This chapter provides a current state-of-the-art on the contourite systems with a major focus on the modern systems (drifts), the processes of deposition and the diagnostic sedimentological and seismic features. A short overview of the ancient contourite problem is also provided.
Firstly, the history of contourites is briefly reminded since the pionner works during the sixties. The major stages in the advances of the knowledge of these deposits are underlined, and a consensus view is proposed on the definitions of contourites (“deep or shallow contourites”) and drifts, and on the large diversity of bottom currents that can be involved in contourite deposition.
The second part of the chapter is then dedicated to the Ocean geostrophic circulation and the main characteristics of the surficial and the thermohaline circulation. It drives to the contour current definition and physical features. The sedimentary processes (erosion, transport and deposition) related to contour currents form the third part with an emphasis on the processes occurring in the nepheloïd layer and in the Benthic Boundary Layer as demonstrated by the results of the HEBBLE project.
The two following parts concern the contourite deposits: facies, sequences, bedforms and geometry within drift sedimentary body. Examples of detailed studies of contourite core using combined physical methods are necessary to identify this deposit. Similarly a multi-scale approach is necessary to recognize drift construction from seismic lines only. Some sedimentological and seimic diagnostic features are proposed to identify Contourites.
The last part point out how difficult is the recognition of ancient contourite. The lack of recent progress is due in part to diagenesis, outcrop discontinuities and tectonic deformation. Two types of ancient contourites, the bottom-current-reworked turbidites and the shallow-water ancient contourites, are presented in more details in order to highlight the debate that still surrounds their recognition and interpretation.