The distribution of carbonate eolianite

Abstract

Carbonate eolianite forms distinctive coastal landforms on many mid-latitude continents and islands. Numerous studies of extensive continental and smaller island deposits in both hemispheres have shown the eolianites are predominantly Pleistocene in age. The Coorong coastal plain of South Australia contains the world's longest record of eolianite deposition, revealing that major phases of carbonate accumulation occurred during interglacial and some interstadial sea-level highstands throughout the Quaternary. Similarly, the well-studied eolianite islands of Bermuda and the Bahamas record a close match between dune accretion and sea-level highstands since the Middle Pleistocene. Several other eolianite deposits appear to have formed, at least partially, during glacial periods. The glacial-age deposits are eolian-reworked relict shelf or coastal sediments, or remnants of former highly mobile coastal dunes sourced from low sea-level shorelines. The distribution and bioclastic composition of large-scale eolianite deposits suggests carbonate production on shallow shelves and banks is the ultimate control on the formation of eolianite. The bulk of the carbonate comprising those eolianites is Heterozoan, being produced where there is low terrigenous sediment input in dominantly temperate (cool-water) and subtropical carbonate provinces. Quaternary cyclical movements of sea level have also controlled the form and rate of coastal carbonate deposition, with repeated pulses of sedimentation during highstands forming laterally coalesced, vertically stacked or composite dune successions. Major unconformities within the deposits are marked by paleosols, which record hiatuses in coastal sedimentation. In several regions, major eolianite units overlie coastal deposits of terrigenous sediment. Those successions suggest that the trend towards aridity and reduction in the supply of terrigenous sediment to shelves during the Quaternary has enhanced the production of carbonate and the deposition of eolianite.