Late Quaternary foraminifera from the southern part of offshore South West Africa/Namibia

Abstract

Abstract taken from unidentified publication, section E4d: Palaeontology, p. 1364:

Detailed analyses of foraminifera faunas from the Quaternary intervals of nine selected vibracores from the inner and middle Orange Shelf, southern offshore South West Africa/Namibia have provided data on a number of aspects of the latest Pleistocene- Holocene hIstory of the region. The essentially benthonic foraminifera assemblages initially provided only a generalised indication of the ages of the vibracore sections, but extensive studies of equivalently aged sequences from a number of other locations around the South African coast have provided a workable model for the accumulation of all Pleistocene marine deposits in southern Africa. The vibracore sections thus consist of a lower regressive sequence which accumulated as sea-level fell at the end of the Eemian interglacial. The sequence shows shallowing-up characteristics, and probably reflects diachronous sedimentation of littoral and sub-littoral deposits as the shoreline retreated across the continental shelf. This sequence can be divided into a clayier lower unit of diverse foraminifera faunas, considered to be of latest Eemian age, and a sandier upper unit of more restricted, littoral faunas, which is regardcd as being of earliest Weichselian age. Unconformably overlying the Weichselian sands are variable thicknesses of Holocene clayey sands. The latest Pleistocene retreat of the sea seems to have occurred in phases: a -4Om level in the latest Eemian is followed by a -6Om earliest Weichselian level, after which sea-level fell to at least -140m for most of Weichselian time. Early in the Holocene a major advance of the sea occurred, transgressing the continental margin rapidly at first, later more slowly. This chronos- tratigraphy is not supported by previously determined C-14 dates, and correlation with internationally established sea-level curves for this time period has resulted in rather ambiguous conclusions. Poorly oxygenated sea-floor conditions have had a strong influence on the preservation of foraminifera faunas during the Holocene, and sea-floor acidity has attained levels high enough to corrode calcareous tests, but such processes were not active in the latest Pleistocene. Swell and wave action, with possible current activity, was much more pronounced at the time of the -6Orn sea-level, when severe reworking of older rocks and their contained foraminifera occurred, particularly the soft sediments of the Late Cretaceous, the Late Eocene to Early Oligocene and the Early to early Middle Miocene. Apparent long - distance transport of Dwyka (permian) foraminifera tests down the Orange River has also been recognised. The Quaternary foraminifera faunas of the Orange Shelf are typical of shallow marine environments world-wide, but the total assemblages are unique to the west coast of southern Africa