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Associate Editor -Nick LancasterABSTRACT Aeolian processes and ephemeral water influx from the Variscan Iberian Massif to the mid-Cretaceous outer back-erg margin system in eastern Iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements. Remains of aeolian dunes encased in ephemeral fluvial deposits (aeolian pods) demonstrate intense erosion of windblown deposits by sudden water fluxes. The alternating activity of wind and water led to a variety of facies associations such as deflation lags, desert pavements, aeolian dunes, pebbles scattered throughout dune strata, aeolian sandsheets, aeolian deposits with bimodal grain-size distributions, mud playa, ephemeral floodplain, pebble-sand and cobble-sand bedload stream, pebble-cobble-sand sheet flood, sand bedload stream, debris flow and hyperconcentrated flow deposits. Sediment in this desert system underwent transport by wind and water and reworking in a variety of sub-environments. The nearby Variscan Iberian Massif supplied quartzite pebbles as part of mass flows. Pebbles and cobbles were concentrated in deflation lags, eroded and polished by winddriven sands (facets and ventifacts) and incorporated by rolling into the toesets of aeolian dunes. The back-erg depositional system comprises an outer backerg close to the Variscan highlands, and an inner back-erg close to the centralerg area. The inner back-erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits. In the inner back-erg area ephemeral wadis, desiccated after occasional floods, were mud cracked and overrun episodically by aeolian dunes. Subsequent floods eroded the aeolian dunes and mudcracked surfaces, resulting in largely structureless sandstones with bouldersize mudstone intraclasts. Floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes. The remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands. Upon desiccation, deflation resulted in lags of coarser-grained sediments. A renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions. Synsedimentary tectonics caused the outer back-erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands. Ephemeral water flow to the outer back-erg area supplied pebbles, eroded aeolian dunes, and produced hyperconcentrated flow deposits. Fluidization
Associate Editor -Nick LancasterABSTRACT Aeolian processes and ephemeral water influx from the Variscan Iberian Massif to the mid-Cretaceous outer back-erg margin system in eastern Iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements. Remains of aeolian dunes encased in ephemeral fluvial deposits (aeolian pods) demonstrate intense erosion of windblown deposits by sudden water fluxes. The alternating activity of wind and water led to a variety of facies associations such as deflation lags, desert pavements, aeolian dunes, pebbles scattered throughout dune strata, aeolian sandsheets, aeolian deposits with bimodal grain-size distributions, mud playa, ephemeral floodplain, pebble-sand and cobble-sand bedload stream, pebble-cobble-sand sheet flood, sand bedload stream, debris flow and hyperconcentrated flow deposits. Sediment in this desert system underwent transport by wind and water and reworking in a variety of sub-environments. The nearby Variscan Iberian Massif supplied quartzite pebbles as part of mass flows. Pebbles and cobbles were concentrated in deflation lags, eroded and polished by winddriven sands (facets and ventifacts) and incorporated by rolling into the toesets of aeolian dunes. The back-erg depositional system comprises an outer backerg close to the Variscan highlands, and an inner back-erg close to the centralerg area. The inner back-erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits. In the inner back-erg area ephemeral wadis, desiccated after occasional floods, were mud cracked and overrun episodically by aeolian dunes. Subsequent floods eroded the aeolian dunes and mudcracked surfaces, resulting in largely structureless sandstones with bouldersize mudstone intraclasts. Floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes. The remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands. Upon desiccation, deflation resulted in lags of coarser-grained sediments. A renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions. Synsedimentary tectonics caused the outer back-erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands. Ephemeral water flow to the outer back-erg area supplied pebbles, eroded aeolian dunes, and produced hyperconcentrated flow deposits. Fluidization
Large‐scale deformation structures in late Permian aeolian dune sands are associated with sand fluidization and injection. Exceptional precipitation and flooding of the desert margin are believed to have caused mass‐wasting by gravitational collapse and sliding of water‐saturated dunes, which loaded down‐dip strata, thus generating overpressure and triggering sand injection. This short‐lived but heavy precipitation seems to have been associated with a climatic change from arid Rotliegend dune deposition to widespread Zechstein marine conditions within the greater North Sea area, probably just before or coinciding with deposition of the rapidly expanding marine Kupferschiefer.
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