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11.
Ihsan Ketin 《International Journal of Earth Sciences》1949,37(1):72-75
Ohne Zusammenfassung 相似文献
12.
Waulsortian-like mounds of the Mississippian Pekisko Formation, Northwestern Alberta: Petrographic and chemical attributes 总被引：1，自引：1，他引：0
The Tournasian age Pekisko carbonates in the Normandville Field (northwestern Alberta) form waulsortian-like, bryozoan/crinoid mounds that developed in fairly deep, low energy, cool water systems, close to the ramp margin. Three main depositional environments occur: (1) crinoidal apron with wackestone, grainstone and floatstone facies; (2) mound flank with grainstone, wackestone, packstone and floatstone facies dipping 35°; and (3) bryozoan mound core, composed of rudstone and floatstone facies with fenestrate bryozoa, minor crinoids and carbonate mud. Local highs due to fault-bounded blocks, created from the collapse of the Devonian Peace River High, may have controlled the location of mound nucleation.Diagenesis of the bryozoan/crinoid mounds included calcite cementation, compaction, dolomitization, silicification, and hydrocarbon emplacement events. The mound core facies contains submarine fascicular optic calcite and bladed/prismatic calcite cements, and later ferroan, brightly luminescent, pore-filling blocky spar cement. The crinoid apron facies contains syntaxial cement associated with crinoids, and the ferroan blocky spar cement. The mounds are dominantly limestone; however, in one well, dolomite dominates the lower section. Four types of dolomite have been identified: partial replacive; chemical-compaction-related, pervasive dolomite and saddle dolomite cement. All dolomites are non-stoichiometric (CaCO3 mole% 56.6–62.6). The partial, zoned replacive dolomite replaces micrite and syntaxial rim calcite in mound flank and crinoid apron facies. The chemical compaction-related dolomite is found along dissolution seams and stylolites and has similar CL characteristics to the replacive dolomite. The pervasive dolomite is fabric destructive and has dull cores and bright rims in CL. Saddle dolomite (0.15 mm) has brightly-luminescent, concentric zoning and occurs in vugs and fossil pore spaces.Chemical and isotopic analysis of the bryozoan/crinoid mounds indicate that the original marine signatures in micrite, early cements, some crinoids and brachiopods have been preserved. However, carbon isotopic values for some crinoids, matrix and dolomite show more positive values compared to known Mississippian carbonate values. Recrystallization during shallow burial has reset the oxygen isotopic composition of some crinoids and micrite. Oxygen and carbon isotopic compositions of most dolomites overlap with altered crinoids and early calcite cements. However, saddle dolomites have lighter δ18O values, similar to saddle dolomites from the Devonian Wabamun Group in this area. The isotopic variations in later ferroan calcite cements show an inverted-J trend, possibly due to variable amounts of water-rock interaction. While the Sr-isotopic ratio of submarine calcite cement coincides with that of Mississippian seawater, the later ferroan calcite cement is more radiogenic, indicating a different source of fluids. 相似文献
13.
In this paper, the Einstein field equations have been solved for a cloud of string with heat flux in Bianchi type III space-time. The physical and geometrical properties of the model have been examined. 相似文献
14.
Ihsan Ketin 《International Journal of Earth Sciences》1948,36(1):100-101
Ohne Zusammenfassung 相似文献
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16.
Mahnaz SABBAGH BAJESTANI Asadollah MAHBOUBI Reza MOUSSAVI-HARAMI Ihsan AL-AASM Mehdi NADJAFI 《《地质学报》英文版》2017,91(5):1797-1819
The study area is located in the east Tabas Block in Central Iran. Facies analysis of the Qal’eh Dokhtar Formation (middle Callovian to late Oxfordian) was carried out on two stratigraphic sections and applied to depositional environment and sequence stratigraphy interpretation. This formation conformably overlies and underlies the marly-silty Baghamshah and the calcareous Esfandiar formations, respectively. Lateral and vertical facies changes documents low- to high energy environments, including tidal-flat, beach to intertidal, lagoon, barrier, and open-marine. According to these facies associations and absence of resedimentation deposits a depositional model of a mixed carbonate–siliciclastic ramp was proposed for the Qal’eh Dokhtar Formation. Seven third-order depositional sequences were identified in each two measured stratigraphic sections. Transgressive systems tracts (TSTs) show deepening upward trends, i.e. shallow water beach to intertidal and lagoonal facies, while highstand systems tracts (HST) show shallowing upward trends in which deep water facies are overlain by shallow water facies. All sequence boundaries (except at the base of the stratigraphic column) are of the no erosional (SB2) types. We conclude eustatic rather than tectonic factors played a dominant role in controlling carbonate depositional environments in the study area. 相似文献
17.
