VU Research Portal Contour current imprints and contourite drifts in the Bahamian archipelago Mulder, Thierry; Ducassou, Emmanuelle; Hanquiez, Vincent; Principaud, Mélanie; Fauquembergue, Kelly; Tournadour, Elsa; Chabaud, Ludivine; Reijmer, John; Recouvreur, Audrey; Gillet, Hervé; Borgomano, Jean; Schmitt, Anais; Moal, Paul published in Sedimentology 2019 DOI (link to publisher) 10.1111/sed.12587 document version Publisher's PDF, also known as Version of record document license Article 25fa Dutch Copyright Act Link to publication in VU Research Portal citation for published version (APA) Mulder, T., Ducassou, E., Hanquiez, V., Principaud, M., Fauquembergue, K., Tournadour, E., Chabaud, L., Reijmer, J., Recouvreur, A., Gillet, H., Borgomano, J., Schmitt, A., & Moal, P. (2019). Contour current imprints and contourite drifts in the Bahamian archipelago. 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Oct. 2021 Sedimentology (2019) 66, 1192–1221 doi: 10.1111/sed.12587 Contour current imprints and contourite drifts in the Bahamian archipelago THIERRY MULDER*, EMMANUELLE DUCASSOU*, VINCENT HANQUIEZ*, MELANIE PRINCIPAUD*, KELLY FAUQUEMBERGUE*, ELSA TOURNADOUR*, LUDIVINE CHABAUD*, JOHN REIJMER†, AUDREY RECOUVREUR*, HERVE GILLET*, JEAN BORGOMANO‡, ANAIS SCHMITT* and PAUL MOAL* *UMR 5805 EPOC, Universite de Bordeaux, 33615, Pessac Cedex, France †College of Petroleum Engineering & Geosciences, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia ‡Geologie des Systemes et Reservoirs Carbonates Cerege, Universite de Provence, 13331, Marseille Cedex 3, France Associate Editor – Christian Betzler ABSTRACT New data collected along the slopes of Little and Great Bahama Bank and the abyssal plain of the Bahama Escarpment provides new insights about contour current-related erosive structures and associated deposits. The Baha- mian slope shows abundant evidence of bottom current activity such as fur- rows, comet-like structures, sediment waves and drifts. At a seismic scale, large erosion surfaces and main periods of drift growth resulted from current acceleration related to plate tectonic processes and progressive opening and closure of gateways and long-term palaeoclimate evolution. At present-day, erosion features and contourite drifts are either related to relatively shallow currents (<1000 m water depth) or to deep currents (>2500 m water depth). It appears that the carbonate nature of the drifts does not impact the drift morphology at the resolution addressed in the present study. Classical drift morphologies defined in siliciclastic environments are found, such as mounded, plastered and separated drifts. In core, contourite sequences show a bi-gradational trend that resembles classical contourite sequences in silici- clastic deposits showing a direct relationship with a change in current veloc- ity at the sea floor. However, in a carbonate system the peak in grain size is associated with increased winnowing rather than increased sediment supply as in siliciclastic environments. In addition, the carbonate contourite sequence is usually thinner than in siliciclastics because of lower sediment supply rates. Little Bahama Bank and Great Bahama Bank contourites con- tain open-ocean input and slope-derived debris from glacial episodes. Inner platform, platform edge and open ocean pelagic input characterize the classi- cal periplatform ooze during interglacials. In all studied examples, the drift composition depends on the sea floor topography surrounding the drift loca- tion and the type of sediment supply. Carbonate particles are derived from either the slope or the platform in slope and toe of slope drifts, very deep contourites have distant siliciclastic sources of sediment supply. The recent discovery of the importance of a large downslope gravitary system along Bahamian slopes suggests frequent interactions between downslope and along-slope (contour currents) processes. The interlayering of mass flow deposits and contourites at a seismic scale or the presence of surface struc- tures associated with both contour currents and mass flow processes shows 1192 © 2019 The Authors. Sedimentology © 2019 International Association of Sedimentologists Contourite drifts, Bahamas 1193 that both processes act at the same location. Finally, contour currents have an important impact on the repartition of