Figure F22. Thin section photomicrographs of the Coniacian section (Sample 198-1207B-14R-CC, 15-21 cm). The transition from nannofossil chalk on the right to porcellanite to calcareous chert on the left is pictured here. Some isotropic, tan opal was noted in the matrix of the porcellanite. The upper view is under plane-polarized light, whereas the lower view is with nicols crossed.

Figure F22. Thin section photomicrographs of the Coniacian section (Sample 198-1207B-14R-CC, 15-21 cm). The transition from nannofossil chalk on the right to porcellanite to calcareous chert on the left is pictured here. Some isotropic, tan opal was noted in the matrix of the porcellanite. The upper view is under plane-polarized light, whereas the lower view is with nicols crossed.