Stratigraphical and sedimentological features of the Neogen to Quaternary succession around Luanda (Angola, southwestern Africa)

The Miocene to Quaternary succession exposed around Luanda is divisible into (from bottom to top): the pelitic sediments of the Quifangondo Formation, interpreted as deposited on a neritic ramp of Burdigalian age; bioclastic deposits of the Cacuaco Formation, characterised by "foramol"-type fossil assemblages pointing to a high-energy open shelf environment of Burdigalian age; terrigenous and carbonate sediments of the Luanda Formation referred to a transitional environment (lagoon, beach, estuary) of Miocene or Pliocene age; the alluvial deposits of the Areias Cinzentas Formation; and continental sediments of the Quelo Formation. These last sediments are locally overlain by dark grey to Wack shales of "Argillas Petras unit" interpreted as a solum related to the weathering of a pre-existing deposit, during the Holocene. The Tertiary succession records a 2nd order transgressive-regressive cycle, from offshore (the Quifangondo Formation) to infralittoral (the Cacuaco Formation) and to swamp or supralittoral deposits (the Luanda Formation), driven by tectono-eustasy. Since the end of this 2nd order cycle the study area was subaerially exposed as testified by the continental Quaternary deposits.