3. Sedimentary rocks and processes
3.1. Sedimentology posters
Early mid-Devonian volcanism dates initiation of the Orcadian basin in the Orkney Islands, Scotland
Lars Eivind Augland1, Anders Mattias Lundmark2, John F. Brown and Audun D. Bjerga
1CEED, University of Oslo, 2Department of Geosciences, University of Oslo
Early mid-Devonian sedimentary rocks forming the Orcadian basin constitute large parts of the exposed geology on the Orkney Islands. The lower sedimentary pile rest unconformably on foliated granites of the ca. 430 Ma Orkney granite complex and marks the onset of Lake Orcadia in the Orkney Islands with deposition of the lower Stromness flagstones (LSF), comprising alternating lacustrine strata of fine grained sandstones and shales. In the lower part of the Stromness flagstone sequence we have identified and dated, using zircon U-Pb ID-TIMS, a rhyolite dome or flow that constrain the age of the LSF and essentially the onset of Lake Orcadia to ca. 390 Ma. This new age combined with recent cyclostratigraphic results provide an improved estimate for the Efelian-Givetian boundary and the Kačák event marked by the top of the Achanarras level (Sandwick Fish Bed) constituting the top of the LSF. The rhyolite magmatism on Orkney is overlapping in age with intrusive rocks on Shetland and we suggest that this magmatism is related to an episode of important displacements on the Great Glen Fault.
Topographic Development as a result of regional incision, faulting, and deposition at the onset of relative sea-level rise; The upper Entrada Sandstone and the lower Curtis Formation, Utah, USA.
Sigrid Østmo da Costa1, Nikoline Bromander1, Valentin Zuchuat1, Alvar Braathen1, Anja Sundal1 and Ivar Midtkandal1
1University of Oslo
A 43 km North-south section on the North-Eastern margin of the San Rafaell Swell has been studied,
focusing on the Upper Jurassic eolian Entrada Sandstone, the J-3 regional Unconformity, and the
overlying Curtis Formation of Oxfordian age. Emphasis is on the distribution of sedimentary facies in
direct contact with the unconformity, and those affected by erosional topography during deposition.
The J-3 Unconformity displays at least 3 generations of erosive incision, possibly 6. The composite
unconformity has been subaerially eroded by eolian and fluvial action, besides tidal denudation postdating the onset of regional deposition. Present-day erosional relief, magnitude, and wavelength
contribute to multi-phase erosional processes resulting in inconsistent erosional patterns, and
distribution of sedimentary facies above and below the unconformity. Tectonic activity has influenced the development concerning substratum fluidisation and brittle deformation.
Generations of J-3s erosive incision varies regionally and locally across the section. A series of 5-10 m
deep channel-like scours linked to a stratigraphic level several meters above the J3 Unconformity,
erode to a deeper stratigraphic level than J3s original level. Intra-formational faults in Entrada
Sandstone suggest contribution to focused erosion at the Entrada-Curtis boundary.
Similarly, erosive lower boundaries of tidal sandstone bodies in direct contact with J3 suggest that
repeated relative sea-level changes lead to deeper stratigraphic erosion of the J3 Unconformity.
The on-going investigation will improve constraints on how reservoir-quality sandstone volumes are
affected by erosional topography in tidal environments, by determining distributional factors.
Distinguishing between local and regional variability is a target, to filtrate basin-specific anomalies.
Recognizing sandstone diagenesis from outcrop to microscopic scale
Rikke Weibel1, Nynke Keulen2, Mette Olivarius2 and Margrethe Thorup Nielsen2
1GEUS (Geological Survey of Denmark and Greenland), 2GEUS
Sandstone diagenesis is visible on many scales, ranging from the microscopic scale to the outcrop scale. Traditionally, diagenetic features are investigated by optical microscopy on core and outcrop samples. Extending the investigations to micron scales may help to define a set of features, which might be recognized in the field and hence useful for future field campaigns. The mineralogy and petrography of the sandstones are evaluated from thin sections by transmitted and reflected light microscopy, and from carbon-coated thin sections and gold- or platinum-coated rock chips by scanning electron microscopy (SEM), applying GEUS’ Zeiss Sigma 300VP field emission SEM, besides X-ray diffraction of bulk rock samples. Among the studied sandstone types, ‘rusty’ sandstones proved to be siderite-cemented where the siderite had partly altered to iron-oxide/hydroxides during diagenesis. Sandstone boulders or cliffs were intensively calcite-cemented, though with calcite of smaller/larger crystal sizes and different morphologies. Spectacular reddish and purple colored sandstones contained opal cement, which enclosed iron-oxides/hydroxides. Bluish or yellowish concretions or cemented intervals proved to be pyrite, altered to different alteration products (e.g. jarosite, szomolnokite). The mineral distribution at the microscopic scale can easily be shown by applying the Mineralogic software of the SEM. Altogether, investigations at a smaller scale can therefore explain the appearance of sandstones at the outcrop scale, and this appearance is largely depending on the type and abundance of the cementing phases.
