Maarten Prins - Profile on Academia.edu (original) (raw)
Papers by Maarten Prins
Age determination and clay content of sediment core GeoB5804-4
Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the... more Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost Red Sea were used to infer hydrological changes at the southern margin of the Mediterranean climate zone during the Holocene. Between approximately 9.25 and 7.25 thousand years ago, about 3 per mil reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff, which thereafter decreased to modern values. The northern Red Sea humid interval is best explained by enhancement and southward extension of rainfall from Mediterranean sources, possibly involving strengthened early-Holocene Arctic Oscillation patterns and a regional monsoon-type circulation induced by increased land-sea temperature contrasts. We conclude that Afro-Asian monsoonal rains did not cross the subtropical desert zone during the early to mid-Holocene.
Soil archives of a Fluvisol, part II. Archaeostratigraphical model of the subsurface of the medieval city centre of Vlaardingen, the Netherlands
EGU General Assembly Conference Abstracts, Apr 1, 2017
Grain size and XRD analysis on Site 162-983
The grain size of deep-sea sediments provides an apparently simple proxy for current speed. Howev... more The grain size of deep-sea sediments provides an apparently simple proxy for current speed. However, grain size-based proxies may be ambiguous when the size distribution reflects a combination of processes, with current sorting only one of them. In particular, such sediment mixing hinders reconstruction of deep circulation changes associated with ice-rafting events in the glacial North Atlantic because variable ice-rafted detritus (IRD) input may falsely suggest current speed changes. Inverse modeling has been suggested as a way to overcome this problem. However, this approach requires high-precision size measurements that register small changes in the size distribution. Here we show that such data can be obtained using electrosensing and laser diffraction techniques, despite issues previously raised on the low precision of electrosensing methods and potential grain shape effects on laser diffraction. Down-core size patterns obtained from a sediment core from the North Atlantic are similar for both techniques, reinforcing the conclusion that both techniques yield comparable results. However, IRD input leads to a coarsening that spuriously suggests faster current speed. We show that this IRD influence can be accounted for using inverse modeling as long as wide size spectra are taken into account. This yields current speed variations that are in agreement with other proxies. Our experiments thus show that for current speed reconstruction, the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modeling meaningful current speed reconstructions can be obtained from mixed sediments.
Sedimentation processes in Svalbard: A comparison between Dicksonfjorden and Kongsfjorden
EGUGA, Apr 1, 2018
Early Pliocene record of ice-rafted debris from ice-proximal site U1359 (IODP Exp 318), Wilkes Land continental rise, Antarctica
AGUFM, Dec 1, 2012
(Table 2) Branched GDGT abundance, and MBT/CBT-derived temperatures of paleosol-loess sequence MS2008W
Human impact on the Middle and Late Holocene floodplain sediment characteristics along the River Rhine
EGUGA, Apr 1, 2012
Correcting for the influence of ice‐rafted detritus on grain size‐based paleocurrent speed estimates
Paleoceanography, Oct 1, 2015
The grain size of deep-sea sediments provides an apparently simple proxy for current speed. Howev... more The grain size of deep-sea sediments provides an apparently simple proxy for current speed. However, grain size-based proxies may be ambiguous when the size distribution reflects a combination of processes, with current sorting only one of them. In particular, such sediment mixing hinders reconstruction of deep circulation changes associated with ice-rafting events in the glacial North Atlantic because variable ice-rafted detritus (IRD) input may falsely suggest current speed changes. Inverse modelling has been suggested as a way to overcome this problem. However, this approach requires high-precision size measurements that register small changes in the size distribution. Here we show that such data can be obtained using electro sensing and laser diffraction techniques, despite issues previously raised on the low precision of electro sensing methods and potential grain shape effects on laser diffraction. Down-core size patterns obtained from a sediment core from the North Atlantic are similar for both techniques, reinforcing the conclusion that both techniques yield comparable results. However, IRD input leads to a coarsening that spuriously suggests faster current speed. We show that this IRD influence can be accounted for using inverse modelling as long as wide size spectra are taken into account. This yields current speed variations that are in agreement with other proxies. Our experiments thus show that for current speed reconstruction the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modelling meaningful current speed reconstructions can be obtained from mixed sediments.
