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Carbon and oxygen isotope characteristic of Pannonian-Pontian marl and ostracode samples of Hrvatsko Zagorje, Croatia

Carbon and oxygen isotope analyses were made on carbonate component of marls (ten samples) and ostracode shells (three samples). Investigations included deposits from two outcrops in the south-western part of Hrvatsko Zagorje, located close to villages Donja Pušća and Kupljenski Hruševec. The measurements were made on a Finnigan MAT Delta S stable-isotope-ratio mass spectrometer in Laboratory for Geochemical Research of Hungarian Academy of Science in Budapest. Upper Pannonian age was determined on the lower and middle part of Pušća outcrop by ostracodes: Hugarocypris hierogliphica (MEHES), Amplocypris recta (REUSS), A. acuta KRSTIĆ, Cyprideis heterostigma (REUSS), Candona (Lineocypris) nonreticulata SOKAČ, C. (Taminocypris) improbus KRSTIĆ, C. (Sinegubiella) illyrica KRSTIĆ, Hemicytheria dubokensis KRSTIĆ and on Kupljenski Hruševec outcrop by: Hemicytheria cf. marginata SOKAČ, H. reticulata SOKAČ, Cyprideis spinosa SOKAČ, Candona (Thaminocypris) cf. labiata (ZAL.), C. (Zalanyiella) longissima KRSTIĆ, C. (Bakunella) balcanica (ZAL.). Lower Pontian age on upper part of outcrop Pušća was determinated by: Amplocypris nonreticulata (ZAL.) KR., Candona (Lineocypris) cf. Inflexa SOKAČ. Early Pontian age of the lower part of Kupljenski Hruševec outcrop was determinated by Upper Pannonian ostracodes Candona (Lineocypris) reticulata (MEHES). The XRD analyses on marl samples revealed presence of calcite and low magnesium calcite (1-5% MgCO3) indicating lesser diagenetic changes. The measured δ 13C values are 1, 26‰ to 3, 42‰ for Pannonian and 0, 77‰ to 3, 52‰ for Pontian samples respectively. The values of δ 18O for Pannonian samples are -4, 91‰ to -0, 79‰ , and for Pontian samples -6, 16‰ to 0, 10‰ . The results of oxygen and carbon isotope analysis are comparable with the results for the Miocene Pannonian Lake from MÁTYÁS et al. (1996) and GEARY et al. (1989) (Fig. 1). Observed lowered δ 18O values probably are result of lesser diagenetic changes (DEMÉNY, A., personal communication ; PARRISH, 1998). MÁTYÁS et al. (1996) considered the lowered values of δ 18O and δ 13C in the Pannonian-Pontian border as results of increased humidity. Positive δ 18O values of about 0, 10‰ for ostracode samples probably indicate less saline water in Pontian Lake than in the Pannonian Lake. These results are in accordance with δ 18O values (+0, 3‰ to +2, 5‰ ) for fresh water ostracodes given by XIA et al. (1997), von GRAFENSTEIN et al. (1999) and HOLMES & CHIVAS, (2002). References: GEARY, D.H., RICH, J., VALLEY, J.W. & BAKER, K. (1989): Stable isotopic evidence of salinity change: Influence on the evolution of melanopsid gastropods in the Late Miocene Pannonian basin. - Geology, 17, 981-985. HOLMES, J.A. & CHIVAS, A.R. (2002): Ostracod shell chemistry - overview. In the ostracoda: applications in quaternary research. - Geophysical Monograph 131, 185-204. MÁTYÁS, J., BURNS, J.S., MÜLLER, P. & MAGYAR, I. (1996): What can stable isotopes say about salinity? An example from the Late Miocene Pannonian Lake. - Palaios, 11/1, 31-39. PARRISH, J.T. (1998): Interpreting Pre-Quaternary Climate from the Geologic Record. - Columbia University Press, New York, 338. Von GRAFENSTEIN, U., ERLLENKEUSER, H. & TRIMBORN, P. (1999): Oxygen and carbon isotopes in modern fresh-water ostracode valves: assessing vital offsete and autecological effects of interest for paleoclimate studies. - Paleogeography, Paleoclimatology, Paleoecology, 148, 133-152. XIA, J., ITO, E. & ENGSTROM, D.R. (1997): Geochemistry of ostracode calcite: Part 1: an experimental determination of oxygen isotope fractionation. - Geochimica et Cosmochimica Acta, 61, 377-382.

carbon isotope; oxygen isotope; ostracode; marl; Pannonian Lake; Hrvatsko Zagorje

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