Architecture of the Focşani Depression: A 13 km deep basin in the Carpathians bend zone (Romania)

Abstract

In front of the SE Carpathians Bend a very deep basin (Focşani Depression) developed in Miocene to Recent times. An important part of its subsidence occurred after the main stages of thrusting in the Carpathians. Apparently, the basin lies in the “wrong” place and evolved in the “wrong” time. In this study, we constrain its architecture and evolution by analyzing a large database consisting of more than 1000 km two‐dimensional seismic lines and more than 60 wells. Around 13 km thick, Badenian‐to‐Quaternary (<16.5 Myr) sediments were deposited in the central part of the Focşani Depression. During the Badenian (16.5–13 Myr), the foreland (south of Trotuş fault) underwent NE‐SW directed extension and NW trending basins opened in the eastern Moesian platform. A NW‐SE oriented area of subsidence stretched from the Transylvania basin through the Focşani Depression to the SE of the Moesian platform while thrusting was going on in the East European/Scythian platform, East Carpathians, and Getic Depression. Starting with the Sarmatian (13–10 Myr), the Focşani Depression depocenter moved out of the Carpathian belt coeval with the exhumation of the south and the East Carpathians north of the Trotuş fault. The basin became wider and was tilted toward the belt. Tilting was accompanied by dextral shearing mainly along the Intramoesian and Peceneaga‐Camena faults. After Sarmatian times, subsidence occurred practically only SSE of Trotuş fault. During Meotian‐Pontian (10–5 Myr), subsidence slowed down. Stronger, Pliocene‐Quaternary subsidence is coeval with normal faulting and shearing in Moesian platform. The western margin of the Focşani Depression was then tilted eastward, coeval with the exhumation of the bend zone and opening of the intramontane basins in the inner part of the belt.