Mastergradsoppgaver i geologi

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Mastergradsoppgaver i geologi

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• Petrogenesis and tectonic setting of the mafic-ultramafic rock association from NW Senja, West Troms Basement Complex

  Priyatkina, Nadezda (Master thesis; Mastergradsoppgave, 31-Jan-2013)

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  Abstract:

  The studied mafic-ultramafic rock association occurs within Archean tonalitic gneisses and metasupracrustal suites of the Astridal belt belonging to the West Troms Basement Complex in the northwestern part of the Senja Island. The rock association appears in lens-shaped bodies, up to 200 m long, which are oriented conformal to the major metamorphic fabric of the host rock. The rock association is made up by interlayered units of green spinel-bearing olivine orthopyroxene-hornblendite, hornblende peridotite, olivine hornblendite, hornblendite and amphibolite (metagabbroic rock). Microscope studies and whole rock geochemical data indicate that the ultramafic rocks represent a single magmatic series of mafic and ultramafic olivine-amphibole cumulates, which have been significantly affected by metamorphism. Igneous mineral and whole rock trace element data indicate MORB affinity of the cumulates and suggest their emplacement in oceanic rift or rifted continental margin setting. The studied cumulates may represent a crustal remnant of the Paleoproterozic Svecofennian ocean. The rocks were metamorphosed together with the supracrustal suites of the Astridal belt during the major Svecofennian event about 1.74 Ga ago as indicated by a U-Pb age of metamorphic zircons from the metagabbroic rock belonging to the studied suite.

  URI:

  http://hdl.handle.net/10037/4843

  File(s) in this item: 1

  thesis.pdf   (13.80Mb)
• Sand waves and sediment transport on the SW Barents sea continental slope

  Waage, Malin (Master thesis; Mastergradsoppgave, 15-Nov-2012)

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  Abstract:

  I study a sand-wave field in ~600 meters water depth on the continental slope offshore Northern Norway. Using multibeam bathymetry data from 2008 and 2011 and P-Cable high-resolution 3D seismic data from 2011, I characterize the field. Sand waves reach up to 6.6 m in height and have wavelengths as large as 140 m. They are mostly asymmetric in shape with the steepest side dipping to the northwest, indicating that current flow over the field is predominantly to the northwest. Larger sand waves (>2 m in height, >100 m wavelength) are observed on topographic highs in the sand-wave field, whereas smaller sand waves (<2 m in height, <100 m wavelength) are present in topographic lows. These topographic lows occur where three ~1-2-km-wide channels cut down the continental slope through the sand-wave field. Seismic data reveal that there are no buried sand waves beneath the seafloor, suggesting that the sand waves are being continually eroded and redeposit at the seabed. Seismic data reveal that the depositional environment over the last ~1 Ma has been largely controlled by debris flows during the glaciations and melt-water plumes and channel formation during the glaciations. High-resolution imaging of the first few meters below the seabed shows that winnowing and associated sand-wave migration is currently the dominant sedimentary process. Data across the study area show that there are no buried sand waves beneath the seafloor. This suggests that the sand waves are being continually eroded and redeposited at the seabed. By measuring the offset of the crest of sand waves in the 2008 and 2011 bathymetry data, I calculate that sand waves migrate from 0 to 3.3 m/yr and have an average migration rate of 1.6 m/yr to the northwest. This migration direction which I directly observe in the bathymetry data is in agreement with the migration direction that I infer from the asymmetry of the sand waves. Integrating these migration rates over the cross section of the sand-wave field, I estimate that sand is transported along the continental slope at a rate of 22.3-118x106 m3/yr. These results provide hard constraints for numerical sand-wave migration models trying to identify the link between ocean currents and sand-wave migration. Furthermore, I show that sand-wave migration has the potential to rapidly move large volumes of sand across the deep water. This movement of sand can complicate drilling and production procedures in the energy industry and may affect slope stability on continental margins around the world.

  URI:

  http://hdl.handle.net/10037/4668

  File(s) in this item: 2

  Errata_MW.pdf   (429.4Kb)

  thesis.pdf   (13.12Mb)
• Holocene sedimentary environments in Smeerenburgfjorden, Spitsbergen

  Velle, Julie Heggdal (Master thesis; Mastergradsoppgave, 15-Nov-2012)

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  Abstract:

  Multi-proxy analyses of six sediment cores (including lithostratigraphy, physical properties, granulometric analyses, and XRF scanning), and analyses of swath bathymetry and chirp data were integrated to elucidate the Holocene sedimentary processes and palaeoenvironments in Smeerenburgfjorden, northwest Spitsbergen. Three basins separated by two sills define the present-day large-scale bathymetry. A transverse ridge in the innermost part of the fjord represents the Little Ice Age (LIA) maximum position of Smeerenburgbreen. Slide scars along the fjord sides and mass transport deposits in the basins indicate repeated mass wasting. Recessional moraines deposited during the last deglaciation suggest a mean annual retreat rate of 140 m/year. Another set of recessional moraines deposited between the maximum LIA position of Smeerenburgbreen and its present day terminus indicate a mean retreat rate of the ice front of ~87 m/year. Although only some of the recessional moraines deposited during the last deglaciation are expressed on the modern seafloor, chirp data reveal that they occur throughout the entire fjord. Suspension settling, ice rafting and mass wasting are the main sedimentary processes acting in Smeerenburgfjorden. Suspension settling is most important in the inner parts of the fjord, resulting in high sedimentation rates that rapidly decrease with increasing distance from the main sediment sources. Strong out-fjord decreasing trends in magnetic susceptibility and Fe-content indicate that these properties are related to material originating from the Hornemantoppen granite in the catchment of Smeerenburgbreen and are, thus, useful proxies for the reconstruction of the activity of the glacier. Relatively little ice rafting, most likely related to warmer surface water conditions, occurred between 8650 and 7350 cal. years BP. Ice rafting from both sea-ice and icebergs increased around 6200 cal. years BP and peaked at ~5200 cal. years BP, associated with a regional cooling. Smeerenburgbreen became more active around 2000 cal. years BP. It probably retreated during the Roman Warm Period (50 BC – AD 400) and advanced during the Dark Ages Cold Period (AD 400 – 800). From AD 1300 – 1500 (late Medieval Warm Period; AD 900 – 1500), ice rafting, sedimentation rates and productivity increased in the inner fjord. The Little Ice Age was characterised by reduced ice rafting, possibly linked to an increased sea-ice cover suppressing iceberg drift. An increase in Ice Rafted Debris (IRD) commencing around AD 1880 is suggested to represent the beginning of Smeerenburgbreen’s retreat from its LIA maximum towards its present position.

