FRAGMENTA PALAEONTOLOGICA HUNGARICA 2 1 , BUDAPEST, 2 0 0 3

Palaeocommunity studies on Eocene larger Foraminifera of the Bakony Mountains (Transdanubia, Hungary)

by

Tibor K E C S K E M É T I

Abstract — The paper introduces five Nummulites-pzlaeocommumties which succeeded each other in the seas of the Bakony region during the Early Lutetian to Latest Eocene to Earliest Oligocène time interval. Two of the palaeocommunities are Lutetian, two others are Bartonian and

one is Priabonian. Their reconstruction below is presenting the composition, the dominant population, the density, the diversity and also the

relation of nummulits to the most important other large formainifers. Tracing of the changes in the palaeocommunities received a special respect.

From the factors inducing the changes, those are discussed which are connected to tectonism, global sea-level changes, climate, and water

chemistry (salinity, Sr-content). Formation of the so-called "monospecific" faunas and the possible influence of ontogenetic and phylogenetic

factors, independent from the environment are also discussed.

Key words — Nummulites, Eocene, palaeocommunities, Bakony Mountains, Hungary.

KECSKEMÉTI, T. (2003): Palaeocommunity studies on Eocene larger Foraminifera of the Bakony Mountains (Transdanubia, Hungary). —

Fragmenta Palaeontologica Hungarica, 21: 33-41.

Introduction

In Hungary no palaeocommunity studies have been done so far on larger Foraminifera. Consequently, no home literature was available. The majority of the more and more numerous relevant papers published abroad are dealing with general problems, interrelations, of the evolution and the ecosystems, and investigations on the higher macrobenthos. Few papers have been published on palaeocommunities of benthic and planktonic small fora-minifera. Some of these concern recent faunas ( H l L -TERMANN & TÜXEN 1974; GRÜNIG & HERB 1980;

H lLTERMANN, B R O N N I M A N N & Z A N I N E T T I 1981; H l L -

TERMANN 1982; GRÜNIG & HERB 1984; HOFFMANN &

KlTCHELL 1984; HERB 1988). Beside these, I have found many interesting, mainly ecological data, in papers on reef communities (FRAGERSTROM 1987; COPPER 1988). ROLLINS, C A R O T H E R S & D O N A H U E (1979) published interesting observations concerning succession changes brought about by sea level changes (transgressions, regres-sions).

The two main aims of the studies summarized in the present paper were:

- to define the taxonomic composition of the Nummu-lites communities in the Bakony Mountains,

— to trace the changes occuring in the palaeocom-munities from the Early Lutetian to the Eocene/Oligo-cene boundary.

In order to attain the first aim, it was necessary to establish the dominant Nummulites populations, as well as their relations to the stratigraphically and palaeoecologi-cally most important other genera of larger Foraminifera.

In order to approach the second aim, it was necessary to consider all the environmental factors that affect the Nummulites communities. It had to be studied, how do they effect the composition of the communities, the

areas of individual populations, their bathymétrie distribu-tion, living conditions, and their relations to other fora-minifer genera. Furthermore, attention had to be paid also to evolutionär}' factors and effects that operate inde-pendentiy of the environment, because these may have played the role of an "internal engine" in the changes and evolution of the communities.

The starting point was the factual evidence accumu-lated during the previous studies of taxonomic, stratigra-phical, palaeoecological and palaeobiogeographical nature. Out of these, the palaeogeographical data ( K E C S K E M É T I 1978) proved to be the most useful (areas, relationships, provinciality, diversity etc.). Relying upon these, I selec-ted five profiles out of the more than 50 profiles which had been thoroughly investigated, in a way that they should represent a fair areal coverage of the Eocene formations of the Bakony Mountains.

The representative profiles are Eocene core columns of boreholes Somlóvásárhely 1. (Sv. 1.), Csehbánya 1. (Cseh. 1.), Pénzesgyőr térképező 31 (Pgyt. 31.), Dudar 218. (D. 218.) and Balinka 219 (Ba. 219.).

In a next step, intervals were chosen, each of which represents a chronostratigraphic unit, i.e. a zone.

