GM8.1

EDI
Drylands: paleoenvironmental and geomorphic perspectives and challenges

Arid to sub-humid regions are home for >40% of the world’s population, and many prehistoric and historic cultures developed in these regions. Due to the high sensitivity of drylands to small-scale environmental changes and anthropogenic activities, ongoing geomorphological processes but also the Late Quaternary geomorphological and palaeoenvironmental evolution as recorded in sediment archives are becoming increasingly relevant for geological, geomorphological, palaeoenvironmental, palaeoclimatic and geoarchaeological research. Dryland research is constantly boosted by technological methodological advances, and especially by emerging linkages with other climatic and geomorphic systems that allow using dryland areas as indicator-regions of global environmental changes.
This session aims to pool contributions that deal with current and former geomorphological processes and environmental changes, as well as with all types of sediment archives in dryland areas (dunes, loess, slope deposits, fluvial sediments, alluvial fans, lake and playa sediments, desert pavements, soils, palaeosols etc.) at different spatial and temporal scales. Besides case studies from individual regions and archives and review studies, methodical and conceptual contributions are especially welcome in this session, e.g. dealing with the special role of aeolian, fluvial, gravitational and biological processes in dryland environments, sediment preservation, methods to obtain chronological frameworks and process rates, emerging geo-technologies and the role of such processes for current and former societies.

Co-organized by CL1.2/SSP3
Convener: Hans von Suchodoletz | Co-conveners: Markus Fuchs, Joel Roskin, Abi StoneECSECS, Lupeng Yu
Presentations
| Tue, 24 May, 17:00–18:23 (CEST)
 
Room 0.16

Presentations: Tue, 24 May | Room 0.16

Chairperson: Joel Roskin
17:00–17:05
17:05–17:11
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EGU22-3093
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Virtual presentation
Abi Stone, Yijian Zeng, and Martine van der Ploeg

Sand dunes sediments are a commonly used archive for palaeoenvironmental reconstruction, with chronologies for their accumulation rates, and migration rates, used in a large number of palaeoenvironmental reconstructions across global sand-rich drylands. A less common use of sand dunes as an archive is to explore the chemical and isotopic composition of the pore moisture stored within the sand. Sand dunes, constitute the uppermost unit above dryland aquifers, and represent part of the unsaturated (or vadose) zone in terms of hydrogeology. Chloride is a chemical tracer within the vadose zone that is commonly used to understand, and quantify rates of, recharge to the groundwater table, using a chloride mass balance (CMB) approach (e.g. Scanlon et al., 2006). In doing so, any variations in the concentration of pore-moisture chloride between discrete depths in the sand profile can also be used to provide a novel archive for tracking changes in palaeomoisture availability and land-use change (see review in Stone and Edmunds, 2016). This approach is known as a ‘hydrostratigraphy’.

This presentation will explore the utility of the CMB hydrostatigraphy approach for Kalahari linear dunes above the Stampriet Basin, which is a transboundary aquifer within southern Africa. This is a region for which palaeoenvironmental proxies for rainfall are extremely scarce, owing to poor preservation of organic-rich material in this oxygen-rich environment. Three repeat field visits for sampling the dunes (2011, 2013 and 2016) were used in the research design in order to explore the repeatability of this CMB hydrostratigraphy approach at this location. In addition, a transect of dunes, including dunes close to a pan, were sampled. It was hypothesised that those dunes in close proximity to the pan would be unsuitable, owing to the possible presence of Cl-rich evaporites and capillary zone influences on the behaviour of moisture in the sand-rich sediment. The trends in these profiles will be presented, along with attempts to understand the moisture pathway behaviour in these dune sediments.  

 

References

Scanlon, B.R., Mukerhjee, A., Gates, J., Reedy, R., Sinha, A.K., 2010. Groundwater recharge in natural dune systems and agricultural ecosystems in the Thar Desert region, Rajasthan, India. Hydrogeology Journal 18, 959–972.

Stone, A. E. C., Edmunds, W. M. (2016) Unsaturated zone hydrostratigraphies: A novel archive of past climates in dryland continental regions. Earth-Science Reviews 157, 121-144.

How to cite: Stone, A., Zeng, Y., and van der Ploeg, M.: Reconstructing rainfall in sandy drylands of southern Africa: exploring the potential of the chloride mass balance hydrostratigraphy approach in Kalahari sand dunes. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3093, https://doi.org/10.5194/egusphere-egu22-3093, 2022.

