ICG2022-11

ICG2022
Aeolian Geomorphology 

Aeolian processes are related to the wind´s ability to shape the surface of the Earth or other planets. The wind erodes (by the means of deflation or abrasion), transports (in the form of suspension, saltation, or creeping) and deposits material in the surface, as well as sculpts rocks and pre-existing deposits. These processes create shapes of different types, which results in a very specific kind of landscape. Aeolian landforms hold clues to past as well as to present climate because they preserve structures resulting from different wind directions with variable wind intensities. The wind is an effective agent in regions with sparse vegetation, a lack of soil moisture and a large supply of unconsolidated sediments. Therefore, Aeolian features are common in deserts, beaches, and fluvial plains of semi-arid areas on Earth, as well as in other appropriate environments of other planets of the Solar system. Aeolian processes and landforms are studied, analyzed, and mapped from the use of many different tools and equipment, and represent one of the most important branches of geomorphology.

Conveners: Vanda de Claudino-Sales, António Campar, Ana Ramos-Pereira, Amadou Abou Sy, Jorge Trindade, Abdessamad CHARIF
Orals
| Fri, 16 Sep, 09:00–10:30, 14:30–16:30|Room Sala Almedina-C2D
Poster
| Attendance Fri, 16 Sep, 10:30–10:45 | Display Thu, 15 Sep, 09:00–Fri, 16 Sep, 19:00|Poster area

Orals: Fri, 16 Sep | Room Sala Almedina-C2D

Chairpersons: António Campar, Ana Ramos-Pereira, Jorge Trindade
09:00–09:15
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ICG2022-672
Robert Matthew Joeckel, Paul Hanson, and Jesse Korus

We have mapped >200,000 roughly northwest-southeast-oriented ridgelines, >10,000 deflation basins, the outlines of small dune fields, and associated, presumptively aeolian landforms across an area of 660,000 km2 between 39° and 48° N and 93° to 108° W in the USA.  Our study area lies east of the Rocky Mountain front and, effectively, west of the Late Pleistocene limit of Laurentide glaciation. It includes parts of Iowa, Missouri, Kansas, Nebraska excluding the Sand Hills, Colorado, Wyoming, South Dakota, North Dakota, and Montana.  The oriented ridgelines lie within the western periphery of the Central Lowlands in the Dissected Till Plains (where multiple pre-Illinoian ice advances occurred) and across a large part of the Great Plains (including some of the glaciated Coteau Slope in North Dakota). Most of the ridgelines are developed on Cretaceous, Paleogene, and Neogene sedimentary rocks and Pleistocene loesses.  Northwest-southeast-oriented ridgelines are a prominent, and in some cases the dominant component (e.g., on the Pierre Shale in northernmost Nebraska and much of western South Dakota, and on loess in parts of western Iowa and east-central Nebraska) of local to regional landscapes.  Thus, the ridges impart a pronounced geomorphic “grain.”  Oriented ridgelines may be sharp- or broad-crested, straight to slightly sinuous, and they range in length from 0.1 to 15 km.  We interpret the oriented ridgelines on pre-Pleistocene strata to have resulted primarily from aeolian erosion.  Those on loess may have been produced by a combination of erosion and deposition.

Multiple lines of evidence support a hypothesis that the oriented ridgelines were produced chiefly by wind erosion during the Late Pleistocene.  The study area encompasses many Pleistocene–Holocene dune fields, including the largest dune field in the Western Hemisphere (Nebraska Sand Hills). There are also widespread dust deposits, such as the Peoria Loess.  Erosional features, ranging from local ventifacts to widely distributed deflation basins, that have already been identified as aeolian features in the study area.  Moreover, the orientations of deflation-basin axes, the long axes of small dune fields, and other presumptively aeolian features tend to accord with the general trend of the oriented ridgelines, suggesting a commonality in their geomorphic origins.  Additionally, other authors have interpreted MIS/OIS (29–14 ka), at the end of the Pleistocene, as a time of dry, windy, and dusty conditions, during which vegetation cover was reduced at least locally in the interior of North America.

How to cite: Joeckel, R. M., Hanson, P., and Korus, J.: The Grain of the Plains Remains: Widespread Northwest-Southeast Ridgelines and Associated Oriented Landforms, Northern Interior Plains, USA , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-672, https://doi.org/10.5194/icg2022-672, 2022.

09:15–09:30
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ICG2022-538
Federica Vanzani, Alessandro Fontana, Livio Ronchi, Jacopo Boaga, and Irka Hajdas

Continental aeolian dunes are a major feature in many alluvial plains of Central and Western Europe, whereas they are completely unknown in the alluvial environments of northern Italy. Thanks to the analysis of satellite images, aerial photos, Lidar-derived DEMs, Ground Probing Radar (GPR) profiles and field survey we identified a large system of dunes formed in the LGM in NE Italy. The study area is located in the distal portion of the Friulian Plain, between the city of Aquileia and the Grado Lagoon, where a series of small elongated sandy reliefs is present and locally called “dunes of Belvedere – San Marco”. The zone is part of the distal sector of the megafan of Isonzo River and is surrounded by lagoon areas reclaimed since the 19th century. This peculiar geographical position led many scholars to consider them as Holocene coastal dunes.

The investigated landforms cover an area of about 25 km2 and they are mainly elongated in the ENE-WSW direction. The dunes have been largely quarried along history, but the highest crests reach up to 10 m above sea level (asl), in contrast with the surrounding reclaimed coastal plain (-1 m asl). The deposits consist of sands ranging from fine to medium-coarse. Near the dune’s ridges, concretions of cemented sand are abundant and largely exposed by ploughing practices. In outcrops and GPR radargrams the cross sections document an internal structure made of 20-30° inclined foresets, a few centimeters thick. The investigated dunes lay over the LGM alluvial plain forming the distal sector of Isonzo River and their base is radiocarbon dated to about 21 ka cal BP. Considering that vegetation should be scarce during the formation of the dunes, it is likely that they were built between the end of the LGM and the first stadial phases of Late Glacial.

The new data allow to interpret the Belvedere – San Marco reliefs as a system of parabolic dunes consisting of parallel and linear ridges, merging on the lee side in frontal lobes. They currently represent the largest and most complex continental aeolian dunes system in Italian Peninsula. Moreover, the orientation of the dunes is concordant with that of Bora, a katabatic wind which blows in Northern Adriatic from ENE and even today can reach peak velocity of 40 m/s. Similar wind, supported by the North European and Alpine ice caps could blow stronger and more frequently during the onset of deglaciation, when sandy sediment was largely available, supplied by braided channels of Isonzo River.

