Palaeoenvironmental reconstruction on the basis of Quaternary palaeo dune sequences on Fuerteventura

The volcanic origin of the Canarian Archipelago widely determines the landscape of these islands. Partially in coastal near areas the volcanic rocks are covered by dune fields. The eastern Canary Islands show the largest areas of sand deposits. On northern Fuerteventura sandpits and deep incised gully systems allow broader insight into generations of these archives. The dune material originates from the shallow shelf. Hence, the mineral composition is dominated by calcite and aragonite. The outcrops show the layering of several generations of biogenic carbonate sands which are separated by palaeosurfaces. These surfaces suggest soil-forming processes by their (often) reddish colour. Generally, the occurrence of several palaeosurfaces promises a high potential of those Quaternary dune archives on northern Fuerteventura. Former studies focussed on just few quarries being situated in close distances. Differing formation concepts and contradicting chronologies (Middle to Late Pleistocene versus Late Pleistocene) suggest the need for further investigation of landward palaeo dune sections, resulting in a DFG funded project with regard to palaeo dune sequences within the catchments of two Barrancos on northern Fuerteventura. Firstly, the project called for defining representative sections of the two catchments for the purpose of working out a correlation and deducing a standard profile, both should be based on stratigraphic findings. IRSL dating shall contribute to finally establishing a chrono-stratigraphy. Besides the carbonate sands, the dune archives are influenced by the imprint of volcanic material (tephra, lapilli, and basaltic rock) and Saharan dust. Generally, the archives’ composition and appearance raise several further questions: Are periods of surface formation dependent on reduced sand supply or on changes in climatic conditions? Which soil forming processes contribute to the characteristics of palaeosurface layers? How about the influence of Saharan dust? As dating of lava flows on northern Fuerteventura revealed Middle to Late Pleistocene ages, a further question refers to the relationship of dune formation and volcanic activity. Mainly deduced from findings in the field but also by use of grain size distribution, elemental composition, content of CaCO3, determination of Fed, measurements of rock magnetic parameters, analyses of gastropod associations, micromorphological analyses, determination of quartz content via Morphologi G3-ID measurements, XRD analyses, and IRSL dating, this thesis provides a chronostratigraphy of palaeo dune archives of northern Fuerteventura deduced from a correlation of sections close to the western coast and sections close to the eastern coast. The derived standard profile shows 15 units divided into 5 main sequences. These 5 sequences mainly differ in sand supply and accumulation, in changing humidity, and in imprint of volcanic activity. The chrono-stratigraphy dates back to about 450 ka. Generally, the archives are very site-specific, because features of a stratigraphic layer often change within close distances, depending on connectivity to erosion pathways and distance to sand sources. Micromorphological analyses indicate soil forming processes which are restricted to de- and recalcification and recrystallisation of iron and manganese. Ultimately, the palaeosurfaces are primarily dominated by the characteristics of Saharan dust (silt dominated, yellow to red in colour, containing hematite and goethite). The archives indicate a cyclicity of predominant processes, starting with I) sand accumulation, followed by II) dust accumulation and weak soil formation, leading to III) water-induced relocation. On the basis of this cyclicity a conceptual approach of the archives’ relationship to changes in sea level could be drawn. We assume highest sand supply during starting regression after sea level maxima. With dropping sea level, the distance between the studied sites and the sand source area (which are the gradually exposed shallow shelf areas) increases, leading to reduced sand accumulation. Starting transgression at the end of glacials suggests the lowest potential of sand accumulation. Furthermore, the concept is based on the assumption that with lower sea levels, more precipitation can reach the Canary Islands. Deduced from periods of lowest potential of sand accumulation in combination with periods of increased precipitation, best conditions for predominant dust accumulation and in-situ processes should be given at terminations. Generally, prevalence of palaeosurface formation is related to transgression periods. These periods are in good agreement with increased dust supply, which, in turn, seem to be affected by precession minima (according to Moreno et al., 2001). The predominance of dust accumulation and in-situ processes causes the fining of sediments, leading to reduced morphological resistance and, finally, water-induced relocation. Ultimately, site-specific sand availability seems to determine whether surfaces are exposed for longer durations, whereas the availability of precipitation (and dust) suggests determining the intensity of surface formation. The studied sections indicate a strong relationship to local volcanic activity because lava flows are able to cut off sand pathways and cover former sand source areas. In combination with dated lava flows the findings point to three different periods of volcanic activity which ceased the sand supply gradually. A first period around 180-170 ka, a next period around 135 ka, and a third period after 100 ka but latest around 50 ka which, finally, completely stopped the sand supply. Regarding the northern part of Fuerteventura, the latest period has so far not been described

