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Jurgen Mienert - One of the best experts on this subject based on the ideXlab platform.
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repeated Fluid Expulsion through sub seabed chimneys offshore norway in response to glacial cycles
Earth and Planetary Science Letters, 2011Co-Authors: Andreia Plazafaverola, Stefan Bunz, Jurgen MienertAbstract:Abstract Focused Fluid flow through sub-seabed sediments is a common phenomenon on continental margins worldwide. However, the governing controls and timing of this Fluid release have been difficult to understand, in particular, for Fluid flow features buried beneath sub-surface sediments. A link between Fluid flow activity, ensuing pockmark formation and the last glacial maximum has been hypothesized on the formerly glaciated Norwegian margin. New high-resolution P-Cable 3D seismic data from the Nyegga area on the mid-Norwegian margin reveal at least two more periods of Fluid Expulsion from sub-seabed sediments. The 3D seismic data show depositional patterns within chimney features, expressed as truncations of seismic horizons against the flanks of the chimneys. The truncations are interpreted, by analogy with present day observations, as evidence for buried carbonate mounds and/or sediment wash-out during formation of pockmarks in the past. The truncations are, hence, an indicator and a chronological marker for Fluid Expulsion in the past. The classification of chimneys results in three major groups: (1) chimneys that have been formed and consecutively reactivated one or two times during the last 200 kyr and that have a Fluid flow expression at the present seafloor; (2) chimneys that are approx. 125–160 ka BP old without any associated Fluid-flow expression at the present day seafloor; (3) chimneys with no stratigraphical evidence for reactivation formed after the last glacial maximum (18–25 ka BP). The observations suggest that each activity period was likely related to the last stages of maximum glaciations in the region. The emplacement of thick sequences of glacigenic debris flow deposits during these maximum stages most likely caused rapid increase in overpressure and subsequently the formation of focused Fluid flow features piercing through sediments of the Naust formation at Nyegga.
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three dimensional seismic analysis of the morphology and spatial distribution of chimneys beneath the nyegga pockmark field offshore mid norway
Basin Research, 2009Co-Authors: Steinar Hustoft, Stefan Bunz, Jurgen MienertAbstract:Three-dimensional (3D) seismic data analysis has identified 415 seismic chimneys in the Nyegga area, on the mid-Norwegian continental margin. The majority of the seismic chimneys connect with pockmarks at the modern seafloor, suggesting that the seismic chimneys represent the acoustic imprint of highly focused, cross-stratal Fluid flow. A semi-quantitative spatial analysis of the seismic chimney complex, measuring parameters describing the dimension, geometry and root zone, provides constraints on the geological controls on chimney formation. Most of the seismic chimneys in the Nyegga region descriptively fall into the categories of ‘blowout chimneys’, because they diagnostically link to topography-controlled leakage locations within strata showing acoustic indications of free gas. We find that approximately 60% of the Fluid-escape chimneys emanate from free gas layers below the gas hydrate stability zone. The timing of highly focused Fluid Expulsion through chimneys and the formation of the Nyegga pockmark field postdate the last glacial maximum at 25 000 years before present.
