Physical properties and core-log seismic integration from drilling at the Danube deep-sea fan, Black Sea

Riedel, Michael; Freudenthal, Tim; Bergenthal, Markus; Haeckel, Matthias; Wallmann, Klaus; Spangenberg, Erik; Bialas, Jörg; Bohrmann, Gerhard

doi:10.1016/j.marpetgeo.2019.104192

Cited by 32 publications

(38 citation statements)

References 8 publications

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“…As a result, the BGHSZ moves more slowly in sediments with lower permeability. In three MeBo drilling sites, Riedel et al (2020) describe “sand layers several millimeters in thickness” as “typical” in the deeper units, between 45 and 140 mbsf. The analysis of long‐piston cores also shows the presence of sandy layers of thickness increasing with depth (Martinez‐Lamas et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

“…The prerequisite of such variability is a rapid alternation between marine and lacustrine sequences. Such a rapid alternation has never been documented and has not been reported from borehole data (Calvert & Batchelor, 1978;Riedel et al, 2020). In addition, the sharp boundaries required seem unrealistic, as salt diffusion would have occurred since sedimentation, even in the least permeable layers.…”

Section: In a Transient State Systemmentioning

confidence: 96%

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Irregular BSR: Evidence of an Ongoing Reequilibrium of a Gas Hydrate System

Colin

Ker

Riboulot

et al. 2020

Geophysical Research Letters

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Gas hydrate (GH) systems constitute methane sinks sensitive to environmental changes such as pressure, temperature, and salinity. It remains a matter of debate as to whether the large GH system of the Black Sea has reached a steady state since the last glacial maximum (LGM). We report on an irregular free gas distribution in specific sediment layers marking an irregular bottom-simulating reflector (BSR). This anomalous free gas distribution revealed by very high resolution seismic images, acquired by a deep-towed multichannel seismic system, might be evidence of an ongoing migration of the base of the GH stability zone (GHSZ). We show that the reequilibrium is not occurring homogeneously as overpressure from hydrate dissociation slows their decomposition in specific sedimentary layers. The Black Sea example highlights that dissociation and the associated methane release in the water column or even in the atmosphere could be largely delayed by overpressure accumulation. Plain Language Summary Methane hydrate is an ice-like compound composed of a cage of water molecules enclosing a methane molecule. Hydrates can form where water and methane are present under high pressure and low temperatures, for example, in deep-sea sediments. As a result of climate change (e.g., seawater temperature increase), hydrates can melt and release free gas and water. Yet we observe that hydrates are present where they should have melted according to modeling. We explain this irregular melting by differing properties of the host sediments and different quantities of hydrate in the sediments. Methane in the Earth's atmosphere is a strong greenhouse gas. The release of methane from hydrate melting has been proposed as a runaway process where the methane released increases global warming, which further increases hydrate melting and methane release, repeating the cycle. Our results show that the destabilization of a hydrate system is actually a slow process, spanning several millennia. As such, a catastrophic destabilization of a gas hydrate system is unlikely.

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Section: Discussionmentioning

confidence: 99%

Section: In a Transient State Systemmentioning

confidence: 96%

Irregular BSR: Evidence of an Ongoing Reequilibrium of a Gas Hydrate System

Colin

Ker

Riboulot

et al. 2020

Geophysical Research Letters

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“…Below a depth of ca. 20 mbsf, we observe low pore-fluid salinities near 3-4 with little variation with greater depth (Bohrmann, 2018;Riedel et al, 2020). Salinity increases toward the seafloor to the average value of ∼22 of the Black Sea water body (Özsoy and Ünlüata, 1997).…”

Section: Temperature and Pressure Control On Solubilitymentioning

confidence: 90%

“…The upper boundary is often irregular and lacks a coherent reflection. MTDs show a positive impedance contrast at the top, but a negative impedance contrast at the base (Riedel et al, 2020), which indicates that they are of denser material than the surrounding sediment layers. One could infer that the MTDs are therefore less permeable than hemipelagic sediments (as e.g.…”

Section: Mass-transport Depositsmentioning

confidence: 99%

Controls on Gas Emission Distribution on the Continental Slope of the Western Black Sea

et al. 2021

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The continental slopes of the Black Sea show abundant manifestations of gas seepage in water depth of <720 m, but underlying controls are still not fully understood. Here, we investigate gas seepage along the Bulgarian and Romanian Black Sea margin using acoustic multibeam water column, bathymetry, backscatter, and sub-bottom profiler data to determine linkages between sub-seafloor structures, seafloor gas seeps, and gas discharge into the water column. More than 10,000 seepage sites over an area of ∼3,000 km2 were identified. The maximum water depth of gas seepage is controlled by the onset of the structure I gas hydrate stability zone in ∼720 m depth. However, gas seepage is not randomly distributed elsewhere. We classify three factors controlling on gas seepage locations into depositional, erosional, and tectonic factors. Depositional factors are associated with regionally occurring sediment waves forming focusing effects and mass-transport deposits (MTDs) with limited sediment drape. Elongated seafloor depressions linked to faulting and gas seepage develop at the base between adjacent sediment waves. The elongated depressions become progressively wider and deeper toward shallow water depths and culminate in some locations into clusters of pockmarks. MTDs cover larger regions and level out paleo-topography. Their surface morphology results in fault-like deformation patterns of the sediment drape on top of the MTDs that is locally utilized for gas migration. Erosional factors are seen along channels and canyons as well as slope failures, where gas discharge occurs along head-scarps and ridges. Sediment that was removed by slope failures cover larger regions down-slope. Those regions are devoid of gas seepage either by forming impermeable barriers to gas migration or by removal of the formerly gas-rich sediments. Deep-rooted tectonic control on gas migration is seen in the eastern study region with wide-spread normal faulting promoting gas migration. Overall, gas seepage is widespread along the margin. Gas migration appears more vigorous in shallow waters below ∼160 m water depth, but the number of flare sites is not necessarily an indicator of the total volume of gas released.

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“…39,40 We focused on developing a system for a straightforward and quick characterization of natural sample material that was expected from the planned drilling campaign in the Romanian sector of the Black Sea Danube deep-sea fan. 41 Besides this, the system should allow studying the influence of artificially formed gas hydrate content on the sediment strength properties. Since no existing system could easily be adjusted for this purpose, we developed a new easy to use ring shear test rig (ESTER).…”

Section: Motivationmentioning

confidence: 99%