The tectono-stratigraphy of the Solan Basin, west of Shetland

Abstract

The Solan Basin lies in a part of the West Shetland continental margin that has had a complex tectonic history, dominated by extension but punctuated by several episodes of inversion, transpression and extensive erosion. The oldest sedimentary sequence, identified on seismic but not yet penetrated by drilling, may comprise Devono–Carboniferous clastics. In the Permo-Triassic a large system of half-grabens was filled with a thick succession of coarse, continental clastics. These appear to have entered the basin system in two discrete pulses and it is speculated that a third pulse, representing a transition to marginal and fully marine environments, occurred in the Early Jurassic. The area was effectively peneplaned in the late Middle to early Late Jurassic, with the removal of up to 1.5 km of section. Overlying this unconformity is a thin sequence of marginal marine sandstones and organic-rich marine shales, deposited in the latest Jurassic to earliest Cretaceous. Although parts of the region received a major influx of sand derived from the West Shetland Platform in the Early Cretaceous, the equivalent strata throughout most of the Solan Basin are a thin succession of pelagic shales and carbonates. In the early Turonian the basin was inverted. During the Late Cretaceous, extension, related to rifting along the line of the Faeroe–Shetland Trough, resulted in the development of large normal fault systems, providing the space in which a thick sequence of deep marine shales was deposited. In the earliest Paleocene, transpressional reactivation of some faults produced intense, but localized, inversion structures. Generally, however, sedimentation continued uninterrupted through the Paleocene, with the accumulation of deep marine sandstones in the east of the basin. The culmination of Thulean volcanism in the earliest Eocene was marked by the deposition of tuffaceous mudstones, which are overlain by thin coal-bearing, paralic to continental sediments. Regional thermal subsidence began in the early Eocene and continued into the Oligocene with the deposition of a thick sequence of marine clastics. In the Miocene, erosion removed up to 1.2 km of sediment from parts of the Rona Ridge and produced a basin-wide unconformity. This is overlain by Pliocene to Recent glacio-marine sands and gravels.