Geochemical signature of the Devonian/Carboniferous boundary was analyzed using standard and compositional approaches. • Outputs of principal component analysis were compared for raw, log-transformed and clr transformed geochemical data. • Q-mode clustering extracted predicative logratio coordinates – balances to reveal differences between shale layers. • Standard and compositional approaches have shown synergic effects. • It seems advisable to use both absolute and relative information to discern predominant and subtle geochemichal trends.