Precambrian aeolian systems: A unique record?

The Precambrian is associated with a set of geologically unique palaeoenvironmental conditions arising from differences in the Earth's atmosphere, biosphere and geosphere. The extent to which these conditions operated to generate an aeolian stratigraphic record that is geologically distinct from that of the Phanerozoic remains poorly understood. This study presents a quantitative comparison of the preserved sedimentary architectures of 87 globally distributed aeolian successions from the Precambrian (30 case studies) and the Phanerozoic (57 case studies). Compared to those of the Phanerozoic, Precambrian aeolian successions are characterised by: (1) thinner aeolian dune sets, mostly documenting the accumulation of small, rapidly migrating barchan dunes; and (2) a greater occurrence of sandsheet, zibar, and damp and wet interdune deposits, many occurring interdigitated with non-aeolian strata. The nature of the Precambrian aeolian stratigraphic record reflects in part the absence of sediment-stabilizing terrestrial vegetation: compared to Phanerozoic systems developed since the evolution of land plants, aeolian processes (erosion, transport and deposition) were more active, even under markedly more humid climates. Precambrian aeolian successions record greater evidence of fluvial and marine incursions into contiguous aeolian dune fields. Water tables were commonly elevated close to the level of the accumulation surface for protracted episodes; extensive damp and wet substrates restricted the availability of dry sand for aeolian dune construction, thereby limiting dune size. In some Precambrian aeolian systems, sediment supply was additionally restricted by the development of cryptobiotic films and crusts that preferentially developed on damp substrates in the absence of vegetation. Common fluvial and marine aqueous interactions promoted the reworking of aeolian dunes into sandsheet deposits; many such accumulations likely represent eroded remnants of larger aeolian dune fields. Given the absence of vegetation-induced sediment binding and baffling, and wind-buffering effects, coarser sand fractions were more readily transported by the wind in the Precambrian; this led to the preferential development of coarse-grained zibar deposits. This study demonstrates how the Precambrian aeolian sedimentary record is geologically distinct from that of the majority of the Phanerozoic, providing new insights into the controlling factors that governed aeolian sedimentation during the Precambrian through interactions between the geosphere, biosphere and atmosphere.