| 1. |
- Mansurbeg, Howri, et al.
(författare)
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Meteoric-water diagenesis in late Cretaceous canyon-fill turbidite reservoirs from the Espirito Santo Basin, eastern Brazil
- 2012
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 37:1, s. 7-26
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Tidskriftsartikel (refereegranskat)abstract
- Parameters controlling the diagenetic evolution of passive margin, marine turbidites, which are important targets of hydrocarbon exploration, are poorly constrained in the literature. This study aims to unravel the conditions of diagenesis and its impact on the reservoir quality evolution from late Cretaceous canyon-filling turbiditic sandstones of the onshore portion of Espirito Santo Basin, eastern Brazil. Kaolinization (delta O-18 = +13.3 parts per thousand to +15.2 parts per thousand; delta D = 96.6 parts per thousand to -79.6 parts per thousand) and dissolution of framework silicate grains is attributed to meteoric water incursion during eodiagenesis in response to a considerable fall in relative sea-level. Eogenetic alterations also include cementation by siderite (average delta O-18 = -72 parts per thousand; delta C-13 = +9.3 parts per thousand) and pyrite. Progressive sediment burial (present depths = 1530-2027 m) resulted in the formation of poikilotopic calcite, ferroan dolomite-ankerite (average delta O-18 = -7.9 parts per thousand; delta C-13 = +2.9 parts per thousand), minor amounts of quartz overgrowths and in partial dickitization of kaolinite. Isotopic values of calcite and dolomite-ankerite follow two trends of co-variance of delta C-13 with decreasing delta O-18 and increasing temperature. From a composition closer to marine (approximate to 0 parts per thousand), one trend goes towards positive delta C-13 values (up to +22.4 parts per thousand for calcite; +18.6 parts per thousand for dolomite-ankerite), indicating increasing input of carbonate from methanogenic fermentation. The other trend develops towards negative delta C-13 values (down to -17.2 parts per thousand for calcite; 15 parts per thousand for dolomite-ankerite), suggesting increasing contribution from thermal decarboxylation with increasing temperature and depth. Despite the presence of various cement types, mechanical compaction was more important than cementation in reducing depositional porosity in the onshore Urucutuca sandstones.
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| 2. |
- Morad, Sadoon, et al.
(författare)
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Hydrothermal alteration of plagioclase in granitic rocks from Proterozoic basement of SE Sweden
- 2010
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Ingår i: Geological Journal. - : Wiley. - 0072-1050 .- 1099-1034. ; 45:1, s. 105-116
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Tidskriftsartikel (refereegranskat)abstract
- Petrographic examinations and electron microprobe analyses of Proterozoic granitic rocks, SE Sweden aimed to characterize and unravel the mechanisms and conditions of plagioclase alterations. These alterations include saussuritization, albitization and replacement of plagioclase by K-feldspar. The hydrothermal alterations, which are inferred to have occurred at ca. 250-400°C, resulted in concomitant formation of Alrich titanite, epidote, calcite, pumpellyite, prehnite and iron oxides. Replacement of plagioclase by K-feldspar occurs in red-stained zones, which have developed close to thin fractures owing to the precipitation of tiny Fe-oxide pigment particles within the altered plagioclase, whereas saussuritized plagioclase has less systematic spatial relationships to these fractures. Albitization of plagioclase occurred in rocks that are poor in biotite compared to rocks that suffered extensive saussuritization. The chemical and textural characterization of various types of plagioclase alterations allows elucidation of the granitic hydrothermal systems. Features of feldspar alteration in the granitic rocks are similar to those encountered in feldspathic sandstones and should hence be considered in studies on diagenetic changes of siliciclastic successions during basin evolution.
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| 3. |
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| 4. |
- Morad, Sadoon, et al.
(författare)
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Chloritization in Proterozoic granite from the Äspö Laboratory, southeastern Sweden : record of hydrothermal alterations and implications for nuclear waste storage
- 2011
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Ingår i: Clay minerals. - : Mineralogical Society. - 0009-8558 .- 1471-8030. ; 46:3, s. 495-513
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Tidskriftsartikel (refereegranskat)abstract
- Hydrothermal alteration of Proterozoic granitic rocks in the Aspo underground laboratory, southestern Sweden, resulted in the formation of chlorite with large variations in textural and chemical characteristics, which reflect differences in formation temperatures, fluid composition, and reaction mechanisms. The mineral assemblage associated with chlorite, including Ca-Al silicates (prehnite, pumpellyite, epidote, and titanite), Fe-oxides, calcite, albite and K-feldspar, suggests that chloritization occurred at temperatures of between 200-350 degrees C during various hydrothermal events primarily linked to magmatism and rock deformation. Petrographic and electron microprobe analyses revealed that chlorite replaced biotite, amphibole and magnetite, and hydrothermal chlorite phases filled fractures and vugs in the granitic rocks. While fracture-filling chlorite reduces fracture permeability, chloritization reactions in the host granite resulted in the formation of new localized microporosity that should thus be taken into consideration when evaluating the safety of the granitic basement rocks as a repository for nuclear waste. It is also important to take into account that similar alteration reactions may occur at the site of stored nuclear waste where temperatures in excess of 100 degrees C might be encountered.
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| 5. |
- Caja, M., et al.
