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221.
A relatively undeformed quartzite sample from the Weverton formation was experimentally deformed in plane strain at a temperature of 700° C, a confining pressure of 15 kb and a constant strain rate of 10−6/sec, in a modified Griggs apparatus. A comparison of the known experimental strain for the sample with that measured from deformed rutile needles within the quartz grains shows fairly close agreement between the two values. This confirms the validity of using the needles as intracrystalline strain markers. A comparison has been made of the microstructures and preferred orientations in the experimentally deformed sample and a naturally deformed sample of the same quartzite which has undergone the same strain. The experimentally deformed sample exhibits more inhomogeneous intragranular deformation and a “double funnel” pattern of c axes, while the naturally deformed sample exhibits more homogeneous intragranular deformation and a broad great circle girdle of c axes normal to the foliation and lineation. 相似文献
222.
This study evaluates changes in streamflow, temperature and precipitation over a time span of 105 years (1906–2010) in the Colorado River Basin (CRB). Monthly precipitation and temperature data for 29 climate divisions, and streamflow data for 29 naturalized gauges were analyzed. Two variations of the Mann-Kendall test, considering lag-1 auto correlation and long-term persistence, and the Pettitt test were employed to assess trends and shifts, respectively. Results indicated that streamflow increased during the winter–spring months and decreased during the summer– autumn period. Decreasing trends in winter precipitation were identified over snow-dominated regions in the upper basin. Significant increases in temperature were detected over several months. Major shifts were noticed in 1964, 1968 and in the late 1920s. Increasing temperature while decreasing streamflow and precipitation were noticed after major shifts in the 1930s, and these shifts coincided with coupled phases of El Niño Southern Oscillation and Pacific Decadal Oscillation.
EDITOR A. Castellarin; ASSOCIATE EDITOR R. Hirsch 相似文献
223.
A variety of sediment types were identified in sediment cores taken at the dredged material dumpsite in the New York Bight.
Black sandy mud is characteristic of dumped dredged material while glauconitic and quartzose sands are typical of the naturally
deposited sediments underlying the deposit. The sedimentological investigation indicates that largescale differentiation of
dumped material occurs at the dumpsite. Laminated sediments and discrete beds are typical of the central part of the deposit,
the area that receives the bulk of direct dumping. Relatively homogeneous, fine-grained sediments, presumably derived from
the area of direct dumping, are characteristic of the material present at the periphery of the deposit. Preferential transport
of fine-grained material to the fringes of the deposit may be an important contaminant transport mechanism in the area. Incursion
of glauconitic sand, derived from surrounding areas, onto the edges of the deposit is also believed to occur. Based on bathymetric
surveys of the area conducted in 1936, 1973, and 1978, rates of dredged material accumulation at the dumpsite have been estimated
for the period 1936–1978. The calculated rates range from 50 cm/yr at the apex of the deposit to 6 cm/yr at the periphery.
Contribution 294 of the Marine Sciences Research Center (MSRC) of the State University of New York at Stony Brook. 相似文献
224.
Kailasa Pandarinath Rajasekhariah Shankar Ignacio S. Torres-Alvarado Anish Kumar Warrier 《Arabian Journal of Geosciences》2014,7(7):2851-2860
Magnetic susceptibility and petrographic studies of drilled rock cuttings from two geothermal wells (Az-26 and Az-49) of the important electricity-generating geothermal system, Los Azufres, Mexico, were carried out to determine the relation between the magnetic susceptibility of rocks, the concentration of magnetic minerals and hydrothermal alteration. For this purpose, low-frequency magnetic susceptibility (χ lf) was measured and compared its distribution trends with those of magnetic and Fe–Mg silicate minerals, and with the extent of hydrothermal alteration in rocks of the two geothermal wells. The study indicates a decrease in χ lf values with depth in the two geothermal wells corresponding with: (1) an increase in the reservoir temperature and hydrothermal alteration; and (2) a decrease in the concentrations of Fe–Mg silicates and opaque minerals. The data suggest that ferromagnesian minerals and opaque minerals like ilmenite are the main contributors to the χ lf of rocks. The decrease in χ lf, ilmenite, and Fe–Mg mineral contents with an increase in the hydrothermal alteration degree, pyrite and haematite contents suggests the hydrothermal alteration of ilmenite and Fe–Mg minerals (characteristic of high χ lf values) to pyrite, haematite and other opaque minerals (with low χ lf values). The interaction of hydrothermal fluids with rocks results in the hydrothermal alteration of primary minerals. In a geothermal area, an anomaly of low magnetic susceptibility values of rocks in a homogenous litho unit characterized by high magnetic susceptibility may suggest hydrothermal alteration. Magnetic susceptibility can be a useful parameter, during the initial stages of geothermal exploration, in identifying hydrothermally altered rocks and zones of hydrothermal alteration both at the surface and from drilled wells in geothermal systems. 相似文献
225.