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effects of rapid sedimentation on developing the nyegga pockmark field constraints from hydrological modeling and 3 d seismic data offshore mid norway
Geochemistry Geophysics Geosystems, 2009Co-Authors: Steinar Hustoft, Brandon Dugan, Jurgen MienertAbstract:[1] Three-dimensional (3-D) seismic data in the Nyegga region expose hundreds of seafloor pockmarks and Fluid escape chimneys in close proximity to the northern sidewall of the Storegga Slide, on the formerly glaciated Norwegian margin. As the up to 350 m wide individual craters of the Nyegga pockmark field postdate the Late Glacial Maximum (∼25 calendar (cal) ka B.P.) and because modern Fluid flux is characterized as microseepage at most, it appears that the pockmarks developed nearly simultaneously with some specific event. External types of forcing such as earthquake loading, the Storegga Slide (8.1 cal ka B.P.), or rapid sediment loading represent potential trigger mechanisms for developing hundreds of pockmarks within a millennial time window. We integrate the 3-D seismic observations with a two-dimensional (2-D) sedimentation–Fluid flow model to quantify the effects of sediment loading and erosion on overpressure generation and Fluid Expulsion. The models simulate the temporal evolution of compaction-driven overpressure and Fluid Expulsion based on sedimentation rates estimated from seismic data and hydrologic and sediment properties obtained from laboratory experiments and petrophysical data. The 2-D model predicts rapid overpressure generation in response to high sedimentation rates during the last (Weichselian) deglaciation period (25–18 cal ka B.P.). The high pressures significantly increase Fluid Expulsion, which peaks between 19 and 16 cal ka B.P. The modeled high-flux period and the following declining flux period exhibit an excellent correlation with existing age dates of methane-derived authigenic carbonate retrieved from Nyegga pockmarks. Accordingly, rapid sediment loading provides a mechanism to drive extensive cold seep formation. Our model suggests that the Nyegga pockmark field developed between 19 and 16 cal ka B.P. and therefore predates the giant Storegga Slide event.
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the fugloy reef at 70 n acoustic signature geologic geomorphologic and oceanographic setting
International Journal of Earth Sciences, 2007Co-Authors: Bjorn Lindberg, Christian Berndt, Jurgen MienertAbstract:This is the first in-depth study of a cluster of cold-water coral reefs, the Fugloy Reefs, found at 70°N on the Norwegian margin. Combining high-resolution seismic reflection data, side-scan sonar, video-images, and oceanographic measurements reveals the geologic, geomorphologic and oceanographic setting in which the reefs occur. The reefs consist mainly of the scleractinian ahermatypic Lophelia pertusa, and exist below the thermocline at water depths between 140 m and 190 m. The reefs appear as cone-shaped, acoustically transparent features on seismic reflection data, consistently located in places characterized by the availability of hard substrate, high relief, and periodical exposure to high tidal currents (>30 cm/s). These currents transport water of the Norwegian Atlantic Current to the reefs from an area with Fluid Expulsion-related pockmarks. The spatial relationship between reef, pockmark locations, and current directions suggests that seepage of biogenic gas might be a catalyst to reef growth. With a height of more than 40 m some of the Fugloy reefs are among the highest reported from the Norwegian Margin. This indicates highly favourable growth conditions, and conservative estimates indicate a net growth rate for the reefs of ~5 mm/year. We expect that cold-water reefs will be found further north along the Barents Sea margin as general awareness on the geophysical signature and appearance of the reefs increases, because all known factors involved in reef establishment and growth are within the required intervals also further north.
Daniel L Orange - One of the best experts on this subject based on the ideXlab platform.
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widespread Fluid Expulsion on a translational continental margin mud volcanoes fault zones headless canyons and organic rich substrate in monterey bay california
Geological Society of America Bulletin, 1999Co-Authors: Daniel L Orange, Gary H Greene, Don Reed, Jonathan B Martin, C M Mchugh, William B F Ryan, Norman Maher, Debra S StakesAbstract:Remotely operated vehicle (ROV)-based mapping of tectonic features, zones of anomalous reflectivity, and geomorphic targets in Monterey Bay, California, demonstrates the regional abundance of Fluid Expulsion along the active transform margin between the Pacific and North American plates. Cold seeps—extant communities characterized by chemosynthetic bivalves, bacterial mats, and rare tubeworms—are the surface manifestations of present-day Fluid Expulsion of sulfide- and methane-rich Fluids, whereas slabs, veins, and chimneys of authigenic carbonate represent regions of either dormant methane-rich Fluid Expulsion, or areas where the present rate of flow is too low to support chemosynthetic fauna. We have found both active and dormant Fluid seepage along fault zones, at the surface expression of mud volcanoes, on organic-rich or permeable substrate, and within headless canyons across a wide range of depths within Monterey Bay. The Fluid egress at these sites may be driven by a combination of (1) pore-space reduction caused by rapid sedimentation and/or tectonic compaction related to residual Pacific–North America compression, and (2) increased buoyancy due to a decrease in pore-Fluid density related to diagenesis and/or catagenesis at depth. Although provocative, the relationship between topographically driven aquifer discharge and sea-floor Fluid Expulsion remains speculative for Monterey Bay. The widespread distribution of Fluid Expulsion features controlled by a variety of conduits in Monterey Bay implies that cold seeps may be common features on translational margins.
