Ash‑bearing transgressive coastal dune on São Vincente (Cape Verde Islands): dune history and evidence of explosive volcanic activity around 35 ka

摘要

Climbing, transgressive dunes are developed at the relief-controlled narrow desert coast of Praia Grande on Sao Vicente (Cape Verde Islands) and this paper describes one of these spectacular coastal dunes. The dune was initiated during a low sea level in the Late Pleistocene; the dune migrated landwards presumably during the influence of persistent northeasterly trade winds and it reached the present coast of the island some time before 35 ka, when it was covered with volcanic ash. Volcanic activity in the Cape Verde archipelago is presently limited to the island of Fogo or is submarine. However, Late Pleistocene eruptions have been identified on many of the islands, but few eruptions younger than 100 ka have been absolutely dated. The revelation of a 35 ka pyroclastic deposit on Sao Vicente is evidence for the continued activity in the northern part of the archipelago. The Praia Grande ash is not readily reconciled with the young Strombolian or effusive Sao Vicente volcanism, which is also geochemically different. The geochemical composition of the fractionation corrected Praia Grande ash is compared to a large database for volcanic rocks of the northern part of the Cape Verde archipelago. Major and trace elements as well as incompatible element ratios in combination allow identification of the likely source for the Praia Grande ash as the Monte Gordo volcano at the island Sao Nicolau 70 km to the SE and the eruption possibly was of VEI >= 5.