The Nummulites laevigatus Zone of the Lower Lutetian is represented by the following depth intervals: 829.0 m in borehole Sv. 1., 181.2-183.6 m in borehole Cseh. 1. The Nummuites lorioli Zone in represented by the interval 146.2—148.2 m in borehole Cseh. 1. The Nummulites perforates Zone of the Bartonian is represented by core 780.0 m in borehole Sv.l., as well as by the intervals of 56.0— 59.6 m in borehole Pgyt. 31., 172.2—172.7 m in borehole D. 218., and 443.0-443.3 m in borehole Ba. 219. The Nummulites millecaput Zone of the Bartonian is sented by the core 759.9 m of borehole Sv. 1. and of the interval

3 4 KECSKEMÉTI, T .

414.5-415.8 m in borehole Ba. 219. The Nummulites jabianii Zone of the Priabonian is represented by the core 552.2 m of borehole Sv. 1. and interval 368.1-375.4 m in borehole

Ba. 219. All the mendoned zones are assemblage zones. Location of the profiles and the representative intervals in them are shown in Figure 1.

Figure 1 — Sketch map of the investigated boreholes, showing also the intervals of the representative palaeocommunities in their respective profiles.

Discussion of the palaeocommunities by sections

The representative Nummulites communities are presented in chronological order. Their composition, the relationships to other larger foraminfera and the trends of change are discussed below. In all figures, the palaeogeographic distribution

of palaeocommunities is shown; the representative profiles are visible on both sides with the taxonomic composition of the palaeocommunities (genera and species) in the middle, in form of columns, with the respective percentages.

Lutetian palaeocommunities Nummulites laevigatus Zone (Figure 2) — Tine calca

reous marl sample taken at 829.0 m from borehole Somlóvásárhely 1. has yielded a very rich fauna (abundance index = 4). In its Nummulites community, the dominant species is the reticulate zone marker species N. laevigatus (70 %). It is followed by the punctuate species N lehnen, N sismondai, N. deshajesi and N. baconicus (20 % combined). The small striate species N. variolarius, N, apertus and N. suemegensis (the latter described from the South Bakony) make up only 4 %. (Unidentifiable fragments have been indicated as "others".)

Along with the Nummulites, the fauna comprises also Assilina (25 %), Alveolina (25 %) , Orbitolites (10 %) and Operculina (5 %).

The sample taken from the interval 181.2-183.6 m of borehole Csehbánya 1. consists of sandy limestone. In its medium to high-diversity Nummulites community' (abundance index — 3-4) again N. laevigatus is the dominant species (51 %). The other half of the community- is made up mainly (to 35 %) by punctuate species (N. lehneri, N. sismondai, N.

deshajesi, N. baconicus, N. obesus and N. gallensis), and (to 10 %) by N. variolarius and N. apertus. Nummulites make up 70 %, while Assilina 30 % of the fauna.

The above composition characterizes only the two representative palaeocommunities.

Those of the other profiles of the area are more abundant and more varied. In the profiles of the Eocene terrains extending from Ajka to Sümeg some rare "colouring elements" also occur, such as AT. britannicus and N. hagni.

Comparing the palaeocommunities of the two representative profiles, it is found that the percentage of N. laevigatus in the High Bakony is much lower than in the Southern Bakony (51 % and 70 %, respectively), while the abundance and diversity (in this case simply the number of taxa) of punctuate Nummulites are higher (6 and 4 taxa, corresponding to 22 and 35 %, respectively). Also the striate taxa are more common (10 % versus 6%).

As far as the community-building of the genera, it can be stated that the Somlóvásárhely 1. community is more varied

than the Csehbánya 1. In the former, Asslilina, Alveolina, is especially varied). In the latter, the community of Orbitolites and Operculina are associated with the Nummulites, larger foraminifera consists essentially of Nummulites and represented by quite a number of taxa (the Alveolina fauna Assilina only.

Figure 2 — Geographic extension and stratigraphie position of the Nummulites communities of the Lutetian Nummulites laevigatus Zone.

Niimmiilites lorioliZone (Figure 3) — It is developed in the western half of the High Bakony only. To analyze its palaeocommunity, the borehole Csehbánya 1. was chosen, in the 146.2 to 148.2 m interval of which the palaeocommunity of this zone is the most typical in Hungary. From the limestone core a well-preserved medium-quantity fauna (abundance index = 3—4) was obtained. The medium-size, reticulate N. lorioli is the dominant taxon (60 % ) . Punctuate species (N. baconicus, N. uranensis, N. praeaturicus, ) make up 17 %, while the striates (N. variolarius, N. ^rcensis, N. dudar-ensis) 16 %. A new element is a small-size taxon of smooth Nummulites: N. millecaput "petit" (sensu SCHAUB). It is rather

subordinate (3 %), its appearence forecasts, however, the forthcoming completion of the Nummulites fauna.