This discovery underlines the importance of wind-driven processes in the evolution of alluvial plain in northern Italy and suggests the presence of other continental dune systems, also on the seafloor of the Northern Adriatic, which was part of the continental plain until Late Glacial and was then submerged by sea-level rise.

How to cite: Vanzani, F., Fontana, A., Ronchi, L., Boaga, J., and Hajdas, I.: The Sandy Hills Of Belvedere – San Marco of Aquileia: The Largest System of LGM Continental Dunes In Northern Italy, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-538, https://doi.org/10.5194/icg2022-538, 2022.

09:30–09:45
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ICG2022-448
Michał Łopuch, Zdzisław Jary, Robert Sokołowski, Piotr Moska, Paweł Zieliński, Jacek Skurzyński, Marcin Krawczyk, Jerzy Raczyk, Przemysław Mroczek, Grzegorz Poręba, Agnieszka Szymak, and Konrad Tudyka

The age of aeolian deposits and duration of conditions favorable for aeolian processes within the European Sand Belt (ESB) are still debated. Nowadays combined 14C and OSL data are proper tools to establish the chronology of ESB dunes. However, both methods have significant limitations. They can be used only in existing outcrops limiting spatial coverage of results and making them not reliable for whole dune fields. The second issue is that the oldest dune sediments can be already reworked during dune migration. Finally, the measurement error of OSL data is too high to determine the constructional time of dune fields. To overcome these limitations, we used LiDAR data to examine the pattern properties of 31 dune fields located within the central part of ESB. Dune field pattern is recognized as a self-organizing system, where pattern evolution is a function of constructional time. This is reflected by increasing dune spacing and crest length, a decrease in defect density, and an overall reduction in the statistical variance of these parameters as the pattern matures. Curves describing the relationship between these parameters and constructional time were already established.

Results of the pattern analyses show that studied dune fields represent a wide range of spatial patterns, from irregular parabolic dune fields through a variety of transitional types to well-developed and regular patterns of large transverse dunes. The study confirms that periglacial dune fields undergo the same self-organization of pattern as dune fields located in hot and temperate areas. Regardless of the specific periglacial conditions, the temporal relationship between crest length, spacing, and defect density is preserved. Calculated constructional time for dune fields ranges between 1.2-4.2 ka for defect density, 0.3-5.9 ka for crest length, and 2.2-6.8 ka for spacing, indicating high spatial and temporal variability in the development of dune fields and a lack of zonation regarding to ice-sheet retreat. The coexistence of a few dune fields characterized by different degrees of pattern maturity in close vicinity suggests that the evolution of these dune fields was individual for each site and driven mainly by local events leading to the release of sand, such as subsequent incision of rivers, lowering of groundwater table, forest fires or human-induced deforestation. 

Presented results were obtained with the support of Polish National Science Centre, contracts number 2018/30/E/ST10/00616 and 2021/41/N/ST10/00350.

How to cite: Łopuch, M., Jary, Z., Sokołowski, R., Moska, P., Zieliński, P., Skurzyński, J., Krawczyk, M., Raczyk, J., Mroczek, P., Poręba, G., Szymak, A., and Tudyka, K.: The development of the periglacial dune fields within the central part of the European Sand Belt – insights from the pattern analysis, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-448, https://doi.org/10.5194/icg2022-448, 2022.

09:45–10:00
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ICG2022-279
Xiaodong Miao, Chongyi Ee, Shujian Xu, Qiansuo Wang, Paul Hanson, Haitao Chen, and Yunkun Shi

Coastal loess is a unique and intriguing eolian sediment on Earth, but understanding its formation time, provenance, composition and the geomorphic processes that resulted in its accumulation is very limited compared to its inland counterpart. In this paper, we focused on a loess section at Xiazhupan (XZP) Village, Penglai City in the Shandong Peninsula, the only known coastal loess bluffs preserved in China. The coastal loess here not only has characteristics that are common to loess terrains such as being composed of predominantly silt-sized particles and the tendency to stand in vertical exposures, but it also reportedly preserves planktonic foraminifera, sizable pebbles, and volcanic glass. In addition to its peculiar near-shore locality, these features make it more unusual compared to other loess deposits. Systematic optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL and pIRIR) and radiocarbon dating reveal it was deposited mostly during 60-20 ka, Marine Isotope Stage (MIS) 4-2, which correlates to the deposition of the Malan loess (L1) in the Chinese Loess Plateau. High-resolution grain size data indicate that the coastal loess is relatively coarse-grained, suggesting a source terrain that is at least partially proximal. We argue that, given its proximal source and the geochronological evidence, this coastal loess was sourced from the exposed continental shelf during the sea-level lowstand of the last glacial period, and this hypothesis is further supported by a core collected from the Bohai Sea in which silt was present and would have been subaerially exposed during MIS 4-2. In addition, this source area of the exposed continental shelf is comparable to coastal loess in Europe. The coastal loess in Shandong can be regarded as a special type of desert or dryland loess, rather than glacial loess. Finally, future sea-level rise will likely increase the erosion potential of these vulnerable coastal loess bluffs, making it urgent to study this special landform.

How to cite: Miao, X., Ee, C., Xu, S., Wang, Q., Hanson, P., Chen, H., and Shi, Y.: Age and source of coastal loess in the Shandong Peninsula, Bohai Sea, China, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-279, https://doi.org/10.5194/icg2022-279, 2022.

10:00–10:15
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ICG2022-533
György Varga, János Kovács, Fruzsina Gresina, and Zoltán Szalai

Annual emission of mineral dust from Saharan sources can be set into the range of 1-5 billion tons per year. Besides several other climatic and environmental effects, fine-grained dust addition to clastic sedimentary units (aeolinites, loess-paleosol sequences, sand sheets) has a definite impact on the granulometric properties of these deposits. Interpretation of grain size data is greatly affected if all these factors are ignored.

Here we present an overview of Saharan dust addition to loess-paleosol sequences with special attention to interglacial paleosols. According to our findings on modern Saharan dust events and dust deposition in Central Europe, the mass accumulation of North African dust is around 3-5 g/m2/year. Stratigraphic and sedimentary data of loess-paleosol sequences allowed the determination of the relative contribution of Saharan dust to interglacial paleosols. Saharan dust material represents 20-30% of the clay- and fine silts-sized population of peodogene units of loess sections.

Support of the National Research, Development and Innovation Office (Hungary) under contract NKFIH FK138692 is gratefully acknowledged.

