Sedimentology and palaeogeography of conglomerates from the Aghajari Formation in Zagros Basin, SW Iran

Abstract

Conglomerates, the lithified equivalent of gravels alternate with sandstones and mudstones in the upper parts of the Aghajari Formation in the Zagros Basin, southwestern Iran. The thickness of the Aghajari Formation in this studied area is 2221 meters. Polymictic conglomerates form excellent outcrops in the central parts of the study area. From the view of its (coarse) clast composition, the Aghajari Formation consists of two types of conglomerates: 1) limestone-chert clast-supported conglomerate (LCCSC) and 2) limestone clast-supported conglomerate (LCSC). The chronological and spatial relationships between these conglomerates are not easily determined caused by existence some thrust faults at their approximate boundaries. In the vertical succession, various lithofacies were recognized; their textural characteristics and sedimentary structures suggest a non-marine depositional system as they match with standard lithofacies of meandering rivers. Epirogenic movements in the region started in the Oligocene, showed by a polymictic conglomerate beds at the Jahrum-Asmari Formation boundary. These movements then changed to orogenic ones with the depositioning gravelly alluvium now known as Aghajari (upper parts) Formation.