Out of the taxa enumerated above, N. ^rcensis and N du-darensis are present in all palaeocommunities of the boreholes in this area. They are characteristic for the High Bakony.

As far as the genera are concerned, the percentage of Nummulites is 84, that of Orbitolites 11. Other genera of larger foraminifera are absent, unlike the case of the N. laevigatus Zone in the High Bakony. The sporadic presence of the smaller foraminifera genus Miliolina (4 %) as well as that of coralline red algae is, howewer, worth of mention, since they are valuable ecological indicators.

Bartonian palaeocommunities Nummulites perforatus 'Lone. (Figure 4) —This zone

is illustrated by 4 palaeocommunities, one from each of the four Eocene facies regions of the Bakony Mountains.

In the sample taken at 780.0 m from borehole Sv. 1. located at the westernmost margin of the Bakony Mountains, Nummulites occur in rock-forming quantity (abundance index = 5). The Nummulites fauna of the limestone core is of low diversity. The zone marker punctuate N.

perforatus is by far the predominant species: 88 %. At first look it seems that the fauna is monospecific, consisting of 20—25 mm diameter specimens of JV. perforatus only. However, the detailed investigation has revealed the (scarce) presence of the other species as well: the striate N. variolarius, N. discorbinus, N. anomalus and N. millecaput (virtually its megaspheric generation only). These "acces-sorycal" taxa make up 2—5 % of the community.

Figure 3 — Geographic extension and stratigraphie position of the Nummulites communities of the Lutetian Nummulites lorioli Zone.

The percentages of genera are as follows: Nummulites 80, Assilina 15, Discocylina 5.

The borehole Pénzesgyőr térképező 31. is located in the central part of the High Bakony. In the core taken from the interval 56.8—59.6 m (clay-marl), N. perforatus makes up 68 % of the community. Both the generic and the specific diversity are higher. Along with JV. perforatus the punctuate species are represented by JV. aturicus and N. meneghinii (2 % each). The group of reticulate Nummulites is considerable (13 %) and rather varied: N.puschi, N. sordensis, N. pen^esgyoerensis and N. praefabianii. Six rare species represent the striate Nummulites: N. variolarius, N. discorbi-nus, N. anomalus, N. -^ircensis, N. anomaloides and N. striatus. The two species of smooth Nummulites, N. millecaput and N. maximus combined make up 6 %.

The generic composititon is: 87 % Nummulites, 13 % Discocyclina, 9 % Operculina.

The Zirc Basin is represented by borehole Dudar 218. The 172.2—172.7 m interval is very rich in larger foraminifera (abundance index = 4), 83 % of which is a medium diversity Nummulites community. The dominant taxon is N. perforatus (58 %). The punctuate species are represented by N. meneghinii (2 %). Out of the reticulate Nummulites, JV. brongniarti has to be pointed out (10 %), while JV. sordensis is but a "colouring element" (2 %). The percentage of the striate Nummulites is relatively high: 20 %. Among these, JV. discorbinus makes up 8 % of the community, while JV. variolarius, N. anomalus and JV. sinensis 3 to 7 % each. The smooth Nummulites make their appearance: a few specimens of N. dufrenoyi could be identified.

The predominant Nummulites (83 %) are accompanied in the community of larger foraminifera by Alveolines (11 %) and discocyclinids (6 %).

The N. perforatus community of the Northeaster Bakony was studied on core 443.0—443.3 m of borehole Balinka 219. The friable limestone contained a suprisingly rich and varied Nummulites fauna (abundance index = 4). Its dominant species is N. perforatus, with 65 %. The reticulate Nummulites (JV. praegarnieri, N. garniert, N. stun) are rather accessor)- elements (8 %). On the contrary, the striate Nummulites excel with a richer and more varied fauna as compared to the previously described communities. Their 8 taxa (JV. variolarius, N. discorbinus, JV. anomalus, N. striatus, N. carpenteri, N. anomaloides, N. kopeki, N. subtilis maior) make up 22 % of the community. N. variolarius has the highest percentage (8), the others range from 1 to 4 %. A forerunner of the smooth Nummulites, N. millecaput is present also here (a few specimens).

