A record of Eocene (Stronsay Group) sedimentation in BGS borehole 99/3, offshore NW Britain: implications for early post-break-up development of the Faroe-Shetland Basin

A punctuated Eocene succession has been recovered in British Geological Survey borehole 99/3 from the Faroe-Shetland Basin. The borehole was drilled close to the crest of the Judd Anticline and penetrated 110.5 m into the post-breakup Stronsay Group. The borehole proved 23.8 m of Ypresian–earliest Lutetian paralic to shallow-marine deposits, unconformably overlain by 43.85 m of mid-Lutetian lower shoreface to shallow-marine shelf deposits, in turn unconformably overlain by 42.85 m of late Bartonian–Priabonian mass-flow (slope apron) and basinal deposits. At the borehole site, the Ypresian–earliest Lutetian sediments were subaerially exposed in early Lutetian times; these deposits were subsequently transgressed by the mid-Lutetian shelf – itself eroded in the late Lutetian with reworked material transported northwards and redeposited in the Mid-Eocene basin-floor fan complex in Quadrants 213 and 214. The eroded mid-Lutetian shelf was subsequently downlapped and buried beneath prograding late Bartonian–Priabonian slope apron-to-basinal sediments as the borehole site subsided. Integrating the borehole data with the regional seismic-stratigraphy indicates three major intervals of regression – early/mid-Lutetian, late Lutetian and late Bartonian – which, it is suggested, coincide predominantly with tectonic activity, particularly compressional deformation, possibly linking the early post- breakup development of the Faroe-Shetland Basin to the evolution of the adjacent Norwegian Basin.