Glacial, fluvial and contour-current-derived sedimentation along the northern North Sea margin through the Quaternary

Christine L Batchelor,Benjamin Bellwald,Sverre Planke,Dag Ottesen,Sverre Henriksen,Reidun Myklebust,Ståle E Johansen,Julian A Dowdeswell

doi:10.1016/j.epsl.2021.116966

Abstract

The thick sequence of Quaternary sediments preserved within the northern North Sea contains important information about the glacial history, palaeo-oceanographic conditions and slope stability of this region during the last 2.6 million years. The interplay between glacial, fluvial and contouritic processes can be determined from seismic stratigraphic studies. Here, seismic horizon, attribute and geomorphological interpretations of an extensive 2D seismic dataset (∼100,000 km2) and two 3D seismic cubes (∼18,400 km2) are integrated with lithological data from eight exploration wells to map sandy sedimentary units. Mapping of seismic horizons and facies reveals that, in addition to prograding glacial sediments derived from the Norwegian mainland, the Quaternary succession includes wedge-shaped units with prograding internal clinoforms building out from the East Shetland Platform, relatively flat-lying units of acoustically stratified sediments within the central northern North Sea, and aggrading to prograding units with low-amplitude internal reflections on the continental slope. The lowermost unit of Quaternary sediment is interpreted as an ∼800 km3 earliest Pleistocene (∼2.6 Ma) turbidite-contourite deposit, in which turbidites derived from a fluvial delta building out from the East Shetland Platform transition seaward into aggrading to prograding sediments of the Shetland Drift. The wedge-shaped units are intercalated with glacigenic sediments in the central northern North Sea, showing that the East Shetland Platform was a major source area for the delivery of coarse-grained sediments during the Early Pleistocene (∼2.6–0.8 Ma). The distribution of units of aggrading to prograding geometries suggests that contourites continued to develop on the continental slope, including on the North Sea trough-mouth fan, throughout the Quaternary. These interpretations constrain a new model for the Quaternary evolution of the northern North Sea that reconciles the development of the eastern and western sides of this margin, and shows the importance of fluvial-deltaic and contouritic sedimentation during periods of reduced glacigenic sediment input. Our model also provides a high-resolution analogue for the sedimentary architectures and seismic facies that can be produced by the interplay of down-slope and along-slope processes on other continental margins.

Highlights

At the onset of the Quaternary, the northern North Sea was dominated by a north-south-orientated sub-basin of the North SeaBasin (Fig. 1) (Ottesen et al, 2014, 2018)
A fluvial delta has been identified beyond the East Shetland Platform (Ottesen et al, 2014), and part of the Shetland Drift contourite system is suggested to have extended into the northern part of the sub-basin (Fig. 1a) (Batchelor et al, 2017)
The aims of this work are to: 1) map the distribution and thickness of the Basal Pleistocene Unit and interpret its composition and origin; 2) interpret several other, potentially sandy, units of sediment that are preserved within the Quaternary succession; 3) produce new reconstructions of the evolution of the entire northern North Sea margin that show the changing relative importance of glacial, fluvial and contour-current-derived sedimentation through the Quaternary

Summary

Introduction

At the onset of the Quaternary, the northern North Sea was dominated by a north-south-orientated sub-basin of the North SeaBasin (Fig. 1) (Ottesen et al, 2014, 2018). A distinctive flat-lying unit of uncertain extent and origin, termed the Basal Pleistocene Unit, has been identified underlying prograding glacigenic sediments on the basin floor (Eidvin and Rundberg, 2001; Eidvin et al, 2019). Together, these sediments contain information about past environmental and climatic conditions in the northern North Sea, and provide insights into the configuration of past river drainage networks and the changing location and intensity of ocean currents. An easterly component of the Utsira Formation is present west of Sognefjorden, Norway (Fig. 1a). 3D seismic data have revealed that the Utsira Formation east is a fluvial delta that contains numerous anastomosing and bifurcating channels (Løseth et al, 2020)

Objectives

Discussion

Conclusion