scholarly journals Sedimente und Ablagerungsmechanismen in instabilen proglaziären Seen (Eisrandstauseen) in Westgrönland

1997 ◽  
Vol 47 (1) ◽  
pp. 42-77
Author(s):  
Herbert Scholz
Keyword(s):  
Lake Sediments ◽  
Water Levels ◽  
Mass Movements ◽  
Sedimentary Record ◽  
Fluvial Deposits ◽  
Fine Grained ◽  
Dry Lake ◽  
Type 3 ◽  
Inland Ice ◽  
Lake Basins

Abstract. Close to Søndre Strømfjord in West Greenland, a number of ice contact lakes with unstable water levels are dammed by the margin of the inland ice. From time to time they drain more or less completely beneath the glacier. Thus, the sediments at the bottom of such dry lake basins can be eliminated in an easy way. 7 lakes of this type, 3 of which were empty in summer 1993, could be investigated in detail by help of a grant of the DFG. The sedimentary infill of the lakes mainly consists of dia miktons, presumably sediments of drift ice. besides of the debris of mass movements, derived from the flanks of the lake basins, deltaic and fluvial deposits play an important role. Fine grained lake sediments, however, which may be expected within a lake close to a glacier, are scarcely to be found. The sedimentary infill of unstable lakes of this type is obviously different from normal glacilacustrine successions. The sedimentary record of fossil lakes of this type, which may have been as common in Pleistocene Europe as in modem Greenland, should be identified easily in the future, due to the investigations presented in this paper.

Linking rivers to the rock record: Channel patterns and paleocurrent circular variance

Geology ◽  
2021 ◽  
Author(s):  
C.P. Galeazzi ◽  
R.P. Almeida ◽  
A.H. do Prado
Keyword(s):  
Water Discharge ◽  
Global Scale ◽  
Sedimentary Record ◽  
Discharge Data ◽  
Alluvial Rivers ◽  
Channel Pattern ◽  
Fluvial Deposits ◽  
Circular Variance ◽  
Rock Record ◽  
Channel Patterns

Alluvial rivers are the most important agents of sediment transport in continental basins, whose fluvial deposits enclose information related to the time when rivers were active. In order to extract the most information from fluvial deposits in the sedimentary record, it is imperative to quantify the natural variability of channel patterns at the global scale, explore what controls may influence their development, and investigate whether channel pattern information is preserved in the alluvial plains in order to develop tools for recognizing them in the sedimentary record. By surveying 361 reaches of modern alluvial rivers with available water discharge data at a global scale, we present a quantitative channel pattern classification based on sinuosity and channel count index applicable to the recognition in the rock record. A continuum of channel patterns ranging from high-sinuosity single channel to lowsinuosity multichannels is documented, along with the proportion of depositional elements in their alluvial plains and their conditions of occurrence. Preserved barforms in the alluvial plains of these rivers are used to infer and quantify paleoflow directions at the channel-belt scale and result in ranges of paleocurrent circular variance that may lead to channel pattern identification in the rock record. Data from this work indicate that the recognition of channel patterns may be used to predict paleogeographic features such as the scale of drainage basin area and discharge, slope, and annual discharge regimes.

scholarly journals Anthropogenic Influences on Environmental Changes of Lake Bosten, the Largest Inland Freshwater Lake in China

2020 ◽  
Vol 12 (2) ◽  
pp. 711 ◽  
Author(s):  
Wen Liu ◽  
Long Ma ◽  
Jilili Abuduwaili
Keyword(s):  
Central Asia ◽  
Lake Sediments ◽  
Human Activities ◽  
Environmental Changes ◽  
Living Environment ◽  
Water Levels ◽  
Aral Sea ◽  
Anthropogenic Factors ◽  
Large Spatial Scale ◽  
The 1960S