The generic composition is the following: Nummulites 90 %, discocyclinids 8 %, Alveolina 2 %.

Comparing the four profiles it can be stated that the diversity of Nummulites communities is low to medium, increasing from the West towards the East being the highest in the High Bakony and the NE Bakony areas.

The dominating species of the communities is N perforatus. In the Sv. 1. sample it constitutes an almost monospecific fauna (88 %). Eastwards its predominance is somewhat decreasing (down to 60 %), and a considerable number of reticulate and striate species are associated to it. Particularly common associates are the small-size Nummulites, such as JV. variolarius, N. discorbinus and N. anomalus, which are constant community members. It has to be pointed out that in these communities, most of the species are new for Hungary or for science (JV. pen^esgyoerensis, N. ^rcensis, N. anomaloides, N kopeki, N. meneghinii, N. sordensis, N. praefabianii, N. praegarnieri, N. garniert' sturi, N. carpenteri,

N. subtilis maior). The smooth Nummulites are present with a few percent in all four profiles. Their presence forecasts their forthcoming upswing.

In the generic composition of the communities the Nummulites are overwhelming (78 to 90 % ) . Their predominance increases from the West to the East. The genus Discocyclina in constandy present, but subordinate

(5-13 %), Alveolina (15 %) and Operculina (9 %) exist in the Western Bakony, while Alveolina (2 to 11 %) in the Eastern Bakony. Each of these, but in particular the genera Discocyclina and Alveolina, are represented by quite a number of taxa. The role of these in the communities will be studied in a later stage of the ongoing investigations.

1 - N. perforatus, 2- N. brongniarti, 3 - N. variolarius, 4 - N. meneghinii, 5 - N. aturicus, 6 - N. puschi, 7 - N. sordensis, 8 - N. discorbinus, 9 - N. anomalus, 10 - N. zjrcensis, 11 - N . pen^esgyoerensis, 12 - A7. maximus, 13 - N . millecaput, 14 - N . dufrenqyi, 15 - N . praefabianii, 16 - N . striatus, 17 - N. subtilis,

18 - N . kopeki, 19 - AÍ. carpenteri, 20 - N . anomaloides, 21 - N. garniert sturi, 22 - N. praegarnieri, 23 - indet. Nummulites species

Figure 4 — Geographic extension and stratigraphie position of the Nummulites communities of the Bartonian Nummulites perforatus Zone.

Nummulites millecaput Zone (Figure 5) — One profile was chosen in the westernmost and another in the NE-most area of the Bakony Mountains: boreholes Somlóvásárhely 1. and Balinka 219., respectively.

Core 759.9 m of borehole Sv. 1. is glauconitic sandstone. In its Nummulites community, which is of low diversity, but rich in specimens (abundance index = 4) the zone marker JV. millecaput is represented with 78 %. The big specimens of this dominant member of the community (40—50, in some cases even 60—70 mm in diameter) make the smaller ones of other taxa much less conspicuous. Reticulate Nummulites are present only in 2 %, while 4 species of striate Nummulites (JV.

variolarius, JV. discorbinus, N. anomalus, JV. striatus) combined make up 18 %.

The generic percentages are follows: Nummulites 71, disco-cyclinids 15, Assilina 11, Operculina'3,

They clay marl of the 414.5-415.8 m core of borehole Balinka 219. contains Nummulites in rock-forming quantity (abundance index = 5). The most characteristic and most important species is the smooth N. millecaput (81 %). The other 8 Nummulites species (JV. perforatus, N. brongniarti, JV. praegarnieri, JV. praefabianii, N variolarius, JV. discorbinus , JV. anomalus, N. beaumonti) are subordinate (2 to 5 % each).

The generic composition of the community is: Nummulites 62 %, Discocyclina 36 %, Operculina 2 %.

