Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 21. 2003. (Budapest, 2003)

Early Jurassic Isztimér Limestone, Márkó, Som-hegy — This classical locality, having been first studied by BÖCKH (1874), is situated at the southwestern edge of the Hajag-Papod horst. The investigated 10m thick section (DULAI in prep.) consists predominandy of micritic limestone with crinoidal limestone and chert beds, intercalating (Isztimér Limestone Formation). A significant part of the sequence contains redeposited sediments from the higher areas. The upper part of the section (between layers 23 and 31) most probably belongs to the Asteroceras obtusum Zone (Sinemurian). At the lower part (between layers 2 and 20) the Arterites bucklandi Zone is the most probable age, but the possibility of younger age (Arnioceras semicostatum Zone) cannot be precluded (PÁLFY pers. com.). On the basis of the 800 specimens, 35 brachiopod species were distinguished. In the brachiopod fauna, rhynchonellids are predominant (79%), whereas spiriferinids (12%) and terebratulids (9%) are less frequent at this locality. The genus Rhynchonellina strongly predominates the fauna (65%) and this genus has been identified as a cold-seep related taxon (SANDY 1995b; RUGGIERO TADDEI 1997). The locality is situated at the edge of the horst, where nutrient-rich cold-seeps could have occurred along the synsedimentary tectonic faults (DULAI in prep.) Relatively frequent genera are Liospiriferina (13%) and Zeilleria (7%), but all the other genera are rare (Apringia, Prionorhynchia, Cirpa, Calcirhynchia, Homoeorhynchia, Cuneirhynchia, Pisirhynchia, Gibbirlynchia, Dispiriferina, Lobothyris, Unguithyris, Phymatothyris, S ecutin a, Antiptychina) (Figure 3). brachiopods Bakony Mountains 45 Figure 3 — Generic composition of the brachiopod faunas at the Early Sinemurian localities of the Bakony Mts. Pisznice Limestone, Gerecse Mountains Figure 4 — Generic composition of the Early Sinemurian brachiopod faunas, Gerecse Mts. Lábatlan, Tölgyhát quarry — The Pisznice Limestone rests unconformably on the Dachstein Limestone at this locality. Nine brachiopod species were collected from the 3.5 m thick section of the thick-bedded Pisznice Limestone Formation (DULAI 1998a, b). The small brachiopod fauna is rather diverse, but no ammonites were found. This and the next three localities (Póckő, Kisgerecse, Vöröshíd quarry) are situated in the Pisznice Basin of the Gerecse Mts (VÖRÖS & GALÁCZ 1998, Figure 5). Among the identified brachiopods, terebratulids and rhynchonellids prevail the fauna (46% of both), whereas spiriferinids are less significant (8%). Relatively few genera are present in the fauna: Cakirhynchia (31%), Zélleria (26%), Plymatotlyris (20%), Cuneirfynchia (15%), Liospiriferina (8%) (Figure 4). Lábatlan, Póckő— This locality is situated near the Tölgyhát quarry. Brachiopods were also collected from the lowest 3.5 m of the Pisznice Limestone (21 species) (DULAI 1998a, b). No ammonites were found at this locality. The ratio of brachiopod orders is nearly the same as at Tölgyhát quarry: terebratulids and rhynchonellids are prevailing the fauna (44% of both), whereas spiriferinids and adiyridids are less common (6-6%). Among the brachiopod genera, Phymatothyris is the most frequent (33%) but Calcirhynchia (18%) and Cuneirhynchia (10%) are also common. All the other taxa are rare in the fauna (prionorhynchia, Cirpa, Salgirella, Liospiriferina, Koninckodonta, Lobothyris, Unguithyris, Zeilleria, Bakonyithyris) (Figure 4).