Geochemical appraisal of palaeovegetation and climate oscillation in the Late Miocene of Western Bulgaria Maya Stefanova a,⇑ , Dimiter A. Ivanov b , Torsten Utescher c a Bulgarian Academy of Sciences, Institute of Organic Chemistry, Acad. G. Bonchev Bl. 9, 1113 Sofia, Bulgaria b Bulgarian Academy of Sciences, Institute of Biodiversity and Ecosystem Research, Acad. G. Bonchev Bl. 23, 1113 Sofia, Bulgaria c University of Bonn, Geological Institute, Nussallee 8, 53115 Bonn, Germany article info Article history: Received 12 May 2011 Received in revised form 25 July 2011 Accepted 22 August 2011 Available online 3 September 2011 abstract Palaeobotanical methods and geochemical techniques were used to assess plant contribution and pala- eoenvironment for the Staniantsi Basin, Bulgaria. The aim was to connect palaeovegetation change and climate oscillation based on pollen and statistical analysis with organic geochemical proxies for a Late Miocene lacustrine to paludial sedimentary succession. Three samples from lignite/marl cycles were studied. The biomarker assemblage and bulk chemical data indicated that gymnosperms were not important in the palaeomire. The presence of des-A-triterp- enoids, 17,21-seco-triterpenoids, hopanes, a high content of a D-ring monoaromatic hopane, and aroma- tized triterpenoids suggested that photochemical and microbial processes significantly contributed to the alteration of the organic matter (OM). A prolonged period of high water table and severe mechanical destruction promoted microbial activity prior to burial and enhanced decay. A geochemical appraisal of short term climate oscillation (ca. 21.7 kyr) was attempted within the limitations of the small number of samples studied. The cycles are expressed as lignite/marl–clay layers combined with cyclic changes in swamp vegetation related to cyclic changes in groundwater level and inundation of the basin. In periods of low water level (swamp phase) lignite accumulation took place. Preliminary results for selected sam- ples suggest that the oscillation may be reflected in the content of friedelin vs. possible degradation prod- ucts. The ratio of a chromatographic peak tentatively assigned as A-norfriedel-8-en-10-one to friedelin is proposed as a means of detecting short term environmental cycles, where values <1 represent the swamp phase and those >1 reflect periods of inundation. However, time-series analysis using densely sampled lignite–clay layer oscillations are needed to confirm the value of this biomarker ratio for environmental reconstruction. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The Neogene basins in Bulgaria, part of a system of sedimentary complexes on the Balkan Peninsula, contain important information on the development of the flora during the Miocene. Because of its geographical location between the Tethyan and Paratethyan ba- sins, the Balkans territory played a crucial role in the evolution of Mediterranean flora and appears to be one of the major migration routes in the floral exchange between Asia Minor and Europe. Changes in vegetation, the emergence of sclerophyllous woody plants and the dissemination of herbaceous communities reflecting regional palaeogeography, as well as the strong dependence of plant composition on climate conditions, offers a unique opportu- nity for assessing climate in ancient times. Reconstructing palaeo- climate is essential for understanding recent and future changes in the climate system under the influence of internal/external forcing factors. Recently, various quantitative palaeobotanical techniques for reconstructing palaeoclimate have been developed [e.g. Climate Leaf Analysis Multivariate Programme, CLAMP (Wolfe, 1993), Coexistence Approach (Mosbrugger and Utescher, 1997), Climate Amplitude Method (Fauquette et al., 1998), European Leaf Physiog- nomic Approach, ELPA (Traiser et al., 2005, 2007)] and refined (e.g. Utescher et al., 2009a). Besides traditional palaeobotanical meth- ods, geochemical techniques can supply new insights into plant composition and inferred palaeoenvironment. The application of both approaches significantly improves knowledge about the evo- lution of the climate system and vegetation dynamics. Bulgarian Neogene coals are characterized by low grade techno- logical parameters but are interesting from a fundamental point of view as they still retain precursor – product relationships. Oxygen-containing derivatives of terpenes, i.e. phenols, ketones, 0146-6380/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.orggeochem.2011.08.015 ⇑ Corresponding author. Tel.: +359 29606162; fax: +359 28700225. E-mail address: maia@orgchm.bas.bg (M. Stefanova). Organic Geochemistry 42 (2011) 1363–1374 Contents lists available at SciVerse ScienceDirect Organic Geochemistry journal homepage: www.elsevier.com/locate/orggeochem