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surficial evidence of Fluid Expulsion from the costa rica accretionary prism
Geophysical Research Letters, 1996Co-Authors: L M Kahn, Daniel L Orange, Eli A Silver, R Kochevar, Brian G McadooAbstract:The nature and distribution of authigenic carbonates, chemosynthetic bacterial mats, and unique macrobenthic chemosynthetic communities of bivalves and tube worms are important for evaluating and reconstructing present and past Fluid venting of accretionary complexes. This paper describes the authigenic carbonates, chemosynthetic fauna, and Fluid venting observed at the four tectonic regions of the Costa Rica accretionary wedge in February 1994 during an ALVIN diving program of 20 submersible dives. We found no surficial evidence of highly focused Fluid venting at the toe of the prism (outermost 3 km), as implied by the absence of authigenic carbonates and chemosynthetic fauna. The absence of vent communities on the lower 3 km of the prism and the relatively elevated heat flow with respect to the adjacent, incoming Cocos plate (Langseth and Silver, this issue), suggests diffuse, rather than focused flow through the toe of the prism. Twelve active and relict vent sites marked by small clusters of live vesicomyid clams are localized at the bases and tops of out-of-sequence-thrusts, implicating fracture permeability as the Fluid conduit in the lower slope region (but upslope from the toe). Vast authigenic carbonates and seven active and relict vent sites marked by large, dense clusters of chemosynthetic organisms predominate the largest mud diapir in the mid-slope region. Fluid Expulsion appears to be more restricted on the upper slope, with only 2 small but dense vents marked by chemosynthetic fauna observed at one wall of one canyon.
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ROV observation of Fluid Expulsion in Monterey Bay, California
AAPG Bulletin, 1996Co-Authors: Daniel L Orange, James P. Barry, N. MaherAbstract:ROV dives in Monterey Bay have been used to examine the relationship of Fluid flow to tectonic and stratigraphic conduits along an active transpressional continental margin. We used side-scan sonar to identify dive targets for the ROV, since anomalous reflectivity can be caused by the presence of biological [open quote]cold seep[close quotes] communities or authigenic carbonate. On a compressional ridge west of the San Gregorio Fault, cold seep clams are found along with extensive fields of authigenic carbonate in an elliptical region of anomalous reflectivity [approximately]400m in diameter. The reflectivity and Fluid Expulsion suggest that this feature is an active mud volcano. Analyses of push cores from the ridge site indicate high concentrations of both methane and sulfide and the presence of higher-order hydrocarbons. Many carbon isotopic ratios of the carbonate crusts indicate a methane carbon source; some values represent a mixture of methane carbon and normal marine carbon. Fluids charging the seeps west of the San Gregorio Fault may originate in tectonically-compacted sediments affected by residual Pacific-North America plate convergence, and may have an additional component of hydrocarbon charging from the underlying Monterey Formation. At the intersection of the Monterey Fault Zone and the Monterey Canyon a number ofmore » cold seeps occur in headless side canyons characterized by intense fracturing. This supports the hypothesis that submarine canyons act as hydrologic sinks for any overpressured Fluid flowing toward the surface. On the San Gregorio Fault itself we have found in echelon ridges of carbonate. The Fluids seeping out along fault zones may originate deep in the section and utilize the deformation-induced fracture permeability of the fault zone. Alternatively, aquifer-forcing from the uplifted Santa Cruz Mountains may provide a source of Fluids venting along these fault zones (aquicludes ) and at seeps east of the fault zones.« less
Earl E Davis - One of the best experts on this subject based on the ideXlab platform.
