Sequence stratigraphy and sea level history of the upper Paleocene strata in the Kopet-Dagh basin, northeastern Iran

The intracontinental Kopet-Dagh basin formed after the Middle Triassic orog eny in northeastern Iran and southwestern Turkmenistan. This underexplored basin could provide significant petroleum reserves in the 21st century. The upper Paleocene Chehel-Kaman Formation is exposed along northwest-southeas t-trending folds and is composed of carbonate strata and minor amounts of s iliciclastic and evaporite beds. Six stratigraphic sections in the central and eastern parts of the basin have been used to divide the upper Paleocene (Thanetian) carbonate supersequence into four major carbonate lithofacies, each having multiple subfacies. These lithofacies represent open-marine, s hoal, semirestricted lagoon, upper intertidal, and tidal-nat subenvironment s that formed on a shallow carbonate ramp. In addition, there are two silic iclastic lithofacies consisting of calcareous shale (marl) and calcite-ceme nted sandstone. The upper Paleocene interval consists of three depositional sequences (DS1, DS2, and DS3), bounded by type 2 (within the top of the underlying Pestehl eigh Formation), type 2, and type 1 sequence boundaries, respectively. Sea level changes during the Thanetian in the Kopet-Dagh basin are similar to g lobal changes proposed by Haq et al. (1988), with differences related to lo cal and regional geological events. Upper Paleocene strata were deposited i n about 4 m.y., within the range of second-order cycles. Each depositional sequence was developed as a third-order cycle composed of several shallowin g-upward parasequences (fourth- to fifth-order cycles). We estimate that se a level fluctuations in the study area were between 5 and 11 m during devel opment of parasequences.