FROM FORE REEF TO LAGOON: EVOLUTION OF THE UPPER TRIASSIC DACHSTEIN CARBONATE PLATFORM ON THE TENNENGEBIRGE (SALZBURG, AUSTRIA)

Carnian and Norian (Upper Triassic) limestones and dolostones along the Eisriesenwelt trail on the Tennengebirge (Salzburg, Austria) reveal a progression from fore-reef to lagoonal environments, including a small Norian reef with both Carnian and Norian characteristics. Here, we provide high-resolution biostratigraphic age constraints of the Tennengebirge platform carbonates and describe an early Norian patch reef that is built by large Retiophyllia corals and encrusted by “Tubiphytes,” sponges, and microbial fabrics. The tall (up to 4 m), narrow phaceloid Retiophyllia coral colonies exhibit phototropic growth patterns—coral branches that are at the top of the colony grew longer than those on the side of the colony—thus, we suggest that these corals had a symbiotic association with photoautotrophs (most likely zooxanthellae). The well-constrained ammonoid and conodont biostratigraphy presented here establish that the Tennengebirge patch reef was deposited in the early Norian, nevertheless, it contains features typically associated with Carnian reefs (small, encrusting sponges, Carnian-style microbial crusts, and “Tubiphytes”). The Carnian traits of the Norian reef emphasize the importance of accurate biostratigraphic dating; obtaining independent age estimates for reef outcrops is crucial to correctly determine the timing and magnitude of transitions in Triassic reef ecology.