Mohamed Ali Kalefa El-ghali Howri Mansurbeg Sadoon Morad Ihsan Al-Aasm Karl Ramseyer 《Sedimentary Geology》2006,190(1-4):323-351
The spatial and temporal distribution of diagenetic alterations has been constrained in relationship to depositional facies and sequence stratigraphy of the Upper Ordovician glaciogenic quartzarenite sandstones in the Murzuq Basin, SW Libya, which were deposited during the Haritanian glaciation when the basin was laying along the continental margin of Gondwana. Eogenetic alterations encountered include: (i) replacement of detrital silicates, mud matrix and pseudomatrix by kaolinite in paraglacial, tide-dominated deltaic, in foreshore to shoreface (highstand systems tract; HST) and in post-glacial, Gilbert-type deltaic (lowstand systems tract; LST) sandstones, particularly below the sequence boundaries (SB). Kaolinite formation is attributed to the influx of meteoric water during relative sea level fall and basinward shift of the shoreline. (ii) Cementation by calcite (δ18OVPDB = − 3.1‰ to + 1.1‰ and δ13CVPDB = + 1.7‰ to + 3.5‰) and Mg-rich siderite in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, in the glacial, tide-dominated estuarine (transgressive systems tract; TST) sandstones and in the post-glacial, shoreface TST sandstones is interpreted to have occurred from marine pore-waters. (iii) Cementation by Mg-poor siderite, which occurs in the post-glacial, Gilbert-type deltaic LST sandstones and in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, is interpreted to have occurred from meteoric waters during relative sea level fall and basinward shift of the shoreline. (iv) Pervasive cementation by iron oxides has occurred in the glacial, shoreface–offshore TST sandstones and post-glacial, shoreface TST sandstones immediately below the maximum flooding surfaces (MFS), which was presumably enhanced by prolonged residence time of the sediments under oxic diagenetic conditions at the seafloor. (v) Formation of grain-coating infiltrated clays mainly in the glacial, fluvial incised-valley LST sandstones and in the post-glacial, Gilbert-type deltaic LST sandstones as well as, less commonly, in the paraglacial, foreshore to shoreface HST sandstones and in the tide-dominated deltaic HST sandstones below the SBs.
Mesogenetic alterations include mainly the formation of abundant quartz overgrowths in the glacial, fluvial incised-valley LST sandstones, post-glacial, Gilbert-type deltaic LST sandstones and glacial, shoreface TST sandstones, in which early carbonate cements are lacking. Illite, chlorite and albitized feldspars, which occur in small amounts, are most common in the glacial, tide-dominated estuarine TST sandstones and paraglacial, shoreface HST sandstones. This study demonstrates that the spatial and temporal distribution of diagenetic alterations and their impact on reservoir-quality evolution in glacial, paraglacial and post-glacial sandstones can be better elucidated when linked to the depositional facies and sequence stratigraphic framework. 相似文献
18.
This study applies the Ricardian technique to estimate the effect of climate change on the smallholder agriculture sector
in Sri Lanka. The main contribution of the paper is the use of household-level data to analyze long-term climate impacts on
farm profitability. Household-level data allows us to control for a host of factors such as human and physical capital available
to farmers as well as adaptation mechanisms at the farm level. We find that non-climate variables explain about half the variation
in net revenues. However, our results suggest that climate change will have a significant impact on smallholder profitability.
In particular, reductions in precipitation during key agricultural months can be devastating. At the national level, a change
in net revenues of between −23% and +22% is likely depending on the climate change scenario simulated. These impacts will
vary considerably across geographic areas from losses of 67% to gains that more than double current net revenues. The largest
adverse impacts are anticipated in the dry zones of the North Central region and the dry zones of the South Eastern regions
of Sri Lanka. On the other hand, the intermediate and wet zones are likely to benefit, mostly due to the predicted increase
in rainfall. 相似文献
19.
The shrinkage of the Aral Sea ranks as one of the world's greatest man-made environmental disasters. While there is some hope for a separated northern part, the main sea is doomed 相似文献
20.
Ihsan S. Al-Aasm 《Aquatic Geochemistry》2000,6(2):227-248
Mississippian shoal carbonates of Western CanadaSedimentary Basin are important hydrocarbon hosts.Dolomitization plays a major role in the evolution ofreservoir porosity in these carbonates. This processvaries across the basin and reflects, in part, divergentsources and chemistry of pore fluids. Dolomites fromseveral petroleum reservoirs were analyzed formineralogical, geochemical and isotopic variation. Thedata clearly demonstrate the progressive and complexrecrystallization of dolomite during shallow and deepburial in modified marine, meteoric and burial fluids.These data include: change in crystal size,stoichiometry, cathodoluminscence characteristics,stable oxygen and carbon isotopic shifts and changesin radiogenic Sr isotopic composition. However,regional geology, tectonic history and fluid flowevolution play important roles in the diageneticimprints and the degree of recrystallization.Early microcrystalline dolomite formed in normalmarine and evaporative conditions in Mississippiancarbonates from Western Canada Sedimentary Basinhave undergone variable degrees of recrystallization, frompristine dolomite akin to Holocene sabkha dolomitewith preserved mineralogical and chemical attributesto highly recrystallized mesodolomite, however stillnonstoichiometric, but with highly altered chemicalsignatures. Careful attention should be made to localgeology, hydrodynamics and fluid flow when investigatingdolomite recrystallization in sedimentary basins. 相似文献