Characterization of the Govanda Formation limestones: chemostratigraphy and tectonic setting of the last marine carbonate rocks in the Arabia–Eurasia suture zone, NW Zagros fold-thrust belt

Abstract

To demystify the geochemical properties of the shallow marine Govanda Formation that are ~ 1500 m high Arabia-Eurasia suture zone, three stratigraphic sections were sampled in the NW Zagros fold-thrust belt in the Kurdistan region of Iraq. This study examined the petrography and geochemistry of major, trace, and rare earth elements (REE) of the lower-middle Miocene Govanda Formation. Microfacies analysis shows that packstone and wackstone dominate the ticker western section, whereas the eastern sections contain grainstone and clastic units. The carbonates were deposited in shallow marine reef-fore-reef environments that were not affected by diagenetic alterations. The limestone beds have a consistent seawater-like REE pattern, slightly negative Ce anomalies (Ce/Ce* = 0.79 in MSL and =0.89 in ML), relatively positive Eu anomalies (Eu/Eu* = 1.18 in MSL and =1.14 in ML), and moderately high Y/Ho ratios (37.69 n=29). The REE + Y pattern of samples mainly retains its original characters but the variations in the total rare earth element (ΣREE) content are related to the quantity of detrital materials inputs. Authigenic U, negative Ce anomalies, trace element ratio indices such as V/Cr, U/Th, Ni/Co, and V/(V + Ni) indicate suboxic-anoxic deposition conditions. Positive correlation of Al2O3% contents with Fe2O3% related the carbonate of Govanda Formation to the Open-ocean limestones. The Rb-Sr-Ba ternary diagram, and Sr/Ba vs. Sr/Rb, Al2O3% vs. Fe2O3%, and Ce/Ce* vs. Sm/Yb bivariate analyses imply that the studied limestones originated in the passive margin tectonic setting.