The Alai Range of the southwestern Tien Shan, southern Kyrgyzstan, is an integral part of the Cenozoic Tien Shan orogen in the continental interior of central Asia. Separated by the 2000-m-high intramontane Alai Valley, the southern Alai is located immediately to the north of the >7000-m-high Pamir mountains that mark the Eurasia/India collision zone. We use stratigraphic and structural relationships in the southwestern Alai Range at about 072E to constrain the deformational history and paleogeography of the region. Fold and fault structures in the southwestern Alai Range contain deformed Cretaceous through Paleogene sedimentary strata overlying Carboniferous bedrock and flat-lying Neogene through Quaternary conglomerates and gravels. The lowermost Carboniferous is characterized by metasedimentary rock overlain by a 370 meter Cretaceous sequence of reddish-colored, unsorted conglomerates, conglomeratic sandstones and siltstones. These grade upward into cross-bedded sandstones interbedded with argillite and conglomerate-filled paleochannels that indicate southeast to northwest migration of southwest to northeast flowing channels. Gypsiferous siltstone and gypsum are capped by fossiliferous limestone with a total thickness of 390 m. The upper unit (470 meters thick) contains a gypsum sequence overlain by a dolostone sequence. From the above data, we interpret a gradual and uninterrupted change from alluvial fans and alluvial braidplains in the lower to middle Cretaceous to brackish conditions followed by a shallow marine environment in the upper Cretaceous. The Paleogene sequence represents sustained quiet water conditions.

Following deposition, the area experienced shortening that was accommodated by folding and faulting. East plunging drape folds are the result of slip along a north-vergent east-west trending reverse fault as basement uplift occurred. In the eastern part of the study area, the throw on the fault is low, resulting in east plunging folds with local overturning. To the west where the throw increases, the fault is exposed and juxtaposes Carboniferous metasedimentary units with the overlying sedimentary strata. Neogene blocky to coarse conglomerates are unconformable with folded Paleogene sediments, as well as gently southward sloping geomorphic surfaces. This confirms that after a major phase of deformation affecting the Tien Shan in the Alai region between late Paleogene to early Neogene time, the southwestern Tien Shan has remained tectonically inactive.