scholarly journals Textural and mineralogical maturities and provenance of sands from the Budhi Gandaki-Narayani Nadi, central Nepal

2020 ◽  
Vol 22 ◽  
pp. 1-9
Author(s):  
Sanjay Singh Maharjan ◽  
Naresh Kazi Tamrakar
Keyword(s):  
Tectonic Setting ◽  
Main Stem ◽  
Rock Fragment ◽  
Compositional Variation ◽  
High Mountain ◽  
Rock Fragments ◽  
Central Nepal ◽  
Depositional Processes ◽  
Statistical Measures ◽  
Hilly Region

The Budhi Gandaki-Narayani Nadi in the Central Nepal flows across fold-thrust belts of the Tethys Himalaya, Higher Himalaya, Lesser Himalaya, and the Sub-Himalaya, and is located in sub-tropical to humid sub-tropical climatic zone. Within the Higher Himalayas and the Lesser Himalayas, a high mountain and hilly region give way the long high-gradient, the Budhi Gandaki Nadi in the northern region. At the southern region within the Sub-Himalayas, having a wide Dun Valley, gives way the long low-gradient Narayani Nadi. Sands from Budhi Gandaki-Narayani Nadi were obtained and analysed for textural maturity and compositional maturity. The textural analyses consisted of determining roundness and sphere city of quartz grains for shape, and determining size of sand for matrix percent and various statistical measures including sorting. The analysis indicates that the textural maturity of the majority of sands lies in sub mature category though few textural inversions are also remarkable. Sands from upstream to downstream stretches of the main stem river show depositional processes by graded suspension in highly turbulent (saltation) current to fluvial tractive current, as confirmed from the C-M patterns. The compositional variation includes quartz, feldspar, rock fragments, mica, etc. The quartz grain percent slightly increases from the mountains to the lower relief areas. The percent feldspar decreases rapidly whereas the percent rock fragment decreases gradually along the downstream transport of sediment. The Budhi Gandaki-Narayani Nadi sands range from sublitharenite to lithic arenite composition in QFL diagram, and are remarkably poorer in feldspar compared to rock fragment. Among the rock fragments, the high-grade metamorphic rock fragmentsare dominant in the upstream stretch of the main stem Narayani Nadi stretch while the sedimentary lithics are remarkable in the downstream stretch. The QFL plots also show that the studied sands belong to recycled orogeny provenance and agree with the current tectonic setting of the Himalayas. Mineralogically, the sands (MMI=100%–203%) are not as matured as the normal sands. MMI fluctuates along downstream distance due to mixing of sediments from the major tributaries at various places along the main stem river.

Pore size distribution and pore functional characteristics of soils as affected by rock fragments in the hilly regions of the Sichuan Basin, China

2020 ◽  
pp. 1-10
Author(s):  
Jiangwen Li ◽  
Zhen Han ◽  
Shouqin Zhong ◽  
Pengfei Gao ◽  
Chaofu Wei
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Sichuan Basin ◽  
Total Porosity ◽  
Rock Fragment ◽  
Functional Characteristics ◽  
Rock Fragments ◽  
Hilly Region ◽  
Rock Fragment Content

Soil pore size distribution and pore functional characteristics are the most important for soil physical properties, water retention, and transmission. Furthermore, considerable amounts of rock fragments are present in hilly region soils. In this study, we discuss the pore size distribution and pore functional characteristics of soils as affected by rock fragments in the hilly regions of Sichuan Basin, China. The soil water characteristic curve was measured to calculate the soil total porosity and the ratio of equivalent pores in each diameter class. The results suggest that the soil total porosity decreases with increasing rock fragments size. The proportion of transmission pores increased gradually with increasing rock fragment content, whereas the fractions of storage pores and residual-bonding pores decrease gradually. Furthermore, the ratio of effective soil porosity to total porosity is higher than that of ineffective porosity to total porosity with increasing rock fragment content. In summary, increasing the rock fragment content can notably increase the proportion of soil transmission pores, thereby increasing soil aeration and water permeability. However, a high rock fragment content is not conducive to maintaining the water needed for normal plant growth.