17:11–17:17
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EGU22-10249
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ECS
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Virtual presentation
Lucy Mokaya, Revital Bookman, Joel Roskin, Sagi Filin, and Ayelet Koren

High-resolution analysis of late Quaternary aeolianites on the southeastern Mediterranean coast of Israel

Mokaya, B.L.1,2, Roskin, J.2,3, Koren, A.4, Filin, S. 4, Bookman, R1.,

  • Charney School of Marine Sciences, Department of Marine Geosciences, University of Haifa, Israel
  • Geomorphology and Portable Luminescence Laboratory, the Leon Recanati Institute for Maritime Studies (RIMS), University of Haifa, Israel
  • Department of Geography and Environment, Bar-Ilan University, Israel
  • Mapping and Geo-Information Engineering, Technion - Israel Institute of Technology, Israel

 

Aeolianites ridges are petrified sand dunes deposited at low to mid-latitude coasts. The location, structure and lithification properties of aeolianite ridges is generally understood to reflect changes in sea level, strong wind power, fetch parameters, and sediment availability. The Israeli coast has a chain of both submerged and inland aeolianites ridges running parallel to the southeastern Mediterranean coastline. The aeolianites consist of discontinuous accumulations of fine-and cross-bedded Nilotic sands, differentially lithified by carbonate. Red, sandy palaeosoils divide the aeolianite units and represent periods of reduced wind power and stabilization. Previous studies present low-resolution dating and finds are poorly correlated with climatic and environmental events related to deposition or lithification.

This study describes the vertical and lateral evolution of an elongated aeolianite ridge, at first a sand dune that accumulated and lithified along the palaeo Israeli Mediterranean coast during the last glacial period. The main objective is to explore the dune development at single-bed to sand package stages in time and their relation to local environmental conditions and regional climatic trends and possible changes.

The methodology included high-resolution LiDAR scanned enriched by RGB image data of exposed sections, detailed Portable OSL analysis accompanied with OSL dating, and sedimentological characterization. Sedimentological analysis shows that aeolian accumulation occurred as discrete laminae that built-up cross-bedded sediment packages. Beds continuously alternate between loose sand to cemented ones. The loose laminae consist almost entirely of quartz grains, while the lithified laminae are dominated by calcium carbonate cement. Since cementation is parallel to the aeolian accumulation, it is proposed that this incipient lithification may represent a surficial process that occurred while the dune was still active and accumulating. It may represent microbiotic crusts activated by moisture conditions. These can serve as biomarkers for wind power and wetness duration.

POSL measurements have bright blue OSL signals (12-17 million) and very similar depletion and IRSL-OSL ratios that demonstrate sedimentological similarity that is suitable for reliable POSL profiling. POSL profiling revealed a high-resolution and in-order chronostratigraphy. This may suggest that the sand laminations represent specific wind events at a very high seasonal to even diurnal resolution. Lateral POSL results reveal a certain value range and it does not demonstrate evidence for a significant change in depositional age, while the vertical profile demonstrates a linear upwards decrease in count values. The trends also demonstrate that the quartz grains do not possess a saturated OSL signal. Upcoming OSL dating and outcrop image analysis will better constrain the accumulation rates and their possible connection to environmental and climatic drivers. 

How to cite: Mokaya, L., Bookman, R., Roskin, J., Filin, S., and Koren, A.: High-resolution analysis of late Quaternary aeolianites on the southeastern Mediterranean coast of Israel , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10249, https://doi.org/10.5194/egusphere-egu22-10249, 2022.

17:17–17:23
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EGU22-12809
Kathryn Fitzsimmons, Sergey Gromov, and Nicholas Porch

The Western Victorian Volcanic Plains of southeastern Australia is the third largest basalt province in the world. Whilst the climate of this region is presently temperate, it lies east and south of extensive dunefields which were active during more arid phases in the past.

While investigating the timing of fossil deposition at the Spring Creek megafaunal site – a locality initially argued to provide evidence for last glacial survival of extinct invertebrate taxa – we discovered a surprising quantity of sand-sized quartz within the clayey sediments of the deposit. Since quartz sand is not common in the Western Victorian basalt province or within underlying Tertiary marls, we propose this sand to be allochthonous and transported some distance. The quartz sand yields a particularly bright luminescence signal characteristic (although not diagnostic) of aeolian quartz from dune sediments to the west, and dates using single-grain optically stimulated luminescence to just prior to the Last Glacial Maximum.

