Figure 2 - uploaded by Nick Drake
Content may be subject to copyright.
Playas and gypsum deflation mapped from Landsat TM image. Zone 1 features extensive dolerites dykes which promote groundwater seepage. Substantial sabkhas along the coast show evidence of fluvial inputs from the Namib Desert interior
Source publication
The formation of Namibia's extensive pedogenic gypsum crusts (CaSO4·2H2O) is interpreted in a new light. It is suggested that gypsum primarily precipitates at isolated points of evaporitic concentration, such as inland playas, and that deflation of evaporitic-rich gypsum dust from these playas contributes to the formation of pedogenic gypsum duricr...
Context in source publication
Similar publications
The soil microarthropods were sampled in the three major habitats of the Namib Desert, namely the gravel plain, an ephemeral river and sand dunes. In spite of severe climatic conditions and low soil organic matter content, microarthropods extracted through CCl4 flotation were found to be surprisingly diversified and abundant. A total of 47 microart...
Informal settlements in rapidly-growing African cities are urban and peri-urban spaces with high rates of formal unemployment, poverty, poor health outcomes, limited service provision, and chronic food insecurity. Traditional concepts of food deserts developed to describe North American and European cities do not accurately capture the realities of...
The factors that trigger sudden, seasonal movements of elephants are uncertain. We hypothesized that savannah elephant movements at the end of the dry season may be a response to their detection of distant thunderstorms. Nine elephants carrying Global Positioning System (GPS) receivers were tracked over seven years in the extremely dry and rugged r...
The South African campaign in German South West Africa (GSWA) during the First World War depended largely on the access, availability and control of all water sources in the operational area. The Union Defence Force (UDF) appreciated the strategic nature of water before the invasion of GSWA in 1914, because it was well known that there were no perm...
Kundelungua meridionalis Schouteden, 1966 (Heteroptera, Pentatomidae, Podopinae) is reported from Namibia for the first time. It has been found in Kuzikus Wildlife Reserve in the Kalahari desert, among the roots of grasses. Habitus and biotope are illustrated and a distribution map and biological data are provided.
Citations
... Typically, Ca-sulphates (gypsum, bassanite, anhydrite) can be formed under different temperature conditions of the arid environment and are significant for palaeo-environment and palaeo-climatic studies as well as for many industrial applications (cement industry, making plaster of Paris, nitrogen chalk, sheets, tiles, etc.,). Exploration of gypsum deposits, and estimating its concentration for an accurate evaluation of the environmental processes is essential since gypsum is strongly coupled with the biological sulphur cycle (Eckardt et al., 2001), and related to the hydrological conditions such as groundwater level, and geomorphology of a region (Shaw & Bryant, 2011). ...
Evaporites like calcrete and gypsum are found largely in arid regions in association with playas, palaeochannels, and different source rocks. Identification and precise mapping of these minerals is important for the economy. The present study aims to identify and map the spatial distribution of gypsum in the Bikaner district (an arid region in western Rajasthan, Bharat) based on the analysis of distinct spectral responses. Recently high spectral resolution and atmospherically corrected PRISMA data were used in this study. During the initial processing of the data, bad bands were spectrally subset after a detailed visual inspection. Also, a minimum noise fraction was performed to remove noise as well as to reduce the dimensionality of the data as per the analysis of eigenvalues. Then, the distribution map of gypsum was generated using the application of Spectral Angle Mapper after matching the spectra obtained from the spectral library and image. The results were validated through a detailed field investigation as well as from lab-based analysis like X-ray Diffraction. Moreover, we have delineated a course of a palaeochannel based on the interpretation of ALOS PALSAR, Sentinel-2A, and their fused images using two different fusion algorithms such as Gram Schmidt and Intensity Hue and Saturation. Our analysis revealed that the gypsum deposits are mostly situated along the identified palaeochannel and with lithology such as fine aeolian sand and calcrete (Kankar).