3.2. Depositional basins
Triassic of the Wandel Sea Basin, North Greenland
Morten Bjerager1, Peter Alsen1, Jussi Hovikoski1 and Sofie Lindström1
In Triassic times the Wandel Sea Basin formed the western continuation of the basins in the southern part of the Barents Sea and the northern continuation of the Danmarkshavn Basin offshore Northeast Greenland. The results of recent GEUS fieldwork campaign in the area show that the exposed Triassic of North Greenland spans a near complete Induan (Dienerian) – Norian succession, up to 700 m thick. The succession rests unconformably on Upper Permian sediments and it is unconformably overlain by Upper Jurassic – Lower Cretaceous deposits.
The Lower Triassic (Dienerian, Induan) consists of marine sandstones, fluvial conglomerates and sandstones, and muddy flood-plain deposits. It is conformably overlain by the Lower Triassic (Smithian – lower Spathian) offshore mudstones with minor sand-dominated intervals. The upper Spathian to Ladinian is represented mainly by shallow marine sandstones in the western proximal part and laminated mudstones with minor thin sandstone units that were deposited in slope and deep basinal settings in the eastern deeper part of the Wandel Sea Basin. A marked erosional unconformity characterises the base of the overlying Upper Triassic (Carnian – Norian) of marine massive sandstones, conglomerates as well as cross-bedded and biomottled marine sandstones and minor mudstone units. The Triassic succession of the Wandel Sea Basin represents a well-constrained basin margin to deep basin transect and thus forms an excellent outcrop analogue to the time equivalent intervals in the western Barents Sea basins and the Danmarkshavn Basin offshore North-East Greenland.
Flint in the Danian København Limestone Formation
The Danian age København Limestone Formation was examined in 219 cored boreholes drilled in connection with the “Cityringen” metro project in central Copenhagen. Shape and colour of flint bodies were described during macroscopic visual inspection of core samples, as well as from digital core photos, and four diagnostic flint types were identified in the limestone. They are 1) grey flint bands, 2) light grey flint bars, 3) irregular flint bodies, and 4) dark grey flint blots. The well-known informal tripartition of the København Limestone Formation into the upper regularly bedded, the middle nodule-rich and the lower laminated unit (Stenestad 1976, Knudsen et al. 1995, Klitten et al. 1995, Olsen & Nielsen 2002) is largely supported by the distribution of the four flint types: Type 1 dominates the upper unit, Type 2 dominates the middle unit, while Type 4 is the only type found in the lower unit. Types 1, 2 and 3 all occur to some extent in both the upper and middle unit. Type 4 is also characteristic of the underlying Bryozoan Limestone, making it difficult in core samples to determine the boundary between København Limestone and Bryozoan Limestone.
The conspicuous changes in shape and colour of flint bodies up through the København Limestone Formation seem to indicate that the flint bodies display different stages of flint formation and that this limestone may conceal narratives yet to be told about flint formation and depositional environment.
Stenestad, E. 1976: Københavnsområdets geologi især baseret på citybaneundersøgelserne. DGU 3. Rk., 45, 149 pp.
Klitten, K., Plough, C. & Olsen, H. 1995: Geophysical log stratigraphy of the København Limestone. Proceedings from XI ECSMFE, Copenhagen 1995, Dansk Geoteknisk Forening Bulletin 11, Vol. 5, 127-134.
Knudsen, C., Andersen, C., Foged, N., Jacobsen, P.R. & Larsen, B. 1995: Stratigraphy and engineering geology of København Limestone. Proceedings from XI ECSMFE, Copenhagen 1995, Dansk Geoteknisk Forening Bulletin 11, Vol. 5, 117-126.
Olsen, H. & Nielsen, U.T. 2002: Logstratigrafisk inddeling af kalken i Københavns-området. In: Frederiksen, J.K. et al. (eds.): Ingeniørgeologiske forhold i København, Dansk Geoteknisk Forening Bulletin 19, 35-42.
Evidence of hyperpycnally fed turbidites in a basin floor setting, Eocene of Spitsbergen, Arctic Norway
Sten-Andreas Grundvåg1 and William Helland-Hansen2
1Department of Geosciences, UiT–the Arctic University of Norway, 2Department of Earth Sciences, University of Bergen
The Eocene of Spitsbergen, Svalbard, has received considerable attention in the literature because of its spectacular seismic-scale clinoforms exposed along many fiords and valleys. Previous investigations particularly focused on the slope segment of the clinoforms and demonstrated how sustained-type, hyperpycnal flows deriving from shelf-edge deltas played a major role in bringing sand onto the slope, contributing to slope accretion. Periodic sand delivery beyond the slope is evident by the presence of sandstone-dominated turbidite lobes in the basin floor segment of some clinoforms. By combining outcrop and core data from central Spitsbergen, our study focus on sedimentary processes that formed these turbidite lobes. At bed-to-bed scale, many of the turbidite beds deviate from the classical Bouma-type facies patterns typical of deposition from surge-type, low-density turbidity currents. Thick (0.5–3 m) turbidite beds characterized by pervasive amalgamation, internal scouring surfaces, and various soft-sediment deformation structures dominate. Further, beds exhibiting a lower sandstone-dominated turbidite division succeeded by a mud-rich upper division containing abundant coal/plant fragments occur frequently. The latter bed architecture is typical of deposition from hybrid sediment gravity flows and indicate that some turbidity flows transformed into slurry flows or debris flows on their way to their final destination on the basin floor. The dominance of thick, amalgamated turbidite beds and the abundance of coal/plant fragments documented in this study, as well as the presence of hyperpycnal flow turbidites on the slopes documented in previous studies, suggests that hyperpycnal flows are capable of delivering sand onto the basin floor.
