SEDIMENTARY ENVIRONMENTS/Contourites 525 They normally occur as thick (tens to hundreds of metres), uniform, fine-grained sequences (including thin to medium coarser-grained beds), or interbedded with hemipelagites, turbidites, and other resedimented facies, or as coarse lags within gateways They are dominantly homogeneous (Figure 9A), poorly bedded (Figure 10A), and mostly bioturbated (Figure 10B) and mottled throughout, with little primary structures preserved Bioturbation is generally considered an essential characteristic of contourites based on the belief that an active bottom current would increase oxygen concentration in the water and in turn increase organic activity, thus allowing contourites to be distinguished from episodic turbidites However, bioturbation potential is also inferred to be a function of current intensity and other life-favourable environmental conditions As a matter of fact, nonbioturbated contourites have been described as well (Figure 10C) Well-developed but somewhat irregular, fine lamination with indistinct bioturbation may be evident both in shallow-water and in high-latitude facies (Figure 10C), possibly as a result of a hybrid turbidite–controurite deposition Although cyclicity is common, primary silty parallel and cross lamination (Figures 9B, 10C), where present, shows no regular sequence of facies as in turbidites Contourites may show reverse grading, with coarse lag concentrations and sharp or erosive contacts (Figures 9A and Figure 10 Core photos from two different ODP Legs (A, B) ODP Leg 194 in the sediment drifts adjacent to Marion Plateau From Isern AR, Anselmetti FS, Blum P, et al (2002) Proc ODP, Initial Reports, Vol 194 Available from: http://www odp.tamu.edu/publications/ 194_IR/194ir.htm (C) ODP Leg 188, Wild Drift in Cooperation Sea From Shipboard Scientific Party (2001) Site 1165, in: O’Brien PE, Cooper AK, Richter C, et al (eds) (2001) Proc ODP, Initial Reports, Vol 188 Available from: http://www odp.tamu.edu/publications/ 188_IR/VOLUME/CHAPTERS/IR188_03.PDF (A) Core 194 1195B 21H 5, 34 54 cm showing a surface scoured into a light greenish grey wackestone by strong bottom currents in a high energy hemipelagic setting The sediments above the scoured surface consist of alternations between light grey silt and very fine sand sized wackestone and very fine to fine sand sized skeletal packstone dominated by broken planktonic foraminifera (B) Core 194 1195B 44X 1, 94 122 cm showing alternation of silt sized light grey skeletal packstone and greenish gray mudstone with well preserved Chondrites burrows and top and basal sharp scoured surfaces (C) Core 188 1165C 3R 3, 55 75 cm showing a dark grey claystone with