| 1. |
- Ali Kalefa El-ghali, Mohamed, et al.
(author)
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Diagenetic alterations related to marine transgression and regression in fluvial deltaic and shallow marine sandstones of the Triassic Buntsandstein and Keuper formations, the Paris Basin, France
- 2009
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In: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 26:3, s. 289-309
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Journal article (peer-reviewed)abstract
- The distribution of diagenetic alterations in Triassic fluvio-deltaic, quartzarenitic to sublitharenitic, lowstand systems tract (LST) sandstones of the Grès á Voltzia Formation, anastomosing fluvial, quartzarenitic transgressive systems tract (TST) sandstones of the Grès á Roseaux Formation, and shallow marine, quartzarenitic to sublitharenitic, TST sandstones of the Grès Coquiller Formation, the Paris Basin (France), can be linked to transgression and regression events, and thus to the sequence stratigraphic context. Near-surface eogenetic alterations, which display a fairly systematic link to the depositional facies and sequence stratigraphic framework, include: (i) cementation by meteoric water calcite (δ18O=−8.9‰ and δ13C=−9.1‰) in the fluvio-deltaic, LST sandstones, (ii) cementation by mixed marine–meteoric calcite (δ18O=−5.3‰ to −2.6‰ and δ13C=−3.9‰ to −1.3‰) and dolomite (δ18O=−4.6‰ to −2.6‰ and δ13C=−2.9‰ to −2.3‰) in the foreshore, TST sandstones and below parasequence boundaries (PB), and transgressive surface (TS), and in the shoreface, TST sandstones below maximum flooding surfaces (MFS), being facilitated by the presence of carbonate bioclasts, (iii) dissolution of detrital silicates and precipitation of K-feldspar overgrowths and kaolinite, particularly in the fluvio-deltaic, LST sandstones owing to effective meteoric water circulation, and (vi) formation of autochthonous glauconite, which is increases in abundance towards the top of the fluvio-deltaic, LST sandstones, and along TS, and in the shoreface, TST sandstones, by alteration of micas owing to the flux of seawaters into the sandstones during transgression, whereas parautochthonous glauconite is restricted to the TS sandstones owing to marine reworking. Mesogenetic alterations, which include cementation by quartz overgrowths and illite, display fairly systematic link to fluvio-deltaic, LST sandstones. This study has revealed that linking of diagenesis to transgression and regression events enables a better understanding of the parameters that control the spatial and temporal distribution of diagenetic alterations in sandstones and of their impact on reservoir quality evolution.
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| 2. |
- El-Ghali, Mohamed Ali Kalefa, et al.
(author)
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Distribution of diagenetic alterations in within depositional facies and sequence stratigraphic framework of fluvial sandstones : Evidence from the Petrohan Terrigenous Group, Lower Triassic, NW Bulgaria
- 2009
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In: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 26:7, s. 1212-1227
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Journal article (peer-reviewed)abstract
- Sequence stratigraphy of fluvial deposits is a controversial topic because changes in relative sea level will eventually have indirect impact on the spatial and temporal distribution of depositional facies. Changes in the relative sea level may influence the accommodation space in fluvial plains, and hence have impact on types of fluvial system, frequency of avulsion, and style of vertical and lateral accretion. This study aims to investigate whether depositional facies and changes in the fluvial system of the Lower Triassic Petrohan Terrigenous Group sandstones (NW Bulgaria) in response to changes in the relative sea level have an impact on the spatial and temporal distribution of diagenetic alterations. Eogenetic alterations, which were encountered in the fluvial sandstones, include: (i) mechanically Infiltrated clays, particularly in channel and crevasse splay sandstones towards the top of the owstand systems tract (LST) and the base of the highstand systems tract (HST). (ii) Pseudomatrix, which resulted from mechanical compaction