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GM8.1

Arid to sub-humid regions contribute ca. 40 % to the global land surface and are home of more than 40 % of the world’s population. During prehistoric times many important cultures had developed in these regions. Due to the high sensitivity of dryland areas even to small-scale environmental changes and anthropogenic activities, ongoing geomorphological processes but also the Late Quaternary palaeoenvironmental evolution as recorded in sediment archives are becoming increasingly relevant for geomorphological, palaeoenvironmental and geoarchaeological research. Dryland research is also boosted by methodological advances, and especially by emerging linkages with other climatic and geomorphic systems that allow using dryland areas as indicator-regions of global environmental change.
This session aims to pool contributions from the broad field of earth sciences that deal with geomorphological processes and different types of sediment archives in dryland areas (dunes, loess, slope deposits, fluvial sediments, alluvial fans, lake and playa sediments, desert pavements, soils, paleosols etc.) at different spatial and temporal scales. Besides case studies from individual regions and archives, methodical and conceptual contributions, e.g. dealing with the special role of eolian, fluvial, gravitational and biological processes in dryland environments, their preservation over time in the sedimentary records, and emerging opportunities and limitations to resolve past and current dynamics, are especially welcome in this session.

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Co-organized by CL4/SSP2
Convener: Hans von Suchodoletz | Co-conveners: Markus Fuchs, Joel Roskin, Abi Stone, Lupeng Yu
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| Attendance Fri, 08 May, 10:45–12:30 (CEST)

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Chat time: Friday, 8 May 2020, 10:45–12:30

D1031 |
EGU2020-11978
Eric McDonald, Mark Sweeney, Paul Hanson, and Brad Sion

Vesicular A (Av) horizons, and associated overlying desert (rock) pavement, are ubiquitous features across desert environments.  Extensive research has demonstrated that the Av horizons develop from the incorporation of dust (eolian sediment) during soil development; however, two conflicting models have emerged regarding the age of the Av horizons.  Published luminescence (OSL) ages from Av horizons suggest that Av horizons are Holocene, with reported ages commonly ≤5 ka.  In addition, other studies have suggested Av horizons and desert pavements are Holocene in age because Late Pleistocene environmental conditions (primarily an increase in vegetation cover) largely destroyed desert pavements and Av horizons prior to the Holocene, especially for surfaces above 300-400 m elevation.  In contrast, time-related trends in the morphology of Av horizons suggest that Av horizons and pavements must have existed prior to the Holocene. 

Geochronology and soil morphology from two soil chronosequences formed on alluvial fans in the Mojave Desert (soils ~0.5 ka to ~100 ka, ~900 m above sea level) and in the Sonoran Desert (soils ~0.5 ka to ~250 ka; ~200 m above sea level) indicate that Av horizons existed prior to the Holocene and that the strength of Av development coincides with increasing age of the surface.  In both chronosequences, Av horizon properties of eolian derived silt and clay, development of soil structure, horizon thickness, all systematically increase with surface age on soils with no evidence of past erosion or substantial soil mixing.  Soil morphology and depth profile relations further support that soil profiles are intact with no evidence of erosion or mixing just prior to the Holocene.  OSL dates of Av horizons are considerably younger than soil profiles dated with cosmogenic nuclides and OSL.  Some examples include:  Av: 5ka/soil: 10-12ka; Av: 1-3ka/soil: 16-21ka; Av: 2-6ka/soil: 50-60ka; Av: 1ka/soil: 210 ka.  Mixing of the Av and episodic addition of Holocene dust cannot alone account for age inconsistencies. Recent research using OSL for thermochronology indicates that closure of electron traps occurs between 35o to 50o C.  Measured hourly summer temperatures in Av horizons (Sonoran and Mojave Desert sites) commonly exceed 35 o to 50oC May through September.  We suggest that anomalously young ages for Av horizons may be due to high soil temperatures and degradation of the OSL system.