Comparing the two representative palaeocommunities, the following statements can be made. At Somlóvásárhely, JV. millecaput'is almost the unique Nummulites species (78 %), accompanied by only five, mosdy striate species. At Balinka, the dominance of N. millecaput h slightly higher (81 %), but eight different (punctuate, reticulate and striate) taxa are also present. Accordingly, the species spectrum of the community is wider and much more varied. The scarce presence of N. perforatus and N. brongniarti (2 % each) is note

worthy, because of the considerable size of the specimens. The generic picture of the communities is rather mono

tonous: they consist of four genera only. The eastward decrease of the dominant Nummulites (from 71 to 62 %) is an important feature, complemented by the increase of Discocyclina: 15 % at Somlóvásárhely and 36 % at Balinka. Assilina species are present up to 11 % in the Southwestern Bakony. The Operculina species are subordinate (2—3 %).

Flgoire 5 — Geographic extension and stratigraphie position of the NummiiHtes communities of the Bartonian Nummulites mtZ/ecapuf Zone.

Nummulites faibanii Zone (Figure 6) — In the Ha-limba and Balinka Basins, part of the Priabonian sediments has escaped erosion. That is why the representative section has been chosen from these areas.

Core 552.2 m of borehole Sv. 1. is a tuffitic, sandy marl. Its Nummulites community is considerable (abundance index 3—4), but it is of low diversity. The subdominant species is the zone marker reticulate N. fabianii (42 %). It is closely followed by the striate N. incrassatus (AO %) . The other species (JV. chavannesi, N. pulchellus, N. stellatus) combined constitute 15 %. Since also these are striate, this group became dominant (55 %).

The generic composition is the following. There is absolute predominance of Nummulites (70 % ) , followed by Operculina (18 %) and discocyclinids (10 %) . Scarce specimens of two more genera have also been found:

communities Chapmanina and Gyroidina (1—1 % each).

The other representative core is sandy limestone from the interval 368.1-375.4 m of borehole Balinka 219. Its Nummulites community is not very rich (abundance index = 3) and of low diversity. The main element is, also in this case, N. fabianii (49 %). The same percentage is reached by the three striate species combined: N. incrassatus (28 %), JV. chavannesi (14 %) and JV. pulchellus (9 %). A peculiar species of the community is JV. aff. preshvichianus, which is, however, very rare (1 %).

Comparing the two communities, the following statements can be made. The species composition of the two communities is essentially identical. The difference mean only a single species: JV. stellatus is present in borehole Sv. 1., while JV. aff. preshinchianus in Ba. 219, respectively. The diversity is low, there are only five taxa present, and abundance is

lower, too, in comparison with the previously presented communities. The dominant taxon, N. fabianii, is below 50 % in both profiles. Besides N. fabianii, the second most important species is N. incrassatus (28 to 40 %). N. chavannesi (6-11 %) and N. pulchellus (7-9 %) display an eastward increase: the presence of the boreal faunal element N. aff. preshvichianus may be an indicator of the climate cooling which becomes obvious in the Early Oligocène.

At the generic level, the following observations have been made. The genus Nummulites is decreasing from the West to the East, from 70 to 30 %. At Balinka, die genus Operculina overrides Nummulites (40 % against 30). Discocyc-lines are present in both sites in the nearly identical amounts (10-15 %), slighdy more abundant in the East. In the West, two interesting genera of larger Foraminifera appear: Chapmanina and Gyroidina in the East, the coralline red algae are important constituents of the community.

The above analysis reveals that in the larger foraminifera fauna in general, and in the Nummulites fauna in particular

(which arrived in the Bakony Eocene with the early Lutetian transgression), three characteristic types of com-munities can be distinguished.

The oldest community is composed mainly of large reticulate and small punctuate Nummulites species, accom-panied by a rich fauna of Alveolina. The genus Assilina is represented by the species A. spira. The next community is characterized by big punctuate and smooth Nummulites, accompanied by decreasing percentages of Assilina and Alveolina, counterbalanced by the increasing presence of discocylinids. Finally, the youngest community is characterized exclusively by small striate taxa. The boundaries of the three community types coincide with the Lutetian/Bartonian and Bartonian/Priabonian boundaries, respectively. The Bartonian/Priabonian boun-dary is marked also by the disappearance of Assilina, Alveolina and the extralarge Nummulites species.

In the following, the factors that might have caused the changes in community types will be discussed one by one.

