Ammonite stratigraphy of a Toarcian (Lower Jurassic) section on Nagy-Pisznice Hill (Gerecse Mts, Hungary)

Abstract

In the Jurassic rocks exposed in a small abandoned quarry on the northwestern edge of NagyPisznice 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.Key words: Gerecse Mountains, Nagy-Pisznice Hill, Toarcian, Ammonoidea, biostratigraphy IntroductionIn summer of 1996 a minor sensation was created by the announcement that private collectors had unearthed a skeleton of a vertebrate -soon identified as that of a marine crocodile -from the Jurassic beds of the Gerecse Mts. One of the present authors, Géza Császár, then of the Hungarian Geological Institute, Address: A. Galácz, G. Császár, B. Géczy: H-1117 Budapest, Pázmány Péter sétány 1/C, HungaryCorresponding author e-mail: galacz@ludens.elte.hu Z. Kovács: H-1076 Budapest, Liszt Ferenc tér 8, Hungary Received: February 23, 2011; accepted: March 10, 2011 1788-2281/$ 20.00 © 2010 Central European Geology, Vol. 53/4, pp. 311-342 (2010) DOI: 10.1556/CEuGeol.53.2010 Ammonite stratigraphy of a Toarcian (Lower Jurassic) section on Nagy-Pisznice Hill (Gerecse Mts, Hungary)András Galácz Géza Császár Department of Paleontology Department of Regional Geology Eötvös Loránd University, BudapestEötvös Loránd University, Budapest Barnabás Géczy Zoltán Kovács Department of Paleontology Department of Pedagogy Eötvös Loránd University, BudapestLiszt Ferenc University, Budapest realized the importance of the find, and suggested a detailed investigation and bed-by-bed sampling of the sequence immediately above and beneath the skeleton-bearing bed. The initial steps of the sampling work were carried out in November 1997 by Zoltán Sirányi, one of the collectors who discovered the vertebrate remains. In the spring of the following year Attila Fitos, another collector, joined Zoltán Sirányi. Up to the end of the year they collected 21 fossils from the beds. In 1998 Z. Sirányi collected ammonites from a fur...

A new large-bodied thalattosuchian crocodyliform from the Lower Jurassic (Toarcian) of Hungary, with further evidence of the mosaic acquisition of marine adaptations in Metriorhynchoidea

“…The remains of this large-bodied crocodyliform came from a fossiliferous limestone with a well-constrained stratigraphy ( Galácz et al, 2010 ). These beds also yielded diagnostic ammonites, including Grammoceras thouarsense ( d’Orbigny, 1842–51 ) which is an index fossil of the Upper Toarcian (Lower Jurassic) G. thouarsense ammonite Zone.…”

“…Type horizon —Bed 13, Kisgerecse Marl Formation, Transdanubian Central Range. Grammoceras striatulum ammonite Subzone, G. thouarsense ammonite Zone, Upper Toarcian, Lower Jurassic ( Galácz et al, 2010 ).…”

Hardground, gap and thin black shale: spatial heterogeneity of arrested carbonate sedimentation during the Jenkyns Event (T-OAE) in a Tethyan pelagic Basin (Gerecse Mts, Hungary)

“…A detailed biostratigraphic study at nearby Nagy-Pisznice Hill documented that the upper part of the Kisgerecse Fm. belongs to the Gradatus Zone and the topmost bed of the formation represents the base of the overlying late Toarcian Thouarsense Zone, revealed by the occurrence of zonal index species Merlaites gradatus and Grammoceras thouarsense, respectively (Galácz et al 2010). On top of the Kisgerecse Fm.…”