deep-water coral mounds. Currents can actively interact with mounds as a nutrient and oxygen supplier or have a passive interaction, with mounds solely being obstacles orienting erosion and deposition. Keywords Bahamas, contour currents, contourites, drifts. INTRODUCTION grained deposits (Stow, 1994) but also in sandy facies (Viana et al., 1998). Shanmugam (2006, Contour currents flow along continental margins 2008) underlines the importance of sharp upper at various water depths depending on their tem- contacts and tractive structures in contour-cur- perature and salinity, and determine erosion, rent related deposits such as cross-bedding, len- transport and depositional processes involving ticular, horizontal and flaser bedding. The clay, silt and fine sand. They can form erosional sedimentation rate is low, and bioturbation is and depositional features from a centimetric to usually intense leading to the erasing of primary metric scale called ‘contourites’ (Gonthier et al., sedimentary structures (Faugeres & Stow, 2008). 1984) and to a plurikilometric scale, so-called The sediments are mainly mud, silty mud and ‘contourite drifts’ (Stow et al., 2009). Con- muddy silt, and more rarely fine sand (Stow tourites were initially defined as deep-sea et al., 2002a,b). Most of the aforementioned refer- sediment deposited by contour currents initiated ences deal with siliciclastic systems and litera- by thermohaline circulation (Heezen & Hollister, ture about carbonate contour current-related 1971). This initial and restrictive definition was systems is rare (Bein & Weiler, 1976; Cook & extended by Stow et al. (2002a,b) and Rebesco Mullins, 1983), with the few examples known (2005) to any sediment substantially reworked consisting of periplatform ooze with minor clayey by bottom currents. This allowed the inclusion intervals. Most studies deal with Bahamian of deposits affected by surface currents mostly slopes in particular; including, the Little Bahama generated by wind–ocean interactions or to Bank (Mullins & Neumann, 1979; Mullins et al., ancient deposits for which the hydrodynamic 1980, 1984; Austin et al., 1988; Harwood & Tow- context is poorly known. From a general view- ers, 1988; Rendle et al., 2000; Rendle-Buhring€ & point, contour currents flow parallel to isobaths Reijmer, 2005; Lantzsch et al., 2007; Mulder and can be considered as semi-permanent to et al., 2012b; Rankey & Doolittle, 2012; permanent quasi-steady geostrophic flows that Tournadour et al., 2015; Chabaud, 2016; Chabaud sunk at their equilibrium level (Rebesco et al., et al., 2016), the Great Bahama Bank (Brunner, 2008). The velocity of contour currents usually 1986; Eberli et al., 1997a; Bergman, 2005; Mulder À varies between 5 cm and 20 cm sec 1 but can be et al., 2012a), the Santaren Channel (Anselmetti affected by surface hydrodynamic processes or et al., 2000; Ludmann€ et al., 2016; Wunsch et al., by sea-floor topography and may reach velocities 2018), the Tongue of the Ocean (Schlager & À of up to 2Á5 m sec 1 in particular cases when Chermak, 1979; Grammer & Ginsburg, 1992; the flow section is restricted (Wynn & Masson, Grammer et al., 1993) and Exuma Sound 2008). Topographic restrictions are mainly con- (Crevello & Schlager, 1980; Austin et al., 1988; trolled by sea-floor morphology such as the pres- Grammer et al., 1999). Other examples are ence of a fault wall, a ridge, a channel or a strait reported from the Maldives (Ludmann€ et al., that can change through time (Faugeres & Mul- 2013, 2018) and in ancient environments der, 2010). (Huneke€ & Stow, 2008). The sedimentary contourite depositional Current velocity controls sea floor erosion and sequence was initially defined in the Faro Drift drift construction. In addition, drift geometry is (Gulf of Cadiz; Faugeres et al., 1984; Gonthier controlled by the permanency of the current et al., 1984). It shows a bi-gradational trend with activity along the sea floor, the nature of the the superposition of inverse and normal grading particles carried by the current, particularly corresponding, respectively, to a waxing and grain size, and amount of available particles waning current. Laminated facies are frequently (Stow et al., 2008). Larger drifts can show con- interpreted as contourites, most often in fine- tinuous deposition over several millions of years © 2019