... The Namib Desert is one of the oldest deserts in the world, estimated to have been hyper-arid for the last 5 million years (4), and is characterized by the presence of numerous playas (3). Although salt pans occupy less than 5% of the central Namib Desert gravel plains, they are a major water source for the desert fauna and play an important role in the Namib Desert's geomorphology via gypsum (CaSO 4 × 2 H 20) deposition and landscape erosion through salt weathering (3,5,6). Furthermore, they produce some of the most saline inland waters in southern Africa, with measured salinities reaching up to 160 g of the total dissolved solids per liter (values > 3 g/L are considered saline water) (5,7). ...
... Consequently, in order to investigate the taxonomic composition and functional potentials of microbial and viral communities in desert playa microbial mats and associated salt crusts (i.e., halites), we investigated 10 shotgun metagenomes from two central Namib Desert playas belonging to two different saline spring clusters (3,6,7). We noted that the microbial and viral mat communities from both distant salt pans were highly similar in their taxonomic distribution and functional potential. ...
... Thus, the similarities in the geological and physicochemical composition of the Hosabes and Eisfeld playas (6, 7, 13) may explain the taxonomic and functional resemblance of both stream mat microbiomes. The groundwater system ensures the presence of water all year round and could potentially contribute to the distribution of ions and possibly microorganisms across salt pans (6,39). ...
Salt pans or playas, which are saline-rich springs surrounded by halite evaporates in arid environments, have played an essential role in landscape erosion during the formation of the Namib Desert and are numerous in its central region. In this study, we used shotgun metagenomics to investigate the phylogenetic and functional capacities of the microbial communities from two salt pans (namely, Eisefeld and Hosabes) located in central Namib Desert, located in Southwest Africa. We studied the source and sink sediment mat communities of the saline streams, as well as those from two halites (crystallized structures on the stream margins). The microbial assemblages and potential functions were distinct in both niches. Independently from their localization (Eisfeld vs Hosabes and source vs sink), the sediment mat communities were dominated by members of the Alpha- and Gamma-proteobacteria classes, while halites were Archaea dominated and also contained high abundances of the extremely halophilic bacterium Salinibacter sp. (phylum Bacteroidota ). Photoheterotrophy and chemoheterotrophy were the principal lifestyles in both niches, with halite communities having a reduced diversity of metabolic pathways. Intense microbial-virus interactions in both niches were implied by the widespread detection of CRISPR-Cas defense systems. We identified a putatively novel clade of type II CRISPR-Cas systems, as well as novel candidate viral lineages of the class Caudoviricetes and of Halobacteriales - infecting haloviruses. Putative gene transfer agent-like sequences within the Alphaproteobacteria were identified in the sediment mat communities. These horizontal gene transfer elements have the potential to drive genome plasticity and evolution of the Alphaproteobacteria in the Namib Desert salt pan microbiomes.
IMPORTANCE
The hyperarid Namib Desert is one of the oldest deserts on Earth. It contains multiple clusters of playas which are saline-rich springs surrounded by halite evaporites. Playas are of great ecological importance, and their indigenous (poly)extremophilic microorganisms are potentially involved in the precipitation of minerals such as carbonates and sulfates and have been of great biotechnological importance. While there has been a considerable amount of microbial ecology research performed on various Namib Desert edaphic microbiomes, little is known about the microbial communities inhabiting its multiple playas. In this work, we provide a comprehensive taxonomic and functional potential characterization of the microbial, including viral, communities of sediment mats and halites from two distant salt pans of the Namib Desert, contributing toward a better understanding of the ecology of this biome.
... The Kuiseb River flows, on average, for only 16 days each year, with water reaching the Atlantic ocean only on rare occasions [38]. It is likely that much of the rainfall evaporates before reaching the Kuiseb and there are a few small active playas, such as Tsondab Vlei and Zebra Pan [39]. Nevertheless, the palaeochannels are charged with groundwater, as is amply evidenced by drilling [30,33,40]. ...
