Figure F19. Thin section photomicrographs of a manganese crust from the Miocene condensed section (Sample 198-1207A-18H-5, 44-47 cm). The upper view is of microstromatolitic lamination and columnal structures that were likely products of microbial growth on the seafloor. Light patches are microfossils, now largely replaced by Fe-Mn oxide minerals, which were concentrated in the topographic lows between Fe-Mn oxide columns as the crust developed. The lower view is more representative of the thin section, which is mostly composed of opaque Fe-Mn oxides, but here is shown with a spherulitic cluster of zoned phillipsite crystals. Both views are under plane-polarized light.

Figure F19. Thin section photomicrographs of a manganese crust from the Miocene condensed section (Sample 198-1207A-18H-5, 44-47 cm). The upper view is of microstromatolitic lamination and columnal structures that were likely products of microbial growth on the seafloor. Light patches are microfossils, now largely replaced by Fe-Mn oxide minerals, which were concentrated in the topographic lows between Fe-Mn oxide columns as the crust developed. The lower view is more representative of the thin section, which is mostly composed of opaque Fe-Mn oxides, but here is shown with a spherulitic cluster of zoned phillipsite crystals. Both views are under plane-polarized light.