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151.
Mehrdad Sardar Abadi Anne-Christine Da Silva Abdolhossein Amini Ali Akbar Aliabadi Frédéric Boulvain Mohammad Hossein Sardar Abadi 《International Journal of Earth Sciences》2014,103(8):2233-2254
The Kashafrud Formation was deposited in the extensional Kopeh-Dagh Basin during the Late Bajocian to Bathonian (Middle Jurassic) and is potentially the most important siliciclastic unit from NE Iran for petroleum geology. This extensional setting allowed the accumulation of about 1,700 m of siliciclastic sediments during a limited period of time (Upper Bajocian–Bathonian). Here, we present a detailed facies analysis combined with magnetic susceptibility (MS) results focusing on the exceptional record of the Pol-e-Gazi section in the southeastern part of the basin. MS is classically interpreted as related to the amount of detrital input. The amount of these detrital inputs and then the MS being classically influenced by sea-level changes, climate changes and tectonic activity. Facies analysis reveals that the studied rocks were deposited in shallow marine, slope to pro-delta settings. A major transgressive–regressive cycle is recorded in this formation, including fluvial-dominated delta to turbiditic pro-delta settings (transgressive phase), followed by siliciclastic to mixed siliciclastic and carbonate shoreface rocks (regressive phase). During the transgressive phase, hyperpycnal currents were feeding the basin. These hyperpycnal currents are interpreted as related to important tectonic variations, in relation to significant uplift of the hinterland during opening of the basin. This tectonic activity was responsible for stronger erosion, providing a higher amount of siliciclastic input into the basin, leading to a high MS signal. During the regressive phase, the tectonic activity strongly decreased. Furthermore, the depositional setting changed to a wave- to tide-dominated, mixed carbonate–siliciclastic setting. Because of the absence of strong tectonic variations, bulk MS was controlled by other factors such as sea-level and climatic changes. Fluctuations in carbonate production, possibly related to sea-level variations, influenced the MS of the siliciclastic/carbonate cycles. Carbonate intervals are characterized by a strong decrease of MS values indicates a gradual reduction of detrital influx. Therefore, the intensity of tectonic movement is thought to be the dominant factor in controlling sediment supply, changes in accommodation space and modes of deposition throughout the Middle Jurassic sedimentary succession in the Pol-e-Gazi section and possibly in the Kopeh-Dagh Basin in general. 相似文献
152.
Anthropogenic activities have always been the cause of most environmental degradation, and mangrove disappearance is no exception. A comparative assessment on the biodiversity of natural and degraded mangrove forests has been undertaken, looking at the biomass, both above-ground and below-ground. The natural and the degraded mangrove forests were situated at Kuala Selangor and Sungai Haji Dorani, respectively, both on the West coast of Peninsular Malaysia. A random sample scheme with quadrate sample plots (10 m × 10 m) was adopted for the measurement of the diameter at breast height and total height of individual tree species at both forests. Diversity indices and above- and below-ground biomass were estimated from this inventory. Eight mangrove tree species were identified at both study areas, namely: Bruguiera parviflora, Avicennia officinalis, Rhizophora mucronata, Sonneratia alba, Avicennia marina, Bruguiera cylindrica, Xylocarpus mekongensis and Excoecaria agallocha. The mangrove species in Sungai Haji Dorani showed high diversity with a Shannon–Weiner Index (H′) value of 0.91, compared to the natural mangrove of Kuala Selangor which has a lower value, H′ = 0.55. The dominant species in the natural mangrove area was B. parviflora, with the highest Important Value Index (IVI) of 70.96 %, as opposed to A. marina which was the most common species in the degraded mangrove area, with IVI of 49.16 %. An estimate of 305.46 t/ha of above-ground biomass was calculated for the natural mangrove, while 122.78 t/ha was obtained for the degraded mangrove forest. This contrasts with the below-ground biomass estimates, which were 14.09 t/ha for the natural mangrove and 36.35 t/ha for the degraded mangrove. 相似文献
153.
Gardner solitons (GSs) and double layers (DLs) of dust ion acoustic (DIA) waves in an electronegative plasma (composed of inertial positive and negative ions, Maxwellian cold electrons, non-thermal hot electrons, and negatively charged static dust) are studied. The reductive perturbation method is employed to derive the Korteweg-de Vries (K-dV), modified K-dV, and standard Gardner equations, which admits solitary wave and DLs solutions for σ around its critical value σ c (where σ c is the value of σ corresponding to the vanishing of the nonlinear coefficient of the K-dV equation). The parametric regimes for the existence of the GSs and DLs, are obtained. The basic features of DIA GSs and DLs (associated with negative structure only) are analyzed. It has been found that the characteristics of DIA GSs and DLs, are different from that of the K-dV solitons and mK-dV (mixed K-dV) solitons. The implications of our results to different space and laboratory plasma situations are discussed. 相似文献
154.