A short lacustrine sediment core (41 cm) from Lake Bosten in arid central Asia was used to investigate the environmental changes that occurred in the past ≈150 years based on the superposition of climate and anthropogenic factors. Geochemical elements, total organic carbon (TOC) and nitrogen (TN), and stable isotope data (δ13Corg and δ15N) were used to identify abnormal environmental changes. The average C/N ratio in the sediments of Lake Bosten suggested that the organic matter in lake sediments was mainly from aquatic plants. The δ13Corg and δ15N in the lake sediments mainly reflect changes in the structure of the lake’s ecosystem. Before the 1960s, the primary productivity of the lake was relatively low with a relatively stable lake water environment. From the 1960s to the mid-1980s, the lake’s ecosystem was closely related to a significant decline in water levels caused by human activities and an increase in salinity. From the late 1980s to ≈2000, the aquatic plant structure of Lake Bosten did not change significantly. After 2000, the upper part of the sedimentary record suggested enhanced productivity due to urban and industrial development in the catchment area. However, sedimentary perspectives of the responses of different environmental proxies in sediments to human activities were anisochronous, and the increasing heavy metal (Pb and Cu) and P accumulations appeared in 1970, reflecting heightened human impacts. Through the comparison between the Aral Sea and Lake Bosten, it was inferred that, under the intervention of human activities, the lake experienced a completely different evolution trend. Humans, as geological agents, should protect our living environment while satisfying social development. The results will provide an important supplement to a large spatial scale study of the influences of human activities on the environment in Central Asia, which also has some significant implications for the protection of the ecological environment and the realization of sustainable development in arid regions.

Was There a Pliocene-Pleistocene Fluvial-Lacustrine Connection between Death Valley and the Colorado River?

1995 ◽  
Vol 43 (3) ◽  
pp. 286-296 ◽  
Author(s):  
William J. Brown ◽  
Michael R. Rosen
Keyword(s):  
Colorado River ◽  
Drainage Basin ◽  
River System ◽  
Turn Of The Century ◽  
Death Valley ◽  
Hydrologic Systems ◽  
Dry Lake ◽  
Middle Pliocene ◽  
River Drainage Basin ◽  
Lake Basins

AbstractSince the turn of the century, a Pliocene-Pleistocene connection between the Death Valley-Owens River pluvial system and the Colorado River drainage basin has been frequently postulated. The two most commonly proposed routes involve (1) a southward overflow from the Death Valley Lake system or (2) southward migration of the Mojave River between its present course and a more southerly route. Under the present topographic regime, a Death Valley Lake capable of overflowing the bedrock saddle at Ludlow, California and discharging southward into the Bristol, Cadiz, and Danby Lake basins (and eventually the Colorado River) would be over 12,000 km2 in size. Few surface and subsurface indicators exist to support either a fluvial or lacustrine connection. Evidence from deep cores and boreholes drilled in Soda, Bristol, Cadiz, and Danby dry lake basins indicate that a hydrologic connection has not occurred during the past 4 myr. No well-documented paleoshoreline features have been located at elevations corresponding to the above hydrologic systems in Death Valley, Silver-Soda, Bristol, or Danby Lake basins. In the Cadiz, Silurian, and Broadwell basins these features have not been found at all. Therefore, we conclude that a hydrologic connection between the Death Valley-Owens River system and the Colorado River has not occurred along either of these routes since the middle Pliocene.

scholarly journals Luminescence Dating of Fluvial Deposits from the Weser Valley, Germany

2015 ◽  
Vol 42 (1) ◽  
Author(s):  
Julia Roskosch ◽  
Sumiko Tsukamoto ◽  
Manfred Frechen
Keyword(s):  
Late Pleistocene ◽  
Luminescence Dating ◽  
Marine Isotope Stage ◽  
Coarse Grained ◽  
Performance Tests ◽  
Luminescence Signal ◽  
Fluvial Deposits ◽  
Fine Grained ◽  
Infrared Stimulated Luminescence ◽  
Off Time

Abstract Luminescence dating was applied on coarse-grained monomineralic potassium-rich feld-spar and polymineralic fine-grained minerals of five samples derived from fluvial deposits of the Riv-er Weser in northwestern Germany. We used a pulsed infrared stimulated luminescence (IRSL) single aliquot regenerative (SAR) dose protocol with an IR stimulation at 50°C for 400 s (50 μs on-time and 200 μs off-time). In order to obtain a stable luminescence signal, only off-time IRSL signal was rec-orded. Performance tests gave solid results. Anomalous fading was intended to be reduced by using the pulsed IRSL signal measured at 50°C (IR50), but fading correction was in most cases necessary due to moderate fading rates. Fading uncorrected and corrected pulsed IR50 ages revealed two major fluvial aggradation phases during the Late Pleistocene, namely during marine isotope stage (MIS) 5d (100 ± 5 ka) and from late MIS 5b to MIS 4 (77 ± 6 ka to 68 ± 5 ka). The obtained luminescence ages are consistent with previous 230Th/U dating results from underlying interglacial deposits of the same pit, which are correlated with MIS 7c to early MIS 6.

