Abstract

Analysis of Mid-Palaeozoic successions in the northern part of the Alai Range (Kyrgyzstan and bordering Uzbekistan), Southern Tien Shan, Central Asia, has identified a Silurian–Devonian deep-marine depositional system of basin-slope facies-associations. Here, we document the stratigraphy and sedimentology of a region in Central Asia that, through conflict, has become inaccessible for geological research. The turbidite-dominated Pul'gon Formation (Silurian) accumulated in sea-floor depressions and within the inferred basin axis. The large-scale, coarse clastic lenses of the Dzhidala Formation (mostly Devonian) represent the fills of submarine channels, canyons or gullies of the palaeoslope; other slope apron processes include sediment slides, debris flows and olistoliths. The partly time-equivalent condensed sequences of the Mid- to Late Silurian Kursala Formation and Early Devonian Tamasha Formation represent graptolitic mudstone and chert accumulation, respectively, together with thin dolomitic limestones, that accumulated over c. 10–15 Ma, probably on seamounts in the Turkestan (Fergana) Ocean between the continental margin of Kazakhstania and the Alai microcontinent. The graptolitic shale-rich Chakush Formation (early Silurian) is geographically and petrographically different from the Pul'gon and Dzhidala formations and suggests a different provenance (opposing continental margin or seamount talus).

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