Stratigraphy and facies development of the marine Late Devonian near the Boulongour Reservoir, northwest Xinjiang China

Late Devonian to Early Carboniferous stratigraphic units within the ‘Zhulumute’ Formation, HonggulelengFormation (stratotype), ‘Hebukehe’ Formation and the Heishantou Formation near the BoulongourReservoir in northwestern Xinjiang are fossil-rich. The Hongguleleng and ‘Hebukehe’ formations are biostratigraphicallywell constrained by microfossils from the latest Frasnian linguiformis to mid-Famenniantrachytera conodont biozones. The Hongguleleng Formation (96.8 m) is characterized by bioclastic argillaceouslimestones and marls (the dominant facies) intercalated with green spiculitic calcareous shales. Ityields abundant and highly diverse faunas of bryozoans, brachiopods and crinoids with subordinatesolitary rugose corals, ostracods, trilobites, conodonts and other fish teeth. The succeeding ‘Hebukehe’Formation (95.7 m) consists of siltstones, mudstones, arenites and intervals of bioclastic limestone (e.g.‘Blastoid Hill’) and cherts with radiolarians. A diverse ichnofauna, phacopid trilobites, echinoderms(crinoids and blastoids) together with brachiopods, ostracods, bryozoans and rare cephalopods have beencollected from this interval. Analysis of geochemical data, microfacies and especially the distribution ofmarine organisms, which are not described in detail here, but used for facies analysis, indicate a deepeningof the depositional environment at the Boulongour Reservoir section. Results presented here concernmainly the sedimentological and stratigraphical context of the investigated section. Additionally, oneLate Devonian palaeo-oceanic and biotic event, the Upper Kellwasser Event is recognized near the sectionbase.