scholarly journals Geological framework of the Laurentian trough aquifer system, southern Ontario

2018 ◽  
Vol 55 (7) ◽  
pp. 677-708 ◽  
Author(s):  
David R. Sharpe ◽  
André J.-M. Pugin ◽  
Hazen A.J. Russell
Keyword(s):  
Lake Ontario ◽  
Water Levels ◽  
Coarse Grained ◽  
Oak Ridges Moraine ◽  
Aquifer System ◽  
Fine Grained ◽  
Niagara Escarpment ◽  
Base Level ◽  
Glacial Periods ◽  
East West

The Laurentian trough (LT), a depression >100 km long, >3000 km2 in area, and 100 m deep at the base of the Niagara Escarpment, extends from within Georgian Bay to Lake Ontario. It has a complex erosional history and is filled and buried by up to 200 m of interglacial and glacial sediment. The primary depression fronts a cuesta landscape and is attributed to differential erosion by fluvial, glacial, and glaciofluvial processes, exposing Ordovician rocks along the Canadian Shield margin. The fill succession includes sediments from the last two glacial periods (Illinoian, Wisconsinan) and the intervening interglacial time (Sangamonian), a poorly dated succession with at least three regional unconformities. A subaerial (interglacial, Don Formation) unconformity relates to low base level mainly preserved in lows of the LT, succeeded by a long period of rising water levels and glaciolacustrine conditions as ice advanced into the Lake Ontario basin. A second unconformity, within the Thorncliffe Formation, is the result of rapid channel erosion to bedrock, forming an ∼north–south network filled with coarse-grained glaciofluvial, transitional to fine-grained glaciolacustrine subaqueous fan sediment. The overlying drumlinized Newmarket Till, up to 50 m thick, is a distinct regional unit with a planar to undulating base. A third unconformity event eroded Newmarket Till, locally truncating it and underlying sediment to bedrock. Three younger sediment packages, Oak Ridges Moraine (channel and ridge sediment), Halton, and glaciolacustrine overlie this erosion surface. Significant regional aquifers are hosted within the LT. Upper Thorncliffe Formation sediments, north–south glaciofluvial channel–fan aquifers, are protected by overlying mud and Newmarket Till aquitards. Similarly, Oak Ridges Moraine sediments comprise a north–south array of glaciofluvial channel–fans and east–west fan aquifers, locally covered by silt–clay rhythmite and till aquitards.

scholarly journals What are the key drivers of regional differences in the water balance on the Tibetan Plateau?

2015 ◽  
Vol 12 (4) ◽  
pp. 4271-4314 ◽  
Author(s):  
S. Biskop ◽  
F. Maussion ◽  
P. Krause ◽  
M. Fink
Keyword(s):  
Tibetan Plateau ◽  
Water Balance ◽  
Hydrological Modeling ◽  
Integrated Approach ◽  
Water Levels ◽  
The Tibetan Plateau ◽  
Nam Co ◽  
Water Balance Components ◽  
South Central ◽  
Lake Basins

Abstract. Lake-level fluctuations in closed basins on the Tibetan Plateau (TP) indicate climate-induced changes in the regional water balance. However, little is known about the region's key hydrological parameters, hampering the interpretation of these changes. The purpose of this study is to contribute to a more quantitative understanding of these controls. Four lakes in the south-central part of the TP were selected to analyze the spatiotemporal variations of water-balance components: Nam Co and Tangra Yumco (indicating increasing water levels), and Mapam Yumco and Paiku Co (indicating stable or slightly decreasing water levels). We present the results of an integrated approach combining hydrological modeling, atmospheric-model output and remote-sensing data. The hydrological model J2000g was adapted and extended according to the specific characteristics of closed lake basins on the TP and driven with "High Asia Refined analysis (HAR)" data at 10 km resolution for the period 2001–2010. Our results reveal that because of the small portion of glacier areas (1 to 7% of the total basin area) the contribution of glacier melt water accounts for only 14–30% of total runoff during the study period. Precipitation is found to be the principal factor controlling the water-balance in the four studied basins. The positive water balance in the Nam Co and Tangra Yumco basins was primarily related to larger precipitation amounts and thus higher runoff rates in comparison with the Paiku Co and Mapam Yumco basins. This study highlights the benefits of combining atmospheric and hydrological modeling. The presented approach can be readily transferred to other ungauged lake basins on the TP, opening new directions of research. Future work should go towards increasing the atmospheric model's spatial resolution and a better assessment of the model-chain uncertainties, especially in this region where observational data is missing.