scholarly journals Geochemistry of Sphalerite from the Permian Volcanic-Hosted Massive Sulphide (VHMS) Deposits in the Tasik Chini Area, Peninsular Malaysia: Constraints for Ore Genesis

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 728
Author(s):  
Mohd Basril Iswadi Basori ◽  
Sarah E. Gilbert ◽  
Khin Zaw ◽  
Ross R. Large
Keyword(s):  
Variable Temperature ◽  
Mineral Chemistry ◽  
Peninsular Malaysia ◽  
Massive Sulphide ◽  
Compositional Variation ◽  
Volcanic Origin ◽  
Sedimentary Deposits ◽  
Depositional Processes ◽  
Tasik Chini ◽  
Vhms Deposits

The Bukit Botol and Bukit Ketaya deposits are two examples of volcanic-hosted massive sulphide (VHMS) deposits that occur in the Tasik Chini area, Central Belt of Peninsular Malaysia. The mineralisation is divided into subzones distinguished by spatial, mineralogical, and textural characteristics. The primary sulphide minerals include pyrite, chalcopyrite, sphalerite, and galena, with lesser amounts of Sn- and Ag-bearing minerals, with Au. However, pyrrhotite is absent from both deposits. This study presents the results of sphalerite chemistry analysed by using an electron microprobe. Two types of sphalerite are recognised: sphalerite from the Bukit Botol deposit reveals a range of <DL to 24.0 mole% FeS, whereas sphalerite from the Bukit Ketaya deposit shows a range of <DL to 3 mole% FeS. Significant variations are shown in Zn, Cu, Cd, and Ag levels. Although the sphalerite has a wide variation in composition, a discernible decreasing Fe trend is exhibited from the stringer zone towards massive sulphide. This compositional variation in sphalerites may in part reflect variable temperature and activity of sulphur in the hydrothermal fluids during ore formation. Alternatively, the bimodal composition variations suggest that mineral chemistry relates to contrasting depositional processes. The Zn/Cd ratios for sphalerite from both these deposits are similar to those exhibited by volcano−sedimentary deposits with a volcanic origin. Therefore, the consistently low Cd concentrations and moderate to high Zn/Cd ratios suggest mixing of seawater and minor magmatic fluids controlling the chemistry of sphalerite at both deposits during their formation.

Evidence for pyroclastic emplacement of the Crowsnest Formation, Alberta

1996 ◽  
Vol 33 (5) ◽  
pp. 715-728 ◽  
Author(s):  
R.N. Adair ◽  
R.A. Burwash
Keyword(s):  
Elevated Temperatures ◽  
Pyroclastic Flows ◽  
Coarse Grained ◽  
Rock Fragment ◽  
Fine Grained ◽  
Rock Fragments ◽  
Explosive Phase ◽  
Graded Structures ◽  
Textural Evidence ◽  
Charred Wood

The middle Cretaceous Crowsnest Formation west of Coleman, Alberta, is composed of bedded alkaline volcanic deposits containing heterolithic volcanic rock fragments and crystal clasts. Comparison with modern examples of subaerial pyroclastic rocks suggests that pyroclastic flows, surges, fallout of material from vertical eruption columns, and minor mud flows emplaced the deposits. Textural evidence in the form of plastically deformed volcanic fragments, chilled deposit margins, baked rock fragment margins, recrystallization, and the presence of charred wood and charred wood molds indicate emplacement at elevated temperature. Massive deposits containing a fine-grained basal zone are interpreted as the product of pyroclastic flows, whereas deposits characterized by a block-rich base overlain by a thin layer of block-depleted stratified material are interpreted as the product of density-stratified surges. Deposits exhibiting pronounced stratification were emplaced by ash-cloud surges. Thickly bedded breccias exhibiting rheomorphic textures were emplaced as vent-proximal pyroclastic flows. Deposits characterized by parallel beds and graded structures are interpreted as fallout tephra deposits, and deposition by lahars is indicated by coarse-grained beds that lack evidence for emplacement at elevated temperatures. The eruptions of the Crowsnest Formation were cyclical. An initial explosive phase generated deposits by pyroclastic flows, surges, fallout, and lahars. As an eruption progressed, it evolved into a poorly gas-charged effusive stage that emplaced coarsely porphyritic domes, plugs, spines, and vent-proximal lava flows. Subsequent eruptions destroyed the effusive vent facies deposits and produced abundant heterolithic clasts typical of the formation.

