Sedimentology and depositional environments in the Mesozoic, West of Shetland

Dodd, Thomas J.H.. 2018 Sedimentology and depositional environments in the Mesozoic, West of Shetland. Nottingham, UK, British Geological Survey, 65pp. (CR/18/025N) (Unpublished)

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As part of Phase 3 of the Faroe-Shetland Consortium project on the UK sector of the Faroe-Shetland Basin, BGS completed detailed (10 cm-scale) sedimentary logging of 604.77 m of conventional core recovered from 19 wells, drilled between 1974 and 1995. The project originally focussed solely on Jurassic-aged sediments, as identified in BGS held well databases. In reality, the project examined a suit of sediments ranging from the Triassic, Jurassic and Lower Cretaceous. In addition, a suite of complementary palynological sampling was completed. The goal was to provide additional depositional environment information from palyno-facies analysis, along with age determination for the sediments. Together, the two new datasets form an integrated re-assessment of the Mesozoic-aged depositional environments located to the West of Shetland. The Triassic-aged deposits of the Papa Group record deposition in a fluvial environment, whereby the fluvial systems display meandering to braided characteristics. In places, particularly in the upper parts of the cored Triassic-aged strata, the sediments display evidence for nearshore, wave-working processes. The nearshore working may be evidence for a transgression event at the top of the cored Triassic interval; something which should be investigated further in the future. Within the Jurassic-aged succession, two main groups were analysed: the Skerry Group and the Humber Group. Sediments within the Skerry Group were deposited within a fully marine, shelfal environment (the Stack Skerry Formation) and a relatively deeper-water, outer shelf to bathyal environment (the Sule Skerry Formation). Late Jurassic-aged sediments from the Humber Group are represented by the Rona Member, the Solan Sandstone Member and the Ridge Conglomerate Member. BGS has subdivided the Rona Member into five “facies”, largely on the basis of depositional environment. These include: Rona R1 (Fluvial), Rona R2 (Fan Delta), Rona R3 (Marginal Marine), Rona R4 (Shoreface/Littoral) and Rona R5 (Shallow Marine). Deposits of the Rona R4 facies represent good hydrocarbon reservoir targets, whilst the Rona R3 facies has the potential to form a sourcing lithology. The Solan Sandstone Member, interpreted to be contemporaneous with the deposition of the Rona Member, was deposited in a deep-marine, turbidite fan system. The Kimmeridge Clay Formation is encountered in a number of wells, typically represented by a dark grey- to black-coloured, hemi-pelagic mud-prone succession. The Early Cretaceous-aged Cromer Knoll Group is also present in the core data, represented by: turbidite fan deposits, formed in a deep marine environment (204/19-1 & 205/21-1A); and by shoreface/littoral deposits representative of a marine setting (205/26a-2). These sediments appear to rest unconformably on the Kimmeridge Clay Formation.

Item Type: Publication - Report
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed, but not externally peer-reviewed. Report made open in June 2021.
Date made live: 09 Jul 2021 09:18 +0 (UTC)

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