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)

ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Volume 90. Budapest, 1998 pp. 35-55. Early Jurassic brachiopods from the basal layers of the Pisznice Limestone of Lábatlan (Gerecse Mts, Hungary) A. DULAI Department of Geology and Paleontology Hungarian Natural History Museum H-1431 Budapest, P. O. Box 137, Hungary DULAI, A. (1998): Early Jurassic brachiopods from the basal layers of the Pisznice Limestone of Lábatlan (Gerecse Mts., Hungary). - Annls hist.-nat. Mus. natn. hung. 90: 35-55. Abstract - This is the first detailed (taxonomical, taphonomical, paleoecological, stratigraphical) study of the Early Jurassic brachiopods of the eastern Gerecse Mts. A rich, Mediterranean-type Early Liassic (probably Late Hettangian-Early Sinemurian) brachiopod fauna was collected bedby-bed from the Tölgyhát quarry and a section at Póckő. The lowest 3.5 m of the Pisznice Limestone yielded 17 species of rhynchonellids, spiriferids and tcrebratulids. Four additional brachiopod species were found in the collection of the Hungarian Geological Institution from Póckő. The geological setting of these localities (significant distance from seamounts, basin-type sedimentation) and the low ratio of disarticulated valves suggest that the brachiopods were not transported from a seamount. Therefore the brachiopod fauna of these layers represents the composition of an Early Jurassic moderate to deep-water community. On the basis of the stratigraphie distribution of the brachiopod species, the examined layers at Tölgyhát and Póckő, can probably be correlated with the lower, thick-bedded part of the Jurassic section of Vöröshíd quarry near Tardos. With 17 figures. INTRODUCTION The Gerecse Mts are situated at the northeastern part of the Transdanubian Central Range. The southern part of the mountains are underlain by exclusively Triassic formations. Younger Mesozoic (Jurassic and Cretaceous) rocks are exposed only at the northern part of the area (VÉGH-NEUBRANDT 1960). The Lofer-cycles of the Upper Triassic Dachstein Limestone are well-correlated along great distances (HAAS 1988). On the other hand, the Lower Jurassic formations, which unconformably overlie the Triassic limestone, show much greater variability which suggests that the uniform carbonate platform, evolved at the end of the Triassic, started to subside differentially during the Early Jurassic. Various blocks subsided at different rates, leading to the development of relatively emerged seamounts and intervening basins (GALÁCZ & VÖRÖS 1972, VÖRÖS & GALÁCZ 1998). The tectonic collapse of the platform probably started already during the Hettangian in the Bakony Mts (DULAI 1993«). On the basis of facies differences among and within the Jurassic formations, the