IODP Expedition 328: Early Results of Cascadia Subduction Zone ACORK Observatory

Integrated Ocean Drilling Program (IODP) Expedition 328 was devoted to the installation of an "Advanced CORK" (Circulation Obviation Retrofit Kit) in the Cascadia subduction zone accretionary prism to observe the physical state and properties of the formation as they are influenced by long-term and episodic deformation and by gas hydrate accumulation. Pressures are monitored at four levels on the outside of a standard 10 3/4-inch casing string, two above and two below the base of the gas-hydrate stability zone at 230 mbsf (m below seafloor). The casing was sealed at the bottom, leaving the inside open down to 302 mbsf for installation of a tilt meter, seismometer, and thermistor cable (scheduled for 2013). The initial data, recovered in July 2011, document an initially smooth recovery from the drilling perturbation followed by what may be a sequence of hole-collapse events. Pressure at the deepest screen is roughly 40 kPa above hydrostatic; higher pressures (80 kPa) are observed at the two screens close to the level of hydrate stability. Tidal variations at the deepest screen are in phase with ocean tides, and define a loading efficiency of 0.6, which is reasonable in light of the consolidation state of the for-mation (porosity ~0.5). Tidal signals near the level of gas hydrate stability display large phase lags, probably as a consequence of hydraulic diffusion stimulated by the large contrast in interstitial fluid compressibility at the gas-hydrate boundary. The degree of isolation among the screens, the anticipated good coupling, and the estimated strain-to-pressure conversion efficiency (~5 kPa μstrain−1) indicate that this installation will serve well to host a variety of hydrologic, seismic, and geodynamic experiments. doi:<a href="http://dx.doi.org/10.2204/iodp.sd.13.02.2011" target="_blank">10.2204/iodp.sd.13.02.2011</a>

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Authigenic carbonates from the Cascadia subduction zone and their relation to gas hydrate stability

Geology ◽

10.1130/0091-7613(1998)026<0647:acftcs>2.3.co;2 ◽

1998 ◽

Vol 26 (7) ◽

pp. 647 ◽

Cited By ~ 289

Author(s):

Gerhard Bohrmann ◽

Jens Greinert ◽

Erwin Suess ◽

Marta Torres

Keyword(s):

Subduction Zone ◽

Gas Hydrate ◽

Cascadia Subduction Zone ◽

Authigenic Carbonates ◽

Hydrate Stability

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A Long-Term Geothermal Observatory Across Subseafloor Gas Hydrates, IODP Hole U1364A, Cascadia Accretionary Prism

Frontiers in Earth Science ◽

10.3389/feart.2020.568566 ◽

2020 ◽

Vol 8 ◽

Author(s):

Keir Becker ◽

Earl E. Davis ◽

Martin Heesemann ◽

John A. Collins ◽

Jeffrey J. McGuire

Keyword(s):

Control Unit ◽

Accretionary Prism ◽

Temperature Data ◽

Cascadia Subduction Zone ◽

Pressure Monitoring ◽

Linear Temperature ◽

Bottom Simulating Reflector ◽

Thermal Transients ◽

Integrated Ocean Drilling Program ◽

Hydrate Stability

We report 4 years of temperature profiles collected from May 2014 to May 2018 in Integrated Ocean Drilling Program Hole U1364A in the frontal accretionary prism of the Cascadia subduction zone. The temperature data extend to depths of nearly 300 m below seafloor (mbsf), spanning the gas hydrate stability zone at the location and a clear bottom-simulating reflector (BSR) at ∼230 mbsf. When the hole was drilled in 2010, a pressure-monitoring Advanced CORK (ACORK) observatory was installed, sealed at the bottom by a bridge plug and cement below 302 mbsf. In May 2014, a temperature profile was collected by lowering a probe down the hole from the ROV ROPOS. From July 2016 through May 2018, temperature data were collected during a nearly two-year deployment of a 24-thermistor cable installed to 268 m below seafloor (mbsf). The cable and a seismic-tilt instrument package also deployed in 2016 were connected to the Ocean Networks Canada (ONC) NEPTUNE cabled observatory in June of 2017, after which the thermistor temperatures were logged by Ocean Networks Canada at one-minute intervals until failure of the main ethernet switch in the integrated seafloor control unit in May 2018. The thermistor array had been designed with concentrated vertical spacing around the bottom-simulating reflector and two pressure-monitoring screens at 203 and 244 mbsf, with wider thermistor spacing elsewhere to document the geothermal state up to seafloor. The 4 years of data show a generally linear temperature gradient of 0.055°C/m consistent with a heat flux of 61–64 mW/m2. The data show no indications of thermal transients. A slight departure from a linear gradient provides an approximate limit of ∼10−10 m/s for any possible slow upward advection of pore fluids. In-situ temperatures are ∼15.8°C at the BSR position, consistent with methane hydrate stability at that depth and pressure.

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Gas hydrate destabilization and sea-level changes: insights from Miocene seep carbonate deposits of the northern Apennines (Italy)

10.5194/egusphere-egu21-8529 ◽

2021 ◽

Author(s):

Daniela Fontana ◽

Stefano Conti ◽

Chiara Fioroni ◽

Claudio Argentino

Keyword(s):

Sea Level ◽

Gas Hydrate ◽

Leading Edge ◽

Accretionary Prism ◽

Northern Apennines ◽

Hydraulic Pressure ◽

Continental Margins ◽

Sea Level Changes ◽

Level Lowering ◽

Hydrate Stability

The effects of global warming on marine gas hydrate stability along continental margins is still unclear and discussed within the scientific community. Long-term datasets can be obtained from the geological record and might help us better understand how gas-hydrate reservoirs responds to climate changes. Present-day gas hydrates are frequently associated or interlayered with authigenic carbonates, called clathrites, which have been sampled from many continental margins worldwide. These carbonates show peculiar structures, such as vacuolar or vuggy-like fabrics, and are marked by light &#948;13C and heavy &#948;18O isotopic values. Evidences of paleo-gas hydrate occurrence are recorded in paleo-clathrites hosted in Miocene deposits of the Apennine chain, Italy, and formed in different positions of the paleo foreland system: in wedge-top basins, along the outer slope of the accretionary prism, and at the leading edge of the deformational front. The accurate nannofossil biostratigraphy of sediment hosting paleo-clathrites in the northern Apennines allowed us to ascribe them to different Miocene nannofossil zones, concentrated in three main intervals: in the Langhian (MNN5a), in the upper Serravallian-lower Tortonian (MNN6b-MNN7) and the upper Tortonian-lowermost Messinian (MNN10-MNN11). By comparing paleo-clathrite distributions with 3rd order eustatic curves, they seem to match phases of sea-level lowering associated with cold periods. Therefore, we suggest that the drop in the hydraulic pressure on the plumbing system during sea-level lowering shifted the bottom of the gas hydrate stability zone to shallower depths, inducing paleo gas-hydrate destabilization. The uplift of the different sectors of the wedge-top foredeep system during tectonic migration might have amplified the effect of the concomitant eustatic sea-level drop, reducing the hydrostatic load on the seafloor and triggering gas-hydrate decomposition. We suggest that Miocene climate-induced sea-level changes played a role in controlling gas hydrate stability and methane emissions along the northern Apennine paleo-wedge, with hydrate destabilization roughly matching with sea-level drops and cooling events.&#160;

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