| 1. |
- Al-Ramadan, Khalid, et al.
(författare)
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Distribution of Diagenetic Alterations in Siliciclastic Shoreface Deposits within a Sequence Stratigraphic Framework : Evidence from the Upper Jurassic, Boulonnais, NW France
- 2005
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Ingår i: Journal of Sedimentary Research. - : Society for Sedimentary Geology. - 1527-1404 .- 1938-3681. ; 75:5, s. 943-959
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of diagenetic alterations in Upper Jurassic, siliciclastic shoreface sediments from NW France has been linked to the sequence stratigraphic framework. Calcite cement in mudrocks and sandstones of the transgressive (TST) and lower part of the highstand (HST) systems tracts is microcrystalline and occurs as continuously cemented layers and stratabound concretions. The average δ18OV-PDB (−2.6‰) and 87Sr/86Sr (0.7078) compositions of microcrystalline calcite indicate precipitation from largely marine pore waters.Calcite cement in sandstones of the forced regressive wedge (FRWST) and lowstand (LST) systems tracts is poikilotopic and occurs mainly as stratabound concretions. Complete dissolution of the carbonate grains and concomitant precipitation of poikilotopic calcite cement with low average δ18O (−5.3‰) and radiogenic Sr-isotope (0.70882) signatures suggest incursion of meteoric waters into sandstones during relative sea-level lowstand. The poorly lithified sandstones interbedded with sandstones cemented by poikilotopic calcite concretions display evidence of diagenesis under episodes of arid to semiarid paleoclimate, including: (i) partial cementation by opal, chalcedony, gypsum, and minor vadose calcite cement, (ii) mechanically infiltrated clays and Fe-oxides, and (iii) secondary porosity owing to partial dissolution of carbonate grains. The integration of diagenesis into sequence stratigraphy allows better elucidation and prediction of the spatial and temporal distribution of diagenetic alterations and related reservoir-quality modifications in shoreface sediments.
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| 2. |
- Khalifa, Muftah A., et al.
(författare)
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QUARTZ AND Fe-DOLOMITE CEMENTS RECORD SHIFTS IN FORMATION-WATER CHEMISTRY AND HYDROCARBON MIGRATION IN DEVONIAN SHOREFACE SANDSTONES, GHADAMIS BASIN, LIBYA
- 2018
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Ingår i: Journal of Sedimentary Research. - : SEPM-SOC SEDIMENTARY GEOLOGY. - 1527-1404 .- 1938-3681. ; 88:1, s. 38-57
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Tidskriftsartikel (refereegranskat)abstract
- Cementation by quartz overgrowths and subsequently by carbonates is a very common global paragenetic phenomenon in sandstones of many basins that is poorly constrained in the literature. Integrated petrography, electron microprobe, stable isotopes, fluid inclusion microthermometry, and Raman spectroscopy have helped unravel the diagenetic conditions, fluid flow, and hydrocarbon migration during the development of quartz overgrowths and later Fe-dolomite cement in the Devonian shoreface sandstones (oil and gas reservoirs), Ghadamis Basin, NW Libya. The high homogenization temperatures of Fe-dolomite (Th = 119 to 140 degrees C) together with its low delta(18) OVPDB values (-17.6% to -13.2%) and saddle-crystal morphology suggest the flux of hot basinal brines. The fluid-inclusion microthermometry shows a shift from NaCl-dominated brines during quartz cementation (16.0 to 17.3 wt.% NaCl eq.) to NaCl and CaCl2-dominated brines during Fe-dolomite cementation (15.6 to 18.4 wt.% NaCl eq.). The latter brines probably circulated through overlying Mesozoic carbonate and evaporite strata before descending deep into the basin. The similarity in T-h ranges for Fe-dolomite and quartz overgrowths, despite the shift in formationwater chemistry suggests precipitation under similar geothermal conditions. The presence of oil-filled inclusions in quartz overgrowths suggests that cementation occurred during oil migration, whereas the presence of methane in inclusions in the Fe-dolomite cement suggests precipitation during gas migration. This study shows that fluid inclusion microthermometry and Raman spectroscopy of the widespread paragenetic sequence of quartz overgrowths followed by carbonate cement are crucial to unravel changes in formation-water chemistry and fluid (including hydrocarbon) migration in sedimentary basins.
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| 3. |
- Kroger, Bjorn, et al.
