Arid to sub-humid regions contribute > 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.
vPICO presentations: Fri, 30 Apr
At least 10% of the Earth surface and large areas of the Eurasian continent are covered by aeolian silt and sand deposits. The origin and distribution of these deposits is indicative for the (paleo-) environment and represent an important edaphic factor for eco-zone evolution, which in turn controls past and present land use.
Here we present a conceptual model of loess landscapes in relation to past and present drylands based on the spatial analysis of loess and loess facies' in Europe (Lehmkuhl et al., 2020). Corners of our conceptual 'loess-triangle' represent three eco-zones (nival, humid, and arid environments) peripheral to 'typical' loess formation (placed in the center). The modes of loess formation are controlled by climatic factors, namely water availability and temperature, which also constrain the prevailing vegetation: Mode 1 - Periglacial and tundra loess; Mode 2 - Temperate and subtropical loess; Mode 3 - Desert margin loess. In-between these three peripheral modes of loess facies we illustrate that ‘typical’, continuous and silt dominated loess formation takes place.
At the Chinese Loess Plateau, there is a gradual transition in grain-size from the humid regions in the south and southeast to the semi-arid and arid regions in the northwest (from Mode 2 towards typical loess and Mode 3). Reduced vegetation cover at desert margins, along dry riverbeds and lakes leads to increased aeolian deflation facilitating also mid- and long-distance transport of silt-sized particles. The resulting deposits range from silty loess to sandier loess in the direction of increasing aridity towards the deserts in Central Asia and in China. This transition towards the desert margin loess can be found also in eastern and southeastern Europe towards Central Asia, e.g. at the Sea of Azov and the Caspian Lowlands. Furthermore, in northern Mongolia and Siberia periglacial or mountain / tundra loess appears (Mode 1).
The concept also has relevance if used vertically: At higher elevations in semi-arid regions of central-eastern Europe and Asia (e.g. at the eastern margin of the Tibetan Plateau and the western part of the Qilian Shan) humidity controlled forest belts do not contain any loess deposits. However, in the rather high mountains and plateaus of arid Central Asia, mountain loess close to typical loess can be found. The uppermost boundary of loess is periglacial loess (Mode 1), whereas the lowermost parts are desert margin loess (Mode 3). For these regions, there are still debates on the influence of glaciers and deserts on loess formation.
Lehmkuhl et al. (in press). Loess landscapes of Europe – Mapping, geomorphology, and zonal differentiation. Earth-Science Reviews, Doi: https://doi.org/10.1016/j.earscirev.2020.103496
How to cite: Lehmkuhl, F., Hambach, U., Nett, J. J., Schulte, P., Jary, Z., Sprafke, T., Antoine, P., Wacha, L., Zerboni, A., Hošek, J., and Marković, S.: Eurasian drylands and the conceptual model of loess landscapes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8586, https://doi.org/10.5194/egusphere-egu21-8586, 2021.
New insights into Southern Caucasian glacial-interglacial climate conditions inferred from Quaternary gastropod faunas
Dr. Christiane Richter1, Dr. Daniel Wolf1, Dipl.-Biol. Frank Walther2, Dr. Stefan Meng3, Dr. Lilit Sahakyan4, M. Sc. Tilmann Wolpert5, Prof. Dr. Markus Fuchs5, Prof. Dr. Michael Zech1, Prof. Dr. Dominik Faust1
1Dresden University of Technology, Helmholtzstr. 10, 01069 Dresden, Germany
2 University Hamburg, Centrum für Naturkunde, Martin-Luther-Platz 3, 20146 Hamburg, Germany
3 Ernst-Moritz-Arndt-University Greifswald, Friedrich-Ludwig-Jahn-Str. 17a, 17489 Greifswald, Germany
4 National Academy of Sciences of the Republic of Armenia, Baghramyan Ave. 24a, 0019 Yerevan,
5 Justus-Liebig-University Giessen, Senckenbergstr. 1, 35390 Gießen, Germany
We present our latest results from gastropod analyses conducted on loess palaeosol sequences from northeast Armenia (Southern Caucasia) covering at least three glacial-interglacial cycles. The ecostratigraphy shows significant patterns of species composition related to the succession of pedocomplexes and loess, respectively. Pedocomplexes included species that can be associated with highgrass- to forest-steppe biomes, indicating increased humidity for these sections compared to loess layers. In contrast, loess layers that relate to glacial periods are associated with gastropod species of semidesert environments with shrub- and shortgrass-steppes, indicating semiarid to arid conditions. Furthermore, the loess deposits do not show any evidence for cold-adapted gastropod species. Therefore we suggest that average July temperatures in the study area were above 10°C, even during periods of loess deposition. We propose, that the limiting factor for bios during glacial periods was aridity, rather than temperature. In addition, we observe environmental differences between the various glacial times, with our results indicating a trend towards steadily increasing aridity in Southern Caucasia across the Middle to Late Pleistocene.