Bioreactor landfills are operated to enhance refuse decomposition, gas production, and waste stabilization. The major aspect
of bioreactor landfill operation is the recirculation of collected leachate back through the refuse mass. Due to the presence
of additional leachate and accelerated decomposition, the characteristics of Municipal Solid Waste (MSW) in bioreactor landfills
are expected to change. About 50% of the continental United States comes under the designated seismic impact zone. The federal
regulations have focused increase attention on seismic design of solid waste fills, and have mandated that the solid waste
landfills located in the seismic impact zones should be designed to resist the earthquake. Accordingly, assessment of dynamic
properties of landfills is one of the major geotechnical tasks in landfill engineering. In order to understand the changes
in dynamic properties of bioreactor waste mass with time and decomposition, four small scale bioreactor landfills were simulated
in laboratory and samples were prepared to represent each phase of decomposition. The state of decomposition was quantified
by methane yield, pH, and volatile organic content (VOC). A number of Resonant Column (RC) tests were performed to evaluate
the dynamic properties (stiffness and damping) of MSW. The test results indicated that the normalized shear modulus reduction
and damping curves are significantly affected by the degree of decomposition. The shear modulus increased from 2.11 MPa in
Phase I to 12.56 MPa in Phase IV. The increase was attributed to the breakdown of fibrous nature of solid waste particles
as it degrades. Therefore, considering MSW properties to be uniform throughout the bioreactor landfill is not a reasonable
assumption and the shear modulus reduction curves should be evaluated based on the degree of MSW decomposition, rather than
the sample composition itself. 相似文献
155.
Bioreactor landfills are operated for rapid stabilization of waste, increased landfill gas generation for cost-effective energy
recovery, gain in landfill space, enhanced leachate treatment, and reduced post closure maintenance period. The fundamental
process of waste stabilization in bioreactor landfill is recirculation of generated leachate back into the landfills. This
creates a favorable environment for rapid microbial decomposition of the biodegradable solid waste. In order to better estimate
the generated leachate and design of leachate recirculation system, clear understanding of the permeability of the Municipal
Solid Waste (MSW) with degradation and the factors influencing the permeability is necessary. The objective of the paper is
to determine the changes in hydraulic properties of MSW in bioreactor landfill with time and decomposition. Four small-scale
bioreactor landfills were built in laboratory and samples were prepared to represent each phase of decomposition. Then, the
changes in hydraulic properties of MSW in bioreactor landfill with time and decomposition were determined. A series of constant
head permeability tests were performed on the samples generated in laboratory scale bioreactor landfills to determine variation
of permeability of MSW with degradation. The test results indicated that the permeability of MSW in bioreactor landfills decreases
with decomposition. Based on the test results, the permeability of MSW at the first phase of degradation was estimated as
0.0088 cm/s at density 700 kg/m3. However, with degradation, permeability decreased to 0.0013 cm/s at the same density, for MSW at Phase IV. 相似文献
156.
Ismail Hossain Krisna Kanta Roy Pradip Kumar Biswas Mahbubul Alam Md. Moniruzzaman Farah Deeba 《中国地球化学学报》2014,33(4):336-350
The present research deals with the geochemical characteristics of the Holocene sediments from Alamdanga area, Chuadanga district, Bangladesh. Main goals of the study are to delineate source rock characteristics, degree of chemical weathering and sorting processes and behavior of redox conditions during deposition of the sediments. Geochemical characteristics of the sediments show comparatively a wide variation in accordance with stratigraphy in their major element contents (e.g. SiO2 69.46-82.13, A1203 2.28-8.88 in wt%), reflecting the distinctive provenance and in part an unstable period in terms of tectonic activity. Geochemical classification of the sediments shows mostly sub-arkose with few sub-litharenites. Some major and trace elements display comprehensible correlation with A1203 confirming their possible hydraulic fraetionation. The chemical index of alteration (CIA*), W* index, index of compositional variability (ICV), plagioclase index of alteration (PIA*) values and the ratio of SIO2/Al2O3, suggest low degrees of chemical weathering in the source areas as well as immature to moderately mature the sediments. The sediments suggest semi-arid climatic trends within oxic deltaic depositional conditions during the Holocene, at 3-12 ka. Whole rock geochemistry and discrimination diagrams demonstrate the continental signature derivatives, which might have been derived from the felsic to intermediate igneous rocks (granitic plutonic rocks) as well as from quartzose sedimentary/metamorphic provenance. These typical sources are present in a vast region of the Himalayan belt and catchment areas of Ganges. The tectonic setting of the sediments demarcates typically passive margin with slightly continental arc system. 相似文献