Pre-alpine mire sediments as a mirror of erosion, soil formation and landscape evolution during the last 45ka (original) (raw)
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Late glacial environmental history and early soil formation in Northwest Switzerland
In 1996, well preserved deer bones, antler fragments and black grouse bones were found in a filled karst crack. Those animal remains were discovered in a limestone quarry in the Jura Mountains near Dittingen (canton Basel-Landschaft, Northwest Switzerland). The site is situated in a gully of a dry valley beneath a loess covered high plain. In the framework of an archaeological excavation, the karst crack filling and overlying sediments (hill-washed loess, soils and colluviums) were documented. Samples for granulometry, geochemistry, micromorphology and palynology were analysed. The animal remains derived from the karstic fissure were radiocarbon dated to the early Bølling Interstadial (14’800 to 14’200 cal. BP). In addition, the palynological study shows that the overlying gully sediments were deposited between the Younger Dryas and the Middle Ages. The interdisciplinary investigation of the sediments revealed new insights into early soil formation processes, morphogenetic events and the vegetation history of periglacial environments. The new results clearly show that soil formation started immediately in the early Late Glacial. Decalcification and clay illuviation quickly developed in the course of intense vertical water flow through the sediment. It is therefore evident that luvisol development took place during the Late Glacial Interstadial (Bølling-Allerød Interstadial).
The Holocene, 2012
The deposition of Late Pleistocene and Holocene sediments in the high-altitude lake Meidsee (located at an altitude of 2661 m a.s.l. in the Southwestern Alps) strikingly coincided with global ice-sheet and mountain-glacier decay in the Alpine forelands and the formation of perialpine lakes. Radiocarbon ages of bottom-core sediments point out (pre-) Holocene ice retreat below 2700 m a.s.l., at about 16, 13, 10, and 9 cal. kyr BP. The Meidsee sedimentary record therefore provides information about the high-altitude Alpine landscape evolution since the Late Pleistocene/Holocene deglaciation in the Swiss Southwestern Alps. Prior to 5 cal. kyr BP, the C/N ratio and the isotopic composition of sedimentary organic matter (δ 15 N org , δ 13 C org ) indicate the deposition of algal-derived organic matter with limited input of terrestrial organic matter. The early Holocene and the Holocene climatic optimum (between 7.0 and 5.5 cal. kyr BP) were characterized by low erosion (decreasing magnetic susceptibility, χ) and high content of organic matter (C org > 13 wt.%), enriched in 13 C org (> −18‰) with a low C/N (˜10) ratio, typical of modern algal matter derived from in situ production. During the late Holocene, there was a long-term increasing contribution of terrestrial organic matter into the lake (C/N > 11), with maxima between 2.4 and 0.9 cal. kyr BP. A major environmental change took place 800 years ago, with an abrupt decrease in the relative contribution of terrestrial organic material into the lake compared with aquatic organic material which subsequently largely dominated (C/N drop from 16 to 10). Nonetheless, this event was marked by a rise in soil erosion (χ), in nutrients input (N and P contents) and in anthropogenic lead deposition, suggesting a human disturbance of Alpine ecosystems 800 years ago. Indeed, this time period coincided with the migration of the Walser Alemannic people in the region, who settled at relatively high altitude in the Southwestern Alps for farming and maintaining Alpine passes.