Quaternary Science Reviews, 2014
Our current understanding of past changes in East Asian summer monsoon (EASM) precipitation inten... more Our current understanding of past changes in East Asian summer monsoon (EASM) precipitation intensity derives from several loessepaleosol sequences and oxygen isotope (d 18 O) records of well-dated stalagmites. Although temperature is generally presumed to have had minimal impact on EASM records, past air temperature dynamics over East Asia are, so far, relatively poorly understood, mainly due to the lack of tools to reconstruct continental paleotemperatures. Here we report a high-resolution record of East Asian air temperature over the past 130,000 years, based on soil bacterial lipid signatures preserved in a loessepaleosol sequence from the Mangshan loess plateau in China. We find that maximum local insolation is the main driver of air temperature, although greenhouse gas concentrations and southern hemisphere climate may influence temperature at times when insolation is weak, causing a decoupling with EASM precipitation intensity. Direct comparison of our temperature record with precipitation-induced changes in past soil pH, derived from the same suite of lipids confirms this decoupling. Subsequent cross-spectral analysis of the two molecular proxy records reveals that variations in monsoon precipitation consistently lag those in air temperature throughout the whole record at the dominant precession band. The length of this lag is variable however, and increases as glaciation develops. This observation is consistent with an increasing influence of northern hemisphere ice sheets on the modulation of EASM response to insolation forcing during ice ages.
EGU General Assembly Conference Abstracts, Apr 1, 2017
The thick loess-palaeosol sequences in the Mangshan Loess Plateau (MLP; central China) along the ... more The thick loess-palaeosol sequences in the Mangshan Loess Plateau (MLP; central China) along the south bank of the lower reach of the Yellow River provide high-resolution records of Quaternary climate change. In addition, substantial increases in grain-size and accumulation rate have been inferred in the upper part of the loess sequence, above palaeosol layer S2. This study investigates the sources of the long-term dust supply to the MLP and explores the mechanism behind the sudden increase in sediment delivery and coarsening of the loess deposits since S2 (~240 ka) by using end member modelling of the loess grain-size dataset and single-grain zircon U-Pb dating. Our results indicate that the lower Yellow River floodplain, directly north of the MLP, served as a major dust supply for the plateau at least since the deposition of loess unit L9 and indirectly suggest that the integration of the Yellow River and the disappearance of the Sanmen palaeolake took place before L9 (~900 ka). The sudden change in sedimentology of the Mangshan sequence above palaeosol unit S2 may result from an increased fluvial sediment flux being transported to the lower reaches of the Yellow River because of tectonic movements (initiated) in the Weihe Basin around 240 ka. Furthermore, sediment coarsening can be explained by the gradual southward migration of the lower Yellow River floodplain towards the MLP since the deposition of palaeosol S2. The migration is evidenced by the formation of an impressive scarp, and is likely caused by tectonic tilting of the floodplain area.
Raw grain size analysis as measured by Coulter counter at Hole 162-983A, size fraction range 10-63 µm
Modern and early Holocene ice shelf sediment facies from Petermann Fjord and northern Nares Strait, northwest Greenland
Quaternary Science Reviews, May 1, 2022
Past Global Changes Magazine, Oct 1, 2014
Palaeogeography, Palaeoclimatology, Palaeoecology, May 1, 2016
Loess-paleosol sequences in the Vojvodina region in the southeastern Carpathian Basin have been i... more Loess-paleosol sequences in the Vojvodina region in the southeastern Carpathian Basin have been intensively studied to obtain a high-resolution stratigraphical framework for the Upper Pleistocene in this part of Europe. In these studies, millennial-scale sedimentation variations in the Upper Pleniglacial have been coupled to the Greenland Ice dust record, indicating that the rapid climate variability characterizing the North Atlantic and Greenland areas, is reflected in the loess deposits at the southern edge of the European loess belt. Rapid variations were recently also reported for the stable isotopic composition of organic matter in the Surduk loess-paleosol sequence, located in the Vojvodina region, and were interpreted as episodes of increased C 4 -vegetation over the last glacial period. Based on potential coinciding changes in oceanic and atmospheric circulation patterns, these episodes were attributed to plant moisture stress rather than by fluctuations in temperature, although exclusive proof has not yet been provided. Here we report a high-resolution record of continental air temperature and precipitation over the past 40,000 years based on soil bacterial lipid signatures preserved in the Surduk loesspaleosol sequence. Our temperature record shows a gradual warming trend, suggesting that moisture availability indeed seems to be the main factor driving the excursions to C 4 -vegetation around Surduk. We also find that continental air temperature changes in this region may be seasonally biased, and were driven by regional influences rather than by Northern Hemisphere climate forcings, likely as a result of the inland isolation of the Carpathian Basin by surrounding mountains. Support for a regional climate driver comes from comparison of our lipidbased temperature and precipitation records with similar records from the near-by Crvenka loess-paleosol sequence, which resemble the climatic trends recorded at Surduk.
