EGU General Assembly Conference Abstracts, Apr 1, 2017
The Quaternary strandflat along the Norwegian coast is normally considered to be controlled by co... more The Quaternary strandflat along the Norwegian coast is normally considered to be controlled by combinations of inherited Late Paleozoic-Mesozoic weathering and Quaternary erosion. We demonstrate that 1) the distribution of this important geomorphological element was controlled by the inherited structure of the necking domain and proximal margin and 2) that the width of the strandflat changes with crustal taper and thus reflects the tectonic evolution of the margin from the Paleozoic to present day. In particular, the distribution of the strandflat reflects the structural configuration developed during the phase of deformation coupling. Where coupling structures combine to produce the main breakaway complexes along the margin, structural style will reflect the thickness, rheology and inherited structure of the crust and, tentatively, the efficiency of the coupling process. During deformation coupling, large-magnitude faults cut previously extended crust, resulting in laterally variable footwall uplift and variable erosional incision. Along the Mid-Norwegian margin this led to stacking of incised erosional surfaces along the most sharply tapered margin segments, whereas the footwall uplifts associated with more gently tapered margin segments were characterized by shorter wavelengths. Later Cenozoic uplift rotated earlier incised surfaces and caused coastwards incision by younger ones; the youngest is the so-called Quaternary strandflat. It has been proposed that the strandflat represents, wholly or in part, reworking of a Mesozoic or older basement weathering surface. We show that in sharply tapered margin segments, the preservation potential for such a surface inboard of the basement-sediment contact is controlled by the angle between that surface and the incising strandflat. This angle depends on inherited fault-block tilt, plus or minus the tilt superimposed by Cenozoic uplift. In sharply tapered margin segments, preservation of these old surfaces in the coastal zone is less likely due to more widely distributed Jurassic-Cretaceous footwall uplift and the successive incision of younger surfaces of Cretaceous and Cenozoic age. In some of the sharply tapered margin segments (notably the Møre area), strands of large-magnitude, Jurassic-Cretaceous faults, once the agents of deformation coupling, reach the present-day seafloor, where they constitute the contact between sedimentary rocks and crystalline basement. In these areas, the strandflat does not extend outboard of the faults. Thus, inboard of gently tapered margin segments in the Trøndelag Platform area, the width of the Quaternary strandflat reflects a reworked submesozoic surface whereas inboard of sharply tapered margin segments in the Møre region, it reflects the extent of eroded crystalline rocks in the footwalls of coupling faults.
Dedicated : 'Fluids and Fluid Flow' The southwestern Barents Sea is a large hydrocarbon-p... more Dedicated : 'Fluids and Fluid Flow' The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A significant portion of hydrocarbon gases has leaked/migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The leakage of these fluids through marine sediments, due to glacio-tectonics and denudation, may have controlled the evolution of various sedimentary basins of this region. We analyzed 2D seismic data from the southwestern Barents Sea to identify different fluid flow features and study their relationship with the geological setting. Gas chimneys were the most abundant feature observed. Among the various observed fluid flow features were giant gas chimneys covering large areas, associated shallow gas accumulations and fluid leakage along faults. Fluid flow features were located above deep-seated faults in the area suggesting a relation with tectonic processes and glacial cycles.The amount of net erosion in the area showed no direct relation to the distribution of fluid flow features. This suggests fluid flow in the region is caused mainly by repeated glacial cycles and differential geographic uplift, which caused tilting and spilling of various structural traps in the area, although erosion might have had an added effect.
The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A... more The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A significant portion of hydrocarbon gases has leaked/migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The leakage of these fluids through marine sediments,due to glacio-tectonics and denudation, may have controlled the evolution of various sedimentary basins of this region. We analyzed 2D seismic data from the southwestern Barents Sea to identify different fluid-flow features and study their relationship with the geological setting. Gas chimneys were the most abundant feature observed. Among the various observed fluid-flow features were giant gas chimneys covering large areas,associated shallow gas accumulations and fluid leakage along faults. Fluid-flow features were located above deep-seated faults in the area suggesting a relation with tectonic processes and glacial cycles.The proximity of large gas chimneys with major petroleum discoveries suggest a close link between the fluid flow and petroleum systems. The amount of net erosion in the area showed no direct relation to the distribution of fluid-flow features. The strong correlation between major faults and fluid-flow features suggests that extensional tectonics, glaciations and uplift could have played major roles in the timing and activity of fluid leakage.
