The tectono-sedimentological interpretation of the albian–cenomanian basin evolution of the Northern Bakony, Hungary

Abstract

The goal of the present work is to demonstrate the relationship between the structural development and the depositional environment of the Gajavölgy Member of the Zirc Limestone Fm, and the Villóhegy, and Nána Beds of the Pénzeskút Marl Fm. On the basis of drill-core and quarry descriptions I plotted the thickness maps of the Gajavölgy Member and the Villóhegy and Nána Beds. I also mapped two local hiatuses, bordering the base and the top of the Gajavölgy Member. Based on these results, I found a few evidence for the syn-sedimentary (N)NW–(S)SE compression, which is coincident with the structural data of KISS (2009).
The Gajavölgy Member, which was formed in toe-of-slope environment, has a basin-ward (NNW) decreasing thickness. This direction could be the trend of the progradation as well. Therefore the hiatus at the base of the member can be considered as a downlap surface. The resedimented Triassic extraclasts of the Gajavölgy Member derive form the southern limb of the Transdanubian syncline. These fact show the uplift of the southern limb of the Transdanubian syncline, caused by reactivation of the Early Cretaceous thrusts (e.g. Litér thrust).
During the next transgression, the hemipelagic Pénzeskút Marl was deposited. A gap between the Zirc and Pénzeskút Fm was developed in the NNW part of the basin. This hiatus is located along the deep part of the basin, where continuous transition between the two formations is expected. Therefore the NNW part of the basin, where the hiatus is located, could have been uplifted. I suggest a working model, in which I explain this uplift by the activation of a supposed thrust ramp, whose upper detachment is in the underlying Tés Clay Fm. The related ramp-anticline could be the same, which was mapped on the Hajag Hill by GYALOG & CSÁSZÁR (1982).
The maximal thicknesses of the Villóhegy and Nána Beds are measured in the axis of the basin. These basin-fill sediments reached the maximal thicknesses in a supposed syncline, located between two ramp-anticlines. In this scenario, the Litér thrust would have been reactivated again.