J. M. McArthur, M. L. Coleman, J. M. Bremner; Carbon and oxygen isotopic composition of structural carbonate in sedimentary francolite. Journal of the Geological Society ; 137 (6): 669–673. doi: https://doi.org/10.1144/gsjgs.137.6.0669
δ 13C values for carbonate in francolite clearly distinguishes between authigenic varieties precipitated within anoxic sediments and diagenetic varieties produced by phosphatization of carbonates. δ18O values are characteristic of a deposit and, whilst apparently in equilibrium with pore-water in Recent deposits, are probably unreliable as palaeotemperature indicators generally. The isotopic composition of carbonate may therefore be used as a pointer to the mechanism of origin of francolite.