scholarly journals Conglomerate recycling in the Himalayan foreland basin: Implications for grain size and provenance

2019 ◽  
Vol 132 (7-8) ◽  
pp. 1639-1656 ◽  
Author(s):  
Laura Quick ◽  
H.D. Sinclair ◽  
M. Attal ◽  
V. Singh
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Significant Proportion ◽  
Foreland Basin ◽  
Source Area ◽  
Mountain Range ◽  
Gangetic Plain ◽  
Mountain Front ◽  
Gravel Bars

Abstract The nature of coarse sediment in rivers emerging from mountain ranges determines rates of downstream fining, the position of the gravel-sand transition, sediment entrainment thresholds, and channel morphologies. Additionally, in the stratigraphic record, clast size distributions and lithologies are used to reconstruct paleo-hydraulic conditions and source area provenance. Using Himalayan rivers, we demonstrate that the signal of first-generation clasts derived from the hinterland of a mountain range can be significantly altered by recycling older, structurally exhumed foreland deposits. The Siwalik foothills of the Himalaya comprise Neogene fluvial sandstones and quartzite-rich conglomerates with well-rounded clasts that were deposited in the Indo-Gangetic foreland basin and later exhumed by erosion, following uplift along the Himalayan mountain front. Mass balance calculations reveal that the Upper Siwalik conglomerate may contribute a significant proportion of the total gravel flux exported from the main Himalayan catchments (up to 100%) despite forming <1% of the catchment geology. Three end-member catchments with variable proportions of gravel flux from Siwalik conglomerates are analyzed to test for the effects of conglomerate recycling. Catchments that recycle the most Upper Siwalik conglomerate form quartzite-rich gravel bars comprising well-rounded pebbles and a narrow grain size distribution, mimicking the characteristics of the Upper Siwalik conglomerate. Conversely, catchments that recycle the least Upper Siwalik conglomerate form gravel bars with a range of Himalayan lithologies, angular quartzite pebbles and a wider grain size distribution. This study highlights that recycling of quartzite-rich conglomerate can dramatically modify the flux, lithology, grain size, and shape of gravel entering the Indo-Gangetic Plain.

scholarly journals PODMÍNKY TRANSPORTU A AKUMULACE SEDIMENTŮ V ČLOVĚKEM OVLIVNĚNÝCH KORYTECH BESKYDSKÝCH TOKŮ: PŘÍKLADOVÁ STUDIE SOUTOKU ŘEKY MORÁVKY A MOHELNICE

2012 ◽  
Vol 19 (1-2) ◽  
Author(s):  
Václav Škarpich ◽  
Tomáš Galia ◽  
Jan Hradecký
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Transport Parameters ◽  
Sediment Delivery ◽  
Load Transport ◽  
Gravel Bars ◽  
Gravel Bed Streams

This paper summarizes results of grain-size distribution of gravel bars and transport conditions in the context of sediment sources in the confl uence area of the Morávka and Mohelnice rivers (Moravskoslezské Beskydy Mts). We deal with a hypothesis that general changes of grain-size distribution of gravel bars are controlled by disconnection in sediment flux in the Morávka River and, by contrast, that higher sediment delivery is related to the Mohelnice river basin. The second focus is the evaluation of fluvial transport parameters of a channel influenced by control works and sediment mining. Bed load transport research was conducted with the application of BAGS (Bedload Assessment for Gravel-bed Streams) spreadsheet-based program. Sediment analysis of the channel confluence showed limited sediment supply character indicated by coarser sediment delivery from the Morávka River. This fact is related to the effect of hungry water caused mainly by the Morávka Reservoir. On the other hand, the Mohelnice River displayed trends of relatively higher sediment delivery without potential disconnectivities in sediment flux. Results of this analysis brought an insight into a potential scheme of the future development of the studied reaches. We suppose preservation of recent trends in case of the occurrence of signifi cant changes in land use or watershed management.