Stratigraphic treasures of an “ugly duckling”: towards an integrated basin model of the Lower Cretaceous Rurikfjellet Formation, Arctic Svalbard
Mads E. Jelby1, Sten-Andreas Grundvåg2, Peter Alsen3, Kasia K. Śliwińska3, Lars Stemmerik1, William Helland-Hansen4 and Snorre Olaussen5
1Natural History Museum of Denmark, University of Copenhagen, 2Department of Geosciences, UiT The Arctic University of Norway, 3Geological Survey of Denmark and Greenland, 4Department of Earth Science, University of Bergen, 5Department of Arctic Geology, The University Centre in Svalbard
The Lower Cretaceous (Valanginian–Hauterivian) Rurikfjellet Formation in Spitsbergen, Svalbard, forms an up to c. 300 m thick succession of fine-grained shelf and lower shoreface shales, siltstones and sandstones (Dypvik et al. 1991). The formation constitutes the regressive part of an >1000 m thick first-order sequence which formed during a long-term shoreline progradation (the Rurikfjellet Formation) and back-stepping (the Helvetiafjellet and Carolinefjellet formations) in response to a full cycle of relative sea-level change (Gjelberg & Steel 1995). In contrast to the overlying Lower Cretaceous succession, the Rurikfjellet Formation has received relatively little attention and is relatively poorly exposed. Its age is also rather uncertain. We present a revised basin-scale sedimentological and sequence stratigraphic model of the formation, tied to a new biostratigraphic framework. The model is based on data recently collected across the Lower Cretaceous outcrop belt, including >3500 m of measured outcrop sections; seven subsurface cores; >130 palaeocurrent measurements; >50,000 photos; three bulk-rock δ13Corg curves with a mean resolution of 2 m; and hundreds of dinocyst, ammonite, belemnite and bivalve biostratigraphic samples. Our data reveal a regionally persistent regressive–transgressive sequence development of the formation, as well as several hitherto unrecognised progradational pulses of apparently diachronous clastic wedges. We argue that their depositional architecture and interfingering were controlled by prodeltaic coupled storm-dominated and hyperpycnal sedimentation across a wide, low-gradient ramp, with important implications for palaeogeographic reconstructions for the Valanginian–Hauterivian of Svalbard and nearby areas.
Dypvik, H., Nagy, J., Eikeland, T.A., Backer-Owe, K., Andersen, A., Haremo, P., Bjærke, T., Johansen, H. & Elverhøi, A. 1991: The Janusfjellet Subgroup (Bathonian to Hauterivian) on central Spitsbergen: a revised lithostratigraphy. Polar Research 9, 21–43.
Gjelberg, J. & Steel, R.J. 1995: Helvetiafjellet formation (Barremian–Aptian), Spitsbergen: characteristics of a transgressive succession. Norwegian Petroleum Society Special Publications 5, 571–593.
Elastic moduli, stiffness and effective stress of chalk from Zealand (Denmark) and from Dan field (North Sea).
Laura Paci1, Irene Rocchi1 and Ida Lykke Fabricius1
1Technical University of Denmark,Department of Civil Engineering,Nordvej Building 119 2800 Kgs.Lyngby
The successful employment of the Underground Thermal Energy Storage in the subsurface of Copenhagen is investigated. The study considers the geotechnical and physical properties (i.e. stiffness and porosity) of the medium depth (400-800 mbgl) Chalk Group. The majority of geotechnical data available covers shallow depth, while deep well logs data are fewer and of variable quality. In order to overcome the lack of information, this work evaluates Dan field as an analog for the chalk from Zealand comparing the effective stress and stiffness at the two locations. The chalk formation is found at much greater depth in the Dan field (1800 mbsl compared to an average of 200 mbsl in Zealand), resulting in a greater overburden stress. However, the effective stress is comparable to the maximum value encountered in Zealand (i.e. before uplift and erosion), due to overpressure. The results shown were obtained calculating the maximum effective stress based on the burial anomaly as studied by Japsen (1998). In addition, the stiffness was calculated by means of P-wave velocity and density data (Fabricius, 2003). The model allows to estimate the degree of cementation and hence the Biot´s coefficient by comparing the elastic modulus obtained by P-wave measurements with the theoretical one obtained under the assumptions of either particles in suspension or close-packed particles. The results show similarity between the two locations concerning the elastic moduli and porosity, but not for the same sample. This discrepancy could be caused either by a different heating history or by different texture.