How to cite: Richter, C.: New insights into Southern Caucasian glacial-interglacial climate conditions inferred from Quaternary gastropod faunas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5284, https://doi.org/10.5194/egusphere-egu21-5284, 2021.
Initial soils covering archaeological ruins in the southern Levant include fine grain size fractions that may stem from aeolian sediments. Thus, ruins could act as effective dust traps which preserved rare Holocene aeolian records. We assessed physical parameters and chemical composition of initial soils covering archaeological ruins in the Negev and southern Jordan, including clay mineralogy and Sr- and Nd-isotopes, which we compared with modern dust from collectors installed close to the sites. A significant contribution from local weathered rocks could be observed in southern Jordan. In the Negev, the contribution of rocks was negligible, probably due to greater rock hardness and abundant biological crusts sealing surfaces. However, loessial paleosols surrounding the sampled archaeological ruins were "recycled" in the Negev. Compared to modern settled dust, archaeological soils in southern Jordan are enriched with various major and trace elements associated with clays and oxide coatings of fine silt particles. This was not due to in-situ weathering, which was found to be minimal. However, site-specific fixation processes may explain variations of dust records at the studied sites. In addition, modern dust samples associated with precipitation, in particular snow, were found associated with higher amounts of major and trace elements. Initial soils covering ruins in the southern Levant therefore suggest that the formation of soils in desert fringes may less be a function of dust supply, but more of dust deposition and fixation processes. There are multiple, local and regional dust sources and dust-generating processes active in drylands, but deep loessial soils form only when dust fixation is effective.
How to cite: Sandler, A. and Lucke, B.: Holocene dust accumulation in the southern Levant: the role of local sources and fixation processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14882, https://doi.org/10.5194/egusphere-egu21-14882, 2021.
Transversal dunes are widespread in many deserts, but the application of these un-stabilized dunes in the palaeoclimate region is limited. Because transversal dunes normally migrate too fast, which means this kind of dune has a low possibility to record long period paleoclimate information. Nevertheless, both model simulations and field observation demonstrate that larger (higher) dunes containing a greater mass of sand have longer turn-over times. If so, there may be particular giant transversal dunes, in which long periods of climate changes are actually preserved and could be used as geoproxy to reconstruct paleoenvironment changes.
The Badain Jaran desert, situated in north-western China, features the tallest dunes (about 480 m) on the earth. More than 50% of the sand sea is covered by transversal dunes with an average height of 200 to 300 m. Here, we investigated two representative mega-dunes in the center of the desert and took 22 OSL samples systematically to try to reconstruct the deposition history of these two mega-dunes. Our result demonstrates that one of the dunes is formed since ~62 ka, with two phases of superposed dunes dated to 26~32 ka and modern time. Another mage-dune started to deposited from 29 ka and climbed by early to middle Holocene superposed-dunes and modern ones. Furthermore, while other active sand seas preserve scarcely aeolian sand deposited during the LGM period (Last Glacial Maximum: 26.5-19.0 ka BP), 11 of our 22 OSL dating results fall into the LGM period, which indicates that mega-dunes in the Badain Jaran desert continue aggradation during LGM. In that case，we speculate there are at least three factors facilitating the mega-dunes in Badain Jaran desert different from other transversal dunes that can preserve LGM sediments. (1) Badain Jaran desert, situated in a relatively subsiding basin, has a favor deposition condition; (2) The desert is close to the aeolian sand provenance area, an alluvial fan stored abundant silt-sand material derived from the southeast Tibet; (3) the shallow buried wet sand in Badain Jaran desert may promote the formation of the mega-dunes and reduce their migration speed, so that extend the turn-over times of the mega-dunes.
