Serpulid-bryozoan-foraminiferal biostromes controlled by temperate climate and reduced salinity: Middle miocene of the Styrian Basin,Austria

Summary Reduced salintiy and a temperate climate prevailed during the Sarmatian in the Styrian Basin, the westernmost embayment of the Central Paratethys. At its northern margin (in the study area) tectonic processes initiated a transgression causing the incision of a cliff into the metamorphic basement and the formation of a carbonate buildup in the latest Sarmatian. The buildup consists of two serpulid-bryozoan-foraminiferal biostromes separated by a microbialite. Serpulids, bryozoa and the encrusting foraminifer Sinzowella caespitosa (Steinmann) as well as microbial mats formed a rigid framework, in which biogenic debris and siliciclastics were baffled. The different biota show complex growth relationships. Stromatolitic crusts and laminated micritic microbial crusts with birdseyes grew in a small sheltered lagoon. The upper biostrome is truncated by a ravinement surface of eustatic orgin and is overlain by ooid grainstone. The buildup drowned during maximum sea-level rise.