25th International Meeting on Organic Geochemistry IMOG 2011

P-302
Carbonaceous rocks of the Neoproterozoic (Vendian) Khatyspyt
Formation as a possible source of oils in the northeastern
Siberian Platform
Tatyana Parfenova, Vladimir Kashirtsev, Lubov Borisova, Elena Ivanova, Boris Kochnev,
Konstantin Nagovitsyn, Vasily Melenevsky
Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsc, Russian Federation
(corresponding author:parfenovatm@ipgg.nsc.ru)
Organic-rich carbonate rocks of the Khatyspyt
Formation of the Neoproterozoic (Vendian – 544-
550 Ma) in the western and northern slopes of the
Olenek uplift are considered as potential oil source
rocks in the northeastern Siberian Platform. The
organic carbon content (TOC) in the rocks is known to
vary from 0.04 to 14 % [1, 4-6, and oth]. Comparative
analysis of the molecular composition of saturated
hydrocarbons (HCs) of the Khatyspyt Formation has
allowed identification of the features similar to those of
bitumens occurring in Vendian-Cambrian deposits of the
Olenek uplift. The major of them include the absence
of 12- and 13-monomethylalkanes, anomalously high
contents of ethylcholestane in sterane HCs and
gammacerane in terpane HCs, and the presence of
29,30-bisnorhopane. The authors suggest that
bitumens of the Olenek uplift and bitumen extracts
from the examined carbonate deposits have been
generated from a single source, the Khatyspyt
Formation rocks [1-5, and oth.].
A collection of rocks (8 samples) of Khatyspyt
deposits of 245 m thick from the outcrops of the
Khorbusuonka R. has first been studied by pyrolysis
method. It has been established that the organic
matter content in 2 samples is below the limit of
satisfactory estimate of generative properties of rocks.
S1 in 6 samples vary from 0.01 to 0.50 mg HC/g rock.
S2 is within the range 0.08-16.00 mg HC/g TOC. Thus,
the generative potential (S1+S2) of rocks varies from
0,00 до 16.50 mg HC/g TOC. Hydrogen index (HI) in
OM of rocks varies from 56 to 382 mg HC/g TOC.
High values of HI indicate that OM is type II.
Generally, the low values (less than 150-200 mg HC/g
TOC) suggest that OM is of type III. Lower HI values
seem to be related to the hydrogen loss in oxidizing of
OM in diagenesis or hypergenesis. Tmax of rocks vary
within the range of 437-444 °С.
Kerogens were extracted from 3 samples. Two
samples contain 75.9 and 81.58 % carbon (C), 6.9
and 7.1 % hydrogen (H), 0.01 and 3.8 % sulfur (S),
2.4 and 1.2 % nitrogen (N), 14.8 and 6.30 % oxygen
(O), respectively. HI values in these samples amount
to 322 and 364 mg HC/g TOC. One sample shows an
anomalously low content of C in bitumens (71.4 %)
and H (4.7 %), and high content of O (21.8 %). Its HI
is 184 mg HC/g TOC. The lower HI values and the H
and C content in kerogen are likely to be resulted
from OM oxidation. For the first time, stable carbon
isotopes (δ 13 С) of kerogens (2 samples) have been
examined, δ 13 С is equal to –32.3 and –33.5 ‰. The
δ 13 С average value of bitumens is –33.0 ‰ in Vend-
Cambrian deposits of the Olenek uplift [1, and oth.].
Tmax of kerogens varies from 438 to 441 °С. They
confirm the estimates obtained from rock analysis,
and agree with the known values of molecular
coefficients of maturity [5].
Conclusion. The OM-depleted rocks have a low
generative potential according to [7]. Organic-rich
limestones are characterized by a moderate and high
generative potential. The results of rock and kerogen
pyrolysis, elemental composition of kerogens, and
molecular parameters suggest that Khatyspyt
deposits entered the oil window during their geologic
history. In some intervals of the section of the
Khatyspyt Formation, OM is oxidized. Similar values of
δ 13 С in the examined kerogens and bitumens of the
Olenek uplift have first allowed the confirmation of
genetical relation of bitumens and OM of the
Khatyspyt Formation at the atomic level. New results
show that the section of the Vendian Khatyspyt
sequence contains carbonaceous rocks, a source of
naphthides in the northeast of the Siberian Platform.
References
[1] Kashirtsev V.A., ―Organic Geochemistry of
Naphthides of the East Siberian Platform―. (Yakutsk, 2003)
[in Russian].
[2] Kashirtsev V.A., et al. Deposits of natural
bitumens in the northeastern Siberian Platform (Russian
Arctic sector) // Rus. Geol. and Geophys. 2010. No 1.
[3] Kontorovich A.E., et al. // DAN. 2005. V. 402. № 5.
[4] Kontorovich A.E., et al. // DAN. 1995. V. 345. № 1.
[5] Kontorovich A.E., et al. Organic geochemistry of
the Vendian Khatyspyt Formation (northeast of the Siberian
Platform) // The 24 th <strong>International</strong> meeting on organic
geochemistry. Bremen. Germany. 2009. P. 174.
[6] Natapov L.M. // Soviet Geology. 1962. № 11.
[7] Tissot B., Welte D. Petroleum formation and
occurrence. Moscow: Mir, 1981. 502 p.
435