of mud intraclasts, occurs mainly in channel sandstones at the base of the LST and towards the top of the HST and thus led to porosity and permeability deterioration. (iii) Calcite (delta O-18(VPDB)= -8.1 parts per thousand to -7.5 parts per thousand and delta C-13(VPDB) = -7.87 parts per thousand to -6.3 parts per thousand) and dolomite (delta O-18(VPDB) = -8.3 parts per thousand to -5.2 parts per thousand and delta 13C(VPDB) = -8.3 parts per thousand to -7.1 parts per thousand), which are associated with palaeosol horizons developed on top of crevasse splay and channel sandstones of transgressive systems tract (TST) and LST: Such extensive eogenetic calcite cements may act as potential layers for the formation of reservoir compartments for underlying sandstones. Mesogenetic alterations include: (i) calcite (delta O-18(VPDB) = -18.4 parts per thousand to -12.8 parts per thousand and delta C-13(VPDB) = -8.6 parts per thousand to -6.8 parts per thousand) and dolomite (delta O-18(VPDB) = -14.7 parts per thousand to - 12.4 parts per thousand and delta C-13(VPDB) = -8.0 parts per thousand to -7.0 parts per thousand), which were formed in all depositional facies and systems tract´sandstones, (ii) illite, which is the dominant diagenetic clay mineral in all depositional facies and systems tracts, was associated with albitization of detrital K-feldspars, and (iii) quartz overgrowths, which are most abundant in TST rather than LST and HST sandstones, because of the presence of suitable infiltrated clays and pseudomatrix in the latter sandstones. Such cementation by calcite, dolomite, and quartz overgrowths and formation of illite led to porosity and permeability deterioration during mesodiagenesis. The results of this study revealed the importance of integration of diagenesis with depositional facies and sequence stratigraphy of fluvial sandstones in improving our ability to predict the spatial and temporal distribution of eogenetic alterations and their subsequent impact on mesogenetic alterations, and thus on reservoir quality modifications.
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| 3. |
- El-ghali, Mohamed, et al.
(author)
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Origin and timing of siderite cementation in Upper Ordovician glaciogenic sandstones from the Murzuq basin, SW Libya
- 2006
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In: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 23:4, s. 459-471
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Journal article (peer-reviewed)abstract
- The origin and timing of siderite cementation have been constrained in relation to depositional facies and sequence stratigraphy of Upper Ordovician glaciogenic sandstones from the Murzuq basin, SW Libya. Optical microscope, backscattered electron imagery, and carbon and oxygen stable isotope analysis have revealed that siderite is of eo- and mesogenetic origin. Eogenetic siderite is Mg-poor with a mean composition Of (Fe91.7Mg1.5Ca0.3Mn6.5)CO3, and occurs in paraglacial, tide-dominated deltaic highstand systems tract (HST) sandstones, in paraglacial, foreshore to shoreface HST sandstones and in postglacial, Gilbert-type deltaic lowstand systems tract (LST) sandstones. This siderite is typically of meteoric water origin that influxed into the LST and HST sandstones during relative sea level fall and basinward shift of the strandline.Mesogenetic siderite, which engulfs and thus postdates quartz overgrowths and illite, is Mg-rich with a mean composition of (Fe72.2Mg21.7Ca0.8Mn5.3)CO3 and occurs in the paraglacial, tide-dominated deltaic HST sandstones, in paraglacial foreshore to shoreface HST sandstones, in glacial, tide-dominated estuarine transgressive systems tract (TST) sandstones, in postglacial, Gilbert-type deltaic LST sandstones, and in postglacial, shoreface TST sandstones. delta O-18(V-PDB) values of this siderite, which range between -22.6 and -13.8 parts per thousand, suggest that precipitation has occurred from evolved formation waters with delta O-18 values between -14.0 and +1.0 parts per thousand and was either meteoric, mixed marine-meteoric and/or marine in origin by assuming postdating quartz overgrowths and illite temperature between 80 and 130 degrees C.
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| 4. |
- Mansurbeg, Howri, et al.
