Jurassic–Cretaceous transition in the Transdanubian Range (Hungary): integrated stratigraphy and paleomagnetic study of the Hárskút and Lókút sections

Abstract

A high-resolution stratigraphic calibration is presented using biostratigraphic (calpionellids, calcareous dinoflagellates, calcareous nannofossils), magnetostratigraphic and chemostratigraphic (delta 13C, Al) techniques on the uppermost Jurassic-lowermost Cretaceous sedimentary successions from Harskut and Lokut in the Bakony Mountains (Transdanubian Range, Hungary). These localities are characterized by noticeably distinct facies developments, despite their geographic proximity. Relatively condensed deposits of early Tithonian-early Valanginian age (ca. 15 m thick; M22r-M13r magnetozones) in the Harskut succession revealed stratigraphic discontinuities; however, our methodology allowed us to identify hiatuses and condensation levels within the magnetostratigraphic record. The Tithonian-Berriasian boundary, marked by the base of the Alpina calpionellid Subzone, falls in the M19n magnetozone, below the base of the NC0 calcareous nannofossil Zone. In turn, the Berriasian-Valanginian boundary, marked by the base of the Calpionellites darderi calpionellid Subzone, is located in magnetozone M14r, below the base of the NC3 nannofossil Zone. A continuous record of Maiolica-type lower Berriasian limestone is exposed in the Lokut succession, between magnetozones M21r-M17n. A consistently decreasing lithogenic influx throughout the Tithonian-lower Berriasian is correlated with a Tithonian trend of climate aridization, while elevated upper Berriasian influxes primarily correspond to tectonic activity within the Neotethyan Collision Belt. The demise of the Saccocoma microfacies and the timing of Nannofossil Calcification Events are interpreted as both mutually related to paleoceanographic changes.