Morphology and fluvio-aeolian interaction of the tropical latitude, ephemeral braided-river dominated Koigab Fan, north-west Namibia.

Krapf C, Stanistreet IG, Stollhofen H (2005)

Publication Language: English

Publication Type: Book chapter / Article in edited volumes

Publication year: 2005

Edited Volumes: Fluvial Sedimentology VII

Series: IAS Special Publication

Book Volume: 35

Pages Range: 99-120

Journal Issue: 35

DOI: 10.1002/9781444304350.ch6

Abstract

The Koigab Fan is the largest of the active fan systems formed by some of the
west-south-west flowing ephemeral river systems of the Skeleton Coast area,
north-west Namibia. Issuing from the volcanic Etendeka Plateau, the Koigab
River flows towards the Atlantic Ocean across a considerable climatic gradient
from semi-arid summer rainfall in the mountainous catchment, to hyperarid in
the coastal depositional setting.
The morphology of channels can be discerned over the whole fan surface
(gradient 1.011), the majority of which appears as a vast deflation surface on
which lithic and heavy mineral grains are concentrated by aeolian removal of
fines. The Koigab catchment restricts source-rock lithologies to flood basalts and
interleaved quartz latites of the Etendeka Plateau, so components that unequivocally
relate to a volcanic source (e.g. volcanic lithics, Ti-magnetite, pyroxenes)
indicate fluvial transport, whereas grains reflecting a metamorphic basement
source (e.g. garnet, muscovite, staurolite) must be aeolian derived. Both heavy
mineral and grain-size data were used to estimate the amount of fluvio-aeolian
interaction at the Koigab Fan surface. This aspect is significant because it comprises
not only winnowing of the fan surface and of ‘fresh’ sandy channel
deposits but also fluvial recycling of aeolian material. The contribution of
aeolian-derived grains to river deposits increases from 5% in the fan apex area
to as much as 50% in the distal fan reaches.
In the spectrum of fan types, the Koigab Fan takes an intermediate position
both in size and in terms of the braided river style between debris flow and low
sinuosity meandering fan systems. Within the braided fluvially dominated fan
class itself the Koigab Fan is also intermediate in size, but its ephemeral channels
contrast sharply with those of perennial glacial outwash fans previously
described from the sub-Arctic. Within low-latitude fan systems, the Koigab also
contrasts with other highly vegetated fans in the tropics, for example the subaerial
portion of the Yallahs Fan-delta, Jamaica. Thus, the Koigab Fan is important
as a potential analogue for Precambrian and early Palaeozoic low-latitude
fan systems that lacked surface vegetation prior to the evolution of land plants.

Authors with CRIS profile

Harald Stollhofen Lehrstuhl für Geologie (Exogene Dynamik)

Involved external institutions

The University of Liverpool GB United Kingdom (GB) Julius-Maximilians-Universität Würzburg DE Germany (DE)

How to cite

APA:

Krapf, C., Stanistreet, I.G., & Stollhofen, H. (2005). Morphology and fluvio-aeolian interaction of the tropical latitude, ephemeral braided-river dominated Koigab Fan, north-west Namibia. In Blum, M., Marriott, S., Leclair, S. (Eds.), Fluvial Sedimentology VII. (pp. 99-120).

MLA:

Krapf, Carmen, Ian G. Stanistreet, and Harald Stollhofen. "Morphology and fluvio-aeolian interaction of the tropical latitude, ephemeral braided-river dominated Koigab Fan, north-west Namibia." Fluvial Sedimentology VII. Ed. Blum, M., Marriott, S., Leclair, S., 2005. 99-120.

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