Integrated calcareous nannofossil and ammonite data from the upper Barremian–lower Albian of the northeastern Transdanubian Range (central Hungary): Stratigraphical implications and consequences for dating tectonic events

Abstract

The transition of post-obduction Neotethyan contraction to Eo-Alpine ("Austroalpine") nappe stacking that took place during the Early Cretaceous is an important event in the Cretaceous history of the Alpine-Carpathian-Dinaridic orogenic system. The Transdanubian Range (TR) in Hungary has been shown to have been impacted by both events. Dating of this transition has proved to be difficult; several interpretations were published during the last decades. Uniquely exposed in and around the Gerecse Mountains, the L abatlan Sandstone Formation (LSF) and the V ertessoml o Aleurolite Formation (VAF) bracket this time interval. The last phase of Neotethyan contraction occurred after the deposition of the LSF, and the Eo-Alpine nappe stacking started during the deposition of the VAF. Earlier stratigraphical studies provided valuable data for our understanding of geodynamics, but precise bio-and chronostratigraphy e to constrain the interval of deformations e became possible only with systematic correlation of macrofossil-poor outcrops to ammonite-rich series with the help of calcareous nannofossil data. Here new nannofossil data, and whenever still available, a re-examination of the original smear slides yields new constraints on the age of the younger part of the sequence. The nannofossil and ammonite record is now combined to create a local chronostratigraphical correlation, with records tied in to the integrated Tethyan nannofossil and ammonite biozonation, which, in turn, is numerically calibrated by international zonal standards and radiometric ages. Our study demonstrates that the youngest part of the sandstone-dominated LSF is in nannozone NC7B of late Aptian age. The overlying K€ osz€ or} uk} ob anya Conglomerate Member has a closely similar age in NC7A/B, noticeably older than previously suggested. On the other hand, the VAF clearly is of early Albian age (NC8). This latter unit is not represented in the inner Gerecse Mountains, in contrast to what has been suggested in previous studies. The observed earlier two sub-phases of Neotethyan compression with NeS to ENEeWSW shortening possibly are latest Aptian in age and are within nannofossil subzone NC7C, while the following Eo-Alpine deformation has an early Albian age (NC8) and is marked by WeE to NWeSE compression. The Aptian/Albian boundary (around 113 Ma) may indicate the switch of the TR from lower to upper position with respect to Neotethyan subduction to "Austroalpine" nappe stacking. Our data on deformational ages may support the idea that the onset of "Austroalpine" transpressional deformation at c. 114e112 myr ago could be related to the start of Penninic subduction, or, alternatively, to the onset of intra-oceanic subduction within the Austroalpine realm.

Complex deformation history of the Keszthely Hills, Transdanubian Range, Hungary

“…Cretaceous contractional structures show various trends (shortening directions) (Fig. 1b), which is traditionally explained by two or even three phases of folding and thrusting in the TR, well separated in time and in tectonic context (Tari, 1994;Csontos and Vörös, 2004;Csontos et al, 2005;Pocsai and Csontos, 2006;Palotai et al, 2006;Sasvári, 2008Sasvári, , 2009Tari and Horváth, 2010;Fodor et al, 2018;Szives et al, 2018). In contrast, our early results suggested that deviations of fold trends can be explained rather by inheritance of Triassic and Jurassic pre-orogenic normal faults than by multiphase folding (Héja et al, 2016(Héja et al, , 2017(Héja et al, , 2022.…”

“…The Gerecse Hills (NE TR) represent an additional complexity, where even three different sets of folds and characteristic shortening directions seem to be present (Bada et al, 1996;Sasvári, 2008Sasvári, , 2009Fodor et al, 2018), namely folds or thrust with E-W, NE-SW and NW-SE strikes. Recently Fodor et al (2018) and Szives et al (2018) arranged the folding in a successive deformation story, and gave time constraints for two of them.…”

Integrated stratigraphy of the Upper Barremian–Aptian sediments from the south-eastern Crimea

“…Tethyan late Barremian-Aptian standard stratigraphy and PF zonations of different authors. Correlation of ammonite and nannofossil zonations after Aguado et al 1999;Szives et al 2018 heating, magnetite becomes the only magnetic mineral left . The effect of Fe hydroxides, such as hydrogoethite (peak around 100-150 ºC on the second derivative), on thermomagnetic curves is negligible .…”

Kora-Kréta (Albai) Őskörnyezeti Rekonstrukció Dunántúli-Középhegységi Rétegsorok Sekélytengeri És Édesvízi Kagylósrák Együtteseinek Változásai Alapján

“…A Vértessomlói Aleurolit kora alsó-középső-albai a biosztratigráfiai vizsgálatok alapján (Bodrogi 1993;Császár 1995;Császár 1998;Szinger 2008;Szives 2007;Szives et al 2018). A palinológiai vizsgálatok is ezt a kort támasztják alá (Juhász 1983).…”