How to cite: Shen, Q. and Lai, Z.: The aggradation process of transversal dunes since late-Pleistocene in Badain Jaran Desert, northwest China revealed by OSL dating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15919, https://doi.org/10.5194/egusphere-egu21-15919, 2021.
The distribution, characteristics and formation of mega-dune forms (esp. star dunes) is, compared to smaller dune forms, for example barchans and linear dunes, much more complex and still poorly investigated. Although occurring globally nearly in all sand seas (ergs), due to their location in often remote and hyper-arid environments and their complexity, they are highly underrepresented in recent research. Last methodological research and reviews, apart from regional case studies (e.g. Zhang et al. 2016), were published decades ago (e.g. Lancaster 1989). In consequence, definitions and development theories remain more or less constant over time, describing star dunes of pyramidal shape with three to four arms, of significant size and mostly situated in depositional centers. Recognized by most researcher, their formation seems to be bound to a regional wind system with a high directional variability by concurrent and sufficient sediment availability. However, a modern assessment of the global star dune distribution is missing.
Therefore, we will present first results of an analysis of global star dune occurrence and distribution via freely available and also highly resolute satellite data provided by Google Earth and ESRI base map services in order to summarize their locations, morphometric characteristics as well as their environmental setting and to explore similarities and differences. Overall, an assessment of a global star dune inventory can lead to a more precise morphometric description, definition, and a better comparison of these dune forms and therefore can contribute to a better understanding of their evolution.
Lancaster, N. (1989). Star dunes. Progress in Physical Geography 13, 67-91.
Zhang, W., Qu, J., Tan, L., Jing, Z., Bian, K. and Niu, Q. (2016). Environmental dynamics of a star dune. Geomorphology 273, 28-38.
How to cite: Herzog, M. and Bubenzer, O.: Star dunes: Global distribution, characteristics and formation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8276, https://doi.org/10.5194/egusphere-egu21-8276, 2021.
Dunefield margins are prone to changing domination between aeolian and fluvial systems. Dominating aeolian systems divert or block fluvial systems or/and reduce their erosional forces often leading to amplified sedimentation by a wide range of unique aeolian-fluvial (A-F) sediments. Other arid environments are mainly dominated by eroding ephemeral fluvial systems that usually characterized by sediment degradation.
The late Pleistocene encroachment of vegetated linear dunes into the northwestern Negev desert dunefield (Israel) comprised a distinct period of aeolian domination upon ephemeral drainage systems originating in the loess-clad Central Negev highlands. This study analyzes the sediments, geomorphology and landscape evolution caused by A-F processes along dunefield margins, in particular sediments deposited by dune-dammed water bodies slightly upstream of the dunefield edge and between VLDs, using high-resolution field mapping, relative (portable) and absolute OSL dating, stratigraphy and sedimentological analyses. These sediments have been generally mapped as playa sediments, understood to be deposited in a fluvial-dominated environment.
Six main A-F sediment types were identified and interpreted: (a) Aeolian sand appears to be remnants of fluvial eroded VLD. (b) Fluvial sand originates from dune erosion and deposited nearby. (c) Massive loam to silty-clay loam relates to abrupt changes in the hydraulic parameters (width/depth ratio and water losses through infiltration) which induce sudden change in flow velocity, resulting in unsorted massive deposits of upstream loess and other desert soil bedload. (d) Couplets, similar to the massive loam, contains loess and upstream sediments deposited in a standing water body. (e) Laminated silty-clay-loam units were identified only between VLDs. (f) High-energy fluvial deposits, which contain loam, sand and pebbles, with a clear erosional boundary that mark the upstream edge of A-F sedimentation.
The landscape of the Negev dunefield margins developed since the late Pleistocene by short-term aeolian domination, which gradually changed into fluvial domination during the Holocene. Dune-damming depositions occurred during this transition. First outside the dunefield, then propagated downstream into the dunefield. Fluvial aggradation of A-F sediments resulted in a vast playa-like flats, that following dune-dam breaching underwent incision, let alone in small (~<20 km2) basins.
