Ephemeral river systems at the Skeleton Coast, NW-Namibia Sedimentological and geomorphological studies on the braided river dominated Koigab Fan, the Cenozoic succession in the Uniabmond area and comparative studies on fluvio-aeolian interaction between ephemeral rivers and the Skeleton Coast Erg Dissertation zur Erlangung des naturwissenschaftlichen Doktorgrades der Bayerischen Julius-Maximilians-Universität Würzburg vorgelegt von Carmen Krapf aus Arnstein Würzburg 2003 Eingereicht am: 1. Gutachter: PD Dr. Harald Stollhofen 2. Gutachter: Prof. Dr. Volker Lorenz 1. Prüfer: Prof. Dr. L Lorenz 2. Prüfer: Prof. Dr. D. Busche Tag der Prüfung (öffentlicher Vortrag und Disputation): 18.06.2003 Doktorurkunde ausgehändigt am: _______________ Table of content 1 Table of contents................................................................................................................ 1 Acknowledgements ............................................................................................................ 5 Abstract .............................................................................................................................. 7 German Summary............................................................................................................. 9 1 Introduction ....................................................................................................................11 1.1 Objective of the study...............................................................................................11 1.2 Overview of the study area .......................................................................................11 1.2.1 Location............................................................................................................11 1.2.2 Climate ..............................................................................................................13 1.2.2.1 Precipitation and temperature....................................................................13 1.2.2.2 Wind as a geological factor ......................................................................15 2 Geological setting............................................................................................................18 2.1 Palaeo- to Middle Proterozoic rocks.........................................................................20 2.2 Late Proterozoic Pan-African Damara metamorphic rocks......................................20 2.3 Etendeka Group ........................................................................................................21 2.3.1 Twyfelfontein Formation ..................................................................................21 2.3.2 The Etendeka Igneous Province........................................................................22 2.4 Cenozoic deposits .....................................................................................................23 2.4.1 Red Canyon Formation: Tertiary Red-beds......................................................23 2.4.2 Whitecliff Formation: Plio- to Pleistocene carbonate-cemented sediments .....24 2.4.3 Uniabmond Formation: Pleistocene semi- to unconsolidated sediments..........24 2.4.4 Skeleton Coast Erg (Late Pleistocene)..............................................................25 2.4.5 Holocene deposits .............................................................................................26 2.4.5.1 Ephemeral river deposits...........................................................................26 2.4.5.2 Aeolian sediments and landforms .............................................................26 2.4.5.3 Marine terraces and coastal sabkhas .........................................................28 2.5 Tectonic setting.........................................................................................................28 3 Methods ...........................................................................................................................30 3.1 Field studies ..............................................................................................................30 3.2 Remote sensing data, image processing and data interpretation ..............................31 3.3 Laboratory analysis...................................................................................................31 Table of content 2 4 The ephemeral braided river dominated Koigab Fan ................................................33 4.1 Significance and setting of the Koigab Fan system..................................................33 4.1.1 Geodynamic framework, tectonic setting and drainage evolution....................35 4.1.2 Catchment and source area characteristics .......................................................35 4.1.3 Depositional site and climate ...........................................................................38 4.1.4 Drainage system of the Koigab Fan .................................................................38 4.2. Fan Morphology ......................................................................................................39 4.2.1 Principal anatomy and dimensions of the Koigab Fan ....................................39 4.2.2 Channel and surface characteristics of the Koigab Fan ...................................42 4.2.2.1 Koigab River and Koigab Canyon Poort .......................................................42 4.2.2.2 The lower Koigab River - active channel of the Koigab Fan....................43 4.2.2.3 Abandoned channels of the Koigab Fan....................................................46 4.3 Sedimentological processes shaping the Koigab Fan...............................................47 4.3.1 Sedimentological characteristics of the active channel ....................................47 4.3.2 Ancient fluvial sequences of the Koigab Fan ...................................................49 4.3.3 Fluvio-aeolian interaction affecting the Koigab Fan surface............................50 4.4 Interaction of the fan with the marine environment .................................................56 4.4.1 Active channel and oceanic interaction ...........................................................56 4.4.2 Flanking shoreline barriers and coastal sabkhas...............................................57 4.5 The Koigab Fan compared to other fans and rivers along the Namibian coast........59 4.6 Classification of the Koigab Fan and comparison with worldwide fans and fan systems...............................................................................................................61 4.6.1 Fan, terminal fan or fan-delta?..........................................................................62 4.6.2 Position and contrasts within alluvial fan classifications .................................62 4.7 Koigab Fan: significance for Precambrian and Early Palaeozoic fans.....................65 4.8 Conclusion................................................................................................................66 5 The Cenozoic succession in the Uniabmond area.......................................................68 5.1 The Uniab River system and the Uniabmond area ...................................................68 5.1.1 Catchments and source area characteristics......................................................69 5.1.2 Climate and flood characteristics......................................................................70 5.2 The lithostratigraphic framework of the Uniabmond area ....................................... 70 5.3 Red Canyon Formation.............................................................................................73 5.3.1 Waterfall Member .............................................................................................74 5.3.2 Bone-Area Member...........................................................................................76 5.3.3 Tectonic structures ............................................................................................77 5.3.4 Interpretation and age estimates........................................................................78 5.4 Whitecliff Formation ................................................................................................80 5.4.1 Facies of the Whitecliff Formation ...................................................................82 5.4.1.1 Fluvial facies.............................................................................................82 5.4.1.2 Aeolian facies............................................................................................85 5.4.1.3 Marine facies.............................................................................................86 5.4.2 Investigated sections and outcrops of the Whitecliff Formation ......................90 5.4.2.1 Waterfall and C2 section ...........................................................................90 5.4.2.2 Red Canyon Exit section A .......................................................................93 Table of content 3 5.4.2.3 Red Canyon Exit section B .......................................................................95 5.4.2.4 Red Canyon Exit section C .......................................................................95 5.4.2.5 Bivalves section.........................................................................................96 5.4.2.6 Whitecliff section in C5c...........................................................................97 5.4.2.7 Palaeo-dunefield