KIREYEV G.I., PREOBRAZHENSKAYA E.N., ZONN, M.S., MENNER V.VL., SHUVALOVA G.A., ABUSHIK A.F., EVDOKIMOVA I.O., MODZALEVSKAYA T.L, YUDINA YU.A., MOSKALENKO M.N., VEVEL YA.A., OBUKHOVSKAYA
T.G., OBUKHOVSKAYA V. YU., BEZNOSOVAT.M., SOBOLEV N.N.; STOLBOVA V.P.

FSUE ArktikMorNefteGazRazvedka. Russia, FSUE VNIIOkeanGeologiya, Russia, FSUE IGiRGI, Russia, WSEGEL Russia, TP NITs, Russia, VNIGRI, Russia, BelNIGRI, Russia, IGKNT UroRAN, Russia, SPBGU, Russia

Studies of the sections of offshore wells drilled in the southern Pechora Sea showed that the stratigraphic subdivision and correlation of Devonian strata can be conducted using regional stages, horizons and formations recognized in adjacent onshore Devonian sequences.

Correlation of offshore well sections and onshore sequences, regional stages, stages, and zonal biostratigraphic schemes was conducted using the regional well log marker grid, new paleontological and palynological datings, and the specific features of lithofacies variations in the basin during its Devonian evolution.

Devonian deposits consist predominantly of shallow shelf lithofacies; similar lithofacies variations have been identified over the whole transition zone.
The Khataykha (up to 400 m) and Toravey (up to 300 m) formations (Ovinparma and Sotchemkyrta horizons - regional stages Rs) of the Lochkovian Stage of the Lower Devonian are clearly traceable in well sections from the offshore extension of the Varandey-Adzva zone. The age of the Khatayakha Formation was established from tabulates, brachiopods, ostracodes and, for the first time, from spores. Mudstone-carbonate sequences at the base of the Khatayakha and Toravey formations and the sulfate-bearing member of the Toravey Formation are correlation markers.

The Pragian, Emsian, and Middle Devonian deposits are of limited occurrence because of the pre-Timan scour corresponding to the Taganyik global event. The lower Frasnian mudstones with occasional sandstone and siltstone interbeds of the Timan and Sargayevo Rs (30-120 m) are widespread and rest unconformably upon various Devonian horizons. However, they lack guide fossils for biostratigraphic identification, and this impedes the correlation of well sections with the exact Rs volumes and leaves the presence of the Dzhyer Rs and the age of pay sandstones as open issues.

In recent years, new paleontological and palynological data provided a possibility to reliably correlate the Middle Frasnian multifacies deposits of the Domanik Rs. In the western and northwestern areas, this interval is represented by shallow-water mudstones and carbonates of the Sercheyyu Formation with signatures of anoxic environment (Dresvyanka and Prirazlomnaya prospects, thickness 48-120 in). Farther south, In the Pakhancheskaya prospect the upper part of the sequence contains numerous coral-stromatolporate beds. In the Varknavtskaya and Medyn More prospects still farther south, the Domanik Rs occurs as an essentially carbonate sequence (up to 50 m) with brachiopods representing the fades of the upper part of a ramp slope, from shallow shelf to a starved deep-sea basin. Basinal "domanikoid" lithofacies of this horizon were penetrated by onshore well Toravey 25. The carbonate members of the slope and basinal lithofacies of the Domanik Rs are considered as a reliable correlation marker. Rdm.

The Upper Frasnian sequence begins with the mudstone member of the Vetlasyan Rs (0-20 m). It is dated by spores in well Medyn More 1. The lower part of the next Sirachoy Rs is represented in the western areas by the Laya Formation (48-80 m) consisting of shallow-water biogenic carbonates with small coral-stromatoporate bioherms and biostromes. These grade southeastward into ramp lithofades (compact, sometimes muddy limestones) and then into thin members of basinal domanikoid lithofacies. The deposits of the Upper Sirachoy, Yevlanovo and Livny Rs of the Frasnian in the northern Pechora-Kolva aulacogen and Khoreyver depression have been recognized as shallow shelf facies the Inzyrey Formation (120-250 m). It is subdivided into members, which exhibit clearly traceable