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permeability of a decollement zone results from a two well experiment in the barbados accretionary complex
Journal of Geophysical Research, 2000Co-Authors: Elizabeth J Screaton, Bobb Carson, Earl E Davis, Keir BeckerAbstract:Fault zones are hypothesized to play a major role in focusing Fluid Expulsion from accretionary complexes. A small number of previous investigations have examined the hydrogeologic properties of these fault zones using borehole packer or submersible-based slug and constant rate flow tests. While these single-well experiments yielded the first data on the permeability of active fault zones, they could only investigate a small area around the borehole and could not ensure reliable determination of formation storage properties. Recent data from an unplanned experiment in the decollement zone of the Barbados accretionary prism demonstrate the potential for multiple-well hydrogeologic tests. Pressure data from a sealed borehole show a clear signal of drilling activity ∼45 m away. Analysis of the pressure response suggests that decollement zone permeability lies between 1.0 and 1.2 x 10 -14 m 2 . This permeability is ∼2-4 orders of magnitude greater than overlying and underlying sediment and thus appears sufficient to focus Fluid flow along the decollement zone. This inadvertent test evaluated fault zone hydrogeologic parameters over a larger radius and longer timescale and at pressures closer to in situ than previous single-well tests.
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Thermal effects of sediment thickening and Fluid Expulsion in accretionary prisms: Model and parameter analysis
Journal of Geophysical Research, 1993Co-Authors: K. Wang, Roy D. Hyndman, Earl E DavisAbstract:We investigate the thermal consequences of sediment thickening and Fluid Expulsion in subduction zone accretionary prisms using a model where the rate of Fluid Expulsion in a uniformly thickening wedge is obtained analytically and the Fluid flow and temperature fields are computed numerically. Variations landward across the wedge in the porosity-depth function are included in the model. The most important contribution to the thermal regime arises from the thickening of the wedge, which can reduce the heat flow at the seafloor relative to the deep lithospheric heat flow by up to a few tens of percent. This effect is countered by an opposite but lesser contribution of the heat advected upward by the Fluid expelled from the reconsolidating sediments. The total thermal perturbation is sensitive to the prism taper angle, the incoming sediment thickness, and the convergence velocity. Anomalously low seismic velocities observed in a zone several tens of kilometers wide near the toe of some accretionary prisms suggest that there is a delay between the initial thickening of the sediment section and reconsolidation toward equilibrium porosity at depth. The thermal consequences of retarded Fluid Expulsion are significant, and result in locally depressed seafloor heat flow in this region. For the full observed range of accretion parameters, the rates of Fluid Expulsion are not sufficient to cause a detectable depth variation in heat flow on a depth scale of less than 1 km.
