Fig. 6

Thin section microphotographs. a Characteristic plane-polarized light photomicrograph of the shaly facies (×25 magnification). Argillaceous fine mudstone typical of SF1. Yellow arrows indicate thin discontinuous lenses, probably compacted mud aggregates. Blue arrows show cracks and areas where the matrix was washed out during thin section preparation. b Characteristic plane-polarized light photomicrograph of SF2 (×25 magnification). Yellow arrow points to a bioclastic lamina; blue arrows indicate quartz-rich lenses and laminae; and white arrow shows an argillaceous lamina. The white layer in the centre is a crack due to thin section preparation. c Plane-polarized light photomicrograph of SF3 (×25 magnification). Yellow arrow evidences an individual, siliceous–calcareous lens within a homogenized silty to sandy matrix. Blue arrows point to diverse bioclasts. d Plane-polarized light photomicrograph of SF4 (×25 magnification). Yellow arrows show thin, wavy, mud laminae (mud drapes) within a homogenized silty to sandy matrix. e Cross-polarized light photomicrograph of typical components within SF4 (×100 magnification). Dark-blue-coloured components (yellow arrow) are sparitic Fe-calcite cement. Green arrow shows a muscovite flake. White to grey, angular to subangular components (black arrows) are quartz silt to sand grains. Blue arrow points to a bioclast. Pink arrow evidences an argillaceous floccule. Black and round components correspond to framboidal pyrite (red arrow). f Characteristic cross-polarized light photomicrograph of SF5 (×25 magnification). Main bioclasts are bivalve shell fragments (yellow arrow), crinoids (blue arrows) and sea urchin plates (red arrow). g Plane-polarized light photomicrograph of an accumulation of calcitic shell fragments (red-coloured; yellow arrow) and up to 0.5 mm thick, sparitic Fe-rich calcite crystals (blue-coloured; white arrow) within SF5 (×25 magnification). Quartz grains, muddy aggregates and framboidal pyrite constitute the matrix. h Characteristic cross-polarized light photomicrograph of the 6 cm thick authigenic, calcareous bed within the shaly facies (×50 magnification). Yellow arrow shows small-scale cone-in-cone structures and blue arrow indicates shell fragments