Orthophragminid and operculinid events at the Middle-Upper Eocene boundary in Europe.

In some Middle Lutetian (Gibret, Nousse and Angoumé, France), Upper Lutetian (Ajka and Padragkút in Hungary) and Lower Bartonian (Dudar in Hungary, San Pancrazio in Italy and Biarritz, Rocher de Peyreblanque in France) localities (see Less, 1998) the richest orthophragminid assemblages ever seen can be found. The members of nineteen evolutionary lineages are represented in them. By comparing the orthophragminid content of the Middle and Upper Priabonian localities (Priabona, Sorgente, Valle Granella and the Middle-Upper Priabonian of Mossano in Italy and Kisgyör, Remete-kút in Hungary) with them, we find that eleven of the nineteen lineages had been lost and only five new (and rare) species appeared. The eight lineages that are coming from the Middle Eocene and surviving until the end of the Eocene are: Discocyclina dispansa, D. augustae, D. radians, D. trabayensis, Orbitoclypeus varians, O. furcatus, Asterocyclina stellata and A. stella.The orthophragminid events in the Late Bartonian and Early Priabonian can be followed in correlating them with three other successive larger foraminiferal events, such as (from top to bottom):- Event 3: The appearance of Spiroclypeus that has never been found in the Middle Eocene and with large Nummulites.- Event 2: The extinction of large Nummulites that have never been found with Spiroclypeus. Their supposed occurrence (especially of N. ex gr. millecaput) in the Upper Eocene of Slovakia and Armenia has to be carefully studied. Papazzoni & Sirotti (1995) recognized a considerable gap between Events 2 and 3 in N Italy whose duration however, has to be analysed in other regions, too. Papazzoni (this volume) stressed the possible bias of local paleoecological conditions on the biostratigraphical distribution of some species.- Event 1: The appearance of involute Heterostegina (former Grzybowskia) that can be found with the last large Nummulites in some sections of N Italy (Papazzoni & Sirotti, 1993 and 1995), Poland (Bieda, 1963), Armenia (Nemkov, 1967) and Urhida in Hungary (our new data).Recently Event 3 seems to be the most adequate for placing the lower boundary of the Priabonian as it has been found by Papazzoni & Sirotti (1995) because it appears exactly at the base of the Priabonian in the Mossano section. At the same time, the rapid nepionic acceleration of Heterostegina reticulata manifested in the strong reduction of non-subdivided, operculinid chambers (parameter X shows their number in the spire of the A-forms, including the proloculus) can be considered the most reliable evolutionary clock in order to calibrate the events listed above. By using the Papazzoni & Sirotti (1993) data from the Mossano section and our new data from Urhida and Noszvaj, Hungary the evolution of parameter X can be sketched as follows:- X (mean) reduces from at least 15-16 to 7-9 between Events 1 and 2 (sample Mossano 2 of Papazzoni & Sirotti, 1993 and two new samples from Urhida, Hungary).- No statistical data from between Events 2 and 3.- X (mean) is about 5 just after Event 3 (sample Mossano 10 of Papazzoni & Sirotti, 1993).- It reduces until 3 in the following part of the Priabonian (sample Mossano 16 in Papazzoni & Sirotti, 1993 and a new sample from Noszvaj, Hungary).The lineage of Assilina schwageri-alpina also shows a rather rapid increase of the proloculus of the A-forms in the Bartonian-Priabonian interval as indicated by Papazzoni (1998) and confirmed by our data from Urhida, Noszvaj and Kisgyör, Remete-kút (Less, 1999), too. According to these, the inner cross diameter of the proloculus of A-forms is about 125-135 µm at the Middle-Upper Eocene boundary (Event 3). At the same time, it is difficult to follow the development of the Operculina roselli-gomezi lineage in the context of the events listed above, mostly because the boundary of the two successive species is not clearly defined. However, this lineage is very frequent in some samples listed below after Event 1, so it needs further studies.For characterizing the orthophragminid events around the Middle-Upper Eocene boundary several samples have been used: The Middle-Upper Lutetian (O.9-11 orthophragminid zones) and Lower Bartonian (O.12-13) ones listed at the beginning of this paper were formed before Event 1, while the Middle-Upper Priabonian (O.15-16) ones well after Event 3. The other samples (their orthophragminid fauna was seen and evaluated by the author: all they indicate the O.14 zone with a few exceptions shown in brackets) are:- Between Events 1 and 2: Gurb (O.13) in Spain (Papazzoni & Sirotti, 1995 using also Hottinger, 1977, fig. 38 and C. Ferrández's unpublished data), Siest in France (Less, 1998), samples from Mossano, Italy: MOSS 1 and 11 in Papazzoni & Sirotti (1995) (MOSS. 001 and 2 in Papazzoni & Sirotti, 1993), Mossano 31 (~MOSS 11) (Schweighauser, 1953, see also in Less, 1998), new samples from Hungary (see them in the Field-trip guide-book of IGCP 393 for 2000): Bajót, Domonkos Creek section, "millecaput" beds, Urhida "millecaput" beds.