scholarly journals Provenance of Bengal Shelf Sediments: 2. Petrology and Geochemistry of Sand

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 642 ◽  
Author(s):  
Eduardo Garzanti ◽  
Giovanni Vezzoli ◽  
Sergio Andò ◽  
Mara Limonta ◽  
Laura Borromeo ◽  
...  
Keyword(s):  
Equatorial Indian Ocean ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Estuarine Sediments ◽  
Heavy Minerals ◽  
Geochemical Data ◽  
Nd Isotope ◽  
Shelf Sediments ◽  
Compositional Variability ◽  
The Impact

The Bangladesh lowlands are traversed by the largest sediment flux on the planet. Detritus generated mostly in Himalayan highlands and conveyed through the Ganga–Brahmaputra rivers and Meghna estuary reaches the Bay of Bengal, where it forms a composite deltaic system. This study integrates the vast existing database on Ganga–Brahmaputra sediments of all grain sizes from clay to sand with new petrographic, mineralogical, and geochemical data on estuarine and shallow-marine sands. A large spectrum of compositional signatures was used to: (i) assess the relative supply of the Ganga and Brahmaputra rivers to estuarine and shelfal sediments; (ii) define the compositional variability of estuarine sediments and the impact exerted by hydraulic sorting and climate-related chemical weathering on provenance signals; (iii) define the compositional variability of shelf sediments and the potential hydrodynamic segregation of fast-settling heavy minerals in coastal environments and of slow-settling platy micas on low-energy outer-shelf floors; (iv) consider the potential additional mud supply from the western subaerial part of the delta formerly built by the Ganga River; and (v) draw a preliminary mineralogical comparison between fluvio-deltaic sediments and turbidites of the Bengal–Nicobar deep-sea fan, thus tracing sediment dispersal across the huge sedimentary system extending from Tibet to the equatorial Indian Ocean. All investigated mineralogical and geochemical parameters, as well as Sr and Nd isotope ratios and clay–mineral assemblages, showed a clear prevalence in sediment supply from the Brahmaputra (60–70%) over the Ganga (30–40%). Heavy-mineral suites and Sr and Nd isotope fingerprints of Bengal shelf sediments are nearly identical to those of the Brahmaputra River and Meghna estuary, also because the Brahmaputra carries almost twice as many Ca-plagioclase grains and heavy minerals including epidote than the Ganga, and these minerals control the large majority of the Sr and Nd budgets. The experience gained in modern settings can be directly extrapolated only to the recent past, because sediments older than the late Pleistocene and buried more than a few hundred meters begin to lose less durable ferromagnesian minerals by selective chemical dissolution, which makes quantitative estimates progressively less robust in more deeply buried older strata.

scholarly journals Three Decades Monitoring of Shoreline Change Pattern of Damietta Promontory, Nile Delta, Egypt

2020 ◽  
Vol 8 (2) ◽  
pp. 1
Author(s):  
Ayman A. El-Gamal ◽  
Sherif H. Balbaa ◽  
Mohamed A. Rashed ◽  
Ahmed S. Mansour
Keyword(s):  
Grain Size ◽  
Coastal Area ◽  
Nile Delta ◽  
Shoreline Change ◽  
Sediment Flux ◽  
Heavy Minerals ◽  
Nile River ◽  
Physical Parameters ◽  
Change Pattern ◽  
The Impact