scholarly journals Relating Hydrological Extremes with Area - A Case on Extreme Floods in South Central Nepal

1970 ◽  
Vol 6 (1) ◽  
pp. 44-48 ◽  
Author(s):  
Suresh Marahatta ◽  
Jagat Kumar Bhusal
Keyword(s):  
Extreme Rainfall ◽  
Flash Floods ◽  
Central Nepal ◽  
South Central ◽  
Hilly Region ◽  
Extreme Flood ◽  
Depth Analysis ◽  
Rainfall Depth ◽  
History Of ◽  
Forecasting System

Flash floods, debris flows and landslide disaster on the steep sloping terraces of hilly region are so challenging that even a real time hydro-meteorological forecasting system would not be applicable for all cases in Nepal. Flash floods are localized in short ranges with respect to time and distance; and it is very difficult to measure these flash floods in time. On the other hand, such phenomena need to be assessed for sustainable design of hydro- structures and for relocating the settlements from risk areas. A study was carried out to find the suitable relationship between area and extreme flood as well as area and extreme rainfall depth. Analysis is mainly based on the case of torrential rains in July 1993 over south central Nepal, which caused floods and debris torrents those were probably the worst in the disaster history of Nepal damaging lives and properties in Nepal during the 20th century. A relation for rainfall depth and other relation for specific flood are presented in this paper.Keywords: South-central Nepal; specific discharge; rainfall intensity; depth area duration.DOI: http://dx.doi.org/10.3126/jhm.v6i1.5487Journal of Hydrology and Meteorology, Vol. 6, No. 1 44-48

Early Cretaceous redbeds from the Minle Basin, Hexi Corridor, northwest China: Mineralogy and geochemistry implications for paleoweathering, provenance, and tectonic settings

2019 ◽  
Vol 7 (2) ◽  
pp. T525-T545
Author(s):  
Yaxiong Sun ◽  
Wenlong Ding ◽  
Yang Gu ◽  
Gang Zhao ◽  
Siyu Shi ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Lower Cretaceous ◽  
Chemical Weathering ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Northwest China ◽  
Hexi Corridor ◽  
Sediment Supply ◽  
Compositional Variation ◽  
Tectonic Settings

Redbeds with a large thickness in the lower Cretaceous record abundant geologic information in the Minle Basin. We have conducted the paleoweathering conditions, provenance, and tectonic settings based on mineralogy and geochemistry. Our results indicate that mudstone samples are characterized by abundant illite with negligible amounts of K-feldspars and analcime. The lower part of the lower Cretaceous is rich in quartz, whereas the upper part is dominated by dolomite and analcime. We suggest that this is caused by the decreasing input of the clastic influx during the middle-late early Cretaceous. High index of compositional variation values (average 1.33) indicate first-cycle sediment supply, suggesting an overall compositional immaturity and short-distance transportation. These characteristics are consistent with an active regional extension tectonic setting. The [Formula: see text] system ([Formula: see text];[Formula: see text];[Formula: see text]) and Th/U versus Th consistently reveal that the lower Cretaceous experienced a positive gradient in chemical weathering from young to old formations. Although the patterns of trace elements in three formations of the lower Cretaceous are different, those of the rare earth elements (REEs) tend to be consistent. The significant enrichment of light REEs, heavy REEs fractionation, and distinctive negative Eu anomalies suggest derivation from an old, upper continental crust composed of predominantly felsic sediments. This interpretation is supported by several discrimination diagrams such as titanium dioxide-nickel ([Formula: see text]), which shows the characteristics of immature recycled sediments. A few sensitive elements, ratios, and normalized REE patterns indicate a provenance of an active continental margin and a continental island arc (CIA). The La-Th-Sc, Th-Co-Zr/10, and Th-Sc-Zr/10 discrimination plots further confirm the CIA signature. Thus, we conclude that the early Cretaceous redbeds in the Minle Basin, Hexi Corridor, were deposited in a dustpan-shaped half-graben basin in a CIA setting when northwest China was influenced by intense regional extension.

