Nadeau M-J, Grootes PM, Voelker A, Bruhn F, Duhr A, Oriwall A.  2001.  Carbonate 14C Background: Does it have Multiple Personalities? Radiocarbon. 43(2A):169-176.

Veizer J, Davin A, Azmy K, Bruckschen P, Buhl D, Bruhn F, Carden GAF, Diener A, Ebneth S, Godderis Y et al..  1999.  87Sr/86Sr, delta 18O evolution of Phanerozoic seawater. Chemical Geology. 161:59-88.