Precambrian alluvial fan and braidplain sedimentation patterns: Example from the Mesoproterozoic Rjukan Rift Basin, southern Norway

The following criteria, observed from the Heddersvatnet Formation, are suggestive of an ancient alluvial fan and associated braidplain sedimentation: (1) deposition close to the source area; (2) slightly divergent paleoflows; (3) high-energy flows with waning flood-cycles; (4) abundance of poorly sorted and laterally extensive subaerial debris flows, and related streamflows, possible sheetfloods, hyperconcentrated flows, and their associations; (5) great distribution of grain size and lithofacies changes in proximal vs. distal parts; (6) limited suite of sedimentary structures (cross-stratification, ripple-marks, and desiccanation cracks); (7) fault bounded basin (graben) with hanging wall close to uplifted flank(s); (8) paleoslope estimation indicating at least moderate paleotopographic highs; (9) colluvial and scree apron breccias; (10) lack of any typical braided stream channel fill conglomerates and floodplains; and (11) channelized sediment bodies lacking extensive lateral continuity.