Turbidite and contourite sediment waves in the northern Rockall Trough, North Atlantic Ocean

• Published in: Sedimentology
• Main Author: HOWE, JOHN A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1996
• Subjects: Rockall Trough; Barra; North Atlantic
• Online Access: http://dx.doi.org/10.1046/j.1365-3091.1996.d01-1.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1365-3091.1996.d01-1.x; https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3091.1996.d01-1.x

ABSTRACT Two sediment wave fields have been identified in the northern Rockall Trough; one from the north‐eastern part of the trough, developed on the flank of an elongate sediment drift, and the other at the distal edge of the Barra Fan. Wavelengths in both areas vary from 1 to 2 km and wave heights from 5 to 20 m. The seismic character of both the wave fields is similar with a lower package of well‐layered, medium‐ to high‐intensity reflectors migrating upslope, overlain by a dominantly acoustically transparent unit containing irregular, semicontinuous reflectors. Eight cores have been recovered from the two wave fields, seven from the crest‐trough areas of the distal Barra Fan wave field, and a single core from the crest of the sediment‐drift waves. Lithologically, the cores show that different processes have been active across the two wave fields. Cores from the Barra Fan field contain thin turbidites with thicker, draped hemipelagites and hemiturbidites, corresponding to the well‐layered, reflective seismic units and transparent seismic unit, respectively. These waves have been maintained by turbidity currents, perhaps over older, originally bottom‐current‐formed waves. The single core from the small sediment‐drift wave field recovered hemipelagites and glaciomarine sediments grading upwards into muddy‐silty contourite deposits, topped by a sandy contourite. These waves were constructed by contour currents. Dating of cores from these two small wave fields revealed that the sequences of thin turbidite and hemipelagite sediments from the Barra Fan correspond to the Late Glacial‐Allerød/Bölling Interstadial with the overlying hemipelagite of Younger Dryas‐Holocene age. The contourite deposits from the north‐east Rockall Trough wave field have been dated as early Holocene, reflecting increasing bottom‐current activity at the changeover from a glacial to an interglacial regime.