How to cite: McDonald, E., Sweeney, M., Hanson, P., and Sion, B.: When Did Vesicular Av Horizons Form in the Desert SW U.S.: Elucidating Between Soil Processes and Luminescence Ages, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11978, https://doi.org/10.5194/egusphere-egu2020-11978, 2020

D1032 |
EGU2020-19878
Simon Matthias May, Dirk Hoffmeister, Tobias Ullmann, and Olaf Bubenzer

Recent analysis of spatio-temporal variations of Sentinel-1 InSAR coherences for the entire Atacama Desert have revealed that about 70% of the area show hardly any detectable surface change in an ENSO-affected time series between 2015 and 2018. This validates that geomorphic processes in the central Atacama are of remarkable slowness or even stagnant, as also suggested by the age of surfaces and landforms, i.e. the age of the landscape in general. Most of these surfaces in the central desert are characterized by rather smooth morphologies, which is a result of thick atmospherically derived salt and dust deposits masking the desert surface, supported by the presence of gypsum crusts and/or Biological Soil Crusts (BSCs). In contrast, geomorphic activity on recent time scales is typically linked to episodic Andean discharge or severe precipitation events, which can cause overland flow or flash flood activity even in the hyperarid core of the Atacama as recently shown by the 2015 rainfall event. Likewise, fog-related atmospheric moisture is assumed to provoke salt-driven shrink-swell processes, and episodic activity by slumping and/or seismicity may successively alter landforms in the central desert over longer time scales as well.

Based on Sentinel-1 InSAR coherence data, this contribution presents the spatial pattern of morphodynamic activity in the central Atacama Desert, which is paired with further independent variables achieved by remote sensing such as soil surface indices and geomorphometric parameters (e.g., using TanDEM-X WorldDEMTM, DLR science grant), ultimately characterising the different types of desert surfaces. The satellite-based regional morphodynamic pattern is compared to on-site field evidence collected between 2016 and 2019, which suggests (limited) geomorphic activity rather than stability on late Pleistocene time scales at a variety of locations. Among these locations are flood-affected channel systems and alluvial fans, but also patterned ground structures, zebra stripes, slump- or creep-related slope deposits, or BSC-covered surfaces, which are assumed to support aeolian deposition. Except for the flooding activity, field sites with inferred late Pleistocene to Holocene activity seem to be located in the fog-affected zones of the Coastal Cordillera. Our study shows that the combination of field and remote sensing data may contribute to a better understanding of past and present – particularly rainfall-independent – geomorphic processes in the hyperarid Atacama.

How to cite: May, S. M., Hoffmeister, D., Ullmann, T., and Bubenzer, O.: Geomorphic processes and the stability of surfaces in the central Atacama Desert (Chile) – comparing Sentinel-1 InSAR coherence time series and field evidence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19878, https://doi.org/10.5194/egusphere-egu2020-19878, 2020

D1033 |
EGU2020-19968
Dennis Wolf, Simon Matthias May, Dominik Brill, Dirk Hoffmeister, Benedikt Ritter, Steven Binnie, and Olaf Bubenzer

The hyperarid parts of the Atacama Desert, N Chile, are among the driest places on Earth, and a number of studies have emphasized the remarkable slowness of Earth surface processes since the late Tertiary. Despite episodic overland flow or flash flood activity, salt-driven shrink-swell processes, dust deposition, and seismic shaking have significantly contributed to the formation of the characteristic landscape. The enigmatic and Atacama-specific zebra stripes are contour-parallel, thin lateral bands of rather angular gravels on hillslopes, characterized by grain sorting, a lateral succession of 1-3 m-wide frontal lobes, and specific wavelengths, occurring generally in areas with lowest rainfall and low to no fog occurrence. While previous investigations suggest that zebra stripes represent fossil evidence of overland flow, a recent study challenged their water-related evolution and emphasized the role of seismicity in their formation, and in shaping the Atacama landscape in general. Similar landforms may also be found on Mars, although related processes may be different to those on Earth.

We use UAV-derived orthophotos and digital elevation models, geomorphological surveys and sediment sampling, as well as OSL rock surface dating and cosmogenic nuclide (21Ne, 10Be) analysis of surface clasts to provide new insights into zebra stripe activity and stability in the Atacama Desert. Our investigations show that zebra stripes are found in numerous areas in the hyperarid core of the Atacama, implying a wider distribution of zebra-striped hillslopes than previously suggested. Inter-site comparison illustrates considerable differences between individual zebra stripe sites, and geomorphological characteristics suggest that zebra stripes may be active or inactive forms, depending on their location. Active forms are indicated by well-developed frontal lobes, reduced dust contents, and clearly developed downslope sorting trends with a high percentage of freely floating clasts, whereas inactivity seems to be indicated by poorly visible frontal lobes, high dust contents, poor sorting trends and a high proportion of clasts embedded into the underlying vesicular soil horizon. At the same time, preliminary chronological data based on OSL rock surface dating suggests that active stripes contain clasts with active bleaching fronts at top and bottom sides, pointing to late Pleistocene to Holocene activity and clast overturning. Inactivity, in contrast, is indicated by similar IR50 and pIR225 bleaching curves (equilibrium of bleaching and dosing) in upper clast surfaces and the lack of a bleaching front at the bottom side, pointing to long exposures without clast overturning. Combined with cosmogenic nuclide concentrations, our results allow for inter-site comparisons and a better understanding of (relative) stripe chronologies and activity-stability patterns. Alongside further investigations on the significance of fog, wind, rain and seismicity, future work will aim at constraining time scales on which active/young and inactive/old forms have developed. If these forms are seismicity-related, our study contributes important information on the paleoseismic evolution of the central Atacama.

