Neogene Tectono-Stratigraphic Evolution of the Intermontane Tarom Basin: Insights Into Basin Filling and Plateau Building Processes Along the Northern Margin of the Iranian Plateau (Arabia-Eurasia Collision Zone)

The intermontane Tarom Basin of NW Iran (Arabia-Eurasia collision zone) is located at the transition between the Iranian Plateau (IP) to the SW and the Alborz Mountains to the NE. This basin was filled by upper Cenozoic synorogenic red beds that retain first-order information on the erosional history of adjacent topography, the vertical growth of the plateau margin and its orogen perpendicular expansion. Here, we perform a multidisciplinary study including magnetostratigraphy, sedimentology, geochronology and sandstone petrography on these red beds. Our data show that Eocene arc volcanism in the region terminated at 38-36 Ma, while intrabasinal synorogenic sedimentation (endorheic conditions) occurred from at least 16.2 to <7.6 Ma, implying that the red beds are stratigraphically equivalent to the Upper Red Formation. After 7.6 Ma, the basin experienced intrabasinal deformation, uplift and erosion with the establishment of external drainage. Fluvial connectivity with the Caspian Sea, however, was interrupted by at least four episodes of basin aggradation. During endorheic conditions, the basin fill did not reach the elevation of the plateau interior and hence the Tarom Basin was never integrated into the plateau. Furthermore, our provenance data indicate that the northern margin of the basin (Alborz Mountains) experienced a greater magnitude of Miocene deformation and erosional exhumation than the southern one (IP margin). This agrees with recent Moho depth estimates, suggesting that crustal shortening and thickening cannot be responsible for the vertical growth of the northern margin of the IP, and hence surface uplift must have been driven by deep-seated processes.

Automated summary

The study shows that the Tarom Basin in NW Iran was filled with upper Cenozoic red beds, providing key information on the erosional history of adjacent topography, the vertical growth of the plateau margin and its orogen perpendicular expansion. The basin experienced intrabasinal synorogenic sedimentation prior to 7.6 Ma, followed by intrabasinal deformation, uplift, and erosion, with interruptions in fluvial connectivity with the Caspian Sea. Provenance data suggests greater Miocene deformation and erosional exhumation on the northern margin of the basin compared to the southern margin, indicating vertical growth driven by deep-seated processes.