In this study we investigate the potential for long-distance sand transport to the Spring Creek site on the Western Victorian basalt plains, by means of climate reanalysis and wind regime modelling for the LGM compared with the present-day time slices. We find that LGM wind regimes were dominated by strong, unidirectional westerly air flow at Spring Creek, compared with more variable and weaker wind orientations and velocities in the present day. Our results suggest stronger potential for eastward distal sand transport from the dunefields west of the basalt plains during the LGM. This enhanced wind strength and transport was coeval with enhanced aeolian activity in those dunefields, and with reactivation of sandy palaeoshorelines just to the south of them. Additional modelling of LGM wind vectors compared with aeolian accumulation onto securely dated transverse shoreline dunes of the same age in the Willandra Lakes to the north supports our findings, by indicating an intensification of westerly winds over the southeastern part of the Australian continent just prior to the LGM.

How to cite: Fitzsimmons, K., Gromov, S., and Porch, N.: Long-distance sand transport to the temperate basalt plains of southeastern Australia: implications for atmospheric circulation just prior to the last glacial maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12809, https://doi.org/10.5194/egusphere-egu22-12809, 2022.

17:23–17:29
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EGU22-4344
Joel Roskin, Lotem Robins, Lupeng Yu, and Noam Greenbaum

Here, we review four decades of research on Aeolian-Fluvial (A-F) interactions, in particular, dune-damming impoundments that deposited expanses of playa-like fine-grained sediments in the Sinai-Negev erg. We focus mainly on the erg’s eastern edge, the arid northwestern Negev dunefield (Israel), where wadis flood 1-2 times a winter. The review relates to the mechanisms of formation, timing, morphology, sedimentology, landscape response, relations with prehistoric settlements, palaeoclimate, and methodological approaches.

Vegetated linear dune (VLD) incursion, mainly during the Heinrich 1 and Younger Dryas, indicated by spatially dense but well-spread OSL chronologies, initially dammed and impounded medium-sized (101-102 km2) fluvial systems, usually in a perpendicular angle. The impounded water bodies generated a dunefield margin landscape of widespread, playa-like flats comprised of sequences of A-F sediments. These sequences, usually <7 m thick, found to often lay over eroded dune sand, reveal distinct sedimentological structures such as massive loam and couplets that in some places overlap sand, and fluvial sand associated with adjacent VLD truncation. Couplets, indicative of single dune-dammed impoundment events are usually <dozen, per section, representing several flood seasons within a sequence spanning several thousands of years. This discrepancy may imply that impoundments were seasonally successive for only several years, recording high discharge floods transporting large amounts of fine-grained bedload. More likely, the sequences are incomplete, having gone through depo-erosional cycles.

Despite VLD stabilization at the end of the Younger Dryas, fluvial fine-grained sediments continued to accumulate until the early Holocene due to successions of dune-dammed impoundments, inland of the dunefield margins. This process demonstrates that the reopened fluvial systems gradually propagated downstream. Previously reported anomalic amounts of lithic-dominated concentrations and hearths, usually from the Epipalaeolithic period, appear near and within mapped A-F sediments. Recent OSL chronologies of the A-F deposits and radiocarbon dates of hearths and hearth-like remains, support these and newly found sites, some dating to the Neolithic period. The resultant landscape is a result of unique environmental transitions at a time-window of high up-basin loess availability, from open fluvial domination to aeolian domination (dune-damming) and finally, partial and gradual dune-dam breaching, reopening of the fluvial systems and incision within A-F sediments. The patchy landscape response during this transition is controlled by basin size and its accumulated sediment load, and dune-dam properties. Altogether, the studies reveal a dramatic geomorphic and direct fluvial landscape response to dune incursion during windy late Pleistocene periods where precipitation changes appear to constitute only a minor role.

How to cite: Roskin, J., Robins, L., Yu, L., and Greenbaum, N.: Palaeoclimatic and geomorphic implications of late Quaternary aeolian-fluvial interactions in the northwestern Negev dunefield (Israel) - A review, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4344, https://doi.org/10.5194/egusphere-egu22-4344, 2022.

17:29–17:35
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EGU22-9965
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ECS
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On-site presentation
Guido Pastore, Thomas Baird, Eduardo Garzanti, Alberto Resentini, Abi Stone, Shlomy Vainer, and Pieter Vermeesch

Deserts are virtually the largest exposed sand depository on earth and their interaction with the river network may unveil information of present and past routing systems. Provenance studies of Sahara, Kalahari Deserts intend to apply common petrographic, geochemical and isotopic analysis to propose suggestive sedimentological information of dryland areas.

