Dating of marine sediments and faunal remains they contain in stratotype and reference sections by the methods of infrared optically stimulated luminescence (IR-OSL) of K-feldspar, optically stimulated afterglow (OSA) of quartz, electron spin resonance (ESR), and 230Th/U provides new constraints on deposition in the Yenisei mouth during the Kazantsevo interglacial. The luminescence and U–Th ages in the 120–68 ka range and 93–70 ka ESR ages show that the deposition spanned the whole marine isotope stage (MIS) 5. The sediment structures and textures, grain sizes and mineralogy, and faunal records indicate tidal and shelf deposition environments. The sampled assemblages of marine mollusks comprise taxa that typically live in relatively shallow and warm water, as well as abundant subarctic and boreal species, including the Arctica islandica index species. The variations of faunal patterns, more likely, had facies rather than climatic controls, while the sediments were deposited during transgression, in a warm climate, when the area was ice-free.