The rise and fall of the giant stromatolites of the Lower Permian Irati Formation (Paraná Basin, Brazil): A multi-proxy based paleoenvironmental reconstruction

High‐frequency palaeoenvironmental changes in the mixed siliciclastic–carbonate sedimentary system from a lower Permian restricted basin (West Gondwana, southern Brazil)

“…Laminated fenestral dolomudstone and finely‐laminated dolomudstone occur throughout the ramp, and giant stromatolites have been described at the northern border of the Paraná Basin (e.g. Antunes et al ., 2022). Recent studies, mainly in the coastal sabkha of Abu Dhabi, have recognized that extracellular polymeric substances (EPS), which form microbial mats, are an important component for the formation of Mg‐rich carbonates, with EPS favouring the incorporation of Mg into the carbonate mineral, leading to the formation of dolomite (Bontognali et al ., 2010; Krause et al ., 2012; Roberts et al ., 2013; Brauchli et al ., 2016).…”

“…The positive freshwater balance and low salinity produced favourable conditions for algae such as Botryococcus to thrive in the photic zone. Nutrient‐rich freshwater inflow in the Irati Sea is supported by lexane indices, TPP/Dia27, C29/C27 sterane and C28/C26 TAR ratios, and the occurrence of cadalene, simonellite, β‐carotane, sempervirane and rare earth element (REE) ratios (Martins et al ., 2020; Nascimento et al ., 2021; Antunes et al ., 2022). Furthermore, under hypersaline and anoxic conditions, the elevated amount of organic matter also causes algal blooms of halophilic and photosynthetic sulphur bacteria (Fig.…”

“…The well-defined oxic-anoxic conditions were reduced only during the return of dry periods. Antunes et al (2022) recognized five growth stages in giant stromatolites at the northern edge of the Paran a Basin. The growth stages are the result of variations in hydraulic energy and accommodation of the ramp, recording the environmental variation from shallower and calm water to deep, more energetic and terrigenous-rich conditions.…”