How to cite: Wolf, D., May, S. M., Brill, D., Hoffmeister, D., Ritter, B., Binnie, S., and Bubenzer, O.: Activity and stability of zebra stripes in the central Atacama Desert based on geomorphological and geochronological evidence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19968, https://doi.org/10.5194/egusphere-egu2020-19968, 2020

D1034 |
EGU2020-862
Joel Roskin, Bernhard Lucke, Kim André Vanselow, Hendrik J. Bruins, Nizar Abu-Jaber, Naomi Porat, and Rupert Bäumler

Pleistocene primary and secondary loess remains cover large parts of the landscape in the Negev in Israel and have been postulated in southern Jordan, but Holocene deposits are absent. We hypothesized that archaeological structures might represent effective dust traps which preserve Holocene dust, and investigated soils developed on archaeological hilltop ruins. These were compared them with local soils, paleosols, geological outcrops, and current dust. Statistically modeled grain size end-members were identified and demonstrate that the ruin soils in both regions consist of mixtures of local and remote sediment sources that differ from dust compositions deposited during current storms. This discrepancy is attributed to fixation processes connected with sediment-fixing agents such as vegetation, biocrusts, and/or clast pavements associated with vesicular layers (similar to desert pavements). It suggests that dust deposition depends not only on supply, but that sedimentation processes play a major role. Precipitation may have contributed to dust accretion, as a snowstorm in the Petra region delivered a significantly higher amount of sediment than rain or dry deposition. Snowfall dust had a unique particle size distribution relatively similar to the ruin soils. Wet deposition and snow might catalyze dust deposition and enhance fixation by fostering vegetation and crust formation, which suggests that more frequent snowfall during the Pleistocene may have been an important mechanism of primary loess deposition in the southern Levant.

How to cite: Roskin, J., Lucke, B., Vanselow, K. A., Bruins, H. J., Abu-Jaber, N., Porat, N., and Bäumler, R.: Environmental Significance of Holocene Dust Accumulation in Archaeological Hilltop Ruins in the Southern Levant, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-862, https://doi.org/10.5194/egusphere-egu2020-862, 2019

D1035 |
EGU2020-4057
Jie Chen

Loess-paleosol sequences in eastern Europe, especially those at the Azov region, are among the sensitive terrestrial archives for past aeolian dynamics identification and paleoclimatic reconstruction within the Quaternary. Grain size analyses of loess sediments are widely used to interpret these transporting mechanisms and paleoclimatic changes, based on granulometric parameters and statistical decomposition methods. It is therefore of growing interest in the Earth Sciences and has been a major focus of sedimentary studies. Here, we present the unmixing grain size distribution results of a loess-paleosol section by jointly applying the standard deviation method and the end-member modeling in the Sea of Azov, Russia. The results indicated that two methods can produce the similar result on grain size decomposition, while the end-member modeling has advantage on quantitative and objective character. In addition, three main loess subpopulations or end-members with mode sizes of 8 μm, 18 μm and 32 μm respectively which represent distinct aerodynamic environments are identified from the grain size distribution in the Azov region. Thereinto, EM1 with mode size of 8 μm is the integrative result of combining atmosphere circulation with other environmental processes. EM2 with mode size of 18 μm is inferred to represent continuous background dust under non-dust storm conditions. EM3 with mode size of 32 μm is fraction that being transported in short-term, low-altitude suspension clouds during dust storm outbreaks. Of the three EMs, EM1 and EM2 have multiple origins due to their complex formation, whereas EM3 are primarily derived from the alluvial plains of different rivers in the Sea of Azov.

