25th International Meeting on Organic Geochemistry IMOG 2011

P-476
Geochemical appraisal of palaeovegetation and climate
oscillation in the Late Miocene of Western Bulgaria
Maya Stefanova 1 , Dimiter Ivanov 2
1 Insitute of Organic Chemistry Bulgarian Academy of Sciences, Sofia, Bulgaria, 2 Institute of Biodiversity and
Ecosystems Research Bulgarian Academy of Sciences, Sofia, Bulgaria (corresponding
author:maia@orgchm.bas.bg)
The Neogene basins in Bulgaria are very important in
the system of sedimentary complexes on the Balkan
Peninsula. They contain valuable information on the
development of the flora during the Miocene. The
territory of the peninsula played a crucial role in the
evolution and migration of the Mediterranean flora
because of its specific geographical location between
the Tethyan and Paratethyan basins. Changes in the
vegetation, emergence of sclerophyll woody plants,
and dissemination of the herbaceous communities
reflect the regional palaeographic and climate
changes.
The aim was to relate palaeobotanical observations
with chemical data for Late Miocene sediments some
with lignitic-clayey units. In the study assumptions for
palaeovegetation changes and climate oscillations in
the late Miocene of Western Bulgaria based on pollen
and statistical analysis will be appreciate with
geochemical proxies.
Samples from Western Bulgaria, i.e. sediments of 5-
10 m and 20-26 m as well as coal-bearing material
were characterised by bulk and spectral methods.
GC/MS study of ―free‖ bitumens (20 ÷ 66 mg/gCorg)
revealed the presence of n-alkanes and terpenoids.
The n-alkanes, hopanes and C27 D-ring mono
aromatic hopane were present in the first fractions,
while alkan-2-ones, mid-chain ketones, polar di-and
triterpenoids were registered in the polar aromatics.
Extremely high quantities for keto triterpenoids and
products of their photochemical degradation were
determined, 50 ÷60 ug/gCorg in clay sediments and 30
ug/gCorg in coal-bearing sample.
Diterpenoids were determined only in clay sediment
sample of 20-26 m depth, up to 4.3 rel. % aromatic
hydrocarbons and 2.3 rel % polar diterpenoids.
Registered compounds were assigned to the abietane
and phyllocladane structural groups. 16�(H)-
Phyllocladane was identified in the neutral fraction,
while abietanes occurred as aromatic hydrocarbons
(dehydroabietane, simonellite, retene) and polar
derivatives like ferruginol, dehydroferruginol and 7oxo-dehydroabietane
in the aromatic/polar fraction.
Diterpenoids were observed only in sample
palaeobotanically characterized by dry and cool
climate. Friedelin, M + 426, in comparable quantities of
25 ug/gCorg was registered in all polar aromatic
fractions It is a common epicuticular wax component.
Taken alone high quantity of friedelin is not unusual in
Miocene sediments. Its high presence was registered
in Neogene lignites, Bulgaria and potential progenitor
Taxodium dubium. It is highly abundant in clay
sediments, fossil plants, oak covered soil, etc.
The novelty in this study is the extremely high
quantities of A-Norfriedel-8-en-10-one, M + 342, m/z
123 (100%), ~ 45 ug/gCorg in clay samples and in
comparable quantity with the parent friedelin, in coalbearing
sample, 27.3 ug/gCorg.
In fact A-Norfriedel-8-en-10-one could be regarded as
a product of loss of ring A in triterpenoids. First Corbet
et al. [1] described 3,4-seco-triterpenoids as major
products of photochemical/photomimetric alteration of
3-oxygenated triterpenoids. Later on reactivity of high
plant 3-oxy-triterpenoids to sunlight under real solar
exposure is investigated and assumed an analogy in
behaviour in sediments during diagenetic reworking of
parent triterpenoids [2-4]. In the set of species of the
series one more compound in high content appeared,
A-Norfriedel-dien-10-one, M + 340, with similar pattern
of mass fragmentation. Its retention time with
appearance just before A-Norfridel-8-en-10-one, gave
as ground to assume ―diene‖ structure.
The biomarker assemblage accompanied by bulk
chemical data indicated that for samples under
consideration gymnosperms were not an important
vegetation component in the palaeo mire. For organic
matter formation results accept highly reworked
angiosperm rich flora altered by climate oscillations
during the Late Miocene of Western Bulgaria.
References
[1] Corbet et al., 1980. JACS 102-3, 1171.
[2] Jaffé,R. et al., 2006. Chemosphere 64, 1870.
[3] Simoneit, B.R.T. et al., 2009. Ibid 74, 543.
[4] Bakar, N.A. et al., 2011. Ibid (submitted).
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