The Toarcian ammonite stratigraphy of the so-called ‘Crocodile’ section on the Nagy-Pisznice Hill in the Gerecse Mountains (North-west Hungary)

Abstract

In the Jurassic rocks exposed in an abandoned small quarry on the north-western edge of the Nagy-Pisznice Hill of
the Gerecse Mts, rather well-preserverd parts of a crocodile skeleton were found in 1996. The age of the bed which yielded
the exceptional skeletal remains was determined as belonging to the Upper Toarcian Grammoceras thouarsense Zone.
This particular bed is the uppermost layer of the exposed Kisgerecse Marl Formation. The beds of the sequence were
carefully collected in the late 1990s, and the 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 recognized. Within most of these
zones the subzones and even the faunal horizons were successfully identified. The lowermost beds above the underlying
Pliensbachian red limestone did not yield faunal elements which would have enabled the tracing of the lowermost
Toarcian Dactylioceras tenuicostatum Zone. The highest Toarcian ammonite zones also remained unidentified, because
the beds of the Tölgyhát Limestone above were not collected all the way up the sequence. This paper gives a detailed
description of the litho- and biostratigraphy of the sequence, while the palaeontological descriptions will be presented in
another publication.