Microfacies and Stratigraphic Observations from the Bulz Dolomite Formation (Apuseni Mountains, Romania): Implications for Paleoenvironment and Regional Correlation

The Middle Triassic Bulz Dolomite Formation in the Apuseni Mountains (Romania) lacks detailed microfacies documentation and paleoenvironmental reconstruction, leaving its regional correlation unresolved. This study aims to describe the microfacies and fossil assemblages of the Bulz Dolomite to reconstruct the Anisian depositional environment and establish regional stratigraphic links. More than twenty outcrop samples were analyzed using conventional microfacies analysis, UV/VIS-fluorescence, and cathodoluminescence microscopy. Results reveal that early, fabric-retentive dolomitization preserved microbial boundstones, dasycladalean algae (Teutloporella peniculiformis, Physoporella pauciforata), and benthic foraminifers (Hoyenella sinensis), indicating shallow-marine, peritidal, and restricted lagoonal environments. The multiphase diagenetic history involves early reflux dolomitization from hypersaline brines, burial recrystallization forming nonplanar and saddle dolomites, and late-stage meteoric calcite cementation. The diagnostic fossil assemblage firmly constrains the formation to the Anisian age. Consequently, the Bulz Dolomite shares compelling lithological, diagenetic, and biostratigraphic affinities with the Szeged Dolomite Formation in the basement of the southeastern Pannonian Basin, demonstrating the presence of a unified, expansive evaporitic carbonate shelf extending across the Tisza Megaunit along the Neotethyan passive margin.