How to cite: Chen, J.: Interpretation of sedimentary subpopulations extracted from grain size distributions of loess deposits in the Sea of Azov, Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4057, https://doi.org/10.5194/egusphere-egu2020-4057, 2020

D1036 |
EGU2020-5666
Georg Stauch, Veit Nottebaum, and Frank Lehmkuhl

For this study we analysed OSL (optical stimulated luminescence) ages from aeolian sands or sandy deposits in Mongolia and the north-eastern Tibetan Plateau for the last 21 ka. While the north-eastern Tibetan Plateau is at the northern boundary of the Asian summer monsoon extent, the mid-latitude Westerlies control the climate in Mongolia. Aeolian sediments are widespread in both areas, ranging from thin sand covers with a high silt content in the mountains to large sand sheets with well-developed dune systems in the basins. We collected all available OSL ages, which were published until 2019 and analysed them for their spatial and temporal distribution. The dataset comprises nearly 350 OSL ages. However, while there is a large number of OSL ages available from the north-eastern Tibetan Plateau, only 68 ages from aeolian sediments from central and western Mongolia meet our quality criteria.

There are some remarkable differences in the timing of aeolian sediment deposition between these two areas. While in both areas only few ages from the last glacial maximum are available, aeolian deposition in Mongolia incepts at the beginning of the late glacial at 17 ka. In contrast, permanent aeolian deposition on the north-eastern Tibetan Plateau did not start before 13 ka. We interpret this signal as a time lag between the strengthening of the mid-latitude westerlies and the Asian summer monsoon after the last glacial. An increase in moisture caused by the two atmospheric systems resulted in an enhanced vegetation cover and consequently in the trapping and permanent fixation of aeolian sediments.

Furthermore, during the early Holocene at around 10.5 to 8.5 ka no OSL ages are available from Mongolia while on the monsoon influenced north-eastern Tibetan Plateau a comparably high number of OSL ages point to an enhanced trapping of aeolian sediments. At this stage, a straightforward explanation for the gap in the age distribution in Mongolia is not obvious. It might be caused by the generally wet climate conditions due to enhanced moisture transport to the area due to strong westerlies and thus the diminishing of source areas for aeolian entrainment by denser vegetation covers. The enhanced westerlies would be caused by higher insolation values and are reflected in several archives, especially from northern Mongolia. However, the gap might also just be related to the generally low number of OSL ages from Mongolia.

Both areas show an increase in aeolian activity in the late Holocene, indicating a return to drier conditions after wetter climate conditions in the mid-Holocene. Drier conditions started on the north-eastern Tibetan Plateau at around 3.5 ka and in Mongolia at 2 to 3 ka. This trend is documented in a large number of archives in central Asia and is related to a weakening of the Asian summer monsoon as well as the mid-latitude Westerlies.

How to cite: Stauch, G., Nottebaum, V., and Lehmkuhl, F.: Aeolian sediments as a palaeoclimate proxy in the transition zone between the Asian summer monsoon and the mid-latitude westerlies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5666, https://doi.org/10.5194/egusphere-egu2020-5666, 2020

D1037 |
EGU2020-20199
Christopher-B. Roettig, Thomas Kolb, Christoph Schmidt, Ludwig Zöller, and Dominik Faust

Generally, the Quaternary palaeo dune fields on the Eastern Canary Islands are built up by different dune generations which are seperated by reddish silty layers. The biogenic carbonate sands originate from the shallow marine shelf around the islands and reach the dune fields from northern direction.

On northern Fuerteventura different lava flows were formed during the Late Pleistocene, and gradually interrupted the sand pathways of the dune fields close to the western coast. The sedimentation pattern in these dune fields indicates that this cut off was completed not later than 50 ka. A huge calcium carbonate crust in the outcrops marks the stratigraphic position of that final cut off. This crust was a subject of intensive debates, and was formerly linked to unstable environmental conditions. However, within the dune fields on the neigbouring island Lanzarote we did not find a comparable carbonate crust at the similar stratigraphic position. Instead, the El Jable dune field on northwestern Lanzarote shows a well-resolved dune sequence with intercalated silty layers during that period.

Consequently, the dune fields on the Eastern Canary Islands point to the importance of carbonate sand transport as the main driving force within the sediment system. Finally we can conclude that unimpaired sand pathways are a mandatory prerequisite for the buildup of palaeoclimatic signals in the Quaternary dune archives.

