Deep-T-platform responses to the global sea-level fluctuations, Oligocene Asmari and Pabdeh Formations of the Zagros foredeep Kalhur sub-basin, SW Iran

Abstract

A sequence stratigraphic analysis of the Asmari and Pabdeh Formations (Oligocene) carbonate factory in the Kalhur sub-basin of the Zagros foredeep in SW Iran established the depositional attributes and facies patterns of the abnormally deep-T-platforms in response to global sea-level fluctuations. The paleoecology, paleogeography and hydrodynamic properties affected symbiotic large benthic foraminifers (SLBF) to determine the carbonate generation window and steepened ramp systems building from gravel-producing biota within the oligophotic zone. Four facies belts, containing five lithofacies and ten microfacies like those of C-platforms, were identified from grain associations and standard depositional criteria. Highstand systems tracts formed of uncemented and unconsolidated close-cluster reefs developed in the lower mid-ramp to upper part of the outer ramp and prograded below storm wave base (SWB). Portions of the reefs above SWB were eroded and transported downslope to the distal portion of the outer ramp and the proximal part of the basin as tempestites, created by periodic storms. In the subsequent sea-level fall, these platforms were eroded during periodic storms, shedding large volumes of calciturbidites, just as they do in C-platforms. The Rupelian succession consists of three third-order sequences, namely Ru. 1, Ru. 2 and Ru. 3. Further comparison of sea-level and onlap curves in the study area with global and Arabian platform sea-level and onlap curves, provides an exact chronostratigraphic framework, revealing a close correlation with eustatic events in the Zagros foredeep.