The Nile Delta is located on the Egyptian Mediterranean coast extending along nearly 240 km from the east of Alexandria to Port Said. The coastal area of the Nile Delta Promontories has been suffering extensive erosion problem. This was achieved after the construction of many water regulation structures in Nile River as dams and barrages, particularly the Aswan High Dam. It has nearly stopped the sediment flux carried by the Nile River to the Delta. This process has caused the Mediterranean Sea to reshape the Nile Delta coastal area. In order to cease these problems several engineering hard structures have been built. These structures avoided in ceasing the problem in the site of construction but shifted the erosion problem to the adjacent sites. This study aimed to analyze the shoreline change pattern on the term of three decades during the period between 1985 to 2015 at the coastal strip of Damietta Promontory and the impact of these protective structures on the coastal area. This was accomplished by the automated delineation of the successive shorelines covering this period using remote sensing imagery. The shorelines were extracted using the MNDWI index. The extracted shorelines were manipulated through the Digital Shoreline Analysis System (DSAS) software. The shoreline change rates were compared with sediments grain size for the past thirty years, heavy minerals content and radioactivity of recent marine sediment samples collected from different locations of marine profiles over the study area. The study revealed that Damietta Promontory has suffered from erosion during the study period reached its maximum shoreline retreat at the eastern side, nearly – 43 m/y. The total cumulative shoreline regression during the study period at this area was 1311m. The relation between the shoreline change process (erosion or accretion) and the physical parameters of coastal sediment showed that; as erosion increases, the heavy minerals content and radioactivity increases, while the mean grain size decreases and vice versa.

Width control on event scale bedload dynamics in bedrock-confined channels

2021 ◽  
Author(s):  
Kristen Cook ◽  
Jens Turowski ◽  
Niels Hovius
Keyword(s):  
Random Sequence ◽  
Bedload Transport ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Channel Width ◽  
Sediment Grain Size ◽  
Event Scale ◽  
Narrow Channels ◽  
Coarse Sediment ◽  
The Impact

<p>In mixed bedrock-alluvial rivers, the response of the system to a flood event can be affected by a number of factors, including coarse sediment availability in the channel, sediment supply from the hillslopes and upstream, flood sequencing, and coarse sediment grain size distribution. However, the impact of along-stream changes in channel width on bedload transport dynamics remains largely unexplored. We combine field data, theory, and numerical modeling to address this gap. Observations from two flood events in the Daan River gorge in western Taiwan suggest that coarse sediment evacuation and re-deposition can cause intra-flood changes of up to several meters in channel bed elevation that are distinct from measured before/after bed changes. We hypothesize that this could be related to the abrupt change in width between the 1 km long bedrock gorge and the river upstream and downstream. An analysis of the theoretical relationships between discharge, channel width, and bedload transport capacity shows that for a given slope, narrow channels transport bedload more efficiently than wide ones at low discharges, while wider channels are more efficient at high discharges. We used the model sedFlow to explore this effect, running a random sequence of floods through a channel with a narrow gorge section bounded upstream and downstream by wider reaches. Channel response to imposed floods is complex, as high and low discharges drive different spatial patterns of erosion and deposition, and the channel may experience both of these regimes during the peak and recession periods of each flood. Our modeling suggests that width differences alone can drive substantial variations in sediment flux and bed response, without the need for variations in sediment supply or mobility. Further, the deposition or erosion that takes place within a flood is often not reflected in the before/after changes to the bed, and this disconnect increases with increasing flood size.</p>

scholarly journals Did the Construction of the Bhumibol Dam Cause a Dramatic Reduction in Sediment Supply to the Chao Phraya River?

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 386
Author(s):  
Matharit Namsai ◽  
Warit Charoenlerkthawin ◽  
Supakorn Sirapojanakul ◽  
William C. Burnett ◽  
Butsawan Bidorn
Keyword(s):  
Saltwater Intrusion ◽  
River System ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Hydroelectric Power ◽  
Chao Phraya River ◽  
The Impact ◽  
Total Sediment ◽  
Hydroelectric Power Generation

The Bhumibol Dam on Ping River, Thailand, was constructed in 1964 to provide water for irrigation, hydroelectric power generation, flood mitigation, fisheries, and saltwater intrusion control to the Great Chao Phraya River basin. Many studies, carried out near the basin outlet, have suggested that the dam impounds significant sediment, resulting in shoreline retreat of the Chao Phraya Delta. In this study, the impact of damming on the sediment regime is analyzed through the sediment variation along the Ping River. The results show that the Ping River drains a mountainous region, with sediment mainly transported in suspension in the upper and middle reaches. By contrast, sediment is mostly transported as bedload in the lower basin. Variation of long-term total sediment flux data suggests that, while the Bhumibol Dam does effectively trap sediment, there was only a 5% reduction in sediment supply to the Chao Phraya River system because of sediment additions downstream.