How to cite: Varga, G., Kovács, J., Gresina, F., and Szalai, Z.: On the impact of Saharan dust addition to sedimentary units, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-533, https://doi.org/10.5194/icg2022-533, 2022.

10:15–10:30
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ICG2022-301
Marijana Z. Petrovic, Dan G. Blumberg, Leah Orlovsky, and Shimrit Maman

Much geomorphological research has been conducted on the origin and evolution of sand seas, some of which focused on categorizing dune types, some determining past climatic conditions using Optically Stimulated Luminescence (OSL) dating, and some, understanding dune patterns and stability in relation to the current climate. Sand seas are, in essence, climate archives. Even though the central Asian sand seas, Karakum and Kyzylkum, occupy more than 450.000 km2, relatively little climatic research has been conducted on the formation and evolution of these aeolian deserts. The meteorological data (current & historical) for these regions is scarce and incomplete. Moreover, the area is not extensively recognized in the worldwide available aeolian literature, which has little information about its climatic performances. Using the common method for the examination of wind data—Fyberger’s Drift Erosion equations (1979) and the most recent Copernicus ERA5 wind reanalysis model conducted on 5081 control grid points, we show that both the Karakum and Kyzylkum Deserts are and have been low-energy environments for the statistical period 1950–2019. The data set was transferred into the form of a space-time cube, a multidimensionally-orientated raster, enabling time-series analysis and data mining. Such analysis has revealed that 93% of the desert was under a low-energy wind setting during the past 70 years. The directionality index shows that erosive winds didn’t deviate extensively from their primal directions as observed from the same statistical period. Such performance favors vegetation growth and biogenic crust development, thus, dune stabilization. Alongside, a similar type of procedure was performed for the wind data obtained from NOAA weather stations that are at close distance or within the study area. Both data sets were mutually analyzed with respect to the Resultant Drift Direction (RDD) calculated for the period 2010-2019 and all available portions of time. By comparing dune orientation and characteristics of their current morphology to the wind directions, the results indicate that the morphology of active aeolian features, (e.g. complex barchanoid ridges, star and seif dunes) are in high correlation with current winds and their erosive powers. Simultaneously, stable aeolian formations that overlay most of the observed area (determined as different formations of Vegetated Linear Dunes - VLDs) show disassociation between the dune's orientation and the wind power (RDP), direction (RDD) and variability (UDI), confirming that most of the vegetated aeolian formations were not developed, or presently reworked, by contemporary winds. An analysis of wind parameters in both active and stable aeolian morphologies in these deserts has permitted the discovery of present and paleo-wind interactions, as well as putative paleo-environmental climatic conditions.

How to cite: Z. Petrovic, M., G. Blumberg, D., Orlovsky, L., and Maman, S.: Linking aeolian geomorphology with climate for the Karakum and Kyzylkum Deserts, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-301, https://doi.org/10.5194/icg2022-301, 2022.

Coffee break and poster session
Chairpersons: António Campar, Abdessamad CHARIF, Jorge Trindade
14:30–14:45
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ICG2022-21
Shlomy Vainer, Ari Matmon, Yoav Ben Dor, Eric Verrecchia, Frank Eckardt, and Aster Team

Evaluating the impact and implications of eolian repositories that mark large-scale climatic transitions requires knowledge about the timing of their emplacement and the mechanisms responsible for their production, which remain highly uncertain. We apply numerical modeling of cosmogenic nuclide data, measured in the largest continuous terrestrial body of sand on Earth, to determine settings under which the sand was generated, by constraining the timing of sand introduction into the interior of southern Africa. Our findings reveal that major events of sand formation and accumulation in the Kalahari Basin occurred between ~2.2 and 1 Myr ago. The establishment of the Kalahari sand field corresponds to regional, continental, and global scale morphotectonic and climatic changes that contributed to the mass production and widespread dispersion of sand. These changes substantially altered existing habitats, thus constituting a crucial milestone for floral, faunal, and hominin evolution throughout the African continent during the Pleistocene. 

 

How to cite: Vainer, S., Matmon, A., Ben Dor, Y., Verrecchia, E., Eckardt, F., and Team, A.: Eolian chronology reveals causal links between tectonics, climate, and erg generation , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-21, https://doi.org/10.5194/icg2022-21, 2022.

14:45–15:00
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ICG2022-490
Douglas Sherman, Pei Zhang, Jinsu Bae, and Robert Butler

Barchan morphology has been the subject of considerable research, mainly because they frequently occur as stand alone features with iconic, aerodynamic forms. Barchans retain their distinctive shape independent of size, indicating proportionate change of key shape metrics. The early work of Pompeckj (1906), Finkel (1959), and others, noted that barchan widths and heights displayed this property. Hesp and Hastings (1998) recognized this as an allometric relationship. Allometric relationships are identified by power law ratios between shape elements.  

              We present the results of a study where we measured barchans of different sizes and from different environments to develop new shape metrics and to evaluate potential allometric relationships between those metrics. We used remote sensing imagery obtained from Google Earth Pro (Google Earth and Google Mars) to sample barchan morphology from 40 dunes fields: 30 on Earth and 10 on Mars, comprising 3,406 barchans: 2,687 from Earth and 720 from Mars. We measured six morphometric variables and derived three dimensionless ratios for each dune.  Body length (L1) is the shortest distance from the upwind point of the barchan to the bottom of the slipface. Total length (L2) is the body length plus the average length of the two horns (. Body width (W1) is the length measured from the outside edges of the barchan along a line at the base of the slipface and perpendicular to the body length line. Horn-to-horn width (W2), is calculated using the Pythagorean Theorem as , where T is the distance between the tips of the two horns, H1 is the length of the left horn (looking into the slipface) and H2is the length of right horn.  The dimensionless shape metrics are the width ratio,  (); the length ratio,  (); and the symmetry ratio,  (longer horn length/shorter horn length).

              Regression analysis to test for allometric relationships requires the designation of independent and dependent variables. For the former, we chose body width (W1) as a potential control on variability in L1, and , for assessment of dimensional relationships. For assessment of dimensionless relationships, we used WR as the independent variable with the dependent variables of LR, and SR. For Earth and Mars data combined, the dimensional ratios had R2 of 0.90 for W1 and L1, and 0.80 for W1 and . The power law relationships both had exponents near 1.00; 0.995 and 0.999, respectively. Coefficients of determination and exponents differed, however, between the two planets. Data for the two ratios indicated that for Earth, R2 was 0.91 and 0.80, with exponents of 0.904 and 1.065, respectively. The equivalent values for Martian dunes are 0.64 and 0.60, with exponents of 0.761 and 0.983. Similar differences are found for the two planets using the dimensionless variables, although the relationships between WR and SR are weak (R2 < 0.19).