(author)
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Diagenesis and reservoir quality evolution of paleocene deep-water, marine sandstones, the Shetland-Faroes Basin, British Continental Shelf
- 2008
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In: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 25:6, s. 514-543
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Journal article (peer-reviewed)abstract
- The Palaeocene, deep-water marine sandstones recovered from six wells in the Shetland-Faroes Basin represent lowstand, transgressive and highstand systems tract turbiditic sediments. Mineralogic, petrographic, and geochemical analyses of these siliciclastics are used to decipher and discuss the diagenetic alterations and subsequent reservoir quality evolution. The Middle-Upper Palaeocene sandstones (subarkoses to arkoses) from the Shetland-Faroes Basin, British continental shelf are submarine turbiditic deposits that are cemented predominantly by carbonates, quartz and clay minerals. Carbonate cements (intergranular and grain replacive calcite, siderite, ferroan dolomite and ankerite) are of eogenetic and mesogenetic origins. The eogenetic alterations have been mediated by marine, meteoric and mixed marine/meteoric porewaters and resulted mainly in the precipitation of calcite (δ18OV−PDB=−10.9‰ and −3.8‰), trace amounts of non-ferroan dolomite, siderite (δ18OV−PDB=−14.4‰ to −0.6‰), as well as smectite and kaolinite in the lowstand systems tract (LST) and highstand systems tract (HST) turbiditic sandstone below the sequence boundary. Minor eogenetic siderite has precipitated between expanded and kaolinitized micas, primarily biotite. The mesogenetic alterations are interpreted to have been mediated by evolved marine porewaters and resulted in the precipitation of calcite (δ18OV−PDB=−12.9‰ to −7.8‰) and Fe-dolomite/ankerite (δ18OV−PDB=−12.1‰ to −6.3‰) at temperatures of 50–140 and 60–140 °C, respectively. Quartz overgrowths and outgrowth, which post- and pre-date the mesogenetic carbonate cements is more common in the LST and TST of distal turbiditic sandstone. Discrete quartz cement, which is closely associated with illite and chlorite, is the final diagenetic phase. The clay minerals include intergranular and grain replacive eogenetic kaolinite, smectite and mesogenetic illite and chlorite. Kaolinite has been subjected to mesogenetic replacement by dickite. The K-feldspar and plagioclase grains have been albitized. Dissolution of calcite cement and of framework grain (feldspar, volcanic fragments and mud intraclasts) has resulted in a considerable enhancement of reservoir quality.
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| 5. |
- Talbot, Christopher J.
(author)
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Hydrothermal salt - but how much?
- 2008
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In: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 25:2, s. 191-202
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Journal article (peer-reviewed)
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| 6. |
- Larsson, Olof, 1962, et al.
(author)
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Seismic stratigraphy of Late Quaternary deposits in the eastern Skagerrak
- 2008
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In: Marine and Petroleum Geology. - 0264-8172. ; 25:10, s. 1023-1039
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Journal article (peer-reviewed)abstract
- High resolution seismic profiles from the Swedish west coast have been used in this study. The Quaternary deposits have been divided into six seismic sequences, containing together thirteen different seismic facies. Documentation of these sequences and facies, their stratigraphic and geographic variability is the first step in a basin-fill analysis aiming at interpreting the depositional environments and the major controlling processes. The deposits are interpreted to consist of one deglaciation cycle. The sequences are; I) bedrock, II) coarse glacial deposits, III) Weichselian glaciomarine ice-proximal deposits, IV) Weichselian glaciomarine ice-distal deposits, V) channel fill deposits, VI) Holocene marine deposits. The major part of the sediment package is the Weichselian glaciomarine ice-proximal deposits, deposited during the ice recession period, close to or adjacent to the retreating ice. Typical for these deposits are conformably, well stratified deposits with high amplitude. The second large part is the Holocene marine deposits, these are mainly found in the southern part. They have typically a near transparent seismic configuration with only weak parallel stratification. These two major sequences are separated by a regional unconformity, creating a hiatus of at least 6000 year.
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