| 1. |
- Carrillo, Emilio, et al.
(författare)
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Structural significance of an evaporite formation with lateral stratigraphic heterogeneities (Southeastern Pyrenean Basin, NE Spain)
- 2017
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Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 86, s. 1310-1326
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Tidskriftsartikel (refereegranskat)abstract
- We run a series of analogue models to study the effect of stratigraphic heterogeneities of an evaporite formation on thin-skinned deformation of the Southeastern Pyrenean Basin (SPB; NE Spain). This basin is characterized by the existence of evaporites, deposited during the Early-Middle Eocene with lateral variations in thickness and lithological composition. These evaporites are distributed in three lithostratigraphic units, known as Serrat Evaporites, Vallfogona and Beuda Gypsum formations and acted as decollement levels, during compressional deformation in the Lutetian. In addition to analogue modeling, we have used field data, detailed geological mapping and key cross-sections supported by seismic and well data to build a new structural interpretation for the SPB. In this interpretation, it is recognized that the basal and upper parts of the Serrat Evaporites acted as the main decollement levels of the so-called Cadi thrust sheet and Serrat unit. A balanced restoration of the basin indicates that thrust faults nucleated at the stratigraphic transition of the Serrat Evaporites (zone with lateral variations of thickness and lithological composition), characterized by a wedge of anhydrite and shale. The analogue models were setup based on information extracted from cross-sections, built in two sectors with different lithology and stratigraphy of the evaporites, and the restored section of the SPB. In these models, deformation preferentially concentrated in areas where thickness change, defined by wedges of the ductile materials, was inbuilt. Based on the structural interpretation and model results, a kinematic evolution of the SPB is proposed. The kinematic model is characterized by the generation of out-of-sequence structures developed due to lateral stratigraphic variations of the Serrat Evaporites. The present work shows a good example of the role of stratigraphic heterogeneities of an evaporite formation which acts as decollement level on structural deformation in a fold-thrust belt. The results of this work have implications for hydrocarbon exploration and are relevant for studying structural geometry and mechanics in shortened evaporite basins. (C) 2017 Elsevier Ltd. All rights reserved.
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| 2. |
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| 3. |
- Fleming, E.J., et al.
(författare)
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Provenance of Triassic sandstones on the southwest Barents Shelf and the implication for sediment dispersal patterns in northwest Pangaea.
- 2016
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 78, s. 516-535
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Tidskriftsartikel (refereegranskat)abstract
- Thick Triassic siliciclastic units form major reservoir targets for hydrocarbon exploration on the Barents Shelf; however, poor reservoir quality, possibly associated with variation in provenance, remains a key risk factor in the area. In this study, sandstone dispersal patterns on the southwest Barents Shelf are investigated through petrographic and heavy mineral analysis, garnet and rutile geochemistry and zircon U-Pb geochronology. The results show that until the Early Norian Maximum Flooding Surface, two contrasting sand types were present: (i) a Caledonian Sand Type, characterised by a high compositional maturity, a heavy mineral assemblage dominated by garnet and low chrome-spinel:zircon (CZi) values, predominantly metapelitic rutiles and mostly Proterozoic and Archaean detrital zircon ages, interpreted to be sourced from the Caledonides, and (ii) a Uralian Sand Type, characterised by a low compositional maturity, high CZi values, predominantly metamafic rutiles and Carboniferous zircon ages, sourced from the Uralian Orogeny. In addition, disparity in detrital zircon ages of the Uralian Sand Type with contiguous strata on the northern Barents Shelf reveals the presence of a Northern Uraloid Sand Type, interpreted to have been sourced from Taimyr and Severnaya Zemlya. As such, a coincidental system is inferred which delivered sand to the Northern Barents Shelf in the late Carnian/early Norian. Following the Early Norian Maximum Flooding Surface, a significant provenance change occurs. In response to Late Triassic/Early Jurassic hinterland rejuvenation, supply from the Uralian Orogen ceased and the northern Scandinavian (Caledonian) source became dominant, extending northwards out on to the southwest Barents Shelf. The data reveal a link between reservoir quality and sand type and illustrate how provenance played an important role in the development of clastic reservoirs within the Triassic of the Barents Shelf.
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| 4. |
- Miller, Dennis J., et al.
