In the context of global climate change, flooding becomes an increasingly serious threat to moder... more In the context of global climate change, flooding becomes an increasingly serious threat to modern societies, and future flooding can only be understood using long-term geological flood records also encompassing Holocene climate variability. Unlike other regions, Holocene flooding in the Caucasus region is only poorly understood so far: Whereas some rivers originating from the Lesser Caucasus were investigated, no studies exist about rivers originating from the Greater Caucasus. This study investigated the Holocene fluvial dynamics of the upper Alazani River in the southern Greater Caucasus using chronostratigraphic and sedimentologic methods applied to a fluvial sediment-paleosol sequence. By comparing these data with other paleoenvironmental and regional recent hydroclimatic data, we aimed to identify the main drivers of Holocene flooding in the southern Greater Caucasus. Our study shows a link between fluvial sedimentation around 7.3, 5.4, 3.8–2.9 and around 1.7 cal. ka BP and North Atlantic Bond events. Although probably caused by a discharge maximum during spring, fluvial sedimentation is coeval with low regional spring precipitation. As supported by recent hydroclimatic data, intensified floods during Bond events could possibly be explained with more intensive precipitation but also a prolonged snow season during colder winters. The latter would lead to more spring meltwater and thus more intensive spring discharge. Consequently, given increasing annual temperatures because of human-caused global warming, the flood maxima of pluvio-nival rivers in the southern Greater Caucasus may be expected to decrease during the next decades. Our findings underline the need of geological flood records to understand future flood patterns of rivers in mountain regions with complex runoff regimes.
During the Last Glacial Maximum, ca. 25,000 to 20,000 calBP, the settlement remains of European h... more During the Last Glacial Maximum, ca. 25,000 to 20,000 calBP, the settlement remains of European hunter-gatherers show a patchy pattern with clusters of sites in some regions and no reported settlement in others. Using a density-based upscaling approach, we calculate regionally differentiated population densities. To test our results and assess possible biases, we compare the spatial distribution of sites against environmental preference scores derived from palaeoclimate model data and loess/forest distributions. We find pronounced demographic differences between Western Europe and eastern Central Europe that coincide with different environmental preferences: cool temperate conditions in the West as opposed to colder and drier conditions in the East. Comparatively few people and an adaptation to cold and dry conditions eventually may have led to an extinction of the local population in western Central Europe around 22,000 calBP.
Egu General Assembly Conference Abstracts, May 1, 2010
Colour data from deep-sea cores has become an important tool in past climate reconstructions and ... more Colour data from deep-sea cores has become an important tool in past climate reconstructions and stratigraphy to characterise changes in lithology. This is because image scanning is a fast, inexpensive and non-destructive method to retrieve high-resolution records. Cracks in the sediment, however, may significantly alter the colour data. Here we present new algorithms to correct the colour data for cracks. As an example, we will discuss the application of this method using a core from the Ocean Drilling Program. In images, cracks may be recognised as dark areas, especially when images are illuminated to gain quantitatively comparable results. We use the differences in brightness to separate between cracks and non-cracked sediment. The adjustment of threshold values for crack recognition is not straightforward and has to be done and checked manually. We analyse images in a way that we calculate mean values, median values and standard deviations of Red, Green, Blue (RGB) and grayscale data. To correct for dark/cracked areas within images, we exclude from analysis: 1) all data darker than a user-defined threshold value (which leaves 'uncracked' data from pixels brighter than the threshold) 2) only pixel-rows which are darker than the threshold for a user defined percentage (e.g. 80%). This way only horizontal cracks are accounted for. In this case a correction for the potentially new amount of analysed pixel rows is made. We also compute a combination of the previous points: both pixel rows and individual datapoints darker than the defined threshold value are excluded from calculations, a correction for the potentially new amount of analysed pixel rows is made. Further, we compute colour data from the original image for comparison. We have applied this technique to ODP core C26 of Site 926 (Ceara Rise) in the equatorial Atlantic and compared results from these image correction techniques. Further, we discuss the influence of image resolution, and compare high-resolution colour scans to original ODP images provided by ODP in the initial reports of expeditions. The research within the GTSnext project leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° [215458].