- Between Events 2 and 3: Samples Igualada 4-5 in Spain (Papazzoni & Sirotti, 1995, using also C. Ferrández's unpublished data) and MOSS 16 (former MOSS. 7) of Mossano, Italy (Papazzoni & Sirotti, 1995).- After Event 2 but in uncertain relationship with Event 3: New samples from Bajót, Hungary, "Discocyclina + Operculina" beds: Domonkos Creek section and the quarry W of the village (O.15).- Just after Event 3: Samples in Mossano, Italy: MOSS 20 (former MOSS. 10) in Papazzoni & Sirotti (1995), Mossano 44 (O.14/15) and 50 (O.15) (Schweighauser, 1953, see also in Less, 1998 as well as sample MOSSA), a new sample from Hungary: Urhida, "Discocyclina" beds.Therefore, two main orthophragminid extinction events could be distinguished at the Middle-Upper Eocene boundary, the first (Event α) occurring before or simultaneously with Event 1, while the second (Event β) after Event 3.- Event α: Five of the eleven lost lineages cannot be found after Event 1. These are: Discocyclina pulcra, D. spliti, Nemkovella katoae, Orbitoclypeus douvillei, and O. schopeni (the latter is extremely rare already in the Middle-Upper Lutetian and Lower Bartonian). These lineages became extinct very likely well before the end of the Bartonian, in the SBZ 17 zone of Serra-Kiel et al. (1998) (or in the case of D. spliti maybe even in SBZ 16). This event roughly coincides with the extinction of some nummulitid lineages such as Assilina exponens and probably also Nummulites brongniarti and N. puschi.- Event β: Four of the six lineages having survived the first orthophragminid extinction event, Nemkovella strophiolata, Asterocyclina alticostata, A. kecskemetii and Discocyclina pratti can still be found with the first Spiroclypeus (the first two in Mossano, the last three in Urhida), thus they surely survived Event 3. The fifth lineage, D. discus also survived at least Event 2 as it can be found in the Bajót, Domonkos Creek section. Since Event 3 could not be detected so far in this region, this extinction is joined with that of the previous four lineages. Finally, the sixth lineage, Orbitoclypeus daguini (with last occurrence in Gurb) is so rare (altogether 10 specimens from 6 localities are known) that its extinction can be tentatively placed together with that of the other five lineages.As it is mentioned earlier, five new orthophragminid species appeared in the Priabonian. They are so rare that here only their first occurrences are listed without any further conclusions: Discocyclina nandori in sample MOSSA (O.14 zone), between Events 3 and 4; D. euaensis in the quarry W of Bajót (O.15), between Events 2 an 4; D. samantai (the ribbed variant of D. pratti minor, the last member of that lineage) in the "Discocyclina" beds of Priabona (O.14), after Event 3 and in the Lábatlan, Raibl-patak quarry (Less, 1987) (O.15), before Event 4; D. ruppi (see Rasser et al., 2000) in the "Discocyclina + Operculina" beds of the Bajót, Domonkos Creek section (O.14), after Event 2; Asterocyclina priabonensis in sample Mossano 44 (O.14/15), between Events 3 and 4.As it is clear from the list of orthophragminid samples representing the Bartonian-Priabonian transition, Event 1 can very probably be placed into the uppermost part of O.13 zone, Events 2 and 3 into the O.14 zone while Event 4 into the lower part of O.15 zone, thus almost the whole interval between Events 1 and 4 belongs to the O.14 zone within which the development of orthophragminid lineages is hardly detectable. By using our new data from Urhida and Bajót, Domonkos Creek, the only change is that Discocyclina pratti pratti is succeeded by D. pratti minor (their limit based on the population mean of the outer cross diameter of the deuteroconch is 700 µm) that could happen between Events 1 and 2.This research is a contribution to IGCP 393 and was supported by the National Scientific Fund of Hungary (OTKA, grants 23880, 32370), and by the Italian MURST 60% fund (responsible Prof. A. Sirotti, Italy).