Modes of development of slope canyons and their relation to channel and levee features on the Ebro sediment apron, off-shore northeastern Spain |
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| Authors: | S. O'Connell W.B.F. Ryan W.R. Normark |
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| Affiliation: | 1. CSIRO Oceans and Atmosphere, GPO Box 1538, Hobart, Tasmania 7001, Australia;2. Australian National University, Research School of Earth Sciences, Canberra, ACT 0200, Australia;3. University of Tasmania Central Science Laboratory, Sandy Bay, Tasmania 7005, Australia;1. Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, New York, NY 10027, USA;2. School of Earth Sciences, University of Bristol, Bristol BS8 1JA, UK;3. Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;4. Earth and Planetary Sciences, University of California-Davis, Davis, CA 95616, USA;5. Bodega Marine Laboratory, University of California-Davis, Bodega Bay, CA 94923, USA;1. Zhirmunsky National Scientific Center of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, ul. Palchevskogo, 17, 690041, Russia;2. Senckenberg Research Institute and Natural History Museum, Senckenberganlage 25, 60325 Frankfurt am Main, Germany;3. Institute for Ecology, Evolution and Diversity, Goethe-University of Frankfurt, FB 15, Max-von-Laue-Str. 13, 60439 Frankfurt am Main, Germany;1. School of Chemical Sciences, Central University of Gujarat, Gandhinagar 382030, India;2. Department of Mechanical Engineering, Pandit Deendayal Energy University, Gandhinagar 382007, Gujarat, India;3. Heriot Watt University, Academic City 294345, Dubai, United Arab Emirates;1. Department of Microbiology, The University of Hong Kong, Hong Kong SAR, China;2. State Key Laboratory of Emerging Infectious Diseases, The University of Hong Kong, Hong Kong SAR, China;3. Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong SAR, China;1. University of Hamburg, Centre of Natural History (CeNak), Zoological Museum, Hamburg, Germany;2. Senckenberg am Meer, German Centre for Marine Biodiversity Research (DZMB), c/o Biocenter Grindel, Martin-Luther-King-Platz 3, 20146 Hamburg, Germany;3. Senckenberg Research Institute and Natural History Museum, Department Marine Zoology, Crustacea, Senckenberganlage 25, 60325 Frankfurt, Germany;4. Goethe-University of Frankfurt, FB 15, Institute for Ecology, Evolution and Diversity, Max-von-Laue-Str. 13, 60439 Frankfurt am Main, Germany |
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| Abstract: | Six submarine slope canyons in an area of the northwestern Mediterranean, offshore from the Ebro River and Delta, were surveyed with bathymetric swathmapping (SeaBeam) and mid-range side-looking sonar (SeaMARC I). All of the canyons have slightly winding paths with concave-upwards gradients that are relatively steep shallower than 1,200 m. Two major types of canyons are identified on the basis of their morphologic character at the base of the slope; Type-I canyons lead to an unchannelled base-of-slope deposit and Type-II canyons are continuous with channel-levee systems that cross the rise.Four Type-I canyons were surveyed in the area. Two of these are broad, U-shaped, steep (average gradients of 1:14), do not indent the shelf, and terminate downslope at debris-flow deposits. These two canyons, the most northern in the area, have rounded heads with extensive gullies separated by knife-edge ridges. Relief of the canyon walls is about equal on both sides of the canyons, although the right-hand walls (looking downslope) are generally steeper. The other two Type-I canyons in the area are similar in that they do not indent the shelf, but they are much smaller and shallower and coalesce before terminating in the base-of-slope region. The two Type-II canyons that feed leveed-channels are U-shaped with flatter floors, longer profiles and gentler gradients than Type-I canyons. They are closer to the Valencia Valley and have relatively small cross-sectional areas.We propose a four-stage evolutionary sequence to explain the development of the canyons observed in this section on the prograding Ebro margin. During the initial stage, slumping and erosion on the slope creates a network of small gullies. During the next stage, headward growth of one (or more) gully leads to a major indentation of the shelf. This is the critical factor for developing a channel that will incise the slope and provide a major conduit for moving sediment to the basin. Stage 3 is characterized by the development of a continuous channel accompanied by levee growth across the lobe. In the final stage, the channel-levee system becomes inactive either through destruction by mass wasting, infilling of the channel, or loss of the major sediment source. |
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| Keywords: | Slope canyons channel-levee ebro sediment apron |
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