How to cite: Roettig, C.-B., Kolb, T., Schmidt, C., Zöller, L., and Faust, D.: Interpretability of Quaternary palaeo dune fields (Eastern Canary Islands), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20199, https://doi.org/10.5194/egusphere-egu2020-20199, 2020

D1038 |
EGU2020-202
Lotem Robins, Joel Roskin, Lupeng Yu, and Noam Greenbaum

Vegetated Linear Dunes (VLDs) are common in arid environments such as in Australia and southern-Africa. They propagate in a linearly fashion in accordance with strong unidirectional winds. Their elongation and accumulation mechanisms are not well-understood (Telfer, 2011). Here we report on VLD construction based on high-resolution Portable Optically Stimulated Luminescence (POSL), particle-size distribution (PSD), Optically Stimulated Luminescence (OSL) and inorganic carbon content of a rare, exposed and consolidated 8-m high section of a VLD axis, at the margins of the northwestern Negev dunefield, Israel.

The POSL profile results of sand (<300µm) samples (25 cm interval) in the Infra-Red (IR) and Blue (B) spectra display a similar pattern and are differentiated into three statistically distinct clusters, using an unclassified clustering (Mean-Shift) algorithm. Mean values and standard deviation of the B net values (Sanderson & Murphy, 2010) of the three clusters are: 858.1±62 [103], 702.8±39.5 [103] and 552.9±50.7 [103] counts. ANOVA single factor analysis illustrate significant variation between the groups (p.<0.05). These discrete clusters plotted with depth, nicely fit observed stratigraphic units and CaCO3 content, interpreted to represent episodes of sand accumulation. PSD analysis shows a (classic for Negev VLDs) unimodal distribution for sand (peak at 225mm) of the upper unit but a bimodal pattern (peaks at 65-70mm and 200-225mm) for samples of the two lower units. This rare bimodal pattern suggests short-distance fine-grained aeolian contribution from exposed sediments of dune-dammed water bodies that developed around the construction time of the VLD.

OSL ages fit previous studies (Roskin et al., 2011) but could not be discretely differentiated into the three units since both the middle- and upper-units date to the Younger Dryas event. Partial bleaching of some of the samples may have impaired dating accuracies. OSL ages of the lower unit date to the time of the Heinrich 1 event.

The finds, the first of their kind in high-resolution with POSL, demonstrate that VLDs accrete in discrete accumulation phases. The results strengthen the prevailing hypothesis based on lower resolution OSL dating (Roskin et al. 2011, 2014), advocating VLD construction in the Negev by several rapid phases of sand accumulation during periods of high wind power.

  • Telfer, M. W. 2011. Growth by extension, and reworking, of a south-western Kalahari linear dune. Earth Surface Processes and Landforms, 36: 1125-1135.
  • Roskin, J., Tsoar, H., Porat, N., & Blumberg, D. G. 2011. Palaeoclimate interpretations of Late Pleistocene vegetated linear dune mobilization episodes: Evidence from the northwestern Negev dunefield, Israel. Quaternary Science Reviews, 30(23–24), 3364–3380.
  • Roskin, J., Blumberg, D. G., & Katra, I. 2014. Last Millenium development and dynamics of vegetated linear dunes inferred from ground-penetrating radar and optically stimulated luminescence ages. Sedimentology. 61: 1240-1260.
  • Sanderson, D. C. W., & Murphy, S. 2010. Using simple portable OSL measurements and laboratory characterisation to help understand complex and heterogeneous sediment sequences for luminescence dating. Quaternary Geochronology, 5(2–3): 299–305.

How to cite: Robins, L., Roskin, J., Yu, L., and Greenbaum, N.: High-resolution analysis of Vegetated Linear Dune construction - The northwestern Negev dunefield, Israel, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-202, https://doi.org/10.5194/egusphere-egu2020-202, 2019

D1039 |
EGU2020-21453
Lupeng Yu, Noam Greenbaum, and Joel Roskin

Aeolian sediments sensitively respond to climatic changes. Continuous Quaternary loess deposits plays important roles in palaeoclimatic reconstructions. However, application of aeolian sand for such reconstructions is limited by its discontinuous depositional nature. Aeolian-fluvial sediments are widely distributed in arid and semi-arid regions where dunefields interact with watercourses. These palaeoenvironmental archives have been sparsely studied mainly due to their mixed character that requires new interpretation approaches.

We have found that climate fluctuations lead good preservation of aeolian sand deposits that underlay fluvial sediments, making the sedimentary records more continuous. In this study, aeolian and fluvial sediments (elevation of 3400-3500 m a.s.l.) were studied in the eastern margin of Qaidam Basin (QB), northeastern Tibetan Plateau to reconstruct palaeoenvironmental and palaeoclimatic changes since the MIS6, based on sedimentary facies, 120 OSL ages (with age range of 143-1 ka), grain size distribution, MS, TOC, and carbonates.

