Climate and vegetation change during the late Miocene in southwest Bulgaria based on pollen data from the Sandanski Basin Dimiter Ivanov Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 23, 1113 Sofia, Bulgaria abstract article info Article history: Received 23 May 2014 Received in revised form 7 May 2015 Accepted 21 May 2015 Available online 14 June 2015 Keywords: Pollen Paleobotany Climate reconstruction Late Miocene Bulgaria Late Miocene sediments from the Sandanski Basin in southwest Bulgaria are studied by means of the spore and pollen analysis. Vegetation in the studied basin is described and its dynamics and development are traced out. The main vegetation types are distinguished. The flora of this time interval was characterized by a change in the structure of communities and of the dominant species. Quercus, Castanea, Corylus, Ulmus, and Carya used to prevail in the composition of mesophytic forest paleocoenoses. Paleogeographic and climatic changes at the beginning of late Miocene had determined the emergence of suitable conditions for a broader participation of herbaceous coenoses. The first herbaceous coenoses were comparatively poor in their taxonomic composition, which became enriched for the first time in the late Tortonian. The traced-out dynamics of paleoclimatic data testify to notable climatic changes. The beginning of the late Miocene witnessed a certain drying and slight cooling, resulting in a moderately warm climate. It had a distinct seasonality with respect to temperature and precipitation. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Changes in climate and vegetation during the late Miocene have been the subject of scientific interest over the last several decades, which has encouraged investigation of the fossil floras and environmen- tal details in that time interval. After the middle Miocene, the climatic system of the Earth manifested a progressive cooling trend (Zachos et al., 2001), which entailed global transformations in the flora and veg- etation. In the eastern Paratethys the late Miocene was characterized by the emergence of open habitats and in the distribution of herbaceous vegetation, which occupied new territories after periods of marine regression (Ivanov et al., 2002, 2007c). The territory of Bulgaria with its numerous lake and lake-and-marsh Miocene basins is a key region for the investigation of the Neogene evolution of the flora and vegeta- tion, of migration routes and exchange corridors of many plant species, and of the floristic bonds between Central and East Europe and Asia Minor (Meulenkamp et al., 1996; Rögl, 1998, 1999; Meulenkamp and Sissingh, 2003; Popov et al., 2006). This region apparently played a substantial role in the survival of a number of paleotropical species in various refuges, on one hand, and in the processes of speciation of many plant species, on the other hand (Palamarev, 1989; Palamarev and Ivanov, 1998, 2001, 2004; Palamarev et al., 1999). Spatial distribution of vegetation strongly relies on climatic condi- tions. Vegetation reconstruction thus makes it possible to reconstruct the climate of the past. The last three decades have witnessed the development of several quantitative methods – e.g., the Coexistence Approach Method (Mosbrugger and Utescher, 1997), the Climatic Amplitude Method (Fauquette et al., 1998), CLAMP (Wolfe, 1993), and Leaf Margin Analysis (Wilf, 1997) – to reconstruct the climate of the past. As a result of many reconstructions, a number of local and regional climatic models have been developed for the Neogene period (Bertini, 2002, 2006; Bruch and Gabrielyan, 2002; Bruch and Mosbrugger, 2002; Ivanov et al., 2002, 2007a,2007b,2007c, 2011; Bruch and Kovar-Eder, 2003; Fauquette and Bertini, 2003; Uhl et al., 2003, 2006, 2007a,2007b; Bruch et al., 2004, 2006, 2007, 2011; Mosbrugger et al., 2005; Traiser et al., 2005, 2007; Fauquette et al., 2006, 2007; Jiménez-Moreno, 2006; Jiménez-Moreno and Suc, 2007; Jiménez-Moreno et al., 2007a,2007b, 2007c, 2008a,2008b, 2009; Utescher et al., 2007, 2009, 2011a,2011b). Miocene fresh-water basins are widely distributed in southern Bulgaria. Sediments often include various plant fossils: seeds and fruits, leaf imprints, cuticles, spores and pollen. In the last decade, palynologi- cal studies of the late Miocene sediments from the Sandanski Basin have been carried out, attempting to elucidate the development of the taxonomic composition and characteristics of the vegetation (Ivanov, 2000, 2001a,2001b,2001c,2001d). This article is a follow-up of the earlier studies of the fossil flora and vegetation of the Sandanski Basin in order to further clarify the development of vegetation and climate evolution during the late Miocene. 2. Geology and paleogeography The non-marine Sandanski Basin (southwest Bulgaria) is a geologi- cal structure (Fig. 1) surrounded by several horsts (Zagorchev, 1970): Ograzhden in the west, Pirin in the east, Kresna in the north, and Roupel Review of Palaeobotany and Palynology 221 (2015) 128–137 E-mail address: dimiter@bio.bas.bg. http://dx.doi.org/10.1016/j.revpalbo.2015.05.011 0034-6667/© 2015 Elsevier B.V. All rights reserved. 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