Abstract
Seafloor elongated depressions are indicators of gas seepage or slope instability. Here we report a sequence of slopeparallel elongated depressions that link to headwalls of sediment slides on upper slope. The depressions of about 250 m in width and several kilometers in length are areas of focused gas discharge indicated by bubble-release into the water column and methane enriched pore waters. Sparker seismic profiles running perpendicular and parallel to the coast, show gas migration pathways and trapped gas underneath these depressions with bright spots and seismic blanking. The data indicate that upward gas migration is the initial reason for fracturing sedimentary layers. In the top sediment where two young stages of landslides can be detected, the slopeparallel sediment weakening lengthens and deepens the surficial fractures, creating the elongated depressions in the seafloor supported by sediment erosion due to slope-parallel water currents.
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Baeten, N. J., Sverre, J., Forwick, M., Vorren, T. O., Vanneste, M., Fredrik, C., Kvalstad, T. J., and Ivanov, M., 2013. Morphology and origin of smaller-scale mass movements on the continental slope off northern Norway. Geomorphology, 187 (5): 122–134.
Bøe, R., Rise, L., and Ottesen, D., 1998. Elongate depressions on the southern slope of the Norwegian Trench (Skagerrak): Morphology and evolution. Marine Geology, 146: 191–203, DOI: 10.1016/S0025-3227(97)00133-3.
Chapron, E., Van Rensbergen, P., De Batist, M., Beck, C., and Henriet, J. P., 2004. Fluid-escape features as a precursor of a large sublacustrine sediment slide in Lake Le Bourget, NW Alps, France. Terra Nova, 16 (5): 305–311, DOI: 10.1111/j.1365-3121.2004.00566.x.
Çifci G., Dondurur, D., and Ergün, M., 2003. Deep and shallow structures of large pockmarks in the Turkish shelf, Eastern Black Sea. Geo-Marine Letters, 23 (3-4): 311–322, DOI: 10.1007/s00367-003-0138-x.
Dimitrov, L., and Dontcheva, V., 1994. Seabed pockmarks in the southern Bulgarian Black Sea Zone. Bulletin of the Geological Society of Denmark, 41 (1): 24–33.
Driscoll, N. W., Weissel, J. K., and Goff, J. A., 2000. Potential for large-scale submarine slope failure and tsunami generation along the U.S. mid-Atlantic coast. Geology, 28 (5): 407–410.
Genov, I., and Dimitrov, O., 2003. Faults and fault activity determined on the basis of seismic stratigraphy in the region east from the West-Ahtopol Rise–Southern Bulgarian Black Sea Shelf. Comptes Rendus de L’academie Bulgare des Sciences, 56: 71, DOI: 10.1007/s13398-014-0173-7.2.
Georgiev, G., 2012. Geology and hydrocarbon systems in the western Black Sea. Turkish Journal of Earthences, 21: 723–754, DOI: 10.3906/yer-1102-4.
Greene, H. G., Murai, L. Y., Watts, P., Maher, N. A., Fisher, M. A., Paull, C. E., and Eichhubl, P., 2006. Submarine landslides in the Santa Barbara Channel as potential tsunami sources. Natural Hazards & Earth System Sciences, 6 (1): 63–88, DOI: 10.5194/nhess-6-63-2006.
Hill, J. C., Driscoll, N. W., Weissel, J. K., and Goff, J. A., 2004. Large-scale elongated gas blowouts along the U.S. Atlantic margin. Journal of Geophysical Research Atmospheres: Solid Earth, 109: B09101, DOI: 10.1029/2004JB002969.
Hovland, M., Gardner, J. V., and Judd, A. G., 2002. The significance of pockmarks to understanding fluid flow processes and geohazards. Geofluids, 2 (2): 127–136, DOI: 10.1046/j.1468-8123.2002.00028.x.
Laberg, J. S., Baeten, N. J., Lågstad, P., Forwick, M., and Vorren, T. O., 2013. Formation of a large submarine crack during the final stage of retrogressive mass wasting on the continental slope offshore northern Norway. Marine Geology, 346: 73–78, DOI: 10.1016/j.margeo.2013.08.008.