Middle Holocene environmental reconstruction and climatic inferences through multi-proxy records from Seymareh lake sediments (Zagros Mts., Iran)

2021 ◽  
Author(s):  
Michele Delchiaro ◽  
Giulia Iacobucci ◽  
Francesco Troiani ◽  
Marta Della Seta ◽  
Paolo Ballato ◽  
...  
Keyword(s):  
Sedimentation Rate ◽  
Water Discharge ◽  
Sediment Supply ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
The Holocene ◽  
Middle Holocene ◽  
Lake System ◽  
Proxy Records ◽  
The Impact

<p>The Seymareh landslide is the largest rock slope failure (44 Gm<sup>3</sup>) ever recorded on the exposed Earth surface. It detached ∼10 ka BP from the northeastern flank of the Kabir-Kuh anticline (Zagros Mts., Iran) originating the natural dam responsible for the formation of a three-lake system (Seymareh, Jaidar, and Balmak lakes, with an area of 259, 46, and 5 km<sup>2</sup>, respectively). The lake system persisted for ∼3000 yr during the Holocene before its emptying phase due to overflow. A sedimentation rate of 21 mm yr<sup>−1</sup> was estimated for the Seymareh lacustrine deposits, which increased during the early stage of lake emptying because of enhanced sediment yield from the lake tributaries. </p><p>To reconstruct the climatic and environmental impact on the lake infilling, we reviewed the geomorphology of the basins and combined the results with multi-proxy records from a 30 m thick lacustrine sequence in Seymareh Lake. Major analyses comprise grain size analysis, carbon and oxygen stable isotopes of carbonate-bearing sediments, and X-ray diffraction analysis of clay minerals.</p><p>Lake overflowing is largely accepted as the main response to variations in water discharge and sediment supply since the alternation from dry to wet phases enhances sediment mobilization along hillslopes decreasing the accommodation space in the downstream sedimentary basins. In this regard, during the early-middle Holocene, the Seymareh area, as well as the entire Middle East, was affected by short-term climate changes at the millennial-scale, as testified by both paleoecological and archaeological evidence. Indeed, several records from Iranian lakes (i.e., Mirabad, Zeribar, Urmia) well documented the temperature and the moisture conditions of the western Zagros Mountains during the Holocene. During the early Holocene, the precipitation remained low up to 6 ka BP, reaching the driest condition around 8-8.2 ka BP. The impact of this abrupt climate change is evident across West Asia, where the first large villages with domesticated cereals and sheeps disappeared, converting to small hamlets and starting habitat-tracking. As regards the Seymareh area, a more irregular distribution of rainfalls and their increasing seasonality may support rhexistasy conditions, during which the scarce vegetation cover enhances both the hillslope erosion and sedimentation rate in the basins, most likely contributing to the overflow of Seymareh Lake. </p>

Feasibility of sedimentation strategies for the Mekong delta to counterbalance relative sea-level rise

2021 ◽  
Author(s):  
Frances E. Dunn ◽  
Philip S. J. Minderhoud
Keyword(s):  
Land Use ◽  
Sea Level Rise ◽  
Sea Level ◽  
Mekong Delta ◽  
Sediment Deposition ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Relative Sea Level ◽  
Fluvial Sediment ◽  
Relative Sea Level Rise

<p>As one of the largest deltas in the world, the Mekong delta is home to over 17 million people and supports internationally important agriculture. Recently deposited sediment compacts and causes subsidence in deltas, so they require regular sediment input to maintain elevation relative to sea level. These processes are complicated by human activities, which prevent sediment deposition indirectly through reducing fluvial sediment supply and directly through the construction of flood defence infrastructure on deltas, impeding floods which deliver sediment to the land. Additionally, anthropogenic activities increase the rate of subsidence through the extraction of groundwater and other land-use practices.</p><p>This research shows the potential for fluvial sediment delivery to compensate for sea-level rise and subsidence in the Mekong delta over the 21st century. We use detailed elevation data and subsidence scenarios in combination with regional sea-level rise and fluvial sediment flux projections to quantify the potential for maintaining elevation relative to sea level in the Mekong delta. We present four examples of localised sedimentation scenarios in specific areas, for which we quantified the potential effectiveness of fluvial sediment deposition for offsetting relative sea-level rise. The presented sediment-based adaptation strategies are complicated by existing land use, therefore a change in water and sediment management is required to effectively use natural resources and employ these adaptation methods. The presented approach could be an exemplar to assess sedimentation strategy feasibility in other delta systems worldwide that are under threat from sea-level rise.</p>

