Mineralogy and geochemistry of the middle to upper jurassic sargelu, naokelekan, and barsarin formations from northeastern Iraq: Implications for paleoenvironmental, provenance, and tectonic setting proxies

Abstract

This study investigates the mineralogical and geochemical characteristics of the middle-upper Jurassic Sargelu, Naokelekan, and Barsarin formations in the Sargelu area, northeastern Iraq. The study aims to interpret the provenance, tectonic setting, paleoclimate, and paleoweathering processes that shaped these formations using X-ray diffraction, X-ray fluorescence, and stable isotopes of carbon and oxygen. The findings provided valuable insights into the geological history and environmental conditions of the region during the Jurassic period. XRD analysis revealed that the clay minerals in the shale samples primarily consist of illite, kaolinite, and mixed-layer illite-smectite. Geochemical analysis of major and trace elements, along with clay mineralogy and stable oxygen and carbon isotopic data, indicate that arid to semi-arid and semi-humid climatic conditions prevailed during the deposition of the Jurassic formations. The shales from the Sargelu, Naokelekan, and Barsarin formations were derived from a felsic igneous source, as evidenced by multiple multidimensional diagram plots and a bivariate plot of SiO₂ vs log (K₂O/Na₂O). Variations in oxygen and carbon isotopes, along with trace element data, suggested that the Sargelu Formation was deposited in a saline marine environment, the Naokelekan Formation in a saline marine to freshwater environment, and the Barsarin Formation in a highly saline, brackish-to-freshwater environment. Paleoredox and paleoproductivity proxies indicated deposition under anoxic to suboxic conditions, with particularly high productivity observed in the Naokelekan Formation.