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

FRAGMENTA PALAEONTOLOGICA HUNGARICA 21, BUDAPEST, 2003 Taxonomic composition of Mediterranean Early Jurassic brachiopod faunas from Hungary: niche replacement and depth control by Alfréd DULAI Abstract — Recent bed-by-bed collections at 16 Lower Jurassic localities in the Bakony and Gerecse Mts (Transdanubian Central Range, Hungary) yielded rich brachiopod faunas. The taxonomic composition of the faunas, representing biotopes of different depths and facies, reveals that the evolutionär}' intra-phvlum niche replacement within the Brachiopoda, thought to occur at the Triassic/Jurassic boundary (SANDY 1995a), took place only after the Hettangian in the Mediterranean region. At the Gerecse localities, the distribution of spiriferinids contradicts to what was found by SANDY (1995a): the proportion of spiriferinids increases from the basin towards the submarine horsts. The ratio of the brachiopod orders at the different Hungarian localities suggests that Early Jurassic basins in the Bakony Mts were deeper than in the Gerecse Mts. Keywords — Brachiopoda, Early Jurassic, taxonomic composition, niche replacement, depth, Hungary, Mediterranean region DULAÍ, A. (2003): Taxonomic composition of Mediterranean Early Jurassic brachiopod faunas from Hungary: niche replacement and depth control. — Fragmenta Palaeontologica Hungarica, 21: 43—50 Introduction The Transdanubian Central Range provides excellent opportunities to study Early Jurassic brachiopods. During the last decade, new collections have been obtained from 16 localities of the Bakony and the Gerecse Mts (Figure 1). The embedding rocks belonged to the oldest Jurassic formations, which unconformably deposited on the Upper Triassic Dachstein Limestone. With the exception of the localities of the Kardosrét Limestone Formation, that is massive and not stratified, the collections were done bed-by-bed. Stratigraphie results of these studies and some evidences of a rapid diversification of the Mediterranean Early Jurassic brachiopods have already been summarised recendy (DULAI 2001). The aim of this paper is to present the taxonomic composition of these brachiopod faunas and, on the basis of the new data, to discuss the progress of the intra-phylum niche replacement and the depth control proposed by SANDY (1995a). The Transdanubian Central Range is a NE—SW elongate hilly region in western Hungary. The Mesozoic carbonate sequences show facies similarities to the Southern Alps and the Austroalpine units (CSÁSZÁR et al. 1998). The Jurassic palaeogeography of the area has been recendy reconstructed (VÖRÖS & GALÁCZ 1998). They identified five main steps in the palaeogeographic evolution, of which the first two are important for this study. During the Hettangian, carbonate oolitic shoals predominated in the Bakony Mts (Kardosrét Limestone Formation) but, at the same time, neritic limestones (Pisznice Formation Formation) deposited in the Tata depression (VÖRÖS & GALÁCZ 1998; Figure 4). Relatively diverse brachiopod faunas are known from both the shallow and the deeper marine Hettangian environments. <= Figure 1 — Sketch map showing the location of the studied faunas. — a: Bakony Mountains; 1: Bakonybél, Kőris-hegy; 2: Borzavár, Páskom; 3: Kardosrét, Cuha-völgy; 4: Kardosrét, Szesztra-hegy; 5: Olaszfalu, Eperkéshegy; 6: Lókút, Lókúti-domb; 7: fíplény, Kávás-hegy; 8: Márkó, Som-hegy; 9: Herend, Alsóhajag; 10: Szentgál, Tűzköves-hegy; 11: Városlőd, Csalánosvölgy; b: Gerecse Mountains; 12: Tata, Kálvária-domb; 13: Lábatlan, Tölgyhát quarr)*; 14: Lábatlan, Póckő; 15: Tardos, Kisgerecse; 16: Tardos, Vöröshíd quarry).