Japsen, P. 1998: Regional velocity-depth anomalies, North Sea chalk: a record of overpressure and Neogene uplift and erosion. Bulletin of the American Association of Petroleum Geologists 82, 2031-2074.
Fabricius, I.L. 2003: How burial diagenesis of chalk sediments control velocity and porosity. Bulletin of the American Association of Petroleum Geologists 87, 1755-1778.
The Miocene-Pliocene Skade-Utsira aquifer, North Sea: Updated maps and new insights in depositional patterns and syn-sedimentary deformation
Fridtjof Riis1, Tor Eidvin1 and Yngve Rundberg2
1Norwegian Petroleum Directorate, 2YR Geo AS
During Miocene-Pliocene the deltaic system east of Shetland prograded into the Norwegian sector of the North Sea. Sands were deposited in a slope and basin setting. Thick deposits of high porosity and high permeability Utsira and Skade formations cover an area more than 300 km long and 60 km wide. The maximum total thickness of sands in the aquifer reaches more than 500 m. Maps of the aquifer were published by the NPD as part of the CO2 Storage Atlas (www.npd.no).
In this updated study, NPD has included new well and seismic data, as well as new results from micropaleontology and Sr isotope stratigraphy. In addition to the lower Miocene Skade Formation and the upper Miocene to lower Pliocene Utsira Formation, the top of the middle Miocene sandy unit (Eir formation, informal) is also available. The depocenter of the Skade Formation is found in the central part of the area. During the middle Miocene there was a shift to the north, while in the late Miocene, a major lobe developed in the south. During the latest late Miocene and the Pliocene the basinal depression was filled in, and a shelfal setting is interpreted.
The whole basin region is strongly affected by large scale soft sediment deformation. Mobilization of sands took place where sandy formations were sealed by deep-water clay and ooze. Evacuation structures, pillow-like structures and injectites are found at several stratigraphic levels and were apparently triggered by deposition of turbidites or mass flows.
Norwegian Petroleum Directorate 2013: Investigation of Oligocene to Lower Pliocene deposits in the Nordic offshore area and onshore Denmark. NPD Bulletin 10, http://www.npd.no/engelsk/cwi/pbl/NPD_papers/Hyperlink-NPD-Bulletin-10.pdf
Norwegian Petroleum Directorate 2014: CO2 Storage Atlas. Norwegian Continental Shelf. http://www.npd.no/en/Publications/Reports/Compiled-CO2-atlas/
Aeolian silt transport processes as fingerprinted by dynamic image analysis of the grain size and shape characteristics of Chinese loess and Red Clay deposits
Yuan Shang1, Anu Kaakinen1, Christiaan J. Beets2 and Maarten A. Prins2
1Department of Geosciences and Geography, P.O. Box 64, 00014, University of Helsinki, Finland, 2Department of Earth Sciences, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De B
This study applied dynamic image analysis (DIA) to characterize the grain size and shape of Chinese aeolian sediments in order to fingerprint their transportation processes. We selected four well-studied Quaternary loess-palaeosol sequences along a north-south transect across the Chinese Loess Plateau and compared their grain size distribution obtained by DIA with that yielded by laser diffraction(LD) particle size analysis. The results demonstrated that DIA is able to characterize clearly spatiotemporal variations in the grain size records of loess-palaeosol sequences formed during the last two glacial and interglacial periods. This is consistent with grain size results obtained using LD. DIA is also able to characterize spatial variations in the more fine-grained aeolian Red Clay deposits and to allow the quantification of the fluvial contribution to Red Clay sequences. DIA of the grain shapes characteristics in loess-palaeosol and Red Clay deposits revealed a systematic pattern, whereby the aspect ratio decreased with increasing grain size, indicating systematic shape sorting occurred during the aeolian transportation of these dust particles. Also evident from our DIA data was a subtle but systematic downwind decrease in the aspect ratio of the particles in the loess units. This observation suggests that elongated and/or flat particles (with a low aspect ratio) were transported further downwind than more symmetrically shaped particles (with a high aspect ratio). This study indicates that DIA of grain size and shape characteristics can be an additional powerful tool for fingerprinting grain size and shape sorting trends and reconstructing the transportation pathways of silt-sized aeolian sediments.
A new observation of a biosiliceous opal bearing sequence in the Miocene Lark Formation in the Danish North Sea.
Henrik Sulsbrück1 and Jørgen Toft1
1Mærsk Olie og Gas A/S
The Paleogene – Lower Neogene Lark Formation of the Danish North Sea consists of a biosiliceous, opal-bearing sequence of sediments which extend into the German, Norwegian and UK sectors of the North Sea. The uppermost 50-100 m part of the Lark Formation is characterized by abundant biogenic silica in the form of diatoms, radiolarians, Bolboforma and sponge spicules. This biosiliceous-rich section is of Early to Mid-Miocene age and formed during a period of climatic optimum. The interval can contain up to 40% biosiliceous material, together with detrital clay and quartz. Carbonate stringers and pyrite occur in minor amounts. The content of organic matter can be significant with TOC’s of up to 8%. In the lower parts of Lark (Early Miocene), diagenesis has transformed the biogenic silica from Opal A into Opal CT. No Opal has been observed in the Oligocene part of the Lark Formation. This talk discusses the key characteristic of this biosiliceous section of the Lark Formation, and the regional controls on it’s development.