(författare)
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Provenance of siliciclastic and hybrid turbiditic arenites of the Eocene Hecho Group,Spanish Pyrenees : implications for the tectonic evolution of a foreland basin
- 2010
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Ingår i: Basin Research. - : Wiley. - 0950-091X .- 1365-2117. ; 22:2, s. 157-180
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Tidskriftsartikel (refereegranskat)abstract
- The Eocene Hecho Group turbidite system of the Aínsa-Jaca foreland Basin (southcentral Pyrenees) provides an excellent opportunity to constrain compositional variations within the context of spatial and temporal distribution of source rocks during tectonostratigraphic evolution of foreland basins. The complex tectonic setting necessitated the use of petrographic, geochemical and multivariate statistical techniques to achieve this goal. The turbidite deposits comprise four unconformity-bounded tectonostratigraphic units (TSU), consisting of quartz-rich and feldspar-poor sandstones, calclithites rich in extrabasinal carbonates and hybrid arenites dominated by intrabasinal carbonates. The sandstones occur exclusively in TSU-2, whereas calclithites and hybrid arenites occur in the overlying TSU-3, TSU-4 and TSU-5. The calclithites were deposited at the base of each TSU and hybrid arenites in the uppermost parts. Extrabasinal carbonate sources were derived from the fold-and-thrust belt (mainly Cretaceous and Palaeocene limestones). Conversely, intrabasinal carbonate grains were sourced from foramol shelf carbonate factories. This compositional trend is attributed to alternating episodes of uplift and thrust propagation (siliciclastic and extrabasinal carbonates supplies) and subsequent episodes of development of carbonate platforms supplying intrabasinal detrital grains. The quartz-rich and feldspar-poor composition of the sandstones suggests derivation from intensely weathered cratonic basement rocks during the initial fill of the foreland basin. Successive sediments (calclithites and hybrid arenites) were derived from older uplifted basement rocks (feldspar-rich and, to some extent, rock fragments-rich sandstones), thrust-and-fold belt deposits and from coeval carbonate platforms developed at the basin margins. This study demonstrates that the integration of tectono-stratigraphy, petrology and geochemistry of arenites provides a powerful tool to constrain the spatial and temporal variation in provenance during the tectonic evolution of foreland basins.
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| 6. |
- El-Ghali, M. A. K., et al.
(författare)
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Distribution of carbonate cements within depositional facies and sequence stratigraphic framework of shoreface and deltaic arenites, Lower Miocene, the Gulf of Suez rift, Egypt
- 2013
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 45, s. 267-280
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to unravel the spatial and temporal distribution of diagenetic alterations of the Mheiherrat Member, the Rudeis Formation (lower Miocene) of the Gulf of Suez rift, Egypt within depositional fades and sequence stratigraphy. The Mheiherrat member is represented by shoreface calcarenites and hybrid arenites (transgressive and highstand systems tracts; TST and HST; respectively) and deltaic rudites and coarse-grained calcarenites and hybrid arenites (lowstand systems tracts; LST). Petrographic, stable O- and C-isotopes, mineral chemical and geochemical analyses have revealed that the arenites are pervasively cemented by eogenetic carbonates and, to small extent, by zeolite and pyrite as well as by telogenetic palygorskite. The shoreface TST and HST calcarenites and hybrid arenites were dominantly cemented by microcrystalline grain-rimming and inter- and intragranular pore-filling calcite (delta O-13(V-PDB) = -3.6 parts per thousand to -0.3 parts per thousand and delta C-13(V-PDB) = -2.3 parts per thousand to -0.7 parts per thousand) and rhombic dolomite (delta C-13(V-PDB) = -3.9 parts per thousand to +0.9 parts per thousand and delta C-13(V-PDB) = -2.5 parts per thousand to -0.7 parts per thousand). These cements are interpreted to be formed by marine to brackish waters with delta O-13(V-SMOW) -1.2 parts per thousand to +3.2 parts per thousand, at temperature of 20-55 degrees C. The deltaic LST coarse-grained calcarenites and hybrid arenites were dominantly cemented by coarse-crystalline, inter- and intragranular pore-filling calcite (delta O-13(V-PDB) -4.4 parts per thousand to -2.3% and delta C-13(V-PDB) = -2.8 parts per thousand. to -1.3 parts per thousand.), which are interpreted to have precipitated from pore waters with delta O-13(V-SWOM) +3.5 parts per thousand. to +5.5 parts per thousand, at temperatures of greater than 55 degrees C. Such pervasive cementation by carbonates is attributed to the occurrence of abundant intrabasinal carbonate grains. The carbonate cement texture is suggested to be controlled by changes in pore-water chemistry owing to transgression and regression events. This case study revealed that better understanding of factors controlling the extent and textural habits of carbonate cements can be achieved when it is linked with depositional facies and sequence stratigraphy.
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| 7. |
- Morad, Sadoon, et al.
(författare)
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Linking Diagenesis to Sequence Stratigraphy : An Integrated Tool for Understanding and Predicting Reservoir Quality Distribution
- 2013
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Ingår i: Linking Diagenesis to Sequence Stratigraphy. - West Sussex, UK : John Wiley & Sons. ; , s. 1-36
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Bokkapitel (refereegranskat)abstract
- Sequence stratigraphy is a useful tool for the prediction of primary (depositional) porosity and permeability. However, these primary characteristics are modified to variable extents by diverse diagenetic processes. This chapter demonstrates that integration of sequence stratigraphy and diagenesis is possible because the parameters controlling the sequence stratigraphic framework may have a profound impact on early diagenetic processes. The latter processes play a decisive role in the burial diagenetic and related reservoir-quality evolution pathways. Therefore, the integration of sequence stratigraphy and diagenesis allows a proper understanding and prediction of the spatial and temporal distribution of diagenetic alterations and, consequently, of reservoir quality in sedimentary successions.
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