Upper Maastrichtian depositional environments and sea-level history of the Kopet-Dagh Intracontinental Basin, Kalat Formation, NE Iran

Abstract

The Kopet-Dagh Basin is located in northeastern Iran and southern Turkmenistan. The Late Maastrichtian Kalat Formation caps the Cretaceous interval in this Basin. Based on eight measured stratigraphic sections, the depositional environments and the sea-level history of the Kalat Formation have been interpreted. Petrographic and field observations led to identification of four major carbonates (A–D) and two siliciclastic lithofacies types. Carbonate rocks were deposited on a ramp setting within three zones including restricted and semi-restricted lagoons, bars, and open marine environments, while the siliciclastics were deposited at the shoreline. Sequence stratigraphic analysis identified two depositional sequences in the western and eastern parts and three depositional sequences in the central parts of the study area. Comparing the sea-level curve of Late Maastrichtian time in the Kopet-Dagh Basin with the global sea-level curve for the same time interval, there are some geometrical similarities and differences. The variations in the Basin are related to regional tectonic settings and sediment loading of the study area. Reconstructions of depositional environment during eight time slices of the Late Maastrichtian are presented. These results could be used for comparison with other localities worldwide and provide additional data for Late Cretaceous paleogeographic reconstructions.