The mineralogical composition of aeolian dunes and its variability across a sand sea reflect the relative importance of fluvial and aeolian processes and the degree of their interplay. Sand seas largely fed by river systems are typically characterized by partly first-cycle detritus including various amounts of diverse types of rock fragments, feldspars and heavy minerals, generally allowing identification of a single dominant source. The opposite end member is represented by dunefields where sand is dominantly generated in situ from disaggregation of locally exposed rocks with high sand-generation potential (e.g., quartz-rich sandstones) and next reworked and homogenized by winds during several sedimentary cycles. In these cases, sand typically bears a distilled homogenous composition consisting almost exclusively of mostly rounded monocrystalline quartz associated with an extremely poor tHM suite dominated by durable ZTR minerals, as for the Sahara Desert (Pastore et al., 2021).

The Kalahari Basin, which extends over twenty degrees of latitude, is characterized by a pronounced increase in precipitation from the southwest to the subequatorial north and has seen repeated changes in climatic conditions through the recent and less recent past, provides both end-member examples, as well as a series of intermediate situations. Sand mineralogy is rather homogeneously pure quartzose in the north, closer to humid equatorial regions, but presents peculiar feldspar-rich or even lithic-rich compositions at both western and eastern margins of the erg, where detrital modes with more abudant and varied tHM suites indicate largely first-cycle supply from local rivers (Garzanti et al., 2022) . The evidence shows that a better developed fluvial network can interrupt the “recycling factory” of the desert, introducing first cycle eroded sediment deflated from river flanks into the dunes.

The geographic distribution of such contrasting desert types is mainly controlled by precipitation in adjacent highlands fueling fluvial discharge. In hyper-arid tropical deserts dominated by aeolian dynamics, such as the Sahara, river action may be weakened to the point that fluvial supply to the aeolian system becomes insignificant. Fluvial sources are instead readily identified for dunefields accumulated in drylands at the foot of high mountain areas, as in Kalahari flanks or central Asia and Argentina (e.g., Rittner et al., 2016, Garzanti 2020, 2021).

Pastore, G., et al., 2021. Provenance and recycling of Sahara Desert sand. Earth-Science Reviews, 216.

Garzanti, E., et al., 2022. Provenance of Kalahari Sand: Paleoweathering and recycling in a linked fluvial-aeolian system. Earth-Science Reviews, 224.

Rittner, M., et al., 2016. The provenance of Taklamakan desert sand. Earth and Planetary Science Letters, 437.

Garzanti, E.,  et al., 2020. Provenance of Thal Desert sand: Focused erosion in the western Himalayan syntaxis and foreland-basin deposition driven by latest Quaternary climate change. Earth-Science Reviews, 207.

Garzanti, E. et al., 2021. Transcontinental retroarc sediment routing controlled by subduction geometry and climate change (Central and Southern Andes, Argentina). Basin Research, 33.

How to cite: Pastore, G., Baird, T., Garzanti, E., Resentini, A., Stone, A., Vainer, S., and Vermeesch, P.: Fluvial-aeolian interactions and sand provenance in large African Sand Seas (Sahara and Kalahari), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9965, https://doi.org/10.5194/egusphere-egu22-9965, 2022.

17:35–17:41
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EGU22-13303
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ECS
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Virtual presentation
Lotem Robins, Joel Roskin, Lupeng Yu, and Noam Greenbaum

Aeolian-Fluvial (A-F) processes formed vast and flat landscapes during the late-Pleistocene along dunefield margins. A-F research examines the impacts of extrinsic processes of the aeolian and fluvial systems on one another, which formed these unique landscapes. However, the mechanisms and depositions of A-F processes are not fully understood. In this study, a 120 m wide and 7 m high, wadi bank exposure of an A-F sequence reveals the sedimentary units, where the northwestern Negev (Israel) dunefield desert margins interact with the Atadim fluvial system (64 km2). A chrono-stratigraphic analysis by laboratory measurements (Particle size distribution & Total of carbon), relative and absolute luminescence dating (POSL & OSL), radiocarbon and archeological dating, enabled conclusions regarding the depositional mechanisms and environment. Finally, DEM (~12.5 m pixel) and GPS-RTK (0.3 m resolution) were used to assess A-F depositional boundary.

The results demonstrate a unique perseverance of aeolian sand units covered by low-energy fluvial deposits. The sand and dune units illustrate several sand incursions into the fluvial system since the Last Glacial Maximum until the mid-Holocene. We observed  low-energy fluvial deposits, which resulted from these sand incursions: (a) couplets deposited in an ever-emptying waterbody, impounded by a dune-dam. (b) massive fine-grained formation – deposition of suspended sediments in an impounded waterbody, near the damming-dune where the waterbody is the deepest. (c) Fining upwards with fine laminas deposits – embedded between couplet formations, deposited in a low-energy fluvial environment. The fine laminas indicate small tributaries income to the main low-energetic flow.