¹⁸O analyses of bulk lipids as novel paleoclimate tool in loess research – a pilot study

The analysis of the stable oxygen isotopes 18O and 16O has revolutionized paleoclimate research since the middle of the last century. Particularly, δ18O of ice cores from Greenland and Antarctica is used as a paleotemperature proxy, and δ18O of deep-sea sediments is used as a proxy for global ice volume. Important terrestrial archives to which δ18O as a paleoclimate proxy is successfully applied are speleothems, lake sediments, or tree rings. By contrast, δ18O applications to loess–paleosol sequences (LPSs) are scarce. Here we present a first continuous δ18O record (n=50) for the LPS Crvenka in Serbia, southeastern Europe, spanning the last glacial–interglacial cycle (since 145 ka). From a methodological point of view, we took advantage of a recently proposed paleoclimate/paleohydrological proxy based on bulk δ18O analyses of plant-derived lipids. The Crvenka δ18Obulk lipid values range between −10.2 ‰ and +23.0 ‰ and are systematically more positive in the interglacial and interstadial (paleo-)soils corresponding to marine oxygen-isotope stage (MIS) 1, 3, and 5, compared to the loess layers (MIS 2, 4, and 6). Our Crvenka δ18Obulk lipid record provides no evidence for the occurrence of interstadials and stadials comparable to the Dansgaard–Oeschger events known from the Greenland δ18Oice core records. Concerning the interpretation of our Crvenka δ18Obulk lipid record, plant-derived lipids such as fatty acids and alcohols are certainly strongly influenced by climatic factors such as temperature (via δ18Oprecipitation) and relative air humidity (via 18O enrichment of leaf water due to evapotranspiration). However, pool effects in the form of non-water-correlated lipids such as sterols or the input of root-derived lipids need to be considered, too. Similarly, the input of soil-microbial lipids and oxygen exchange reactions represent uncertainties challenging quantitative paleoclimate/paleohydrological reconstructions based on δ18Obulk lipid analyses from LPSs.Die Analyse der stabilen Sauerstoffisotope 18O und 16O hat die Paläoklimaforschung seit Mitte des letzten Jahrhunderts revolutioniert. Insbesondere wird δ18O von Eisbohrkernen aus Grönland und der Antarktis als Paläo-Temperaturproxy sowie δ18O von Tiefseesedimenten als Proxy für das globale Eisvolumen verwendet. Wenngleich sich in terrestrischen Archiven, wie Speläothemen, Seesedimenten oder Baumringen, paläoklimatische Rekonstruktionen unter der Anwendung von δ18O als Proxy bewährt haben, wurden solche Analysen bislang in Löß-Paläobodensequenzen (LPS) selten durchgeführt. In dieser Studie präsentieren wir einen ersten kontinuierlichen δ18O Datensatz (n=50) für die LPS Crvenka in Serbien, der den letzten Glazial-Interglazial-Zyklus (∼ 145 ka) abdeckt. Die δ18O-Werte basieren auf der Analyse von pflanzlichen Lipiden, deren Anwendung als paläoklimatischer/hydrologischer Proxy vor Kurzem vorgeschlagen wurde. Die δ18Obulk−lipid-Werte von Crvenka liegen zwischen −10.2 ‰ und +23.0 ‰ und sind in den interglazialen und interstadialen (Paläo-)Böden, die den marinen Sauerstoff-Isotopenstufen (MIS) 1, 3 und 5 entsprechen, systematisch positiver als in den Lößlagen (MIS 2, 4 und 6). Sie liefern keine Hinweise für das Auftreten von Interstadialen und Stadialen, die mit den aus den grönländischen δ18Oice−core bekannten Dansgaard-Oeschger-Ereignissen vergleichbar wären. In Bezug auf die Interpretation der δ18Obulk−lipid-Werte gilt es zu berücksichtigen, dass die Isotopie pflanzlicher Lipide, wie z.B. von Fettsäuren und Alkoholen, stark durch die Klimafaktoren Temperatur (über δ18O-Niederschlag) und relativer Luftfeuchtigkeit (über die 18O-Anreicherung des Blattwassers aufgrund von Evapotranspiration) beeinflusst werden. Weiter zu beachtende Faktoren stellen Einträge von Sterolen sowie von generell wurzel-bürtigen Lipiden dar (Pool-Effekte). In ähnlicher Weise bergen der Einfluss von bodenmikrobiellen Lipiden und Sauerstoffaustauschreaktionen Unsicherheiten, die quantitative paläoklimatische/hydrologische Rekonstruktionen auf der Grundlage von δ18Obulk−lipid-Analysen aus LPS erschweren können

