Palaeoenvironmental reconstructions by stable isotopes of Middle Miocene gastropods of the Central Paratethys Christine Latal a, * , Werner E. Piller a , Mathias Harzhauser b a Institute for Geology and Palaeontology, University of Graz, Heinrichstrage 26, A-8010 Graz, Austria b Museum of Natural History Vienna, Geological-Palaeontological Department, Burgring 7, A-1014 Vienna, Austria Received 11 April 2003; received in revised form 9 April 2004; accepted 5 May 2004 Abstract The stable isotopes of carbon and oxygen were used to provide information of mixing of marine and freshwater and subsequently used to determine palaeosalinities. In the Middle to Late Miocene St. Margarethen bZollhausQ section (Upper Sarmatian bMactra ZoneQ/Pannonian), a succession of three gastropod assemblages indicates changing environmental conditions from a limnic-fluviatile to littoral mudflat and a sublittoral marine environment. Several shells of the main representatives of the three assemblages [Potamides hartbergensis (Hilber), Granulolabium bicinctum (Brocchi), Potamides disjunctus (Sowerby)], and additionally shells of Lymnaea sp., a typical freshwater gastropod, and Pomatias conicus ,a terrestrial gastropod, were taken for stable isotope analyses. Oxygen and carbon isotope data of the freshwater endmember are distinctively lower (d 18 O~À4.5x/d 13 C~À9x) than of the marine endmembers (d 18 O~À2.2x/d 13 C~2.3x). In contrast to the expected intermediate isotopic composition between the freshwater and marine environment, the shells of supposed brackish environments have higher d 18 O values than the shells of the marine environment. These higher d 18 O values are explained by evaporation, which affected the protected areas of riverine to lacustrine environments and small pools on mudflats, formerly considered to be the habitats of the brackish assemblages. Thus, the oxygen and carbon isotope data extend the already existing palaeoenvironmental information. D 2004 Elsevier B.V. All rights reserved. Keywords: Gastropods; Stable isotopes; Palaeoenvironment; Middle Miocene; Central Paratethys 1. Introduction Investigations of stable isotope ratios of carbon and oxygen on carbonate shells are a powerful tool for the reconstruction of palaeoenvironmental parameters. Though the Paratethys underwent distinct changes in environmental conditions forced by palaeogeograph- ical changes, the use of stable isotopes on Miocene fossils of the Paratethys has been rather scarce (Geary et al., 1989; Sutovska and Kantor, 1992; Matyas et al., 1996; Durakiewicz et al., 1997; Hladilova et al., 1998; Gonera et al., 2000; Bojar et al., 2004). The Badenian/ Sarmatian (Middle Miocene regional stages) boun- 0031-0182/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2004.05.003 * Corresponding author. Fax: +43 316 380 9871. E-mail address: christine.latal@uni-graz.at (C. Latal). Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 157–169 www.elsevier.com/locate/palaeo