Chronostratigraphic overview of the Toarcian (Early Jurassic) ammonite fauna from the Mecsek Mountains (Hungary)

Abstract

: Many localities worldwide yielded rich Toarcian (Early Jurassic) ammonoid faunas whose diversity history enhanced our understanding of global events and their geographic distribution aided paleogeographic and paleoceano-graphic reconstructions. However, major differences remain in the intensity of studies as some areas have received significantly less attention, yet their study would improve regional and global correlations and reconstructions. The Toarcian faunas of the Mecsek Mts (SW Hungary) represented one such knowledge gap that is filled herein on the basis of the large Hetényi Collection and other material, totaling more than 5000 specimens. The Toarcian Ammonitina assemblages are outlined, documenting the occurrence of 43 species, of which 14 stratigraphically important species are described systematically. The studied assemblages bear a close affinity to the NW European faunal province, hence the standard ammonite chronostratigraphic scale is conveniently applicable for subdividing the Toarcian sequence of the Mecsek Mts. All of the Toarcian zones and most subzones are documented by their index taxa and the ranges established from NW European localities allow chronostratigraphic assignment of the ammonite-bearing localities in the Mecsek Mts. A comparison with other coeval faunas from the widespread spotted marl facies reveals that taxon richness here is comparable with that recorded from other parts of the Tisza Mega-Unit in the Apuşeni Mts and the Eastern Carpathians in Romania. Temporal patterns of diversity changes, with peaks in the Bifrons and Thouarsense zones, may be interpreted in the framework of biotic changes in the aftermath of the Jenkyns Event.