Within a deeply (10-65 m) incised 1.5-km-long valley, aeolian-fluvial cycles displayed frequent dune-damming of a stream since MIS6. Dune sands were dated to MIS's 6, 5d, 4, 3c, 3a, and the last deglaciation, while fluvial and dune-dammed lake sediments were dated to MIS's 5c, 3c, 3a, and deglaciation.

Large-scale A-F interactions mainly occurred during MIS3 and deglaciation, when the QB dunefields were still mobile after LGM and MIS4 and precipitation started to increase. No ages fall within LGM, suggesting an extremely arid and windy environment in which the dune sand kept reworking and cannot record OSL ages. This further confirms that only with the covering of fluvial sediments, aeolian sand can be well preserved. On the other hand, OSL ages of aeolian sand might only present periods when aeolian activities were not too strong.

During the Holocene, loess-paleosol accumulated in the QB margins, with loess accumulation since 10 ka and development of paleosols during ca. 8.5-3 ka, the Holocene optimum. These results demonstrate that aeolian-fluvial sediments are important palaeoenvironmental records in arid region and indicate that the climate of the eastern QB was mainly controlled by the temperature (solar insolation) and precipitation (Asian Summer Monsoon) changes since MIS6.  

How to cite: Yu, L., Greenbaum, N., and Roskin, J.: Aeolian-fluvial sediments as palaeoenvironmental records in the eastern Qaidam Basin, NE Tibetan Plateau, since MIS6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21453, https://doi.org/10.5194/egusphere-egu2020-21453, 2020

D1040 |
EGU2020-5888
Markus Lothar Fischer, Fabian Sittaro, Claudia Manntschke, Chad Yost, Verena E Foerster, Frank Schäbitz, Christian Schepers, Martin H Trauth, and Annett Junginger

Modern-day southern Ethiopia exhibits a complex mosaic of vegetation types. These types range from desert scrubland along the shores of Lake Turkana, to woodlands and wooded grasslands in the Omo-River-Lowlands and Chew Bahir catchment, and Afromontane forests of the Ethiopian Highlands. Over the past 20 ka, this region has experienced a variable climate, from the dry Last Glacial Maximum (25-18 ka BP) to the wet African Humid Period (15-5 ka BP), and back to present-day dry conditions. These oscillations likely had an impact on the biosphere and its human inhabitants. The biosphere, especially climate-induced changes in vegetation, in turn have a feedback effect on the local climate – and must therefore be considered in climate models and hydro-balance models. However, there are hardly any data on changes in vegetation during the dry-humid-dry transition of the AHP that could be used to parameterize such models.

As a contribution to an enhanced understanding of the role that paleo-vegetation could have played during those transitions, we present here a new comprehensive vegetation model. This study links a Predictive Vegetation Model (PVM) with the available vegetation-proxy records from southern Ethiopia, including a new phytolith record from Chew Bahir. The PVM uses an 18-year averaged time series of the Global Precipitation Measurement as well as SRTM elevation data to predict an 18-year averaged time series of MODIS landcover and vegetation parameters using boosted regression trees. We linked the PVM and resulting surface parameters (moisture availability, surface drag coefficient, albedo) with an existing hydro-balance model of the southern Ethiopian Rift to calculate precipitation during the AHP and hence also model the paleo-vegetation during this period. Available paleo-vegetation data including a new grass phytolith record from the sediments of an 11 m-meter long sediment core from the margin of paleo-Lake Chew Bahir were then used to compare model and proxy results. Being able to validate our new model data with actual vegetation proxy data for the first time enables us to gain valuable insights into the paleo-dimension of the vegetation mosaic of southern Ethiopia, a possible habitat of early Homo sapiens.

How to cite: Fischer, M. L., Sittaro, F., Manntschke, C., Yost, C., Foerster, V. E., Schäbitz, F., Schepers, C., Trauth, M. H., and Junginger, A.: Linking Paleo Vegetation Modelling with a Phytolith Record for the African Humid Period (15 - 5 ka BP) of the Omo-River-Lowlands and the Chew Bahir Basin, southern Ethiopia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5888, https://doi.org/10.5194/egusphere-egu2020-5888, 2020

D1041 |
EGU2020-4054
| Highlight
Steffen Mischke, Zhongping Lai, Galina Faershtein, Naomi Porat, Paul Braun, Johannes Kalbe, and Hanan Ginat

