Premium
Sedimentary processes in the Selvage sediment‐wave field, NE Atlantic: new insights into the formation of sediment waves by turbidity currents
Author(s) -
Wynn Russell B.,
Weaver Philip P. E.,
Ercilla Gemma,
Stow Dorrik A. V.,
Masson Douglas G.
Publication year - 2000
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1046/j.1365-3091.2000.00348.x
Subject(s) - geology , turbidity current , turbidite , sediment , geomorphology , sedimentary rock , sediment transport , hydraulic jump , sedimentary depositional environment , geophysics , flow (mathematics) , paleontology , structural basin , geometry , mathematics
An integrated geophysical and sedimentological investigation of the Selvage sediment‐wave field has revealed that the sediment waves are formed beneath unconfined turbidity currents. The sediment waves occur on the lower continental rise and display wavelengths of up to 1 km and wave heights of up to 6 m. Wave sediments consist of interbedded turbidites and pelagic/hemipelagic marls and oozes. Nannofossil‐based dating of the sediments indicates a bulk sedimentation rate of 2·4 cm 1000 years –1 , and the waves are migrating upslope at a rate of 0·28 m 1000 years –1 . Sediment provenance studies reveal that the turbidity currents maintaining the waves are largely sourced from volcanic islands to the south. Investigation of existing models for sediment‐wave formation leads to the conclusion that the Selvage sediment waves form as giant antidunes. Simple numerical modelling reveals that turbidity currents crossing the wave field have internal Froude numbers of 0·5–1·9, which is very close to the antidune existence limits. Depositional flow velocities range from <6 to 125 cm –1 . There is a rapid increase in wavelength and flow thickness in the upper 10 km of the wave field, which is unexpected, as the slope angle remains relatively constant. This anomaly is possibly linked to a topographic obstacle just upslope of the sediment waves. Flows passing over the obstacle may undergo a hydraulic jump at its boundary, leading to an increase in flow thickness. In the lower 15 km of the wave field, flow thickness decreases downslope by 60%, which is comparable with results obtained for other unconfined turbidity currents undergoing flow expansion.