End-Member Modeling of Siliciclastic Grain-Size Distributions<subtitle>The Late Quaternary Record of Eolian and Fluvial Sediment Supply to the Arabian Sea and its Paleoclimatic Significance</subtitle>
SEPM (Society for Sedimentary Geology) eBooks, 1999
Quaternary Science Reviews, Jun 1, 2017
The Luo River is located in the southern part of the Chinese Loess Plateau and the northern part ... more The Luo River is located in the southern part of the Chinese Loess Plateau and the northern part of the Weihe Basin, in Central China. In the basin it flows proximal to the site of the Luyang Wetland core, which is an important archive of climate change over the past 1 Myr in this region. In this paper, the contribution of the Luo River to the sedimentary record is analyzed by reconstructing the evolution of this river during the Middle to Late Pleistocene. It is argued that an alluvial fan of the Luo River has contributed to the sedimentary archive until approximately 200e240 ka. From this moment onwards, the fan became incised and terraces began to form. The formation of a new alluvial fan further downstream led to the disconnection of the Luo River from the Luyang Wetland core site. We propose that this series of events was caused by the displacement of an intra-basinal fault and the resultant faulting-forced folding, which caused increased relative subsidence, and thus increased sedimentation rates at the core site. Therefore, a complete sediment record in the 'Luyang Wetland' was preserved, despite the disconnection from the Luo River. The chronology of the fans and terraces was established using existing age control (U-series, ESR, OSL, pIRIR 290 and magnetic susceptibility correlation), and through correlation of the loess-paleosol cover to marine isotope stages. Based on sedimentological characteristics of the fluvial sequence, we suggest that incision of the Luo River occurred in two steps. Small incisions took place at transitions to interglacials and the main incision phases occur at the transition from an interglacial to glacial climate. Due to the incision, basal parts of the oldest Luo River alluvial fan are exposed, and it is in one of these exposures that the famous Dali Man skull was retrieved. This study shows that the Dali Man did not live on a river terrace as previously thought, but on an aggrading alluvial fan, during wet, glacial conditions.
An ephemeral meandering river system: Sediment dispersal processes in the Río Colorado, Southern Altiplano Plateau, Bolivia
Zeitschrift Fur Geomorphologie, Sep 1, 2015
ABSTRACT The Río Colorado meandering river system feeds the Salar de Uyuni, the World's l... more ABSTRACT The Río Colorado meandering river system feeds the Salar de Uyuni, the World's largest salt pan in the southern Altiplano plateau (Bolivia). It is characterized by ephemerality due to the high aridity of the region, and a downstream decrease of river bankfull width and depth in the river terminus. Dryland meandering river systems in high-altitude regions have rarely been reported. We investigated the active processes in this system from the alluvial fan to the lower coastal plain. On-site surveys combined with high-precision GPS and high-resolution satellite imagery show that Río Colorado area is typified by generally fine sediment and a low gradient in the coastal plain. In the alluvial fan, where channel meandering is weak but still recognizable, the deposits are characterized by fining-upward sequences with gravel-prone sediments at the bottom, paleosols in the middle and clay-dominated sediments at the top. In the coastal plain the channel deposits consist of coarse to fine sand with sparse basal gravel, while the river banks and thus much of the floodplain consist of clay and silt in the upper coastal plain and very fine sand, silt and clay with salt deposits in the lower coastal plain. Grain-size distribution analysis show a linear decrease in bed load sediments downstream and a concurrent increase in suspended load sediments. These longitudinal variations in the proportions of sediment load are found to be consistent with changes in the topographic slope. The river gradient shows six intervals with downstream decreasing but internally quite constant slopes and sediment composition. Characteristic geomorphologic features are found to be head-cutting channels, chute channels, avulsions and crevasse splays. They illustrate the processes of erosion and deposition in this low-gradient river system and help understand sediment dispersal and their preservation potentials.
