Microfacies and Sedimentary Environments of Gurpi and Pabdeh Formations in Southwest of Iran

Abstract

Problem statement: The Upper Cretaceous Gurpi and lower Tertiary Pabdeh formations as units of folded Zagros Zone were studied in three different regions (Tang-e-Abolhiat, Tang-e-Zanjiran and Maharloo) in Fars Province, Iran. Approach: Gurpi formation consisted of thin to medium sized layers of gray marl and marlstone interbedded with thin layers of argillaceous limestone and shale. The dominant microfacies in this formation biomicrite; Index species of Globotruncana give the age of the Formation from lower companion to upper Maastrichtian. Pabdeh formation consisted of bluish gray, thin to medium sized layers of 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 limestones in the middle andalternative 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. Results: The sedimentary environment of both formations is a bathymetrical carbonate floored basin (deep shelf or basin margin) which had deposited its facies in transgressive stage. The contact between the two formations is of disconformity type. In Tang-e-Abolhiat it lies at the base of purple shale. In this region and also in Tang-e-Zanjiran and Maharloo, in addition to recognition of Globorotalia velascoensis, which was attributed to lower part of the Pabdeh formation, a glauconitic-phosphatic bed separates the two formations. Conclusion/Recommendations: The boundary between Gurpi and Pabdeh formations represented a non-depositional period from the late Maastrichtian to the end of early Paleocene.