We demonstrate that in A-F sequences, not only are the aeolian sand units preserved but also they act as palaeo-fluvial archives. The section reflects that late-Pleistocene dune-damming build-up resulted in a lagged fluvial response enabled by a climatic change during the early-Holocene. The combination of stabilized dune-dams within the fluvial systems and high discharge flows with large available sediment supply resulted in vast aggregation of A-F sediments, forming the alluvial plain.

How to cite: Robins, L., Roskin, J., Yu, L., and Greenbaum, N.: Aeolian-Fluvial response to late-Pleistocene dunefield encroachments along the northwestern Negev dunefield margins (Israel), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13303, https://doi.org/10.5194/egusphere-egu22-13303, 2022.

17:41–17:47
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EGU22-13298
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Virtual presentation
Joseph Mason, Taylor McDowell, Tien Vo, Chase Kasmerchak, and Erika Marín-Spiotta

Thick loess of the central Great Plains, USA, preserves a detailed record of Holocene climate change, extremely thick loess accumulated during and just after the last glacial maximum, and a sequence of older loess units and paleosols. This loess sequence is only well-preserved beneath the summits of tablelands, plateau-like landforms with flat to undulating summits and steep gully-dissected marginal slopes. These loess tablelands are also a key setting for preservation of organic carbon in buried soils and for long-term storage of sediment in the form of loess. Even under tableland summits, however, at some sites interbedded or surficial sand aeolian sand interrupts the loess sequence and/or parts of the loess sequence are missing. These are interpreted as the result of downwind/upwind shifts in the boundary between thick loess and the dune fields or bedrock surfaces of sand transport that occur upwind of the loess.

 

We are testing a set of hypotheses on how landscape evolution through aeolian, hillslope, and fluvial processes controls the development and long-term persistence of loess tablelands. Here we focus on three of those hypotheses: 1) closed depressions on tableland summits, produced by aeolian erosion, disconnect runoff on the summits from the drainage network on marginal slopes, enhancing tableland preservation; 2) episodic migration of aeolian sand into the loess region has truncated the loess record locally, but in the long term the sands enhance tableland persistence through effects on infiltration and runoff; and 3) loess tablelands in the region all developed on older bedrock tablelands that were preserved by similar processes including formation of closed depressions and mantles of aeolian sand or fluvial sand and gravel. The first hypothesis is supported by analysis of surface flowpaths and by landscape evolution modeling using the Landlab toolkit (Hobley et al., 2017; Barnhart et al., 2020). The second is tentatively supported by field and lab measurements of the hydraulic properties of aeolian sand, loess, and loess-derived soils in the study area. The third hypothesis is supported in local areas by reconstruction of the underlying surface using subsurface data and outcrops, as well as observations of nearby bedrock tablelands that are not loess covered. Interesting questions arising from these hypotheses include: 1) Is the destruction of tablelands essentially irreversible or can additional loess “smooth out” dissected surfaces? 2) Are all the loess tablelands relatively old (Middle Pleistocene or older) or did some form more recently?

 

Hobley, D. E. J., Adams, J. M., Nudurupati, S. S., Hutton, E. W. H., Gasparini, N. M., Istanbulluoglu, E. and Tucker, G. E., 2017, Creative computing with Landlab: an open-source toolkit for building, coupling, and exploring two-dimensional numerical models of Earth-surface dynamics, Earth Surface Dynamics, 5(1), p 21-46, 10.5194/esurf-5-21-2017.

Barnhart, K. R., Hutton, E. W. H., Tucker, G. E., Gasparini, N. M., Istanbulluoglu, E., Hobley, D. E. J., Lyons, N. J., Mouchene, M., Nudurupati, S. S., Adams, J. M., and Bandaragoda, C., 2020, Short communication: Landlab v2.0: A software package for Earth surface dynamics, Earth Surf. Dynam., 8(2), p 379-397, doi:10.5194/esurf-8-379-2020.

How to cite: Mason, J., McDowell, T., Vo, T., Kasmerchak, C., and Marín-Spiotta, E.: Loess tableland evolution in the Central Great Plains, USA, and implications for preservation potential of the loess record, stored sediment, and buried soil carbon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13298, https://doi.org/10.5194/egusphere-egu22-13298, 2022.

