Carbon and oxygen isotopic composition of carbonates from saliferous deposits of the Pripyat Trough, Belarus

Abstract

δ 18O and δ 13C in accessory calcite and dolomite from salt rock and in intrasalt carbonate beds of the Upper Frasnian and Upper Famennian evaporite formations of the Pripyat Trough vary over a wide range. Within all the intrasalt carbonate interbeds four distinct groups of rocks have been recognised on the basis of their isotopic composition. The ranges of variation of δ 13C(PDB) and δ 18O(SMOW) within these groups are respectively: (a) +0.7 to +0.8 and +35.4 to +36.4%; (b) −4.5 to −0.9 and +30.0 to +32.2%; (c) −7.0 to −2.8 and +19.8 to +25.5%; (d) −17.5 to −9.7 and +20.9 to +26.4%. The isotopic composition of accessory carbonates is more uniform. The main body of values falls within the range −11 to −3% for δ 13C and +18 to +25% for δ 18O. The carbonate matter with the observed combinations of δ 13C and δ 18O could have been formed during sedimentation and diagenesis in sabkhas, on subaetially exposed islands, on evaporite depression slopes washed by sea water and freshwater and in stagnant zones with hot brines. The carbon isotopic composition of intrasalt carbonate rocks is, on the average, lighter than that of accessory carbonates from the salts. This shows that the organic matter was most readily accumulated in evaporite basins during non-salt sedimentation.