Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 90. (Budapest 1998)

Dulai, A.: Early Jurassic brachiopods from the basal layers of the Pisznice Limestone of Lábatlan (Gerecse Mts, Hungary)

Figure 14 clearly shows that practically all the occurring brachiopod species are known from Sinemurian formations, but there are several species, which are also characteristic elements of the Hettangian faunas. Moreover, Liospiriferina guembeli is known only from the Hettangian. According to ALMÉRAS (1964), "Rhynchonella" triquetra is known from the Pliensbachian, but during the recent, detailed bed-by-bed collections, the range of several species was extended downwards, than it was known earlier. On this basis, the lowest 3.5 m thick section of the Pisznice Limestone was probably deposited during the Late Hettangian and the Early Sinemurian. These results correspond with REZESSY'S (1996) examinations on cyclostratigraphy of the Pisznice Limestone. In his work three sections of the Gerecse Mts (Tölgyhát quarry, Bánya Hill at Tardos and Kálvária Hill at Tata) were correlated via their sedimentary cycles. The results of this study suggest, that Lower Jurassic sedimentation started earliest at the Kálvária Hill, followed at the Tölgyhát quarry, and finally at the Bánya Hill. Recent biostratigraphic study of the Kálvária Hill suggest a Middle Hettangian age of the basal layers of the Kálvária Hill (PÁLFY, pers. comm). So the Late Hettangian - Early Sinemurian age of the basal layers of the Tölgyhát quarry confirms the cyclostratigraphic results. According to REZESSY (1996), the 33.8 meter thick Upper Hettangian - Pliensbachian section of the Tölgyhát quarry represents about 14 million years, so approximately 2.41 meter thick sediment was deposited during one million years. CONCLUSIONS A detailed study of Early Jurassic brachiopod fauna of the eastern Gerecse has been done for the first time. An efficient, bed-by-bed collection yielded a rich fauna (17 species) from the lowermost layers of the Pisznice Limestone at Lábatlan. On the basis of geological and paleontological similarity, the two localities (Tölgyhát quarry and Póckő) are discussed together. The exact stratigraphical position of the Póckő specimens in the collection of the Hungarian Geological Institution is unknown but there are several differences between the old and the new collections (e.g. the absence of L. aspasia and the presence of P. aff. cerasulum in the new collection), hence the material of the Hungarian Geological Institution was presumably collected, at least partly, from higher parts of the section. Thus only a taxonomic revision was made on this material, and only the recently collected material was considered further. The recovery of fossils from the Pisznice Limestone is very difficult, therefore there are lots of undeterminable fragments. However, the determinable specimens indicate a very diverse brachiopod fauna. For example, in layer 3 of Póckő the 10 determinable specimens represent not less than 7 species. It is peculiar in all layers that numerous species are present, but they are represented only by a relatively small number of specimens. Of course there are some exceptions, for example the number of P. aff. cerasulum specimens is remarkable high (24) in layer 4 of Póckő. Regarding the taxonomic composition of the fauna, terebratulids are the predominant group in nearly all layers. The only exception is layer 3 of Póckő, where the ratio of