Sandy soils in silty loess:The loess system of Matmata (Tunisia)

International audienceThe purpose of this study is to better understand the system of Quaternary loess-palaeosol sequences (LPS) of the Matmata region in southern Tunisia. Results from a combination of predominantly classical methods (grain size and mineral analysis, CaCO3- content estimation, environmental magnetism) indicate strong soil formation phases during which the conditions of sedimentation changed drastically. The heavy mineral analysis underlines northwest, west and southwest provenances of the loessic material. Furthermore, we discuss the process of soil formation in LPS and explain why these soils are very sandy in comparison to the loess units. During phases of soil formation, the northwestern sediment transport path was blocked while sandy material was blown dominantly from the southwestern Grand Erg. Therefore, we present a conceptual model including a provenance analysis of the loessic material that support and improve earlier results of Coudé-Gaussen and collaborators.Dans cette étude, nous présentons un modèle conceptuel pour une meilleure compréhension du système de séquences de loess paléosol (LPS) dans la région de Matmata située dans le sud de la Tunisie. Les résultats d'une combinaison de méthodes principalement classiques (analyse granulométrique, analyse minéralogique, détermination de la teneur en CaCO3, magnétisme environnemental) indiquent des phases de formation importante de sols au cours desquelles les conditions de sédimentation ont fondamentalement changé. L'analyse des minéraux lourds met en évidence une origine nord-ouest, ouest et sud-ouest du matériel loessique. En outre, nous discutons la nature de la formation des sols et expliquons pourquoi ces sols sont si sableux par rapport aux unités de loess. Pendant les phases de formation des sols, le trajet des sédiments en provenance du nord-ouest a été bloqué alors que les matériaux sableux pouvaient encore être soufflés à partir du Grand Erg au sud-ouest. Notre modèle conceptuel de la provenance du lœss à Matmata soutient et précise les conclusions de Coudé-Gaussen et collaborateurs

Palaeoenvironmental reconstruction on the basis of Quaternary palaeo dune sequences on Fuerteventura