Quaternary Science …, 2012
Two well-dated ca. Holocene-long sedimentary sequences from deepest parts of Lake Bourget provide new insights onto the evolution of erosion patterns at a regional scale in NW European Alps. The combination of high resolution geochemistry -XRF core scanning, calibrated by 150 punctual measurementsand isotope geochemistry (Nd) of the terrigenous fraction permitted the reconstruction not only of the intensity, but also the type (physical erosion vs. chemical weathering) and the location (Prealpine massifs vs. High Crystalline massifs) of dominant erosion processes. Those data point the persistency of weak erosion fluxes from 9600 to 5500 cal. BP due both to a dry climate and the growing sheltering effect of soils that rapidly progressed between 9600 and 8000 cal. BP. Soils then reached a steady state before being destabilised around 4400 cal. BP, probably in response to human impact. The human impact then reached a sufficient intensity to change erosion patterns at a regional scale, but did not result in a significant increase of the regional terrigenous flux. The following enhancement of erosion processes occurred around 2700 cal. BP. It was first paced by changing climatic conditions, but probably reinforced by human impact during Late Iron Age -Antiquity period. Over the long-term trend, the Lake Bourget record pinpoints an evolution of paleohydrological conditions in the Alps dominated by dry conditions from 9500 to 4400 cal. BP and a subsequent drift toward wetter conditions that culminated during the so-called Little Ice Age (ca. 1350-1900 AD). In such a context the current dry conditions in European Alps appear out-of-trend. At Arnaud et al., Holocene alpine erosion patterns subaquatiques et sous-marines: Bilan Scientifique 2000. Ministère de la culture et de la communication. Paris. pp. 117 -137. . Holocene climate variability. Quaternary Research, 62, 243-255.
Catena, 2001
Two soil chronosequences of mountainous ecosystems in Switzerland served as the basis to calculate the accumulation of soil organic matter, transformation of pedogenic Fe and Al and net Ž . losses of the main elements Ca, Mg, K, Na, Fe, Al, Mn and Si by means of mass-balance calculations. Elemental losses due to deglaciation and exposure to the weathering environment were calculated. These mass balance calculations indicate that extensive mineral weathering Ž resulted in significant leaching losses of Si, major base cations, and Al particularly from the . upper horizons . The losses are especially pronounced in the early stages of soil formation. In most cases, the exponential decay model incorporating an asymptotic or logarithmic regression model seems to provide a good description of weathering. The greatest changes in the soil chemistry of these alpine soils on granitic host material occurred within the first 3000-4000 years of soil development. Later, the weathering rates decreased rapidly and the overall depletion of w x w x elements nearly reached an asymptote. We also found that the mean ratio of Al Fe r Al Fe of t d d t the fine earth of the A, E and B horizons is closely linked to the duration of soil development. A very rapid decrease of this ratio also occurred at the beginning of soil evolution in order to reach asymptotic values after about 3000 years. Consequently, this ratio could be a good indicator of the age of alpine soils. Furthermore, there is a close relationship between the mass of organic C or N in the whole profile and the soil age: the older the soil the higher the corresponding mass per unit area. The chronofunctions presented give a first attempt of the chemical soil evolution in the Alps. However, only little data has been available up until now regarding alpine soils, and this fact ) Corresponding author. Tel.: q41-1-6355-114; fax: q41-1-6356-848. Ž . E-mail address: megli@geo.unizh.ch M. Egli . 0341-8162r01r$ -see front matter q 2001 Elsevier Science B.V. All rights reserved.
Late Glacial/Early Holocene slope deposits on the Swiss Plateau: Genesis and palaeo-environment
Catena, 2017
On the Swiss Plateau, glacial and glaciofluvial sediments deposited during MIS 2 are widespread. They are generally overlain by younger sediments of different origin, mainly related to periglacial and slope wash processes. Depending on their genesis and composition, 3 types of slope deposits can be distinguished, which are classified as units 1, 2a and 2b. Unit 1 is characterized by its wide spatial occurrence and a constant thickness of 40-60 cm, high silt contents, and a sharp lithological discontinuity to the lying sediments, generally forming the parent material for the Ah-and Al-horizons of the Luvisols. Unit 2 represents erosion rills, filled up with loess loam and some gravel (< 5%) due to slope wash. Locally, periglacial deformations led to cryoturbatic structures in these sediments, which is used to differentiate between unit 2a (no indications for periglacial activities) and unit 2b (with cryoturbations). Based on stratigraphic assumptions, the formation of unit 1 has been tentatively attributed to the Younger Dryas. Optical Stimulated Luminescence and radiocarbon dating of unit 2 indicate morphodynamic activity during the Early Holocene up to 7.5 ka, suggesting an open landscape. This scenario is in conflict with the established notion that reforestation in Middle Europe took place during the Bölling-Alleröd warm period. In order to explain this apparent contradiction for the Younger Dryas to Early Holocene environment, we suggest a continental climate with dry summers and drought stress on the vegetation, in combination with very cold winters and deep soil frost at the Pleistocene/Holocene transition, caused by the orbital precession maximum. After 7.5 ka, with the spread of oceanic woodland and reduced seasonal contrasts, the landscape stabilized and soils developed.
