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Cherts, radiolarites, and radiolarian cherts are one of the most important components of accretionary complexes, and much used in the reconstruction of imbricated sections of ocean plate stratigraphy, and of the palaeogeographic and tectonic settings of ophiolitic mélanges. There has been little research on radiolarian cherts in the Kyrgyz South Tianshan, and the tectonic setting and temporal framework of the South Tianshan ocean are controversial. Here, we report well‐preserved radiolarians in ribbon‐bedded cherts in an ophiolitic mélange of the Atbashi accretionary complex (South Tianshan, Kyrgyzstan), which provide key evidence of ambient Palaeozoic oceanic conditions. The hydrofluoric acid technique was used to extract from the cherty rocks siliceous radiolarian, which yielded an age of late Early Carboniferous. Analyses of major, trace, and rare‐earth elements of four cherts indicate they are biogenic and deposited with little hydrothermal influence in a hemipelagic to continental margin environment. Our fossil ages and geochemical results of the radiolarian cherts from the Atbashi accretionary complex indicate that the South Tianshan ocean was still open in the Late Carboniferous, implying that it was a wide, long‐lived, major ocean that closed by northward subduction. [ABSTRACT FROM AUTHOR]

• Nong Pong Formation chert was deposited in a deep marine environment on continental crust. • Radiolarian indicate a late middle Permian age for the studied section. • Deposition was probably in a rift setting, flanked north and south by platform carbonates. The deepwater chert-shale-limestone-tuff Permian Nong Pong Formation (NPF) of the Saraburi Group is a major unit within the Triassic (Indosinian Orogeny) Khao Khwang Fold and Thrust Belt (KKFTB). Whether the NPF was deposited in a continental margin or ocean basin remains uncertain and impacts structural, sedimentary and stratigraphic interpretations of the KKFTB. This study investigates chert geochemistry from a 60 m section of the formation, near Muak Lek town, to determine its depositional environment. Radiolarian fauna from the chert beds includes Follicucullus porrectus Rudenko, (probable late Guadalupian, late middle Permian), indicating the NPF is time-equivalent to adjacent carbonate platform deposition (Khao Khwang and Khao Khad formations). High ratios of SiO 2 /(SiO 2 + Al 2 O 3 + Fe 2 O 3) and Fe-Al-Mn plots indicate a biogenic origin (radiolarians, sponge spicules) for the cherts, far from a hydrothermal source. Trace element ratios for U/Th, Sc/Th and Sr/Ba and Ce anomalies in the NASC-normalized REE distribution are ambiguous, and range between shallow to deep ocean basin, and continental margin settings. Major elements analysis of cherts show: (1) high ratios of SiO 2 /(SiO 2 + Al 2 O 3 + Fe 2 O 3), range: 0.60–0.82 (0.76 average), (2) Al/(Al + Fe + Mn), range: 0.67–0.82 and (3) average MnO/TiO 2 = 0.14. The MnO/TiO 2 and Al 2 O 3 /(Al 2 O 3 + Fe 2 O 3) ratio, 100 × Fe 2 O 3 /SiO 2 vs. 100 × Al 2 O 3 /SiO 2 and Fe 2 O 3 /(100-SiO 2) vs. Al 2 O 3 /(100-SiO 2) diagrams indicate deposition on a continental margin. The La n /Ce n versus Al 2 O 3 /(Al 2 O 3 + Fe 2 O 3) discrimination diagram indicates a pelagic, continental margin setting. Combined geochemical, structural and sedimentary facies analyses suggests the NPF was deposited in a deep marine, normal fault-bounded basin on a rifted, ribbon continent margin where carbonate platforms grew on structural highs. [ABSTRACT FROM AUTHOR]