... Evaporation is clearly an important process in the formation of Australian surficial uranium deposits, which typically occur in active salt lakes [2,46]. While there are some minor salt pans in the Erongo district [39,47], these do not have any spatial association with uranium deposits. Palaeo-evaporitic facies occur within the Tsondab Sandstone, but the tentative stratigraphic correlation of the palaeochannel filled with younger rocks would indicate that these evaporites predate the formation of the palaeochannel fill. ...
Surficial deposits in Namibia's Erongo district contain substantial but low-grade resources of uranium and vanadium (nearly 500 Mlb U 3 O 8), hosted in palaeochannels. This review attempts to develop a mineral systems model for the deposit type, but it is emphasised that research into this important class of deposit has been minimal since the nineteen eighties, largely as a result of a limited investment in uranium exploration. The deposits are the result of groundwater movement in aquifers developed within Cenozoic palaeochannels. The source of uranium was probably granitic rocks traversed by these palaeodrainages, particularly black-quartz rich pegmatites similar to those that make up the hard-rock alaskite deposits of the region. Transport of uranium is generally assumed to have occurred in aqueous uranium species after palaeochannels became filled with sediment. U-enriched clasts within the palaeochannels have yet to be investigated as a local source of uranium. The localised deposition of uranium occurred after regionally extensive carbonate cementation of the palaeochannel sediments, which was the result of climate change (aridification). Pre-uranium calcite may have acted as a chemical buffer (pH) and probably influenced palaeochannel hydrology, restricting groundwater flow to the deeper portions. Uranium is paragenetically related to Mg clays and dolomite, suggesting that the groundwater evolved to a more Mg-rich composition during uranium deposition, probably as a result of more extreme evaporation. The controls on the localisation of mineralisation remain unclear and unpredictable, as are the controls on uranium grade-the fundamental determinant of economic viability. There are few absolute age determinations for any of the deposits, but none occur in rocks likely to be older than the Miocene. This reflects low preservation potential. For example, the Langer Heinrich deposit is incised by active drainage with attendant erosion and probable removal of mineralised material.
... The Namib Desert is one of the oldest deserts in the world, estimated to have been hyper-47 arid for the last 5 million years (Ward, 2010), and is characterized by the presence of numerous playas 48 (Eckardt and Drake, 2010). Although salt pans occupy less than 5% of the central Namib Desert gravel 49 plains, they are a major water source for the desert fauna and play an important role in the Namib Desert's 50 geomorphology via gypsum (CaSO 4 *2H 2 0) deposition and landscape erosion through salt weathering (Day 51 and Seely, 2004; Eckardt and Drake, 2010; Eckardt et al., 2001). Furthermore, they produce some of the 52 most saline inland waters in southern Africa, reaching up to 160 g/L (Day, 1993;Day and Seely, 2004). ...
... including salinity, pH and oxygen levels. Globally, microbial diversity decreases with increasing salinity, and In order to investigate the microbial and viral communities in desert saline springs and associated saline 71 niches, we investigated ten shotgun metagenomes from microbial mats and halites obtained from two 72 central Namib Desert playas belonging to two different saline springs clusters (Day, 1993;Eckardt and 73 Drake, 2010; Eckardt et al., 2001). We noted that mat microbial and viral communities from both salt pans 74 ...
... the Namib Deserts (Eckardt et al., 2001). 417 ...
