STRATIGRAPHY MIDDLE JURASSIC PROFILES IN THE VICINITY OF GYENESPUSZTA To explore the Middle Jurassic sediments available (Text-fig. 2), the staff of the Hungarian Geological Institute carried out diggings on six sites in the vicinity of Gyenespuszta farmstead, northern Bakony Mountains, Hungary (Text-fig. 1). Each profile thus exposed comprises a different rock sequence of different facies and with a different fauna. (For the faunal lists and the profiles, see the Hungarian text.) Profile I The Dachstein Limestone is overlain with a hiatus spanning the entire Middle and Upper Liassic and the Lower Dogger, by red nodular limestone beds (Text-fig. 3), with a fauna characteristic of the Upper Bajocian Parkinsonia parkinsoni Zone. Profile II At the base of the profile (Text-fig. 4) the footwall is represented by lowermost Liassic limestones of Dachstein type that are followed by a thin manganiferous layer with ammonites characteristic of the Toarcian Hildaites serpentinum Zone. This is overlain by the Middle Jurassic ammonitico rosso limestone in which the Middle Bathonian Tulites subcontractus Zone and the Upper Bathonian Prohecticoceras retrocostatus Zone could be identified. The hanging-wall is represented by radio- larites. Profiles III and IV The two profiles have exposed a Middle Jurassic rock suit of similar litho- and biofacies, differing from the other Gyenespuszta profiles. The abundance of Bositra is conspicuous. Both lithology and fauna suggest the presence in Profile III of sediments deposited in a submarine fissure (Q fissure, see W e n d t 1971). Both profiles contain a fauna belonging to the Parkinsoni Zone. Profile V The rock types in this profile (Text-fig. 5) agree with those of the other Gyenespuszta sections, but neither the Toarcian ferromanganese limestone rags, nor the about 1 m of Middle Jurassic red limestone have yielded any macrofauna. Profile VI Most complete of all the Middle Jurassic profiles at Gyenespuszta, the rock sequence (Text-fig. 6) begins, here too, with the lowermost Liassic Dachstein-type limestone. On the rough, subsoluted surface of this limestone there are heavily manganized limestone rags about a few cm thick, of which a rich and well-preserved Toarcian fauna has been recovered. This formation corresponds to the manganiferous bed of Profile II. The rough surface is overlain, with a considerable break in sedimentation, by ammonitico rosso limestones, forming a 420-cm-thick suit, with a total of 21 beds identified. The three basal red lime- 24 stone beds have yielded no ammonite. The 18 beds above them, however, abound with them, so that a relatively complete stratigraphic sequence from the Bajoeian Stephanoceras humphriesianum Zone up to the Upper Bathonian Prohecticoceras retrocostatum Zone could be identified. The Middle Jurassic limestone sequence is heavily condensed; not all the zones are identifiable, the subzones being so just in exceptional cases. Since the detailed Middle Jurassic stratigraphy of the study area has been based on the rich ammonite fauna from Profile VI, the stratigraphic implications of this section are set forth in the following, stratigraphic, chapter. STRATIGRAPHIC SUBDIVISION As shown by the ammonite fauna from the Gyenespuszta profiles, the Bajoeian and the Bathonian are the only Middle Jurassic stages available in limestone facies in the study area. The upper part of the Bajoeian can be shown to occur from the Humphriesianum Zone to the Parkinsoni Zone, the Bathonian from the Zigzag Zone to the Retrocostatum Zone. Curiously enough, Gyenespuszta has so far been the only locality throughout the Transdanubian Central Mountains range, where Bathonian ammonites have been recovered, while elsewhere this stage is already represented by radiolarites. On the other hand, as a result of faunal samplings carried out at several points within the Bakony, the Humphriesianum Zone can be uniformly elaborated. For this reason, the relevant fauna has been omitted from the present monograph. The most complete stratigraphic sequence and the richest fauna have been yielded by Profile VI. The relevant major stratigraphic and faunistic results were presented in a preliminary report (Galácz 1970). The full faunal lists are given, zone by zone, in the Hungarian text. The information presented hereinafter being restricted to the essential stratigraphic data. Upper Bajoeian Subfurcatum and Garantiana Zones Beds 17 and 16 of the section can be assigned to the Subfurcatum and Garantiana Zones. The rich and diversified fauna has come almost entirely from Bed 16. Judging by the fauna, both the Subfurcatum and Garantiana Zones are represented in this heavily condensed layer not more than 30 cm thick. Unfortunately, the bed could not be further subdivided during samplings, so that the exact stratigraphic position of the individual species recovered could not be cleared. Of the faunal elements, Caumontisphincte.s polygyralis, Leptosphinctes (L .) davidsoni and L. (Gleistosphinctes) cleistus indicate the middle, Polygyralis Subzone, while Garantiana baculata and Spiroceras baculatum refer to the