Geochemistry of rare earth elements in carbonate rocks of the Mirga Mir Formation (Lower Triassic), Kurdistan Region, Iraq

Abstract

Major trace and rare earth element (REE) concentrations in carbonate rocks of Mirga Mir Formation were analyzed to study the influence of terrigenous materials on REE distribution and to examine REE geochemistry for redox conditions. Contents of SiO2, Al2O3, Fe2O3, K2O, Na2O, and most of the trace elements are lower than that of a shale standard, whereas the contents of CaO, Nb, and Sr are higher. The ƩREE content however is slightly lower than that in marine carbonate rocks. These values indicate that the carbonates of Mirga Mir Formation possess (1) non-seawater-like REE-Y patterns, (2) positive Gd anomalies (average = 1.18), Gd/Gd* ratio of modern shallow seawater, (3) super chondritic Y/Ho ratio is 30.06, and (4) both negative and positive Ce anomalies (Ce/Ce* = 0.93–1.12) and most of the samples have slightly positive La anomalies. The carbonate rocks show low U content, authigenic U, and negative Ce anomalies suggesting the deposition under oxic conditions, while the positive anomalies are due to the influence of detrital clays. The present study concludes that the character of the carbonate rocks is masked by the terrigenous sediments.