scholarly journals Mineralization of organic matter in boreal lake sediments: rates, pathways, and nature of the fermenting substrates

2020 ◽  
Vol 17 (18) ◽  
pp. 4571-4589
Author(s):  
François Clayer ◽  
Yves Gélinas ◽  
André Tessier ◽  
Charles Gobeil
Keyword(s):  
Organic Matter ◽  
Lake Sediments ◽  
Dissolved Inorganic Carbon ◽  
Biogeochemical Models ◽  
Mineralization Of Organic Matter ◽  
Carbohydrate Fermentation ◽  
Mass Balancing ◽  
Reaction Transport ◽  
Lake Basins

Abstract. The complexity of organic matter (OM) degradation mechanisms represents a significant challenge for developing biogeochemical models to quantify the role of aquatic sediments in the climate system. The common representation of OM by carbohydrates formulated as CH2O in models comes with the assumption that its degradation by fermentation produces equimolar amounts of methane (CH4) and dissolved inorganic carbon (DIC). To test the validity of this assumption, we modelled using reaction-transport equation vertical profiles of the concentration and isotopic composition (δ13C) of CH4 and DIC in the top 25 cm of the sediment column from two lake basins, one whose hypolimnion is perennially oxygenated and one with seasonal anoxia. Furthermore, we modelled solute porewater profiles reported in the literature for four other seasonally anoxic lake basins. A total of 17 independent porewater datasets are analyzed. CH4 and DIC production rates associated with methanogenesis at the five seasonally anoxic sites collectively show that the fermenting OM has a mean (± SD) carbon oxidation state (COS) value of -1.4±0.3. This value is much lower than the value of zero expected from carbohydrate fermentation. We conclude that carbohydrates do not adequately represent the fermenting OM in hypolimnetic sediments and propose to include the COS in the formulation of OM fermentation in models applied to lake sediments to better quantify sediment CH4 outflux. This study highlights the potential of mass balancing the products of OM mineralization to characterize labile substrates undergoing fermentation in sediments.

scholarly journals MINERAL COMPOSITION OF SOME LATGALE LAKE SEDIMENTS

2019 ◽  
Vol 1 ◽  
pp. 304
Author(s):  
Rasma Tretjakova ◽  
Andris Karpovičs
Keyword(s):  
Grain Size ◽  
Lake Sediments ◽  
Size Distribution ◽  
Clay Minerals ◽  
Mineral Composition ◽  
Grain Size Distribution ◽  
Sandy Loam ◽  
Clay Fraction ◽  
Fine Grained ◽  
Two Samples

Our research is focused on sedimentological conditions and postdepositional changes of recent fine grained lake sediments. We used bulk sediment mineralogical composition and grain size distribution as indicators to identify sediment source areas and possible changes during Holocene. We analysed fine grained (clayey) sediments from three Latgale lakes - Zeili, Pauguļi and Plusons, situated in Latgale upland. Lake sediments cover Late Pleistocene glacial deposits – loam and sandy loam. Bulk mineral composition of 6 sediment samples was determined by X-ray diffraction (XRD). Sediments contained typical minerals found in surrounding glacial sediments: rock-forming minerals as quartz, plagioclase, albite, enstatite, dolomite, calcite, and clay minerals - illite, kaolinite. To identify postdepositional changes in lake sediments of Holocene age clay minerals in clay fraction (<2 mkm) should be analysed. Particularly illite, smectite mixed layered minerals - illite/smectite (I/Sm) and chlorite. Additionally, grain size distribution of studied lake sediments was analysed. Accordingly, our studied sediments are clays, silty clays and clayey silts with bimodal particle distribution, except two samples from Zeiļi and Plusons with unimodal distribution.

Sign in / Sign up

Export Citation Format

Share Document