The Holocene, 2012
The deposition of Late Pleistocene and Holocene sediments in the high-altitude lake Meidsee (located at an altitude of 2661 m a.s.l. in the Southwestern Alps) strikingly coincided with global ice-sheet and mountain-glacier decay in the Alpine forelands and the formation of perialpine lakes. Radiocarbon ages of bottom-core sediments point out (pre-) Holocene ice retreat below 2700 m a.s.l., at about 16, 13, 10, and 9 cal. kyr BP. The Meidsee sedimentary record therefore provides information about the high-altitude Alpine landscape evolution since the Late Pleistocene/Holocene deglaciation in the Swiss Southwestern Alps. Prior to 5 cal. kyr BP, the C/N ratio and the isotopic composition of sedimentary organic matter (δ15Norg, δ13Corg) indicate the deposition of algal-derived organic matter with limited input of terrestrial organic matter. The early Holocene and the Holocene climatic optimum (between 7.0 and 5.5 cal. kyr BP) were characterized by low erosion (decreasing magnetic suscep...
Swiss Journal of Geosciences, 2010
A 30 m-deep drill core from a glacially overdeepened trough in Northern Switzerland recovered a *180 ka old sedimentary succession that provides new insights into the timing and nature of erosion-sedimentation processes in the Swiss lowlands. The luminescencedated stratigraphic succession starts at the bottom of the core with laminated carbonate-rich lake sediments reflecting deposition in a proglacial lake between *180 and 130 ka ago (Marine Isotope Stage MIS 6). Anomalies in geotechnical properties and the occurrence of deformation structures suggest temporary ice contact around 140 ka. Up-core, organic content increases in the lake deposits indicating a warming of climate. These sediments are overlain by a peat deposit characterised by pollen assemblages typical of the late Eemian (MIS 5e). An abrupt transition following this interglacial encompasses a likely hiatus and probably marks a sudden lowering of the water level. The peat unit is overlain by deposits of a cold unproductive lake dated to late MIS 5 and MIS 4, which do not show any direct influence from glaciers. An upper peat unit, the so-called «Mammoth peat», previously encountered in construction pits, interrupts this cold lacustrine phase and marks more temperate climatic conditions between 60 and 45 ka (MIS 3). In the upper part of the core, a succession of fluvial and alluvial deposits documents the Late Glacial and Holocene sedimentation in the basin. The sedimentary succession at Wehntal confirms that the glaciation during MIS 6 did not apparently cause the overdeepening of the valley, as the lacustrine basin fill covering most of MIS 6 is still preserved. Consequently, erosion of the basin is most likely linked to an older glaciation. This study shows that new dating techniques combined with palaeoenvironmental interpretations of sediments from such overdeepened troughs provide valuable insights into the past glacial history.