Various sediment types may record properties of the Earth's magnetic field during or short after ... more Various sediment types may record properties of the Earth's magnetic field during or short after deposition. In this contribution we discuss high resolution palaeomagnetic studies of last glacial loess sites from the Danube catchment which contain archaeological remains. Archaeological sites with relatively high sedimentation rates were chosen in order to 1) check whether the loess contains a reliable palaeomagnetic signal 2) check whether palaeosecular variation features may be identified 3) use the existing dating from the archaeological sites (14C and luminescence) to gain a palaeomagnetic record from loess with reasonable age control and 4) compare palaeosecular variation signals to reference section(s) with the aim to construct a relative stratigraphy of archaeological layers from different localities in the Danube catchment. Because the investigated loess and loess-like sediments are not all homogeneous, but in some cases intercalated with humiferous horizons, studies on the relative palaeointensity of the Earth's magnetic field are not possible for all sites. In this contribution we will show the application of palaeomagnetic stratigraphy to a loess site containing archaeological finds. We will demonstrate that the palaeosecular variation pattern can be matched to data from the Lac du Bouchet (France) lacustrine sequence. This comparison works reasonably well, and we are able to construct a stratigraphy based on the comparison to the dated Lac du Bouchet record. However, we are aware of some dating inaccuracies of this reference record at millennial scale. Concluding, we are able to put archaeological layers from different localities in a stratigraphic order using the palaeosecular variation signal as recorded by loess as correlative dating technique.
Orbital-tuned timescales play an important role for many studies in paleoclimatology and integrat... more Orbital-tuned timescales play an important role for many studies in paleoclimatology and integrated stratigraphy. A reliable test for validity stand-alone astronomically-tuned time scales has however not yet been established. Shackleton et al., (1995) suggested that precession amplitude modulation by eccentricity is the best criterion available for a successful tuning. However, Huybers & Aharonson, (2010) oppose this approach and "conclude that the presence of eccentricity-like amplitude modulation in precession-filtered records does not support the accuracy of orbitally tuned time scales". We discuss some approaches to circumvent the potential problem of frequency modulations during the tuning process, thereby allowing the use of amplitude modulations for timescale evaluation. This method is discussed using a geological dataset.
One of the youngest and worldwide documented geomagnetic excursions in the Brunhes Chron is the M... more One of the youngest and worldwide documented geomagnetic excursions in the Brunhes Chron is the Mono Lake excursion (MLE). It has been detected in marine and terrestrial sedimentary archives as well as in lavas. Recent age determinations and age estimates for the MLE centre around an age interval of approximately 31 – 34 ka. Likewise the Laschamp excursion the MLE goes along with a distinct peak in cosmogenic radionuclides in ice cores and sedimentary archives. It provides therefore an additional geomagnetic time marker for various geoarchives to synchronise different climate archives. Here we report on a detailed record of the MLE from a loess site at Krems, Lower Austria. The site is situated on the southern slope of the Wachtberg hill in the vicinity of the old city centre of Krems. The archive comprises Middle to Upper Würmian (Late Pleistocene) loess in which an Upper Palaeolithic (Early Gravettian) cultural layer is embedded. The most spectacular finds are a double infant buri...
ABSTRACT The loess sediment embedding the main Gravettian layer at the Krems-Wachtberg archaeolog... more ABSTRACT The loess sediment embedding the main Gravettian layer at the Krems-Wachtberg archaeological site facilitates exceptional preservation. To gain insight in the sedimentation process before and after the Palaeolithic settlement, the magnetic fabric (preferential orientation of magnetic particles) of loess of the Krems-Wachtberg site was investigated. Magnetic fabric properties clearly show an eolian origin of the loess, but may indicate some relocation in the metre above the cultural layer. The magnetic fabric properties can be divided into three intervals, the top interval shows lowest foliation and inconsistent magnetic fabric directions. The middle interval around the main cultural layer shows low foliation, but a clear preferential NW-SE direction of the lineation. This lineation is interpreted as preferential direction of the eolian loess accumulation from the southeast. The interval below ~0.5 m underneath the main find horizon shows a northeastesouthwest lineation, but an imbrication suggesting that sediment accumulation occurred at 90° to this direction, similar to the interval around the find horizon.
