Title: Conjugate margin architecture of hyperextended basins
Researchers: Dr Sara Martinez, Prof. Peter Haughton
Project Background and Rationale: Most of the world’s giant oilfields occur in extensional basin settings. The research carried out during the last 50 years has allowed us to advance in the understanding of the geological evolution of rift basins that have experienced relatively low (<β=1.5) magnitudes of extension. The models developed to explain the sedimentary and thermal evolution of rift basins fail to adequately and accurately predict the basin response (sedimentary architecture, thermal development and plays) in basins developing above very thin (<10 km thick) crust. Many of the Atlantic margin basins west of Ireland, such as the Porcupine and Rockall basins, together with their conjugate equivalents on the Newfoundland-Labrador margin (Jeanne d’Arc, Flemish Pass and Orphan basins) fall into this category. In the central part of many of the larger basins, the sedimentary succession is underlain by differentially stretched ultra-thin continental crust (e.g. Enachescu, 1987, 2005; Hauser et al., 1995; O’Reilly et al., 1996; Watremez et al., 2017). In the cycle of crustal extension and basin development, a four-stage process can be invoked, processing from stretching, through thinning, to exhumation and finally seafloor spreading. Remnants of the earlier rift basins are preserved beneath the successor basins as the extension and crustal rupture proceeds, resulting in a composite and complex basin architecture. The heat flow and basin architecture are critically determined by the mode of extension (pure, simple or mixed shear) and by the amount and rate of extension. Models for hyperextended crustal development in the large deep-water basins, including the Porcupine and Rockall basins, show polyphase deformation resulting in mantle exhumation along top-basement detachment faults (e.g. O’Reilly et al., 1996; Shannon et al., 1999; Prada et al., 2017). This variation in the style of crustal extension will control the nature and architecture of the overlying sedimentation. Recent scientific publications based on wide-angle seismic (WAS) data along the Porcupine Basin have provided new information related to the nature, geometry and deep structure of the crust underlain the basin. Watremez et al. (2017) propose higher stretching factors (from <6 in the north to 10 in the central of the basin) than previous estimations done by Tate et al. (1993) (from <2 in the north to >6 in the south of the basin). These authors show an asymmetric crustal structure of the basin suggesting some simple shear during extension and postulate the presence of serpentinized mantle below the thin to ultra-thin crust. Prada et al. (2017) present new observational evidence on how crustal strain-dependent serpentinisation influences hyperextension from rifting to possible crustal breakup along the axis of the Porcupine Basin. Based on three WAS profiles, these authors show the seismic structure of the uppermost lithosphere and the geometry of the Moho across and along the basin axis. Furthermore, they relate the identification on multichannel seismic (MCS) data of a major detachment fault surface, the P reflector previously suggested by Reston et al. (2001, 2004), with an inferred degree of serpentinisation >15%.
The main objectives of the project are two: - Document and understand the large-scale sedimentary response and resulting architecture of basins developing above hyperextended crust on the North Atlantic passive margin conjugate system of Ireland and Eastern Canada. Specifically, this project focuses on comparisons and identification of differences in sedimentary timing and style between conjugate margins. - Provide a predictive understanding of critical petroleum play ingredients in hyperextended basins.