Discussion of problems of development of Upper Jurassic and Lower Cretaceous basins in Poland and Hungary, identification of possibilities of using existing databases for global definition of boundary between Jurassic and Cretaceous systems and elaboration of assumptions for further co-operation between geological surveys of Poland and Hungary were the key topics of the meeting of members of the Berriasian Working Group held on 20-26.05.2024 in Hungary, in the area of Bakon Forest (Zadunai Central Highlands).

The Polish Geological Institute-NRI was represented by: prof. Jacek Grabowski and dr Damian Lodowski.

The meeting was coordinated by dr Ottilia Szives from the Mining and Geological Survey of Hungary (now part of the Supervisory authority for Regulatory Affairs, Hungary - SZTFH), and also present were prof. Emő Márton and dr Gabor Imre from the SZTFH Palaeomagnetic Laboratory, and prof. Janos Haas of the University of Budapest.

From the right: dr Ottilia Szives, prof. Janos Haas and prof. Jacek Grabowski at the quarry of the aptu crinoid limestone (Tata Formation), on the castle hill in Sümeg. Photo: O. Szives

As part of the meeting, a field session was held in the region of the Zadunai Middle Mountains. Two Tithonian-Beriassian profiles (Jurassic-Cretaceous border) were inspected in the Bakonian Mountains basin (Lókút profile) and Zalaegerszeg basin (Sümeg profile). During the visit to the Sümeg profile, prof. Jacek Grabowski gave a short lecture on the basics of the palaeomagnetic method to geology students at the University of Budapest.

Prof. Jacek Grabowski and prof. E. Márton conducting classes for geology students at the University of Budapest, Sümeg profile. Photo: O. Szives

The Lókút profile is the reference profile of the Jurassic/Cretaceous interval boundary in Hungary. It is excellently studied stratigraphically, with significant contributions to the identification of the profile made by Polish researchers from PGI-NRI: J. Grabowski, D. G. Lodowski and H. Wierzbowski (magnetostratigraphy, chemostratigraphy, stable isotopes) and PAN (A. Pszczółkowski, microfossil stratigraphy).

Current work focuses on trying to identify orbital astronomical cycles (Milankovich cycles), or so-called astrochronological calibration. The reconstruction of the rhythm of changes in the parameters of the Earth's orbit, i.e. precession (with a period of approx. 26,000 years), obliquity (approx. 41,000 years) and eccentricity (approx. 100,000 and 405,000 years), as well as higher-order cycles, corresponding approximately to the boundaries of the floors and sub-floors (approx. 1.2 and 2.4 million years) in the Lókút profile will allow extremely detailed, i.e. beyond the stratigraphic resolution available to any other method, dating of the Late Tithonian and Early Berean formations.

TSuch detailed chronostratigraphy would facilitate the correlation of Jurassic and Cretaceous boundary layers between remote areas belonging to different palaeobiogeographical provinces, characterised by a different set of fossils and a not always clear record of changes in the polarity of the Earth's magnetic field. Pilot studies have shown that changes in the content of fine grains of magnetite and changes in the composition of planktonic organisms (e.g. quantitative ratios between radiolarians and calpionellae) in deep-sea carbonate formations were conditioned, among other things, by the direction and intensity of palaeoclimatic processes. This, in turn, makes it possible to suspect that these processes may also have been sensitive to the rhythm of orbital changes, a kind of driving force behind cyclical climate change on our planet.

Detailed sampling of the Upper Tobacco Limestone of the Lókút profile (Pálihálás Formation), carried out for orbital stratigraphy. This method requires very dense sampling - in this case samples were taken with a field drill every 2.5-5 cm. Photo: J. Grabowski

Textt: prof. Jacek Grabowski, dr Damian Lodowski