FIG. 7.

Macrostructures of the intertidal zone, 3.48 Ga Dresser Formation, Pilbara, Western Australia, plus possible modern equivalents. The center images show the Dresser Formation structures; for better visualization, the Dresser structures are outlined in the sketches on the left. The right images show possible modern counterparts of such structures. (A) Flat fragments deposited at random on the sedimentary surface in the Dresser intertidal flats. In equivalent modern settings, such fragments represent microbial mat chips; example from Portsmouth Island, USA. Such chips were ripped off their parent site along fringed edges of microbial mats, similar to those shown in the insert of Fig. 1B. (B) Rolled-up fragment. In modern settings, microbial mat chips can be rolled up in this fashion by currents or by desiccation; example from Portsmouth Island, USA. (C) upward-bent, dark-colored sediment lamina. In modern environments, such laminae represent microbial mats separated from their substrate by erosion; example from El Bibane, Tunisia. All scales: 1 cm.