Origin of the Ordovician Mansehra granite in the NW Himalaya, Pakistan: constraints from Sr–Nd isotopic data, zircon U–Pb age and Hf isotopes

2018 ◽  
Vol 481 (1) ◽  
pp. 277-298 ◽  
Author(s):  
Masatsugu Ogasawara ◽  
Mayuko Fukuyama ◽  
Rehanul Haq Siddiqui ◽  
Ye Zhao
Keyword(s):  
Granitic Magma ◽  
Geochemical Data ◽  
Large Contribution ◽  
Crustal Material ◽  
Sr Isotope ◽  
Nw Himalaya ◽  
Nd Isotope ◽  
Isotope Data ◽  
Late Neoproterozoic ◽  
T Values

AbstractThe Mansehra granite in the NW Himalaya is a typical Lesser Himalayan granite. We present here new whole-rock geochemistry, Rb–Sr and Sm–Nd isotope data, together with zircon U–Pb ages and Hf isotope data, for the Mansehra granite. Geochemical data for the granite show typical S-type characteristics. Zircon U–Pb dating yields 206Pb/238U crystallization ages of 483–476 Ma. The zircon grains contain abundant inherited cores and some of these show a clear detrital origin. The 206Pb/238U ages of the inherited cores in the granite cluster in the ranges 889–664, 1862–1595 and 2029 Ma. An age of 664 Ma is considered to be the maximum age of the sedimentary protoliths. Thus the Late Neoproterozoic to Cambrian sedimentary rocks must be the protolith of the Mansehra granitic magma. The initial Sr isotope ratios are high, ranging from 0.7324 to 0.7444, whereas the εNd(t) values range from −9.2 to −8.6, which strongly suggests a large contribution of old crustal material to the protoliths. The two-stage Nd model ages and zircon Hf model ages are Paleoproterozoic, indicating that the protolith sediments were derived from Paleoproterozoic crustal components.

Delayed delivery from the sediment factory: modeling the impact of catchment response time to tectonics on sediment flux and fluvio-deltaic stratigraphy

2014 ◽  
Vol 39 (5) ◽  
pp. 689-704 ◽  
Author(s):  
Andrea Forzoni ◽  
Joep E.A. Storms ◽  
Alexander C. Whittaker ◽  
Gerben de Jager
Keyword(s):  
Response Time ◽  
Sediment Flux ◽  
The Impact

scholarly journals Impact of climate change on sediment yield in the Mekong River basin: a case study of the Nam Ou basin, Lao PDR

2013 ◽  
Vol 17 (1) ◽  
pp. 1-20 ◽  
Author(s):  
B. Shrestha ◽  
M. S. Babel ◽  
S. Maskey ◽  
A. van Griensven ◽  
S. Uhlenbrook ◽  
...  
Keyword(s):  
Climate Change ◽  
Sediment Yield ◽  
General Circulation ◽  
Climate Models ◽  
Greenhouse Gas Emission ◽  
Circulation Model ◽  
Sediment Flux ◽  
Seasonal Temperature ◽  
Impact Of Climate Change ◽  
The Impact