Sibelco Nordic's mine on Stjernøya, North Norway, disposes mine tailings into the fjord Stjernsun... more Sibelco Nordic's mine on Stjernøya, North Norway, disposes mine tailings into the fjord Stjernsundet. The tailings, discharged at the shoreline in the bay of Lillebukt, comprise c. 85% fine silt to medium-grained sand (0.01-0.5 mm). Upon discharge of the mine tailings into the fjord, they are redistributed by slides and density currents along major channels with pronounced levees. Multibeam echosounder data show sand waves in the channels, while seabed samples and cores document sand ripples and layers of mud between the sand layers. Mud accumulates outside of the channels on the seabed in Lillebukt and as a thin veneer along the shores to the east and west. The bathymetry data show partly buried slide escarpments and slide deposits, while smaller slide scars are evident in the levees. Three slide events in the tailings are documented of which the most recent occurred 9 th October 2017. Comparison of bathymetry data collected in 2016 and 2018 show changes in bathymetry in the channels of ± 3 m. Slides are partly initiated along fine-grained layers and caused by hypersedimentation. From 60 m depth, one single channel continues down to 100 m, where the sediment transport is along a gully in the steep (45°) bedrock slope down to c. 400 m depth. A sand-dominated submarine fan has accumulated at the foot of the slope, extending to c. 463 m depth. Bathymetric data, seismic data and core analysis show that the fan has a radius of up to 1500 m and covers an area of c. 1.5 km 2 . Comparison of bathymetry data collected in 1998 and 2016 shows that a large part of the tailings disposed of in that 18-year period (4 million tons) have accumulated on the submarine fan.
The Vestnesa Ridge, a gas and gas-hydrate-charged sediment drift on oceanic crust in eastern Fram... more The Vestnesa Ridge, a gas and gas-hydrate-charged sediment drift on oceanic crust in eastern Fram Strait, is the result of the tectonic rifting processes at the North American-Eurasian plate boundary and the initial water mass exchanges between the Nordic Seas and the Arctic Ocean. A revised chronostratigraphic framework with age control based on correlation to ODP Leg 151 holes, constrain the onset of the drift to at least 11 Ma. The drift deposits consist of fine-grained sediments and large quantities of methane stored as marine gas hydrates. The predominant source for the methane is, however, still debated. Potential gas sources may be a mix of biogenic, abiogenic, and thermogenic gas. For the latter, organic-rich Miocene deposits underlying the drift deposits, and leakage of gaseous hydrocarbons from deep-seated reservoirs are debated. The main objective of this study is to carry out a quantitative study on the controlling mechanisms of hydrocarbon migration from potential kitchen areas in the Fram Strait to the leakage points on the Vestnesa Ridge. The study includes the set-up and application of migration modeling techniques by applying the software package Migri to understand potential sources of hydrocarbons, timing of expulsion, and migration pathways towards the seabed. As a baseline for the study, depth converted seismic lines, fault interpretations, borehole data, and other available data are compiled along a 2D line from the central Fram Strait towards the Vestnesa Ridge at a lateral cell resolution of 100 m. Further input to this basin model comprises a siliciclastic lithology set-up at a high vertical resolution that is based on the log-data from ODP Hole 909C. The included Miocene source rock model accounts for lateral and vertical variations of the organic matter quality derived from ODP Hole 909. The results of this modelling study will be a set of gas migration and leakage scenarios that explain the present day gas leakage on the Vestnesa Ridge for either or likely combinations of the three potential gas sources debated and include the Cenozoic basin's history. Besides a best case basin model scenario, most likely (upper 10%) and least likely (lower 10%) estimates on model solution spectrum are derived. These estimates provide information on the sensitivity of the best case solution as they give insight on the range and span of feasible input parameters permitted to explain the present day gas leakage patterns in the study area.
