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Evolution of the Fahliyan Carbonate Platform (Zagros Fold-Thrust Belt, Southern Iran) in the Early Cretaceous

Abstract

Detailed facies, biostratigraphic and sequential analyses led to identify four depositional models among the Lower Cretaceous shallow-platform carbonates in the Zagros fold-thrust belt in southern Iran. The platform growth evolutionary trend is recognized from the Berriasian up to the top of the Barremian across the area. The Zagros Basin was located on the passive margin of the Arabian Plate during the Early Cretaceous. This stable margin shows a different evolution in the Southeast, where neritic conditions prevailed in the Fars and Khuzestan areas, and in the West, where pelagic facies were deposited in the Lurestan area. The studied area includes the Bandar Abbas Hinterland in the East and the Dezful Embayment in the Khuzestan area in the West. The dataset used for this study includes outcrop and subsurface data (wells), all worked out in details for biostratigraphy and facies analysis. A number of 20 outcrops and 5 wells were used for reconstructing the platform geometries by making several longitudinal and transversal regional transects. Available time controls based on the biostratigraphy are calibrated with isotope (87Sr/86Sr) analyses, allowing to recognize several small-scale transgressive-regressive systems tracts. Age of these progradational-retrogradational cycles varies in different parts of the basin, enabling to identify the platform configuration and construct paleogeographic maps. Platform reconstruction was made in different domains, showing that relative sea-level changes and also local tectonic activities had important effects on the platform setting. A revision of the lithostratigraphic nomenclature led us to introduce new units, correlated with regional equivalents in the Arabian Platform. This new stratigraphic framework comprises both erosional and non-depositional areas. The presence of unconformities defines up-to-now undetected paleo-highs within the studied areas, which have been formed either by the regional uplift of the Arabian Plate, the influence of the Qatar Arch High, or by local tectonic activities, resulting in the formation of thinning (pinch-out) or thickening sequences in different parts of the platform. We are thankful to the Exploration Directorate of the National Iranian Oil Company (NIOC) to permit to publish this abstract as a part of an ongoing Ph.D thesis by the first author.