Salt pans or playas, which are saline-rich springs surrounded by halite evaporates in arid environments, have played an essential role in landscape erosion during the formation of the Namib Desert and are numerous in its central region. In this study, we used shotgun metagenomics to investigate the phylogenetic and functional capacities of the microbial communities from two salt pans (namely, Eisefeld and Hosabes) located in the Central Namib Desert, located in Southwest Africa. We studied the source and sink sediment mat communities of the saline streams, as well as those from two halites (crystallized structures on the stream margins). The microbial assemblages and potential functions were distinct in both niches. Independently from their localization (Eisfeld vs Hosabes and source vs sink), the sediment mat communities were dominated by members of the Alpha- and Gamma-proteobacteria classes, while halites were Archaea-dominated and also contained high abundances of the extremely halophilic bacterium Salinibacter sp. (phylum Bacteroidota ). Photoheterotrophy and chemoheterotrophy were the principal lifestyles in both niches, with halite communities having a reduced diversity of metabolic pathways. Intense microbial-virus interactions in both niches were implied by the widespread detection of CRISPR-Cas defense systems. We identified a putatively novel clade of type II CRISPR-Cas systems, as well as novel candidate viral lineages of the class Caudoviricetes and of Halobacteriales - infecting haloviruses. Putative gene transfer agent-like sequences within the Alphaproteobacteria were identified in the sediment mat communities. These horizontal gene transfer elements have the potential to drive genome plasticity and evolution of the Alphaproteobacteria in the Namib Desert salt pan microbiomes.
Importance
The hyperarid Namib Desert is one of the oldest deserts on Earth. It contains multiple clusters of playas which are saline-rich springs surrounded by halite evaporites. Playas are of great ecological importance and their indigenous (poly)extremophilic microorganisms are potentially involved in the precipitation of minerals such as carbonates and sulfates and have been of great biotechnological importance. While there has been a considerable amount of microbial ecology research preformed on various Namib Desert edaphic microbiomes, little is known about the microbial communities inhabiting its multiple playas. In this work, we therefore provide a comprehensive taxonomic and functional potential characterization of the microbial, including viral, communities of sediment mats and halites from two distant Namib Desert, contributing towards a better understanding of the ecology of this biome.
... Sylvinite can form by direct precipitation from depositional saturated brine (Blanc-Valleron, 1990;Lowenstein and Spencer, 1990;Cendón et al., 1998), as pedogenetic potash in a hyper-arid climate (Eckardt and Spiro, 1999;Eckardt et al., 2001;Gindre-Chanu et al., 2016), by syndepositional replacement of carnallite during freshening events (Szatmari et al., 2021), by syn-tectonic recycling of carnallite (El Tabakh et al., 1999;Krupp, 2005;Warren, 2006), by incongruent dissolution of carnallite during burial (called "metamorphic" sylvite) (Rosell Ortiz andOrtí Cabo, 1981-1982;Koeler et al., 1990;Koeler, 1997), during telogenetic flushing of carnallite by downward pervasive under-saturated connate waters (Wardlaw, 1968;Pedley et al., 2016) or by transformation of bischofite by released potassium and magnesiumrich brines (Pedley et al., 2016). ...
The evaporites of the Aptian Loémé Formation occur along the stable structural domain of onshore Congo as horizontally well-stratified depositional halite interbedded with Mg-poor potash minerals including carnallite, bischofite, tachyhydrite and sylvite. Eleven correlative depositional recharge-to-evaporation cycles are composed of suites of organic-prone shale followed by primary halite and carnallite beds, sometimes punctuated by a bischofite-tachyhydrite end-member.
A sedimentological and petrographical analysis performed on cores and thin sections allowed an interpretation of nine facies associations, named as FA1 to FA9, relying upon the occurrence of bands of fluid inclusions, grain-size, dissolution features, detrital sediments, minute inclusions and sedimentary structures. A depositional model reconciles the spatial distribution of primary textures, hydrology, brine saturation and palaeo-depth during a standard regressive evaporation cycle. Shallow burial eo-diagenesis led to compaction-driven dissolution and recrystallization into fine-grained halite and carnallite laminites but poorly affected the overall preservation of primary deposits.
Measurements and profile analysis of bromine trace element concentrations reveal a palaeo-salinity increase of the parent brine for cycle II to base IX caused by a relative brine level fall and a gradual confinement of the salt basin, likely associated with an excess of saline elements inflow from hydrothermal vents. Similar depositional textures and bromine concentration variations are observed in the lower cycles of the Aptian evaporites from the counter-part Sergipe Basin in the northern part of the Brazilian margin, testifying of a progressive brine salinity rise due to a palaeogeographic confinement along the northern segment of the South Atlantic Ocean.
