Seismic-stratigraphic constraints on the age of the Faroe Islands Basalt Group, Faroe–Shetland region, Northeast Atlantic Ocean

Lower Palaeogene extrusive igneous rocks of the Faroe Islands Basalt Group (FIBG)
dominate the Faroese continental margin, with flood basalts created at the time of
breakup and separation from East Greenland extending eastwards into the Faroe‐
Shetland Basin. This volcanic succession was emplaced in connection with the opening
of the NE Atlantic; however, consensus on the age and duration of volcanism
remains lacking. On the Faroe Islands, the FIBG comprises four main basaltic formations
(the pre‐breakup Lopra and Beinisvørð formations, and the syn‐breakup
Malinstindur and Enni formations) locally separated by thin intrabasaltic sedimentary
and/or volcaniclastic units. Offshore, the distribution of these formations remains
ambiguous. We examine the stratigraphic framework of these rocks on the
Faroese continental margin combining onshore (published) outcrop information with
offshore seismic‐reflection and well data. Our results indicate that on seismic‐reflection
profiles, the FIBG can be informally divided into lower and upper seismic‐stratigraphic
packages separated by the strongly reflective A‐horizon. The Lower FIBG
comprises the Lopra and Beinisvørð formations; the upper FIBG includes the
Malinstindur and Enni formations. The strongly reflecting A‐horizon is a consequence
of the contrast in properties of the overlying Malinstindur and underlying
Beinisvørð formations. Onshore, the A‐horizon is an erosional surface, locally cutting
down into the Beinisvørð Formation; offshore, we have correlated the A‐horizon
with the Flett unconformity, a highly incised, subaerial unconformity, within the
juxtaposed and interbedded sedimentary fill of the Faroe‐Shetland Basin. We refer to
this key regional boundary as the A‐horizon/Flett unconformity. The formation of
this unconformity represents the transition from the pre‐breakup to the syn‐breakup
phase of ocean margin development in the Faroe–Shetland region. We examine the
wider implications of this correlation considering existing stratigraphic models for
the FIBG, discussing potential sources of uncertainty in the correlation of the lower
Palaeogene succession across the Faroe–Shetland region, and implications for the
age and duration of the volcanism.