The volcanic origin of the Canarian Archipelago widely determines the landscape of these islands. Partially in coastal near areas the volcanic rocks are covered by dune fields. The eastern Canary Islands show the largest areas of sand deposits. On northern Fuerteventura sandpits and deep incised gully systems allow broader insight into generations of these archives. The dune material originates from the shallow shelf. Hence, the mineral composition is dominated by calcite and aragonite. The outcrops show the layering of several generations of biogenic carbonate sands which are separated by palaeosurfaces. These surfaces suggest soil-forming processes by their (often) reddish colour. Generally, the occurrence of several palaeosurfaces promises a high potential of those Quaternary dune archives on northern Fuerteventura. Former studies focussed on just few quarries being situated in close distances. Differing formation concepts and contradicting chronologies (Middle to Late Pleistocene versus Late Pleistocene) suggest the need for further investigation of landward palaeo dune sections, resulting in a DFG funded project with regard to palaeo dune sequences within the catchments of two Barrancos on northern Fuerteventura. Firstly, the project called for defining representative sections of the two catchments for the purpose of working out a correlation and deducing a standard profile, both should be based on stratigraphic findings. IRSL dating shall contribute to finally establishing a chrono-stratigraphy. Besides the carbonate sands, the dune archives are influenced by the imprint of volcanic material (tephra, lapilli, and basaltic rock) and Saharan dust. Generally, the archives’ composition and appearance raise several further questions: Are periods of surface formation dependent on reduced sand supply or on changes in climatic conditions? Which soil forming processes contribute to the characteristics of palaeosurface layers? How about the influence of Saharan dust? As dating of lava flows on northern Fuerteventura revealed Middle to Late Pleistocene ages, a further question refers to the relationship of dune formation and volcanic activity. Mainly deduced from findings in the field but also by use of grain size distribution, elemental composition, content of CaCO3, determination of Fed, measurements of rock magnetic parameters, analyses of gastropod associations, micromorphological analyses, determination of quartz content via Morphologi G3-ID measurements, XRD analyses, and IRSL dating, this thesis provides a chronostratigraphy of palaeo dune archives of northern Fuerteventura deduced from a correlation of sections close to the western coast and sections close to the eastern coast. The derived standard profile shows 15 units divided into 5 main sequences. These 5 sequences mainly differ in sand supply and accumulation, in changing humidity, and in imprint of volcanic activity. The chrono-stratigraphy dates back to about 450 ka. Generally, the archives are very site-specific, because features of a stratigraphic layer often change within close distances, depending on connectivity to erosion pathways and distance to sand sources. Micromorphological analyses indicate soil forming processes which are restricted to de- and recalcification and recrystallisation of iron and manganese. Ultimately, the palaeosurfaces are primarily dominated by the characteristics of Saharan dust (silt dominated, yellow to red in colour, containing hematite and goethite). The archives indicate a cyclicity of predominant processes, starting with I) sand accumulation, followed by II) dust accumulation and weak soil formation, leading to III) water-induced relocation. On the basis of this cyclicity a conceptual approach of the archives’ relationship to changes in sea level could be drawn. We assume highest sand supply during starting regression after sea level maxima. With dropping sea level, the distance between the studied sites and the sand source area (which are the gradually exposed shallow shelf areas) increases, leading to reduced sand accumulation. Starting transgression at the end of glacials suggests the lowest potential of sand accumulation. Furthermore, the concept is based on the assumption that with lower sea levels, more precipitation can reach the Canary Islands. Deduced from periods of lowest potential of sand accumulation in combination with periods of increased precipitation, best conditions for predominant dust accumulation and in-situ processes should be given at terminations. Generally, prevalence of palaeosurface formation is related to transgression periods. These periods are in good agreement with increased dust supply, which, in turn, seem to be affected by precession minima (according to Moreno et al., 2001). The predominance of dust accumulation and in-situ processes causes the fining of sediments, leading to reduced morphological resistance and, finally, water-induced relocation. Ultimately, site-specific sand availability seems to determine whether surfaces are exposed for longer durations, whereas the availability of precipitation (and dust) suggests determining the intensity of surface formation. The studied sections indicate a strong relationship to local volcanic activity because lava flows are able to cut off sand pathways and cover former sand source areas. In combination with dated lava flows the findings point to three different periods of volcanic activity which ceased the sand supply gradually. A first period around 180-170 ka, a next period around 135 ka, and a third period after 100 ka but latest around 50 ka which, finally, completely stopped the sand supply. Regarding the northern part of Fuerteventura, the latest period has so far not been described

Palaeoenvironmental reconstruction on the basis of Quaternary palaeo dune sequences on Fuerteventura

