25th International Meeting on Organic Geochemistry IMOG 2011

P-123
Organic matter characteristics of Bazhenov Formation in the
central part of the West-Siberian basin based on biomarker
parameters and pyrolysis
Enver Ablya, Elena Kononchenko
Moscow State University, Moscow, Russian Federation (corresponding author:lena.konon@mail.ru)
Bazhenov Formation (BF) (J3) is just 20m thickness
but it is believed a main source rock in the West-
Siberian basin. It is heterogeneous on the area. There
is a central part in its structure which is characterized
by high content of organic matter. It is considered that
in the central part of the basin BF is presented mainly
by bazhenovites which have TOC reaching to 25%
(on the average more than 7-10 %).
In this work it is shown that the structure of BF
organic matter (OM) is more difficult than it was
represented earlier. As an object of research there
were samples from BF at close area of the central
part. Studying of conditions of accumulation and
transformation of OM was a research objective.
Macroscopic description of core, pyrolysis by Rock-
Eval and GC-MS have been carry out. It has been
established (fig.) presence of two extremely different
types of organic matter (including degree of maturity).
The first type (1) is characterized by low Pr/Ph,
abnormal high content of C27 steranes in comparison
with С29, also high ratio t23/t24 (tricyclic terpanes)
that indicates enough deep-water conditions of
sedimentation. It is possible to interpret high
Dibenzotiofene/Phenantrene index as a sign of low
Eh. Together with the pyrolysis data (high HI) this
type of organic matter can be carried to the typically
marine. The second type (2) of organic matter has
opposite characteristics and also higher concentration
of gammacerane that speaks about conditions of the
high salinity. This type can be named terrigenous.
Different degree of maturity of two types is very
interesting. For the first type maturity is relatively high
according to the Ts/Tm and �� sterane ratios, for the
second type (terrigenous) it is much lower (very low
Ts/Tm and �� sterane ratios, the presence of
moretanes). However, according to Rock-Eval data
(Tmax), which always gives the average rate, maturity
is near. Thus, we have two types of organic matter
with different degrees of transformation, and possibly
generated different hydrocarbons, but, nevertheless,
passed virtually the same thermal history.
Terrigenous type formed apparently under intensive
influence of adjacent continent that early thought is
not typical for the central part of the basin. In the
neighbouring areas zones of distribution of abnormal
BF have been identified (thickness up to 100 m, with
Mass chromatogram m/z 191
seams of sandstones).
Them
genesis is
associated with
descent of
turbidites flows
from the continent.
In the
study area
normal BF is
distributed. However,
descent of
turbidites in
adjacent areas
can affect the
formation of it.
265