<p>Cold seeps are commonly associated with water column and seabed features. Active... more <p>Cold seeps are commonly associated with water column and seabed features. Active seeps form acoustic flares in the water column and can be detected using data from single or multibeam beam echosounders. They may be associated with pockmarks, but the majority of pockmarks on the Norwegian continental shelf have proven to be inactive. Cold seeps are commonly associated with carbonate crust fields exposed at the seabed. <br>Studies using multibeam echosounder water column data in the Håkjerringdjupet region, underlain by the petroleum province Harstad Basin, have revealed more than 200 active gas flares related to cold seeps. We have studied the seabed around some of these, using the HUGIN HUS AUV equipped with HiSAS 1030 Synthetic Aperture Sonar (SAS) from Kongsberg. The SAS gave a 2 x 150 m wide swath. The primary product is the sonar imagery with a pixel resolution up to c. 3 x 3 cm. For selected areas, bathymetric grids with 20x20 cm grids were produced, giving unrivalled resolution at these water depths. The carbonate crust fields have normally a characteristic appearance, with a low reflectivity and a rugged morphology compared to the surrounding sediments. <br>The interpretation of the acoustic data was verified by visual inspection using the TFish photo system on the AUV, and at a later stage by ROV video footage and physical sampling. The integration of hullborne echosounder data with AUV-mounted acoustic and visual tools provides a very powerful approach for studies of cold seep habitats and related seabed features.<br>An important conclusion from the study is that many pockmarks are not associated with active gas seeps today, and that many of the presently active gas seeps are associated with carbonate crust fields which are readily identifiable from synthetic aperture sonar data.</p>
We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of ... more We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of Vesteralen, northern Norway, to assess (1) hydrocarbon sources, (2) migration pathways and (3) the influence of hydrocarbon seepage on sediment pore water and water column chemistry. The seepage area is characterised by the presence of gas flares in the water column as revealed by hydro acoustic surveys and elevated methane concentrations of up to 42 nM ca. 5 m above the seafloor. Pore water analyses of three gravity cores from the seepage area show varying depths of the sulphate-methane-transition zone (SMTZ) between 80 cm and > 250 cm indicating spatially heterogeneous methane ascent. The isotopic composition of methane (d13C from - 40per mil to - 63per mil and d2H from - 191per mil to - 225per mil) and d13C depth profiles of methane and dissolved inorganic carbon show that the hydrocarbons are predominantly of thermogenic origin, consistent with d13C values of C2 to C4 hydrocarbons...
EGU General Assembly Conference Abstracts, Apr 1, 2017
The Quaternary strandflat along the Norwegian coast is normally considered to be controlled by co... more The Quaternary strandflat along the Norwegian coast is normally considered to be controlled by combinations of inherited Late Paleozoic-Mesozoic weathering and Quaternary erosion. We demonstrate that 1) the distribution of this important geomorphological element was controlled by the inherited structure of the necking domain and proximal margin and 2) that the width of the strandflat changes with crustal taper and thus reflects the tectonic evolution of the margin from the Paleozoic to present day. In particular, the distribution of the strandflat reflects the structural configuration developed during the phase of deformation coupling. Where coupling structures combine to produce the main breakaway complexes along the margin, structural style will reflect the thickness, rheology and inherited structure of the crust and, tentatively, the efficiency of the coupling process. During deformation coupling, large-magnitude faults cut previously extended crust, resulting in laterally variable footwall uplift and variable erosional incision. Along the Mid-Norwegian margin this led to stacking of incised erosional surfaces along the most sharply tapered margin segments, whereas the footwall uplifts associated with more gently tapered margin segments were characterized by shorter wavelengths. Later Cenozoic uplift rotated earlier incised surfaces and caused coastwards incision by younger ones; the youngest is the so-called Quaternary strandflat. It has been proposed that the strandflat represents, wholly or in part, reworking of a Mesozoic or older basement weathering surface. We show that in sharply tapered margin segments, the preservation potential for such a surface inboard of the basement-sediment contact is controlled by the angle between that surface and the incising strandflat. This angle depends on inherited fault-block tilt, plus or minus the tilt superimposed by Cenozoic uplift. In sharply tapered margin segments, preservation of these old surfaces in the coastal zone is less likely due to more widely distributed Jurassic-Cretaceous footwall uplift and the successive incision of younger surfaces of Cretaceous and Cenozoic age. In some of the sharply tapered margin segments (notably the Møre area), strands of large-magnitude, Jurassic-Cretaceous faults, once the agents of deformation coupling, reach the present-day seafloor, where they constitute the contact between sedimentary rocks and crystalline basement. In these areas, the strandflat does not extend outboard of the faults. Thus, inboard of gently tapered margin segments in the Trøndelag Platform area, the width of the Quaternary strandflat reflects a reworked submesozoic surface whereas inboard of sharply tapered margin segments in the Møre region, it reflects the extent of eroded crystalline rocks in the footwalls of coupling faults.