Polar Research, Sep 16, 2019
Kongsfjorden, a fjord in north-western Svalbard, is characterized by large environmental gradient... more Kongsfjorden, a fjord in north-western Svalbard, is characterized by large environmental gradients driven by meltwater processes along the margins of tidewater glaciers and the inflow of relatively warm Atlantic Water, the main heat source for the European Arctic. These factors make Kongsfjorden a key area to investigate changes in the polar climate-ocean-glacier system and to examine the resulting effects on the marine environment. The aim of this paper is to synthesize knowledge about the marine sedimentary environment in Kongsfjorden since the last deglaciation. Fjords act as natural sedimentary traps, archiving information about past and present environmental conditions and changes. Geological studies of Kongsfjorden have demonstrated a good potential for reconstructing palaeoenvironments and establishing baselines values for the natural climate changes in the Arctic. Palaeoceanographic reconstructions reveal rising water temperatures similar to modern temperatures ca. 12 000 years ago. The extent of warm Atlantic Water entering the fjords influences processes at, and the stability of, the margins of the tidewater glaciers. Enhanced inflow may cause accelerated glacial melting that, in consequence, leads to an increase in the sediment flux from the glacial catchments into the fjord, as observed ca. 12 000 years ago and at present. However, responses of sediment flux to modern environmental changes remain poorly understood, hence long-term and monitoring studies are needed to quantify and model the effects of climate warming on the sedimentary environment of Kongsfjorden.
Age determination and clay content of sediment core GeoB5804-4
Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the... more Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost Red Sea were used to infer hydrological changes at the southern margin of the Mediterranean climate zone during the Holocene. Between approximately 9.25 and 7.25 thousand years ago, about 3 per mil reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff, which thereafter decreased to modern values. The northern Red Sea humid interval is best explained by enhancement and southward extension of rainfall from Mediterranean sources, possibly involving strengthened early-Holocene Arctic Oscillation patterns and a regional monsoon-type circulation induced by increased land-sea temperature contrasts. We conclude that Afro-Asian monsoonal rains did not cross the subtropical desert zone during the early to mid-Holocene.
Soil archives of a Fluvisol, part II. Archaeostratigraphical model of the subsurface of the medieval city centre of Vlaardingen, the Netherlands
EGU General Assembly Conference Abstracts, Apr 1, 2017
Grain size and XRD analysis on Site 162-983
The grain size of deep-sea sediments provides an apparently simple proxy for current speed. Howev... more The grain size of deep-sea sediments provides an apparently simple proxy for current speed. However, grain size-based proxies may be ambiguous when the size distribution reflects a combination of processes, with current sorting only one of them. In particular, such sediment mixing hinders reconstruction of deep circulation changes associated with ice-rafting events in the glacial North Atlantic because variable ice-rafted detritus (IRD) input may falsely suggest current speed changes. Inverse modeling has been suggested as a way to overcome this problem. However, this approach requires high-precision size measurements that register small changes in the size distribution. Here we show that such data can be obtained using electrosensing and laser diffraction techniques, despite issues previously raised on the low precision of electrosensing methods and potential grain shape effects on laser diffraction. Down-core size patterns obtained from a sediment core from the North Atlantic are similar for both techniques, reinforcing the conclusion that both techniques yield comparable results. However, IRD input leads to a coarsening that spuriously suggests faster current speed. We show that this IRD influence can be accounted for using inverse modeling as long as wide size spectra are taken into account. This yields current speed variations that are in agreement with other proxies. Our experiments thus show that for current speed reconstruction, the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modeling meaningful current speed reconstructions can be obtained from mixed sediments.