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a mechanism for the formation of methane hydrate and seafloor bottom simulating reflectors by vertical Fluid Expulsion
Journal of Geophysical Research, 1992Co-Authors: R D Hyndman, Earl E DavisAbstract:Bottom-simulating reflectors (BSR) are observed commonly at a depth of several hundred meters below the seafloor in continental margin sedimentary sections that have undergone recent tectonic consolidation or rapid accumulation. They are believed to correspond to the deepest level at which methane hydrate (clathrate) is stable. We present a model in which BSR hydrate layers are formed through the removal of methane from upward moving pore Fluids as they pass into the hydrate stability field. In this model, most of the methane is generated below the level of hydrate stability, but not at depths sufficient for significant thermogenic production; the methane is primarily biogenic in origin. The model requires either a mechanism to remove dissolved methane from the pore Fluids or disseminated free gas carried upward with the pore Fluid. The model accounts for the evidence that the hydrate is concentrated in a layer at the base of the stability field, for the source of the large amount of methane contained in the hydrate, and for BSRs being common only in special environments. Strong upward Fluid Expulsion into the hydrate stability field does not occur in normal sediment depositional regimes, so BSRs are uncommon. Upward Fluid Expulsion does occur as a result of tectonic thickening and loading in subduction zone accretionary wedges and in areas where rapid deposition results in initial undercconsolidation. In these areas hydrate BSRs are common. The most poorly quantified aspect of the model is the efficiency with which methane is removed and hydrate is formed as pore Fluids pass into the hydrate stability field. The critical boundary in the phase diagram between the Fluid-plus-hydrate and Fluid-only fields is not well constrained. However, the amount of methane required to form the hydrate and limited data on methane concentrations in pore Fluids from deep-sea boreholes suggest very efficient removal of methane from rising Fluid that may contain less than the amount required for free gas production. In most Fluid Expulsion regimes, the quantity of Fluid moved upward to the seafloor is great enough to continually remove the excess chloride and the residue of isotope fractionation resulting from hydrate formation. Thus, as observed in borehole data, there are no large chloride or isotope anomalies remaining in the local pore Fluids. The differences in the concentration of methane and probably of CO2 in the pore Fluid above and below the base of the stability field may have a significant influence on early sediment diagenetic reactions.
Marco Bonini - One of the best experts on this subject based on the ideXlab platform.
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investigating earthquake triggering of Fluid seepage systems by dynamic and static stresses
Earth-Science Reviews, 2020Co-Authors: Marco BoniniAbstract:Abstract Earthquakes can occasionally trigger the eruption or increase the activity of mud volcanoes and other Fluid seepage systems. One long pending question is how static and dynamic stress changes can trigger eruptions of Fluid Expulsion features and modulate their activity. This study addresses the potential role of static and dynamic stress changes by investigating some well documented examples of triggered historical and recent eruptions in the Northern Apennines (Italy) and partly Azerbaijan. Peak dynamic stress at triggered Fluid Expulsion features has been estimated using measured PGV, or PGV estimated from attenuation relationships. The results suggest that seepage features are often triggered by dynamic stress changes created by earthquake faults located in the intermediate- to far-field. Paroxysmal activity of the considered Fluid Expulsion systems was influenced by minimum dynamic stress thresholds ranging from approximately 30–50 kPa to 15 kPa. Regarding co-seismic static stress changes, their magnitude can be large enough to dilate fault-controlled Fluid pathways located in the near-field of a ruptured fault. This may be the case of the Pede-Apennine thrust (in northern Italy), which ruptured in 1501 (Mw ~6) beneath many mud volcanoes. Apart from this case, the considered Fluid Expulsion systems that responded to the earthquakes were stressed by negligible or subordinate changes in static stress, with few exceptions. Earthquake-related stresses have the ability to influence the eruptive activity of Fluid seepage systems, but the recovery time between two consecutive eruptions is usually irregular. This variability in the repose time suggests that the achievement of a critical or trigger-able state is governed by a complex interplay among independent factors (e.g., production rate of driving gases, plumbing system characteristics, frequency of triggering earthquakes).
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Seismic loading of fault-controlled Fluid seepage systems by great subduction earthquakes
Scientific Reports, 2019Co-Authors: Marco BoniniAbstract:Various types of Fluid Expulsion features (mud volcanoes, pockmarks, authigenic carbonate mounds and associated gas pipes, etc.) are often found above subduction zones, which have the highest seismic potential on Earth. Faults potentially control the liberation of deep-seated greenhouse gases into the feeder systems of seepage features located above subduction thrusts. These feeder systems could be stressed by large earthquakes, yet the mechanisms that can drive episodic mobilization of stored hydrocarbon gases remain poorly understood. Here I address the potential stress loading on Fluid Expulsion systems created by past earthquakes nucleated at both accretionary and erosive subduction margins. The most significant effects occur in the epicentral area where subduction earthquakes can produce normal stress changes as high as 20–100 bar, although these are generally restricted to relatively small regions. Coseismic normal stress changes and elastic strain relaxation upon a ruptured subduction thrust could increase crustal permeability by dilating fault-controlled conduits, and channelling Fluids to the seafloor. Fluid pressure pulses released during subduction earthquakes can greatly contribute to the rupture of Fluid pathways that have been brought closer to failure from coseismic static stress changes, although the inaccessible location of most submarine seepage systems has so far hampered probing these relationships.
