A strongly subsiding rift basin in NE Iran, the Kashafrud Basin, opened in the Late Bajocian with the accumulation of more than 2000 m of Upper Bajocian–Upper Bathonian siliciclastic sediments. These sediments comprise the Kashafrud Formation, which crops out along a NW–SE stretch of more than 200 km and occupies a width of 50 km, situated between the Koppeh Dagh and the Binalud Mountains. Ten sections of the formation were logged. Sedimentary environments range from non-marine alluvial fans and braided rivers in the lowermost part of the succession to deltas, succeeded by storm-dominated shelf, slope and deep-marine basin. Monotonous mudstones and turbidites prevail in the deep-marine part of the basin. The thickness and facies of the Kashafrud Formation vary strongly between localities, and reflect distance from the rift margins as well as submarine topography, which was shaped by block tectonics. The Kashafrud Basin is interpreted as the eastern extension of the South Caspian Basin, which entered the rifting stage in the late Early Jurassic and the spreading stage in the Late Bajocian.