Linking carbonate sediment transfer to seafloor morphology: Insights from Exuma Valley, the Bahamas

Abstract

The depositional record of carbonate slopes provides a valuable archive of past environmental and climatic changes. Modern carbonate slopes reveal morphological variabilities (for example, gullies and canyons) shaped by episodic slope collapses and turbidity currents. Furthermore, climate-induced fluctuations in sea level regulate sediment availability and delivery to the deep-sea. Morphological and climatic controls on calciclastic sediment transfer are often complex to decipher. The aim of this study is to link seafloor morphology and depositional processes in an active carbonate submarine channel (Exuma Valley, the Bahamas) over the last 40 kyr. The dataset includes multibeam and seismic surveys, and two sediment cores retrieved from the valley axis. A series of abrupt slope-breaks, called knickpoints, occurs along Exuma Valley, and plays a key role in sediment transport and accumulation. Initiation processes proposed for knickpoint formation include bank-collapse, side gully erosion and loss of confinement. Slope collapses detected on the bathymetry prevail in the upstream muddy section of the submarine valley, as attested to by a planktic-rich debrite-turbidite couplet in the first core. In contrast, the second core collected downstream of the knickpoints train, includes 32 bioclastic sandy event-beds (i.e. turbidites). Hydrodynamic sorting generates grain segregation (for example, Halimeda-rich base versus planktic-rich top) and geochemical contrasts (Sr/Ca) in turbidites. Turbidite frequency and grain composition within beds reflect the variation of carbonate sources during glacial-interglacial periods. This research allows to link slope morphology with deposits of a modern largescale carbonate factory, and to deduce sea-level changes over that last 40 kyr in the Bahamas. These results can provide new perspectives on the understanding of 'source to sink' mechanisms in carbonate systems.

Shape‐dependent settling velocity of skeletal carbonate grains: Implications for calciturbidites

“…From a process perspective, the hydrodynamic properties of carbonate grains control the vertical and longitudinal sorting of calciturbidites in platform‐to‐basin trajectories (Counts et al ., 2021; Le Goff et al ., 2021). Detailed outcrop studies focused on the distribution of skeletal and non‐skeletal grains in calciturbidites (e.g.…”

“…Longitudinal variation in the composition of calciturbidites, as observed in numerous studies (e.g. Bornhold & Pilkey, 1971; Van Tassell, 1981; Colacicchi & Baldanza, 1986; Brunner & Ledbetter, 1987; Herbig & Mamet, 1994; Bábek & Kalvoda, 2001; Andresen et al ., 2003; Maurer et al ., 2003; Maurer & Schlager, 2003; Jorry et al ., 2020; Counts et al ., 2021; Le Goff et al ., 2021), is ultimately controlled by the hydrodynamic properties of the transported carbonate grains. This perspective on calciturbidites has received less attention, yet is key to a process‐based approach of carbonate slopes.…”

“…Currently, calciturbidites are also being explored for geothermal exploitation (for example, in The Netherlands: Reijmer et al ., 2017; Mozafari et al ., 2019; Mijnlieff, 2020). Carbonate models involving differential shape‐dependent settling velocities may be used to predict which components are likely to be exported from the platform environment towards the basin (Braithwaite, 1973; Counts et al ., 2021; Le Goff et al ., 2021) and are therefore invaluable for source‐to‐sink studies in carbonate systems (Morgan & Kench, 2016; Jorry et al ., 2020). Applications are also found in marine engineering projects in carbonate environments, including beach erosion, coastal construction, dredging and replenishment works (Murff, 1987; Hohenegger, 2006; Ngan‐Tillard et al ., 2009; Gailani et al ., 2016; Lokier & Fiorini, 2016; Mohr et al ., 2016; Shen et al ., 2019).…”

“…Suspensions of carbonate grains are formed when skeletal remains and nonskeletal particles such as ooids and pellets, together with carbonate mud, are shed off carbonate platforms, for example, during storms and subaqueous slope failures (e.g. Haak & Schlager, 1989;Reijmer et al, 1992Reijmer et al, , 2012Reijmer et al, , 2015Wilson & Roberts, 1992, 1995Spence & Tucker, 1997;Hickey et al, 2000;Counts et al, 2021;Le Goff et al, 2021). Such suspended sediments may transform into bottom-hugging flows, known as turbidity currents (Kuenen, 1937).…”

On the settling of marine carbonate grains: Review and challenges

“…Knowledge about the hydrodynamic behaviour of carbonate sediment in terms of deposition and transport has wide applications. Some research is focused on carbonate sediment distribution (Kench and McLean, 1996;Kench, 1997;Cuttler et al, 2017), occasionally specified to a certain mode of transport including storm events (Li et al, 2020), currents and waves (Weill et al, 2010;Durafour et al, 2015;Flemming, 2017;Joshi et al, 2014;Rieux et al, 2019;Riazi et al, 2020) and turbidity currents (Bornhold and Pilkey, 1971;Van Tassell, 1981;Herbig and Mamet, 1994;Hodson and Alexander, 2010;Le Goff et al, 2021). Other studies deal with specific organisms, in particular planktic e ly n o ne q u a n t E q u a n t S li g h t ly n o ne q u a n t M o d e r a t e ly n o ne q u a n t V e r y n o ne q u a n t Blott and Pye (2008).…”