Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 73. (Budapest 1981)

Vörös, A.: A survey of the Rhaetian (Upper Triassic) Bivalvia from Borzavár (Bakony Mts., Hungary)

ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICÏ Tomus73. Budapest, 1981 p. 33-54. A survey of the Rhaetian (Upper Triassic) Bivalvia from Borzavár (Bakony Mts., Hungary) by A. VÖRÖS, Budapest Abstract — 25 species of Bivalvia are described from Borzavár from marly limestones and coquinas intercalated with the Dachstein limestone formation. The composition of the fauna and the occurrence of Rhaetavicula contorta confirms a Rhaetian age. The probable environment was a back-reef lagoon or a shallow "intraplatform" basin. The fauna strongly resembles that of the Southern Alps. With 1 figure and 2 photoplates. Introduction — The fauna, studied and described here, is originating from the locality "Templomdomb" at the village Borzavár. Here, as generally in the Northern Bakony Mts., the Rhaetian stage is represented by the Dachstein limestone formation. The several hundred metres thick Bahamian-type carbonate sequence contains a relatively thin (10 m) intercalation of well-bedded, sometimes nodular, marly limestones and coquinas very rich in fossils. The fauna of these fossiliferous strata was collected by DR. G. CSÁSZÁR and his coworkers (Hungarian Geological Institute) and was given to the author for palaeontological study. Herewith the opportunity is gratefully acknowledged. The detailed stratigraphy, sedimentology and palaeoecology of the Borzavár section are described in an other article (CSÁSZÁR et al., in press). The present paper concentrates on the systematic description of the bivalves; only a brief summary of the general features of the megafauna is presented below. 434 specimens were collected from 10 beds lying in the upper 5 metres of the Borza vár section. The fauna is exclusively benthonic, consisting of 25 bivalve and 2 gastropod species. The species composition indicates a Rhaetian age which is further confirmed by the occurrence of the species Rhaetavicula contorta (PORTLOCK). The predominance of endobyssate bivalves, found sometimes in life position (e.g. Pinna), suggests a muddy, quiet sea floor. The absence of nektonic and planktonic fossils, and analogies with other European Rhaetian localities lead to the conclusion that the environment was a back-reef lagoon or a shallow intraplatform basin. The bivalve fauna has a Tethyan character, showing affinity with so distant areas as Burma. The faunal similarity is the strongest to the Southern Alps (15 common species) but, surprisingly, also rather marked to Western Europe (e.g. 7 species in common with the British Isles). Systematic descriptions Genus PALAEONUCULA QUENSTEDT, 1930 Palaeonucula subovalis (GOLDFUSS, 1837) (Plate I: 1) *1837: Nucula subovalis GOLDFUSS, Petref. Germ., p. 154, pi. 125, fig. 4. 1861 : Nucula subovalis GOLDF. — STOPPANI, Couches à Avicula

..., p. 61, pi. 7, fig. 21-22. 1866: Nucula subovalis GOLDF.

—CAPELLINI, Infralias. Spezia, p. 61, pl. IV. fig. 18-19. Annls hist.-nat. Mus. natn. hung., 73, 1981 3 Természettudományi Múzeum Évkönyve 1981