Microfacies and sedimentary environments of Gurpi and Pabdeh Formations and the type of Mesozoic– Cenozoic boundary in Fars province, Iran

Abstract

The Upper Cretaceous Gurpi and Lower Tertiary Pabdeh formations as units of Folded Zagros were studied in three different regions (Tang-e-Abolhayat, Tang-e-Zanjiran and Maharloo) in Fars Province. Gurpi Formation consists of thin to medium bedded gray marl and marlstone interbedded with thin layers of argillaceous limestone and shale. The dominant Microfacies in this Formation are biomicrite; Index species of Globotruncana give the age of the Formation from Lower Campanian to Upper Maastrichtian. Pabdeh Formation consists of bluish gray, thin to medium bedded shale and marl and interlayers of argillaceous limestones (with purple shales and thin cherty beds) at lower part, dark gray shales and marls with interlayers of argillaceous limestone in the middle, and alternative layers of thinly bedded argillaceous limestone, shale and marl at the upper part. The dominant Microfacies are biomicrite. Index species of Globorotalia and Hantkenina give the age of Formation from Upper Paleocene to Eocene. The sedimentary environment of both formations is a bathymetrical carbonate floored basin (deep shelf or basin margin) which has deposited its facies in transgressive stage. The contact between the two formations is disconform. In Tang-e-Abolhayat it lies at the base of purple shale. In this region and also in Tang-e-Zanjiran and Maharloo, in addition to the recognition of Globorotalia velascoensis, which is attributed to lower part of the Pabdeh Formation, a glauconitic-Phosphatic bed separates the two formations. This bed represents a non-depositional (epirogeny) period from the Late Maastrichtian to the end of Early Paleocene.