How to cite: Robins, L., Roskin, J., Yu, L., and Greenbaum, N.: Aeolian-fluvial sediments and landscapes along the northwestern Negev Dunefield (Israel) margins since the late Pleistocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3262, https://doi.org/10.5194/egusphere-egu21-3262, 2021.
Floods rarely occur in hyper-arid deserts and little is known about the magnitude and frequency of sediment delivery from their basins, despite their importance to changes to the landscape as well as to infrastructures and engineering activities. Sediment yield from the Nahal Nehushtan watershed (15.7 km2) located in the Timna Valley in southern Israel, was determined by assessing stratigraphic sections in its 60-year reservoir deposits. Stratigraphic correlation between event couplets allowed quantification of sediment yields representing 13 former flash-flood events. Based on the sediment volume in the reservoir, the 24.6 t km-2 y-1 average sediment yield is the lowest among other studied warm deserts. Among the event layers, five are voluminously small and seven are medium-sized. The thickest layer, deposited by a flash flood caused by a single short rain event, contributed 29% of the total sediment yield. This demonstrates the overarching effect of medium magnitude events on the rate of sediment production in a hyper-arid setting. Based on event reservoir sedimentation from watersheds located in several hyper-arid areas in the Middle East and North America, sediment load increases with drainage area as expected; however, sediment yield does not decrease with drainage area, as was shown for arid environments. Overall, mean annual sediment yield is very low and increases with flood frequency, with considerable variation generated by local characteristics. Our quantitative results together with previous studies of hyper-arid areas, provide complementary evidence of fluvial sediment transport - the main landscape designer in fluvial desert landscapes.
How to cite: Armoza-Zvuloni, R., Shlomi, Y., Abadi, I., Shem-Tov, R., and Laronne, J. B.: Distribution of fluvial sediment yields in hyper-arid areas, exemplified by Nahal Nehushtan, Israel , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7502, https://doi.org/10.5194/egusphere-egu21-7502, 2021.
Fluvial sediments are valuable paleoenvironmental archives of the Quaternary. Since besides environmental factors they are also affected by local tectonics or intrinsic processes, large instead of small catchments should be studied. In drylands covering ca. 45% of the global terrestrial surface large river systems are generally missing, and most river systems are small rivers originating from mountain ranges. Their sediments are potentially interesting paleoenvironmental archives, but are often affected by intensive tectonics. During this study, to obtain a robust regional paleoenvironmental signal a small river system in the southwestern Binaloud Mountains in semi-arid NE Iran was exemplarily studied with a combined approach that encompassed both alluvial fan and catchment. By using geomorphological mapping and numerical dating, fluvial aggradation followed by incision was independently identified in larger areas or in different parts of the river system ca. 95–88 ka, 40 ka, 20 ka, around/after the Pleistocene/Holocene transition and possibly ca. 2.6 ka. These could be linked with regional and over-regional paleoenvironmental data. Furthermore, large boulders on the alluvial fan suggest anthropogenic destabilisation of the catchment during the last decades. Despite strong local tectonics the fluvial dynamics was mostly controlled by paleoenvironmental changes and human activity. This indicates that despite their small size, such river systems form valuable paleoenvironmental archives in drylands where other archive types are largely missing.
How to cite: Khosravichenar, A., Fattahi, M., Amini, H., and von Suchodoletz, H.: The potential of small mountain river systems for paleoenvironmental reconstructions in drylands - An example from the Binaloud Mountains in northeastern Iran, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3438, https://doi.org/10.5194/egusphere-egu21-3438, 2021.
The alluvial/fluvial fan systems of northern Oman act as sensitive geoproxy records of Late Quaternary palaeohydrology and past landscape evolution, offering records of palaeoenvironmental change which cannot be reconstructed from nearby speleothem records alone (Parton et al., 2013). These systems also provide evidence for the important link between the changing abundance of freshwater in the Arabian interior and the dispersal of anatomically modern humans (AMHs) out of Africa (Rosenberg et al., 2012). Limited previous luminescence dating analyses have reported fan activation west of the Hajar during insolation maxima and monsoon intensification throughout the Late Quaternary (Parton et al., 2015). However, there are currently no studies to date which present chronologies for the fan systems to the east of the Hajar Mountains.
