Timing and progression of the end-Guadalupian crisis in the Fars province (Dalan Formation, Kuh-e Gakhum, Iran) constrained by foraminifers and other carbonate microfossils

Abstract

The Middle-to-Upper Permian in the Kuh-e Gakhum anticline (southeastern Iran) has rarely been studied due to its structural complexity and the difficult access. Rich Permian fusulinid assemblages varying in age from Wordian to Changhsingian were found in a thick carbonate succession corresponding to the Dalan Formation. Three new species of foraminifers are described and a new biostratigraphic framework including five biozones is proposed. One of these, described and defined for the first time in the Dalan Formation, is based on the presence of Praedunbarula simplicissima n. gen. n. sp. When compared to the fossil content of existing bioprovinces, the floro-faunal biota of the Dalan Formation shows an affinity with Central and Western Tethys. A mass extinction of fusulinids and small foraminifers (70%) occurred concomitantly with the onset of a relative sea-level fall. This event led to a change in the carbonate factories from biologically induced carbonate production to ooid-rich chemically induced precipitation. The morphology of the platform at the Guadalupian/Lopingian transition evolves from a bioclastic ramp to a shelf. This transition is also characterized by a major sequence boundary and morphological anomalies in foraminifers. Therefore, as the regression and the changes in floro-faunal contents have been observed at the Guadalupian/Lopingian boundary, the extinction event is considered as end-Guadalupian. It is followed by a Lopingian transgression yielding renewed foraminiferal assemblages.