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UDC 551.732.2/.3.022:(552.53/.54:550.834)(571.5-15)
LOWER-MIDDLE CAMBRIAN FACIES REGIONALIZATION OF THE PODKAMENNAYA AND NIZHNYAYA TUNGUSKA INTERFLUVE
N. V. Melnikov, A. V. Isaev, E. V. Smirnov, E. G. Naumova, M. V. Dontsov, L. V. Medyukhina, M. A. Maslennikov
In the last ten years regional and geological-geophysical study of the Podkamennaya (Middle Tunguska or Stony Tunguska) and Nizhnyaya (Lower) Tunguska interfluve (western Lena-Tungusskaya PP) has been continued. Litho-seismic facies zones were distinguished there by wave pattern differences in time CDP sections. Alternating carbonate and saline formations, Cambrian subformations presented unique features of the wavefi eld structures. Authors present a set of patterns of wavefield types in all the revealed litho-seismic facies zones. A map of litho-seismic facies Cambrian zones shows saline-carbonate, salt free zones and a zone of the uncompensated Toyonian trough filled with Middle-Cambrian saliferous rocks. The trough is fringed by marginal reefs of the Toyonian-Amgian age. In the north-east of the interfluve the Ilimpeya saturation shelf is revealed. It consists of the Turunskaya Tolbachan and Yeika Toyonian zones of potential organogenetic carbonate buildups. It is established that rates of the basin bottom downwarping and degree of its sediment compensation resulted in accumulation of deposits varying in thickness and composition. In the Early Cambrian carbonate deposits formed in the Turukhan and Lebyazhye zones as well as in the Surindakon, Velmo and Chunya ones, but in the last three, saliferous-carbonate units were formed at the Lower Usolye and Tolbachan levels. By and large the progressive decrease in the number of salt members and beds is observed from south to north. The uppermost of the salt-bearing Upper Usolye subformation is shown to be partially and sequentially substituted for the salt free Sygdakhskaya Formation in the central Baikit litho-seismic facies zone. The suggested litho-seismic-facies regionalization of potentially oil-and-gas bearing Cambrian deposits on the mentioned territory can serve as the basis for planning and organization of prospecting for hydrocarbon accumulations in the Cambrian carbonate formations. Seismic exploration is the main instrument of prospect pretreatment for preliminary drilling. A wave pattern displays features of changes in lithologic-and-facies composition of deposits at the boundary of saltforming and normal-sea basins of the Early and Middle Cambrian ages.
Key words: Podkamennaya and Nizhnyaya Tunguska interfluve, Cambrian, refl ecting horizons, wavefields, litho-seismic facies zones.
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