  URI:

  http://hdl.handle.net/10037/4650

  File(s) in this item: 1

  thesis.pdf   (12.51Mb)
• 3D seismisk analyse av rasavsetninger fra Sklinnadjupraset på midtre delen av Vøringmarginen

  Fjellaksel, Torgeir (Master thesis; Mastergradsoppgave, 15-Nov-2012)

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  Abstract:

  I denne oppgaven har 3D seismiske data blitt benyttet for å studere den øvre del av Naustformasjonen fra den midtre delen av Vøringmarginen på den midt-norske kontinentalmarginen. Oppgavens hovedfokus har vært å beskrive og tolke paleomiljøet i perioden 0,8 Ma og frem til nåtid med hovedfokus på Sklinnadjuprasets utvikling og genesen av de ulike rasavsetningene i studieområdet. En seismisk stratigrafi er etablert for de tre hovedenhetene Naust U, S og T. Denne er korrelert med publiserte, regionale 2D linjer, som tidligere har blitt benyttet i studier av Naustformasjonen. Den eldste enheten, Naust U, domineres av avsetninger som viser en pålappende intern seismisk signatur, dominert av undulerende, parallelle og kontinuerlige refleksjoner av medium amplitude. Disse avsetningene relateres til et avsetningsmiljø hvor sedimenter trolig har blitt påvirket av havstrømmer under avsetning. Langstrakte hauger tolkes til å være konturitt-driftavsetninger og representerer derved en videreføring av avsetningsmiljøet i den underliggende Kaiformasjonen. Kaiformasjonen har et polygonalt forkastningssystem som trolig også påvirker den overliggende enheten Naust U. Øvre del av enheten Naust U viser ett skifte i sedimentasjonsmiljø, som et resultat av at det Fennoskandiske isdekket avsatte glasigene sedimenter i form av glasiale debrisstrømmer innenfor studieområdet. Naust S inkluderer tykke glasiale debristrømavsetninger med en mektighet på opptil 100 meter. Disse avsetningene er korrelert til Elster glasiasjonen, som markerer den tredje siste glasiale perioden i Skjoldryggen-regionen. Disse avsetningene har blitt utsatt for betraktelig erosjon og remobilisering som kan knyttes til Sklinnadjupraset. Innenfor studieområdet antas raset å ha utviklet seg i fem ulike faser, basert på tilstedeværelsen av gjennomgående skjærsoner som skiller avsetninger med ulike morfologiske og seismiske karakteristika. Interne skjærsoner indikerer et komplekst samspill mellom erosjons- og avsetningsprosesser også innenfor sonene. Den yngste enheten, Naust T, representerer et markant skifte i sedimentasjonsmiljø til hemipelagiske og konturittiske prosesser som helt, eller delvis draperer de underliggende rasavsetningene.

  URI:

  http://hdl.handle.net/10037/4646

  File(s) in this item: 1

  thesis.pdf   (17.80Mb)
• Shallow gas accumulation in glacigenic sedimentary formation of the mid-Norwegian margin north of Storegga slide (Helland Hansen 3D cube)

  Ahmad, Tanveer (Master thesis; Mastergradsoppgave, 25-Jun-2012)

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  Abstract:

  My master thesis concentrates on the distribution of gas accumulation to infer vertical fluid migration in sedimentary formations of Eocene-Oligocene (Brygge Formation) and Pliocene-Pleistocene (Naust Formation) in the mid-Norwegian margin at the Helland Hansen Arch, north of the Storegga slide. The seismic interpretation is based on “Helland Hansen 3D cube SH9602”. The N-S oriented Helland Hansen Arch (HHA) has a hydrocarbon potential where both tectonic and thermal subsidence has played a role in forming hydrocarbon traps. The oozes and debris flow deposit seal off the vertical migrating fluids allowing them to accumulate along the HHA. At the crest of HHA seismic bright spots are delineated by using acoustic attributes. The area beneath the bright spots shows the depletion of higher frequencies due to absorption of seismic energy. Beneath the bright spot vertical fluid migration features appear as disturbed and distorted wipe-out seismic zone and velocity sags (push down). The vertical fluid migration features occur along major faults and are identified by the low coherency values on variance attribute maps. Gas accumulation zones are extensively disturbed by faulting along the eastern flanks of HHA where polygonal faults provide routes for vertical gas migration. The polygonal faults were reactivated by sediment loading from submarine slides. Pipe structures provide further pathways for vertical gas migration from reactivated polygonal faults. The presence of gas in the glacigenic sedimentary formation of Naust A and U unit is identified by the distinct reduction of P-wave velocities.

  URI:

  http://hdl.handle.net/10037/4320

  File(s) in this item: 1

  thesis.pdf   (14.04Mb)

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