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571.
Partha Pratim Ghosh Saibal Ray A. A. Usmani Utpal Mukhopadhyay 《Astrophysics and Space Science》2013,345(2):367-371
The concept of oscillatory Universe appears to be realistic and buried in the dynamic dark energy equation of state. We explore its evolutionary history under the framework of general relativity. We observe that oscillations do not go unnoticed with such an equation of state and that their effects persist later on in cosmic evolution. The ‘classical’ general relativity seems to retain the past history of oscillatory Universe in the form of increasing scale factor as the classical thermodynamics retains this history in the form of increasing cosmological entropy. 相似文献
572.
Coral bleaching indices and thresholds for the Florida Reef Tract, Bahamas, and St. Croix, US Virgin Islands 总被引:2,自引:0,他引:2
It is well established that elevated sea temperatures cause widespread coral bleaching, yet confusion lingers as to what facet of extreme temperatures is most important. Utilizing long-term in situ datasets, we calculated nine thermal stress indices and tested their effectiveness at segregating bleaching years a posteriori for multiple reefs on the Florida Reef Tract. The indices examined represent three aspects of thermal stress: (1) short-term, acute temperature stress; (2) cumulative temperature stress; and (3) temperature variability. Maximum monthly sea surface temperature (SST) and the number of days >30.5 °C were the most significant; indicating that cumulative exposure to temperature extremes characterized bleaching years. Bleaching thresholds were warmer for Florida than the Bahamas and St. Croix, US Virgin Islands reflecting differences in seasonal maximum SST. Hind-casts showed that monthly mean SST above a local threshold explained all bleaching years in Florida, the Bahamas, and US Virgin Islands. 相似文献
573.
Abnormally high formation pressures are encountered worldwide, ranging in geological age from Cenozoic to Paleozoic, within
a depth range of few hundred meters to as deep as six thousand meters while carrying out exploratory drilling by E and P companies.
Several causes can increase formation fluid pressure i.e. rapid loading of sediments results compaction disequilibrium, thermal
expansion of fluids, compression and/or upliftment of strata by tectonic forces, generation of oil and gas from organic matter
and its volume expansion due to high thermal stress within the restricted pore volume in subsurface condition. Few global
examples on overpressure occurrences have been compiled in the paper with special reference to Bengal Basin. Emphasis has
been given on methodology and interpretation on abnormal pressure detection in Bengal Basin with a compiled data package on
generated curves (Geologs), charts, tables in a systematic way to understand the depth/stratigraphic horizons proved/interpreted
as proved or likely to be within transition and overpressure regime. The integrated analysis indicates that the wells drilled
in the east of Eocene hinge zone in the onshore and offshore parts of Bengal Basin have penetrated overpressure formation
within Miocene in the depth range of 2800 m to 5340 m and the mud weight used to control this overpressure zone was more than
2.0 sp gr mud. The generated Geologs can be used as reference to understand the regime of transition and overpressure, as
a valuable document for exploration drilling planning and monitoring. The generated model curve (modified using available
data after Hottman and Johnson, 1956 curve) using sonic departure (i.e. Δtob(sh) −Δtn(sh)) from drilled wells may be used as an additional tool to find out the expected formation pressure gradient and equivalent
mud weight in all future wells. The correlation of wells based on the trend of dcs and σ logs will be useful for predicting
transition and overpressure top provided all the parameters required for calculating dcs and σ log recorded smoothly during
drilling phase. The study has brought out the detail procedure to generate the pressure profile in the future wells. The generation
of pressure profile of a well prior to drilling has got immense importance in oil industry. The drilling of the well should
be done by maintaining the optimum mud weight generated from the pressure profile. In case, during drilling, formation pressure
is more than the mud pressure, resulted gas kicks or worse, blowouts of the well. Excessively high mud pressure can fracture
the formation and cause lost circulation. The oil and gas companies, worldwide, attributed 15% losses due to various problems
associated with drilling complications, mostly related to improper pressure prediction of a well. The losses include loss
of material as well as drilling process continuity, called non-productive time (NPT). The generation of accurate pressure
profile reduces drilling problems, cuts exploration and development costs and allows billions of dollars now spent on losses
to be better spent-building and replacing reserves. 相似文献
574.
