Sedimentation on basin plains

Rothwell, Robin Guy (1994) Sedimentation on basin plains. University of Southampton, Doctoral Thesis.

Abstract

Deep sea basin plains are commonly characterised by thick sediment sequences dominated by allochthonous sediments deposited by sediment gravity flows. These allochthonous deposits commonly include turbidite muds, especially in distal settings. The present research assesses the significance of thick mud turbidites in deep sea basin plain sedimentation. Investigation of basin plain sequences enhances our understanding of how sediment proceeds from the continental shelves or other high ground to the deep sea, and thereby how basins develop and fill. Deep sea basin plain sediments are generally rare in the geological record, because they tend to be subducted in the long term. Until relatively recently the turbidite facies model was largely based on the study of proximal turbidites from the ancient record. However, effective facies models must combine data from both ancient and recent sediments. Our knowledge concerning the nature and extent of turbidites in modern oceans has increased markedly in recent years and there is a need to refine the turbidite facies model considering new data.

This research uses the extensive database of over 80 good quality piston cores collected from the Madeira Abyssal Plain (Canary Basin, NE Atlantic) over the last decade to describe the evolution of a modern oceanic basin fill. The late Quaternary sequence is dominated by commonly thick, laterally extensive turbidite muds, many of which have been deposited by large volume turbidity currents. Complex coarse-grained basal facies in many turbidites are interpreted as caused by fluctuating flow velocities and reflection from adjacent high ground. In some settings, turbiditic and hemipelagic deep sea muds can appear visually very similar. However, this research demonstrates that they can be distinguished through rigorous sedimentological analysis. Such analysis is used to identify, otherwise obscure, turbidite muds in visually rather uniform sequences of allochthonous and autochthonous clayey nannofossil oozes which form basin fill in small graben within the western Lau Basin, SW Pacific.

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