Geochemical characteristics have been intensively used to assign sediment properties to paleoclim... more Geochemical characteristics have been intensively used to assign sediment properties to paleoclimate and provenance. Nonetheless, in particular concerning the arid context, bulk geochemistry of different sediment archives and corresponding process interpretations are hitherto elusive. The Ejina Basin, with its suite of different sediment archives, is known as one of the main sources for the loess accumulation on the Chinese Loess Plateau. In order to understand mechanisms along this supra-regional sediment cascade , it is crucial to decipher the archive characteristics and formation processes. To address these issues, five profiles in different geomorphological contexts were selected. Analyses of X-ray fluorescence and diffraction, grain size, optically stimulated luminescence and radiocarbon dating were performed. Robust factor analysis was applied to reduce the attribute space to the process space of sedimentation history. Five sediment archives from three lithologic units exhibit geochemical characteristics as follows: (i) aeolian sands have high contents of Zr and Hf, whereas only Hf can be regarded as a valuable indicator to discriminate the coarse sand proportion; (ii) sandy loess has high Ca and Sr contents which both exhibit broad correlations with the medium to coarse silt proportions; (iii) lacustrine clays have high contents of felsic, ferromagnesian and mica source elements e.g., K, Fe, Ti, V, and Ni; (iv) fluvial sands have high contents of Mg, Cl and Na which may be enriched in evaporite minerals; (v) alluvial gravels have high contents of Cr which may originate from nearby Cr-rich bedrock. Temporal variations can be illustrated by four robust factors: weathering intensity, silicate-bearing mineral abundance, saline/alkaline magnitude and quasi-constant aeolian input. In summary, the bulk-composition of the late Quaternary sediments in this arid context is governed by the nature of the source terrain, weak chemical weathering, authigenic minerals, aeolian sand input, whereas pedogenesis and diagenesis exert only limited influences. Hence, this study demonstrates a practical geochemical strategy supplemented by grain size and mineralogical data, to discriminate sediment archives and thereafter enhance our ability to offer more intriguing information about the sedimentary processes in the arid central Asia.
In the context of global climate change, flooding becomes an increasingly serious threat to moder... more In the context of global climate change, flooding becomes an increasingly serious threat to modern societies, and future flooding can only be understood using long-term geological flood records also encompassing Holocene climate variability. Unlike other regions, Holocene flooding in the Caucasus region is only poorly understood so far: Whereas some rivers originating from the Lesser Caucasus were investigated, no studies exist about rivers originating from the Greater Caucasus. This study investigated the Holocene fluvial dynamics of the upper Alazani River in the southern Greater Caucasus using chronostratigraphic and sedimentologic methods applied to a fluvial sediment-paleosol sequence. By comparing these data with other paleoenvironmental and regional recent hydroclimatic data, we aimed to identify the main drivers of Holocene flooding in the southern Greater Caucasus. Our study shows a link between fluvial sedimentation around 7.3, 5.4, 3.8–2.9 and around 1.7 cal. ka BP and North Atlantic Bond events. Although probably caused by a discharge maximum during spring, fluvial sedimentation is coeval with low regional spring precipitation. As supported by recent hydroclimatic data, intensified floods during Bond events could possibly be explained with more intensive precipitation but also a prolonged snow season during colder winters. The latter would lead to more spring meltwater and thus more intensive spring discharge. Consequently, given increasing annual temperatures because of human-caused global warming, the flood maxima of pluvio-nival rivers in the southern Greater Caucasus may be expected to decrease during the next decades. Our findings underline the need of geological flood records to understand future flood patterns of rivers in mountain regions with complex runoff regimes.
During the Last Glacial Maximum, ca. 25,000 to 20,000 calBP, the settlement remains of European h... more During the Last Glacial Maximum, ca. 25,000 to 20,000 calBP, the settlement remains of European hunter-gatherers show a patchy pattern with clusters of sites in some regions and no reported settlement in others. Using a density-based upscaling approach, we calculate regionally differentiated population densities. To test our results and assess possible biases, we compare the spatial distribution of sites against environmental preference scores derived from palaeoclimate model data and loess/forest distributions. We find pronounced demographic differences between Western Europe and eastern Central Europe that coincide with different environmental preferences: cool temperate conditions in the West as opposed to colder and drier conditions in the East. Comparatively few people and an adaptation to cold and dry conditions eventually may have led to an extinction of the local population in western Central Europe around 22,000 calBP.