Sedimentation processes in Svalbard: A comparison between Dicksonfjorden and Kongsfjorden
EGUGA, Apr 1, 2018
Early Pliocene record of ice-rafted debris from ice-proximal site U1359 (IODP Exp 318), Wilkes Land continental rise, Antarctica
AGUFM, Dec 1, 2012
(Table 2) Branched GDGT abundance, and MBT/CBT-derived temperatures of paleosol-loess sequence MS2008W
Human impact on the Middle and Late Holocene floodplain sediment characteristics along the River Rhine
EGUGA, Apr 1, 2012
Correcting for the influence of ice‐rafted detritus on grain size‐based paleocurrent speed estimates
Paleoceanography, Oct 1, 2015
The grain size of deep-sea sediments provides an apparently simple proxy for current speed. Howev... more The grain size of deep-sea sediments provides an apparently simple proxy for current speed. However, grain size-based proxies may be ambiguous when the size distribution reflects a combination of processes, with current sorting only one of them. In particular, such sediment mixing hinders reconstruction of deep circulation changes associated with ice-rafting events in the glacial North Atlantic because variable ice-rafted detritus (IRD) input may falsely suggest current speed changes. Inverse modelling has been suggested as a way to overcome this problem. However, this approach requires high-precision size measurements that register small changes in the size distribution. Here we show that such data can be obtained using electro sensing and laser diffraction techniques, despite issues previously raised on the low precision of electro sensing methods and potential grain shape effects on laser diffraction. Down-core size patterns obtained from a sediment core from the North Atlantic are similar for both techniques, reinforcing the conclusion that both techniques yield comparable results. However, IRD input leads to a coarsening that spuriously suggests faster current speed. We show that this IRD influence can be accounted for using inverse modelling as long as wide size spectra are taken into account. This yields current speed variations that are in agreement with other proxies. Our experiments thus show that for current speed reconstruction the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modelling meaningful current speed reconstructions can be obtained from mixed sediments.
Quaternary Science Reviews, 2014
Our current understanding of past changes in East Asian summer monsoon (EASM) precipitation inten... more Our current understanding of past changes in East Asian summer monsoon (EASM) precipitation intensity derives from several loessepaleosol sequences and oxygen isotope (d 18 O) records of well-dated stalagmites. Although temperature is generally presumed to have had minimal impact on EASM records, past air temperature dynamics over East Asia are, so far, relatively poorly understood, mainly due to the lack of tools to reconstruct continental paleotemperatures. Here we report a high-resolution record of East Asian air temperature over the past 130,000 years, based on soil bacterial lipid signatures preserved in a loessepaleosol sequence from the Mangshan loess plateau in China. We find that maximum local insolation is the main driver of air temperature, although greenhouse gas concentrations and southern hemisphere climate may influence temperature at times when insolation is weak, causing a decoupling with EASM precipitation intensity. Direct comparison of our temperature record with precipitation-induced changes in past soil pH, derived from the same suite of lipids confirms this decoupling. Subsequent cross-spectral analysis of the two molecular proxy records reveals that variations in monsoon precipitation consistently lag those in air temperature throughout the whole record at the dominant precession band. The length of this lag is variable however, and increases as glaciation develops. This observation is consistent with an increasing influence of northern hemisphere ice sheets on the modulation of EASM response to insolation forcing during ice ages.
