Petrology and mineralogy of Middle Jurassic siliciclastic rocks of the Kopet-Dagh rift basin, NE Iran: A comparison with the Binalud intramontane basin

Abstract

The Middle Jurassic Kashafrud Formation of the Kopet-Dagh Basin is a succession of fluvial to turbiditic siliciclastic rocks deposited in a rift basin that was initiated in the Late Bajocian and was filled with conglomerates, sandstones, and mudstones. The sandstones are mainly lithic arkoses and feldspathic litharenites. The sandstones of the Kashafrud Formation contain evidence of numerous diagenetic processes, including compaction and fracturing, cementation, dissolution, and formation of authigenic minerals. For evaluation of the thermal history and diagenetic processes, and the formation of clay minerals, a burial temperature range for the Kashafrud Formation of more than 100 °C has been assumed. Geochemical results point to felsic, mafic, and metamorphic rocks, as well as to Proterozoic recycled sandstones as source rocks. The chemical index of alteration and plagioclase index of alteration indicate a humid to semi-arid climate at the time of sedimentation. Based on petrographic and geochemical data, the main tectonic sources for the sediments of the post-orogenic Middle Jurassic Kashafrud Rift Basin were a recycled orogen and passive margin. The Early Jurassic to early Middle Jurassic Binalud Intramontane Basin, situated at the northern margin of the Binalud Mountains and formed during a late phase of the Early Cimmerian Orogenic Event, was also filled with sediments derived from the Cimmerian mountain belt. The two basins represent different tectonic settings, but both are connected to the closure of the Palaeo-Tethys, reflecting similar source rocks and similar climatic conditions.