Stratigraphic and micromineralogic investigations on Cretaceous Formations of the Gerecse Mountains, Hungary and their palaeogeographic implications

Abstract

Lower to Middle Cretaceous clastic successions are known from the Gerecse Mountains within the Pelso unit in Hungary. As a result of studies during the past decade the model for the formation of the late Mesozoic geological history of the Gerecse Mountains has changed fundamentally. This paper summarizes new data and conclusions as follows. Recognition of spatial and temporal changes in lithology renders the succession divisible into realistic lithostratigraphic units (five formations) reflecting flysch, hemipelagic and platform sedimentary environments. A breccia event (Felsôvadâcs Bveccia Member) is verified to cut a facies boundary between pelagic limestone in the western Gerecse and basinal fine-grained clastics in the eastern Gerecse in the Berriasian. Sedimentation must have taken place in deep water—slope and basinal—conditions in the East Gerecse from the Berriasian and outer shelf conditions in the West Gerecse from the Barremian, at least until the Middle Albian. In the Hauterivian in the West Gerecse, a gap increasing westwards is documented. Rubble of Urgonian limestone testifies to the existence of platform carbonate deposition along the margins of the obducted island arc. Facies and stratigraphic data document a sedimentary basin in the Gerecse Mountains that was the starting point of the Middle Cretaceous sedimentary cycle of the Vértes and Bakony area. In heavy mineral assemblages the predominant chrome spinels suggest an ophiolitic source area to the north. As a part of the Transdanubian Central Range Gerecse was also part of a palaeogeographic unit, elements of which (the Northern Calcareous Alps and the Southern Alps) were united by the Vardar suture zone. This situation lasted until the Albian.