FIGURE 5.

Characteristics of ultrastructures detected from mineralized and fossilized tubes of dead tubeworms, and microbial mats. (a–f) T1 tubeworm. The yellow part contains abundant FeOB-associated stalks and filaments heavily aggregated by tiny Fe-rich flakes (a–c). However, structures produced by FeOB are sporadically scattered in the gray part (d–f). Alternatively, irregularly or spherically S-enriched aggregates (arrows in d,e) are prevailing. (g–l) T2-L and T2-S tubeworms. T2-L’s stalks (g–i) are heavily covered by irregularly tiny granules (h) and often buried into amorphous Fe-rich substances (i). T2-S’s structures (j–l) are mainly dominated by contorted filaments. Magnified images show that these filaments have acanthaceous surfaces (k,l) and they are remarkably thicker than fresh stalks (arrows). (m–o) Typical ultrastructures detected from the fossilized tube wall of T3-1. Abiogenic amorphous Fe-rich precipitations significantly obscure the skeletons of these structures and also thicken them in diameters (m, arrows). (p) Fresh FeOB-associated twisted stalks and structures heavily encrusted by bladelike Fe-rich aggregates (arrow). (q) EDS chemical composition of spherical aggregates in (e), indicating they are enriched in sulfur. (r) EDS spectra of acanthaceous surfaces marked by yellow cross in (j), mainly composed of iron.