Egu General Assembly Conference Abstracts, May 1, 2010
Colour data from deep-sea cores has become an important tool in past climate reconstructions and ... more Colour data from deep-sea cores has become an important tool in past climate reconstructions and stratigraphy to characterise changes in lithology. This is because image scanning is a fast, inexpensive and non-destructive method to retrieve high-resolution records. Cracks in the sediment, however, may significantly alter the colour data. Here we present new algorithms to correct the colour data for cracks. As an example, we will discuss the application of this method using a core from the Ocean Drilling Program. In images, cracks may be recognised as dark areas, especially when images are illuminated to gain quantitatively comparable results. We use the differences in brightness to separate between cracks and non-cracked sediment. The adjustment of threshold values for crack recognition is not straightforward and has to be done and checked manually. We analyse images in a way that we calculate mean values, median values and standard deviations of Red, Green, Blue (RGB) and grayscale data. To correct for dark/cracked areas within images, we exclude from analysis: 1) all data darker than a user-defined threshold value (which leaves 'uncracked' data from pixels brighter than the threshold) 2) only pixel-rows which are darker than the threshold for a user defined percentage (e.g. 80%). This way only horizontal cracks are accounted for. In this case a correction for the potentially new amount of analysed pixel rows is made. We also compute a combination of the previous points: both pixel rows and individual datapoints darker than the defined threshold value are excluded from calculations, a correction for the potentially new amount of analysed pixel rows is made. Further, we compute colour data from the original image for comparison. We have applied this technique to ODP core C26 of Site 926 (Ceara Rise) in the equatorial Atlantic and compared results from these image correction techniques. Further, we discuss the influence of image resolution, and compare high-resolution colour scans to original ODP images provided by ODP in the initial reports of expeditions. The research within the GTSnext project leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° [215458].
Various sediment types may record properties of the Earth's magnetic field during or short after ... more Various sediment types may record properties of the Earth's magnetic field during or short after deposition. In this contribution we discuss high resolution palaeomagnetic studies of last glacial loess sites from the Danube catchment which contain archaeological remains. Archaeological sites with relatively high sedimentation rates were chosen in order to 1) check whether the loess contains a reliable palaeomagnetic signal 2) check whether palaeosecular variation features may be identified 3) use the existing dating from the archaeological sites (14C and luminescence) to gain a palaeomagnetic record from loess with reasonable age control and 4) compare palaeosecular variation signals to reference section(s) with the aim to construct a relative stratigraphy of archaeological layers from different localities in the Danube catchment. Because the investigated loess and loess-like sediments are not all homogeneous, but in some cases intercalated with humiferous horizons, studies on the relative palaeointensity of the Earth's magnetic field are not possible for all sites. In this contribution we will show the application of palaeomagnetic stratigraphy to a loess site containing archaeological finds. We will demonstrate that the palaeosecular variation pattern can be matched to data from the Lac du Bouchet (France) lacustrine sequence. This comparison works reasonably well, and we are able to construct a stratigraphy based on the comparison to the dated Lac du Bouchet record. However, we are aware of some dating inaccuracies of this reference record at millennial scale. Concluding, we are able to put archaeological layers from different localities in a stratigraphic order using the palaeosecular variation signal as recorded by loess as correlative dating technique.
Orbital-tuned timescales play an important role for many studies in paleoclimatology and integrat... more Orbital-tuned timescales play an important role for many studies in paleoclimatology and integrated stratigraphy. A reliable test for validity stand-alone astronomically-tuned time scales has however not yet been established. Shackleton et al., (1995) suggested that precession amplitude modulation by eccentricity is the best criterion available for a successful tuning. However, Huybers & Aharonson, (2010) oppose this approach and "conclude that the presence of eccentricity-like amplitude modulation in precession-filtered records does not support the accuracy of orbitally tuned time scales". We discuss some approaches to circumvent the potential problem of frequency modulations during the tuning process, thereby allowing the use of amplitude modulations for timescale evaluation. This method is discussed using a geological dataset.
One of the youngest and worldwide documented geomagnetic excursions in the Brunhes Chron is the M... more One of the youngest and worldwide documented geomagnetic excursions in the Brunhes Chron is the Mono Lake excursion (MLE). It has been detected in marine and terrestrial sedimentary archives as well as in lavas. Recent age determinations and age estimates for the MLE centre around an age interval of approximately 31 – 34 ka. Likewise the Laschamp excursion the MLE goes along with a distinct peak in cosmogenic radionuclides in ice cores and sedimentary archives. It provides therefore an additional geomagnetic time marker for various geoarchives to synchronise different climate archives. Here we report on a detailed record of the MLE from a loess site at Krems, Lower Austria. The site is situated on the southern slope of the Wachtberg hill in the vicinity of the old city centre of Krems. The archive comprises Middle to Upper Würmian (Late Pleistocene) loess in which an Upper Palaeolithic (Early Gravettian) cultural layer is embedded. The most spectacular finds are a double infant buri...
