Unusual Components Within a Fine-Grained Contourite Deposit: Significance for Interpretation of Provenance and the Contourite Budget

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.