We present the first luminescence based chronology for the fan systems to the east of the Hajar Mountains, providing landform scale data on fan behaviour, including spatial-temporal complexity and variability. This facilitates comparison of the temporal response of fans east and west of the mountains, including differential responses to external forcing. Ages will also be compared with regional palaeoenvironmental and palaeoclimatic records, to inform landscape reconstructions in northern Oman during the late Quaternary.
Rosenberg, T.M., Preusser, F., Blechschmidt, I., Fleitmann, D., Jagher, R. and Matter, A., 2012. Late Pleistocene palaeolake in the interior of Oman: a potential key area for the dispersal of anatomically modern humans out‐of‐Africa?. Journal of Quaternary Science, 27(1), pp.13-16.
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 International, 300, 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. Geology, 43(4), pp.295-298.
How to cite: Woor, S., Durcan, J., Parton, A., and Thomas, D.: Luminescence dating Hajar Mountain alluvial fan systems, northern Oman , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2325, https://doi.org/10.5194/egusphere-egu21-2325, 2021.
Active earth-surface processes in desert environments can be well studied by utilizing recent spaceborne remote sensing imagery e.g. from the European Sentinel Missions. Insights on these processes are important to serve as modern analogues for the long-term landscape evolution of drylands and the preservation of paleoenvironmental archives. The multi-sensor fusion of latest earth-observation data, e.g. multispectral optical imagery, Synthetic Aperture Radar (SAR) data and/or digital elevation models (DEM´s), allows to distinguish landforms between very young and active to stable – presumably older – geomorphological units, the co-existence of which is a striking phenomenon in arid environments. Based upon this methodological approach, the current landscape dynamics in the hyper-arid southern Namib Desert are studied in a key area for past, current and future environmental changes in desert environments of the Southern Hemisphere: the Kaukausib catchment.
The Kaukausib catchment, located in-between two major atmospheric circulation patterns with tropical (summer rainfall) and extratropical (winter rainfall) influence, is highly sensitive to changes and interactions of both climate systems. The catchment is bounded by the Great Escarpment and receives no discharge from the higher hinterland. As such, fluvial activity and resulting landforms are related to local precipitation only. Consequently, the landform inventory of this distinct catchment is a unique recorder of recent and past climate dynamics of the Southern African drylands.
Preliminary investigations identified the high sensitivity of the Kaukausib catchment to recent short-term environmental changes. Rare extraordinary rainfall events, exceeding the average annual amount of less than 50 mm, lead to temporary changes in vegetation cover and density. These events seem to occur in a frequency of 6–11 years, at least during the last 30 years. They are mostly associated with atmospheric interaction of the tropical and extratropical circulation patterns in spring and autumn, e.g. in April 2006 with an unusual northward position of a cut-off-low from the temperate climate system in phase with a Temperate Tropical Through from the tropics unusually far south. The spatio-temporal changes of vegetation cover subsequent to these extraordinary rainfalls are studied by analyzing time series of Landsat 5. Vegetation vitality has its maximum three months after the rainfalls, where in some regions a rather dense cover of annual and ephemeral grass occurred (Henselowsky et al. 2019 Z. f. Geomorph https://doi.org/10.1127/zfg_suppl/2019/0552).
In addition, fluvial events following rainfalls in 2020 and 2018 are studied using Sentinel-1 data to identify short-term surface changes, but also to detect presumable stable sediment surfaces. Sporadic fluvial activity in turn is revealed by investigating signal differences in SAR intensity and InSAR coherence before and after fluvial activity. Information on channel activity is interpreted in the context of the morphometric characteristics and first field-investigations in the Anib and Arasab Pan. These pans limit the current runoff of the upper Kaukausib and represent the largest sediment basins of the southern Namib Desert. Therefore, the identification of current surface processes and sediment provenances, identified by spectral indices of optical satellite data, sets the baseline for future in-depth investigation of its sedimentary record and paleoenvironmental changes in the Kaukausib catchment.
