Late Permian - Early Triassic transition in the carbonate-evaporite strata of the eastern part of the Qatar-Fars Arch, Persian Gulf basin

Abstract

The carbonate – evaporite succession of the Permian upper part of the Dalan formation and the Lower Triassic Kangan formation was studied in four wells (A, C, E, and F) from four different fields situated east of the Qatar-Fars Arc in the central part of the Persian Gulf basin, offshore Iran. Foraminiferal species distribution enabled the establishment of the Paraglobivalvulina-Paradagmarita Assemblage zone assigned to the early Wuchiapingian-Changhsingian age. This biozone is divided into two subzones, the Wuchiapingian Globivalvulina vonderschimitti –Paraglobivalvulina aff. mira Assemblage subzone and the Changhsingian Paradagmarita monodi-P. flabelliformis-Paynita permotaurica Assemblage subzone in the upper member of the Dalan formation. The Microconchus-Claraia-Ammodiscus Assemblage zone was also established in the Kangan formation, indicative of an Early Triassic Induan age. The abundance of Paradagmarita monodi, P. flabelliformis in the upper member of the Dalan plays a significant role in paleobiogeographic sub-province correlation within the Neotethys realm. The final occurrence of foraminiferal genera from the Permian-Triassic boundary across all wells reveals a consistent stepwise extinction pattern between 10 and 5 m below the boundary. Furthermore, the presence of a thin thrombolite unit and small framboidal pyrite particles (5–10 μm in diameter) immediately above the Permian-Triassic Boundary (PTB) in wells A, C, F indicates the dominance of dysoxic conditions, which are consistent with a decrease in δ¹³C and δ¹⁸O values, coinciding with a rapid rise in water levels shortly after the extinction event.