Evidence of high-energy storm and shallow water facies in Pabdeh sedimentary phosphate deposit, Kuhe-Lar-anticline, SW Iran

Abstract

Kuhe-Lar sedimentary phosphate deposit is a major phosphate prospect located in Zagros folded basin in the flank of the Kuhe-Lar-anticline in the southeast of Iran. Phosphate deposits in the Middle East extend in Neo-Tethys basin rim through several countries from North Africa, Syria, Iraq, Turkey, Iran, and Oman. The sedimentary phosphate mineralization occurred in the Pabdeh Formation, which is comprised of a marl, limestone, and shale sequence. Based on comprehensive field and laboratory studies, facies zones, standards microfacies, and standard ramp microfacies were recognized in the Pabdeh Formation. Sedimentary features such as tempestite, hummocky cross stratification, ripple marks, couplets of fine and coarse laminae, erosional surface, graded bedding, and shell lag features strongly supported a high-energy storm and shallow water depositional conditions. The main evidence of storm origin for the Pabdeh Formation is the occurrence of sandstones interbedded with bioturbated mudstones commonly as upward fine grade forms. Negative carbon isotopic composition (δ13C, − 1.85 to − 4.89) of bulk phosphatic rock shows that it may be formed within the suboxic-to-anoxic zone, almost 100-cm depths (under seafloor). These values are within the range of recent and ancient phosphorites, suggesting their good preservation.