Eco-restoration of a high-sulphur coal mine overburden dumping site in northeast India: A case study 总被引:1,自引:0,他引:1
J. Dowarah H. P. Deka Boruah J. Gogoi N. Pathak N. Saikia A. K. Handique 《Journal of Earth System Science》2009,118(5):597-608
Eco-restoration of mine overburden (OB) or abandoned mine sites is a major environmental concern. In the present investigation,
an integrated approach was used to rejuvenate a high-sulphur mine OB dumping site in the Tirap Collieries, Assam, India, which
is situated in the Indo-Burma mega-biodiversity hotspot. A mine OB is devoid of true soil character with poor macro and micronutrient
content and contains elevated concentrations of trace and heavy metals. Planting of herbs, shrubs, cover crops and tree species
at close proximity leads to primary and secondary sere state succession within a period of 3 to 5 years. A variety of plant
species were screened for potential use in restoration: herbs, including Sccharum spontaneum, Cymbopogon winterianus Jowitt (citronella), and Cymbopogon flexuosus (lemon grass) cover plants, including Mimosa strigillosa, M. striata, and M. pigra; shrubs, including Sesbania rostrata (dhaincha) and Cassia streata (cassia); and tree species, including Gmelina arborea (gomari) and Dalbergia sissoo (sissoo). Amendment with unmined soil and bio-organic matter was required for primary establishment of some plant species.
Management of these plant species at the site will ensure long term sustainable eco-restoration of the coal mine-degraded
land. 相似文献
226.
Lane–Emden type equations have been interesting since long time due to their wide applications in mathematical physics and astrophysics. In this paper, a coupled approach has been proposed for the solution of nonlinear singular value problems of Lane–Emden type. 相似文献
227.
Climatic periodicities recorded in lake sediment magnetic susceptibility data: Further evidence for solar forcing on Indian summer monsoon 总被引:1,自引:0,他引:1
The Indian summer monsoon exhibits considerable spatio-temporal variability.It is therefore important to understand its dynamics and the inherent periodicities.In this study,we have performed spectral and wavelet analyses of magnetic susceptibility data for sediments from Thimmannanayakanakere(TK)-a small lake in southern India.The main objective of this investigation is to identify and explain the possible origin of the prominent periodicities present in the magnetic susceptibility data.Significant periodicities in the TK χ_(lf)data are centered at 906,232,147,128,96,61,54 and 44 years,which might have a solar origin.The wavelet power spectrum of the raw and detrended χ_(lf)data confirms the findings of spectral analysis and also provides temporal variations of the significant cyclicities during the past3700 cal.years B.P.Positive correlation is documented between sunspot activity and TK xif data;crossspectral analysis of the reconstructed sunspot data and TK xif data suggest that there is a strong coherence between the two datasets as significant periodicities are documented in both.There is a good match between the TK xif and the reconstructed total solar irradiance data for the past 1200 years.However,an out-of-phase relationship is documented at certain time-intervals,which may be attributed to uncertainties in the age-depth model.The results obtained from this study show that solar variations are the main controlling factor of the southwest monsoon and,like other archives from different regions in India,the TK lake sediments have also recorded these solar signatures. 相似文献
228.
K.K. Abdul Azeez T. Satish Kumar Sharana Basava T. Harinarayana A.M. Dayal 《Marine and Petroleum Geology》2011,28(5):1073-1082
As the Mesozoic sediments contribute most of the oil and gas reserves of the world, we present an integrated interpretation approach using magnetotellurics (MT) and surface geochemical prospecting studies to demarcate hydrocarbon prospective Gondwana (Mesozoic) formations underneath the Deccan flood basalts of Late Cretaceous age across Narmada-Tapti rift (between Bhusawal and Barwah) in Central India. The MT interpretation shows deep (∼5 km) basement structure between southern and central part of the MT profile however, it gradually becomes shallower to either ends of the profile with a predominant basement depth reduction in the northern end compared to the southern end. The geophysical results suggest thick (2-3.5 km) Mesozoic sediments in the area characterized by deep basement structure. The geochemical analysis of the near surface soil samples indicate higher concentrations of light gaseous hydrocarbons constituents over the area marked with thick sub-basalt Mesozoic formations. Analyses of the geochemical data imply that these hydrocarbons are genetically related, generated from a thermogenic source and these samples fall in the oil-producing zone. The temperature-depth estimations in the region supports favorable temperature conditions (80-120 °C) for oil generation at basement depths. 相似文献