Palaeoenvironmental implications of aluminium phosphate-sulphate minerals in Early-Middle Triassic continental sediments, SE Iberian Range (Spain)

APS minerals occur as small disseminated and idiomorphic pseudo-cubic crystals (0.5 to 6 μm long) or as massive and polycrystalline aggregates replacing fragments of fine-grained metamorphic rocks (mainly metapelites). Textural data indicate that the formation of the APS minerals predated the quartz and illite cements, and that they resulted from the destabilisation of pre-existing minerals, as evidenced by the replacement of slate fragments by APS minerals and hematite and by the close association of the disseminated APS crystals and kaolinite with altered detrital mica plates. Electron microprobe analyses and X-ray diffraction study of the APS minerals indicate a rather homogeneous composition in different parts of the basin, corresponding to solid solutions among woodhouseite, svanbergite, crandallite and goyazite. The sources of strontium in the APS minerals remain unclear. Phosphorous was primarily supplied by dissolution of detrital phosphates under acidic conditions, and sulphur derives from the weathering of pyrite.