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21.
Sediment storage and release from Himalayan piggyback basins and implications for downstream river morphology and evolution 下载免费PDF全文
Alexander L. Densmore Rajiv Sinha Swati Sinha S. K. Tandon Vikrant Jain 《Basin Research》2016,28(4):446-461
Piggyback basins developed at the mountain fronts of collisional orogens can act as important, and transient, sediment stores along major river systems. It is not clear, however, how the storage and release of sediment in piggyback basins affects the sediment flux and evolution of downstream river reaches. Here, we investigate the timing and volumes of sediment storage and release in the Dehra Dun, a piggyback basin developed along the Himalayan mountain front in northwestern India. Based on OSL dating, we show evidence for three major phases of aggradation in the dun, bracketed at ca. 41–33 ka, 34–21 ka and 23–10 ka, each accompanied by progradation of sediment fans into the dun. Each of these phases was followed by backfilling and (apparently) rapid fan‐head incision, leading to abandonment of the depositional unit and a basinward shift of the active depocentre. Excavation of dun sediment after the second and third phases of aggradation produced time‐averaged sediment discharges that were ca. 1–2% of the modern suspended‐sediment discharges of the Ganga and Yamuna rivers that traverse the margins of the dun; this sediment was derived from catchment areas that together comprise 1.5% of the drainage area of these rivers. Comparison of the timing of dun storage and release with upstream and downstream records of incision and aggradation in the Ganga show that sediment storage in the dun generally coincides with periods of widespread hinterland aggradation but that late stages of dun aggradation, and especially times of dun sediment excavation, coincide with major periods of sediment export to the Ganga Basin. The dun thus acts to amplify temporal variations in hinterland sediment supply or transport capacity. This conceptual model appears to explain morphological features of other major river systems along the Himalayan front, including the Gandak and Kosi Rivers, and may be important for understanding sediment flux variations in other collisional mountain belts. 相似文献
22.
Emad Nagm Sreepat Jain Kamel Mahfouz Ahmed El-Sabbagh Aziz Abu Shama 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(1):70-92
The changes in macrofauna and microfauna, before, during and after the latest Cenomanian global Oceanic Anoxic Event (OAE2), from the Eastern Desert of Egypt are documented, along with an inferred paleoenvironment. The age of the studied OAE2 interval is constrained by the last occurrence of the marker calcareous nannofossils species Axopodorhabdus albianus along with the previously identified positive δ13C excursion from the coeval ammonite Vascoceras cauvini Zone (= Neocardioceras juddii Zone), enabling correlation with the peak ‘b’ of the OAE2. Based on the studied microfaunal assemblages, a warm shallow restricted lagoonal environment with mesotrophic conditions and strong seasonality is inferred. The presence of a rare ammonite (and ostracods) attest to the intermittent introduction of marine waters within this inner ramp setting. In terms of sequence stratigraphy, two 3rd order depositional sequences are recorded. The top surface of the first depositional sequence, at the sequence boundary, SB Ce 5 (the start of the OAE2), is marked by an abrupt faunal change with reduced abundances of the macrofaunal elements. This is in tune with other Egyptian records of relatively smaller loss (10 %) at the Cenomanian-Turonian boundary, as compared to much higher numbers (53–79% of species), globally. This faunal (biotic bottleneck) and lithological change (from siliciclastic-dominated deposits to a largely carbonate-dominated one) at the SB Ce 5 is attributed as a response to the latest Cenomanian drowning (the highest sea-level during the Phanerozoic), that also resulted in the formation of carbonate platform. 相似文献
23.
Natural Hazards - This study describes the impact of assimilation of INSAT-3D radiances data from both imager and sounder for Indian summer monsoon simulation and rainfall forecast over a hilly... 相似文献
24.
Martha Tapas Ranjan Roy Priyom Jain Nirmala Khanna Kirti Mrinalni K. Kumar K. Vinod Rao P. V. N. 《Landslides》2021,18(6):2125-2141
Landslides - India ranks first in the world in terms of fatal landslides. Large vulnerable area (0.42 million km2), high population density and monsoon rainfall make India’s landslide... 相似文献
25.
Rekha Ghosh 《Journal of the Indian Society of Remote Sensing》1993,21(3):119-126
Jharia coalfield, the chief storehouse of prime coking coal in India, has lost the original controls of ground water conditions. Here, ground water level is dependent mainly upon the presently existing topography, geomorphic features such as abandoned channels, confluence of channels, losing streams etc. and human-induced recharge conditions. These features are reflected by the soil moisture content and presence of vegetative cover. The ground water map of Jharia coalfield has been prepared from the aerial photographs using the grey tone and vegetation cover as the criteria. The observations are supported with field checks. The ground water map prepared will be very much useful to the society because some parts of the coalfield suffer from severe drought during summer. 相似文献
26.
27.
D. P. sharma A. K. Jain S. C. Chakravarty K. Kasturirangan K. R. Ramanathan U. R. Rao 《Astrophysics and Space Science》1972,17(2):409-425
The electron production rates in the night-time D-region arising from the transit of strong celestial X-ray sources Sco X-1,
Tau X-1 and Galactic Center are estimated and compared with the ambient electron production rates resulting from other known
stable agencies. Using the experimentally measured values of the night-time electron densities, the number of additional electrons/cc
expected from the passage of these sources is computed. For the 164 kHz transmission from Tashkent, received at Ahmedabad,
the associated enhancement in the attenuation is calculated using the full wave admittance technique of Barron and Budden.
Reasonable agreement is shown to exist between the calculated values of the attenuation and those of direct observations. 相似文献
28.
A. K. Jain U. B. Jayanthi K. Kasturirangan U. R. Rao 《Astrophysics and Space Science》1976,45(2):433-438
The paper presents experimental evidence for the existence of fast intensity fluctuations with time scales of the order of a minute in the X-ray emission from Cyg X-1 at energies greater than 29 keV. Spectral variations over time intervals of 20–25 min are also observed in the same energy range. Whereas, similar intensity and spectral fluctuations have been reported earlier at lower energies the observations presented here is the first evidence for the existence of similar fluctuations at high energies. 相似文献
29.
A modified expression for dielectronic recombination coefficients for the recombining ions pertaining to the H, He and Ne sequences is presented. The results are in nice agreement with the extensive computations of Ansari et al. (1970) for the cases considered. 相似文献
30.
P. P. Hallan Sanjay Jain K. B. Bhatnagar 《Celestial Mechanics and Dynamical Astronomy》2000,77(3):157-184
The non-linear stability of L
4 in the restricted three-body problem has been studied when the bigger primary is a triaxial rigid body with its equatorial
plane coincident with the plane of motion. It is found that L
4 is stable in the range of linear stability except for three mass ratios:
where A1, A2 depend upon the lengths of the semi axes of the triaxial rigid body.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献