Dating, correlation and stratigraphy of the Triassic sediments in the West Shetlands area

Abstract

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.

The Permian–Triassic transition and the onset of Mesozoic sedimentation at the northwestern peri-Tethyan domain scale: Palaeogeographic maps and geodynamic implications

“…the Western Shetlands; Fig. 2), the Midde-Upper Permian is characterised by coastal plain playa-lake deposits (Swiecicki et al, 1995). In southern England (Devon; Fig.…”

“…An angular unconformity separates Permian from Triassic deposits in the western part of the Germanic Basin (Fig. 2): Western Shetlands (Swiecicki et al, 1995), South England (the Wessex Basin; Goldsmith et al, 1995Goldsmith et al, , 2003Hounslow and Mdntosh, 2003), Central Graben (Goldsmith et al, 1995(Goldsmith et al, ,2003, and the Celtic Sea (Brookfteld, 2008;Shannon, 1995).…”

“…2). They constitute coastal alluvial plain deposits of the Otter Bank Shale Formation, dated by palynology (Swiecicki et al, 1995). The palynological assemblages of the Induan deposits indicate a warm and semi-arid environment (Swiecicki et al, 1995).…”

“…the Devon Basin (Hounslow and McIntosh, 2003), the Central Graben (Goldsmith et al, 1995(Goldsmith et al, ,2003, the Celtic Sea (Shannon, 1995), the Western Shetlands (Swiecicki et al, 1995) and the Lower Triassic successions (Fig. 2) are characterised either by ephemeral fluvial deposits or arid alluvial wadi deposits, associated with aeolian dunes and ventifacts.…”

“…From these sedimentological criteria, these sediments could be Smithian in age. The Spathian, identified in the Western Shetlands (Swiecicki et al, 1995), is difficult to constrain in the other British basins (Fig. 2).…”