In Congo, the sylvite displays horizontal “pseudo-stratifications” that unconformably overlay the crests of anticlines and propagate along flanks as a sharp-based caprock. The flushing and transformation of depositional carnallite – halite into secondary sylvite – halite is interpreted as having been caused by down-stepping incremental dissolutions sourced by younger pervasive connate to phreatic waters. In Sergipe, the sylvite is interpreted as secondary but further results from syndepositional dissolution of carnallite and tachyhydrite due to a regional North Atlantic Ocean ingression.
... Desert conditions likely established by the mid-Miocene, owing to the establishment of the Benguela upwelling system (Siesser, 1980;Tankard and Rogers, 1978;Ward et al., 1983;Partridge, 1993). The Namib Desert has four main subregions (Goudie and Viles, 2015): the southern 'transitional' Namib, including the wind-eroded • terrain of the Sperrgebeit, and chains of rapidly migrating barchan dunes; the ~34,000 km 2 Namib Sand Sea (NSS) between Lüderitz and • the Kuiseb River (Lancaster, 1989a;; the low gradient surface of the central Namib Plains, • containing fluvially-incised terrain, desert pavement, playas and gypsum crusts (Rust and Wienecke, 1974;Eckardt et al., 2001) and inselbergs, including the Brandberg Massif (Goudie and Eckardt, 1999) and; the northern Namib and Skeleton Coast, containing the • Kaokoveld highlands, loess deposits (Brunotte et al., 2009) and a coastal dunefield (Lancaster, 1982). ...
The Namib Desert and the Kalahari constitute the drylands of southern Africa, with the current relatively humid portions of the latter having experienced periodically drier conditions during the Late Quaternary. This study explores the range of dryland archives and proxies available for the past ~190 ka. These include classic dryland geomorphological proxies, such as sand dunes, as well as water-lain sediments within former lakes and ephemeral fluvial systems, lake shorelines, sand ramps, water-lain calcrete and tufa sediments at the interface of surface hydrological and hydrogeological, speleothems and groundwater hydrogeological records, and hyrax middens. Palaeoenvironmental evidence can also be contained within geoarchaeological archives in caves, overhangs and rockshelters. This integration of records is undertaken with the aim of identifying a (or a number of) terrestrial regional chronostratigraphic framework(s) for this time period within southern Africa, because this is missing from the Quaternary stratigraphy lexicon. Owing to a lack of long, near-continuous terrestrial sequences in these drylands, the correspondence between nearby terrestrial records are explored as a basis for parasequences to build this chronostratigraphy. Recognising the modern climatological diversity across the subcontinent, four broad spatial subdivisions are used to explore potential sub-regional parasequences, which capture current climatic gradients, including the hyper-arid west coast and the decrease in aridity from the southwest Kalahari toward the north and east. These are the Namib Desert, the northern Kalahari, the southern Kalahari and the eastern fringes of the southern Kalahari. Terrestrial chronostratigraphies must start from premise that climate-driven environmental shifts may have occurred independently to those in other terrestrial locations and may be diachronous compared to the marine oxygen isotope stratigraphy (MIS), which serves as a global-scale master climatostratigraphy relating to global ice volume. The fragmented nature of preserved evidence means that we are still some way from producing unambiguous parasequences. There is however, a rich record to consider, compile and compare, within which seven broad wetter intervals are identified, with breaks between these inferred to be relatively drier, and some also have proxy evidence for drying. The onset and cessation of these wetter intervals does not align with MIS: they occur with greater frequency, but not with regular periodicity. Precession-paced insolation forcing is often invoked as a key control on southern African climate, but this does not explain the pacing of all of the identified events. Overall, the pattern is complex with some corresponding wetter intervals across space and others with opposing west-east trends. The evidence for drying over the past 10 ka is pronounced in the west (Namib Desert), with ephemerally wet conditions in the south (southern Kalahari). The patterns identified here provide a framework to be scrutinised and to inspire refinements to proposed terrestrial chronostratigraphies for southern Africa. Considering changes across this large geographic area also highlights the complexity in environmental responses across space as we continue to test a range of hypotheses about the nature of climatic forcing in this region.
