FIG. 5.

Crinkled laminae and tufts in microscopic view (thin sections), subtidal zone, 3.48 Ga Dresser Formation, Pilbara, Western Australia. (A) Sketch to point out the situation of the thin section displayed in (B). The thin section shows an area of a vertical cut through ripple marks with their ripple valleys being filled in by sediment. The selected area covers one slope of a ripple mark and about half the ripple valley. Compare this photo also with Fig. 1A. (B) Thin-section view of the area shown in (A). The slope of the ripple mark is draped by a dark lamina (arrow); the horizontal sediment layers that fill in the ripple valley are each covered by a dark lamina as well. Scale: 0.1 cm. Note that none of the dark laminae show any mark of erosion. (C) In close-up the dark laminae include tufted microstructures (compare with modern structure in Fig. 1D; geochemistry of fossil example is shown in Fig. 6). Scale: 50 μm.