17:47–17:53
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EGU22-9516
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ECS
Sam Woor, Julie Durcan, Sallie Burrough, Ash Parton, and David Thomas

Large (1-50 km), coalescing alluvial fan systems extend eastwards from Hajar Mountain catchments to the Batinah Coast of northern Oman, representing an important environment for both sediment transfer and storage. As sediment stores, these alluvial fans have great potential to act as archives of Quaternary palaeohydrological changes in their mountain catchments. This has been shown by work carried out on interior draining fans west of the Hajar (e.g. Blechschmidt et al., 2009; Parton et al., 2013, 2015), which has highlighted the sensitivity of fan systems to periods of intensified Indian Ocean Summer Monsoon (IOSM) rainfall. However, the timing of fluvial activity and fan aggradation on the east of the Hajar Mountains is currently poorly constrained due to limited quantitative geochronology. This is, in part, due to the difficulty of dating Batinah alluvial sediments using luminescence techniques because of their low quartz abundances (Hoffmann et al., 2015).

This study presents new Mid-Late Pleistocene OSL ages from alluvial sediments exposed by incised channel systems in fan-head trenches in the lower reaches of the catchment and one section near the apex of the Rustaq fan. Ages from the upper fan represent the first dates on unconfined fan deposition from the Batinah Coast. The depositional contexts of ages are important for understanding the nature of fan dynamics over time. However, ages will also be considered in the context of regional palaeoenvironmental records to investigate the role of IOSM variability in landscape evolution on the Batinah Coast.  

References

Blechschmidt, I., Matter, A., Preusser, F. and Rieke-Zapp, D., 2009. Monsoon triggered formation of Quaternary alluvial megafans in the interior of Oman. Geomorphology110(3-4), pp.128-139.

Hoffmann, G., Rupprechter, M., Rahn, M. and Preusser, F., 2015. Fluvio-lacustrine deposits reveal precipitation pattern in SE Arabia during early MIS 3. Quaternary International382, pp.145-153.

Parton, A., Farrant, A.R., Leng, M.J., Schwenninger, J.L., Rose, J.I., Uerpmann, H.P. and Parker, A.G., 2013. An early MIS 3 pluvial phase in Southeast Arabia: climatic and archaeological implications. Quaternary International300, pp.62-74.

Parton, A., Farrant, A.R., Leng, M.J., Telfer, M.W., Groucutt, H.S., Petraglia, M.D. and Parker, A.G., 2015. Alluvial fan records from southeast Arabia reveal multiple windows for human dispersal. Geology43(4), pp.295-298.

How to cite: Woor, S., Durcan, J., Burrough, S., Parton, A., and Thomas, D.: Using OSL dating to constrain the timings of Late Quaternary palaeohydrological activity on the Rustaq alluvial fan system, northern Oman., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9516, https://doi.org/10.5194/egusphere-egu22-9516, 2022.

17:53–17:59
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EGU22-456
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ECS
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Virtual presentation
Kelly Kirsten, Torsten Haberzettl, Tara Edwards, Silindokuhle Mavuso, May Murungi, Loyce Mpangala, and Robyn Pickering

The Kalkkop meteorite impact crater, situated within the semi-arid Nama-Karroo biome, has long been the subject of investigation. Palaeolake deposits were confirmed after three cores were drilled in the 1990s describing the fine-grained, laminated limestone stratigraphy interspersed with an abundance of fossil material. Investigations based on these cores, suggested that during the period of deposition the region experienced alternating wetter and drier climates. However, the environmental reconstruction was based on a limited number of samples over the length of the core (~90 m) and very sparse chronology. Additionally, the core was severely disintegrated due to poor handling and storage post-retrieval. New cores were drilled at Kalkkop crater in early 2019 and are curated in a custom-built cold storage facility at the University of Cape Town. Here we present data from the longer of the two cores, an 89 m long core from the centre of the crater with close to 80% core recovery. Surface palaeolake samples have been dated to the beginning of MIS 7 (~250 ka) using U–Th series, suggesting the lake deposits may cover, at least in part, the glacial termination III, a period rarely documented for southern Africa. Here, we provide preliminary results from the top 20 m based on sediment colour characteristics, XRF, ICP, biogenic silica and CNS analyses. Future research will focus on a more detailed U-Th chronology, annual layer counting and the generation of a detailed age model. The implications of this new palaeoclimate archive presented here, plus its future age model, are significant given the sites close proximity to the rich archaeological record of early modern human behaviour on the adjacent southern Cape coast.

How to cite: Kirsten, K., Haberzettl, T., Edwards, T., Mavuso, S., Murungi, M., Mpangala, L., and Pickering, R.: The Kalkkop Impact Crater, South Africa, an environmental archive for MIS 7 and beyond, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-456, https://doi.org/10.5194/egusphere-egu22-456, 2022.

