FIG. 13.

Laminae forming a network typical for microbial mats as seen in thin sections; Archean, Proterozoic, and Phanerozoic (including modern) examples are compared with each other. On the left side, networks of filamentlike textures (laminae) of various ages are compared with each other, starting at the base with the oldest, the Dresser Formation, and continuing upward with younger examples. On the right, rose diagrams summarize the alignment of laminae defining the networks; note that the networks of all periods of Earth history studied show a very similar dumbbell shaped pattern (right; n=number of thin sections studied). Also, the thin sections deriving from the Dresser sedimentary rocks display similar network patterns; compare Fig. 12 for their geochemistry. In contrast, abiotic laminae of a stylolite preserved in the 2.9 Ga Pongola Supergroup, South Africa, are shown in the lower portion of the figure. Note that the stylolite resulted in a different alignment pattern of laminae (from Noffke et al., 2008).