... The Namib Desert salt playas are unique environments with salinities in the range of 3-15% depending on the sampling depth, evaporation rate as a consequence of the time of the day, and the distance from the source [15][16][17][18]. The Eisfeld site explored here has a salinity range of 4.5-8.6% ...
Recent years have seen the classification and reclassification of many viruses related to the model enterobacterial phage P2. Here, we report the identification of a prophage (Smhb1) that infects Salinivibrio kushneri BNH isolated from a Namib Desert salt pan (playa). Analysis of the genome revealed that it showed the greatest similarity to P2-like phages that infect Vibrio species and showed no relation to any of the previously described Salinivibrio-infecting phages. Despite being distantly related to these Vibrio infecting phages and sharing the same modular gene arrangement as seen in most P2-like viruses, the nucleotide identity to its closest relatives suggest that, for now, Smhb1 is the lone member of the Peduovirus genus Playavirus. Although host range testing was not extensive and no secondary host could be identified for Smhb1, genomic evidence suggests that the phage is capable of infecting other Salinivibrio species, including Salinivibrio proteolyticus DV isolated from the same playa. Taken together, the analysis presented here demonstrates how adaptable the P2 phage model can be.
... The development of secondary gypsum crusts is especially linked to the upward movement of groundwater inside the sediment profile due to evaporation. This process, also referred to as "per ascensum", leads to the development of secondary hydromorphic gypsum (ECKARDT et al., 2001). ...
... For instance, the prerequisite for the formation of gypsum (CaSO 4 * 2H 2 O) is the presence of sulphur. Consequently, the course of the geochemical sulphur cycle is vital for the genesis of gypsum (ECKARDT et al., 2001). ...
Surveys by the Universities of Wuerzburg and Berlin, starting in the 1970´s have revealed the existence of palaeolakes in remote areas in Niger. Initial research has shown that the sediments found are suitable for reconstructing its late quaternary palaeoenvironment. Although a high number of investigations focused on the succession of climatological conditions in the Central Sahara, some uncertainties still exist as the results show discontinuities and mostly are of low temporal and spatial resolution. Two expeditions in 2005 and 2006 headed to the northeastern parts of Niger to investigate the known remains of palaeolakes and search some new and undetected ones. Samples were taken at several study sites in order to receive a complete picture of the Late Quaternary environmental settings and to produce high-resolution proxies for palaeoclimate modelling. The most valuable and best-investigated study site is the sebkha of Seggedim, where a core of 15 meters length could be extracted which revealed a composition of high-resolution sections. Stratigraphical, structural and geochemical investigations as well as the analysis of thin sections allow the characterization of different environmental conditions from Early to Mid Holocene. Driven by climate and hydrogeological influence, the water body developed from a water pond of several metres depth within a stable, grass and shrub vegetated landscape, to an alternating freshwater lake in a more dynamic environmental setting. Radiocarbon dates set the beginning of the stage at about 10.6 ka cal BP, with an exceptionally stable regime to 6.6 ka cal BP (at 12.6 metres’ depth), when a major change in the sedimentation regime of the basin is recorded in the core. Increased erosion, likely due to decreased vegetation cover within the basin, led to the siltation/filling of the lake within a few hundred years and the subsequent development of a sebkha/salt pan due to massive evaporation. Due to the lack of dateable material in the upper core section, the termination of the lake stage and the onset