How to cite: Henselowsky, F., Ullmann, T., Engel, M., and Bubenzer, O.: Active earth-surface processes following rainfall events in the southern Namib Desert – Insights from the Kaukausib catchment by means of remote sensing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2525, https://doi.org/10.5194/egusphere-egu21-2525, 2021.
The Seymareh landslide is the largest rock slope failure (44 Gm3) ever recorded on the exposed Earth surface. It detached ∼10 ka BP from the northeastern flank of the Kabir-Kuh anticline (Zagros Mts., Iran) originating the natural dam responsible for the formation of a three-lake system (Seymareh, Jaidar, and Balmak lakes, with an area of 259, 46, and 5 km2, respectively). The lake system persisted for ∼3000 yr during the Holocene before its emptying phase due to overflow. A sedimentation rate of 21 mm yr−1 was estimated for the Seymareh lacustrine deposits, which increased during the early stage of lake emptying because of enhanced sediment yield from the lake tributaries.
To reconstruct the climatic and environmental impact on the lake infilling, we reviewed the geomorphology of the basins and combined the results with multi-proxy records from a 30 m thick lacustrine sequence in Seymareh Lake. Major analyses comprise grain size analysis, carbon and oxygen stable isotopes of carbonate-bearing sediments, and X-ray diffraction analysis of clay minerals.
Lake overflowing is largely accepted as the main response to variations in water discharge and sediment supply since the alternation from dry to wet phases enhances sediment mobilization along hillslopes decreasing the accommodation space in the downstream sedimentary basins. In this regard, during the early-middle Holocene, the Seymareh area, as well as the entire Middle East, was affected by short-term climate changes at the millennial-scale, as testified by both paleoecological and archaeological evidence. Indeed, several records from Iranian lakes (i.e., Mirabad, Zeribar, Urmia) well documented the temperature and the moisture conditions of the western Zagros Mountains during the Holocene. During the early Holocene, the precipitation remained low up to 6 ka BP, reaching the driest condition around 8-8.2 ka BP. The impact of this abrupt climate change is evident across West Asia, where the first large villages with domesticated cereals and sheeps disappeared, converting to small hamlets and starting habitat-tracking. As regards the Seymareh area, a more irregular distribution of rainfalls and their increasing seasonality may support rhexistasy conditions, during which the scarce vegetation cover enhances both the hillslope erosion and sedimentation rate in the basins, most likely contributing to the overflow of Seymareh Lake.
How to cite: Delchiaro, M., Iacobucci, G., Troiani, F., Della Seta, M., Ballato, P., and Aldega, L.: Middle Holocene environmental reconstruction and climatic inferences through multi-proxy records from Seymareh lake sediments (Zagros Mts., Iran), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12511, https://doi.org/10.5194/egusphere-egu21-12511, 2021.
Our understanding of climate changes throughout the Holocene is hampered by representativeness in sedimentary archives. Potential production and preservation biases of the markers are identified by comparing these proxies with modern environments. It is important to conduct robust calibrations on each biome. These calibrations use large database dominated by forest samples. The Mongolian plateau is especially characterized by low annual precipitation and continental annual air temperature. The characterization of the climate system of this area is crucial for the understanding of Holocene Monsoon Oscillations. This study focuses on the calibration of proxy-climate relationships for pollen and glycerol dialkyl glycerol tetraethers (GDGTs) by comparing large published Eurasian calibrations with a set of 49 new surface samples (moss polster, soil and mud from temporary dry pond). These calibrations are then cross-validated by an independent dataset of top-core samples and applied to two Late Holocene paleosequences in the Altai mountains and the Qaidam basin. We show that: (1) preserved pollen assemblages are clearly imprinted on the extremities of the ecosystem range but mitigated and unclear on the ecotones; (2) for both proxies, inferred relationships depend on the geographical range covered by the calibration database as well as on the nature of samples; (3) even if local calibrations suffer from reduced amplitude of climatic parameter due to local homogeneity, they better reflect actual climate than the global ones by reducing the limits for saturation impact, (4) a bias in climatic reconstructions is induced by the over-parameterization of the models and (5) paleoclimate values reconstructed here are consistent with Mongolia-China Late Holocene climate trends, and validate the application of local calibrations for both pollen and GDGTs. We encourage the application of this surface calibration method to reconstruct paleoclimate and especially consolidate our understanding of the Holocene climate and environment variations in Arid Central Asia.
