Depositional architecture and sequence stratigraphy of the Oligo–Miocene Asmari platform; Southeastern Izeh Zone, Zagros Basin, Iran

Abstract

In the easternmost part of the main Izeh Zone of the Zagros Mountains, Iran, the Asmari carbonate platform system of Oligo–Miocene age is superbly exposed in three-dimensional outcrops displaying a variety of carbonate facies associated with well-preserved depositional geometries. The main biogenic components of the Asmari Formation are large benthic foraminifera, corals, coralline algae, and planktonic foraminifera. The Asmari carbonate platform system, based on dating by large benthic foraminifera, biogenic components, and depositional geometries, is divided into four distinct intervals of carbonate platform growth. This depositional system during the Rupelian and Rupelian/earliest Chattian was a carbonate ramp. During the Chattian, the system was dominated by coral buildups, and later, porcellaneous benthic foraminifera and coralline algae were prominent during late Chattian–early Miocene time. Six major depositional sequences are distinguished, with an overall systematic progradation from NE to SW. These progradations are evidenced in the Rupelian and lower Chattian by major changes in facies and stratal architectures, whereas such complex geometries are not observed in the upper Chattian and lower Miocene carbonates, since only platform-top facies are exposed and there are no outcrops of the platform margin. Comparison of the proposed depositional sequences with those reported in the Dezful Embayment and adjacent areas suggests a correlation with the global sea-level curve.