Journal of …, 2003
A 9000 cal. year record of geochemistry was analysed in a sediment core obtained from a Swiss alpine hard-water lake (1937 m a.s.l.) that is located at the present-day tree-line. Geochemical stratigraphies are compared to changes in mineralogy, grain-size, pollen, and macrofossil records. This allows the reconstruction of the effects of changes in vegetation and of 3500 years of land-use in the catchment area on sediment geochemistry. Using principal component analysis, two major geochemical groups are distinguished: (i) Changes in concentrations of Rb, Ti, Zr, Fe, As, and Pb are closely related to corresponding changes in the concentrations of quartz and clay. They are thus considered to represent the silicate fraction which shows an increase from the oldest to the youngest core section. (ii) In contrast, Ca and Sr concentrations are positively correlated with changes in silt, sand, and calcite. They are therefore considered to represent the carbonate fraction which gradually decreased. Based on constrained cluster analysis, the core is divided into two major zones. The oldest zone (A; 9000-6400 cal. BP) is characterised by high concentrations of detrital carbonates. The more open catchment vegetation at that time promoted the physical weathering of these carbonates. The second major zone (B, 6400 cal. BP-1996 AD) is divided into four subsections with boundaries at ca. 3500, 2400, and 160 cal. BP. The lower part of this zone, B1, is characterized by a gradual decrease in the carbonate-silt fraction and a pronounced increase in the silicate-clay fraction. This is concurrent with the expansion of Picea in the catchment area, which probably stabilized the soil. The middle part, B2 and B3 (3500-160 cal. BP), comprises pronounced fluctuations in all elements, especially Ca, Sr, Mn, and Rb, but also in clay and silt. These changes are related to varying intensities of alpine farming. In the same section, Mn/Fe ratios are highly variable, suggesting changes in the mixing regime of the lake with phases of anoxic bottom water. The uppermost section, B4 (since 160 cal. BP), is characterized by a steep decline in the silicate fraction and an increase in Ca and Sr. Despite the decrease in the silicate fraction, Pb increases, due to elevated atmospheric input resulting from early metal pollution, are masked by the high natural variability. Generally, changes in vegetation, which correspond to climate changes in the early Holocene and to human activities since ca. 3700 cal. BP, are the controlling factor for variations in the geochemical composition of the sediment of Sägistalsee. This is the sixth in a series of eight papers published in this special issue dedicated to the palaeolimnology of Sägistalsee. Drs. André F. Lotter and H. John B. Birks were the guest editors of this issue.
Journal of Paleolimnology, 2006
Major and trace elements, minerals, and grain-size were analysed from the early to mid-Holocene (12 to 4 ky BP) period of a sediment core from the Alpine lake Oberer Landschitzsee (ObLAN, 2076 m a.s.l.), which is located on predominantly crystalline bedrock on the southern slopes of the Austrian Central Alps. Geochemistry and mineralogy were compared with diatom-inferred (Di-) 'date of autumn mixing' (A mix), DOC, pH, and selected indicator pollen species from the same sediment core. Principal components analysis (PCA) indicated a positive correlation between processes triggered by temperature and precipitation (e.g., lake mixing, DOC). PCA grouped indicators of physical weathering and enhanced catchment runoff (sand, quartz, feldspar), elements of weathering (e.g., Ti, Rb, Mn) under dryer conditions (clay to silt fractions), and elements that probably were related to changes in redox conditions (Cu, Fe, S, Zn). The duration and height of the snow-pack played an important role in this high-alpine environment, affecting weathering, erosion, pH, and lake stratification. Low Alnus viridis pollen abundance, together with markers for increased elements of erosion, indicated extensive snow-pack. Changes in S coupled with As, and elements indicating increased weathering, reflected climate oscillations. LOI was affected by productivity and erosion. High (late) Di-A mix coupled with increased Di-DOC indicated prolonged summers with increased productivity. Cold and wet (snow-rich) phases and subsequent melting caused low pH and a decoupling of the significant linear correlation between sedimentary Ca and Di-pH. Weathering and leaching during climate deteriorations opposed the long-term trend in a loss of cations and forced in-lake alkalinity generation during the following lake warming. Overall, the multi-proxy study indicated complex climate-driven processes within different timescales (long-term trends, climate oscillations, seasonality). The climate oscillations within 12-5 ky BP corresponded well with the cool and wet phases known from central Europe suggesting a dominant common Atlantic climate impact. When Mediterranean climate established between 5 and 4 ky BP, its influence on the southern slopes of the Alps increased.