Paleoambientes y architectura de cuenca de la Formación Ab-Haji (Lower Jurassic), centro-este de Irán

摘要

The Lower Jurassic Ab-Haji Formation of the Kalmard, Tabas and Lut blocks, east-central Iran, has beenudstudied using an integrated stratigraphic-sedimentologic approach. The Ab-Haji Formation is mostly composed ofudgreenish sandstones and siltstones and locally contains thin coal seams. Four well exposed sections were measuredudand studied in order to identify lithofacies and facies associations and to interpret the palaeoenvironment. Thisudformation reaches a thickness up to 350 m in northern Tabas Block but may locally be reduced to few tens of meters orudeven missing. Field studies have led to the recognition of sixteen lithofacies grouped into five facies associations:udfluvial plain, coastal plain, delta front, prodelta and shallow siliciclastic shelf. Reconstruction of the palaeogeographyudof east-central Iran marks a west–east continental-to-marine gradient. Thickness variations, lateral facies changes andudbasal unconformity of the siliciclastic rocks of the Ab-Haji Formation on the Kalmard, Tabas and Lut blocks showudpalaeo-relief on the fault-bounded Yazd Block in the west and the Shotori Swell at the eastern edge of the Tabas Block.udThe pattern of thickness variations and rapid EW facies changes is best explained by a tectonic model showing largeudtilted fault blocks in an extensional basin. The obtained results are important for palaeogeographic andudpalaeoenvironmental reconstructions of the east-central Iran since its sediments record the geodynamic history of thisudregion, as well as an even larger area, during and in the aftermath of the main Cimmerian event, from the beginning ofudthe Early Jurassic.