The volcanic origin of the Canarian Archipelago widely determines the landscape of these islands. Partially in coastal near areas the volcanic rocks are covered by dune fields. The eastern Canary Islands show the largest areas of sand deposits. On northern Fuerteventura sandpits and deep incised gully systems allow broader insight into generations of these archives. The dune material originates from the shallow shelf. Hence, the mineral composition is dominated by calcite and aragonite. The outcrops show the layering of several generations of biogenic carbonate sands which are separated by palaeosurfaces. These surfaces suggest soil-forming processes by their (often) reddish colour. Generally, the occurrence of several palaeosurfaces promises a high potential of those Quaternary dune archives on northern Fuerteventura. Former studies focussed on just few quarries being situated in close distances. Differing formation concepts and contradicting chronologies (Middle to Late Pleistocene versus Late Pleistocene) suggest the need for further investigation of landward palaeo dune sections, resulting in a DFG funded project with regard to palaeo dune sequences within the catchments of two Barrancos on northern Fuerteventura. Firstly, the project called for defining representative sections of the two catchments for the purpose of working out a correlation and deducing a standard profile, both should be based on stratigraphic findings. IRSL dating shall contribute to finally establishing a chrono-stratigraphy. Besides the carbonate sands, the dune archives are influenced by the imprint of volcanic material (tephra, lapilli, and basaltic rock) and Saharan dust. Generally, the archives’ composition and appearance raise several further questions: Are periods of surface formation dependent on reduced sand supply or on changes in climatic conditions? Which soil forming processes contribute to the characteristics of palaeosurface layers? How about the influence of Saharan dust? As dating of lava flows on northern Fuerteventura revealed Middle to Late Pleistocene ages, a further question refers to the relationship of dune formation and volcanic activity. Mainly deduced from findings in the field but also by use of grain size distribution, elemental composition, content of CaCO3, determination of Fed, measurements of rock magnetic parameters, analyses of gastropod associations, micromorphological analyses, determination of quartz content via Morphologi G3-ID measurements, XRD analyses, and IRSL dating, this thesis provides a chronostratigraphy of palaeo dune archives of northern Fuerteventura deduced from a correlation of sections close to the western coast and sections close to the eastern coast. The derived standard profile shows 15 units divided into 5 main sequences. These 5 sequences mainly differ in sand supply and accumulation, in changing humidity, and in imprint of volcanic activity. The chrono-stratigraphy dates back to about 450 ka. Generally, the archives are very site-specific, because features of a stratigraphic layer often change within close distances, depending on connectivity to erosion pathways and distance to sand sources. Micromorphological analyses indicate soil forming processes which are restricted to de- and recalcification and recrystallisation of iron and manganese. Ultimately, the palaeosurfaces are primarily dominated by the characteristics of Saharan dust (silt dominated, yellow to red in colour, containing hematite and goethite). The archives indicate a cyclicity of predominant processes, starting with I) sand accumulation, followed by II) dust accumulation and weak soil formation, leading to III) water-induced relocation. On the basis of this cyclicity a conceptual approach of the archives’ relationship to changes in sea level could be drawn. We assume highest sand supply during starting regression after sea level maxima. With dropping sea level, the distance between the studied sites and the sand source area (which are the gradually exposed shallow shelf areas) increases, leading to reduced sand accumulation. Starting transgression at the end of glacials suggests the lowest potential of sand accumulation. Furthermore, the concept is based on the assumption that with lower sea levels, more precipitation can reach the Canary Islands. Deduced from periods of lowest potential of sand accumulation in combination with periods of increased precipitation, best conditions for predominant dust accumulation and in-situ processes should be given at terminations. Generally, prevalence of palaeosurface formation is related to transgression periods. These periods are in good agreement with increased dust supply, which, in turn, seem to be affected by precession minima (according to Moreno et al., 2001). The predominance of dust accumulation and in-situ processes causes the fining of sediments, leading to reduced morphological resistance and, finally, water-induced relocation. Ultimately, site-specific sand availability seems to determine whether surfaces are exposed for longer durations, whereas the availability of precipitation (and dust) suggests determining the intensity of surface formation. The studied sections indicate a strong relationship to local volcanic activity because lava flows are able to cut off sand pathways and cover former sand source areas. In combination with dated lava flows the findings point to three different periods of volcanic activity which ceased the sand supply gradually. A first period around 180-170 ka, a next period around 135 ka, and a third period after 100 ka but latest around 50 ka which, finally, completely stopped the sand supply. Regarding the northern part of Fuerteventura, the latest period has so far not been described

Rock magnetics of carbonate systems–investigating palaeodune archives on Fuerteventura (Canary Islands)

The mineral magnetic properties of Pleistocene aeolian dune sands from the island of Fuerteventura (Canary Islands, Spain) were studied in order to reconstruct the palaeoenvironmental evolution of Pleistocene climates during their formation. The palaeodunes on Fuerteventura mainly consist of carbonate sands admixed with dust and material of volcanic origin. Due to the low magnetic background caused by the diamagnetic character of carbonate sands, these archives offer a lot of potential for environmental magnetic studies to detect the imprint of dust, volcanic material and paedogenesis. Four sections of alternating palaeosurface–aeolianite sequences in palaeodune fields have been analysed by means of extensive rock magnetic measurements. These Quaternary archives consist of deposits originating from different sources. I. material blown from the shallow shelf, II. material of volcanic origin, and III. long-range transported dust. The rock magnetic findings enable a more detailed interpretation of the palaeosurfaces within the sequences. We are able to differentiate semiquantitatively between the different source materials on one hand and to distinguish on the other hand those from soil-forming processes. Soil formation is only weakly developed in the dust imprints in the palaeosol aeolianite sequences, linked to sparse vegetation cover during the Pleistocene on Fuerteventura

Lipid biomarkers in aeolian sediments under desert pavements – potential and first results from the Black Rock Desert, Utah, USA, and Fuerteventura, Canary Islands, Spain

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SQUID-based magnetic prospection in interdisciplinary case studies at possible early and high medieval harbour sites in Germany

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