained demise due to latest Aptian maximum sea-level lowstand. So far, much less attention has been given to the distal part of the platform – “Interior Fars” – where the lack of proper geological age interpretations, in particular, has been limiting a full paleoenvironmental reconstruction of the southern shallower Neo-Tethys. In order to establish the chronostratigraphic framework of Interior Fars, this study presents a novel set of planktonic foraminiferal record for the A–A Kazhdumi Formation at the Saroie section. The identified fauna comprises nine species from four genera, all of which are reported for the first time from Fars Platform. The observed new bioevents are generally consistent with those of the proposed reference section at a deeper intrashelf setting (Tang-e-Maghar, Dezful Embayment), allowing for the establishment of a local upper Aptian–Lower Albian zonation and leading to adequate constraints on the local Aptian/Albian boundary and the timing of prominent black shale deposition (possible “Jacob” equivalent). Based on this new Saroie chronostratigraphic scheme, it is evident that sedimentation across the A–A transition was maintained fully marine at the Saroie section, Interior Fars. This finding does not support the previous inference of extensive subaerial exposure of the entire Fars Platform at that time, thereby calling for a major revision of the published prevailing model for latest Aptian paleogeography of this region. These new insights will facilitate better understanding of the Fars Platform evolution in the Zagros Basin as well as paleoenvironmental reconstructions along the southern Neo-Tethys.