Abstract
Deep-water contourite muds are an important component of many continental margin systems and are currently the focus of much interest amongst deep-water researchers. One outstanding gap in our knowledge of these systems is to understand and quantify a contourite budget, both at the small (facies) scale and at the larger drift scale. A second problem concerns the establishing of robust criteria for discriminating between contourites and associated deepwater facies—turbidites and hemipelagites. This paper contributes to these topics by detailed examination of sediment composition, with a particular focus on potentially diagnostic components, within contourites and hemipelagites from the same depositional basin. Samples were selected from Pliocene to Quaternary muddy contourites from the Gulf of Cadiz (IODP 339) and examined by scanning electron microscopy. The presence of tunicate spicules, micro-bored shell fragments, and a particular species of coccolithophore, Braarudosphaera biglowii, all indicate derivation from shallow waters and hence lateral off-shelf supply. In contrast, micro-mudclasts and fragmented bioclasts are indicative of alongslope transport in bottom currents. A normal planktic component of the contourite muds shows a significant vertical input from pelagic settling. Such diagnostic components can also help in the discrimination between contourites, turbidites and hemipelagites.
Highlights
Fine-grained deep-water muds are the dominant sediment type of continental margins, covering large swathes of the outer shelf, slope and rise
The secondary aim is to stimulate additional in-depth investigations into the type of particulate materials within deep-water muds of all facies types, their significance in terms of origin, additional environmental information, and their use in differentiating between these different facies; we look at contourites and hemipelagites
Detailed analysis of the composition of contourites can yield important information about sediment provenance, and provide evidence for establishing a contourite sediment budget. This concept is illustrated by careful study of the fine-grained particulate material from selected International Oceanic Drilling Program (IODP) 339 sites, with a particular focus on some of the more unusual components in the contourite sediments
Summary
Fine-grained deep-water muds are the dominant sediment type of continental margins, covering large swathes of the outer shelf, slope and rise. Contourites are a group of closely related deepwater facies deposited under the influence of semi-permanent current action and are commonly referred to as alongslope deposits resulting from semi-continuous depositional processes. This distinguishes them from other deepwater facies that have been deposited either by episodic downslope processes or events (turbidites, debrites, slides, mass-transport deposits and hyperpycnites), or from continuous vertical settling—the so-called background processes (pelagites and hemipelagites) [3,4,5]. A synthesis of the most important criteria for their distinction is provided by Stow and Smillie [2]
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