Structure and evolution of the Bukhara-Khiva region during the Mesozoic: the northern margin of the Amu-Darya Basin (southern Uzbekistan)

The Bukhara-Khiva region forms the northern margin of the Mesozoic Amu-Darya Basin. We reconstructed several cross-sections across this margin from subsurface data. The objectives included examining the structure of the Bukhara and Chardzhou steps and determining the tectonic–sedimentary evolution of the basin during the Jurassic. Subsequent to the Cimmerian collision in the Middle Triassic, an extensional event controlled the deposition of the Early–Middle Jurassic siliciclastic succession in the Bukhara-Khiva region. The main Late Palaeozoic inherited structures were reactivated as normal faults during this period. Continental coarse-grained siliciclastic sediments are mainly confined to the basal Lower Jurassic section, probably Pliensbachian– Toarcian in age, whereas marine siliciclastic sediments occur in the early Late Bajocian. In the Early–Middle Jurassic the Bukhara and Chardzhou steps were predominantly sourced by areas of relief, the remains of Late Palaeozoic orogens located to the north. The rate of extension significantly declined during the Middle Callovian–Kimmeridgian period. Deposition of the overlying Lower Cretaceous continental red-coloured clastic sediments was related to the interaction of basin subsidence, a fall in eustatic sea-level and sediment supply. Subsequent marine transgression in the Late Barremian, partially related to broad thermal subsidence in the Amu-Darya Basin, resulted in the deposition of an extensive Late Cretaceous clay–marl succession.