ABSTRACT The loess sediment embedding the main Gravettian layer at the Krems-Wachtberg archaeolog... more ABSTRACT The loess sediment embedding the main Gravettian layer at the Krems-Wachtberg archaeological site facilitates exceptional preservation. To gain insight in the sedimentation process before and after the Palaeolithic settlement, the magnetic fabric (preferential orientation of magnetic particles) of loess of the Krems-Wachtberg site was investigated. Magnetic fabric properties clearly show an eolian origin of the loess, but may indicate some relocation in the metre above the cultural layer. The magnetic fabric properties can be divided into three intervals, the top interval shows lowest foliation and inconsistent magnetic fabric directions. The middle interval around the main cultural layer shows low foliation, but a clear preferential NW-SE direction of the lineation. This lineation is interpreted as preferential direction of the eolian loess accumulation from the southeast. The interval below ~0.5 m underneath the main find horizon shows a northeastesouthwest lineation, but an imbrication suggesting that sediment accumulation occurred at 90° to this direction, similar to the interval around the find horizon.
Geochemical characteristics have been intensively used to assign sediment properties to paleoclim... more Geochemical characteristics have been intensively used to assign sediment properties to paleoclimate and provenance. Nonetheless, in particular concerning the arid context, bulk geochemistry of different sediment archives and corresponding process interpretations are hitherto elusive. The Ejina Basin, with its suite of different sediment archives, is known as one of the main sources for the loess accumulation on the Chinese Loess Plateau. In order to understand mechanisms along this supra-regional sediment cascade , it is crucial to decipher the archive characteristics and formation processes. To address these issues, five profiles in different geomorphological contexts were selected. Analyses of X-ray fluorescence and diffraction, grain size, optically stimulated luminescence and radiocarbon dating were performed. Robust factor analysis was applied to reduce the attribute space to the process space of sedimentation history. Five sediment archives from three lithologic units exhibit geochemical characteristics as follows: (i) aeolian sands have high contents of Zr and Hf, whereas only Hf can be regarded as a valuable indicator to discriminate the coarse sand proportion; (ii) sandy loess has high Ca and Sr contents which both exhibit broad correlations with the medium to coarse silt proportions; (iii) lacustrine clays have high contents of felsic, ferromagnesian and mica source elements e.g., K, Fe, Ti, V, and Ni; (iv) fluvial sands have high contents of Mg, Cl and Na which may be enriched in evaporite minerals; (v) alluvial gravels have high contents of Cr which may originate from nearby Cr-rich bedrock. Temporal variations can be illustrated by four robust factors: weathering intensity, silicate-bearing mineral abundance, saline/alkaline magnitude and quasi-constant aeolian input. In summary, the bulk-composition of the late Quaternary sediments in this arid context is governed by the nature of the source terrain, weak chemical weathering, authigenic minerals, aeolian sand input, whereas pedogenesis and diagenesis exert only limited influences. Hence, this study demonstrates a practical geochemical strategy supplemented by grain size and mineralogical data, to discriminate sediment archives and thereafter enhance our ability to offer more intriguing information about the sedimentary processes in the arid central Asia.
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Papers by Christian Zeeden
winters. The latter would lead to more spring meltwater and thus more intensive spring discharge. Consequently, given increasing annual temperatures because of human-caused global warming, the flood maxima of pluvio-nival rivers in the southern Greater Caucasus may be expected to decrease during the next decades. Our findings underline the need of geological flood records to understand future flood patterns of rivers in mountain regions with complex runoff regimes.
winters. The latter would lead to more spring meltwater and thus more intensive spring discharge. Consequently, given increasing annual temperatures because of human-caused global warming, the flood maxima of pluvio-nival rivers in the southern Greater Caucasus may be expected to decrease during the next decades. Our findings underline the need of geological flood records to understand future flood patterns of rivers in mountain regions with complex runoff regimes.