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.
- Programområde 3: Energiressourcer