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)

rhynchonellids is about 75%. Spiriferids are entirely missing or play an insignificant role in the fauna. The ratio of disarticulated valves is very low at the lowermost layers of both localities, but this ratio gradually increases in the higher layers of the sections. This increase is more significant at the Tölgyhát quarry, while less important at Póckő. The ratio of the sparitic infilling of brachiopods is the highest in the lowest layers at both localities (more than 50%) and it decreases at the upper part of the sections. The average size of brachiopods is smaller in the lower layers, and higher in the upper layers. The only exception is layer 4 of Póckő, where the size decreases again. This is related to the very high number of P. aff. cerasulum, which is a very small-sized species. The geological setting of the examined localities (significant distance from seamounts, basin-type sedimentation) as well as the low ratio of disarticulated valves (especially in the lowest layers) indicate that transportation of brachiopods from a distant seamount is not very probable. Therefore the brachiopod fauna of these layers may represent the composition of an Early Jurassic deeper-water community (in contrast to the sections of Lókút Hill and Vöröshíd quarry, which are in a basin-margin position and contain several redeposited specimens from the nearby seamounts). The size distribution of the most frequent species (Calcirhynchia plicatissima and Phymatothyris aff. cerasulum, Figs 15— 17) confirms this statement because they have both juvenile and adult specimens. If transportation occurs, the specimens are usually sorted according to their sizes. In the absence of ammonoids, the age of this formation can be determined on the basis of the distribution of brachiopod species. Nearly all the occurring brachiopod species are known from the Sinemurian, but several species are also frequent in the Hettangian faunas. Therefore the lowest 3.5 m thick section of the Pisznice Limestone at Lábatlan was probably deposited during the Upper Hettangian and the Lower Sinemurian. These results agree with REZESSY'S (1996) conclusions based on cyclostratigraphy of the Pisznice Limestone. Regarding the distribution of brachiopod species at the Lábatlan localities and at the Vöröshíd quarry, the examined Lábatlan sections can probably be correlated with the lower, thick-bedded part of the Vöröshíd quarry. Of course, in the absence of ammonoids in both area, the correlation is slightly uncertain. There is no doubt about the Mediterranean character of the examined fauna. Of the six characteristic Mediterranean Sinemurian taxa, listed by VÖRÖS (1980, 1997) three are present at the Lábatlan localities (Linguithyris aspasia, Zeilleria venusta, Cuneirhynchia cartieri). PALEONTOLOGICAL NOTES Cirpa latifrons (STUR in GEYER) - There is only one specimen in the collection of the Hungarian Geological Institution. This species is known from Sinemurian localities of the Bakony Mts (VÖRÖS 1997). C. latifrons was figured and described in detail from Lókút Hill by DULAI (1992: 43). Cirpa cf. variabilis (SCHLOTHEIM) - Only one fragmentary specimen occurs in the collection of the Hungarian Geological Institution. C. variabilis is known from Sinemurian and Pliensbachian localities of the Transdanubian Central Range (VÖRÖS 1997).