Karaj Formation crops out in a very large area in Central Alborz. This formation is middle Eocene in age and mainly formed of green-tuffites and marine shales. According to field observation, this formation consists of heterogeneous assemblage of tuff, tuffite, various sedimentary rocks and some type of lava.
Field data on depositional environment of Karaj volcaniclastic sequence indicate that some parts of this thick sequence in study area were mainly formed in a deep to semi-deep environment. Vertical and horizontal variations of facies and sedimentary structures such as graded bedding, slumping, convolute bedding, flute cast and … indicate that turbidity currents and mass flows have an essential role in the genesis of some parts of the Karaj Formation, being responsible for transporting of shallow depth (shelf) pyroclastic products.
Submarine channels which filled by massive sediments and olistolites (F facies) are associated with upward thinning and fining sequences on their tops. Main part of shales of the Karaj Formation were formed as pelagic and hemipellagic shales (G facies), in northern parts of the study area. Upward thinning and thickening sequence, and also complete or incomplete Bouma sequences (A-E facies) are abundant in Karaj Formation. Collected data shows that Karaj Formation depositional environment is submarine fan. Data related to paleocurrent directions shows a south to northward one.