Lower–Middle Jurassic facies patterns in the NW Afghan–Tajik Basin of southern Uzbekistan and their geodynamic context

Based on eleven sections, the palaeoenvironments and depositional history of the 26 northwestern Afghan-Tajik Basin in southern Uzbekistan have been reconstructed for the time 27 interval Early Jurassic to Early Callovian. The earliest sediments, resting on Palaeozoic 28 basement rocks, date from the Early Jurassic Period. Up to the end of the Early Bajocian time 29 up to more than 500 m of non-marine sediments accumulated due to extensional tectonics 30 inducing active subsidence. In the Late Bajocian time interval, transgression led to the 31 establishment of siliciclastic ramps that were influenced by storm processes. After a 32 condensed unit in the Middle Bathonian, sedimentation resumed in an outer carbonate ramp 33 basinal setting as the subsidence rate outpaced the diminished siliciclastic sediment supply. 34 The change from siliciclastic to carbonate sedimentation in the Middle Jurassic Period is 35 thought to be multifactorial, reflecting levelling of relief in the hinterland, the subsidence 36 moving to a thermally more quiet stage, and a change from humid to arid climatic conditions. 37 These features are also observed in the area of present-day Iran. Similarly, the timing of the 38 transgression coincides with that in eastern and northern Iran stressing the regional 39 significance of this event. 40