scholarly journals Provenance Studies of Sandstone Facies Exposed Near Igbile Southwestern Nigeria: Petrographic and Geochemical Approach

2014 ◽  
Vol 6 (2) ◽  
pp. 47 ◽  
Author(s):  
Ikhane P. R. ◽  
Akintola A. I. ◽  
Bankole S. I. ◽  
Oyinboade Y. T.
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Inductively Coupled Plasma ◽  
Tectonic Setting ◽  
Source Area ◽  
Rock Fragment ◽  
Petrographic Analysis ◽  
Humid Climate ◽  
Southwestern Nigeria ◽  
Plagioclase Feldspar

The petrography, as well as the major, trace and rare earth element compositions of ten (10) sandstone samples of Maastrichtian Afowo Formation exposed near Igbile, Southwestern Nigeria, have been investigated to determine their provenance, source area weathering conditions, paleoclimate and tectonic setting using petrographic analysis and Inductively Coupled Plasma - Mass Spectrometry (ICP-MS). Results of the petrographic analysis revealed that quartz is the most dominant detrital mineral with (86%) followed by weathered plagioclase feldspar (5.10%) and rock fragments (10.9%). The quartz grain is sub-angular to sub-rounded in shape and the sandstones were classified as quartz arenites, sublitharenites and subarkoses based on framework composition of quartz, feldspar and rock fragment plots. This suggests a recycled orogen source for the sandstones and deposition in a humid climate, evidenced by the weathered feldspars. Eleven (11) major, seventeen (17) trace and fourteen (14) rare earth elements were obtained from the geochemical analysis. The major elements values range in concentration from 0.01%–81.39% with SiO2 being the dominant oxide followed by Al2O3 and Fe2O3 constituting over 95% of the major oxides; K2O, TiO2, Na2O, CaO, MgO and P2O5 made up the remaining 5%. The average ratio of SiO2/Al2O3 valued 4.31 for the sandstone is appreciably high indicating that it has been heavily weathered. The trace elements range in concentration from 0.2 ppm–1651.2 ppm with Zr being the most dominant element an indication of orogenic recycling. The rare earth elements range in concentration from 0.01 ppm–163.7 ppm with Ce having the highest concentration, depicting that the sandstones were deposited in an oxidizing environment. Also, the trace element relationship illustrated from the spider plot shows chemical coherence and uniformity of the sandstones. The chondrite normalized rare earth elements (REE) plot shows enrichment in the Light REE over the heavy REE for the sediment with strong negative Eu anomaly values between (0.57–0.69) suggesting a felsic provenance derived from upper continental crust for the sandstones.

Petrography and geochemistry of the siliciclastic Araba Formation (Cambrian), east Sinai, Egypt: implications for provenance, tectonic setting and source weathering

2015 ◽  
Vol 154 (1) ◽  
pp. 1-23 ◽  
Author(s):  
HOSSAM A. TAWFIK ◽  
IBRAHIM M. GHANDOUR ◽  
WATARU MAEJIMA ◽  
JOHN S. ARMSTRONG-ALTRIN ◽  
ABDEL-MONEM T. ABDEL-HAMEED
Keyword(s):  
Tectonic Setting ◽  
Source Area ◽  
Xrd Analysis ◽  
Climatic Conditions ◽  
Source Rocks ◽  
Northern Margin ◽  
Rock Fragments ◽  
Geochemical Parameters ◽  
Clastic Sediments ◽  
Chemical Index