How to cite: Dugerdil, L., Joannin, S., Peyron, O., Jouffroy-Bapicot, I., Vannière, B., Bazartseren, B., Unkelbach, J., Behling, H., and Ménot, G.: Mongolian dryland paleoenvironment and paleoclimate issues : calibrations and applicability of GDGT and pollen reconstructions over the Late Holocene., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3390, https://doi.org/10.5194/egusphere-egu21-3390, 2021.
Little is known about the tufa deposits within the volcanic Harrats of western Saudi Arabia. This research aims to characterise the fossil tufa system and examine its utility as a palaeoenvironmental archive. This requires us to understand the conditions under which the tufa was deposited. In particular, to ascertain whether they are cool, freshwater tufa, or geothermal travertine. In this presentation we show the extent of the tufa within the basin, describe the stratigraphy and settings, as well as their composition and petrology, alongside U-Th chronological control for a selection of suitable subsamples
The samples are composed of low-Mg calcium-carbonate and their 87Sr/86Sr composition shows there has been water-rock interaction with the mafic metavolcanic Neoproterzoic bedrock as well as metamorphosed marine carbonates from the Arabian Escarpment at the head of the Wadi Dabsa catchment. Their δ13C composition (-6.3 to -12.9 ‰) is indicative of a meteoric water and soil signature, rather than a geothermal source.
The tufa deposits are widespread within the Wadi Dabsa Basin, with at least three phases of deposition, recorded at the basin surface, within incised wadi channels and in a downstream fan region. In some locations, the size of tufa-cemented fluvial bedload represents very high magnitude events, whilst the lacustrine to paludal facies indicate more quiescent phases of increased moisture availability. The U-Th dating indicates that the basin was wet during interglacial stages (Marine Oxygen Isotope Stags [MIS] 7 and 5) with some indication, given the error ranges on dates from multiple-subsamples, that deposition occurred primarily during interstadials (e.g. MIS 5e, 5c and 5a). The MIS 7 age is from a vug-fill tufa deposits within an extensive tufa cascade, which indicates the cascade itself pre-dates MIS 7.
The major concentration of artefacts (> 3000) in this basin make it one of the richest Palaeolithic assemblages so far recorded in southwest Saudi Arabia (Foulds et al., 2015; Inglis et al., 2019). This site is ~ 6 km from the current coastline, which is inland from the MIS 5e shorelines in this region (Inglis, pers comm), and these sites with freshwater mean it is important to continue to consider coastal sites as corridors with habitable landscapes for hominins.
Foulds, F., A. Shuttleworth, A. Sinclair, A. M. Alsharekh, S. Al Ghamdi, R. H. Inglis, G.N. Bailey (2017) A large handaxe from Wadi Dabsa and early hominin adaptations within the Arabian Peninsula. Antiquity. 91:1421–1434.
Inglis, R. H., Fanning, P. C., Stone, A., Barford, D. N., Sinclair, A., Hsing-Chung, C., Alsharekh, A., Bailey, G. (2019). Palaeolithic artefact deposits at Wadi Dabsa, Saudi Arabia: A multi-scalar geoarchaeological approach to building an interpretive framework. Geoarchaeology 34(3), 272-294.
How to cite: Stone, A., Sahy, D., Inglis, R., Candy, I., Alsharekh, A., and Sinclair, A.: Former humid phases in the southwestern Arabian peninsula: climatic and environmental implications of the tufa record over the last 250 ka from the Harrat Al Birk, Saudi Arabia. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16409, https://doi.org/10.5194/egusphere-egu21-16409, 2021.
