MISS from a temperate hypersaline saltpan under continental influence (Salitral de La Vidriera, Argentina)

Abstract

The Salitral de La Vidriera (SDV; 38°44′S, 62°34′W) once occupied the innermost section of a funnel-shaped estuary before its isolation due to sea level drop ∼3000 years BP. It currently is a continental saltpan detached from the Bahía Blanca estuary, having no marine connection, and acting as a hypersaline evaporitic environment. This study provides a first-hand characterization of the epibenthic microbial mats that biostabilize surface sediments in the saltpan, and the environmental dynamics and physical deformation agents behind the formation of modern Microbially Induced Sedimentary Structures (MISS). The microbial community in the hypersaline mats is dominated by cyanobacteria of filamentous (taxonomic order Oscillatoriales) and coccoid morphologies (orders Chroococcidiopsidales and Pleurocapsales). The MISS comprise rolled-up mats, flipped-over mats, folds and wrinkles, reticulate surfaces, gas domes, pinnacles, and desiccation cracks; their genesis is linked to the presence of water that either promotes microbial growth or creates hydrodynamic deformation structures. Gypsum crystals were found in surface and subsurface sediments plausibly linked to a high rate of rainwater evaporation and aided in their preservation by the microbial mat lattice. Furthermore, carbonate precipitation in the form of peloids was identified through petrographic analysis, despite the siliciclastic nature of sediments. The occurrence of modern MISS in this transitional environment, currently under continental influence, is discussed and contrasted with modern peritidal environments. Descriptions from this study, contextualized in a modern depositional setting, may be useful in the study of fossil counterparts and paleoenvironmental reconstructions.