PROVENANCE AND DEPOSITIONAL ENVIRONMENT OF THE CARBONATES FROM BALUTI FORMATION (LATE TRIASSIC), KURDISTAN REGION, IRAQ

Abstract

The carbonate of Late Triassic Baluti Formation, Kurdistan Region, Iraq was geochemically investigated to interpret provenance, depositional environments and sources of the rare earth elements (REEs) based on major, trace, and rare earth elements geochemistry. The predominance of Ca and the low percentage of Mg suggest that mineral phase is calcite at Sararu; in contrast, the dominance of MgO is in Sarki indicates the carbonate is subject to intensive dolomitization. P and Sr are dominated over the other elements, especially for Sararu carbonate. The positive correlation of ΣREE with Ti, Al, K, Sc, V, Rb, Y, Zr, and Nb and negative correlation with Ca in addition to slight enrichment of LREE suggest an input of siliciclastic sediments from the continent. The low values of the Y/Ho ratio (29.83 to 33.85) relative to marine water and approach of Ce anomaly to 1.0 refer to increasing the clastic flux from the adjacent continent and freshwater intrusion to seawater during the precipitation of Baluti carbonates. The low abundance of Cr, Ni, Co, and the Th/Sc, La/Sc, Cr/Th ratios indicate the felsic source rocks; this is confirmed by the slightly LREE enriched and flat HREE patterns and a slightly high average of (La/Yb)sn. Low authigenic U contents, U/Th ratios and slightly negative Ce anomalies suggest the Baluti carbonates were precipitated under oxic conditions and shale at Sarki section was influenced by suboxic conditions. The high Mg/Ca and low Sr/Ca ratios reflect shallow marine environments for Baluti carbonates with diagenetic effect especially in Sarki section. The Mn/Sr ratio implies the Sararu samples have higher degrees of preservation relative to Sarki. Most of REE contents in Sararu is attributed to the terrigenous origin, and the weak non-significant positive correlation of Si, Ti, and Al with REE content suggest little contribution in the Sarki and the biogenic carbonate from the seawater may play a role in the REE concentration. These carbonates possess non-seawater-like REE patterns with slightly LREE enrichment and HREE depletion, and characterized by –ve Ce*.