1 - N. fabianii, 2 - N. incrassatus, 3 - N. chavannesi, 4 - A7, pulchellus, 5 - N. stellatus, 6 - N. aff. preshvichianus,

7 - indet. Nummulites species

Figure 6 — Geographic extension and stratigraphie position of the Nummulites communities of the Priabonian Nummulites

fabianii Zone.

Effects of environmental factors on palaeocommunities

Included are all external factors (events, circumstances, affected also the fauna of larger foraminifera. Their study influence) that affect the formation and development of is still ongoing. Here only the hitherto recognized most communities. Several Eocene events are known which important observations and connections are reported on.

Some of these are of tectonic nature. There is considerable evidence to the occurrence of movements (of varying intensity) during the Lutetian s. 1. Such are: gravel interbeds in profiles of the Farkasgyepű and Bakonyjákó areas, oscillatory sedimentation in the so-called Upper Lutetian coal bearing sequence ( K O P E K 1 9 8 0 ) , fluviatile Tokod Sandstone. All these can be connected with the praepyreneic movements ( D U D I C H & M É S Z Á R O S 1 9 6 3 ) , more recendy called the "terminal Middle Eocene event".

At the Lutetian/Bartonian boundary considerable sea deepening can be recognized in the Bakony region. The corresponding sediments are hemipelagic, bathyal (Padrag Marl Formation). This seems to coincide with the number 3 6 third order cycle of the TA 3 Eocene superqrcle of eustatic sea level changes (HAQ, H A R D E N B O L & V A I L 1 9 8 7 ) .

Climatic reasons may eventually explain the appearance of JV. aff. prestwichianus in the Priabonian of the Balinka Basin, namely boreal influence. With regard to the that-time subtropical to tropical climate of the Tethyan realm, this would correspond to Mediterranean climate. This assumption is supported by the presence of the equally "boreal" species N. rectus in the Nagyegyháza Basin.

An interesting observation refers to the part played by the physical chemistry of seawater. In the larger interval of the andesitic and dacitic tuffs produced by Eocene volcanic activity, in some horizons of the Bartonian and the Priabonian the number of theratologically anomalous specimens is conspicuously high (reversal of growth direction, uni- and bivalent double shells, accessorial chambers etc.).

In this respect, the Nummulites of the Halimba Basin, and even more those coming from the tufaceous-tuffitic beds of the Dorog Basin, are the most significant. A starting point for the explanation of this phenomenon may be found a paper published by VlTÁLIS-ZlLAHY ( 1 9 6 3 ) . She found unexpectedly high strontium contents in some Eocene samples from the Dorog Basin that contains larger foraminifera. This prompted the author of the present paper to inquire into the physiological effects of strontium.

According to the relevant physiological literature, strontium is not only a mutagenic element, but it may also bring about the formation of neoplasma, and, consequendy, irregular shell building. The forthcoming geochemical studies

will have to decide whether this hypothesis is true or not. The next observation concerns salinity. In several pro

files, Alveolina, Orbitolites and Miliolina constitute characteristic communities. It is conspicuous that Nummulites species are almost totally absent. This extremely subordinate role of the stricdy stenohaline Nummulites may be due to a slight decrease from the normal 3 5 permil salinity, which is somewhat better tolerated by Alveolines and Orbitolites, and is even very favourable for Miliolina. However, other kinds of competition are also possible. To reach an unambiguous solution, further studies are needed.

Beyond doubt the external factors contributed to the almost monospecific occurrence of N. perforatus and N. millecaput in the representative profiles (boreholes Sv. Land Balinka 2 1 9 . ) . This phenomenon is known in other regions as well: in Lybia ( A R N I 1 9 6 5 ) , Egypt (AIGNER 1 9 8 3 , 1 9 8 5 ) , Spain ( S E R R A - K l E L «SC R E G U A N T 1 9 8 4 ) , SW Slovenia ( P A V L O V E C 1 9 8 4 ) and Switzerland ( H E R B 1 9 8 6 ) .

The massive accumulation of foraminifera shells, baptized "biofabric" by A I G N E R ( 1 9 8 5 ) , can be approached by two different ways. Namely by analysing (1) the ratio of the microspheric (B) and the megaspheric (A) generations, and ( 2 ) the arrangement of the shells.

On this basis, four types can be distinguished: 1 — autochtonous (undisturbed) arrangement, 2 — parau-tochtonous arrangement, 3 — residual arrangement, 4 — allochtonous arrangement (AIGNER 1 9 8 5 ) .