              From this, and other analysis, we can conclude that the allometric relationships between barchan metrics are different for terrestrial and Martian barchans. This means, further, that typical barchan morphology must also differ between the two planets.

 

How to cite: Sherman, D., Zhang, P., Bae, J., and Butler, R.: Allometric ratios for barchans on Earth and Mars  , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-490, https://doi.org/10.5194/icg2022-490, 2022.

15:00–15:15
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ICG2022-512
Joanna Rotnicka and Maciej Dłużewski

The vertical distribution of aeolian mass flux has been studied mainly on sand surfaces and much less often on gravel surfaces, particularly under natural conditions. We present data of measurements made in three beach settings differed in petrographic composition of the beach sand (quartz, bioclastic, and bioclastic-basaltic sand) and density of pebble coverage (5-70%). We aimed to show the differences in mass flux profiles induced by surface properties resulting from sediment composition. All measurements were made on a dry sand bed under conditions of maximum sand transport rate, i.e. during alongshore wind when the fetch distance was not limited. Sand transport rate was measured by means of passive sand trap, 0.5 m in high and divided into 40 chambers. The obtained dataset contains results of 241 measurements of mass flux made on bare sand surfaces and 127 on sand surfaces covered with discoidal pebbles (with short axis of less than 1 cm). The results showed that (i) regardless of the surface type, all vertical mass flux profiles were well fitted by an exponential decay function, but the regression coefficients differed greatly between those for sand surfaces and surfaces with pebble covers of different densities, (ii) changes in these coefficients with wind speed were much more pronounced in the case of sand surfaces than on surfaces with pebbles, (iii) the exponential model underpredicted mass flux in the near-bed region in the case of sandy surfaces, whereas in the case of pebble surfaces, the departures from the model were insignificant, and (iv) a pebble cover with a low density between 5% and 10% strongly affected the concentration of sand in the vertical profile. All mass flux profiles showed that as wind speed increased, the proportion of sand transported in the near-bed region decreased and the proportion of sand transported at higher elevations increased. For each surface type, the height at which the constant proportion of sand was transported may be defined irrespective of wind speed. This height was equal to 3-4 cm in the case of sand surfaces and changed from 6 cm to 11 cm as the density of pebble coverage increased from 5-10% to 50-70%. We also showed that the average roughness length parameter Z0 was very similar for sandy surfaces irrespective of sand composition (0.0010-0.0011 m) and only two times greater (0.0022-0.0024 m) on sand surfaces covered with pebbles. We observed neither a decrease in this parameter with increasing wind speed nor relationship between Z0 and pebble coverage density. Contrary to many measurements made on the desert surfaces covered with 3D gravels we did not record mass flux distributions with a  peak at a height of few centimetres above the surface that could be described by a Gaussian peak function. We think that the discoidal and more streamlined shape of pebbles (acting more as 2D roughness elements), and their relatively well sorting are responsible for that fact.

This study was supported from Polish National Science Centre (grant no. 2016/23/B/ST10/01700).

How to cite: Rotnicka, J. and Dłużewski, M.: Aeolian mass flux profiles above different sands surfaces versus sand surface with pebble coverages of different density , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-512, https://doi.org/10.5194/icg2022-512, 2022.

15:15–15:30
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ICG2022-380
Guilherme Borges Fernandez, Ivandro Patrick de Oliveira Coutinho, and Thiago Goçalves Pereira

Coastal sandy barriers form a typical environment in wave-dominated coasts. Not rarely, the surface morphology of these features should be interpreted by aeolian sediments, fixed by vegetation, forming foredunes. The morphology observed in the foredunes depends from different processes, related for example the wind speed, wind direction, different types and density of vegetation, variation of wave energy and beach morphodynamics. In this case, some specific geomorphological patterns can be observed in the foredunes, such as blowouts and erosive scarps or even different types of dunes, describe for example by nebkas and parabolic. In the last ten years, the geomorphology experiences a truly revolution by the use of digital photographs obtained by Unmanned Air Vehicles (UAV), where details from the surface were revealed by structure from motion (SfM) photogrammetry. The low-cost and effective results from UAV and SfM provide a high-resolution (centimeters-scale) digital elevation models (DEMs), which allow a more accurate analyses in geomorphology. Using these techniques, the aim of this study is analyzing the morphological characteristics of foredunes submitted by high-energy waves and winds from different directions along Massambaba Beach, southeast Brazil. Massambaba Beach present a more than 50 km of continuous Holocene barrier, classified as stationary barrier. The beach morphodynamic varies from intermediated/reflective on the west side, to intermediated/dissipative in the east. To evaluate the morphological patterns observed by hydrodynamics and aerodynamics effect along the foredunes, we determine changes in the vegetation density by remote sensing, and found that the density decrease from west to the east. After, we select four different areas to survey by UAV. The results showed that the area 1 located in the west Massambaba, the foredunes present disconnected blowouts from the beach, forming a bi-directional parabolic dune, where fair-weather (northeast) and storm winds (south) play an important role. In the central Massambaba the blowouts increase not only in terms of area, but some parabolic dunes can be observed directly connect from the beach, formed by off-shore and onshore winds. In some specific sites, beach scarps eroded the precipitation ridges that reach the berms, and create good conditions for overwash deposits, formed by high-energy waves. The east Massambaba, where we observe the decrease in vegetation density, different types of dunes coexist such as nebkas and parabolic, and the parabolic can be orientated by northeast or southwest depending of prevailed wind. The foredunes in the east Massambaba experience overwash process, which favor washover deposits. We conclude that the morphological complexity observed in the foredunes, revealed by DEM, indicates the importance of these techniques to investigate different process caused by wind and waves. 

How to cite: Borges Fernandez, G., de Oliveira Coutinho, I. P., and Goçalves Pereira, T.: Geomorphological patterns observed in foredunes under storm and fair-weather conditions revealed by UAV images, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-380, https://doi.org/10.5194/icg2022-380, 2022.

15:30–15:45
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ICG2022-567
Joanna Oliwia Tomczak, Maciej Dłużewski, and Joanna Rotnicka-Dłużewska

Aeolian ramp, i.e. the area between upper beach and the seaward foredune toe, serves as a transit zone between the source area (beach) and the foredune. Its morphology greatly impacts sand supply to the foredune and is therefore one of the key factors responsible for the foredune growth dynamics. The aim of the study was to analyse the change of aeolian ramp topography during extreme events manifested by strong onshore winds. The research was made on the Łeba Barrier, south Baltic Sea coast, Poland in winter 2022. Two experimental sites, different in foredune size and coastline orientation, were chosen. Storm periods were determined on the basis of 10-minute averages of wind speed and direction obtained from a 10-m-high reference mast located near the experimental sites on the established foredune and hourly data from 2 mareographs located approx. 15 km west and east of these sites.

