DEPOSITIONAL HISTORY AND SEQUENCE STRATIGRAPHY OF OUTCROPPING TERTIARY CARBONATES IN THE JAHRUM AND ASMARI FORMATIONS, SHIRAZ AREA (SW IRAN)

Abstract

The Oligo‐Miocene Asmari Formation is one of the most important petroleum reservoir units in the Zagros Basin of south and SW Iran. It mainly consists of limestones and dolomitic limestones with interbedded shales, together with a few intervals of sandstone and gypsum assigned to the Ahwaz and Kalhur Members, respectively. The Asmari Formation rests on the thin‐bedded limestones of the Jahrum Formation (Paleocene‐Eocene). In this paper, we report on the lithofacies characteristics of these two formations using data from three measured outcrop sections near Shiraz in SW Iran. From field and petrographic data, we have identified four major lithofacies and twelve subfacies which are interpreted to have been deposited in open‐marine, shoal, lagoon and tidal flat settings.We show that the Asmari and Jahrum Formations constitute two separate depositional sequences which are separated by a thin palaeosol, representing a type‐one sequence boundary which can be correlated with global curves of relative sea‐level. Each depositional sequence is composed of many metre‐scale shallowing‐upward parasequences. This is the first time that the Asmari and Jahrum Formations have been differentiated in the study area. We hope that this study will lead to a better understanding of the Asmari Formation in the subsurface in other parts of the Zagros Basin.