Oscillation of carbon and oxygen isotope compositions of carbonate rocks between evaporative and open marine environments, Upper Permian of East Greenland

Carbon isotope data from the Upper Permian sequence of East Greenland show large variations which can be correlated with changes in sea-level and salinity. During transgression, ¹³C in carbonate minerals becomes enriched by 2-4‰ relative to carbonate representing regressive-evaporitic phases. Similar changes have been found in Zechstein sequences in northern Europe. It is suggested that these δ¹³C variations are not of basinal origin but rather represent changes in the global carbon cycle. These changes may be similar to changes in δ¹³C values in the glacial-interglacial cycles of the Quaternary. During regressive phases, oxidation of organic matter both on land (coal beds) and on exposed shelf areas caused ¹³C depletion in the dissolved inorganic carbon in the ocean. δ¹⁸O values of carbonate minerals from the evaporite part of the sequence are higher by 5-10‰ relative to carbonate from the open marine environment. Because δ¹⁸O values in the open marine carbonate samples are relatively ¹⁸O depleted (up to -9‰) it is reasonable to assume that these values cannot represent the original marine values. It is suggested that the oxygen isotope record reflects the environmental water during stages of diagenesis of the carbonate minerals; the ¹⁸O-depleted values reflect meteoric water, whereas the ¹⁸O-enriched values in the evaporitic part of the sequence reflect evaporated seawater.