To analyse changes in near surface wind speed at different directions of wind attack a set of cap and sonic anemometers was arranged along shore-normal transect. The measurement sites within aeolian ramp were placed every 2 m. Based on 1-minute averages and the data from the reference mast, the speed-up factor was calculated for 10-degree wind direction sectors which were determined based on wind directions from the reference mast. 3D TLS measurements allowed for the development of the high-resolution Digital Elevation Model of each of the experimental sites. Several short term changes in aeolian ramp topography during storm events were measured by means of GPS-RTK supported by measurements of 200 erosion pins.

Comparison of sediment budget with wind speed and direction for 6 storm events showed 3 types of aeolian ramp morphodynamics. During strong alongshore winds, due to higher wind speed in the upper ramp than in its lower part, the greatest deflation occurred in the upper ramp. During oblique onshore storm winds, air flow deceleration in the upper ramp contributed to the slight deposition of sand. In both cases the sediment budget in the middle and lower ramp was small. During onshore storm wind events, much stronger deceleration of airflow was recorded up the ramp and change in its topography was insignificant. We found that during almost 2-month survey during which several extreme wind events occurred, the aeolian ramp was eroded in both experimental sites. The greater erosion (up to 60 cm) was recorded within the ramp adjacent to the lower foredune than to the higher one (up to 30 cm) where deceleration of near-surface airflow on aeolian ramp was much more pronounced. The lack of deposition during onshore wind events, despite great deceleration of the airflow, was caused by a significant reduction in the sand source due to beach flooding by storm waves and unsaturation of air stream approaching the ramp. Aeolian ramp erosion affected sand transfer in the entire beach-ramp-foredune system and resulted in the limitation of sand supply to foredune and thus their degradation during storm events.

This study was supported from Polish National Science Centre (grant no. 2018/31/B/ST10/03051).

How to cite: Tomczak, J. O., Dłużewski, M., and Rotnicka-Dłużewska, J.: Aeolian ramp morphodynamics during storm events, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-567, https://doi.org/10.5194/icg2022-567, 2022.

15:45–16:00
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ICG2022-34
Dénes Lóczy, József Dezső, Marietta Puhl-Rezsek, and Ferenc Tarjányi

The soils of flat alluvial fans mantled by blow sand (Humic Arenosols) usually present unfavourable properties for agriculture: low organic matter and soil moisture content, low levels of aggregation, low clay content to absorb nutrients and high exposure to wind erosion. In dry periods when the protective effect of vegetation is reduced, sand storms detach and carry away large amounts of organic particles. The soil profile of the Hungarian study area shows buried humic horizons which indicate intensive reworking by wind action in historical times. Given the limited choice of crops which can be cultivated in the region, an asparagus field was selected for experimentation. Asparagus rows are aligned in the direction of the prevailing wind. The plastic foil cover of asparagus ridges intensifies wind erosion through a wind channel effect. Two different crop diversifications were introduced to assess possible improvements in ecosystem services including wind erosion control: plots with asparagus monocropping (M as control) alternated with pea (D1) and oat intercropping (D2) between asparagus ridges. The flux of eolian transport captured by sediment traps in a 1-metre high and 100-metre wide cross section, measured and analyzed for composition at four heights: on the ground surface, at 30 cm, 200 cm and 400 cm heights. Meteorological records were evaluated for starting velocities of sand movement estimated from wind tunnel experiments. For the region  critical starting wind velocity at 10 cm height was established at c. 6 m s-1. Large-scale irrigation to allow surface crusting is not feasible because of the lowering of the groundwater table. Cover crops were found to reduce soil erosion by wind in two ways: through providing vegetation cover in the periods critical for sand storms (early spring and late summer) and through enriching the soil with organic matter by way of green manuring, which is also beneficial for soil fertility. There were significant differences between treatments. The pea and oat crops well utilized the moisture derived from occasional thunderstorms and in the second year provided a continuous vegetation cover. There was minimal concurrence between the main crop (root zone at 0-150 cm) and the cover crops introduced (root zone at 0-20 cm). Although no significant rise in total nitrogen contents of the soil could be achieved (explained by the extremely low clay content and aggregate formation capacity), organic matter contents grew due to the biomass added to the soil in form of crop residues. (Although their decomposition rate is low due to the dry environment.) Dust amounts captured at 200 cm above 105.39 kg y-1, at 400 cm above the ground surface amounted to 26.75 kg y-1, while sand saltated along the surface at 0-15 cm reached an average 2130 kg y-1. In sediment traps near the surface saltated sand had a median diameter of 174 µm, at +15 cm 134 µm, at +200 cm 118 µm and grain size substantially reduced to 42 µm (coarse silt) at +400 cm.

How to cite: Lóczy, D., Dezső, J., Puhl-Rezsek, M., and Tarjányi, F.: Crop diversification to reduce wind erosion hazard in a semiarid blown-sand area of Hungary, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-34, https://doi.org/10.5194/icg2022-34, 2022.

16:00–16:15
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ICG2022-674
Patricia Mescolotti, Paulo César Giannini, Fabiano Pupim, and Mario Luis Assine