AbstractCombined petrographic and geochemical methods are utilized to investigate the provenance, tectonic setting, palaeo-weathering and climatic conditions of the Cambrian Araba clastic sediments of NE Egypt. The ~ 60 m thick Araba Formation consists predominantly of sandstone and mudstone interbedded with conglomerate. Petrographically the Araba sandstones are mostly sub-mature and classified as subarkoses with an average framework composition of Q80F14L6. The framework components are dominated by monocrystalline quartz with subordinate K-feldspar, together with volcanic and granitic rock fragments. XRD analysis demonstrated that clay minerals comprise mixed-layer illite/smectite (I/S), illite and smectite, with minor kaolinite. Diagenetic features of the sandstone include mechanical infiltration of clay, mechanical and chemical compaction, cementation, dissolution and replacement of feldspars by carbonate cements and clays. The modal composition and geochemical parameters (e.g. Cr/V, Y/Ni, Th/Co and Cr/Th ratios) of the sandstones and mudstones indicate that they were derived from felsic source rocks, probably from the crystalline basement of the northern fringe of the Arabian–Nubian Shield. The study reveals a collisional tectonic setting for the sediments of the Araba Formation. Palaeo-weathering indices such as the chemical index of alteration (CIA), chemical index of weathering (CIW) and plagioclase index of alteration (PIA) of the clastic sediments suggest that the source area was moderately chemically weathered. On the northern margin of Gondwana, early Palaeozoic weathering occurred under fluctuating climatic conditions.

Grain-size trends and provenance of southwestern Gulf of Mexico beach sands

1995 ◽  
Vol 32 (12) ◽  
pp. 2009-2014 ◽  
Author(s):  
Arturo Carranza-Edwards ◽  
Leticia Rosales-Hoz
Keyword(s):  
Gulf Of Mexico ◽  
Source Region ◽  
Volcanic Rocks ◽  
Breaking Waves ◽  
High Energy ◽  
Rock Fragment ◽  
Triangular Diagram ◽  
Quartz Content ◽  
Rock Fragments ◽  
Beach Sands

Sand samples from 30 beach locations of the southwestern Gulf of Mexico littoral zone were texturally and mineralogically investigated. Based on their source lithology and fluvial network, they were subdivided into two groups: (1) sands with volcanic rocks in the source region and (2) sands with a nonvolcanic source. Sands from foreshore and backshore areas exhibit similar textural characteristics, with less rock fragments than those from the inshore zone, where the high energy of breaking waves and littoral currents is present. A quartz–feldspar–rock fragment triangular diagram indicates that the proximity of volcanic sources is responsible for the enrichment of rock fragment content in the beach sands. Beach sands associated with Tampico and Veracruz embayments have greater quartz content, caused by a greater transport distance. Mineralogical maturity and provenance indexes used in a binary diagram are helpful in discriminating sand samples from volcanic and nonvolcanic domains.

scholarly journals Textural and compositional variation of sand along the Manahara-Bagmati river basin, Kathmandu Valley

2001 ◽  
Vol 23 ◽  
Author(s):  
Naresh Kazi Tamrakar ◽  
Hari Nandan Gurmaita
Keyword(s):  
River Basin ◽  
River System ◽  
Compositional Variation ◽  
Humid Climate ◽  
Quartz Content ◽  
Rock Fragments ◽  
Grain Sizes ◽  
Size Grade ◽  
The Mean ◽  
Bagmati River

