Authigenic whitlockite as an imprint of human presence in a middle pleistocene endokarstic deposit (Cueva del Ángel site, southern Spain)

The genesis of whitlockite under sedimentary conditions in absence of guano in a Middle Pleistocene endokarstic deposit (Cueva del Ángel, southern Spain) is described. The mineralogy of the sediment samples was studied using XRD, FTIR, SEM-EDX and petrographic microscopy. Various aggregates of whitlockite were found in the sediment, with different habits. The formation of whitlockite is attributed to anthropic activities (manipulation, disarticulation, fleshing and burning of fauna) for human consumption. It can be proposed that an incipient diagenesis favouring the dissolution of the host dolomites from the karstic cavity and, in turn, of the bone fragments (more of them burnt), causes the release of magnesium and phosphate ions and leads to the formation of authigenic whitlockite from the solutions circulating in the sediment matrix. This research reports on the first evidence of whitlockite genesis as a diagenetic mineral in a cave deposit in absence of guano. The data suggest that, in absence of guano, whitlockite occurrence in cave sediments with Palaeolithic archaeological remains must be considered as it can serve as a proxy of ancient human activity.