Research on coastal Brazilian Quaternary eolian systems has significantly progressed in recent years. However, few contributions have been published on eolian depositional forms in Brazilian inland areas. Directly associated with the São Francisco River, the Xique-Xique eolian system is the largest quaternary interior dune field in Brazil (8,000 km²). Despite dune reactivation in some sites during the last decades, most Xique-Xique dunes are stabilized. In this study, we characterize dune morphology, vertical stratigraphic sections and sedimentary facies coupled to a dataset of optically stimulated luminescence (OSL). Four geomorphological zones were recognized and mapped: 1 - simple megadunes; 2 - compound dunes; 3 - perched dunes; and 4 - eolian plains. Simple megadunes (SM) occur as well-preserved parabolic dunes with simple elongated or lobate morphologies, and subordinately, nested, digitate, and superimposed dunes also occur. The SM can be recognized on both sides of the São Francisco River, have length of the arms (L) from 1.2 to 16.3 km, the width (W, distance along the transverse line that joins the two most distant points) from 0.9 to 5.7 km, and heights of up to 30 m at their noses. Six sediment samples have been dated by OSL, revealing ages from 26.5±4.4 ka to 4.8±0.9 ka. Compound dunes (CD) consist of well-preserved parabolic landforms comprising morphologies usually en-echelon and nested. They have L of 0.3-2.0 km and W of 0.3-1.4 km, with a predominant L/W ratio <1.7, and up to 50 m high. The ages of the five dated samples span from 14.3±1.5 ka to 5.1±0.7 ka. Perched dunes (PD) are small climbing and cliff-top parabolic dunes that form a narrow and high barrier along the riverbanks on the western margin of the São Francisco River, where they merge to form a dune belt 0.5-1.5 km wide. PD climb other landforms, reaching altitudes up to 160 m higher than the river level and forming stoss side ramps inclined up to 30º towards the river. Two PD samples were dated (14.0±1.0 and 1.2±0.1 ka). Eolian plains (EP) are almost flat stabilized surfaces between the dunes, which may correspond to sand sheets and vegetated deflation areas. They include deflationary eolian features such as kilometers-long trailing ridges. Five samples were dated and showed ages ranging from 16.2±1.1 ka to 6.8±0.6 ka. Sediments of all landforms have similar textural characteristics, fine- to medium-grained, well-sorted, rounded, quartzose unconsolidated sands. The colors of the sands are varied, ranging from dark brown to beige, usually with darker tones in the simple megadunes and eolian plains. A horizon with millimeter-sized charcoal fragments was observed on both sides of the river. Parabolic dunes started to form before 26 ka, but samples of all mapped landforms showed post-LGM ages, revealing a period of strong dune mobility from 15 to 5 ka in the Xique-Xique eolian system.

How to cite: Mescolotti, P., Giannini, P. C., Pupim, F., and Assine, M. L.: Stabilized eolian landforms of the largest quaternary inland eolian system in Brazil , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-674, https://doi.org/10.5194/icg2022-674, 2022.

16:15–16:30
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ICG2022-371
Yoshinori Kodama

In Japan's most famous Tottori Sand Dunes, mega-ripples were observed from 2013 to 2015 around the exposed volcanic ash layer in sand dunes. Gully erosion progressed during rainfall in exposed volcanic ash, and aggregated coarse particles of volcanic ash were supplied to the sand surface of the surrounding dunes. In other words, it is suggested that mega-ripples may have appeared and disappeared depending on the amount of coarse particles supplied to the sand surface. This hypothesis was first confirmed in a wind tunnel experiment.

I made acrylic rectangular cross-section wind tunnel experimental device with a width of 9 cm, a depth of 60 cm, and a length of 7.28 m. The maximum wind speed was 16-17 m / s. Fine sand was spread with a thickness of 10 cm, and polypropylene particles (diameter 4 mm, density 0.9) were evenly sprayed on the surface. Seven preliminary experiments were conducted in which the amount of spray was doubled. The experiment was conducted without sand supply. As a result, when the amount of the polypropylene particles sprayed was small, the polypropylene particles were buried in the sand. On the contrary, if the amount was too large, polypropylene particles covered the sand surface and became stable on a desert pavement-like smooth bed. When the amount of polypropylene particles sprayed was moderate, in a 30-minute experiment, five convex downward mega-ripples were formed at a wavelength of 50-80 cm.

Finally, fine sand was spread with a thickness of 19 cm, the amount of polypropylene particles sprayed was 45 g / m, and this experiment was carried out for 40 minutes under a wind speed of 17 m / s. From the side of the wind tunnel, a cross-section was recorded every minute with five digital cameras. As a result, after one minute elapsed, an accumulation zone of polypropylene particles was formed at a wavelength of about 10 cm, and they repeatedly coalesced, and after 10 minutes, they changed to an accumulation zone with a wavelength of about 25 cm. Gradually, the accumulation zone of polypropylene particles became peak-shaped, and in the polypropylene particles passage area, fine sand was wind-eroded and changed to a convex downward cross-sectional shape. After 20 minutes, mega-ripples with a wavelength of 60 cm were formed, and after 40 minutes, six mega-ripples with an average wavelength of 75 cm and an average wave height of 4.3 cm were formed. Mega-ripples moved downstream at a rate of 4 cm / min.

From the wind tunnel experiment, it became clear that mega-ripple was formed in the sand surface lowering area. This is because the development of mega-ripple became unclear when the sand feeding experiment was conducted. In the field, mega-ripple is observed in a limited range unlike the wind ripples. One of the reasons for this is that the area where the sand surface is lowered is limited in sand dunes. I will introduce the results of mega-ripple investigations at the Great Sand Dunes of the United States at this point.

How to cite: Kodama, Y.: Wind tunnel experiments on the formation of mega-ripples according to the amount of coarse particles, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-371, https://doi.org/10.5194/icg2022-371, 2022.

Display time: Thu, 15 Sep 09:00–Fri, 16 Sep 19:00

Poster: Fri, 16 Sep, 10:30–10:45 | Poster area

Chairpersons: Ana Ramos-Pereira, António Campar, Jorge Trindade
P46
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ICG2022-58
Yoav Ben Dor and Shlomy Vainer

The extensivity of sand dunes in continental interiors testifies to the importance of understanding their morphodynamical properties and their dating for palaeoenvironmental reconstructions and for interpreting landscape evolution. Nevertheless, the study of eolian landscape evolution at the million-years timescale is hampered by the complex interaction of factors affecting dune migration and the inherently self-destructive nature of their chronostratigraphy, thus limiting the applicability of traditional luminescence-based dating methods for configuring processes spanning over ~300 Ka. In this study, a standalone program that simulates eolian transport based on luminescence-derived chronologies coupled with numerical modelling of cosmogenic nuclides accumulation is presented. This integrative approach reveals ancient phases of sand irruption and provides a data-oriented scheme facilitating the study of eolian morphodynamical processes over multiple timescales. The program is applied on a case of the Australian Simpson Desert, where it unfolds multiple pulses of eolian vitality at 3.8-3.4, 2.9-2.5, and 1.5-1 Ma, corresponding to drastic changes in environmental settings. The synchronicity of the results with the independently established environmental framework exemplifies the applicability of process-based modelling in constructing a timeframe revealing key events in landscape evolution in arid environments by studying eolian landforms. Finally, the relationships between the model parameters used for simulating the environmental settings and sand migration patterns demonstrates the potential of the program in further investigating the triggers and mechanisms of eolian processes.

