25th International Meeting on Organic Geochemistry IMOG 2011

P-049
Organic matter of Lower Permian sediments from Subpolar
Urals
Olga Valyaeva, Olga Protsko
Institute of Geology of Komi Science Center of RAS, Syktyvkar, Russian Federation (corresponding
author:valyaeva@geo.komisc.ru)
The object of researches is the Lower Permian
sediments on the outcrops of the river of Kozhym of
Subpolar Urals.
In the studied section the kungurian sediments are
represented by kosyinskaya formation. This is organic
matter (OM) of IV type located in clay sediments of
alluvial fan. The quantity of organic matter, measured
by value of organic carboneum (Сorg) in samples, is
low, changes from 0.56 (sample 5/9/1, siltstone) to
0.91% (sample 5/7, clay siltstone). The sample 5/11 is
marked by the high value of bituminous index - 1,15%
that is characteristic for epigenetic bitumen. Initial OM
has a mixed character and contains components of
inertinite, vitrinite and transitive varieties, which is also
testified by the distribution of n-alkanes and
isoprenoids. The distribution peaks in medium
molecular region fall on С16, С20 that is characteristic
for bioproducers of zoo- and algal material. In the
high-molecular area distribution peaks fall on n-С27,
С29 that is characteristic for terrigenous material.
Among isoprenoids it was possible to determine iso-
С15, С16, С18, С19 and С20. The prevalence of prystane
(Pr/Ph˃1) is considered as indication of humic ОM,
which accumulation occurred in oxidative conditions.
Chernorechenskaya formation
The content of organic carbon varies in the
sediments of Chernorechenskaya formation from 0.11
to 1.47 %. The increased Corg contents were observed
in clay aleurite varieties, and minimum ones - in the
sandy varieties. The general constant level of Corg
contents in aleurite-argillite rocks of verkhneartinsky
sediments testifies to similar to kosyinskaya
sedimentation conditions.
Inclusions of scattered organic matter (SOM) of
inertinite group occur as separate slurry scraps with
cellular structure and uniform mass filling every
possible voids and fractures. Also dendrite-like
accumulations, filled by inertinite OM, were found.
Vitrinite inclusions are represented by gelified
lumpy mass, and liptynite – by deformed remains of
sporingite shells and cutinite scraps.
Often the studied samples revealed development
of ore minerals on the surface of organic inclusions,
forming a kind of joints of organic and or material.
The analysis of samples by the gas-liquid
chromatography revealed that ОM has a mixed
character displayed in bimodal distribution of nalkanes.
However, they differ by quantitative
contribution of humic and sapropelic components that
is displayed in various distribution of n-alkanes in
medium- and high molecular areas. Thus, samples
24/2 24/5 are characterized by the high content of
С11-С18 - to 31.24% and low relative concentrations of
high molecular normal alkanes (С25-С35 from 18.87 to
22.24%). In such bitumoids the distribution peak falls
on n-C16 and n-C20, the prevalence of even alkanes is
determined, which is more noticeable for n- С16
(2*С16/(С15+С17) to 1.84, 2*С20/(С19+С21) – до 1.2).
According to some researchers the prevalence of
even medium molecular n-alkanes is characteristic for
hydrocarbons of bacteria, in particular, n-C16 is a sign
of heterotrophic microorganisms. In high molecular
area the distribution peaks fall on n-C27 and n-C29.
For samples 24/12 and 24/13 the share of medium
molecular alkanes is lower (С11-С18 - 15.63-18.10%),
high molecular compounds dominate (С25-С35 from
31.32 to 32.85%). The predominance of odd nalkanes
of composition С17, С19, С27 and С29 is
observed. The 2*С17/(С16+С19) index fluctuates from
1.06 to 1.19. The prevalence of n-C17 alkane testifies
to the participation of algal ОM (phytoplankton) in the
initial biomass.
All bitumoids among isoprenoids are marked by
increased concentration of phytane (Pr/Ph - 0.51-
0.99) and Ph/C18 index; it can testify to the
regenerative conditions of sedimentation.
According to data in literature the sedimentation
conditions of the given formation are characterized as
delta front.
Thus, on the basis of the conducted researches it
is possible to make a conclusion that initial ОM of
Lower Permian sediments of the river of Kozhym has
a mixed character. The pyrolitic data showed very low
generation potential and hydrogen index of the
rocks.The bacteria-algal component has insignificant
character. Organic matter is at stage of catagenesis
МК1-МК2. The material is oxygenated. The rocks
possess a very low oil-gas generation potential and
are mainly gas source.
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