17:59–18:05
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EGU22-12243
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ECS
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Virtual presentation
Azra Khosravichenar, Mehdi Aalijahan, Saeidreza Moaazeni-Noghondar, Mathias Ulrich, Naser Parvian, Abouzar Sadeghi, and Hans Von.Suchodoletz

Playas are endorheic sediment basins in drylands that are temporally filled with water. During dry seasons, their surfaces are generally covered with a thick crust of clay-rich clastic material and soluble salts. Strong winds can mobilize that fine-grained material, including the salts, from the playa surfaces as aeolian dust that strongly affects the surrounding ecosystems and human livelihood. During recent decades, climate change strongly altered the salinity regimes of many playas, leading to an increase of surface salinity. During this study we investigated the impact of climate change on soil salinity dynamics in the Bajestan Playa, Northeast Iran, over a period of three decades (1992-2021). The studied region is particularly exposed to the "Sistan winds of 120-Days" during the dry season in summer. Therefore, it is one of the main dust source areas in eastern Iran.

In order to better understand and predict the geochemical composition of aeolian dust, it is necessary to monitor and map regional salinization processes. Thus, we applied a multi-disciplinary approach that encompased remote sensing, field-based ground truthing, and climatic data analysis. Remote sensing analysis on Landsat data (first week of July of all studied years) were carried out on three generations of sensors (TM, ETM+, OLI 8) that were uniformly corrected for atmospheric and geometrical conditions. During a field campaign in July 2021, a total number of 130 soil sampleswere collected from the upper 20 cm of soil of areas that represent seven soil salinity classes that were preliminary identified based on multispectral remote sensing analysis and regional geological maps. In addition, the electrical conductivity (EC) was subsequently measured on the soil surface samples in the laboratory. Based on these field measurements and the remote sensing analyzes, we were finally able to derive twelve soil salt indices. Two among all indices (S12 and S13) showed the most satisfactory calibration accuracies between the field and remote sensing-based EC values. Finally, the index SI2 was applied to the Landsat images for temporal and spatial quantitative soil salinity mapping. Furthermore, to validate the impact of climate change on the salinity changes, the Standardized Precipitation Index (SPI) and the Mann-Kendal Index were calculated based on temperature and precipitation data at different time scales of the last 60 years.

How to cite: Khosravichenar, A., Aalijahan, M., Moaazeni-Noghondar, S., Ulrich, M., Parvian, N., Sadeghi, A., and Von.Suchodoletz, H.: Assessing the impact of climate change on three decades of soil salinity dynamics in the Bajestan Playa, Northeast Iran, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12243, https://doi.org/10.5194/egusphere-egu22-12243, 2022.

18:05–18:11
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EGU22-12806
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ECS
Jakub Mares, Tomas Weiss, and Jiri Bruthans

Most of weathering processes are connected to moisture presence and flow that affects salt transport and crystallization. However, knowledge of moisture distribution and capillary flow in areas with cavernous weathering forms is scarce. Honeycombs and tafoni, common cavernous weathering forms, occur on different types of rocks and in different climatic conditions, but in arid environments such as south Jordan, tafoni are clearly actively evolving and abundant in the local sandstones, both on natural outcrops and on ancient carved monuments such as in the historic city of Petra.

The depth of the evaporation front was measured in 3 sites with tafone near Petra in Jordan in November 2018, December 2019 and December 2021 (in a cold and relatively wet period of a year). The first site (A) is a tafone situated 5 m below the sub-horizontal surface allowing infiltration. It is facing to the north.The second site (B) is located at the foot of a 50 m high rock cliff. This tafone is facing to the south.The rock is fractured, so it likely allows faster infiltration.The third site (C) is a tafone situated at the foot of the rock cliff, 15 m below the top, facing to the southeast.

The evaporation front is the boundary within the rock that separates the dry layer usually and the capillary zone, and its depth has a major effect on weathering as salts accumulate and crystallize here. The depth of the evaporation front was measured by the ‘uranine-probe’ method, inside tafoni (6 measuring points) and in visors i.e. the thin rock separating the tafone hollows (5 measurement points). We compared the measured depths of the evaporation front with the period of time since the last precipitation event. In 2018, only 14 days elapsed from the significant 83 mm precipitation event, in 2019 only 33 days elapsed from single 244 mm rain event, while in 2021 there were just 2 mm of rain followed by 316 days of no rain (very dry period).

At the site A, the evaporation front was not detected in any measurement, as it was deeper than 10 cm, meaning that evaporation strongly dominates over inflow from sandstone massive. At the site B, the evaporation front was at nearly constant depth at all visits (the average 75 mm, time oscilation only +-5%).  At the site C, there is the largest fluctuation in the depth of the evaporation front. The greatest depth of the evaporation front (average 52 mm) was measured in 2018. In 2019 the average depth of the evaporation front was 42 mm. In contrast, in 2021, the depth of the evaporation front was only 24 mm below the surface. It is clear from the measured data that the depth of the evaporation front does not correspond to antecedent precipitation. From this we can conclude that water does not respond to individual precipitation events, but changes in water reserves are probably controlled by longer cycles or by evaporation demand, rather than rain.

