New review paper on the Namib Sand Sea - early view

I post a link to my new review of about the long-term Geomorphology and Quaternary dynamics of the Namib Sand Sea, which follows the presentation I gave at Gobabeb for the SAAG conference. It is called: "Age and dynamics of the Namib Sand Sea: a review of chronological evidence and possible landscape development models" and is available online now. 

 

 

 

Abstract

The Namib Sand Sea constitutes a major physiographic feature of the Namib Desert on the west of Namibia, covering a 50-160 km wide region on the west coast of Namibia between Lüderitz and Walvis Bay. It is widely considered to be one of the oldest desert regions, with a Tertiary-aged fossil desert underlying the modern sand sea. The sand sea has been well studied, benefiting from the presence of the Gobabeb Training and Research Centre over the past 50 years. Whilst much is understood about its sediments and geomorphology, it is only recently that new chronological information, using cosmogenic-nuclide burial dating and optically stimulated luminescence dating have offered new insights, and these call for an updated review of the age and landscape development of the sand sea. This assessment of the geomorphological and Quaternary dynamics of the region is complemented by developments in description and analysis of sediment composition.

New age control from cosmogenic dating indicates that the sand sea is in excess of a million years old, whilst the initial data from luminescence dating yield depositional ages for dune sediments in three broad areas of the sand sea that include MIS 5, later in the Pleistocene around the Last Glacial Maximum and the Holocene, although it is not expected that these will be the only, or discrete age groupings. Detailed dating and application of ground penetrating radar in the far northern reaches reveals extensive dune migration and deposition during the Holocene. It is important to stress that the upper limit of luminescence dating here is about ∼200 ka (depending on the environmental dose rate of the site) and that migration and reworking of dunes reset the luminescence signal (so what is recorded is the last phase(s) of preserved sediment accumulation).

Whilst there are three potential sources of material for the Sand Sea (reworked Tsondab Sandstone (TSS), material from the Great Escarpment derived by rivers and water and wind-derived material from the Orange River delta) the weight of evidence points towards the dominance of an Orange River source, with localised contribution from fluvially-derived escarpment material close to river courses. Despite the fact that it remains difficult to definitively distinguish between recent Orange River sediment and recycled TSS because of a great mineralogical similarity, an Orange River source contemporaneous with the accumulation of the sand sea appears to be favoured. Models of landscape development rely on understanding source region, and an Orange River source suggests growth and extension from south to north (a wind-displaced Orange Delta), rather than localised reworking of sediment from the TSS. One model, proposed for the southern part of the sand sea, divides accumulation into two distinct phases with different palaeoenvironmental conditions: large draas accumulating under enhanced Pleistocene trade winds and superimposed features on the eastern dune flanks formed by westerly winds moving material over the crest. However, the latter phase could equally be explained by a northerly migration of the superimposed features, and there is still too little in the way of chronological control to construct a coherent picture of dune accumulation and migration for the sand sea as a whole. There are also interesting insights from conceptualising dune bedform patterning in sand seas as a time-dependent, self-organising, complex system, rather than necessarily requiring changing palaeoenvironmental conditions for different scales of features, with some of this research referring directly to the Namib Sand Sea. Refining the details of the accumulation of the Namib Sand Sea requires both detailed site-specific studies and joined-up analysis.

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Highlights

► Review of age and models of landscape development in the Namib Sand Sea. ► Approaches to assessing the age of dune forms are reviewed. ► Ideas about development of sand sea tightly connected to sediment sources. ► Sand sea is > 1 million years old, with later Pleistocene and Holocene deposition. ► Landscape development may include northerly migration and bedform self-organisation.

Keywords

• Namib Sand Sea;
• Geochronology;
• Geomorphology;
• Quaternary;
• Namibia

Thank yous!
I'd like to take the opportunity to again  thank a number of people for fruitful discussions about the Namib Sand Sea: Andrew Goudie, Charlie Bristow, Kevin White, Mary Seeley, John Ward, Ian Livingstone, Frank Ekhardt, David Thomas and Mark Bateman. The author thanks two anonymous reviewers for their constructive comments, which have improved the manuscript.
And to sources of funding - the paper was drafted whilst in receipt of a John Fell Fund Small Award at the University of Oxford (School of Geography and the Environment), which partly funded attendance of the SAAG and SASQUA conferences in September 2012 at which these ideas were presented. Funding to attend the UK aeolian research meeting ‘Windy Day’ in October in Leicester where revised ideas were presented, came from St John’s College.  

