Oligo-Miocene carbonate platform evolution in the northern margin of the Asmari intra-shelf basin, SW Iran

Abstract

Abstract This study is based on seven outcrops along a regional transect in the central subdivision of the Zagros Foreland Basin. This NE-SW trending transect extends for 140 km and covers the northern margin of the Asmari intra-shelf basin in dip direction (from proximal to distal). Results of facies analysis led to the recognition of eight facies associations (Planktonic Wkt, Nummulitic Eu F/R, Alg LR Pkt, Coralgal F-R/Bdt, LR LPBF P-G, Epy.R PBF P-G, Dol M, and TRGS) along the depositional dip direction. They are dominated by large and flat rotalids (e.g., Nummulites, Lepidocyclina and Spiroclypeus), coral and coralline red algae (e.g., build-up features), porcellaneous benthic foraminifera (e.g., Archaias, Peneroplis, and Borelis), and fossiliferous lime-mud. Spatial and temporal distribution of these facies associations conform five platform types with different depositional profiles: a) a Nummulites-bearing mixed terrigenous/carbonate distally steepened ramp, lower Rupelian, b) a Nummulitidae-Lepidocyclina bearing carbonate distally steepened ramp, upper Rupelian-lower Chattian, c) a Coral bearing flat-topped open shelf, middle-upper Chattian, d) an Aquitanian homoclinal ramp, and e) a very shallow-water Burdigalian carbonate shelf. Amongst these platform types, the Late Rupelian-Early Chattian carbonate ramp additionally consists of three successive phases and the Middle-Late Chattian flatted top open shelf was developed in two phases. The changes in platform type resulted from changes in the carbonate producing biotas, sediment redistribution processes and significant impact of relative sea level changes.