Figure 4

Scanning electron microscopy operating in back-scattered electron (SEM-BSE) photomicrographs. (A) Polymetallic zoned crustiform band of pyrite including sphaleritic inclusions and growing over a clast of apatite; scale bar = 200 µm. (B) Zoned pyrite encrusted by radiating pyrite/glendonite crusts; scale bar = 200 µm. (C) Apatite clast encrusted by pyrite and radiating calcite/pyrite crusts; scale bar = 100 µm. (D) Glendonitic feathery ca1 crystals arranged as stellate clusters (ca) separated by a clayey matrix rich in francolite (fr) crystals and strings; scale bar = 500 µm. (E) Calcite pseudomorphs after anhydrite, encased in the phosphatic limestone of the Kakeled Limestone Bed; scale bar = 1 mm. (F,G) Filamentous cyanobacteria, probably related to Oscillatoriopsis longa, with distinct preservation of trichome and sheath; pyrite occurs as framboids in (F) and as subhedral crystals infilling the primary porosity of the trichome in (G); scale bars = 20 and 10 µm, respectively. ap apatite, ca calcite (glendonite), py pyrite, sh sheath, sp sphalerite and tr trichome.