Best wishes
Abi  

Minutes of the meeting about past work and Future Progress in Geomorphology in the Namib

At the SASQUA meeting at Gobabeb in September, Sue Ringrose chaired a short meeting for us all to discuss work in the Namib and through Gobabeb and where this might go in the future. I post the minutes of that meeting here for our reference and a basis for getting started with further discussions.

PAST WORK AND FUTURE PROGRESS – GEOMORPHOLOGY IN THE NAMIB (GBB)

Chair: Dr Sue Ringrose

Attendees: About forty participants of the SASQUA meeting at Gobabeb

A meeting was held at Gobabeb towards the end of the SAAG-SASQUA conferences on 15/09/12 to discuss the future possible role of GBB in co-ordinating research and disseminating research products in a way that would be both stimulating and interesting to the larger scientific community.

During the course of the meeting, Dr Seely explained that GBB would likely soon find itself within an UNESCO World Heritage Site which should make it easier to promote scientific research and provide the protection needed for endemic (and other) fauna and flora and their habitats/environment.

A particular initiative would be to hold an annual Desert Research Network meeting at GBB where all desert research results could be shared via an international forum starting in 2013 with all welcome.  (see below)..

Most of the SASQUA research scientists and students attended the meeting and considered the potential in terms of services/data that GBB offers in relation to seven possible themes namely:

1. Morphology/movement of sand dunes – dust issue
2. Archaeological questions
3. Palaeohydrology of Kuiseb (and other ephemeral rivers)
4.  Palaeo-climatic reconstruction – from range of sediments and dating techniques
5.  Duricrust formation – gypcrete/calcrete esp. in relation to fog – water table change
6. Soil, landscape, plant inter-relationships
7. (Physical) weathering rates including salt effects

While useful, these themes were generally considered somewhat narrow with a need to broaden the overall scope and promote more integrated work – usefully avoiding the term ‘geomorphology’ – maybe replacing it with integrated earth science (IES)

While details were considered, the general feeling of the group was that:

• GBB is ideally placed as a centre for all aspects of inter/multi-disciplinary desert research
• That the best way to promote inter-active/inter-disciplinary research based out of GBB was to hold annual meetings around integrated desert research and to invite regional and international participants (and possible keynote speakers)
• The inter-disciplinary areas to include earth/biotic/atmospheric and marine sciences
• Biannual SAAG or SASQUA meetings could be run in conjunction with these meetings
• The annual integrated desert research meeting should involve participants from the SPACES project (marine, terrestrial and atmospheric) who could then interact with personnel from the ongoing GBB atmospheric monitoring collaborators, including Max-Plank atmospheric monitoring group, the Karlsruhe Institute of Technology & University of Basel land-surface monitoring and the BSRN stations

Topics of future research could include:

1. Variability of fogs events/intensity in the light of climate change
2. Application of recent remote sensing techniques (lidar, hyperspectral, MISR-HR package, etc)
3. Use of mine exploration data from terminated exploration/operating leases – for stratigraphic control especially on buried alluvial channels
4.  Development of dust related projects (aerosol work)
5. Coastal erosion/deposition in light of recent sea level rises
6. More extensive archaeological/cave midden work along upper-mid Kuiseb. 
7. Plant biotech research on desiccation tolerance

The following ideas were raised with a view of expanding the area of ‘user friendly’ promotional scientific information dissemination (to promote the scientific profile of GBB).

1. The development of scientific materials for international dissemination in earth system science  - SR to follow up with S.A. ACCESS (South African Centre for Earth System Science) who put out similar material on the web
2. Contact University of Stellenbosch to determine whether their Masters students in Scientific writing (in Dept of Journalism) can be involved in research dissemination
3. Promote integrative ideas like the development of the Dune Atlas
4. Promote and protect sites of serious scientific interest (especially known archaeological sites) in the light of increasing tourist numbers (and as result of Adventure Tourism Global Meeting in Namibia)
5. Promote the use of GBB facilities for taught African experience masters programmes with the need for research activities with communities.

Sue Ringrose and Mary Seely

After two fantastic conferences (SAAG and SASQUA) hosted at the Gobabeb Training and Research Centre this September (2012) there was some formal and informal discussion about the future direction of research that involves Gobabeb - research both based at and through this excellent resource (in terms of infrastructure and personnel).

To this end, I hope that a blogpage such as this can serve as a useful forum for sharing information and ideas about current and future research that involves Gobabeb. Please do get involved! (it is easy to add you as an admin/author to the blog - for now contact Abi (abi.stone@gmail.com), but soon any of the authors who become involved should be able to add other authors)!

Many thanks to all at Gobabeb for their part in running these excellent academic meetings and also to Frank Ekhardt, Brian Chase and those they enlisted to help them.