A quantitative assessment of tectonic stretching in the northern North Sea, the Triassic of the Utsira High and greater Tampen Spur area

Understanding the rates and amount of extension during the initiation of rifting in the northern North Sea basin is important for defining the structural framework for the subsequent Mesozoic rifting event. The pre-Jurassic tectonic history of the northern North Sea rift has, to date, been largely overlooked due to difficulties in distinguishing Triassic strata from older Devonian and Permian units, limited quality of deep seismic data and a lack of deep well penetrations within rift basin depocenters. This study integrates recent research on the Triassic of the North Sea region to analyse and restore 2D seismic lines and establish a unified tectonic framework for the northern North Sea Triassic rift system. Four regional transects and nine sections covering the Norwegian and UK sectors are analysed, and the tectonic stretching is calculated for the Devonian-Carboniferous, Permian, Triassic (Early, Middle, and Late), Jurassic, and Cretaceous. Our results demonstrate that during the Triassic, extension occurred primarily in the Early and Late Triassic, with minor extension in the Middle Triassic. Furthermore, the Triassic rift was a significantly lower-magnitude event than previously estimated (between β = 1.20 and 1.50), with an extension of c.a. 4% (β = 1.04). By utilising cross-border datasets, this work reviews the northern North Sea stretching factor throughout the upper Paleozoic and Mesozoic. It also provides a comparative analysis with other rifts, exploring the evolution of the northern North Sea and its relationship with the opening of the Atlantic, ultimately creating a cohesive narrative of the Mesozoic rifting event and its earlier evolutionary stages. • The Permo-Triassic extension has been overestimated in existing literature. • Extension values from Devonian to Cretaceous are β 1.19 across the region. • Triassic β values range from 1.02 to 1.04, compared to β ∼1.40 in the literature. • β values show that the Northern North Sea rift is in an "early stage" of rifting. • Jurassic and Cretaceous β values show migration of the rift towards the east.