Towards a high-resolution chronostratigraphy and geochronology for the Pannonian Stage: Significance of the Paks cores (Central Pannonian Basin)

Abstract

A new stratigraphic standard for the open lacustrine to deltaic Pannonian Stage is emerging from the combinedsedimentological, lithostratigraphical, sequence stratigraphical, biostratigraphical, seismic stratigraphical, geo chrono -logical, and magnetostratigraphical investigations of 6 long drill cores. These were drilled by Paks II Nuclear Power PlantPlc. as a preparatory step for the construction of a new power plant near the city of Paks, Central Pannonian Basin,between 2015 and 2016. The boreholes are in a distance of 8–12 km from each other, and five of them fully penetrated thelocal Pannonian sequence in a thickness of 390 to 662 m. Each core includes offshore clay marl deposited far fromsediment entry points (Endrőd Fm), heterolithic, sandy siltstones of a <200 m high shelf-margin slope (Algyő Fm), andseveral stacked deltaic deposits from prodelta silts to sandy mouth bars, heterolithics, lignite and sandy channel-fills ofthe delta plain (Újfalu Fm). Magnetostratigraphic investigations from two cores and authigenic 10Be/9Be dating from twoothers were combined by means of seismic correlation between the boreholes, and thus they provide a solid geo -chronological and chronostratigraphic basis for the interpretation of the sedimentological and palaeontological recordsof the cores. The continuous representation of the earliest Pannonian (11.6–9.1 Ma) in the cores needs furtherpalaeontological investigation, as both magnetostratigraphy and authigenic 10Be/9Be dating failed to give reliable agedata from the basal, condensed calcareous marls. The 9.1 to 6.5 Ma interval, however, is represented in the cores by various lithologies and abundant and sometimes excellently preserved fossils. In the deltaic succession, 10 sedimentarysequences were correlated between the cores; as their duration is not more than 200 kyr each, they can be regarded as 4th-order sequences. The palaeontological record of the cores shows a very good agreement with the formerly establishedbiochronostratigraphical system. The cores provide an insight into the evolution of the sedimentary environment and thebiota of Lake Pannon between 9.1 and 6.5 Ma with a so far unprecedented temporal and spatial resolution.