Across the Eocene-Oligocene Transition in inland Asia: Bio-, Litho-, and Magnetostratigrapy of Ulantatal, Inner Mongolia, China
Joonas Wasiljeff1, Anu Kaakinen2, Johanna Salminen3 and Zhaoqun Zhang4
1Department of Geosciences and Geography, P.O. Box 64, FI-00014 University of Helsinki, Finland, 2Department of Geosciences and Geography, University of Helsinki, Finland, 3Department of Physics, University of Helsinki, Finland, 4Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, China
Coherent terrestrial sequences are critical in scrutinizing past environmental and climatic changes through successive fossil and sedimentary records. Central Asia has been an exquisite locality for past and ongoing paleontological investigations for Eocene to Oligocene aged mammalian faunas. Transition from Eocene to Oligocene (EOT) at ~34 Ma signified considerable changes in climate, flora, and fauna, externalized by the decrease of mean annual temperature and the change in vegetation from Eocene forests to more bare lands of the Oligocene. The faunal transition in inland Asia was characterized by replacement of Eocene perissodactyl-dominant faunas to the Oligocene rodent-lagomorph-dominant faunas.
Ulantatal is a renowned Oligocene mammalian fossil locality in Inner Mongolia, China. Although the area has produced a significant collection of vertebrate faunas, knowledge of the stratigraphy, ages and depositional environments have remained poor or nearly non-existent. Litho- and magnetostratigraphic context, and correlation of the Ulantatal area sediments with the Geologic Time Scale (GTS) is presented, thus providing age estimations for the fossil-bearing horizons.
Landscape of the Ulantatal formation is characterized by flat lined topography with low uplands and small gullies. Outcrops of the area show a uniform pattern predominated by fine-grained massive sediments occasionally interbedded with coarser grained horizons. The sequence produces fossils along most of the section, with the richest fossil occurrences in the lower half of the sequence. Our magnetic section suggests a correlation in magnetozones C15n to C9n, with an age range of about 35-27 Ma, and places the lowermost fossil site in Ulantatal in the latest Eocene.
3.3. Composition of siliciclastic rocks
How can provenance and sorting effects be differentiated from detrital zircon data? Example from the German Triassic Buntsandstein Group
Carita Augustsson1, Thomas Voigt2, Kristin Bernhard2, Marian Kreißler2, Reinhard Gaupp2, Andreas Gärnter3, Mandy Hofmann4 and Ulf Linnemann4
1Institutt for Petroleumsteknologi, Universitetet i Stavanger, 4036 Stavanger, Norway, 2Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Burgweg 11, 07749 Jena, Germany, 3Senckenberg naturhistorische Sammlungen Dresden, Köningsbrücker Landstr. 159, 01109 Dresden, Germany, 4Senckenberg naturhistorische Sammlungen Dresden, Köningsbrücker Landstr 159, 01109 Dresden, Germany
This study stresses how sorting and provenance effects can be differentiated by combining zircon-grain length and U-Pb-ages for individual detrital grains. We exemplify this by a provenance study for continental deposits of the Lower Triassic, continental Buntsandstein Group in central Germany. The study is based on > 1000 zircon grains from 12 sandstone beds. The unbroken grains in seven of the zircon separates have mean lengths of 190-220 µm and five are composed 100-140 µm long grains in average. All have a main population of 340-320 Ma ages, representative of granitoid from the Variscan Orogen of the Massif Central and the Bohemian Massif. This detritus was mixed with abraded grains from Ediacaran to Palaeozoic (meta)sedimentary units feeding the basin with 610-460 Ma (Ediacaran to Ordovician) and 2 Ga age grains. The 610-460 Ma age population is common only in five samples with mean grain lengths of 100-140 µm. Those grains mainly are < 130 µm in the east, but equally common in all grain sizes in the west. This indicates that the east-west age difference is a provenance effect but that internal differences in the east is a sorting effect. The western group was fed from the Massif Central and the eastern group from the Bohemian Massif. We conclude that interpretation of detrital zircon ages preferably are separately for different size classes, because zircon studies performed on broad grain-size intervals without considering possible size-age correlations may disguise sorting effects that potentially can lead to a misleading source-area interpretation.
Middle Triassic siliciclastic deposits of Svalbard as a part of source to sink framework of the Arctic
Urszula Czarniecka1, Beyene Girma Haile2 and Krzysztof Krajewski1
1Institute of Geological Sciences, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland, 2Department of Geosciences, University of Oslo, P.O.BOX 1047, Blindern, 0316 Oslo, Norway
Sandy facies of the Bravaisberget Formation (Middle Triassic) exposed at the southernmost part of Spitsbergen (Svalbard archipelago) represent an uplifted part of the northwestern corner of the Barents Sea shelf. The deposits are interpreted as an effect of shallow marine and deltaic sedimentation and their facial equivalents in the Barents Sea are considered as good reservoir rocks for hydrocarbon accumulation.