Dedicated : 'Fluids and Fluid Flow' The southwestern Barents Sea is a large hydrocarbon-p... more Dedicated : 'Fluids and Fluid Flow' The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A significant portion of hydrocarbon gases has leaked/migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The leakage of these fluids through marine sediments, due to glacio-tectonics and denudation, may have controlled the evolution of various sedimentary basins of this region. We analyzed 2D seismic data from the southwestern Barents Sea to identify different fluid flow features and study their relationship with the geological setting. Gas chimneys were the most abundant feature observed. Among the various observed fluid flow features were giant gas chimneys covering large areas, associated shallow gas accumulations and fluid leakage along faults. Fluid flow features were located above deep-seated faults in the area suggesting a relation with tectonic processes and glacial cycles.The amount of net erosion in the area showed no direct relation to the distribution of fluid flow features. This suggests fluid flow in the region is caused mainly by repeated glacial cycles and differential geographic uplift, which caused tilting and spilling of various structural traps in the area, although erosion might have had an added effect.
The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A... more The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A significant portion of hydrocarbon gases has leaked/migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The leakage of these fluids through marine sediments,due to glacio-tectonics and denudation, may have controlled the evolution of various sedimentary basins of this region. We analyzed 2D seismic data from the southwestern Barents Sea to identify different fluid-flow features and study their relationship with the geological setting. Gas chimneys were the most abundant feature observed. Among the various observed fluid-flow features were giant gas chimneys covering large areas,associated shallow gas accumulations and fluid leakage along faults. Fluid-flow features were located above deep-seated faults in the area suggesting a relation with tectonic processes and glacial cycles.The proximity of large gas chimneys with major petroleum discoveries suggest a close link between the fluid flow and petroleum systems. The amount of net erosion in the area showed no direct relation to the distribution of fluid-flow features. The strong correlation between major faults and fluid-flow features suggests that extensional tectonics, glaciations and uplift could have played major roles in the timing and activity of fluid leakage.
Sibelco Nordic's mine on Stjernøya, North Norway, disposes mine tailings into the fjord Stjernsun... more Sibelco Nordic's mine on Stjernøya, North Norway, disposes mine tailings into the fjord Stjernsundet. The tailings, discharged at the shoreline in the bay of Lillebukt, comprise c. 85% fine silt to medium-grained sand (0.01-0.5 mm). Upon discharge of the mine tailings into the fjord, they are redistributed by slides and density currents along major channels with pronounced levees. Multibeam echosounder data show sand waves in the channels, while seabed samples and cores document sand ripples and layers of mud between the sand layers. Mud accumulates outside of the channels on the seabed in Lillebukt and as a thin veneer along the shores to the east and west. The bathymetry data show partly buried slide escarpments and slide deposits, while smaller slide scars are evident in the levees. Three slide events in the tailings are documented of which the most recent occurred 9 th October 2017. Comparison of bathymetry data collected in 2016 and 2018 show changes in bathymetry in the channels of ± 3 m. Slides are partly initiated along fine-grained layers and caused by hypersedimentation. From 60 m depth, one single channel continues down to 100 m, where the sediment transport is along a gully in the steep (45°) bedrock slope down to c. 400 m depth. A sand-dominated submarine fan has accumulated at the foot of the slope, extending to c. 463 m depth. Bathymetric data, seismic data and core analysis show that the fan has a radius of up to 1500 m and covers an area of c. 1.5 km 2 . Comparison of bathymetry data collected in 1998 and 2016 shows that a large part of the tailings disposed of in that 18-year period (4 million tons) have accumulated on the submarine fan.