Li, W., Wu, S., Wang, X., Zhao, F., Wang, D., Mi, L., and Li, Q., 2014. Baiyun Slide and its relation to fluid migration in the northern slope of Southern China Sea. In: 6th International Symposium on Submarine Mass Movements and Their Consequences, Advances in Natural and Technological Hazards Research. Krastel, S., et al., eds., Springer International Publishing, Cham, 105–115.
Martel, S. J., 2004. Mechanics of landslide initiation as a shear fracture phenomenon. Marine Geology, 203: 319–339, DOI: 10.1016/S0025-3227(03)00313-X.
Mienert, J., Vanneste, M., Haflidason, H., and Bünz, S., 2010. Norwegian margin outer shelf cracking: A consequence of climate-induced gas hydrate dissociation? International Journal of Earth Sciences, 99 (1): 207–225, DOI: 10.1007/s00531-010-0536-z.
Newman, K. R., Cormier, M. H., Weissel, J. K., Driscoll, N. W., Kastner, M., Solomon, E. A., Robertson, G., Hill, J. C., Singh, H., Camilli, R., and Eustice, R., 2008. Active methane venting observed at giant pockmarks along the U.S. mid-Atlantic shelf break. Earth & Planetary Science Letters, 267 (1-2): 341–352, DOI: 10.1016/j.epsl.2007.11.053.
Pilcher, R., and Argent, J., 2007. Mega-pockmarks and linear pockmark trains on the West African continental margin. Marine Geology, 244 (1-4): 15–32, DOI: 10.1016/j.margeo.2007.05.002.
Reiche, S., Hjelstuen, B. O., and Haflidason, H., 2011. Highresolution seismic stratigraphy, sedimentary processes and the origin of seabed cracks and pockmarks at Nyegga, mid-Norwegian margin. Marine Geology, 284 (1-4): 28–39, DOI: 10.1016/j.margeo.2011.03.006.
Riboulot, V., Cattaneo, A., Sultan, N., Garziglia, S., Ker, S., Imbert, P., and Voisset, M., 2013. Sea-level change and free gas occurrence influencing a submarine landslide and pockmark formation and distribution in deepwater Nigeria. Earth & Planetary Science Letters, 375: 78–91, DOI: 10.1016/j.epsl.2013.05.013.
Ross, D. A., 1978. Black Sea stratigraphy. In: Initial Report of the Deep Sea Drilling Project, Volume 42, Part 2. US Government Printing Office, Washington, D C., 17–26.
Wessel, P., Smith, W. H. F., Scharroo, R., Luis, J., and Wobbe, F., 2013. Generic mapping tools: Improved version released. EOS Transactions American Geophysical Union, 94 (45): 409–410, DOI: 10.1002/2013EO450001.
Yun, J. W., Orange, D. L., and Field, M. E., 1999. Subsurface gas offshore of northern California and its link to submarine geomorphology. Marine Geology, 154 (1-4): 357–368, DOI: 10.1016/S0025-3227(98)00123-6.
Acknowledgements
We acknowledge the captains, the crew and technicians of the R/V Akademik for all support during the SPUX cruise in 2012. The cruise SPUX (AK211) has been funded by the European project EUROFLEETS (Seventh Framework Programme, No. 228344) through transnational access to the research vessel ‘R/V Akademik’ operated by the Institute of Oceanology Bulgarian Academy of Science (Bulgaria). We thank Timo Zander, Peter Urban from GEOMAR for introductions to the Kingdom Suit software, and Linux programming, and Wei Li (from Kiel University) for seismic interpretation. We very much appreciated the comments of Prof. Marc De Batist from Gent University and two anonymous reviewers on an earlier version of this paper. We also thank Inken Preuss and Edna Hütten who were a great help in sorting out the English. This is publication 27 of the DeepSea Monitoring group at GEOMAR.
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Xu, C., Greinert, J., Haeckel, M. et al. The Character and Formation of Elongated Depressions on the Upper Bulgarian Slope. J. Ocean Univ. China 17, 555–562 (2018). https://doi.org/10.1007/s11802-018-3460-7
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DOI: https://doi.org/10.1007/s11802-018-3460-7