How to cite: Ben Dor, Y. and Vainer, S.: HIPSTER: A High-resolution Integrated Program for modeling Sand Transport in Eolian Realms by coupling OSL and cosmogenic nuclides (Cosmolian), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-58, https://doi.org/10.5194/icg2022-58, 2022.

P47
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ICG2022-99
Carlos Arce-Chamorro, Juan Ramón Vidal-Romaní, and Jorge Sanjurjo-Sánchez

The Atlantic coast of Galicia (NW Spain), about 1,700 km long, alternates deep inlets on the mainland (as wide estuaries called rias) with rocky cliffs up to 600 m high (due to neotectonics). Along this irregular coastline, numerous dune deposits (aeolianites) are preserved, which are formed by thin sandy and silty-sandy wedges (<5 m) and a variable extension - not always fully recognisable due to the dense vegetation cover and slope dynamics. These aeolianites are found both in open coastal areas and in the interior of the Galician Rias, reaching heights of up to +45 m above present sea level (and even higher). Grain size, morphological and microscopic analyses (scanning electron microscopy; SEM) have been performed for determining the aeolian origin of sands. Their location on cliff areas, where there are no sand beaches today, suggests that they are ancient climbing dunes deposited during sea level drop events at the end of the Pleistocene. The ages estimated by optically stimulated luminescence (OSL) for these deposits range between 17 ky and 35 ky. Infrared stimulated luminescence (IRSL) was also used for dating four other deposits, providing ages around 66 ky, 128 ky and 131 ky and 166 ky. Additionally, the oldest climbing due to date in the Iberian Peninsula is located in this area, providing an age around 300 ky. All such ages were obtained at the Luminescence Laboratory of the University of Coruña. The formation of such deposits and transport of sand towards the areas now occupied by the present coastline occurred during the isotopic stages MIS2, MIS4, MIS6 and MIS8. During these stages, the sea level dropped between 50 m and 120 m (relative to present sea level), shifting the coastline several kilometres away (>20 km) and exposing a wide strip of the continental shelf covered by sands that would act as a source area. The continuous wind blowing and the wind strength due to the Venturi effect caused by the highest rocky reliefs, favoured the advancing of the climbing dunes to a height of more than 200 m (above sea-level at the time), resulting in the deposits still preserved today. The inland transport of these materials by coastal winds during maximum regressive events was progressively stopped as sea level rose during interglacials (such as the Eemian and Holocene) when sand source areas were flooded. As the sea reaches its maximum transgressive levels, these dunes are severely affected by both alternating wind (blow-out and storm corridors) and then marine erosion (washover fans) that destroys both relict and recent (<10 ky) deposits, contributing to quick erosion process of the sedimentary coastline that is considered a consequence of global warming during the Holocene interglacial.

How to cite: Arce-Chamorro, C., Vidal-Romaní, J. R., and Sanjurjo-Sánchez, J.: Chronology of fossil climbing dunes on the Galician cliff coast (NW Spain) formed during MIS8, MIS6, MIS4 and MIS2 regressive episodes. Past and present of the coastal aeolian record, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-99, https://doi.org/10.5194/icg2022-99, 2022.

P48
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ICG2022-104
Lotem Robins, Joel Roskin, LuPeng Yu, and Noam Greenbaum

The internal structure of dunes often lacks clear internal boundaries and complicates allostratigraphic analyses and correlation with adjacent dunes. Furthermore, several dune studies involved hand-drilling, which exclude allostratigraphic analysis. Here, high-resolution sand  sampling from two linear dune sections and a hand-drilled linear dune, was performed along the northwestern Negev (Israel) dunefield. The bulk samples were used for allostratigraphic analysis by Portable Optically Stimulated Luminescence (POSL) device. The samples were clustered by a Mean-shift unsupervised cluster analysis, applied on the Infra-Red and Blue counts, previously found to vary according to the time of burial, mineralogy and luminescence properties. OSL ages and particle size distribution were reviewed according to the cluster analysis results.

The POSL cluster analysis can reliably outline dosimetric breakpoints between units along  a single stratigraphic section and between adjacent dune sections. The clusters document a distinct depositional period when OSL age ranges match well with the POSL clusters. Textural and mineralogical differences, generated by several mechanisms such as post-depositional processes, dune degradation followed by nearby alluvial sand aggradation, pedogenesis, and shrub root penetration can also account for dosimetric breakpoints and need to be considered.

How to cite: Robins, L., Roskin, J., Yu, L., and Greenbaum, N.: Allostratigraphic analysis of linear dunes without visible erosional boundaries using cluster analysis of portable OSL signals , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-104, https://doi.org/10.5194/icg2022-104, 2022.

P49
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ICG2022-450
Michał Łopuch, Zdzisław Jary, and Sebastian Lindhorst

The influence of periglacial conditions on the development of aeolian bedforms is not well understood. Observations of active dune fields in polar regions show that they can develop as either consistent dune fields, similar to what is known from hot regions, or as isolated sand patches controlled by the ground-water table. However, modern periglacial dune fields are rare, hampering the investigation of the factors that control dune-field evolution in cold regions.

The aim of this project is to define factors controlling the spatial pattern of periglacial dune fields in the central part of the European Sand Belt. Methods will include high-resolution morphometry and GIS analyses, combined with ground-penetrating radar, granulometry, and quartz-grain morphoscopy in an integrated approach. Pleistocene dune fields located in Poland will serve as key areas for similar dune systems elsewhere. Results will be supported by detailed studies of individual dunes. The project will try to answer the questions about 1) the impact of periglacial conditions (seasonal variability in sand supply, patches of permafrost, high surface wetness) and morphological framework (topography, surface inclination, occurrence of morphological barriers) on the development of dunes and dune fields; 2) spatial differentiation of aeolian processes within European Sand Belt.

The scientific hypothesis to test is that dune fields in periglacial regions are controlled by high variability of local depositional conditions, which result in the coexistence of various dune types and weak spatial organization of dune fields.

Results will allow us to develop a model of periglacial dune field evolution. Data will not only shed new light on periglacial aeolian morphology, but will be also valuable for the analyses of climatic conditions at the end of the last glacial.

The project is funded by Polish National Science Centre, contract number 2021/41/N/ST10/00350.

How to cite: Łopuch, M., Jary, Z., and Lindhorst, S.: The COOL-DUNES project:  Factors controlling spatial patterns of periglacial dune fields in the central part of the European Sand Belt, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-450, https://doi.org/10.5194/icg2022-450, 2022.

