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)

A characteristic feature at both localities, that the proportion of sparry calcite is either 0% or 100% at the majority of the specimens, i.e. these brachiopods are infilled entirely by micritic lime mud or entirely by coarse-grained sparry calcite. Sparitic infilling is between 10% and 90% only at a few specimens, i.e. these brachiopods are only partially infilled by sparry calcite. Size distribution of brachiopods The mean maximum size of brachiopods found in different layers was calculated (Fig. 11). The mean size is 8.4 mm in layer 1 and 10.1 mm in layer 2 of the Tölgyhát quarry, i.e. the mean size is larger at the higher part of the section. The specimens of Calcirhynchia plicatissima and Cuneirhynchia cartieri show sizes around the mean values. The specimens of the genera Zeilleria and Liospiriferina are larger, while the specimens of Phymatothyris aff. cerasulum and the undeterminable specimens of Terebratulida are smaller than the mean size of the locality. The mean size of the specimens is 8.1 mm in layer 1, 9.3 mm in layer 2, 10.4 mm in layer 3 and 8.4 mm in layer 4 of Póckő. The mean size for the whole this locality is 8.5 mm. The mean size is also gradually increasing here at the higher part of the section with the exception of layer 4, where the size is smaller again. This fact is related to the very high number of the small-sized species (P. aff cerasulum, "Rhynchonella" triquetra, Terebratulida indet.). From the most frequent taxa, such as C. plicatissima and P. aff. cerasulum, both small-sized juvenile and large-sized adult specimens can be found (see Figs 15-17). COMPARISON WITH THE EARLY JURASSIC FAUNA OF VÖRÖSHÍD QUARRY (TARDOS, GERECSE MTS) The brachiopods of several important Lower Jurassic sections from the Transdanubian Central Range were studied bed-by-bed during the last years (Lókút Hill; Som Hill, Marko in the Bakony Mts and Vöröshíd quarry, Tardos in the Gerecse Mts). Unfortunately determinable ammonites are missing from the basal layers of these sections, and the age of these sections were only constrained by ammonites from the younger layers. In the present case the comparison with the Vöröshíd quarry (see the location of this locality on Fig. 1) will give the most useful informations. The results of the study of the Vöröshíd quarry is not published yet, because the fauna of some additional layers need to be collected. However, the examination of the collected fauna has already been done, therefore a comparison between the Vöröshíd quarry and the Lábatlan localities is possible. An approximately 14 m thick section was collected bed-by-bed above the unconformity between the Triassic and Jurassic formations in the Vöröshíd quarry. This section can be divided into two parts based on the lithology and the distribution of the brachiopods. There is 8 m of thick-bedded, reddish, slightly crinoidal limestone at the bottom of the Jurassic sequence. The lower 5 m of this limestone is shown on Fig. 12. Higher up a thinner-bedded, brownish-grey, micritic limestone can be found. Determinable am-