The Vestnesa Ridge, a gas and gas-hydrate-charged sediment drift on oceanic crust in eastern Fram... more The Vestnesa Ridge, a gas and gas-hydrate-charged sediment drift on oceanic crust in eastern Fram Strait, is the result of the tectonic rifting processes at the North American-Eurasian plate boundary and the initial water mass exchanges between the Nordic Seas and the Arctic Ocean. A revised chronostratigraphic framework with age control based on correlation to ODP Leg 151 holes, constrain the onset of the drift to at least 11 Ma. The drift deposits consist of fine-grained sediments and large quantities of methane stored as marine gas hydrates. The predominant source for the methane is, however, still debated. Potential gas sources may be a mix of biogenic, abiogenic, and thermogenic gas. For the latter, organic-rich Miocene deposits underlying the drift deposits, and leakage of gaseous hydrocarbons from deep-seated reservoirs are debated. The main objective of this study is to carry out a quantitative study on the controlling mechanisms of hydrocarbon migration from potential kitchen areas in the Fram Strait to the leakage points on the Vestnesa Ridge. The study includes the set-up and application of migration modeling techniques by applying the software package Migri to understand potential sources of hydrocarbons, timing of expulsion, and migration pathways towards the seabed. As a baseline for the study, depth converted seismic lines, fault interpretations, borehole data, and other available data are compiled along a 2D line from the central Fram Strait towards the Vestnesa Ridge at a lateral cell resolution of 100 m. Further input to this basin model comprises a siliciclastic lithology set-up at a high vertical resolution that is based on the log-data from ODP Hole 909C. The included Miocene source rock model accounts for lateral and vertical variations of the organic matter quality derived from ODP Hole 909. The results of this modelling study will be a set of gas migration and leakage scenarios that explain the present day gas leakage on the Vestnesa Ridge for either or likely combinations of the three potential gas sources debated and include the Cenozoic basin's history. Besides a best case basin model scenario, most likely (upper 10%) and least likely (lower 10%) estimates on model solution spectrum are derived. These estimates provide information on the sensitivity of the best case solution as they give insight on the range and span of feasible input parameters permitted to explain the present day gas leakage patterns in the study area.
<p>Cold seeps are commonly associated with water column and seabed features. Active... more <p>Cold seeps are commonly associated with water column and seabed features. Active seeps form acoustic flares in the water column and can be detected using data from single or multibeam beam echosounders. They may be associated with pockmarks, but the majority of pockmarks on the Norwegian continental shelf have proven to be inactive. Cold seeps are commonly associated with carbonate crust fields exposed at the seabed. <br>Studies using multibeam echosounder water column data in the Håkjerringdjupet region, underlain by the petroleum province Harstad Basin, have revealed more than 200 active gas flares related to cold seeps. We have studied the seabed around some of these, using the HUGIN HUS AUV equipped with HiSAS 1030 Synthetic Aperture Sonar (SAS) from Kongsberg. The SAS gave a 2 x 150 m wide swath. The primary product is the sonar imagery with a pixel resolution up to c. 3 x 3 cm. For selected areas, bathymetric grids with 20x20 cm grids were produced, giving unrivalled resolution at these water depths. The carbonate crust fields have normally a characteristic appearance, with a low reflectivity and a rugged morphology compared to the surrounding sediments. <br>The interpretation of the acoustic data was verified by visual inspection using the TFish photo system on the AUV, and at a later stage by ROV video footage and physical sampling. The integration of hullborne echosounder data with AUV-mounted acoustic and visual tools provides a very powerful approach for studies of cold seep habitats and related seabed features.<br>An important conclusion from the study is that many pockmarks are not associated with active gas seeps today, and that many of the presently active gas seeps are associated with carbonate crust fields which are readily identifiable from synthetic aperture sonar data.</p>
We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of ... more We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of Vesteralen, northern Norway, to assess (1) hydrocarbon sources, (2) migration pathways and (3) the influence of hydrocarbon seepage on sediment pore water and water column chemistry. The seepage area is characterised by the presence of gas flares in the water column as revealed by hydro acoustic surveys and elevated methane concentrations of up to 42 nM ca. 5 m above the seafloor. Pore water analyses of three gravity cores from the seepage area show varying depths of the sulphate-methane-transition zone (SMTZ) between 80 cm and > 250 cm indicating spatially heterogeneous methane ascent. The isotopic composition of methane (d13C from - 40per mil to - 63per mil and d2H from - 191per mil to - 225per mil) and d13C depth profiles of methane and dissolved inorganic carbon show that the hydrocarbons are predominantly of thermogenic origin, consistent with d13C values of C2 to C4 hydrocarbons...
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