25th International Meeting on Organic Geochemistry IMOG 2011

P-278
Short-chain steranes and isophopanes in Miocene source rocks
from hyperthermal basin (Banat Depression, S.E. Pannonian
Basin, Serbia)
Ksenija Stojanoviš 1,2 , Sanja Mrkiš 2 , Aleksandar Kostiš 3 , Hans Peter Nytoft 4 , Aleksandra
Ńajnoviš 2
1 University of Belgrade, Faculty of Chemistry, 11000 Belgrade, Serbia, 2 Center of Chemistry, IChTM, 11000
Belgrade, Serbia, 3 University of Belgrade, Faculty of Mining and Geology, 11000 Belgrade, Serbia,
4 Geological Survey of Denmark and Greenland, DK-1350 Copenhagen, Denmark (corresponding
author:xenasyu@yahoo.com)
Short-chain (C21 and C22) steranes and isohopanes
were investigated in Miocene source rock samples
originated from Banat Depression, S.E. Panonian
Basin, Serbia. This area, like the entire basin, is
characterized by hyperthermicity (geothermal gradient
4.0-7.5 o C/100m) and by an exceptionally high heating
rate for Miocene sediments (9-21.9 o C/Ma). Organic
matter (OM) of the samples consists predominantly of
Type II kerogen. Oil window began at 110-120 o C and
vitrinite reflectance (Rc) ca. 0.53-0.58%, reached a
maximum at 145-150 o C and Rc ca. 0.72-0.75% and
ended at 170-175 o C and Rc ca. 0.89-0.93%, which
correspond, to relative depths between 1850 and
2100 m, 2600 and 2900 m, and ca. 3500 m,
respectively. Numerous biomarker parameters
indicated a mixed terrestrial-marine origin of the OM,
related to a lacustrine sub-oxic depositional setting.
After bitumen extraction and isolation of saturated,
aromatic and NSO fraction, saturated hydrocarbons
were analyzed using GC-MS-MS.
All the samples contained relatively high amount of
C21 and C22 steranes. [C21+C22(αα+ββ)steranes]/[ΣC27-C29(αα(R+S)+ββ(R+S))-steranes]
ratio, (C21+C22)/ΣC27-C29 showed statistically
significant correlation with present temperature,
production index (PI), Tmax and biomarker maturity
ratios. No statistically significant correlation between
the (C21+C22)/ΣC27-C29 and pristane/phytane (Pr/Ph)
as well as C35H(S)/C34H(S) homohopane ratio was
observed. In addition, the ratio did not correlate with
the source parameters, distribution of C27-C29 regular
steranes, oleanane index and C30 sterane index.
Therefore the ratio was used for an estimate the OM
maturity Samples, whose OM attained a maturity
corresponding to the late stage of oil generation
(present temperature and Tmax >153 o C and 447 o C,
respectively and originate from depths >3050 m) have
values of (C21+C22)/ΣC27-C29>0.25. The value of the
ratio for immature samples is 2), which are also
characterized by slightly higher temperatures are
close to the values of these parameters for
moderately mature samples the OM of which was
deposited in anoxic conditions (Pr/Ph