To cite package 'rioja' in publications use:

Juggins, S. (2012) rioja: Analysis of Quaternary Science Data, R package version (0.8-7). (http://cran.r-project.org/package=rioja).

Corresponding BibTeX entry:

  @Manual{,
    title = {rioja: Analysis of Quaternary Science Data},
    author = {Steve Juggins},
    year = {2013},
    note = {R package version 0.8-7},
    url = {http://www.staff.ncl.ac.uk/staff/stephen.juggins/},
  }