The Upper Jurassic–Lower Cretaceous alluvial-fan deposits of the Kalaza Formation (Central Asia): Tectonic pulse or increased aridity?
Marc Jolivet, Sylvie Bourquin, Gloria Heilbronn, Cecile Robin, Laurie Barrier, Marie-Pierre Dabard, Yingying Jia, Elien De Pelsmaeker, Bihong Fu, 2017. "The Upper Jurassic–Lower Cretaceous alluvial-fan deposits of the Kalaza Formation (Central Asia): Tectonic pulse or increased aridity?", 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 topographical evolution of tectonic systems, as well as the sedimentation pattern and depositional environments in the associated basins, are controlled by both tectonics and climate. In the region of the Tien Shan (Central Asia), the Jurassic–Lower Cretaceous period was marked by complex, low-intensity tectonic deformation and major climate changes from humid to arid conditions (Jurassic) to semi-arid conditions (Cretaceous). Using the sediment record in the Junggar, Tarim and Fergana basins to describe the tectonic evolution of the Tien Shan area during the Mesozoic thus requires differentiation between the tectonic and climatic influences on sedimentation. The conglomerates of the Upper Jurassic–Lower Cretaceous Kalaza Formation were commonly associated with renewed tectonic activity resulting from the docking of the Lhasa block along the southern margin of Asia. From sedimentology and sequence stratigraphy analyses of several sections in the Junggar, Tarim and Fergana basins, we reassess the main factors controlling the deposition of this formation. We show that, while some tectonic activity persisted throughout the Jurassic–Cretaceous transition, the switch from the sandy deposits of the Upper Jurassic Qigu Formation to the coarse deposits of the Kalaza Formation is largely linked to the development of an arid climate.
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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.