Current conditions in the southern Levant are hyperarid and local communities rely on fossil subsurface water resources. However, the Levantine Corridor provided a pathway for the migration of humans out of Africa and their spread in the Near East and beyond in the Pleistocene, but times of more favourable wetter periods are not well constrained yet. To improve our understanding of past climate and environmental conditions in the deserts of the Near East, two nearby sedimentary sections (9.8 and 16.5 m thick, respectively) from the Central Jordanian Plateau containing a layer of stone tools and production debris were investigated using micropalaeontological analysis and OSL dating. Recorded fossils are mostly ostracod valves of the genera Pseudocandona, Potamocypris and Ilyocypris. Additional remains are shells of aquatic and terrestrial gastropods and charophyte gyrogonites and stem encrustations. The organism remains and mostly silty sediments suggest that a wetland with small streams and ponds existed at the location of Jurf ed Darawish in the past. OSL dating of the sedimentary sequence revealed mostly Late Pleistocene ages of the Marine Isotope Stages 4 and 3. The sedimentary layer containing stone tools and production debris was formed ca. 60 ka ago. In contrast, the base of the section provided only minimum ages of ca. 150 ka. The accumulated data indicate that climate conditions supported human activities on the Central Jordanian Plateau in the middle part of the Late Pleistocene.

How to cite: Mischke, S., Lai, Z., Faershtein, G., Porat, N., Braun, P., Kalbe, J., and Ginat, H.: A Late Pleistocene wetland setting in the hyperarid Jurf ed Darawish region in central Jordan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4054, https://doi.org/10.5194/egusphere-egu2020-4054, 2020

D1042 |
EGU2020-5768
Giorgi Kirkitadze, Mikheil Elashvili, Levan Navrozashvili, Mikheil Lobjanidze, Levan Losaberidze, Tiiu Koff, Markus L. Fischer, Anna Skokan, Azra Khosravichenar, and Hans von Suchodoletz

Studying of the interactions between past environmental changes and former human societies delivers key information to understand the future evolution of landscapes under changing environmental conditions and increasing human stress. The combination of these two factors is especially critical for fragile landscapes such as drylands, where even small-scale climatic or anthropogenic factors can have relatively large effects on the landscape dynamics.

Holocene paleoenvironmental changes on the Shiraki Plain, located in Eastern Georgia (South Caucasus), were studied. The selected site is characterized by semiarid climate conditions (annual precipitation <500 mm per year) and an open dry steppic landscape today. Currently the area is devoid of settlements, due to absence of water resources. However, recent archaeological data collected using remote sensing and ground-proven by ongoing archaeological excavations, delivered evidences of an active former human inhabitation of this area mostly during the Late Bronze - Early Iron Ages. Several large, city-type settlements of the given period that were identified on the Shiraki Plain suggest the existence of early state formation under favorable environmental conditions.

During the conducted study we have combined stratigraphical-sedimentological investigations of sediments using drilling cores, trenches and laboratory analyses with high-resolution D-GPS measurements in the RTK mode, remote sensing using drone photogrammetric surveys, paleoecological investigations, and hydrological modeling. Our initial results clearly support the hypothesis of a large shallow lake in the center of the Shiraki Plain that was surrounded by the Late Bronze and Early Iron Age settlements. Therefore, the regional water balance of that period was obviously more positive than today. Furthermore, our investigations indicate that this period of high settlement intensity was characterized by intensive soil erosion processes that washed away the dominant Chernozem soils.

Altogether, our investigations suggest a tipping point of the landscape evolution dynamics that must have been crossed during the Late Bronze and Early Iron period, leading to the current dry steppic landscape. This also provides key information to reconstruct the archaeological past of the region, and to address the main question of rapid depopulation and further abandonment of this area.

How to cite: Kirkitadze, G., Elashvili, M., Navrozashvili, L., Lobjanidze, M., Losaberidze, L., Koff, T., Fischer, M. L., Skokan, A., Khosravichenar, A., and von Suchodoletz, H.: Reconstructing the Holocene paleoenvironment of the semi-arid Shiraki Plain of eastern Georgia – a center of settlement activity during the Late Bronze and Early Iron age, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5768, https://doi.org/10.5194/egusphere-egu2020-5768, 2020

D1043 |
EGU2020-11131
Tony Reimann, Mike van Meer, and Hans von Suchodoletz

Chernozems are among the most productive soils in the world, as they unite several favorable factors such as high fertility, favorable pH, a granular structure and high moisture retention capacity. Because of that they are typically characterized by a high agrarian value and often provide long records of intensive human land-use that reach back several millennia. However, despite their high relevance for soil sciences and geoarchaeology, many important aspects regarding chernozem formation – e.g. the question whether natural or human factors were more important - are still poorly understood (Eckmeier et al., 2007). One important drawback in this context is the lack of powerful methods to get grip on timing and rates of chernozem evolution.

