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Exceptional Mechanisms for Preservation of Eolian Successions

Abstract

The construction and accumulation of eolian dune fields is commonplace in modern desert and non-desert settings. However, the long-term preservation potential of many present-day dune-field accumulations is very low, chiefly because many such systems are currently developed in stable intracratonic settings for which rates of long-term subsidence are very slow. Large bed forms in many present-day tropical eolian desert dune fields are legacy forms that were constructed and underwent accumulation during the last glacial maximum when the climate was generally colder, drier and windier than today. Several factors have promoted the stabilization of these legacy bed forms: (i) the present-day climate is not sufficiently windy to enable the eolian transport of large volumes of sediment for further dune-field construction; (ii) the sediment supply that was used to construct many large present-day dune fields has now been exhausted or flooded during Holocene transgression; (iii) stabilizing agents on dune surfaces (vegetation, precipitate crusts) have become increasingly significant in response to a shift to a more humid climate; (iv) elevated intra-dune-field water tables restrict sand transport across damp or wet interdune surfaces. In the ancient record, many preserved eolian successions are interpreted to have accumulated via the synchronous migration and climb of bed forms that led to the generation of stacked sets of thickly cross-bedded strata. However, several other exceptional preservation mechanisms are also documented, including: (i) flooding by transgression; (ii) inundation by flood basalts; (iii) stabilization of bed forms in response to climate change to preserve relic topography; (iv) migration of bed forms into pre-existing topographic depressions ranging in scale from entire basins to salt-solution pockets; (v) preservation in subsiding salt-walled mini-basins; (vi) the presence of interdune depressions developed between stabilized bed forms that act as local accommodation centers for younger bed forms. These varied preservation mechanisms mean that the eolian stratigraphic record is far more complex than previously thought. From an applied standpoint, varied mechanisms for preservation of eolian successions govern the development of lithological heterogeneity at multiple scales. A primary result arising from this research has been the development of quantitative facies models with which to better predict eolian reservoir characteristics.