a)

Gravity image showing structural framwork of the Rockall–Porcupine region, and location of sections b–d.

b)

Cross-section across the central Rockall Basin. Modified from Nadin et al. (1999) and Stoker (2002)

d)

Geoseismic section of the southern Rockall Basin.
Modified from McDonnell & Shannon (2001)

Geoseismic section of the Porcupine Basin.
Modified from McDonnell & Shannon (2001)

Figure 17. Pre-Neogene framework of the Rockall–Porcupine region

Note on gravity image

To the west of the yellow line, the image is based on gravity values derived from satellite altimetry (Sandwell & Smith 1997); to the east of the line, the image is derived from a BGS compilation of open-file land and marine data (free-air gravity anomaly offshore; bouguer gravity anomaly on land). The abbreviated structural elements are as follows: FSB, Faroe-Shetland Basin; WTR, Wyville-Thomson Ridge; NERB, NE Rockall Basin; WLB, West Lewis Basin; WFB, West Flannan Basin; FT, Flannan Trough; OHP, Outer Hebrides Platform; BT, Barra Trough; DB, Donegal Basin; SB, Slyne Basin; RB, Rónán Basin; LH, Ladra High; GBB, George Bligh Bank; ADL, Anton Dohrn Lineament; GGF, Great Glen Fault; MF, Minch Fault; CGFZ, Charlie Gibbs Fracture Zone; COB, Continent-Ocean Boundary. The abbreviated igneous complexes are as follows: S, Sigmundur; D, Darwin; RMB, Rosemary Bank Seamount; AD, Anton Dohrn Seamount; HT, Hebrides Terrace Seamount; GIC, Geikie Igneous Complex; SK, St. Kilda; BVR, Barra Volcanic Ridge. 

Note on structural terminology

In a structural nomenclature system recently published for the Irish Atlantic margin (Naylor et al. 1999) bathymetric features were separated and distinguished from their underlying geological structures. Hence the structures (e.g. basins and highs) underlying the Porcupine Seabight, Porcupine Bank, Rockall Trough and Rockall Bank were renamed the Porcupine Basin, Porcupine High, Rockall Basin and Rockall High, respectively. Whilst these structural elements are applicable to the syn- and early post-rift phases of margin development, they are less relevant to the late post-rift (Neogene) expression of the margin which is still being shaped today by bottom-current and episodic mass-flow processes. For this reason, and the fact that the new nomenclature does not yet apply to UK waters, the traditional terminology is largely retained in the present study. However, for the purpose of the pre-Neogene framework section the structural terminology is indicated on the gravity image (Fig. 17a) and used throughout the text in WP3, whereas both structural and present-day physiographic terminologies are used on the cross-sections (Figs 17b–d).