of the subsequent sebkha stage cannot be determined precisely but can be narrowed to a period around 6 ka BP. The results obtained from the core are compared with those from terrestrial and lacustrine sediments from outside the depression, situated a few hundred kilometres further to the north. These supplementary study sites are required to validate the information obtained from the coring. Within the plateau landscape of Djado, Mangueni and Tchigai, two depressions and a valley containing lacustrine deposits, were investigated for palaeoenvironmental reconstruction. Depending on modifying local factors, these sediment archives were of shorter existence than IX the lake, but reveal additional information about the landscape dynamics from Early to Mid Holocene. A damming situation within a small tributary at Enneri Achelouma led to lacustrine sedimentation conditions at Early Holocene in the upper reaches of the valley. The remnants of the lacustrine accumulations show distinct changes in the environmental conditions within the small catchment, as the archive immediately responded to local climate-induced changes of precipitation. Radiocarbon dating of the deposited sediments revealed ages from 8780 ± 260 cal a BP to 9480 ± 80 cal a BP. The sites of Yoo Ango and Fabérgé show a completely different sedimentation milieu as they consist of basins within the foothills of the Tchigai. The study sites show increased catchment sizes, probably extending towards the Tchigai massif and are most likely influenced by groundwater charge. The widespread occurrence of wind shaped relicts and the limited amount of lacustrine remnants indicate a generally high aeolian activity in both areas. Only in wind sheltered spots, parts of the lacustrine sequences were preserved, that show ages spanning from Early to Mid Holocene (9440 ± 140 cal a BP – 6810 ±140 cal a BP) and give additional evidence of fires from pre-LGM periods. Although intensively weathered, all profiles indicate distinct changes in the sedimentation conditions by alternating geochemical values and the mineralogical composition. The information obtained from the records investigated in this work confirms the heterogeneity of reconstructed environmental succession in the Central Sahara. The Mid Holocene rapid (within decades) and uniform development from more humid to extremely arid environmental conditions cannot be confirmed for the Central Sahara. In addition, a division of Early and Mid Holocene wet periods cannot be confirmed, either. Actually, the evidences obtained from the palaeoenvironmental reconstructions revealed major variations in the timing and extend of lacustrine and aeolian periods. Evidently, a transitional time has existed between 7 to 5 ka BP where alternating influences prevailed. This is indicated by the varying sedimentation conditions in the Seggedim depression as well as the evidence of soil properties on a fossil dune, with a time of deposition dated to 6200 ± 400 cal a BP and the removal of lacustrine Sediments at the Seeterrassental at Mid Holocene. In respect to provide a complete picture of landscape succession and to avoid misinterpretation, the investigation of several dissimilar spots within a designated study area is prerequisite for further investigations.
... Gypsiferous soils can be found in abundance in wetlands or arid salt pan environments around the world, where information on content and spatial distribution of gypsum is needed for the evaluation of environmental processes, as gypsum is strongly coupled to the biogeochemical sulphur cycle (F. D. Eckardt, Drake, Goudie, White, & Viles, 2001) and relates to hydrological conditions like groundwater level, flow and the geomorphology of the region (Shaw & Bryant, 2011). Information on gypsum can also contribute to facies characterisation (Robert G. Bryant, 1996;Ghrefat & Goodell, 2011;Mees, 1999), as well as mineral exploration efforts (Bharti, Kalimuthu, & Ramakrishnan, 2015;Ferrier & Wadge, 1996). ...