The aim of this study was to characterise and recognise potential source areas for the Middle Triassic siliciclastics based on petrological and geochemical methods. Standard quantitative petrographical analysis of thin sections and bulk rock geochemistry technics have been supplemented by U-Pb and Lu-Hf zircon analysis.
The studied deposits have quartz-dominated framework composition, with minor content of feldspars and lithoclasts therefore they have been classified as quartz arenites, subfeldsarenites, sublitharenites. Concentrations of major, trace elements and REE point to silicic source rocks composition. Distribution of zircon ages shows domination of Paleo- and Mesoproterozoic ages with significant content of Archean ages, minor Caledonian zircons and lack of Uralian grains. This provenance signature has been compared with data from other areas of the Arctic region.
The area analysed in this study represents only small part of the whole Arctic sediment routing system existed in the Mesozoic time and the investigated deposits have provenance signature which is consistent with the Triassic provenance signatures from Canadian Arctic and Greenland and linking their proto-sources to Laurentia, but the deposits components were recycled from older sedimentary rocks, likely from Devonian strata.
This work has been (partially) funded by the Trias North project “Reconstructing the Triassic Northern Barents shelf; basin infill patterns controlled by gentle sags and faults” (www.mn.uio.no/triasnorth/) under grant 234152 from the research Council of Norway (RCN) and with financial support provided by Tullow Oil Norge, Lundin Norway, Statoil Petroleum, Edison Norge and RWE Dea Norge.
Quartz cementation and diagenetic effects in sandstone – an analog study of Cambrian quartz arenite from Scandinavia
Sanne Lorentzen1, Carita Augustsson1, Johan P. Nystuen2, Jens Jahren2 and Niels H. Schovsbo3
1Department of Petroleum Engineering, University of Stavanger, 2Department of Geoscience, University of Oslo, 3Geological Survey of Denmark and Greenland
Lower Cambrian quartz arenitic deposits have a world-wide occurrence. Nevertheless, diagenetic effects are rarely taken into consideration to explain the existence of these mature, shallow marine deposits. In this study, petrographic, geochemical and mineralogical analyses were carried out on core and outcrop samples from the quartz-rich Ringsaker Member from Southern Norway and the corresponding Hardeberga Formation from Bornholm in Denmark and Scania in Sweden. The sandstone units have been examined in a state of complete quartz cementation in order to study the diagenetic history and the effects leading to destruction of porosity and permeability. Quartz cementation was estimated by comparing the amount of cement present to the modelled amount of quartz cement based on its time-temperature history. The quartz arenite from Southern Norway has an intergranular volume of ca. 20%, and close to 100% of the initial porosity has been replaced by quartz cement. For most samples, other authigenic cement minerals, together with detrital phyllosilicates, represent < 5% of the present-day composition. Preliminary petrological investigation on the Hardeberga Formation points to similar quartz-dominated chemical diagenesis. This indicates that the sediment composition was extremely quartz-rich already during deposition throughout Scandinavia, as is supported by the high SiO2 content averaging at 95.6%. Sediment reworking by waves, and subsequent removal of early authigenic components produced from subsurface leaching of unstable grains are likely to have influenced the composition severely. The findings contribute to an increased understanding of the formation of both quartz-rich sediment and the end products of cementation processes.
IMPACT OF METEORIC-WATER DIAGENESIS ON RESERVOIR QUALITY IN PALEOCENE TURBDITIC SANDSTONES, UK CENTRAL GRABEN, NORTH SEA
1Petroleum Geosciences at Soran University/Kurdistan Region-Iraq, and KPS Metal, Czech Republic
This petrographic and stable isotopes study on the distribution of diagenetic alterations and of their impact on reservoir-quality evolution of Paleocene marine turbidite successions (Andrews Formation, UK Central Graben, North Sea) revealed the important roles of tectonic setting, depositional facies, and changes in the relative sea level. Diagenetic modifications include dissolution and kaolinitization of framework silicates, cementation by carbonates and quartz, mechanical compaction of sedimentary rock fragments, and chemical compaction of detrital quartz. Despite tens of km distance from the paleoshore line, kaolinitization is attributed to meteoric-water flux during major fall in the relative sea level. The wide range of δ13CV-PDB values of calcite cement (about -18‰ to +22‰) is attributed to the input of dissolved carbon from microbial methanogenesis and methane oxidation. The wide range of δ18O values (about -17‰ to -1‰) of this cement might reflect the involvement of various fluids including marine, meteoric, and evolved formation waters) and wide range of precipitation temperatures. Preservation of porosity and permeability in sandstones from the passive margin basins (up to 30% and 1 Darcy, respectively) is attributed to the presence of abundant rigid quartz and feldspar grains and to dissolution of carbonate cement as well as mica and feldspars.
