Preservation of ephemeral microbial fabrics: late Messinian filamentous dendrolites from the Salento Peninsula (central Mediterranean)

During the late Messinian, the Mediterranean Sea underwent the “Messinian Salinity Crisis,” a major event that shifted carbonate platforms from coral-dominated to microbialite-dominated systems. While upper Messinian microbial carbonates are well documented in the western Mediterranean, new findings from the central basin, particularly the Salento Peninsula, provide fresh insights into their diversity and evolution. This study focuses on enigmatic carbonate fabrics (ECF) from Salento, previously tentatively identified as dendrolites. A multidisciplinary approach, combining field observations, microscopic fabric analysis, and biogeochemical techniques (UV-epifluorescence and SEM/EDS), was applied to investigate their nature and palaeoenvironment. The Salento ECF consist of fan-like, lobate structures forming vertically elongated aggregates a few centimeters tall, with microstructures containing organic-derived micritic clots and filamentous remains consistent with cyanobacterial microfabrics. These features support their identification as filamentous dendrolites, comparable to modern analogues from Hamelin Pool, western Australia. Stratigraphic and facies analyses suggest they formed in a lagoonal environment, very shallow and with fluctuating conditions, influenced by unstable connections to the open sea. In particular, although strongly affected by reworking, the sedimentary textures and bioclastic assemblages associated with the dendrolites indicate a phase of warm, moderate-energy waters with near-normal marine chemistry. Unlike modern examples, which show minimal or no mineralization, the Messinian dendrolites display a well-cemented, originally aragonitic microfabric, potentially linked to elevated carbonate saturation or to specific microbial assemblages that facilitated their preservation. These findings represent the first fossil record of filamentous dendrolites and highlight the Messinian Mediterranean carbonate factories as a key archive for microbialite research. • Heterogeneous Messinian microbial carbonates are reported in central Mediterranean. • Microscopic and geochemical analyses reveal evidence of cyanobacterial activity. • Microbialites are identified as originally aragonitic filamentous dendrolites. • Salento microbialites are the first fossil evidence of filamentous dendrolites.