New Constraints of Interior Fars Sedimentary Basin Analysis During Asmari Formation (Oligocene-Lower Miocene) Deposition, South Iran

Abstract

Interior Fars region is an important geological province of Zagros basin due to historical events. The present paper focused on the time span of the Asmari deposition (Oligo-Lower Miocene) in Fars area bounded by Kazerun and Nezamabad faults. The studied samples of Asmari Formation were collected from 3 different stratigraphic sections A, B and C. The area is discussed in view of microfacies variation, sequence stratigraphy and environmental factors such as diagenetic processes and sea level changes. Microscopic studies led to identification 13 carbonate facies in this area. The results showed that the Asmari Formation has been deposited in a carbonate shelf in 5 sedimentary sub-environments including open sea, bar, lagoon, shoal and tidal flat. Basin changes were also compared with global sea level changes. Sequential stratigraphic evidence showed that the Asmari Formation consists of two sedimentary sequences of third order. The unconformity in the lower boundary of Asmari Formation with Jahrom Formation in sections-B and C can be ascribed to the result of Pyrenean orogenic phase activity in this area. The Asmari Formation in this area has been undergone extensively by diagenetic processes. Micriticization, dolomitization, cementation, hematitization, stylolitization, neomorphism and dissolution are among the important and noteworthy of diagenetic processes. The intensity of each process is a function of facies characteristics (fabric control). Microfacies data and sea level changes curve in local (the area), regional and global scales revealed that these facies are more correlated to the local sea level variation than others. The present study resulted to new main points related to the Fars basin evolution. Reactivation of faults (such as Kazerun and Nezamabad), regional sea level changes and Alpine orogenic phases impact (i.e., Pyrenean phase) have involved a major role in sedimentary facies distribution and basin evolution.