Al-Ramadan, K., Morad, S., Proust, J. N., Al-Aasm, I., 2005.Distribution of diagenetic alterations in siliciclastic shoreface deposits within a sequence stratigraphic framework: evidence from the Upper Jurassic, Boulonnais, NW France. Journal of Sedimentary Research 75, 943-959.
Armentrout, J.M., 1991.Paleontologic constraints on depositional modeling: examples of integration of biostratigraphy and seismic stratigraphy, Plio-Pleistocene, Gulf of Mexico. In: Weimer, P., Link, M.A.(Eds.), Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems. Elsevier, Amsterdam, pp. 137-170.
Berg, O. R., 1982. Seismic detection and evaluation of delta and turbidite sequences; their application to exploration for the subtle trap. AAPG Bulletin 66, 1271-1288.
Den Hartog Jager, D., Giles, M.R., and Griffiths, G.R., 1993. Evolution of Paleogene submarine fans of the North Sea in space and time. In: Parker, J.R. (Ed.), Petroleum geology of Northwest Europe. Proceedings of the 4th conference, London, The Geological Society, pp. 59–71.
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Factors influencing stylolite development and quartz cementation in the Jurassic Stø Formation sandstone, Tromsø Basin, SW Barents Sea
Mai Britt E. Mørk1
1NTNU, Department of Geoscience and petroleum, N-7491 Trondheim, Norway.
Stylolites are common diagenetic structures in quartz cemented sandstones and provide records of extensive chemical compaction. As documented and modelled in the diagenesis literature, the development of stylolite seams in sandstone involves dissolution of quartz grains as well as “re”-precipitation of the dissolved silica as quartz cement. This study compares microstructures of stylolite and quartz cement in strongly cemented Jurassic sandstones from a well in the southwestern-most part of the Barents Sea to interpret diagenesis and deformation structures. The impact of sedimentary fabric and bioturbation in development of stylolites is emphasized based on comparison of sandstone cores of
different degrees of bioturbation. The stylolite forming processes involved differential compaction in several stages of diagenesis: 1) Initial mechanical compaction inducing folding of softer clay-rich lamina. 2) In deeper burial chemical diagenesis with enhanced grain dissolution at clay contacts accompanied with quartz cementation and 3) continued stylolite growth involving also dissolution of earlier precipitated quartz cement. Micro shear-zones along stylolite fold limbs are interpreted in terms of dissolution-enhanced differential compaction. Deformation accompanying quartz cementation is evidenced by a frequent distribution of dauphine twins at adjacent cement – cement contacts, revealed by use of SEM-backscattered electron diffraction techniques. The latest stage of diagenesis involved abundant pyrite crystallization, in particular along stylolites, questioning if stylolites could have acted as conduits for fluid migration. Further research is suggested to examine regional tectonic and thermal influences on the distributions of extensive quartz cementation in some of the westernmost areas of the Barents Shelf.
Stiffening effect from temperature and stress on sandstones from the deep North Sea Basin
Tobias Orlander1, Katrine Alling Andreassen1 and Ida Lykke Fabricius1
1Technical University of Denmark
We investigate effects of temperature, stress and stress symmetry on the dynamic stiffness of two sandstones from depths of approximately 5 km in the North Sea Basin. The studied temperature range was 25-170°C, whereas the studied stress range was 2.5-15 MPa. Two stress symmetries were compared: 1) hydrostatic stress and 2) uniaxial stress with constant confining stress. We derived dynamic compressional and shear moduli from density and ultrasonic P- and S-wave velocities and show that the stiffness can increase with up to 20% and 100% for respectively increase in temperature and stress. We link the increased stiffness to two physically different mechanisms, both resulting in closure of ruptured grain contacts created by equilibrating sample material to atmospheric conditions. Eventually, the increase is hence recovery stiffness by mechanisms of: 1) frame deformation due to increase in stress and 2) thermal expansion due to increase in temperature. That contact ruptures (micro-cracks) can full or partially close by 1) is an accepted mechanism for partial recovery of in-situ stiffness. We show that stiffness recovery by 1) or 2) have different magnitude, but that both are most pronounced for sandstones with a low degree of cementation. This is probably because cementation hinders progression of micro-cracks during deloading and cooling. The results demonstrate the significance at testing samples at their natural stress and temperature.
