Occurrence of Pleistocene carbonate eolianites in the Marquesas Islands (French Polynesia)

In the volcanic Marquesas archipelago, the Northern islands (Eiao, Ua Uka and Nuku Hiva) exhibit cemented carbonate deposits as islets or coastal reliefs, located along their southern and eastern areas. Locally lying at up to 200 m in elevation, these deposits occur in the form of flatted dome, crescent or collecting cone. Chiefly made up of detritus from marine calcifying organisms, these deposits display cross-bedded strata, thinely layered, several metres in thickness. Earlier interpretations suggested that these limestones are ancient beaches at present uplifted. Investigations focusing on geomorphology, lithostratigraphy (identification of internal structures, estimate of size and dip of sedimentary bodies) and sedimentology (grain-size, identification of earlier cement types) reveal that the relevant sediments are medium to very fine-grained, well-sorted sands, steeply dipping landward (up to 30 degrees) and sub-aerially cemented. These lead to regard them as wind-deposited bodies (so-called coastal dune-rocks or eolianites) resulting from prevailing east-south-east, trade-winds, supplied from exposed, marine sedimentary sources, during one or several, mid to late Pleistocene sea-level lowerings.