Contourite Depositional Systems in the El Arraiche Area, Moroccan Atlantic Margin
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FACULTEIT WETENSCHAPPEN Opleiding Master of Science in de geologie Contourite depositional systems in the El Arraiche area, Moroccan Atlantic margin Freek Vancraeynest Academiejaar 2014–2015 Scriptie voorgelegd tot het behalen van de graad Van Master of Science in de geologie Promotor: Prof. Dr. D. Van Rooij Begeleider: T. Vandorpe Leescommissie: Prof. Dr. S. Bertrand, Dr. M. Garcia ACKNOWLEDGMENTS This master dissertation is the final hurdle in my career as a geology student and is the highlight of my journey in becoming a solid scientist. The happy ending of my studies and this dissertation would not have been possible without the support of a whole bunch of people. Therefore, I would like to thank prof. David Van Rooij for the opportunity he gave me to start my thesis at the RCMG and immerse myself in the interesting study of contourites. I appreciate his advice and support during the writing of this thesis, and not the least the knowledge I gathered from him in the past five years. Secondly I would like to thank Thomas Vandorpe for the excellent guidance and never- ending support throughout this study. He was always stand-by for questions and remarks and put a lot of effort in reading and correcting this master thesis. I do not exaggerate by saying I would not have succeeded without their permanent support. I would like to thank my fellow students for the fun we had during our studentship, in the courses and especially during the time we spent on our days (and nights) out. Not to forget the great times we had on our field trips. Particularly this semester their presence was a huge support, for the joint smart and to put into perspective the struggle we had to go through the past months. Of course I would thank my parents for giving me the chance to begin my studies and for the support they gave me during the past five years. I am grateful for how they trusted me and let me do my thing, whether it was a great plan or not. Thank you! Freek 1 TABLE OF CONTENTS ACKNOWLEDGMENTS 1 TABLE OF CONTENTS 2 TABLE OF FIGURES 3 INTRODUCTION 4 REGIONAL SETTING 8 Geology & geomorphology 8 Oceanography 9 MATERIAL & METHODS 12 RESULTS 14 Geomorphology 14 Seismic stratigraphy 15 Unit 6 22 Unit 5 22 Unit 4 23 Unit 3 25 Unit 2 26 Unit 1 27 DISCUSSION 30 Sedimentary processes 30 Uplift and initiation 30 drift development 31 Tidal currents 33 Chronostratigraphy and palaeoceanographic comparison 34 CONCLUSIONS 43 DUTCH SUMMARY 44 REFERENCES 48 2 TABLE OF FIGURES Figure 1: Morphosedimentary map of the Contourite depositional system on the middle slope of Gulf of Cádiz. (Hernandez-Molina et al., 2003) .............................................................................................. 4 Figure 2: Oceanic circulation in the Gulf of Cádiz. (figure adapted from Vandorpe et al. (2014)) ..... 10 Figure 3: Overview of seismic lines. .................................................................................................... 12 Figure 4: Overview of topographic features in the El Arraiche area.................................................... 15 Figure 5: Seismic profile of the northern part of the area perpendicular to the Renard Ridge ............ 16 Figure 6: Seismic profile near the Western Channel, perpendicular to the Renard Ridge. .................. 17 Figure 7: Seismic profile of the narrow part of the Renard Ridge and the two mounded features along the Vernadsky Ridge ............................................................................................................................. 18 Figure 8: Seismic profile of the Eastern Channel of the Renard Ridge and the two mounded features along the Vernadsky Ridge ................................................................................................................... 19 Figure 9: Seismic profile of the Eastern Channel of the Renard Ridge and only one mounded structure along the Vernadsky Ridge ................................................................................................................... 20 Figure 10: Schematic overview of the (sub-)units in the east of the area as presented in figure 9. ..... 21 Figure 11: Isopach map of unit 5.......................................................................................................... 23 Figure 12: Seismic profile displaying the two mounded parted features along the Vernadsky Ridge..24 Figure 13: Isopach map of unit 4.......................................................................................................... 25 Figure 14: isopach map of unit 3.. ........................................................................................................ 