Figure F25. A. Photomicrograph of the highest degree of diagenesis in siltstones from the lower part of Unit II with abundant neoformation of secondary Ca-rich minerals. Gypsum (Gy) after the habit of anhydrite can be seen as the white mineral with pronounced cleavage traces, which grew in the greenish palagonitized silt groundmass. Other authigenic phases contain zeolites (chabazite and erionite) that are present as black patches of micro-gritty material (Z1) and as whitish wisps (Z2) (plane-polarized light). B. Gypsum shows anomalous brownish to bluish interference colors (thin section from Sample 195-1201D-38R-1, 29-32 cm [436.29 mbsf]) (cross-polarized light).

Figure F25. A. Photomicrograph of the highest degree of diagenesis in siltstones from the lower part of Unit II with abundant neoformation of secondary Ca-rich minerals. Gypsum (Gy) after the habit of anhydrite can be seen as the white mineral with pronounced cleavage traces, which grew in the greenish palagonitized silt groundmass. Other authigenic phases contain zeolites (chabazite and erionite) that are present as black patches of micro-gritty material (Z1) and as whitish wisps (Z2) (plane-polarized light). B. Gypsum shows anomalous brownish to bluish interference colors (thin section from Sample 195-1201D-38R-1, 29-32 cm [436.29 mbsf]) (cross-polarized light).