Deep burial dissolution of K-feldspars in a fluvial sandstone, Pentland Formation, UK Central North Sea

Mark Wilkinson*, R. Stuart Haszeldine, Andrew Morton, Anthony E. Fallick

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The Pentland Formation of the UK Central North Sea is a quartzite in a sequence of more arkosic sandstones. Provenance-sensitive heavy mineral indices are interpreted to indicate that it was probably derived by erosion of arkosic sediments, which also supplied the arkosic marine sandstones of the contemporaneous Fulmar Formation. A lack of apatite within the Pentland Formation suggests that the feldspars could have dissolved during exposure to groundwaters during very shallow burial. However, petrographic and geochemical evidence supports survival of at least some of the feldspar to burial depths in excess of at least 2 km, when the sandstones had been stabilized against compaction by quartz cements or overpressure. Abundant kaolin, which has not reacted to form illite, is preserved at burial depths in excess of 4000 m, suggesting an unusual lack of available potassium. There is a strong contrast in diagenetic pathways with the overlying marine Fulmar Formation, which most probably had the same initial composition but in which kaolin is absent and fibrous illite is present. It is suggested that a lower concentration of potassium (and aluminium) within the Pentland Formation compared with the probable source and the comparably sourced Fulmar Formation represents export of K from the sands on a metre scale.

Original languageEnglish
Pages (from-to)635-647
Number of pages13
JournalJournal of the Geological Society
Volume171
Issue number5
DOIs
Publication statusPublished - Sep 2014

Keywords

  • HEAVY MINERAL ASSEMBLAGES
  • FULMAR FORMATION
  • RESERVOIR SANDSTONES
  • UNITED-KINGDOM
  • CENTRAL GRABEN
  • DIAGENESIS
  • POROSITY
  • ILLITE
  • OIL
  • GENERATION

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