Cenozoic palaeoenvironmental and tectonic controls on the evolution of the northern Fergana Basin
Alejandro Bande, Shukhrat Radjabov, Edward R. Sobel, Tatyana Sim, 2017. "Cenozoic palaeoenvironmental and tectonic controls on the evolution of the northern Fergana Basin", Geological Evolution of Central Asian Basins and the Western Tien Shan Range, M.-F Brunet, T. McCann, E. R. Sobel
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The least well-documented intramountain basin within the Tien Shan is the Fergana Basin. Cenozoic deformation is localized along thrusts on the northern and southern flanks, and by transpressive deformation associated with the dextral Talas–Fergana Fault on the eastern margin. We use sedimentological and stratigraphic observations from well-exposed Cenozoic outcrops to describe depositional environments, provenance and sources. These results are combined with interpreted seismic reflection lines and geological cross-sections are extended laterally based on outcrop geology to the north and east. Following a tectonically quiet early Cenozoic period, a progressive change in palaeocurrent indicators suggests Oligo-Miocene uplift of the hinterland, coupled with an increase in higher energy facies in the Massaget Formation. A renewed pulse of deformation tilted Massaget strata and deposited a considerable volume of coarse sedimentary rocks (Baktriy Formation). The younger episode moved progressively basinwards, as imaged by growth–strata relationships in the subsurface. Published work shows that the accumulation of an impressive c. 8 km of Cenozoic deposits cannot be accommodated only by lithospheric flexure produced by a tectonic load. We agree with the hypothesis that the thick sediments preserved in the basin are accommodated by lithospheric folding and propose that this is driven by compression associated with south-vergent Pamir subduction.
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The geological evolution of Central Asia commenced with the formation of a complex Precambrian–Palaeozoic orogen. Cimmerian blocks were then accreted to the southern margin in the Mesozoic, leading to tectonic reactivation of older structures and discrete episodes of basin formation. The Indian and Arabian blocks collided with Asia in the Cenozoic, leading to renewed structural reactivation, intracontinental deformation and basin development.
This complex evolution resulted in the present-day setting of an elongated Tien Shan range flanked by large Mesozoic–Cenozoic sedimentary basins with smaller intramontane basins distributed within the range.
This volume presents multidisciplinary results and reviews from research groups in Europe and Central Asia that focus on the western part of the Tien Shan and some of the adjacent large sedimentary basins. These works elucidate the Late Palaeozoic–Cenozoic tectono-sedimentary evolution of the area. Emphasis is given to the collision of terranes and continents and the ensuing fault reactivations. The impact of climatic changes on sedimentation is also examined.