Antarctic lunar meteorites Yamato-793169, Asuka-881757, MIL 05035, and MET 01210 (YAMM): Launch pairing and possible cryptomare origin 总被引:1,自引:0,他引:1
Tomoko Arai B. Ray Hawke Keiji Misawa Masamichi Miyamoto 《Geochimica et cosmochimica acta》2010,74(7):2231-3852
The Antarctic lunar meteorite Meteorite Hills (MET) 01210 is a polymict regolith breccia, dominantly composed of mare basalt components. One relatively large (2.7 × 4.7 mm) basalt clast in MET 01210 (MET basalt) shows remarkable mineralogical similarities to the lunar-meteorite crystalline mare basalts Yamato (Y)-793169, Asuka (A)-881757, and Miller Range (MIL) 05035. All four basalts have similar rock texture, mineral assemblage, mineral composition, pyroxene crystallization trend, and pyroxene exsolution lamellae. The estimated TiO2 contents (∼2.0 wt%) of the MET basalt and MIL 05035 are close to the bulk-rock TiO2 contents of Y-793169 and A-881757. These similarities suggest that Y-793169, A-881757, MIL 05035, and the MET basalt came from the same basalt flow, which we designate the YAMM basalt. The source-basalt pairing of the YAMM is also supported by their similar REE abundances, crystallization ages (approx. 3.8-3.9 Ga), and isotopic compositions (low U/Pb, low Rb/Sr, and high Sm/Nd). The pyroxene exsolution lamellae, which are unusually coarse (up to a few microns) by mare standards, imply a relatively slow cooling in an unusually thick lava and/or subsequent annealing within a cryptomare. Reported noble gas and CRE data with close launch ages (∼1 Ma) and ejection depths (deeper than several meters) among the four meteorites further indicate their simultaneous ejection from the moon. Despite the marginally close terrestrial ages, pairing in the conventional Earth-entry sense seems unlikely because of the remote recovery sites among the YAMM meteorites.The high abundance (68%) of mare components in MET 01210 estimated from a two-component mixing model calculation could have resulted from either lateral mixing at a mare-highland boundary or vertical mixing in a cryptomare. The proportion of mare materials in MET 01210 is greater than in Apollo core samples at the mare-highland boundary. The burial depth (>several meters deep) inferred from the lack of surface irradiation of MET 01210 exceeds the typical mare regolith thickness (a few meters). Thus, the source of the YAMM meteorites is likely a terrain of locally high mare-highland mixing within a cryptomare. We searched for a possible source crater of the YAMM meteorites within the well-defined cryptomare, based on the multiple constraints obtained from this study and published data. An unnamed 1.4 km-diameter crater (53°W, 44.5°S) on the floor of the Schickard crater is the most suitable source for the YAMM meteorites.The 238U/204Pb (μ) value of the YAMM basalts is extremely low, relative to those of the Apollo mare basalts, but comparable to those of the Luna 24 very low-Ti basalts. The low-μ source indicates a derivation from a less differentiated mantle with a lack of KREEP components. Although the chemical sources of materials and heat source of melting might be independent, the heat source that generated the source magma of the YAMM and Luna 24 basalts may not be related to KREEP, unlike the case of the Apollo basalts. The distinct chemical and isotopic compositions of mantle sources between the Apollo basalts and the YAMM/Lunar 24 basalts imply differences in mantle composition and thermal evolution between the Procellarum KREEP Terrane (PKT) and non-PKT regions of the nearside. 相似文献
575.
Shift in detrital sedimentation in the eastern Bay of Bengal during the late Quaternary 总被引:1,自引:0,他引:1
C. Prakash Babu J. N. Pattan K. Dutta N. Basavaiah G. V. Ravi Prasad D. K. Ray P. Govil 《Journal of Earth System Science》2010,119(3):285-295
Down-core variations of granulometric, geochemical and mineral magnetism of a 70-cm long sediment core retrieved from the eastern Bay of Bengal abyssal region were studied to understand sedimentation pattern and sediment provenance during the last ~12 kyr BP. Based on down-core physical and elemental variations, three units were identified: unit 3 (70–43 cm) is a ~30 cm thick clayey silt organic carbon-rich (0.5–0.92%) turbidite probably delivered by the Brahmaputra River during the late Quaternary period. Units 2 (43–24 cm) and 1 (24–0 cm) represent enhanced and reduced supply of coarse-grained detrital sediments from the Ganges River during early and late Holocene period, respectively. Increased terrigenous supply dilutes calcium carbonate (CaCO3) and biogenic elements (P, Ba and Cu) in units 3 and 2. On the contrary, a reduction in detrital input enhances CaCO3 and biogenic elements in unit 1. Lithogenic elements (Ti, Al, K and Rb) and shale-normalized REE patterns in all three units suggest terrigenous source. The shift in provenance from the Brahmaputra to the Ganges derived sediments is evident by a sharp increase in sediment grain size, increased concentration and grain size assemblages of magnetic minerals, lithogenic elements concentration and Lan/Ybn ratio. This study highlights terrigenous dilution on biogenic sedimentation in the eastern Bay of Bengal sediments. 相似文献
576.
The Newania carbonatite complex of Rajasthan, India is one of the few dolomite carbonatites of the world, and oddly, does not contain alkaline silicate rocks thus providing a unique opportunity to study the origin and evolution of a primary carbonatite magma. In an attempt to characterize the mantle source, the source of carbon, and the magmatic and post-magmatic evolution of Newania carbonatites, we have carried out a detailed stable carbon and oxygen isotopic study of the complex. Our results reveal that, in spite of being located in a metamorphic terrain, these rocks remarkably have preserved their magmatic signatures in stable C and O isotopic compositions. The δ13C and δ18O variations in the complex are found to be results of fractional crystallization and low temperature post-magmatic alteration suggesting that like other carbonatites, dolomite carbonatites too fractionate isotopes of both elements in a similar fashion. The major difference is that the fractional crystallization of dolomite carbonatites fractionates oxygen isotopes to a larger extent. The modes of δ13C and δ18O variations in the complex, ?4.5?±?1‰ and 7?±?1‰, respectively, clearly indicate its mantle origin. Application of a multi-component Rayleigh isotopic fractionation model to the correlated δ13C versus δ18O variations in unaltered carbonatites suggests that these rocks have crystallized from a CO2 + H2O fluid rich magma, and that the primary magma comes from a mantle source that had isotopic compositions of δ13C ~ ?4.6‰ and δ18O ~ 6.3‰. Such a mantle source appears to be a common peridotite mantle (δ13C = ?5.0?±?1‰) whose carbon reservoir has insignificant contribution from recycled crustal carbon. Other Indian carbonatites, except for Amba Dongar and Sung Valley that are genetically linked to Reunion and Kerguelen plumes respectively, also appear to have been derived from similar mantle sources. Through this study we establish that dolomite carbonatites are generated from similar mantle source like other carbonatites, have comparable evolutionary history irrespective of their association with alkaline silicate rocks, and may remain resistant to metamorphism. 相似文献