Palaeoclimatological interpretation of loess-paleosol sequences using log-ratio transformation of granulometric and geochemical data; Czech Republic

2021 ◽  
Author(s):  
Daniel Šimíček ◽  
Ondřej Bábek ◽  
Karel Hron ◽  
Ivana Pavlů
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Close Contact ◽  
Clay Fraction ◽  
Source Area ◽  
Geochemical Data ◽  
Climatic Fluctuations ◽  
Geochemical Composition ◽  
Log Ratio

<p>The loess-paleosol sequences (LPS) are an important source of proxy data documenting climatic fluctuations in the Quaternary. Understanding the relationship between the grain size distribution and the geochemistry is crucial for the reliable palaeoclimatological and palaeoenvironmental interpretation of the LPS. For this purpose, the large granulometric (389 samples) and geochemical datasets (542 samples measured using EDXRF spectrometer) were acquired at four LPS in Moravia (eastern part of Czech Rep.). Czech loess represent an important part of the European loess belt, because they characterize region with alternating influence of the oceanic and continental macroclimate, modified by close contact to the front of both continental and alpine glaciation during glacial periods. Moreover, a very diverse geology is characteristic for the source area (the Bohemian Massif) of Czech loess. Therefore, distinguishing of provenance and transporting and post-deposition processes effects on the formation of the Czech LPS requires finding new approaches of statistical evaluation of datasets. Centered log-ratio (clr) transformation and scalar-on-function regression allow finding a relationship between the geochemical composition and the grain-size distribution of loess and soils. Centered log-ratio (clr) transformation was applied to the key elemental proxies of grain size, provenance and weathering and their spatial and stratigraphic distribution. Nearly all LPS samples are characteristic by bimodal grain-size distribution with the main modes corresponding to medium/coarse silt and clay fractions. The scalar-on-function regression shows that the grain-size control of the distribution of Al, Si, K, Ca, Fe, Rb, Sr and Zr is highly site-specific. The provenance signal is recorded especially in coarser-grained fractions transported for short distance. The content of the authigenic phyllosilicates in clay fraction, the alteration of feldspars and micas, low contents of K, and high values of Rb/Sr and Sr/Ca ratios reflect the intensity of weathering, which is highest in the weakly developed brown paleosols. The precipitation rates are suggested the most important microclimatic factor, which affect the intensity of loessification and pedogenic processes forming the Czech LPS.</p><p>This research was supported by the Czech Science Foundation (GAČR) research project 19-017685.</p>

Grain size distribution in evaporated permalloy films

1970 ◽  
Vol 2 (2) ◽  
pp. K69-K73 ◽  
Author(s):  
M. Reinbold ◽  
H. Hoffmann
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution

scholarly journals The Domain and Microstructure of Resin-Bonded Magnets

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2849
Author(s):  
Marcin Jan Dośpiał
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Size ◽  
Size Distribution ◽  
Domain Structure ◽  
Grain Size Distribution ◽  
Exchange Interactions ◽  
Force Microscopy ◽  
Transmission Electron ◽  
Scanning Electron

This paper presents domain and structure studies of bonded magnets made from nanocrystalline Nd-(Fe, Co)-B powder. The structure studies were investigated using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy and X-ray diffractometry. On the basis of performed qualitative and quantitative phase composition studies, it was found that investigated alloy was mainly composed of Nd2(Fe-Co)14B hard magnetic phase (98 vol%) and a small amount of Nd1.1Fe4B4 paramagnetic phase (2 vol%). The best fit of grain size distribution was achieved for the lognormal function. The mean grain size determined from transmission electron microscopy (TEM) images on the basis of grain size distribution and diffraction pattern using the Bragg equation was about ≈130 nm. HRTEM images showed that over-stoichiometric Nd was mainly distributed on the grain boundaries as a thin amorphous border of 2 nm in width. The domain structure was investigated using a scanning electron microscope and metallographic light microscope, respectively, by Bitter and Kerr methods, and by magnetic force microscopy. Domain structure studies revealed that the observed domain structure had a labyrinth shape, which is typically observed in magnets, where strong exchange interactions between grains are present. The analysis of the domain structure in different states of magnetization revealed the dynamics of the reversal magnetization process.

scholarly journals Influence of bimodal grain size distribution on the corrosion resistance of Mg-4Li-3Al-1Zn (LAZ431)

2021 ◽  
Author(s):  
Anna Dobkowska ◽  
Boguslawa Adamczyk – Cieślak ◽  
Dariusz Kuc ◽  
Eugeniusz Hadasik ◽  
Tomasz Płociński ◽  
...  
Keyword(s):  
Grain Size ◽  
Corrosion Resistance ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Bimodal Grain Size ◽  
Bimodal Grain Size Distribution
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