EGU General Assembly Conference Abstracts, Apr 1, 2017
The thick loess-palaeosol sequences in the Mangshan Loess Plateau (MLP; central China) along the ... more The thick loess-palaeosol sequences in the Mangshan Loess Plateau (MLP; central China) along the south bank of the lower reach of the Yellow River provide high-resolution records of Quaternary climate change. In addition, substantial increases in grain-size and accumulation rate have been inferred in the upper part of the loess sequence, above palaeosol layer S2. This study investigates the sources of the long-term dust supply to the MLP and explores the mechanism behind the sudden increase in sediment delivery and coarsening of the loess deposits since S2 (~240 ka) by using end member modelling of the loess grain-size dataset and single-grain zircon U-Pb dating. Our results indicate that the lower Yellow River floodplain, directly north of the MLP, served as a major dust supply for the plateau at least since the deposition of loess unit L9 and indirectly suggest that the integration of the Yellow River and the disappearance of the Sanmen palaeolake took place before L9 (~900 ka). The sudden change in sedimentology of the Mangshan sequence above palaeosol unit S2 may result from an increased fluvial sediment flux being transported to the lower reaches of the Yellow River because of tectonic movements (initiated) in the Weihe Basin around 240 ka. Furthermore, sediment coarsening can be explained by the gradual southward migration of the lower Yellow River floodplain towards the MLP since the deposition of palaeosol S2. The migration is evidenced by the formation of an impressive scarp, and is likely caused by tectonic tilting of the floodplain area.
Raw grain size analysis as measured by Coulter counter at Hole 162-983A, size fraction range 10-63 µm
Modern and early Holocene ice shelf sediment facies from Petermann Fjord and northern Nares Strait, northwest Greenland
Quaternary Science Reviews, May 1, 2022
Past Global Changes Magazine, Oct 1, 2014
Palaeogeography, Palaeoclimatology, Palaeoecology, May 1, 2016
Loess-paleosol sequences in the Vojvodina region in the southeastern Carpathian Basin have been i... more Loess-paleosol sequences in the Vojvodina region in the southeastern Carpathian Basin have been intensively studied to obtain a high-resolution stratigraphical framework for the Upper Pleistocene in this part of Europe. In these studies, millennial-scale sedimentation variations in the Upper Pleniglacial have been coupled to the Greenland Ice dust record, indicating that the rapid climate variability characterizing the North Atlantic and Greenland areas, is reflected in the loess deposits at the southern edge of the European loess belt. Rapid variations were recently also reported for the stable isotopic composition of organic matter in the Surduk loess-paleosol sequence, located in the Vojvodina region, and were interpreted as episodes of increased C 4 -vegetation over the last glacial period. Based on potential coinciding changes in oceanic and atmospheric circulation patterns, these episodes were attributed to plant moisture stress rather than by fluctuations in temperature, although exclusive proof has not yet been provided. Here we report a high-resolution record of continental air temperature and precipitation over the past 40,000 years based on soil bacterial lipid signatures preserved in the Surduk loesspaleosol sequence. Our temperature record shows a gradual warming trend, suggesting that moisture availability indeed seems to be the main factor driving the excursions to C 4 -vegetation around Surduk. We also find that continental air temperature changes in this region may be seasonally biased, and were driven by regional influences rather than by Northern Hemisphere climate forcings, likely as a result of the inland isolation of the Carpathian Basin by surrounding mountains. Support for a regional climate driver comes from comparison of our lipidbased temperature and precipitation records with similar records from the near-by Crvenka loess-paleosol sequence, which resemble the climatic trends recorded at Surduk.
End-Member Modeling of Siliciclastic Grain-Size Distributions<subtitle>The Late Quaternary Record of Eolian and Fluvial Sediment Supply to the Arabian Sea and its Paleoclimatic Significance</subtitle>
SEPM (Society for Sedimentary Geology) eBooks, 1999
Quaternary Science Reviews, Jun 1, 2017
The Luo River is located in the southern part of the Chinese Loess Plateau and the northern part ... more The Luo River is located in the southern part of the Chinese Loess Plateau and the northern part of the Weihe Basin, in Central China. In the basin it flows proximal to the site of the Luyang Wetland core, which is an important archive of climate change over the past 1 Myr in this region. In this paper, the contribution of the Luo River to the sedimentary record is analyzed by reconstructing the evolution of this river during the Middle to Late Pleistocene. It is argued that an alluvial fan of the Luo River has contributed to the sedimentary archive until approximately 200e240 ka. From this moment onwards, the fan became incised and terraces began to form. The formation of a new alluvial fan further downstream led to the disconnection of the Luo River from the Luyang Wetland core site. We propose that this series of events was caused by the displacement of an intra-basinal fault and the resultant faulting-forced folding, which caused increased relative subsidence, and thus increased sedimentation rates at the core site. Therefore, a complete sediment record in the 'Luyang Wetland' was preserved, despite the disconnection from the Luo River. The chronology of the fans and terraces was established using existing age control (U-series, ESR, OSL, pIRIR 290 and magnetic susceptibility correlation), and through correlation of the loess-paleosol cover to marine isotope stages. Based on sedimentological characteristics of the fluvial sequence, we suggest that incision of the Luo River occurred in two steps. Small incisions took place at transitions to interglacials and the main incision phases occur at the transition from an interglacial to glacial climate. Due to the incision, basal parts of the oldest Luo River alluvial fan are exposed, and it is in one of these exposures that the famous Dali Man skull was retrieved. This study shows that the Dali Man did not live on a river terrace as previously thought, but on an aggrading alluvial fan, during wet, glacial conditions.
