The upper cretaceous sedimentary sequence in North-West of Iran: Microfacies and geochemistry analysis, evidence of Neotethys

The purpose of the research was to examine the Upper Cretaceous sedimentary sequence in northwest Iran, in particular, the Shahin Dezh geographical region in two stratigraphic sections, Godollu and Tark-e Viran, which revealed a thickness of 156 meters for the former and 114. 5 meters for the latter. Field studies revealed that the lithological features and macroscopic characteristics of the rock sequence of the Godollu section can be divided into 12 lithological units. Sandstone petrofacies exhibit mature textural features and are classified as litharenites based on the composition of the main grains, reflecting sedimentation on a shallow marine shelf and slope. These studies also indicated that the carbonate sequence of the Tark-e Viran section can be divided into 11 separate lithological classes, and based on the laboratory studies, the microscopic samples consisted of three groups, namely, pelagic microfacies with mudstone bioclastic facies, Globotruncana wackestone, and Oligostegina packstone. These classifications are comparable to Flugel's SMF 3 and were deposited in the facies zone of FZ₁ and FZ₃, evoking the depositional environment of relatively deep seas. Geochemical studies on the elements of strontium, sodium, manganese, and iron revealed that the amount of strontium and sodium is very low while the amount of manganese and iron is higher than the carbonate equivalents of the present era. Due to the increased effect of late meteoric diagenesis, the amount of iron increases with the increase of manganese, and the changes of Sr/Ca compared to manganese represent an open diagenetic system reflecting that of the late meteoric diagenesis. As such, the studied limestones can be best classified as semi-polar types with the primary composition of calcite mineralogy.