Contourites in the Gulf of Cadiz: a cautionary note on potentially ambiguous indicators of bottom current velocity

Textural characteristics and facies of sand‐rich contourite depositional systems

“…Previous studies have shown that contourites tend to be poorly sorted on account of sediment mixing by bioturbation and due to their mixed siliciclastic–bioclastic composition (e.g. Stow et al ., ; Wetzel et al ., ; Mulder et al ., ). However, the data here show some sections of moderate sorting that appear to be broadly linked to mean grain size.…”

“…This is confirmed with the observed coarsest grained sediments accumulating in areas of amplified bottom current velocities (for example, BC05 and U1388 located within the contourite channels) and the finest grained sediments being collected from sites more distal from the MOW flow (for example, PC08). There is not, however, a direct linear correspondence for a number of reasons (McCave, ; Stow et al ., , ; Mulder et al ., ):…”

The influence of meltwater on the Labrador Current in Heinrich event 1 and the Younger Dryas

“…The proxy of SS is also influenced by the grain size distribution in the source area of the sediment and the silt component derived from ice-rafting (McCave and Mulder et al, 2013). The effect of variations in source area is minimized in this study by decarbonation, as the siliciclastic and crystalline basement sources of glacial sediment do not appear to change significantly between Heinrich layers and other late Pleistoceneeearly Holocene intervals (Piper and de Wolfe, 2003;Mao et al, 2014), being largely derived from the Labrador margin (Roger et al, 2013).…”

High resolution digital image treatment to color analysis on cores from IODP Expedition 339: Approaching lithologic features and bioturbational influence

“…Considering the narrow relationship between tracemakers and environmental conditions, ichnological analysis may prove useful to approach the genesis of contourite deposits, reflecting parameters such as current dynamics, rate of deposition, erosion, etc. However, in other cases, tracemaker activity can be a handicap for the recognition of contourites and associated sediments, because the diagnosis criteria -e.g., sedimentary structures and grain-size variationsmay be obliterated by intense bioturbation (see Wetzel et al, 2008 for a detailed analysis; Rasmussen and Surlyk, 2012;Mulder et al, 2013). Recently, a high resolution digital image treatment was applied to the ichnological analysis of cores from Expedition 339.…”

“…The scheme proposed by Gonthier et al (1984) and Faugères et al (1984) distinguishes two units from bottom to top: a first coarsening-up unit from mud to sandy sediment; and a second one, fining-up from sand to mud. For this reason, grain size is held to be the main indicator in contourite recognition (Howe, 2008), related to variations in bottom current velocity, or revealing sedimentary processes such as bed load transport or erosion (Mulder et al, 2013).…”