An ephemeral meandering river system: Sediment dispersal processes in the Río Colorado, Southern Altiplano Plateau, Bolivia
Zeitschrift Fur Geomorphologie, Sep 1, 2015
ABSTRACT The Río Colorado meandering river system feeds the Salar de Uyuni, the World's l... more ABSTRACT The Río Colorado meandering river system feeds the Salar de Uyuni, the World's largest salt pan in the southern Altiplano plateau (Bolivia). It is characterized by ephemerality due to the high aridity of the region, and a downstream decrease of river bankfull width and depth in the river terminus. Dryland meandering river systems in high-altitude regions have rarely been reported. We investigated the active processes in this system from the alluvial fan to the lower coastal plain. On-site surveys combined with high-precision GPS and high-resolution satellite imagery show that Río Colorado area is typified by generally fine sediment and a low gradient in the coastal plain. In the alluvial fan, where channel meandering is weak but still recognizable, the deposits are characterized by fining-upward sequences with gravel-prone sediments at the bottom, paleosols in the middle and clay-dominated sediments at the top. In the coastal plain the channel deposits consist of coarse to fine sand with sparse basal gravel, while the river banks and thus much of the floodplain consist of clay and silt in the upper coastal plain and very fine sand, silt and clay with salt deposits in the lower coastal plain. Grain-size distribution analysis show a linear decrease in bed load sediments downstream and a concurrent increase in suspended load sediments. These longitudinal variations in the proportions of sediment load are found to be consistent with changes in the topographic slope. The river gradient shows six intervals with downstream decreasing but internally quite constant slopes and sediment composition. Characteristic geomorphologic features are found to be head-cutting channels, chute channels, avulsions and crevasse splays. They illustrate the processes of erosion and deposition in this low-gradient river system and help understand sediment dispersal and their preservation potentials.
Polar Research, Sep 16, 2019
Kongsfjorden, a fjord in north-western Svalbard, is characterized by large environmental gradient... more Kongsfjorden, a fjord in north-western Svalbard, is characterized by large environmental gradients driven by meltwater processes along the margins of tidewater glaciers and the inflow of relatively warm Atlantic Water, the main heat source for the European Arctic. These factors make Kongsfjorden a key area to investigate changes in the polar climate-ocean-glacier system and to examine the resulting effects on the marine environment. The aim of this paper is to synthesize knowledge about the marine sedimentary environment in Kongsfjorden since the last deglaciation. Fjords act as natural sedimentary traps, archiving information about past and present environmental conditions and changes. Geological studies of Kongsfjorden have demonstrated a good potential for reconstructing palaeoenvironments and establishing baselines values for the natural climate changes in the Arctic. Palaeoceanographic reconstructions reveal rising water temperatures similar to modern temperatures ca. 12 000 years ago. The extent of warm Atlantic Water entering the fjords influences processes at, and the stability of, the margins of the tidewater glaciers. Enhanced inflow may cause accelerated glacial melting that, in consequence, leads to an increase in the sediment flux from the glacial catchments into the fjord, as observed ca. 12 000 years ago and at present. However, responses of sediment flux to modern environmental changes remain poorly understood, hence long-term and monitoring studies are needed to quantify and model the effects of climate warming on the sedimentary environment of Kongsfjorden.