Vol 25, No 6 (2017)

This work presents results of the complex mineralogical, geochemical, and isotope-geochronological investigation of globular dioctahedral 2: 1 phyllosilicates (GPS) of the illite–glauconite series from the Riphean sequences of the Olenek Uplift. It is established that GPS (glauconite, Al-glauconite, Fe-illite) in deposits of the Arymass, Debengda, and Khaipakh formations are represented by mixed-layer varieties of two types: (1) with relatively low (<10%) and (2) higher (10–20%) contents of expandable layers. Among the mixed-layer varieties are those with disordered alternation of micaceous and smectite layers (R = 0), as well as with tendency to ordering (R ≥ 1). The parameter b of an elementary cell of minerals varies from 9.18 to 9.72 Å. The Rb–Sr age dating of GPS was first carried out in combination with the calculation of theoretical pattern of the cation distribution in the mineral structure and comparison of the calculation results obtained with the Mössbauer and IR spectroscopy data. This approach is based on the assumption that development and evolution of isotope systems in GPS are synchronous with the evolution of the crystalline structure of the mineral at various stages of the geological and geochemical history of the development of sedimentary units. Analysis of the obtained data allows us to state that the structural features of the Riphean GPS from the Olenek section reflect the early diagenetic stages of the formation of the minerals studied. The 87Sr/86Sr initial ratios in the studied sediments are consistent with the range of variations in this ratio in the Middle Riphean Ocean (0.7049–0.7061). The Rb–Sr and K–Ar ages of the GPS of the Arymass (1305 ± 8 and 1302 Ma, respectively), Debengda (1265 ± 12 and 1284 ± 22 Ma), and Khaipakh (1172 ± 18 and 1112 ± 24 Ma) formations in the Olenek Uplift section are close to the accumulation time of corresponding deposits and, correspondingly, have significance for stratigraphic correlations.

An assemblage of planktonic foraminifers is recognized for the first time from the Yunusdag Formation (Kelevudag Section, northeastern Azerbaijan) The analysis of foraminifers from the studied sample suggests that it may belong to the upper part of the Marginotruncana coronata Zone, embracing the interval from the upper Turonian to the lower Coniacian inclusive. The taxonomic composition of the assemblage allows the Kelevudag section to be assigned to an intermediate province separating the Boreal and Tethyan realms and including the Late Cretaceous carbonates of Dagestan.

The terms “glaciation” and “interglacial” are considered from the point of view of palaeoclimatic proxies obtained from the Pleistocene deep-water and continental deposits. It is shown that the crucial factor in substantiation of these notions is determination of the cause-and-effect mechanism in the considered climatic oscillations. It is noted that oxygen isotope data on deep-water deposits have an undoubted advantage because a more accurate quantitative estimate of climatic oscillation parameters can be made on their basis. It is concluded that the role played by quantitative estimates of palaeoclimatic changes, represented by, first of all, amplitude and time characteristics of climatic oscillations, will become more significant as the methods of paleogeographic studies of both continental and deep-water deposits of the Pleistocene improve; in contrast, the formal determination of the rank of palaeoclimatic oscillations will become less significant. Special attention is paid to the cases of misfits between the Pleistocene deep-water and continental paleoclimatic records and to the necessity to make them consistently as good as possible, especially in the case of Early Pleistocene deposits.