Abstract
AbstractSand ramps have the potential to provide rich palaeoenvironmental information in dryland regions where proxy records are typically scarce. However, current knowledge of the geomorphic controls and processes of sand ramp formation is limited. This study provides a data‐rich examination of the key factors controlling sand ramp formation. The location and morphology of 75 sand ramps in southern Namibia are examined. The sediments and chronologies of 10 sand ramps are studied in detail using 51 OSL dates and 83 grain‐size and LOI samples. Heavy mineral assemblages are used to determine the provenance of 10 samples and OSL sensitivity is used to explore geomorphic processes of eight samples.Sand ramp morphology can be grouped into one of four classes of increasing size and complexity and is closely linked to the available accommodation space. Heavy mineral assemblages indicate local sediment sources and all 75 studied sand ramps are within 4 km of a large ephemeral river channel or within 5.5 km of a dune field. Therefore, accommodation space and sediment supply are identified as the primary controls of sand ramp formation. Sedimentology and OSL sensitivity suggest a complex interplay of aeolian, fluvial and colluvial processes contribute to sand ramp formation with large variability observed between ramps. Three of the ten dated sand ramps have been present in the Namibian landscape for >100 ka. Eight sand ramps show episodic deposition between >75–12 ka and five show evidence of surface reworking over the past 2 ka. Environmental sensitivity is probably linked to the size and availability of the accommodation space. Therefore, individual sand ramps are expected to reflect local environmental conditions, recording when an abundant sediment supply coincided with available accommodation space, while a regional analysis of multiple sand ramps with chronometric data offers the potential to identify larger scale palaeoenvironmental controls of sediment supply. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
Highlights
Studies of Quaternary environmental change in dryland regions are often hampered by a paucity of preserved proxy records (Thomas and Burrough, 2012)
75 sand ramps were confirmed within the study region (Figure 2 and Supplementary information 2). 90% are climbing features as identified by their position in relation to topography and their morphology (Lancaster and Tchakerian, 1996; Chojnacki et al, 2010; Goudie, 2013; Ellwein et al, 2015). 74% are predominantly east facing and 17% are west facing (Figure 5 and Supplementary information 2)
Accumulation occurs in sheltered alcoves or along elongate mountain fronts aligned perpendicular to the wind with 95% of sand ramps accumulated against inselbergs or inselberg complexes and 5% against the edge of the Great Escarpment
Summary
Studies of Quaternary environmental change in dryland regions are often hampered by a paucity of preserved proxy records (Thomas and Burrough, 2012). The arid climate inhibits the preservation of organic proxies typically used for palaeoenvironmental reconstruction, while ubiquitous ‘geoproxy’ records (e.g. dunes) can be difficult to interpret in terms of past climatic controls (Chase and Meadows, 2007; Stone and Thomas, 2008; Chase, 2009; Thomas and Burrough, 2012) This is the case in the most arid parts of Namibia, including the Namib Sand Sea, where the analysis of geoproxy archives from within the sand sea has been relatively restricted and sometimes difficult to interpret in palaeoclimatic terms (Lancaster, 2002; Livingstone et al, 2010; Stone, 2013). As such their current utility as palaeoenvironmental archives is limited
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
