Petroleum generation and accumulation during the Proterozoic and Phanerozoic has been uneven in time. Stratigraphic distribution of initial delineated oil reserves (produced and delineated) for 45 oil-gas basins was analyzed. These are the largest basins with total initial oil resources of more than 170 billion tons (1200 billion barrels). This comprises more than 80 percent of the initial recoverable resources of the world.
Bitumen resources exceed those of oil by many fold. Some correlation is found between distribution of bitumen and oil resources in individual stratigraphic complexes.
Maximum intensity of oil generation is recorded in the second half of the Mesozoic from Late Jurassic to Late Cretaceous time. Maximum intensity of oil accumulation during this maximum was1467 tons (10,300 bbls) per year. This accounts for 72 percent of the world oil resources.
A second maximum intensity of oil generation was in the Cenozoic from the Eocene to the Pliocene, inclusively. Average intensity of oil accumulation during this interval was about 400 tons (2,800 bbls) per year. This amounts to more than 12 percent of world oil resources.
A Paleozoic maximum was in Late Devonian-Early Carboniferous
time, when average accumulation was 263 tons (1,840 bbls) per year
- or 6 percent of world reasouces.
In the pre-Late Devonian part of the Phanerozoic intensity of oil
generation was an average of only 30 tons (210 bbls) per year; in
the interval from Late Carboniferous to Middle Jurassic - 77 tons
(539 bbls) per year; for the Paleocene - 173 tons (1,211 bbls) per year.
A maximum in oil accumulation is recorded in Late Proterozoic
time. Oil productivity of the Vendian has been demonstrated in East
Siberia, Volga-Ural, Oman, Pakistan, Brazil, but commercial deposits are
known only in the central and south of the Siberian craton and in Oman.
It is difficult to assess intensity of oil accumulation for the Early
and Middle Riphean because resources of these rocks have been
estimated only in one region - the Baykit anteklize on the Siberian
craton. However, oil-source rocks are present in this 1400-1700 m. y.
interval along the margin of the Siberian craton, in China, and in
Australia.
Yet another maximum of oil accumulation can be recognized
conditionally - Early Proterozoic. Corresponding with this stratigraphic
level are large accumulations of solid bitumens - the Karelian
shungites. These resources are generally assessed very high in
hundreds of millions of tons. Rocks of this type have been recorded
in other regions but have been little studied.
Taken from Vyshemirskiy and Kontorovich, 1979; digested in
Petroleum Geology, vol. 35, no. 4, 2001, in preparation, three figures.
Copyright James Clarke, 2001. You are encouraged to print out this
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