P50
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ICG2022-503
Tania Cristina Gomes and Roberto Verdum

In the western part of the state of Rio Grande do Sul, there are sandy spots (called areais) embedded in the landscape of the Brazilian Pampa biome. These sand spots are associated with unstable and/or stable aeolic deposits from the continental interior, and represent the legacy of drier climates than the present one, providing important paleoclimatic evidence for understanding the landscape evolution. Currently, the sand deposits, which have their genesis in dry climates, are subject, at the same time, to wind action, in dry seasons, and surface and subsurface erosions, in rainy seasons, which remobilizes the unconsolidated sediments, initiating the sandization process and the formation of sand spots. It can be stated that the stable eolian deposits exhibit forms remodeled by pluvial and fluvial erosions, still presenting different degrees of morphological preservation concerning those of the recent past, which is why the present hill relief can be associated with the Holocene longitudinal dune fields. However, these eolian formations still lack studies to determine their absolute geochronology and to understand if there were significant climatic fluctuations to infer if the region of occurrence of the sand spots was subjected to more severe conditions of aridity, which would allow the formation of eolian deposits in the interior of the continent. The study also aims to reveal whether the aeolian dune fields of the Brazilian Pampa correlate temporally with the paleoclimate signal of drier events that occurred in other regions of Brazil or South America (Colombia, Argentina, and Chile), in which aeolian activity seems to have been intense during the Last Glacial Maximum (LGM), particularly in the Holocene. Thus, to understand the past and present morphogenesis, it was considered to apply the geochronological method of Optically Stimulated Luminescence (LOE-SAR protocol) to establish the absolute ages of the sediments that make up the aeolian deposits, which, combined with sedimentological data, gave subsidy to the paleoclimatic and paleogeographical reconstitution of the region of occurrence of the stable and/or unstable aeolian deposits of the Brazilian Pampa. According to the results obtained, it was possible to infer that these sediments result from wind action, being the youngest layer to be remobilized and deposited in periods of climatic dryness, with sufficient semiaridity/aridity characteristics to give rise to wind deposits and dune fields, recognizable in the reading of the landscape at present. The particle size distribution of the four collection points indicated sandy textural classification (above 92%), composed of quite homogeneous material, frankly sandy, friable, and unconsolidated, showing that these are well-selected sediments originating from wind transport, a finding confirmed by the distribution of the sand fraction in a fine sand model class above 54% for all the profiles analyzed. The results obtained by LOE-SAR established three climatic drying peaks that occurred during the Holocene. The first episode, 8,200 ± 700 BP, coincides with the end of the Lower Holocene; the second episode, 5,650 ± 1,120 BP, corresponds to the Middle Holocene; and the last episode, 1,910 ±275 BP, corresponds to the Upper Holocene.

 

How to cite: Gomes, T. C. and Verdum, R.: Quaternary aeolian surface formations in the brazilian Pampa, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-503, https://doi.org/10.5194/icg2022-503, 2022.

P51
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ICG2022-715
João Barros, Pedro Dinis, and Pedro Callapez

Tombua is a small fishing village located in SW Angola that was founded during the former colonial period, when it was called Porto Alexandre. Regional climatic conditions are typical of desertic environments, with less than 20 mm of annual precipitation. Low rainfall and persistent southerly winds promoted the advance of aeolian accumulations and the formation of the Moçamedes dune field. This dune field widens to the north until it meets the first major river valley, the Curoca, less than 10 km to the north of Tombua. Hence, coastal landscape is markedly different on the two banks in the vestibular position of this river. Because of aridity and, specially, aeolian processes, Tombua is the southernmost location with paved roads along the coast of Angola, but great human effort has been required to limit the advance of wind sands.

Two sectors with different dune features, bounded by a broadly strait line striking NNW-SSE from the eastern limit of Tombua village southward for about 25 km, can be distinguished in the region. To the east prevail barchan dunes that frequently display a clear pink hue imposed by garnet enrichment. Individual dunes can reach 7 m in height and approximately 50 m in length (along wind direction). To the west occur transverse and parabolic dunes dominated by quartz with secondary amounts of feldspar and substantially less heavy mineral contents. Individual transverse dunes lie on previous sand accumulations, and usually do not reach more than 50 m high. Parabolic dunes, which prevail near the coastline, are usually smaller (~30 m high).

Barchan dunes of the eastern sector lie on a southward tilted surface, rising in elevation from the sea level to approximately 45 meters at the latitude of Tombua. On this platform, with relative sand scarcity, wind deflation is responsible for the preferential removal of more voluminous and lower density particles (such as quartz), leaving behind a residue enriched in heavy minerals. This process culminates with the generation of granatiferous placers, recognized for some decades in the Province of Namibe.

How to cite: Barros, J., Dinis, P., and Callapez, P.: Aeolian accumulations in Tombua region (SW Angola). Structural control on sand composition and dune morphology, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-715, https://doi.org/10.5194/icg2022-715, 2022.

P52
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ICG2022-739
Junsheng Nie, Baotian Pan, Wenbin Peng, Haobo Zhang, and Alex Pullen

The Miocene–Holocene Red Clay, paleosol, and loess sequences composing the Chinese Loess Plateau (CLP) are one of the most complete terrestrial eolian sediment archives on Earth. We present the first large-n detrital zircon U-Pb geochronology dataset for the Miocene–Pliocene sequence from the northeastern CLP. The depositional ages of these samples are like those of other data sets from the central CLP, allowing comparison of spatial-temporal differences. These data show that the CLP had spatially varied provenance over the late Miocene–Pliocene, similar to the Quaternary strata. The data from the northeastern CLP indicate two shifts in dust sourcing around the Miocene-Pliocene and Pliocene-Quaternary boundaries. The shift around the Miocene-Pliocene boundary is consistent with elongation of the proto-Yellow River to incorporate the present-day ‘big bend’—allowing sediment transport to and ultimately through the Yinchuan-Hetao graben. The provenance shift around the Pliocene-Quaternary boundary is consistent with increased sediment contributions from the Lüliang Shan and the Cretaceous strata overlying the North China Craton. These interpretations challenge assertions linking eolian sediment accumulation on the CLP over the late Miocene–Pliocene primarily to aridification within the continental interior of eastern Asia, but rather point to the importance of riverine transport, catchment reorganization, sediment storage, and increased climatic fluctuations.

How to cite: Nie, J., Pan, B., Peng, W., Zhang, H., and Pullen, A.: Spatial and temporal provenance variations of the Chinese Loess Plateau over the late Miocene to early Pleistocene: a window into the reorganization of the Yellow River and monsoon activity, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-739, https://doi.org/10.5194/icg2022-739, 2022.