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.
Very thick sequences, up to 25 000 ft, of Permo-Triassic sediment are preserved within the Papa and East Solan Basins, in the West Shetlands area. The active margin of this Permo-Triassic basin lay along the West Shetland Spine Fault. Due to severe erosional truncation, the position of the westerly passive margin cannot be delineated. The Triassic basin fill, referred to the Papa Group, has been proven by drilling to be at least 8000 ft thick. A combination of palynological, log and sedimentological analyses have allowed the succession to be informally subdivided into lithostratigraphic units. The oldest, of earliest Triassic age, is the Otter Bank Shale Formation deposited in a coastal/alluvial plain setting. This is gradationally succeeded by the coarse-grained Otter Bank Sandstone Formation comprising sediments derived from the interdigitation of sheetflood, braidplain and aeolian environments of deposition. These represent the initial erosional products derived from the uplifted, rifted basin margin. This major phase of Early Triassic rifting is believed to have taken place during the Scythian. The succeeding Foula Sandstone Formation marks the establishment of predominantly axial braidplain systems, deposited during a period of intermittent but waning tectonic influence during Middle to Late Triassic times. The Papa Group is referred to the New Red Sandstone Supergroup.
Hydrocarbon migration from the Faeroe-Shetland Basin source kitchen into the Mesozoic back basins that flank its southern margin is prevented by basement highs such as the Rona Ridge. The back basins have long been considered non-prospective due to a perceived lack of source rock and insufficient burial to generate commercial hydrocarbons. The Triassic Strathmore discovery made in 1990, followed by the Upper Jurassic Solan discovery the following year, have demonstrated the prospectivity of the East Solan Basin and similar back basins along the same trend. The two discoveries typify the potential plays in this area, which consist of tilted Palaeozoic and pre-Upper Jurassic structural traps, and syn-to post-Upper Jurassic pinch-out plays against the surrounding structural highs.Strathmore, which straddles UK Blocks 204/30a and 205/26a
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