(författare)
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Natural gas hydrates in the Rio Grande Cone (Brazil) : A new province in the western South Atlantic
- 2015
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Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 67, s. 187-196
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Tidskriftsartikel (refereegranskat)abstract
- The Rio Grande Cone is a large-scale fanlike feature in the continental slope of the Pelotas Basin, Southern Brazil, where ubiquitous world-class bottom simulating reflectors (BSRs) are readily observed in seismic records. With the purpose of searching for natural gas hydrate deposits in the Cone area, four oceanographic cruises were carried out between May 2011 and July 2013, leading to the discovery of two pockmark fields, active faults and gas hydrates in shallow sediments. Multichannel seismic, multibeam echo sounder, side scan sonar and sub-bottom profiler records were used to map the shallow section and select sites for piston core sampling. Gas hydrates were recovered in several piston cores within muddy sediments collected inside pockmarks displaying high backscatter in the multibeam and side scan sonar data. We present two representative piston cores where numerous levels of gas hydrates occur, along with degassing features, authigenic carbonate and soupy sediments. Gas dissociated from gas hydrate samples is dominantly methane (>99.78%) with minor quantities of ethane. The chemical and isotopic compositions of the gas strongly suggest a biogenic origin for the analyzed samples. These new findings are regarded as strong enough evidence to consider the Rio Grande Cone as a new gas hydrate province. (C) 2015 Elsevier Ltd. All rights reserved.
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| 5. |
- Sattar, Nauman, et al.
(författare)
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Seismic stratigraphy and hydrocarbon prospectivity of the Lower, Cretaceous Knurr Sandstone lobes along the southern margin of Loppa High, Hammerfest Basin, Barents Sea
- 2017
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 85, s. 54-69
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Forskningsöversikt (refereegranskat)abstract
- The Lower Cretaceous Knurr Sandstone deposited along the southern slope of Loppa High and overlain by the Kolje and Kolmule seals forms an attractive play in the Hammerfest Basin of the Barents Sea. Late Jurassic organic-rich Hekkingen shale directly underlies the Knurr Sandstone and acts as a source to provide effective charge. Three wells, 7120/2-2, 7122/2-1 and 7120/1-2, have proven the Knurr-Kolje play in structural traps, with an oil discovery in 7120/1-2. Prospectivity related to stratigraphic traps is, however, highly under-explored. In order to document and map the reservoir distribution and stratigraphic-trap fairway, the Lower Cretaceous sedimentary package containing the Knurr Sandstone is divided into a number of depositional sequences and systems tracts using key regional seismic profiles calibrated with logs. Mapping of the key surfaces bounding the Knurr sandstone has been carried out using all the seismic vintages available from Norwegian Petroleum Directorate (NPD).The thick massive nature of the sandstone (123 m in well 7122/2-1), sedimentary features characteristic of gravity flow deposits, high-resolution internal seismic reflections and stratal geometries (truncations and lapout patterns), and sequence stratigraphic position of the Knurr Sandstone on seismic profiles confirm that the lobes identified on the seismic section are gravity driven base of the slope lobes. These Knurr lobes and slope aprons were formed as a result of uplift of the Loppa paleo-high in the Late Jurassic to Early Cretaceous times which caused subaerial exposure and incision. The characteristic mounded, lobate geometry evident on the seismic can be mapped along the toe-of-slope and records multiple stacked lobes fed by multiple feeder canyons. Lateral partitioning and separation of the lobes along the toe-of-slope could potentially create strati graphic traps. The existing 2D seismic coverage is, however, not sufficient to capture lateral stratigraphic heterogeneity to identify stratigraphic traps. 3D seismic coverage with optimum acquisition parameters (high spatial and vertical resolution, appropriate seismic frequency and fold, long offsets and original amplitudes preserved) can allow for the reconstruction of 3D geomorphologic elements to de-risk potential stratigraphic traps prior to exploratory drilling.
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| 6. |
- Weibel, Rikke, et al.
(författare)
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Thermogenetic degradation of early zeolite cement : An important process for generating anomalously high porosity and permeability in deeply buried sandstone reservoirs?
- 2019
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Ingår i: Marine and Petroleum Geology. - 0264-8172 .- 1873-4073. ; 103, s. 620-645
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Tidskriftsartikel (refereegranskat)abstract
- Diagenetic explanations to anomalously high porosities and permeabilities in deeply buried sandstones have been presented for many reservoirs. For example, grain coatings of microquartz or chlorite can preserve porosity by preventing succeeding quartz overgrowths, and dissolution of grains or cement can generate secondary porosity. Anomalously high porosity and permeability (up to 25% and 500 mD, respectively) characterize the deeply buried (>5 km) Upper Jurassic shoreface sandstones of the Gert Member (Heno Formation) in the Hejre Field in the Danish Central Graben. Optical, cathodoluminescence and scanning electron microscopy were used to characterize the petrography and diagenetic changes that resulted in this high pressure and high temperature (HPHT) reservoir. This was supplemented by chemical analyses (ICP-OES and ICP-MS), mineralogical composition (XRD), and oxygen isotope composition of quartz and calcite cement (SIMS). The petrographic investigation shows that none of the known explanations for anomalously high porosity and permeability can be applied, hence a new hypothesis for deeply buried sandstones in contact with lavas and volcaniclastic lithologies is proposed. The new hypothesis includes reducing mechanical compaction due to early patchy zeolite cement, which was sourced from adjacent lavas and volcaniclastic rocks. Locally, stylolites developed where zeolite cement was less effective, hence the present overpressure formed at a later stage. Increased temperatures during burial resulted in thermal instability of the zeolite cement, which was dissolved and authigenic K-feldspar and quartz precipitated instead. This resulted in a reduction of the cement volume of up to 70% if the zeolite was K-heulandite and a corresponding relative porosity-increase. Thus, a reduction in cement-volume was generated by replacing zeolite of an open crystal structure with mineral phases, K-feldspar and quartz, of denser crystal structures. The thermogenetic breakdown of zeolite was forced by increased temperatures during burial. This process may explain previously enigmatic highly porous and permeable deeply buried sandstone reservoirs.
