Constraining the depth and timing of large-scale conical sandstone intrusions

Abstract

Kilometer-scale sandstone intrusions-a recently recognized end member of the spectrum of soft-sediment deformation structures-are important components of many deep-water sandstone reservoirs. They result from the remobilization of considerable volumes of sand during early stages of burial. This paper uses three-dimensional seismic data, calibrated to nearby wells, to describe an extensive system of large downward-tapering conical sandstone intrusions from the Faeroe-Shetland Basin, on the UK Atlantic margin. The intrusions are derived from a middle Eocene submarine fan and are injected vertically upward through overlying, highly faulted claystones to form conical bodies that interconnect across the ∼700-m-thick claystone interval to feed a set of shallow intrusions located within a few hundred meters of the paleoseabed. The forcible intrusion of these shallow sandstone bodies produced complementary folding of the contemporaneous seabed. The subsequent onlap of these seabed domal folds took place immediately after the intrusion event, and by correlation to biostratigraphic data from nearby wells, we date these intrusions as late Miocene. This is the first time that both the age and emplacement depth range of a system of large-scale sandstone intrusions have been constrained.