Towards an ammonite subzonation of the Toarcian in Bulgaria

• Autorzy: Metodiev L.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland)
• Języki publikacji: EN

Abstrakty

EN

A scheme of 9 ammonite zones and 16 subzones for the Toarcian of the Balkan Mts. is given. It is an amplification of the standard put forward by Sapunov (1968) for the Toarcian in Bulgaria. The subzones and some zones are newly proposed. They are still in working phase and need refinement. This zonal (subzonal) set is enhanced by range chart of the ammonite genera found in Bulgaria and juxtaposed to the scheme of Elmi et al. (1997) (Fig. 1). Tenuicostatum Zone (Crosbeyi and Semicelatum subzones). The zone corresponds to the range of Dactylioceras (Orthodactylites). Protogrammoceras and Tiltoniceras are also available. The subzones are defined by the ranges of D. (O.) clevelandicum and D. (O.) crosbeyi as well as D. (O.) tenuicostatum and D. (O.) semicelatum. Falciferum Zone (Serpentinum and Falciferum subzones). The zone embraces the ranges of Harpoceras and Hildaites. The former were recently found to come out upwards outside the zone. The ranges of H. serpentinum and Hildaites define the Serpentinum Subzone. The advent of the zonal index and the mass-incoming of Hildoceras fix the Falciferum Subzone. Bifrons Zone (Lusitanicum, Bifrons and Semipolitum subzones). The subzones accepted herein are based on the successive ranges of the species of Hildoceras. Associates of Dactylioceratidae are also present, though too sporadically. Haugia and Phymatoceras arise at the top of the zone, which ends at the last occurrence of Hildoceras. Variabilis Zone. The zone was formerly placed in the Lower Toarcian, while here it is laid in the Upper Toarcian. The zone comprises the latest Dactylioceratidae, Chartronia and Denckmannia. It is limited at the top by the advent of Pseudogrammoceras and Podagrosites. Haugia ammonites are rare and of less biostratigraphical value than in NW Europe. Two subzones could be used: Collina spp. and Chartronia- Denckmannia spp. Thouarsense Zone (Bingmanni, Thouarsense and Fascigerum subzones). The zone as here understood is narrower than in the older scheme. It is defined in terms of its subzones, being composed of species of Pseudogrammoceras, Grammoceras and Esericeras. The top is taken at the extinction of Grammoceras and Esericeras. Fallaciosum Zone. Owing to the particular abundance of its index, it is used as separate zone. The extinction of Pseudogrammoceras and Podagrosites and the advent of Phlyseogrammoceras and Pseudolillia trace the upper limit. Dispansum Zone. No authentic record caused it wasn’t be into the standard. It is now clearly discernible by species of Phlyseogrammoceras, Hammatoceras, Hudlestonia and Pseudolillia. Pseudoradiosa Zone (Levesquei and Pseudoradiosa subzones). It is instead of the older Levesquei and Moorei zones as being framed throughout by finely ribbed Dumortieria. These are ruling in the Pseudoradiosa Subzone. Coarsely ribbed species are dominant in the Levesquei Subzone. Aalensis Zone (Mactra and Aalensis subzones). A succession of finely ribbed and more evolute Pleydellia and P. (Cotteswoldia) (Mactra Subzone) followed by P. (Walkericeras) and finely ribbed but less evolute Pleydellia (Aalensis Subzone) defines the zone. First Pseudammatoceras, Bredyia and Czernyeiceras appear at the top.

Słowa kluczowe

EN

Toarcian; ammonite zones; subzones; Bulgaria

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 186--188
• Opis fizyczny: Bibliogr. 2 poz.

Twórcy

autor

Metodiev L.

• Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. Bl. 24, 1113 Sofia, Bulgaria,

Bibliografia

• Elmi S., Rulleau L., Gabilly J. and Mouterde R. 1997. Toarcien. In: Cariou E. and Hantzpergue P. (Eds), Groupe Francais d’etude du Jurassique. Biostratigraphie du Jurassique ouest-europeen et mediterraneen: zonations parall?les et distribution des invertebres et microfossiles. Bulletin Centre Rechearches Elf Exploration et Productions, 17: 25-36.
• Sapunov I. 1968. The ammonite zones of the Toarcian in Bulgaria. Bulletin of the Geological Institute, BAS, Series Paleontology, 17: 133-165, in Bulgarian with English summary.