“…(2) In hydrologically closed lacustrine or palustrine environments, the main mechanism controlling K concentrations may be the neo-formation of K-carriers in sediments in contact with pore waters mineralised during prolonged droughts (Foerster et al, 2015), in particular formation of analcime, illite, and feldspars from dissolved K + , kaolinite and other clay minerals (Larsen, 2008;Kříbek et al, 2017;Foerster et al, 2018). This mechanism is thermodynamically analogous to "retrograde" clay mineral formation in the marine environment (Cuadros et al, 2017) and basinal brines (van den Kamp, 2016). (3) Fine(clayey) siliciclastic sediments may undergo K-metasomatism, either in basinal brines rich in K + , or in closed systems in which fine clastic deposits alternate with arkosic beds and are subjected to K + migration and retrograde reactions in the circulating pore water (van den Kamp, 2016).…”