Fig. 4.

Petrography with SEM and EDX of pyritized string-shaped structures from the Francevillian Series, Gabon. (A and C) Sediment laminae, white arrow, intersected by pyritic strings. Laminae bending around the pyrite string confirm precompactional formation, yellow arrow. (B and D) Bending of sediment layers, yellow arrows, around pyritic strings. (E and F) Element mapping of sections in C and D, showing mineralogical composition of the strings and embedding sediment. White arrow indicates the area of elemental point analyses (G). (Scale bars: 1 cm.) (G) Elemental points analysis indicate the presence of K, Mg, and Fe, which confirm the presence of illite and chlorite, respectively. The picture (Left) shows authigenic illite and chlorite grains and free growth of these minerals within the pore spaces.