26 Figure 15: Isopach map of unit 2.......................................................................................................... 27 Figure 16: Isopach map of unit 1.......................................................................................................... 28 Figure 17: Depthmaps of boundaries B5 to B1. ................................................................................... 29 Figure 18: transverse profile of the study area, parallel and centered between both ridges. ................ 38 Figure 19: schematic overview of figure 18: transverse profile of the study area, parallel and centered between both ridges. .............................................................................................................................. 39 Figure 20: comparison of the evolution of the RND and VSD with the PDE drift (Vandorpe et al., 2014) and with clear MOW-controlled drifts in the northern Gulf of Cádiz (Roque et al., 2002; Brackenride et al., 2013), the Bay of Biscay (Van Rooij et al., 2010) and the Alboran Sea (Juan et al., 2012; Somoza et al., 2012). Figure adapted from Vandorpe et al., 2014.. ............................................ 41 Figure 21: Overview of the currents in the El Arraiche mud volcano field (modified from Vandorpe et al. (subm.)). ........................................................................................................................................... 42 3 Contourite depositional systems in the El Arraiche area, Moroccan Atlantic margin INTRODUCTION Contourites were first identified nearly 50 years ago, but little attention was given to the subject (Faugères et al., 1993). Only the last two decades the field is advancing. The ambiguity in its definition and the non-straightforward characteristics of contourite facies are two reasons why contourite research has not been advanced as fast as it should. The definition of a contourite is ambiguous and they form only an end-member in a continuum of deep-sea sedimentary facies (Rebesco et al., 2014). Some facies models were proposed (Gonthier et al., 1984; Stow and Faugeres, 2008) but diagnostic criteria are still not robust. As such, further research is still needed to find an international accepted definition and diagnostic criteria have to be identified. New techniques have great potential for further research. A triple-stage approach was recommended by Nielsen et al. (2008) and Rebesco and Stow (2001) to identify sediment deposited by bottom currents. The analysis must include the overall architecture of the deposit (gross geometry and large-scale depositional units), the internal architecture (structure and subunits) and the seismic attributes and facies in every subunit. Contourites are sediments deposited or affected by bottom currents (Stow et al., 2002b; Rebesco et al., 2005; Stow and Faugeres, 2008). Bottom currents play an important role in the transport, deposition and erosion of deep-sea sediments. Strictly, contourites are formed by along-slope bottom currents, but not all bottom currents which create contourites follow the contours. Contourites can originate from many possible physical drivers like salinity, heat and atmospheric forcing and from different current types such as density driven currents (Johnson et al., 2002), deep-water tidal currents (Stow et al., 2013) and eddies (Serra et al., 2010). Contourites are widespread and cover large areas of the present ocean floors and continental margins. They occur in a broad range of environments, from the deep ocean (Uenzelmann-Neben and Gohl, 2012) over continental slopes (Li et al., 2013) to shallow margins (Vandorpe et al., 2014) and even in lakes (Heirman et al., 2012). Contourite drifts are sediment bodies build up and maintained by bottom currents (Rebesco et al., 2007). The drifts can be thick and extensive and occur in a broad range of environments, if a significant sediment input is available (Stow and Faugeres, 2008). Contourite drifts have different morphologies which are significantly controlled by the physiographic and geological setting in which they develop and by the different water masses involved (both their velocities and directions). The drift may thus be a palaeocurrent indicator. Drifts have mostly a mounded and elongated geometry accompanied by a concave moat but other depositional and erosional structures are possible. Different classification systems were set up based on drift morphology or location (Rebesco and Stow, 2001; Stow et al., 2002a; Rebesco et al., 2005; Hernandez-Molina et al., 2008b). The contourite drifts are characterized by a degree of mounding and elongation (Rebesco et al., 2014). Although there is some overlap amongst the different drift types forming a continuous spectrum. Elongated, mounded drifts and sheeted drifts can be considered as two end members of the spectrum (see figure 16 in Rebesco et al.