Eocene post-rift tectonostratigraphy of the Rockall Plateau, Atlantic margin of NW Britain: Linking early spreading tectonics and passive margin response

Abstract

A regional study of the Eocene succession in the UK sector of the Rockall Plateau has yielded new insights into the early opening history of the NE Atlantic continental margin. Data acquired from British Geological Survey borehole 94/3, on the Rockall High, provides a high-resolution record of post-rift, Early to Mid-Eocene, subaqueous fan-delta development and sporadic volcanic activity, represented by pillow lavas, tuffs and subaerial lavas. This sequence correlates with the East Rockall Wedge, which is one of several prograding sediment wedges identified across the Rockall Plateau whose development was largely terminated in the mid-Lutetian. Linking the biostratigraphical data with the magnetic anomaly pattern in the adjacent ocean basin indicates that this switch-off in fandelta sedimentation and volcanism was coincident with the change from a segmented/transform margin to a continuously spreading margin during chron C21. However, late-stage easterly prograding sediment wedges developed on the Hatton High during late Mid-to Late Eocene times; these can only 2 have been sourced from the Hatton High, which was developing as an anticline during this interval.This deformation occurred in response to Mid-to Late Eocene compression along the ocean margin, possibly associated with the reorganisation to oblique spreading in the Iceland Basin, which culminated at the end of the Eocene with the formation of the North Hatton Anticline, and the deformation (tilting) of these wedges. A series of intra-Eocene unconformities, of which the midLutetian unconformity is the best example, has been traced from the Rockall Plateau to the FaroeShetland region and onto the Greenland conjugate margin bordering the early ocean basin. Whilst there appears to be some correlation with 3 rd order changes in eustatic sea level, it is clear from this study that tectonomagmatic processes related to changes in spreading directions between Greenland and Eurasia, and/or mantle thermal perturbations cannot be discounted.

The Norway Basin revisited: From continental breakup to spreading ridge extinction

“…Onshore East Greenland, the transition C22/C21 fits with the end of a post-breakup volcanic phase (50e47 Ma) in the Blosseville Coast area (Tegner et al, 1998) followed by the sudden influx and deposition of preserved siliciclastics partly sourced from the uplifted margin and nearby JMMC (Larsen et al, 2005). More recently, Stoker et al (2012) refined the stratigraphy of the post-rift successions in the Rockall Plateau and documented important stratigraphic changes during Early and MidEocene, which coincide well with the phase of reorganisation revealed in the NB. Even if the dynamic link and mechanisms involved are not yet understood, the series of concomitant magmatotectonic and stratigraphic events recorded in the Early/Mid-Lutetian may be contemporaneous of the Mid-Eocene spreading reorganisation highlighted by the new NB-07 survey (Fig.…”

“…The spreading and geodynamic development of the NB and NorwegianeGreenland Sea has also been associated with marginwide tectonic and stratigraphic expression within the stratigraphic record of the NE Atlantic rifted margins Stoker et al, 2005Stoker et al, , 2012 (Fig. 2).…”

Detrital zircon age constraints on basement history on the margins of the northern Rockall Basin

“…(Fig. 5), proved that the material that forms these wedges was derived locally from the Rockall High (Stoker et al, 2012). BGS borehole 94/1 also sampled the East Rockall Wedge, albeit the collapsed outer part of the wedge (Fig.…”

“…9). This wedge was penetrated by BGS borehole 94/7 and proved to consist of bioclastic, carbonate-rich sandstones of Mid-to Late Eocene age (McInroy et al, 2006;Stoker et al, 2012).…”

Regional distribution of volcanism within the North Atlantic Igneous Province

“…On all margins except for Rockall -Hatton, these units are therefore not included. Where drilled along Rockall, Hatton and the Faroes, the thickness of landward lava flows is commonly more than 1 km (Varming 2009), and on the Outer Hebrides High, 2-2.5 km of lava flows are estimated (Stoker et al 2012). For this exercise, a 1.5 km-thick layer of basalt is included for the Rockall-Hatton margins where landward flows and sills are mapped (see Figs 4 and 6).…”