Salt pans also termed playas are common landscape features of hydrologically closed basins in arid and semiarid zones, where evaporation significantly exceeds the local precipitation. The analysis and monitoring of salt pan environments is important for the evaluation of current and future impact of these landscape features. Locally, salt pans have importance for the ecosystem, wildlife and human health, and through dust emissions they influence the climate on regional and global scales. Increasing economic exploitation of these environments in the last years, e.g. by brine extraction for raw materials, as well as climate change severely affect the water, material and energy balance of these systems. Optical remote sensing has the potential to characterise salt pan environments and to increase the understanding of processes in playa basins, as well as to assess wider impacts and feedbacks that exist between climate forcing and human intervention in their regions. Remote sensing techniques can provide information for extensive regions on a high temporal basis compared to traditional field samples and ground observations. Specifically, for salt pans that are often challenging to study because of their large size, remote location, and limited accessibility due to missing infrastructure and ephemeral flooding. Furthermore, the availability of current and upcoming hyperspectral remote sensing data opened the opportunity for the analyses of the complex reflectance signatures that relate to the mineralogical mixtures found in the salt pan sediments. However, these new advances in sensor technology, as well as increased data availability currently have not been fully explored for the study of salt pan environments. The potential of new sensors needs to be assessed and state of the art methods need to be adapted and improved to provide reliable information for in depth analysis of processes and characterisation of the recent condition, as well as to support long-term monitoring and to evaluate environmental impacts of changing climate and anthropogenic activity. This thesis provides an assessment of the capabilities of optical remote sensing for the study of salt pan environments that combines the information of hyperspectral data with the increased temporal coverage of multispectral observations for a more complete understanding of spatial and temporal complexity of salt pan environments using the Omongwa salt pan located in the south-west Kalahari as a test site. In particular, hyperspectral data are used for unmixing of the mineralogical surface composition, spectral feature-based modelling for quantification of main crust components, as well as time-series based classification of multispectral data for the assessment of the long-term dynamic and the analysis of the seasonal process regime. The results show that the surface of the Omongwa pan can be categorized into three major crust types based on diagnostic absorption features and mineralogical ground truth data. The mineralogical crust types can be related to different zones of surface dynamic as well as pan morphology that influences brine flow during the pan inundation and desiccation cycles. Using current hyperspectral imagery, as well as simulated data of upcoming sensors, robust quantification of the gypsum component could be derived. For the test site the results further indicate that the crust dynamic is mainly driven by flooding events in the wet season, but it is also influenced by temperature and aeolian activity in the dry season. Overall, the scientific outcomes show that optical remote sensing can provide a wide range of information helpful for the study of salt pan environments. The thesis also highlights that remote sensing approaches are most relevant, when they are adapted to the specific site conditions and research scenario and that upcoming sensors will increase the potential for mineralogical, sedimentological and geomorphological analysis, and will improve the monitoring capabilities with increased data availability.
... Thus, on the long-term perspective, the east-facing slopes tend to be warmer/ drier, likely promoting the formation of near-surface pedogenic alabastrine gypsum through increased evaporation (e.g. Eckardt et al., 2001;Watson, 1985). ...
Although generally considered to exist under hyperarid conditions over the long term, landscapes in many parts of the Coastal Cordillera of northern Chile have undergone fluvial erosion. Small-scale drainage systems in this mountain range are mostly isolated from river networks and associated processes originating in the Precordillera or the High Andes to the east, thus providing natural laboratories to investigate the interplay between erosion, atmospheric deposition, tectonics and local (micro-) climatic conditions. In this study, we present a set of cosmogenic 10Be and 26Al derived, catchment-wide erosion rates along a short (2.5 km) E-W transect on the northern rim of the Río Loa Canyon in the Coastal Cordillera of northern Chile (latitude 21.4°S). Here, a flat sedimentary gravel surface, which was deposited before the Middle Miocene, becomes increasingly dissected and changes into a badland-like topography to the west. The 10Be erosion rates increase by approximately an order of magnitude from east to west, reflecting (1) localized tectonic movements, (2) geologically recent base level lowering, (3) time-integrated (micro-) climatic gradients and (4) the presence/absence of gypcrete. These findings are corroborated by analysis of geomorphologic parameters, which point towards the presence of two fundamentally different erosional regimes in this small study area. These regimes are sharply delineated along a topographically modest tectonic ridge. To the west, a detachment-limited erosion regime prevails, while in the east a transport-limited regime is dominant. The presence or absence of gypcrete, whose prevalence is governed by (micro-) climatic conditions, generally appears to reflect the respective erosional regimes. The erosion rates we infer point to a long-term process of differential drainage evolution in the study area, likely on timescales of millions of years.
