Figure 6.

Microbe-mineral interactions—First column is the field photo of the hand sample. Second column is a photomicrograph of petrographic “wet” thin section, stained with crystal violet to highlight gram positive bacteria. Third and fourth column are SEM photos of critically dried samples. Orange/brown bulbous mat PBT from transition zone between Puquio 1 and 2 (a–d). (b) Photomicrograph of “wet” thin section under cross-polarized light showing Mg-silicates forming along cyanobacterial sheaths; (c,d) images showing microcrystalline gypsum crystals in an EPS matrix with cyanobacterial filaments. Orange gel mat PBT from transition zone between Puquio 1 and 2 (e–h). (e) Hand sample showing orange gel, green and purple microbial layers, and granular minerals; (g,h) images showing gypsum crystals in an EPS matrix (g) and acicular crystals coating a cyanobacterial filament (h). Spar crystals PBT sampled from a small lagoon near Puquio 2 (i–l). (j) coarse gypsum crystals, often with jagged outer surfaces with dark coatings shown in petrographic thin section; (k,l) images show large flat crystal faces coated with a thin crust, rich in manganese (EDS). Spar crystals PBT sampled from a small lagoon near Puquio 2 (m–p). (n) Cross sections of euhedral prismatic gypsum crystals with dark horizons; (o,p) images show large blocky, flat crystal faces, coated with granular aggregates rich in manganese (EDS). Pinnacles PBT sampled along the northern margin of Puquio 3 (q–t). (r) Gypsum is microcrystalline with an adjacent strip of lenticular sparry gypsum and blocky to prismatic gypsum; (s) images showing lenticular gypsum embedded in EPS and fine-grained gypsum (t) and filamentous cyanobacteria with gypsum crystals on sheaths. Botryoids PBT sampled from within Puquio 4 (u–x). (v) Crystalline matrix of prismatic gypsum; edges are coated with a fine microcrystalline crust; (w) images showing blocky crystals with planar faces and (x) fine cyanobacterial filaments with stellate crystals adhering to the sheaths.