Recently it has been suggested that the nexus of soil mixing and soil evolution can be clarified through single-grain luminescence analyses (Reimann et al., 2017). In this study we apply the suggested protocol for the first time to two chernozem profiles in Central Germany that were buried by the Late Bronze Age burial mound Bornhöck ca. 3.8 ka ago. Our goals are (i) to test the newly developed luminescence methodology, and if successful, (ii) to date the start of chernozem formation and degradation and (iii) to quantify soil formation rates through time.

First results suggest that chernozem formation of the two profiles started most likely in the early Holocene and ceased between ca. 5.5 and 5.0 ka ago. Furthermore, our data demonstrate that chernozem formation was characterized by very intensive vertical soil mixing, most likely related to intensive bioturbation. In a next step we will calculate corresponding biological soil mixing rates to further detail chernozem evolution. Already at this stage of research, however, we can confidently conclude that we are able to trace key processes of chernozem formation through the analyses of single-grain luminescence data.

 

References:

- Eckmeier, E., Gerlach, R., Gehrt, E. & Schmidt, M.W.I.  (2007). Pedogenesis of Chernozems in Central Europe - A review. Geoderma 139, 288-299.

- Reimann, T., Román-Sánchez, A., Vanwalleghem, T. & Wallinga, J. (2017). Getting a grip on soil reworking–Single-grain feldspar luminescence as a novel tool to quantify soil reworking rates. Quaternary Geochronology 42, 1-14.

 

How to cite: Reimann, T., van Meer, M., and von Suchodoletz, H.: Bringing light into the darkness  – Chernozem evolution in Central Germany clarified by single-grain luminescence data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11131, https://doi.org/10.5194/egusphere-egu2020-11131, 2020

How to cite: Reimann, T., van Meer, M., and von Suchodoletz, H.: Bringing light into the darkness  – Chernozem evolution in Central Germany clarified by single-grain luminescence data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11131, https://doi.org/10.5194/egusphere-egu2020-11131, 2020

How to cite: Reimann, T., van Meer, M., and von Suchodoletz, H.: Bringing light into the darkness  – Chernozem evolution in Central Germany clarified by single-grain luminescence data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11131, https://doi.org/10.5194/egusphere-egu2020-11131, 2020

D1044 |
EGU2020-22482
Hicham Elbelrhiti, Joel Roskin, Revital Bookman, and Jamal Oubbih

The geology and geomorphology of Moroccan Atlantic Sahara are dominated by a tabular coastal platform at altitudes of 30-35 m and a Hamada carbonate tableland with altitudes between 200 to 250 m. The coastal platform is marked by the presence of many depressions like sabkhas, lagoons while 2nd-order depressions (dayas) locally known as Grara dominate the tableands. The studied region is situated in the Saharan bioclimatic level characterized by the scarcity of precipitation.

Khnifiss, the biggest lagoon in the Moroccan Atlantic coast is the most important wetland in the Atlantic Moroccan desert. Former studies focused on sedimentary, hydrology, pollution and ecology of the lagoon, but its soil has not been mapped. Here we map the subaqueous sediment and soils of the submerged area and the soil of its surrounding areas based on remote sensing completed by field work and laboratory analysis. The soil classification system is the French Référentiel Pédologique 2008 (RP 2008). We also present a landscape map, which constitutes the first step toward a soil map, and a regional soil map at the scale of 1:150,000. The soil map shows the dominance of weakly developed soils both in fluvio-marine and aeolian dominated environments.

We also present GIS- mapped shape, morphology, size and land use of about 300 2nd-order depressions in a defined 100 sq km of a carbonate plateau. The mapping identified different types of geomorphic, hydrological and agricultural activity that lead to different types of Graras. The total area occupied by Grara covers only 3.2% of the studied area.

How to cite: Elbelrhiti, H., Roskin, J., Bookman, R., and Oubbih, J.: Soil map of Khnifiss lagoon and GIS mapping of 2nd-order depressions in southwestern Morocco, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22482, https://doi.org/10.5194/egusphere-egu2020-22482, 2020