Abstract
Summary Two wells drilled by Sovereign in 1984 NNE of the Shetlands (Wells 219/28-1 & 219/28-2) passed through numerous primary basic ashfall tuff horizons within a sequence of abundantly tuffaceous rocks representing the basal early Eocene ‘ash-marker’. Small amounts of volcanic debris can be recognized in adjacent strata. In one of the wells, two chemically distinct sills of olivine-dolerite were penetrated below the ‘ash-marker’ in late Cretaceous rocks. The probable magmatic sequence revealed by petrographic studies, K/Ar and 40 Ar/ 39 Ar dating is: (1) The near-sediment/sea water interface intrusion of a dolerite sill into Santonian strata around 80 Ma in early Campanian times (Well 219/28-2). (2) A major episode of explosive volcanic eruptions depositing many primary basic ashfall tuffs in the basal early Eocene (both wells). (3) Minor further volcanic activity continuing throughout most of the early Eocene (both wells) with two slightly more significant eruptions in the late early Eocene and early mid-Eocene respectively. (4) The intrusion of a dolerite sill into Campanian strata close to 50 Ma in mid-Eocene times (Well 219/28-2).
Published Version
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