(författare)
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Accretionary Mechanisms And Temporal Sequence Of Formation Of The Boda Limestone Mud-Mounds (Upper Ordovician), Siljan District, Sweden
- 2016
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Ingår i: Journal of Sedimentary Research. - : Society for Sedimentary Geology. - 1527-1404 .- 1938-3681. ; 86:4, s. 363-379
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Tidskriftsartikel (refereegranskat)abstract
- Late Ordovician mud-mounds in the Boda Limestone, Siljan area, central Sweden, consist mainly of massive spiculitic stromatactis limestone similar to other well-known Paleozoic mud-mounds. The mound cores are predominantly formed by spiculite and ostracod-rich mudstone and/or wackestone, and networks of spar-filled syndepositional cavities. The mounds of the Boda Limestone are specific in two ways: (1) large parts of the lower mound cores are formed by a Palaeoporella framestone and/or bafflestone with signs of early recrystallization and cementation; and (2) the stromatactis facies is accompanied by masses of limestone with non-stromatactis cryptocrystalline patches. Cryptocrystalline patches are filled with massive, fibrous low-Mg calcite, have cloudy, transitional margins, contain randomly spaced skeletal grains and dolomitic micro-inclusions, and are interpreted as recrystallized patches of the original host lime mud. Models of formation of Paleozoic mud-mounds generally hypothesize accretionary processes that are based on sponge biomass degradation and associated diagenetic processes. In the Boda Limestone Palaeoporella skeleton disintegration, early recrystallization, and additionally, cementation were essential for the mound formation. The Boda mounds exemplify that formation of Paleozoic mud-mounds reflects a spectrum of different essentially diagenetic accretionary mechanisms. This diversity should be taken into account in future discussions about Paleozoic mud-mound formation. The new name Osmundsberget Formation is given for a Hirnantian succession of brachiopod-rich limestone above the Boda Limestone. The Osmundsberget Formation occurs only in direct geographical vicinity to the mud-mounds.
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| 4. |
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| 5. |
- Mansurbeg, Howri, et al.
(författare)
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Diagenetic evolution and porosity destruction of turbiditic hybrid arenites and siliciclastic sandstones of foreland basins: Evidence from the Eocene Hecho Group, Pyrenees, Spain
- 2009
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Ingår i: Journal of Sedimentary Research. - : Society for Sedimentary Geology. - 1527-1404 .- 1938-3681. ; 79:9-10, s. 711-735
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to unravel the impact of diagenetic alterations on porosity loss of foreland-basin turbiditic hybrid arenites and associated siliciclastic sandstones of the Eocene Hecho Group (south-central Pyrenees, Spain). In this succession, hybrid arenites and calclithites are extensively cemented by mesogenetic calcite cement (delta O-18(VPDB) = -10.0 parts per thousand to -5.8 parts per thousand; T-h, mode = 80 degrees C salinity mode = 18.8 wt% eq. NaCl), Fe-dolomite (delta(18)(OVPDB) = -8.5 parts per thousand to -6.3 parts per thousand) and trace amounts of siderite. The extent of carbonate cementation is interpreted to be related to the amounts of extrabasinal and intrabasinal carbonate grains, which provided nuclei and sources for the precipitation and growth of carbonate cements. Other diagenetic alterations, such as pyrite and albitization, had no impact on reservoir quality. Scarce early diagenetic cements, coupled with abundant ductile carbonate and siliciclastic framework grains, have led to rapid porosity loss owing to compaction. Conversely, abundant quartz in the sandstones prevented rapid loss of porosity by mechanical compaction. Reservoir quality was affected by mesogenetic cementation by quartz overgrowths, calcite and dolomite intergranular pressure dissolution of quartz grains, and formation of fracture-filling calcite cement (delta O-18(V-PDB) values from -10.4 parts per thousand to -7.8 parts per thousand; T-h temperatures of approximate to 150 degrees C), which are attributed to deep circulation of hot meteoric waters during extensional stages of tectonism. The results of this study illustrate that diagenetic evolution pathways of the arenites and sandstones are closely linked to the variation in detrital composition, particularly the proportion and types of extrabasinal noncarbonates, extrabasinal carbonates, and intrabasinal carbonate grains. These insights suggest that marine turbiditic hybrid arenites and calclithites of foreland basins are subjected to more rapid and extensive porosity loss owing to compaction and cementation than associated siliciclastic sandstones. Degradation of reservoir quality makes these hybrid arenites, calclithites, and sandstones suitable as tight gas reservoirs, but only if fracture porosity and permeability develop during tectonic deformation.
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| 6. |
- Möller, Per, et al.
(författare)
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Gravel and sand flotation: a sediment dispersal process important in certain nearshore environments
- 1994
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Ingår i: Journal of Sedimentary Research. - 1938-3681. ; 64:4, s. 894-898
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Tidskriftsartikel (refereegranskat)abstract
- Small rafts of floating sediment, predominantly of granule and small pebble size, were observed along a tidewater coast on James Ross Island, Antarctica. The sediment was lifted from the beach by the advancing tidewater and kept afloat by surface tension. The current transported the rafts at least 100-150 m off the beach, where the rafts broke up due to wind agitation of the sea surface and the gravel sank. This process can transport considerable volumes of sediment from the beach: it is estimated that flotation at the Naze launch ea. 500 kg per kilometer of shoreline per tidal cycle during calm and dry weather conditions, which for one summer season might end up in a total of 0.022 tons of sediment per meter of shoreline. The resulting sediments and sedimentary structures are concluded to be similar to those resulting from iceberg-, sea ice-, and algae rafting, and sediment gravity flows. Floating can be an important way of rafting gravels into fine-grained sublittoral or shallow-marine facies, and should be included when dealing with processes related to sedimentation in the nearshore marine environment.
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