What are the different styles of calcite precipitation within a hyperalkaline leachate? A sedimentological Anthropocene case study

This study aims to compare the fabrics of anthropogenic carbonates downstream of lime and steel disposal sites with models of carbonate precipitation from natural systems to elucidate potential drivers, precipitation mechanisms, morphological similarities, predictability in 3D facies distributions and depositional models of these systems. For this purpose, a combination of sedimentological, mineralogical and geochemical approaches is conducted including analysis of microfacies (petrographic microscope and electron microscopy), X-ray diffraction and hydrochemistry. The data show that both anthropogenic and natural systems exhibit clear proximal, middle and distal zones of carbonate precipitation. The main macroscopic differences are the dominance of swamp environments in the proximal zone, and the prevalence of tufa-like barrage-and-pool sequences in the middle and distal zones. Microfabrics in anthropogenic sites are comparable to travertines but lack the sub-surface facies and at extreme pH exhibit sparry crusts without clear equivalents in travertines. This sedimentology of anthropogenic carbonates shows that calcite mineral formation is complex and not homogeneous or purely driven by thermodynamic processes. Considering the sedimentology of these human-induced systems will help us understand precipitation mechanisms which will aid both efforts to utilise anthropogenic alkaline wastes for carbon capture and manage their environmental impacts.