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| 7. |
- Soussi, Mohamed, et al.
(författare)
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Middle Triassic (Anisian-Ladinian) Tejra red beds and Late Triassic (Carnian) carbonate sedimentary records of southern Tunisia, Saharan Platform : Biostratigraphy, sedimentology and implication on regional stratigraphic correlations
- 2017
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Ingår i: MARINE AND PETROLEUM GEOLOGY. - : Elsevier BV. - 0264-8172. ; 79, s. 222-256
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Forskningsöversikt (refereegranskat)abstract
- The "red beds" of the Triassic succession outcropping at Tejra-Medenine (southern Tunisia, Saharan Platform) have yielded rich fossil assemblages of both freshwater and brackish-marine invertebrates and vertebrates. The new discovered fauna indicates an Anisian-Lower Ladinian age for the Tejra section. Its lowermost part is considered as equivalent of Ouled Chebbi Formation, while the medium and upper parts are considered as equivalent of the Kirchaou Formation. Both sedimentological characteristics and fossil assemblages indicate the increasing marine influences within the middle part of the section and the migration of brackish and freshwater fauna into the lacustrine/playa environment at the top. The marine fauna-rich interval of the Tejra section correlates well with the well-known Myophoria-rich carbonate stratigraphic marker confirming the Middle Triassic (Ladinian) major transgression well recorded eastward in the Tunisian Jeffara basin and in Libya. The use of this Ladinian stratigraphic event in addition to the Carnian carbonate transgressive events of the Jeffara escarpment outcrops was of great help for regional lithostratigraphic correlations between the Triassic outcropping series and those currently buried in Ghadames and Berkine basins. The age of the sandstones of "Trias Argilo-Greseux Inferieur" (TAGI) which forms the main oil and gas reservoir in the Saharan domain is attributed to the Anisian-Carnian and considered as coeval of Ouled Chebbi and Kirchaou Formations of the Dahar escarpment. An updated synthetic stratigraphic chart is proposed for the Triassic of Saharan Platform domain on the basis of the compilation of the new obtained results and the subsurface data taken from published literature.
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| 8. |
- Mikusinski, Grzegorz
(författare)
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Is the impact of loggings in the last primeval lowland forest in Europe underestimated? The conservation issues of Bialowieza Forest
- 2018
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Ingår i: Biological Conservation. - : Elsevier BV. - 0006-3207 .- 1873-2917. ; 227, s. 266-274
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Tidskriftsartikel (refereegranskat)abstract
- Loggings in biodiversity hot-spots are perceived as very serious threat to forest species and habitats of high conservation interest. In this paper we scrutinize the spatial impacts of recent loggings in the Polish part of the renowned Bialowieia Forest being the last remaining area of lowland temperate forest with a primeval character in Europe with the status of World Heritage and Natura 2000 site. The loggings have been applied in order to cope with the outbreak of the spruce bark beetle Ips typographus. We used satellite images to perform cover change detection analysis that delineated areas being logged in Bialowieia Forest between July 2015 and June 2018. Next, we assessed the extent of forest loss in areas with different management regimes as well as landscape-scale impacts. The total area of detected clear-cuts amounted to at least 675 ha, including 229 ha of old-growth stands. Assuming a buffer of 100 m from the edge of cleared forest patches, the cumulative direct and indirect impact of recent logging activities was estimated to amount to at least 4073 ha of affected forest. Logging activities resulted in a 26% increase in fragmentation in the entire Natura 2000 area. We argue that the ecological impact of logging extends beyond the logged areas by modifying the landscape structure and affecting ecosystem functioning on a landscape scale. As such, the recent salvage loggings in the Bialowieia Forest clearly damaged the conservation value of this precious area, not in the least by increasing its fragmentation. To avoid further degradation, we strongly argue for allowing natural tree regeneration on clear cuts and also for the extension of Bialowieia National Park to cover the entire forested area.
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