The Manahara-Bagmati river basin is located in a humid climate and has a 51 km long low gradient profile. It collects sediments from metamorphic, metasedimentary, and fluvio-lacustrine sources. The sediment samples collected from 17 localities were studied texturally and compositionally to infer how sediment modifies due course of transport and whether the trends are interfered by mixing, recycling, and weathering. For this purpose, two size grades (i.e., 0-1ϕ and 2-3ϕ) were studied. Between them, the trends were more conspicuous in the 0-1ϕ sand grade. Mean (M2) and median (M6) grain sizes increase downstream exponentially. Sorting (σ1) also improves along the river course. Quartz content gradually increases downstream, whilst feldspars and rock fragments decrease remarkably along the river course.  Rapid dilution of feldspars and rock fragments (from coarser size grade) occurs after 27 km of transport. The Modified Maturity Index, which ranges from 19.8 to 214, increases from the Manahara to Bagmati River sands. The mica content in the Bagmati River is from 2 to 8 times higher than in the Manahara River. Within the studied river course, the mean projection sphericity (ψp) of quartz remains high (0.80 in average) but does not show any consistent trend. The mean roundness (ρ) of the 0-1ϕ sand grade increases conspicuously against the distance of transport. The majority of samples belong to submature class. Local influx of sediments and recycling are profound from Sankhu to Sanothimi and from Chobhar to Hasdol. Rapid weathering of labile grains is inferred in the middle reach of the Manahara- Bagmati river system (i.e., between Sanothimi and Chobhar).

scholarly journals Morphology and classification of the main stem Bagmati River, Central Nepal

2013 ◽  
Vol 15 ◽  
pp. 23-34
Author(s):  
Pramila Shrestha ◽  
Naresh Kazi Tamrakar
Keyword(s):  
Main Stem ◽  
Aerial Photographs ◽  
Radius Of Curvature ◽  
Moderate Degree ◽  
Lesser Himalaya ◽  
Valley Fill ◽  
Central Nepal ◽  
Belt Width ◽  
Bagmati River ◽  
Type Stream

Rivers are significant geomorphic agents which can carry huge amounts of sediments and water from their catchments to depositional basins. Due course of flow they can bring various hazards such as flooding, inundation of flood plains, erosion of banks and trigger various slope movements. To understand nature and behavior of the Bagmati River, which is a perennial, storm and spring-fed, eight order river of central Nepal, the planiform morphological parameters of this river were analysed and river segments along the main stem stretches were classified into various stream-types, using topographic maps, aerial photographs, and satellite imageries. The Bagmati River is an 8th order perennial river. The Bagmati River basin comprises 39 sub-basins of 4th order and higher. The averages of meander wavelengths (Lm), meander belt width (Wblt), radius of curvature (Rc) and sinuosity (K) of the 7th order main stem Bagmati River are 598.27 m, 164.07 m, 252.35 m and 1.38, respectively. Similarly, the averages of Lm, Wblt, Rc, and K of the 8th order main stem rivers are respectively, 496.77, 126.58 m, 286.13 m, and 1.55. All these parameters reflect fluctuating trends of variation along the downstream stretch. However, the portion of the 7th order river shows abrupt increase of Lm after the Bagmati River crosses the Main Boundary Thrust. The Rc also indicates slight increase in this region. The sinuosity reflects overall increase from the 7th to the 8th order rivers. This increase in sinuosity is attributed to the decrease in slope and competency of the river. There exists a moderate degree of correlation between K and Wblt showing that the Wblt of the Bagmati River tends to increase as the sinuosity increases. The stream segments of the Bagmati River fall on A-, B-, C-, G- and D-type rivers. All the segments of the Bagmati River, lying within the Kathmandu Valley and having substrate of the fluvio-lacustrine valley-fill sediments, fall on C-type stream because of low entrenchment and high width/depth ratio. Similarly, A-type streams are developed at segments which flow through the Tistung Formation of the granite terrain of the Lesser Himalaya most probably due to entrenched and gorged valley and high slope. Likewise, B- and G-type streams are developed in terrains of the Lesser Himalaya and the Sub-Himalaya. The B-type streams are moderately entrenched with sinuous to meandering and wide channels. The D-type stream segment which is a multi-thread channel is characteristically developed within the terrain of the Sub-Himalaya presumably due to the change in slope caused by thrusting, and greater input of sediments from the Siwaliks in relation to weak and loosely consolidated lithology. DOI: http://dx.doi.org/10.3126/bdg.v15i0.7415 Bulletin of the Department of Geology, Vol. 15, 2012, pp. 23-34

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