Precambrian storm wave-base deposits of Early Proterozoic age (1.9 Ga), preserved in andalusite-cordierite-rich granofels and quartzite (Rämsberg area, Värmland, Sweden)

Well preserved laminites, wave ripples and thin hummocky cross-stratified beds arranged in several, thickening- and thinning-upward sequences have been interpreted as lobe-like storm wave-base deposits. Delicate features in thin sections confirm the importance of wave activity over current activity. These features include thinning- and fining-upwards sequences on a centimetre-scale with a great variety of laminae (graded, inversely graded, non-graded); with diffuse or sharp tops due to winnowing; micro-flaser bedding on millimetre-scale with 2 cm wavelength; lateral sorting and grain-size differences; and silty streaks of single grain thickness of approximately 0.5–1 cm in length. These structures are exceptionally well preserved in the medium-grade metamorphics, due to the lack of burrowing in Early Proterozoic sediments and to the non-deformational character of the thermal metamorphism. The Proterozoic sequence is compared with existing depositional models of storm-influenced shelves from the recent and fossil record.