Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 11. 1983. (Budapest, 1983)

The palaeobiogeographical significance (VÖRÖS 1977, 1980) and some palaeoecology cal aspects (VÖRÖS 1973, 1974) of the fauna have been discussed in earlier papers. STRATIGRAPHY A fortunate quality of the Pliensbachian fauna of the Bakony Mts. is that the brac­hiopods have been collected in almost all localities together with abundant ammonoids. The ammonoid fauna has been investigated and evaluated very thoroughly by GECZY (1971­1976) and this enables us to establish the stratigraphical ranges of our Mediterranean brachiopod species more precisely than ever previously. In Western Europe Jurassic brachiopods have been used for biostratigraphy for a long time. Recently, attempts have been made to correlate Liassic brachiopod and ammo­noid biozones (REVERT 1971, TCHOUMATCHENCO 1972) and correlation between brachio­pod biozones of distant areas (Southern France and Bulgaria) has been carried out as well (REVERT & TCHOUMATCHENCO 1973). However, only a few Western European species occur in the Mediterranean province, therefore the brachiopod biostratigraphy must be de­veloped on new basis here. There is an old Italian term "Zona a Terebratula Aspasia " suggesting that brachiopods can well be used for biostratigraphy in the Mediterranean areas. At present, however, this term is proved to be inadequate since " aspasia " has an extraordinarily long stratigraphical range: Sinemurian - Pliensbachian - Lower Toarcian. Unfortunately, in the classical localities (in the Alps and in Italy) there are no detailed bed-by-bed collections and generally the "ammonoid control" is missing too. Therefore, with its favourable conditions, the Bakony Mts. seems to be suitable as a starting point. In a further step, the results obtained here must be confirmed in other localities of the Mediterranean province. The stratigraphical ranges of Pliensbachian brachiopods known from the Bakony Mts. ar;j shown in Table I. The substage and zonal scheme in the heading is that applied by GECZY (1971a) for the Pliensbachian of the Bakony Mts. It can be seen that a lot of Pliensbachian species (25) appeared in the Sinemurian while only Linguithyris aspasia went up to the Toarcian. Otherwise, the Toarcian is practically 1 sterile for brachiopods in the Bakony Mts; the impoverishment of the fauna begins already in the Spinatum Zone. It is worth to mention that there are only 6 species in common between the 83 discussed by REVERT & TCHOUMATCHENCO (1973) and the 101 listed in the present paper. These 6 have almost the same range but Homoeorhynchia acuta , Gibbirhynchia ? orsinii and Spiriferina alpin a appear a little earlier in the Mediterranean fauna than in the NW-Euro­pean province. Looking through Table I it would seem that many brachiopod species are excellent biostratigraphical markers since their ranges are restricted to a single ammonoid zone. Unfortunately this is only an illusion. Namely, the majority of these species are repre­sented by only one or a few specimens occurring in a single bed of one section, there­fore they remain useless stratigraphically until they are found at further localities. Reg­rettably, the most frequent species with great specimen numbers have rather long ranges. To obtain a clearer picture, Fig. 4 shows the ranges of 24 species, regarded as really important stratigraphically, in order of their appearance. These species have rela­tively short ranges and they occur in several localities with numerous specimens. It is clearly seen from Fig. 4 that - as it has always been known - the biostratigraphical role of brachiopods is less than that of the ammonoids. Nevertheless, an attempt can be ma­de to develop a brachiopod "para-stratigraphy". Very sharp faunal changes or complete turnover of species cannot be seen either in Table I or in Fig. 4. But on the basis of the numbers of appearances vs. disappearances at ammonoid zone boundaries, three brachiopod zones can be outlined. 1. Cuneirhynchia ? palmata zone . Characteristic taxa (beside the name-species) are Septocrurella ? uhlig i, Gibbirhynchia ? sordellii and Aulacothyris ? amygdaloides . Extends from the Sinemurian to the Pliensbachian; its probable time-span: Echioceras raricosta- tum Zone + Uptonia jamesoni Zone.

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