First data on the Cenozoic section of the Bering Sea Chukchi Shelf

The first deep hole (Tsentral'naya-1) drilled on the Russian shelf of the Bering Sea in 2002 recovered the Cenozoic sedimentary section up to depths of 2785 m(1) This paper discusses results from the log, core, and slime study. The section is composed of Paleocene-Quaternary sediments. It comprises nine sequences (from the top downward): upper Miocene-Pliocene sandy-silty; middle-upper Miocene tuffaceous-diatomite, silty-sandy, shale-siltstone, and coquina-sandstone-siltstone; Eocene-lower Miocene coaliferous and sandstone-shale; Paleocene-lower Eocene volcano-sedimentary. These sequences are correlated with onshore stratigraphic units. The section includes three large unconformities: at the base of the Pliocene (depth of 380 m, base of the Aleksandrovka stratigraphic horizon), at the base of the middle Miocene (depth of 1390 m, base of the Avtakul Horizon), and, presumably, at the base of middle Eocene (depth of 1390 m, base of the Tanyurer Horizon). The last unconformity is accompanied by a kaolinite weathering crust. The section drilled into by Tsentral'naya-1 Hole shows common features for the Cenozoic sedimentary cover through the entire Anadyr basin, despite its significant facies variability.