Steinar Hustoft - One of the best experts on this subject based on the ideXlab platform.
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three dimensional seismic analysis of the morphology and spatial distribution of chimneys beneath the nyegga pockmark field offshore mid norway
Basin Research, 2009Co-Authors: Steinar Hustoft, Stefan Bunz, Jurgen MienertAbstract:Three-dimensional (3D) seismic data analysis has identified 415 seismic chimneys in the Nyegga area, on the mid-Norwegian continental margin. The majority of the seismic chimneys connect with pockmarks at the modern seafloor, suggesting that the seismic chimneys represent the acoustic imprint of highly focused, cross-stratal Fluid flow. A semi-quantitative spatial analysis of the seismic chimney complex, measuring parameters describing the dimension, geometry and root zone, provides constraints on the geological controls on chimney formation. Most of the seismic chimneys in the Nyegga region descriptively fall into the categories of ‘blowout chimneys’, because they diagnostically link to topography-controlled leakage locations within strata showing acoustic indications of free gas. We find that approximately 60% of the Fluid-escape chimneys emanate from free gas layers below the gas hydrate stability zone. The timing of highly focused Fluid Expulsion through chimneys and the formation of the Nyegga pockmark field postdate the last glacial maximum at 25 000 years before present.
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effects of rapid sedimentation on developing the nyegga pockmark field constraints from hydrological modeling and 3 d seismic data offshore mid norway
Geochemistry Geophysics Geosystems, 2009Co-Authors: Steinar Hustoft, Brandon Dugan, Jurgen MienertAbstract:[1] Three-dimensional (3-D) seismic data in the Nyegga region expose hundreds of seafloor pockmarks and Fluid escape chimneys in close proximity to the northern sidewall of the Storegga Slide, on the formerly glaciated Norwegian margin. As the up to 350 m wide individual craters of the Nyegga pockmark field postdate the Late Glacial Maximum (∼25 calendar (cal) ka B.P.) and because modern Fluid flux is characterized as microseepage at most, it appears that the pockmarks developed nearly simultaneously with some specific event. External types of forcing such as earthquake loading, the Storegga Slide (8.1 cal ka B.P.), or rapid sediment loading represent potential trigger mechanisms for developing hundreds of pockmarks within a millennial time window. We integrate the 3-D seismic observations with a two-dimensional (2-D) sedimentation–Fluid flow model to quantify the effects of sediment loading and erosion on overpressure generation and Fluid Expulsion. The models simulate the temporal evolution of compaction-driven overpressure and Fluid Expulsion based on sedimentation rates estimated from seismic data and hydrologic and sediment properties obtained from laboratory experiments and petrophysical data. The 2-D model predicts rapid overpressure generation in response to high sedimentation rates during the last (Weichselian) deglaciation period (25–18 cal ka B.P.). The high pressures significantly increase Fluid Expulsion, which peaks between 19 and 16 cal ka B.P. The modeled high-flux period and the following declining flux period exhibit an excellent correlation with existing age dates of methane-derived authigenic carbonate retrieved from Nyegga pockmarks. Accordingly, rapid sediment loading provides a mechanism to drive extensive cold seep formation. Our model suggests that the Nyegga pockmark field developed between 19 and 16 cal ka B.P. and therefore predates the giant Storegga Slide event.