25th International Meeting on Organic Geochemistry IMOG 2011

P-331
Organic-geochemical characteristics of sediments from the
Lopare basin, Bosnia and Herzegovina
Nenad Grba 1 , Aleksandra Ńajnoviš 2 , Ksenija Stojanoviš 3 , Branimir Jovanţiševiš 3
1 Faculty of Ecology and Environmental Sciences, 11000 Belgrade, Serbia, 2 Center of Chemistry, IChTM,
11000 Belgrade, Serbia, 3 University of Belgrade, Faculty of Chemistry, 11000 Belgrade, Serbia
(corresponding author:sajnovica@chem.bg.ac.rs)
In this study the molecular composition and biomarker
distribution of sediments of Neogene age (Lopare
basin, Bosnia and Herzegovina) were investigated. A
total of 46 samples originated from two boreholes
POT-1 (depth of 193 m) and POT-3 (depth of 344 m).
The organic carbon content was determined by
elemental analysis after carbonate removal with dilute
HCl (1:3, v/v). The bitumen was extracted from
sediments using a soxhlet with an azeotropic mixture
of dichloromethane and methanol. The saturated and
aromatic fractions were isolated using column
chromatography. Saturated and aromatic
hydrocarbons were analyzed by gas chromatographymass
spectrometry (GC-MS).
The organic carbon content, Corg varies in
approximately similar ranges in the sediments of both
boreholes, with average values of 0.86 and 0.80%.
The relative proportions of hydrocarbons in the
bitumen are low (< 20%).
The distribution of saturated hydrocarbons is
dominated by phytane, β-carotane and regular C27-
C29αα(R)-steranes, indicating the low maturity of the
organic matter (OM). n-Alkane distribution of the
almost all the sediments is characterized by marked
dominance of lower homologues n-C17, n-C21 or n-
C22, typical of organic matter of algal.
Domination of phytane in the majority of samples and
values of pristane/phytane (Pr/Ph) ratio < 0.60; for a
great number of sediments are even below 0.20,
indicate reducing to anoxic conditions during
deposition of OM.
All the samples contain squalane. Values of
squalane/n-C26 alkane ratio are in average 2.89 and
3.14 in the boreholes POT-1 and POT-3, respectively
(in some sample are more than 8) indicating saline to
hypersaline depositional environment [1].
Distributions of polycyclic alkanes of sterane and
hopane types are characterized by the domination of
thermodynamically less stable isomers. Values of the
maturation parameters, C31(S)/(C31(S+R) < 0.40;
C29ααS/(ααS+ααR) < 0.30 indicate that the samples
contain OM with maturity, which corresponds to the
diagenetic phase. In the majority of the samples C28
sterane content accounts for approximately 30 % in
total distribution of C27-C29 regular sterane
homologues. This fact is consistent with literature
data for regular sterane distribution in hypersaline
environments [2].
β – Carotane, the relative percentage of which in the
total distribution of hydrocarbons is up to 25%, and
many other diagenetic derivates of β – carotene were
identified. These compounds are associated primarily
with anoxic, saline lacustrine, or highly restricted
marine settings, where organisms such as unicellular
algae Dunaliella, developed as the dominant biota [3].
Some of the samples contained diagenetic products
of isorenieratene, such as diaromatic carotenoids with
40 carbon atoms, C33 and C32 compounds and short -
chain compounds - aryl isoprenoids. The presence of
mentioned compounds indicates contribution of green
sulfur bacteria (Chlorobiaceae) to precursor OM
deposited in photic zone anoxia (PZA) [4].
Sediments from both boreholes POT-1 and POT-3 of
the Lopare basin contain immature algal organic
matter deposited under anoxic, saline to hypersaline
conditions. The biomarker patterns are in agreement
with geological history of the basin. Namely, during
Oligocene and Lower to Middle Miocene, Lopare
basin was the part of the same deposition basin which
included also Tuzla basin with salt formation, which is
exploited for decades.
References
[1] Grice, K. et al., 1998. Organic Geochemistry 28,
349-359.
[2] Yangming, Z., et al. 2005. Applied Geochemistry
20, 1875-1889.
[3] Peters, K.E., Walters, C.C., Moldowan, J.M., 2005.
The Biomarker Guide, Volume 2: Biomarkers and
Isotopes in Petroleum Exploration and Earth History.
Cambridge University Press, Cambridge, UK.
[4] Clifford, D. et al. 1998. Organic Geochemistry 29,
1253-1267.
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