Orbital cyclicity and astronomical calibration of the Upper Miocene continental succession cored at the Iharosberény-I well site, western Pannonian basin, Hungary

The cyclic Upper Miocene continental succession of the Pannonian basin cored in western Hungary at the Iharosberény-I (Ib-I) well site (1826 m) was calibrated to the Late Miocene astronomical record on the basis of an integrated stratigraphic approach. The study section is represented by a 1350-m-thick shallowing-upward succession consisting of deep lacustrine strata and interbedded turbidites evolving upwards to lake-margin (delta front-foreshore) and delta-plain deposits. Sedimentary cycles associated with variations of the mean grain size across the cored succession display thickness ranging from 5- 6 m to 24-25 m (13 m on average) and show good to excellent correlation with precession cycles (ca. 21 ky) or with the short-eccentricity cycles (ca. 100 ky). Individual lignite layers or clusters and/or organic-rich silt-clay beds often mark minima of the curve of mean grain size in marginal lacustrine and delta-plain facies between 760 m and 50 m. Because they correlate with precession minima and insolation maxima, these beds are likely to represent a continental equivalent of sapropels in coeval pelagic successions of the Mediterranean. The astronomical calibration of the Upper Miocene section cored at the Ib-I well yields accurate ages for individual sedimentary cycles and other stratigraphic events discussed in this study. In terms of sequence stratigraphy, the base of the Pontian stage (cycle 90) correlates with a third-order maximum flooding surface (mfs-3) and is dated at 7.455 Ma. The top of the Pannonian stage (cycles 14/15) also correlates with a third-order maximum flooding surface (mfs-2) and is dated at 9.075 Ma. Both mfs-3 and mfs-2 correspond to distinct long-eccentricity maxima. The stratigraphic unit bounded by these surfaces includes four long-eccentricity cycles (1.6 My) and correlates with the Transdanubian stage (or substage) we adopt in this study as a chronostratigraphic unit intermediate between the Pannonian stage sensu stricto and the Pontian stage sensu stricto of the Paratethys (central to eastern Europe and western Asia) regional system. The boundary between mammal zones MN10 and MN11 (Vallesian-Turolian), dated astronomically at 8.75 Ma in Spain, correlates with sequence boundary Pan-2 (cycle 30). The FAD of endemic cardiids Prosodacnomya (gen.) (cycle 54) and Prosodacnomya cf. dainellii (cycle 61) are dated at 8.293 Ma and 8.109 Ma, respectively. The Tortonian-Messinian boundary, calibrated astronomically and dated at 7.251 Ma on Mediterranean sections, is correlated with our cycle 100.