The Timan-Pechora Basin Province of Northwest Arctic Russia:  Domanik Paleozoic Total Petroleum System

Sandra J. Lindquist

averaging around 5 wt % (Alsgaard, 1992; Pairazian, 1993; Bazhenova, 1995; Sobornov and Rostovshchikov, 1996; Abrams and others, 1999). Hydrogen indices (HI) range from 500-700 mg/gC, documenting the oil-prone nature of the organic matter (Abrams and others, 1999). Domanik source rocks are present, with adequate thicknesses and maturity level, almost everywhere production has been established. Geochemical data (gas chromatography mass spectrometry, Rock Eval pyrolysis, biomarker analysis, total organic carbon content, thermal maturity indicators, gas chromatography and kerogen type) derived from the source rock and its extracts confirm Domanik source rocks as providing most of the Timan-Pechora hydrocarbons (Smale and others, 1994; Schamel and others, 1994; Abrams and others, 1999). 

     Other Source Rocks
Although immature to charge Timan-Pechora reservoirs, extensive Late Jurassic to Early Cretaceous (mostly Kimmeridgian) type II shales in the Barents Sea have TOC content of 10-17 wt % (Oknova, 1993). Permian core samples have TOC content documented as high as 2 wt %, with kerogen type ranging from sapropelic to humic in a west-to-east direction (Timoshenko and others, 1998). Siluro-Ordovician source rocks have not been geochemically identified, but analyzed core samples had TOC content of 0.5-1.5 wt % and HI as high as 302-457 mg/gC (Abrams and others, 1999), with type I and type II kerogens (Sobornov and Rostovshchikov, 1996).

Geographic and Stratigraphic Location
Timan-Pechora overburden of the primary Domanik source rock generally thickens in an easterly direction, corresponding to the paleolocations of the Uralian seaway and the Hercynian and Early Cimmerian foredeep basins. But that trend is irregular around old aulacogen borders because marginal grabens experienced periodic structural inversions since late Early Carboniferous time and thus less overall burial than adjacent regions. Domanik overburden includes Late Devonian through Cretaceous strata (Figure 6). The South Barents Basin potentially impacting the northernmost part of the offshore Timan-Pechora Basin Province has accumulated overburden continuously since Early Permian subsidence began.

Thickness, Lithology and Depositional Environment
Late Devonian through Early Permian time was dominated by carbonate deposition on the Uralian marine shelf. Development of Hercynian foredeep basins changed not only the provenance direction

(from westerly sourced to easterly sourced), but also the dominant lithology of the basin (from platform carbonates to molasse siliciclastics). Mesozoic sedimentation varied between continental and marine, and the Jurassic and Cretaceous rock records contain evidence for marine transgressions from the north.

Total Domanik overburden in the province ranges from approximately 2-8 km (Ulmishek, 1982). Pairazian (1993) published a comparative family of burial history curves and maturation profiles across the Timan-Pechora basin (Figure 7a, Figure 7b, Figure 7c, Figure 7d, Figure 7e, Figure 7f). Exact locations for each profile were not provided, and it should be noted that other authors report significantly later and contradictory times of generation and migration. The Figure 7 series should be used primarily to compare regional differences in burial history and not absolute times of hydrocarbon generation. Deepest burial histories are in foredeep areas (Figure 7f) and portions of the Pechora-Kolva Aulacogen (Figure 7c), and shallowest burial histories are in the western Izhma-Pechora Depression (old craton margin) (Figure 7a, Figure 7b). The 100-km-wide Pechora-Kolva Aulacogen has post-Domanik isopachs that thicken westward both because of western provenance and a listric, down-to-the-east origin for its western bounding fault (Sobornov and Yakovlev, 1996).

A recently published burial history curve (Martirosyan and others, 1998, Figure 8) for the Sorokin Swell coastal area illustrates the Permo-Triassic time frame more typically proposed for the maturation of Domanik source rocks.

Pre-Hercynian strata overlying Domanik source rocks range from 0.8-4 km in thickness, with syn- and post-Hercynian rocks through Triassic age ranging from approximately 0.5-4 km in thickness (Ulmishek, 1982). Whereas pre-Triassic rocks generally thicken only from west to east, Triassic rocks additionally thicken to the north offshore. Jurassic and Cretaceous strata range from thicknesses of about 0.2-1 km on the Timan-Pechora platform to 2.5-3.5 km offshore into the South Barents Depression (Ulmishek, 1982; Johansen and others, 1993).

Geothermal Gradient(Continued on Next Page)
Present thermal gradients in the Timan-Pechora Basin Province are moderate, from 19° -35° C/km (1.0° -1.9° F/100 ft), but heat flow was probably higher in Early to Middle Mesozoic time, as suggested by the presence of Triassic extrusive rocks (Ulmishek, 1982; Pairazian, 1993; Nevskaya, 1995;Abrams and others, 1999). Higher thermal gradients

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U. S. Geological Survey Open-File Report 99-50G