The role of organic carbon in the Southern Uplands-Down-Longford Terrane accretionary prism, Scotland and Ireland

Parnell, J., Armstrong, J., Blamey, N.J.F., Boyce, A. J. , Schito, A. and Muirhead, D. (2023) The role of organic carbon in the Southern Uplands-Down-Longford Terrane accretionary prism, Scotland and Ireland. Petroleum Geoscience, 29(3), 2022-059. (doi: 10.1144/petgeo2022-059)

Abstract

Carbonaceous shales in the Southern Uplands-Down-Longford Terrane accretionary prism had extremely high potential for hydrocarbon generation in the Lower Paleozoic. Structural thickening in the prism enhanced the rapid generation of oil. Shale horizons are separated by thick turbidites composed of low-permeability greywackes, so oil under high fluid pressure either pooled along shale bedding surfaces or migrated into fractured greywackes. Pooled oil became solidified to bitumen, which locally formed deposits on a scale of tonnes, mined as coal. The carbon-rich shale also sequestered large amounts of sulfur from seawater, which precipitated as pyrite firstly during early diagenesis, then further during fluid flow through the shale beds. The oil was also sulfur-bearing. Deformation focused on the shale beds during the evolution of the accretionary prism would have been closely related to the fluid flow which precipitated bitumen and sulfides. The palaeo-fluids were also anomalously rich in methane and hydrogen, similar to fluids venting from modern accretionary prisms.

• Item Type: Articles
• Additional Information: This work was funded by the Natural Environment Research Council (NE/T003677/1).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Boyce, Professor Adrian
• Authors: Parnell, J., Armstrong, J., Blamey, N.J.F., Boyce, A. J., Schito, A., and Muirhead, D.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Petroleum Geoscience
• Publisher: The Geological Society of London for GSL and EAGE
• ISSN: 1354-0793
• ISSN (Online): 2041-496X
• Published Online: 29 June 2023
• Copyright Holders: Copyright © 2023 The Author(s)
• First Published: First published in Petroleum Geoscience 29(3):2022-059
• Publisher Policy: Reproduced under a Creative Commons license