This research was funded by the Charles University Grant Agency (GAUK - 265421).

How to cite: Mares, J., Weiss, T., and Bruthans, J.: Temporal changes in moisture distribution in sandstones near Petra, Jordan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12806, https://doi.org/10.5194/egusphere-egu22-12806, 2022.

18:11–18:17
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EGU22-6835
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ECS
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Virtual presentation
Ryo sasaki, Haruyuki Fujimaki, and Aki Yanagawa

Desertification has been estimated by various perspectives such as meteorology and geography. Desertification indicates the changing of the vegetation and the ecosystem function. However, the evaluation of the desertified area in terms of ecosystem function is not fully understood. Therefore, we calculated the time series fluctuation of desertification using the ecosystem function index (resistance and resilience). We used MODIS satellite-based Normalized Difference Vegetation Index (NDVI) and short-term Standardized Precipitation Evapotranspiration Index (SPEI) data. Resistance and resilience calculated from NDVI. We estimate desertification by resistance and resilience during drought period. The results show trends of fluctuation of resistance and resilience, which indicates a condition of desert areas.

How to cite: sasaki, R., Fujimaki, H., and Yanagawa, A.: Desertification assessment using ecosystem resistance and resilience in drylands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6835, https://doi.org/10.5194/egusphere-egu22-6835, 2022.

18:17–18:23
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EGU22-10444
György Varga, Fruzsina Gresina, János Kovács, and Zoltán Szalai

The granulometric properties and grain size data of fine-grained clastic sediments have been used in many different ways to make paleoenvironmental interpretations. This is particularly true for the eolian environments of arid regions. However, the modern methods of grain size determination that are increasingly available to many people sometimes mislead researchers and suggest that the results of measurements are infallible.
Here we present findings that are worth considering when using granulometric data. Different chemical pretreatment methods, particle-sizing techniques, and various devices (laser diffraction devices [Fritsch Analysette 22 Microtec Plus, Horiba Partica LA-950 v2 and Malvern Mastersizer 3000], and an automated image analyser [Malvern Morphologi G3-IDSE]) were applied to measure the grain size of aeolian dust deposits and soils and to quantify the effects of different approaches on particle size data. 
(1) Grain: What does it mean grain? Single grain? Aggregated particles? Coated particles? Pretreatment techniques have a significant impact on clumped particles, aggregates, and single grain granulometric parameters. According to our findings, different widely used chemical treatments have substantial and significantly different effects on the results. The purpose of studies determines the required pretreatments (e.g. particles could have been supplied as silt-sized aggregates; then it is not very useful to decompose them to reconstruct past wind flow mechanisms or post-depositional alterations, but from a geotechnical point of view, the situation is different). Our results on particle size modification effects of five widely applied chemical pretreatment procedures demonstrate the importance of pre-measurement handling of samples.
(2) Size: What is the size of an irregularly shaped particle? Mineral particles are not spheres; their size can only be estimated by applying equivalent diameters. Irregular particle shapes also have an effect on sizing. Automated image analysis provides a wide-scale of shape parameters, which can be used as a novel approach for granulometric characterisation, transport mechanism reconstruction and offers an opportunity to develop granulometric alteration indices. 
(3) Measurement: Particle size differences can also result from measurement technique differences. Direct (image analysis) and indirect (laser scattering) measurement techniques require different prior information about the mineral material to be measured. At a starting point of laser scattering measurements, it is assumed that the analysed particles are spherical, and their complex refractive index is known. In fact, due to the shape anisotropy and mineralogical heterogeneity of particles, fulfilling these requirements is impossible in the case of sedimentary samples and soils. However, even similar approaches (e.g. laser scattering devices of different manufacturers) can provide significantly different size results applying the same optical settings. Grain size distributions were calculated using both the Fraunhofer and Mie scattering theories and a wide variety of optical settings. The unknown 3rd-dimensional size (thickness) of mineral particles is the key source of the uncertainties during image analysis. 
Support of the National Research, Development and Innovation Office (Hungary) under contract NKFIH FK138692 is gratefully acknowledged.

How to cite: Varga, G., Gresina, F., Kovács, J., and Szalai, Z.: Three major problems of grain size measurements: (1) grain, (2) size, and (3) measurement, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10444, https://doi.org/10.5194/egusphere-egu22-10444, 2022.