Effects of salinity, organic acids and alkalinity on the growth of calcite spherulites: Implications for evaporitic lacustrine sedimentation

Lacustrine non-skeletal carbonates exhibit a diversity of petrographies due to interactions between physico-chemical and biologically influenced mechanisms. Despite the suggestion that evaporative concentration was involved in formation spherulite shrubby-bearing carbonate successions Pre-Salt Cretaceous alkaline lakes South Atlantic, no consensus exists about water chemistries promoting these exotic mineral textures. In this work, an experimental approach developed evaluate how changes salinity (NaCl) biopolymer concentrations (alginic acid) impact calcite growth dynamics from saline synthetic solutions. Hydrochemical petrographical data selected modern saline/alkaline environments were compared with datasets further estimate underlying (bio)chemical conditions lake locations probably converge allow grains evaporitic settings. Spherulitic Recent experiments arise waters moderate high [Calcium]/[Alkalinity] ratios ([Ca]/[Alk]) rather than calcium-depleted alkaline-rich which tend produce single-crystal calcites during abiotic mixing or evaporation. This observation is consistent assembly polycrystalline textures being kinetically controlled feature, forced by remarkably rates nucleation. Also, analysed do not support causative relationship evaporite-driven fluctuations preferential spherulites, shrubs their intermediate Ubiquitous lakes, organic substances can lower kinetic thresholds for spherulitic aggregation while microbial photosynthesis also raise pH, altogether enhancing supersaturation moderate-high [Ca]/[Alk] salinities. Localised observations spherulites soda occur restricted zones where are enhanced. work highlights roles regimes associated biopolymers metabolism against background determining morphological textural transitions lacustrine minerals.