Zander, Timo, Haeckel, Matthias , Berndt, Christian , Chi, Wu-Cheng, Klaucke, Ingo , Bialas, Jörg , Klaeschen, Dirk , Koch, Stephanie and Atgin, Orhan (2017) On the origin of multiple BSRs in the Danube deep-sea fan, Black Sea. Earth and Planetary Science Letters, 462 . pp. 15-25. DOI 10.1016/j.epsl.2017.01.006.

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Abstract

Highlights

• A stack of four BSRs were identified in levee deposits of the Danube deep-sea fan.
• The multiple BSRs are not caused by overpressure compartments.
• The multiple BSRs reflect stages of stable sealevel lowstands during glacial times.
• Gas underneath the previous GHSZ does not start to migrate for thousands of years.

Abstract

High-resolution 2D seismic data reveal the character and distribution of up to four stacked bottom simulating reflectors (BSR) within the channel-levee systems of the Danube deep-sea fan. The theoretical base of the gas hydrate stability zone (GHSZ) calculated from regional geothermal gradients and salinity data is in agreement with the shallowest BSR. For the deeper BSRs, BSR formation due to overpressure compartments can be excluded because the necessary gas column would exceed the vertical distance between two overlying BSRs.

We show instead that the deeper BSRs are likely paleo BSRs caused by a change in pressure and temperature conditions during different limnic phases of the Black Sea. This is supported by the observation that the BSRs correspond to paleo seafloor horizons located in a layer between a buried channel-levee system and the levee deposits of the Danube channel. The good match of the observed BSRs and the BSRs predicted from deposition of these sediment layers indicates that the multiple BSRs reflect stages of stable sealevel lowstands possibly during glacial times. The observation of sharp BSRs several 10,000 of years but possibly up to 300,000 yr after they have left the GHSZ demonstrates that either hydrate dissociation does not take place within this time frame or that only small amounts of gas are released that can be transported by diffusion. The gas underneath the previous GHSZ does not start to migrate for several thousands of years.

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