Foraminiferal assemblages and microfacies analysis of Triassic − Jurassic boundary successions in Bitlis Massif Carbonates, eastern Türkiye: Insights into depositional environments and paleoenvironmental changes

Triassic-Jurassic boundary carbonate deposits of the Bitlis Massif (Çakmakkaya village, Elazığ, Türkiye) are considered to delineate paleoenvironmental changes, extinction events, and post-extinction recovery patterns through a combined approach of foraminiferal biostratigraphy and microfacies analysis. The studied sequences representing the most complete records of this boundary in eastern Türkiye are mainly dominated by peritidal carbonates. A high-resolution biostratigraphic investigation has defined four main biozones: (1) Aulotortus ex gr. sinuosus Assemblage Zone (Norian), (2) Triasina hantkeni Range Zone (Norian-Rhaetian), (3) Thaumatoporella sp. Zone (Hettangian), and (4) Everticyclammina sp. Zone (Sinemurian). The Late Triassic interval of the successions is generally characterized by involutinid forms, which abruptly disappear at the Triassic-Jurassic boundary. Following this extinction, the Early Jurassic is generally depicted by fossil-poor levels dominated by Thaumatoporella algae and by the appearance of siphovalvulinids and everticyclammins. The extinction of Triasina hantkeni and the disappearance of particular benthic foraminifers depict the Triassic-Jurassic boundary within the studied carbonate sequences, consistent with other Tethyan carbonate successions. Detailed microfacies analyses have revealed distinct microfacies types, suggesting a depositional model encompassing a transition from low-energy lagoonal environments to high-energy shoal settings and open marine conditions. The biotic events and microfacies characteristics underscore the global impact of this boundary event on the shallow marine carbonate platforms.