*5.1.3 Filamentous microstructures*

Occurrence of filamentous structures, detectable by a different color and tone variation, normally appear to be formed by septate bodies having transversal dimensions of 0.05–0.3 mm (**Figures 6** and **7**). These structures are more evident on amplified/slightly blurred images of Martian sediments and on clean/abraded surfaces. Occasionally, they are more resistant and in relief, conditioning the shape of the laminar surface and their mutual contacts (**Figure 7**). They were observed, both as single features as well as intertwined structures and cover the rock surface resulting in a "woven" texture. Similar settings (**Figure 6**, frame G) have been investigated in previous work and interpreted, by visual and numerical approaches on a consistent number of terrestrial sampling analogues, as microbial/stromatolitic structures [12, 13, 17].