Desert research has a bold track record in deciphering the evolution of landforms. While iconic objects such as inselbergs, yardangs, wadis or dune fields have attracted the attention of scientists for decades and inspired them to develop numerous formation concepts, it is the actual processes, which are suggested to govern their formation, that are usually quite hard to survey as they happen in nature. This amiguitity is due to the often unpredictable, event based, rapid yet episodic nature of their occurrence. While dedicated devices for measuring these processes inevitably exist, they are either confronted with a small spatial footprint (point measurement) or temporal discontinuousity (time lapse data), or even both of these drawbacks. As a consequence, important processes like flash floods, bedload agitation, mass movement on hillslopes, thermal weathering, dune migration rate and mechanism, or averaged information about ground moisture change, substrate rheology, and temperature diffusion can be studied as they happen under natural conditions only in exceptional cases.
Here I summarise recent developments from the field of environmental seismology, an emerging discipline that studies the seismic signals emitted by Earth surface processes, with a focus on existing and potential applications to desert environments. I present seismic approaches to detecting, tracking and quantifying flash floods and the sediment they convey, provide an overview of the capabilites of seismology to survey hillslope activity at the catchment scale, and discuss the potential to monitor surface and subsurface activity at the plot scale. The overarching aim of the contribution is to foster a discussion about potential research questions that could be tackled in future joint (i.e., established and seismic sensor) instrumentation projects.
How to cite: Dietze, M.: Listen to a spectre – the potential role of environmental seismology in desert process research, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3350, https://doi.org/10.5194/egusphere-egu21-3350, 2021.
Badland areas are present in all continents, excluding Antarctica, and play a critical role in establishing local erosion and sedimentation rates. The presence of unconsolidated rocks (e.g., marls, sandstone, mudstone etc.) is a major driver controlling the distribution of badlands, which together with other environmental components, such as climate, tectonics, vegetation, and topography, determine their forms and processes. The mutual interaction of controlling factors in badlands areas provides a basis for developing a holistic approach to clarify their distribution patterns. Turkey's geodynamic evolution has led to the emergence of marine sedimentary rocks, pyroclastics, and continental clastics, especially in line with the uplift of the Anatolian Plateau and volcanism during the last 8 Ma.
This study aims to explore the country-scale distribution of badlands and the controlling factors of this badland distribution in Turkey. Remarkably wide badlands landscapes (4494 km2) have been visually inspected using Google Earth ProTM to further digitize and extract geomorphological units by applying high-resolution multispectral images provided by WorldView-4/Maxar Technology and CNES/Airbus. To obtain exact boundaries, we eliminated contiguous flat areas surrounding the identified badlands by using red relief image map (RRIM) mosaics that express surface concavity and convexity combined with topographic slope derived from a digital elevation model of 5-m spatial resolution. Last, to determine the controlling factors of badlands distribution, we have compiled a global data set comprising 1-km resolution layers of mean annual precipitation, temperature and precipitation seasonality, aridity, NDVI, rainfall erosivity factor, elevation, and majority values of regional lithology in sub-catchments units. The enhanced investigation of the complex relationship that expresses the controlling factors of badlands distribution, has been conducted by K-means unsupervised cluster analysis.
Our comprehensive regional analyses exploring the distribution and environmental attributes of major Turkish badlands identified five different groups or clusters of badlands that display spatial coherence with climatic and tectonic settings. We argue that Turkey's climatic and topographic transition zones, varying from Mediterranean climate dominated areas to the more arid Central Anatolian Plateau, and tectonically‑induced topographic barriers play a relevant role in discriminating these groups of badlands. Moreover, the Anatolian diversity of sedimentary rocks, which consists of Neogene and Paleogene continental clastics, volcano clastics & pyroclastics, and lacustrine deposits, makes an essential contribution to the identified, extensive badland distribution.
This study has been produced benefiting from the 2232 International Fellowship for Outstanding Researchers Program of the Scientific and Technological Research Council of Turkey (TUBITAK) through grant 118C329. The financial support received from TUBITAK does not mean that the content of the publication is approved in a scientific sense by TUBITAK.
How to cite: Avcioglu, A., Gorum, T., Akbas, A., Moreno de las Heras, M., and Yetemen, O.: The climatic, topographic and litho-tectonic characteristics of badlands in Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7788, https://doi.org/10.5194/egusphere-egu21-7788, 2021.
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