upper, Baculata Subzone within the Subfurcatum Zone (cf. P a v ia 1972, P arsons 1976). Bed 17, which has yielded much fewer evaluable ammonites, can be certainly assigned, again, to the middle subzone of the Subfurcatum Zone, as the Stephanoceras and Teloceras species characteristic of the lower Banksi Subzone are not represented. In Bed 16, the characteristic elements of the Subfurcatum Zone are accompanied by Hlawiceras, some Spiroceras and Bigotites species, all representative of the Garantiana Zone. Hlawiceras refers to the middle, Trauthi Subzone, Bigotites to the upper, Tetragona Subzone (cf. P a v ia 1972). Parkinsoni Zone Beds 15, 14 and 13 of Profile VI can be assigned to the uppermost zone of the Bajoeian. The three subzones of the zone could not be exactly identified. The ammonite assemblage of Bed 15, especially the numerous Vermisphincies species as well as the representatives of Parkinsonia, suggests the presence of the middle part of the Parkinsoni Zone. That the lower, Acris Subzone may also be included, in a condensed form though, is not unlikely, however. Bed 14 has yielded a fauna poorer and less characteristic compared to that of the preceding one, standing closer rather to the top of the Parkinsoni Zone. Phylloceras kunthi and Ptychophylloceras triplicatum n. sp. forms more frequent in Bed 13, appear here. Bed 13 appears to correspond to the Bomfordi Subzone, the frequency of the Dimorphinites species, fii’st of all D. dimorphus, being conspicuous. 25 Lower Bathonian Zigzag Zone Unlike the Bajocian, the Bathonian beds of the profile have yielded a meagre ammonite fauna, poor in species. What is certain is that Beds 12 to 9 span the Lower Bathonian Zigzag Zone. Procerites and Zigzagiceras species, suggestive of the middle part of the Zigzag Zone have been recovered from Beds 11 and 10. For lack of diagnostic fossils of the Macrescens Subzone (Bathonian morphoceratids and parkinsoniids) the lower part of the zone cannot be identified, while the upper part is absent. Middle Bathonian Prograeilis Zone By virtue of the occurrence of the characteristic Oxycerites cf. oxus and Suspensites suspensum species, Bed 8 can be assigned to the Prograeilis Zone. Subcontractus Zone Represented by the thickest sequence in Profile IV, the Subcontractus Zone comprises Beds 7 to 2. At its base (Beds 6 — 7) Suspensites suspensum and Subgrossouvria uriniacensis are characteristic, in the higher parts (Beds 5 to 2) Bugiferites and Bullatimorphites species and Prohecticoceras o. ochra- ceum are typ ica l. Morrisi Zone The Morrisi Zone could not be identified, owing to the absence of zonal indices. Upper Bathonian Retrocostatum Zone The topmost layer, Bed 1, of Profile VI. has yielded a representative fauna undoubtedly indicative of the basal part of the Retrocostatum Zone with characteristic Procerites and Choffatia species ( = “ large perisphinctid fauna” , see T o r r e n s 1967). BIOSTRATIGRAPHIC CORRELATION The six profiles explored in the vicinity of Gyenespuszta are readily correlable both faunistically and lithologically (Text-fig. 7). The Middle Jurassic sediments rest, in all sections, with a marked hiatus, on the rough surface of the Dachstein-type limestone. In Profiles II, V and VI, subsolution residues of an episodical Toarcian sedimentation can be found between the two formations. The deposition of the overlying radiolarites in the study area must have started in the higher part of the Upper Bathonian Retrocostatum Zone. 26 PALEONTOLOGY GENERAL CHARACTERISTICS OF THE AMMONITE FAUNA The fauna of the Middle Jurassic at Gyenespuszta corresponds to that of the red nodular lime­ stones typical throughout the Tethys, so that it contains hardly any macrofossils other than ammo­ nites. Just a few belemnite rostra, pseudoplanktonic Inoceramus and nautiloids have come to daylight. And the very subdued benthonic fauna is represented by one or two gastropods of Pleurotomaria type, a couple of brachiopods and irregular echinoids. Profile VI was most suitable for a quantitative evaluation of the ammonite fauna, as here the fossils were sampled layer by layer and the sampled surfaces were precisely recorded. The surface area sampled in the upper part of the profile was 5 m2, in the lower part — 2.8 m2. The quantitative analytical results obtained for more than 4,000 ammonites were reported in an earlier paper (Galácjz 1970), so that only some essential data need to be presented here. The quantitative predominance of phylloceratids and lytoceratids is a typical Tethyan feature (Text-fig. 8). Proceeding towards the overlying radiolarites, the fauna tends to get impoverished by and large ; on the other hand, the ratio of the Ammonitina decreases, too. Similar tendency is manifested in other Bakony Mountains ammonite faunas as well (K onda 1970, G éczy 1971). The variation of the generic and specific diversity of the ammonite fauna has been evaluated (Text-fig. 9). According to the results obtained by E ürsich and Sy k e s (1977) for Oxfordian ammonites, the Tethyan ammonite faunas are characterized by a generic diversity higher than 10.