The diagenetic impact on reservoir sandstones of the Heno Formation in the Ravn-3 well, Danish Central Graben, Denmark
Simone Suhr Pedersen1, Niels Hemmingsen Schovsbo2 and Rikke Weibel2
1University of Copenhagen, Department of Geosciences and Natural Resource Management, 2GEUS, Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
The Upper Jurassic Heno Formation in the Ravn-3 well is the deepest producing sandstone reservoir in the Danish North Sea. A combined approach including petrography, geochemistry, porosity and permeability analysis and core description have been achieved to investigate variations in diagenesis up through the formation and how post-depositional changes impacts the sandstone reservoirs. Three depositional environments characterize the reservoir sandstones: lower shoreface, middle shoreface and foreshore. Results show that the reservoir potential of the sandstones predominantly depend on occurring digenetic phases and not depositional environment. The dominating diagenetic phases are eogenetic microcrystalline quartz, mesogenetic precipitation of illite, extensive mesogenetic quartz overgrowth and extensive Fe-dolomite and ankerite cementation. The different diagenetic phases are present in all three depositional environments. Diagenesis had a major impact on either preserving or destroying porosity, but did in all cases highly reduce the permeability. The different diagenetic phases can be recognized in the Ravn-1 well and in less degree in the Ravn-2 well.
Terrestrial paleoweathering and the presence of deep biosphere in fractured granites, Utsira High, Norwegian North Sea
Lars Riber1, Steven G. Driese2, Henning Dypvik1, Gary E. Stinchcomb3, Ronald Sørlie4 and Liz Thompson4
1Department of Geosciences, University of Oslo, 2Department of Geosciences, Baylor University, 3Watershed Studies Institute and Department of Geosciences, Murray State University, 4Lundin Norway AS
Whereas the global stratigraphic record is dominantly marine, deeply buried paleoregolith profiles are rare and important remnants of the terrestrial paleoenvironment. On the Utsira High, Norwegian North Sea, the crystalline basement was probably close to the surface from the Permo-Triassic until the early Cretaceous (Ksienzyk et al., 2016). Recent K-Ar ages of illite clays from weathered granites in the area suggested commencement of regolith/paleosol formation in mid-Triassic (Fredin et al., 2017). Drill cores from well 16/1-25S in the Rolvsnes discovery include ~21 m of fractured and weathered granite below Cretaceous cover. In the studied regolith, two intensely weathered, clay-rich intervals were identified in the upper part of the profile. They contain randomly interstratified mixed-layer illite-smectite and poorly crystalline kaolinite clays, pseudomorphically kaolinitized biotite, and dendritic aggregates of fine-grained hematite. Although quartz is preserved, feldspars are affected by chemical weathering with plagioclase nearly completely removed. The fracture network facilitated deep percolation of meteoric water and in samples more than 20 m below the basement-sediment contact weathering is evidenced by minor amounts of well-crystallized kaolinite and moderately altered feldspars. Estimates of MAP and MAT using the Paleosol-Paleoclimate Model (PPM1.1) (Stinchcomb et al., 2016) from the clay-rich intervals indicate formation under subhumid and temperate conditions. Use of geochemical proxies is complicated because of heterogeneous protolith composition, truncation of the original paleosol, and the likelihood of multiple alteration episodes. Mycorrhizal fungal hyphae have been observed down to about 20 m below the basement-sediment contact, indicating the presence of deep biosphere.
Fredin, O., Viola, G., Zwingmann, H., Sørlie, R., Brönner, M., Lie, J.E., Grandal, E.M., Müller, A., Margreth, A., Vogt, C. & Knies, J. 2017: The inheritance of a Mesozoic landscape in western Scandinavia. Nature Communications 8.
Ksienzyk, A. K., Jacobs, J., Fossen, H., Woznitza, T., Wemmer, K., & Dunkl, I. 2016: Comparing offshore and onshore thermal histories: low-T thermochronology of the Utsira High, western Norway. EGU General Assembly Conference Abstracts 18, p. 11723.
Stinchcomb, G. E., Nordt, L. C., Driese, S. G., Lukens, W. E., Williamson, F. C. & Tubbs, J. D. 2016: A data-driven spline model designed to predict paleoclimate using paleosol geochemistry. American Journal of Science 316, 746 – 777.
Impact of electrostatic forces on sediment porosity
Leonardo Teixeira Pinto Meireles1, Einar Madsen Storebø1 and Ida Lykke Fabricius1
1Technical University of Denmark, Kogens Lyngby, Denmark
In this paper, we assess the impact of electrical double layer related forces on sediment porosity using low field Nuclear Magnetic Resonance Spectrometry. Samples of Calcite, Quartz or Kaolinite powder were saturated with brines containing ions found in seawater (Na+, Ca2+, Mg2+, Cl– and SO42−) at varying ionic strengths and as a non-polar reference, with ethylene glycol. The difference in porosity between a sample saturated with ethylene glycol and a sample saturated with a given brine reflects the repulsive pressure resulting from the electrostatic forces.
We found that for calcite samples, saturation with solutions containing divalent cations (Ca2+ and Mg2+) lead to higher repulsive forces between the grains, while adsorption of SO42– counteracts the initially positive surface charge, leading to a decrease of the repulsive forces. For kaolinite, differences in potential between the silica and alumina faces as well as the edges can either lead to repulsion between particles or to flocculation depending on ionic strength and ionic species of the fluid. For quartz, relatively high porosity for powders saturated with sodium chloride brine indicates that Na+ is a potential determining ion for the quartz surface. The repulsive pressure inferred from the experiments could be correlated to zeta potential measurements available in the literature.