Abstract. This paper evaluates the impact of climate change on sediment yield in the Nam Ou basin located in northern Laos. Future climate (temperature and precipitation) from four general circulation models (GCMs) that are found to perform well in the Mekong region and a regional circulation model (PRECIS) are downscaled using a delta change approach. The Soil and Water Assessment Tool (SWAT) is used to assess future changes in sediment flux attributable to climate change. Results indicate up to 3.0 °C shift in seasonal temperature and 27% (decrease) to 41% (increase) in seasonal precipitation. The largest increase in temperature is observed in the dry season while the largest change in precipitation is observed in the wet season. In general, temperature shows increasing trends but changes in precipitation are not unidirectional and vary depending on the greenhouse gas emission scenarios (GHGES), climate models, prediction period and season. The simulation results show that the changes in annual stream discharges are likely to range from a 17% decrease to 66% increase in the future, which will lead to predicted changes in annual sediment yield ranging from a 27% decrease to about 160% increase. Changes in intra-annual (monthly) discharge as well as sediment yield are even greater (−62 to 105% in discharge and −88 to 243% in sediment yield). A higher discharge and sediment flux are expected during the wet seasons, although the highest relative changes are observed during the dry months. The results indicate high uncertainties in the direction and magnitude of changes of discharge as well as sediment yields due to climate change. As the projected climate change impact on sediment varies remarkably between the different climate models, the uncertainty should be taken into account in both sediment management and climate change adaptation.

scholarly journals THE IMPACT OF SEASONAL CHANGES ON HEAVY MINERALS CONCENTRATION FROM A PART OF EAST COAST OF INDIA

2020 ◽  
Vol 5 (1) ◽  
pp. 12-21
Author(s):  
Ali Mohammad ◽  
E.N. Dhanamjayarao
Keyword(s):  
Seasonal Changes ◽  
East Coast ◽  
Heavy Mineral ◽  
Heavy Minerals ◽  
Sediment Characteristics ◽  
Seasonal Fluctuations ◽  
Post Monsoon ◽  
Seasonal Circulation ◽  
Mineral Concentrations ◽  
The Impact

Pre and post monsoonal changes in the environment have led to a noticeable variation in sediment characteristics, heavy mineral concentrations and their distribution. The current study aimed to find out the effect of seasonal fluctuations on the concentration of heavy minerals along the coast and the variations in sediment textures and distribution. The study has revealed the effect of seasons on the sediments supply and its distribution along coast in the study area. The total heavy minerals concentrations are more in post monsoon than in pre monsoon and the concentration also increases from south to north in parts of the study area because of seasonal circulation of currents from south to north along the shore. The micro textural study of the heavy mineral grains from different locations in the study area revealed the mechanical and chemical erosions on the grain surfaces.

scholarly journals Impact of climate change on sediment yield in the Mekong River Basin: a case study of the Nam Ou Basin, Lao PDR

2012 ◽  
Vol 9 (3) ◽  
pp. 3339-3384
Author(s):  
B. Shrestha ◽  
M. S. Babel ◽  
S. Maskey ◽  
A. van Griensven ◽  
S. Uhlenbrook ◽  
...  
Keyword(s):  
Climate Change ◽  
Sediment Yield ◽  
Assessment Tool ◽  
Negative Impact ◽  
Lao Pdr ◽  
Sediment Flux ◽  
Monthly Precipitation ◽  
Sediment Yields ◽  
Impact Of Climate Change ◽  
The Impact

Abstract. This paper evaluates the impact of climate change on sediment yield in the Nam Ou Basin located in Northern Laos. The Soil and Water Assessment Tool (SWAT) is used to assess future changes in sediment flux attributable to climate change. Future precipitation and temperature series are constructed through a delta change approach. As per the results, in general, temperature as well as precipitation show increasing trends in both scenarios, A2 and B2. However, monthly precipitation shows both increasing and decreasing trends. The simulation results exhibit that the wet and dry seasonal and annual stream discharges are likely to increase (by up to 15, 17 and 14% under scenario A2; and 11, 5 and 10% under scenario B2 respectively) in the future, which will lead to increased wet and dry seasonal and annual sediment yields (by up to 39, 28 and 36% under scenario A2; and 23, 12 and 22% under scenario B2 respectively). A higher discharge and more sediment flux are expected during the wet seasons, although the changes, percentage-wise, are observed to be higher during the dry months. In conclusion, the sediment yield from the Nam Ou Basin is likely to increase with climate change, which strongly suggests the need for basin-wide sediment management strategies in order to reduce the negative impact of this change.

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