Lower cretaceous (Neocomian) fluvial deposits in eastern Kopet-Dagh Basin, northeastern Iran

Abstract

The Kopet-Dagh intracontinental basin of northeastern Iran, formed after Middle Triassic orogeny, was a site of relatively continuous sedimentation from Jurassic through Miocene time. An epicontinental sea covered the eastern portion of the basin from near the end of the Jurassic through the Early Cretaceous, at which time the sea regressed toward the northwest. The resulting regressive depositional phase is represented in the stratigraphic record of the basin by a thick interval of cyclic redbeds that were deposited in fluvial environments. Sedimentological analysis of these regressive sediments indicate that the coarser-grained sediments of the lower and middle parts of this interval were deposited as sheet-like bodies in a low sinuosity, coarse-grained braided-stream system. The upper part of the interval consists primarily of finer-grained sediments that were deposited in a lower-gradient meandering stream system. Paleocurrent analysis of cross-beds and the thinning of coarser-grained sediment toward the northeast indicate that the source of these Neocomian siliciclastics were to the south and southwest of the Kopet-Dagh basin. Because the lower part of this interval is a gas-producing reservoir in the Khangiran gas field, northeast Iran, the results of this study are applicable to future exploration efforts in the Kopet-Dagh Basin and similar basins elsewhere.