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  • Author or Editor: Barnabás Géczy x
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In the Gerecse Mts, Jurassic successions built of sedimentary rocks characteristic of the peri-Mediterranean region are found. The lower part of the Toarcian stage, largely representing the "Ammonitico Rosso marl" facies, contains very diverse and abundant ammonite faunas. Bed-by-bed sampling of four sections carried out during the late seventies and early eighties of the last century has resulted in the collection of more than 15 000 specimens, the bulk of them belonging to the orders Phylloceratina and Lytoceratina. Due to the presence of very rare index forms of the suborder Ammonitina, the successions could be fitted into the zonal scheme established for the NW European Toarcian. The aim of the present paper is to provide information on the stratigraphic distribution of Ammonitina in the Bifrons and Gradata Zones as well as to present a subzonal subdivision of these beds.

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Abstract

In the Jurassic rocks exposed in a small abandoned quarry on the northwestern edge of Nagy-Pisznice Hill in the Gerecse Mts, fairly well preserved parts of a crocodile skeleton was found in 1996. The bed which yielded the skeletal remains is the uppermost layer of the Kisgerecse Marl Formation exposed here and was determined as belonging to the Upper Toarcian Grammoceras thouarsense Zone. The beds of the sequence above and below were carefully sampled in the late 1990s, and the encountered ammonites were evaluated biostratigraphically. As a result, the Lower Toarcian Harpoceras serpentinum Zone, the Middle Toarcian Hildoceras bifrons and Merlaites gradatus Zones, and the Upper Toarcian Grammoceras thouarsense and Geczyceras speciosum Zones were identified. Within most of these zones the subzones and even the faunal horizons were successfully recognized. The lowermost beds above the underlying Pliensbachian red limestone did not yield any fossils; thus the lowermost Toarcian Dactylioceras tenuicostatum Zone could not be documented. The highest Toarcian ammonite zones also remained unidentified, because the beds of the Tölgyhát Limestone above were not sampled all the way up. This paper presents the lithostratigraphic and biostratigraphic details of the sequence, and the paleontological descriptions of the most important ammonites.

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