In the investigated profiles type 1 (JV. perforatus, N. millecaput in borehole Sv. 1.) and type 3 (N. millecaput in borehole Ba. 2 1 9 . ) could be identified. In type 1 the generation A is dominating (A:B ratio = 1 0 : 1 ) , while in type 3 the generation B is dominating. In the latter type the B forms make up fascicles, eventually tile-on-tile structures intercalated by A forms. In some intervals of the Balinka samples, Form A has been almost completely removed hydrodynamically, leaving behind a residual "package", consisting only of Form B. In the case of type 1, the energy level of the medium was low, while in that of type 3 the water must have been rather agitated.

The depth distribution was dealt with in a previous paper ( K E C S K E M É T I 1 9 8 9 ) , so there is no need to elaborate on it here.

Role of the evolutive factors in the development of palaeocommunities

The test of the larger Foraminifera, just as the test of any other fossil, reflects the process of ontogeny and phy-logeny, their level and trend. Consequendy, its morpho-genetic study provides us with valuable information about the process of evolution.

The general evolutionary trend of Nummulites and other larger Foraminifera, which display an alternation of gene, can be best traced on the ontogeny of the microspheric (B) generation.

Three statements may serve as a starting point. — The spire of the microspheric generation consists

of three successive sectors: the inner or embryonal one (core with the diameter of the initial chamber in the megaspheric generation), the middle one (corresponding

with the full test diameter of the adult megaspheric generation), and the outer one, exceeding the shell diameter of the megaspheric generation.

— In ontogeny, the changes of the shape of the chamber are of particular importance. These are also relevant for phylogeny: the primitive taxa are characterized by high (operculinoid) or isometric (assilinoid) chambers, while the more evolved ones by long (nummulitoid) chambers.

— The middle spire sector of the microspheric generation is characteristic for each taxon, while the features of the three sectors combined provide information about the general evolutionary level of the taxa, which defines the place of a given taxon in the phylogenetic lineage.

Beside these main ontogentic and phylogeneric regularities several more connections and relationships have been revealed by studies discussed in this paper. The more important ones are the following.

— In every lineage, the evolution resulted in two kinds of components, namely: progressive and regressive elements. Progressive elements are: more and more compact spire, larger chambers, increase in the diameter of the shell and the megasphere, thickening of the marginal lath, increase in the number of septa, complication of the suture line, appearance of granulation. Regressive elements are: loosening of the spire, increase in chamber height, decrease in the diameter of the shell and of the megasphere, and degeneration phenomena. The ratio of progressive and regressive elements defines the direction, nature and rate of evolution. The progressive elements are dominating in the cases of N. perforatus, N. brongniarti and N. millecaput. They are characterized by big, even gigantic size (up to 80—100 mm), hundreds, in extreme cases thousands of chambers, and three-sectoral spire. With time, these features become overdeveloped. This, along with degeneration phenomena, resulted in parakme during the

Bartonian, terminating with the extinction of the species. None of them passed the Middle/Late Eocene boundary.

— The appearing new taxa evolve mainly by divergence, not by anagenesis.

This means that an evolutionarily "plastic" (mosdy very variable) species bears in itself the general evolutionary trend of features, and new taxa are produced by the factors of evolution (spreading, shift, isolation, selection etc.). Examples: the separation of N. striatus minor, N. subtilis, N. kopeki from N. stiratus, the separation of the N. dudarensis, N. maj^oni, N. iohannis, and N. sinensis from N. variolarius.

— It could be established that in the investigated faunas, there are numerous taxa, which have evolved under the influence of ecological and geographical factors (N. suemegensis, N. pen^esgyoerensis, N. dudarensis, N. sinensis). As a rule, the diferrence from the original taxon is not very significant. This would suggest that the populations might have been more or less interrelated. All these, as far as the Bakony Mountains region is concerned, is in connection with the temporarily and locally prevailing shallow marine influence and the environmental variability.

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Author's address: Dr. Tibor KECSKEMÉTI Geological and Palaeontological Department Hungarian Natural History Museum Budapest, M ú z e u m krt. 14—16

Mail: 1431 Budapest, pf. 137 Hungary

e-mail: kecs@paleo.nhmus.hu