Archean fluvial deposits: A review

The recognition of Archean fluvial deposits is complicated in many cases by post depositional deformation and metamorphism. Most surviving deposits can be categorized as deposits of alluvial fans with and without debris flows, and sand and gravel-bed braided rivers. Examples of possible intermediate to high sinuosity meandering systems have been tentatively identified in Africa, Australia and India: all lack clear evidence of lateral migration and can be reinterpreted in terms of esturine deposition, shallow tide-influenced marine, and deep-water mass-flow deposits respectively. Mudstone intervals in Archean fluvial strata are rare, and where present, are typically of silt grade. These may represent ponds developed within channel thalwegs, or where more extensive may be of lacustrine rather than floodplain origin. Prior to 3.2 Ga preserved fluvial deposits appear to be largely confined to the flanks of volcanic cones or plateau, perhaps reflecting globally high sea level combined with the small-scale of cratonic nuclei. The onset of modem style plate tectonics in the early Mesoarchean allowed for more extensive generation and preservation of fluvial strata: most of these are first cycle deposits, preserved in rift, strike-slip, and foreland basins, with rare examples accumulating in forearc and syn-tectonic piggy-back basins. This article is part of a special issue entitled: Archean Earth Processes; Edited by: Rajat Mazumder and Patrick Eriksson.