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| Titel |
Middle Eocene (Bartonian) Nummulites perforatus bank from the Transylvanian Basin, Romania: an example from a classical occurrence |
| VerfasserIn |
Kövecsi Szabolcs Attila, Silye Lóránd, György Less, Filipescu Sorin |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124899
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| Publikation (Nr.) |
 EGU/EGU2016-4402.pdf |
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| Zusammenfassung |
| Giant uni-cellulars, Nummulites lived in stable oligotrophic environments throughout the Eocene of the Tethys forming large accumulations called “banks” (Arni, 1965), which were identified on the top of the Căpușu Formation, Transylvanian Basin (Popescu, 1978).
The studied outcrop is located near Căpușu village, Cluj County where we studied two sections (CA1, CA2). They consist of medium to coarse grained sands with abundant Nummulites perforatus (A and B forms). Sporadically specimens of Nummulites beaumonti are also present. According to the larger foraminiferal zonation of Serra-Kiel et al. (1998) the studied nummlitic bank is referred to the SBZ 17 Zone (early Bartonian). Specimens were recovered from 6 samples, about 2 kg each, prepared by standard methods.
In section CA1 the A/B ratio ranges between 42/1 and 117/1 while in section CA2 the A/B ratio varies between 27/1 and 52/1. The higher A/B ratio suggests that the original Nummulites assemblages was winnowed in situ. By contrast, the lower A/B ratio indicates that the original assemblage was supposedly selectively winnowed (Ainger, 1985), but they are in situ (Seddighi et al., 2015). This interpretation is supported by the fact, that in all samples the Nummulites specimens (both A and B form) are bioeroded and abraded, which indicates a shallow water environment with high hydrodynamic activity (Racey, 2001; Papazzoni, 2008).
Based on our observations the studied nummulitic accumulations consist mostly of monospecific assemblages, and they form a bank. The identified biofabrics, the A/B ratio of the assemblages and the presence of both A and B forms support this interpretation. The presence of the abraded Nummulites tests further suggest that the studied deposits were sedimented in a shallow water environment with high hydrodynamic activity, probably in a wave dominant setting.
References:
Aigner, T. 1982. Event-stratification in nummulite accumulations and in shell beds from the Eocene of Egypt. In: Einsele G. & Seilacher A. (Eds.), Cyclic and Event Stratification. Springer, Berlin, 248-262.
Arni, P. 1965. L’évolution des Nummulitinae en tant que facteur de modification des dépôts littoraux. Mém. Bur. Rech. Géol. Min., 32: 7-20.
Papazzoni, C., A. 2008. Preliminary palaeontological observations on some examples of "nummulite banks": sedimentary or biological origin?. Rend. online SGI, 2: 135-138.
Popescu, B., 1978. On the lithostratigraphic nomenclature of the NW. Transylvania Eocene. Rev. roum. Géol. Géophys. Géogr. (Géologie). 22: 99-107.
Racey, A. 2001. A review of Eocene Nummulite accumulations: structure, formation and reservoir potential. Journal of Petroleum Geology, 24(1): 79-100
Seddighi, M., Briguglio, A., Hohenegger, J. and Papazzoni, C.A., 2015. New results on the hydrodynamic behaviour of fossil Nummulites tests from two nummulite banks from the Bartonian and Priabonian of northern Italy. Bollettino della società Paleontologica Italiana, 54(2): 106-116.
Serra-Kiel, J., Hottinger, L., Caus, E., Drobne, K., Ferrandez, C., Jauhri, A. K., Less, G., Pavlovec, R., Pignatti, J., Samso, J. M., Schaub, H., Sirel, E., Strougo, A., Tambareau, Y., Tosquella, J., and Zakrevskaya, E., 1998, Larger foraminiferal biostratigraphy of the Tethyan Paleocene and Eocene. Bulletin de la Société Géologique de France, 169 (2): 281-299. |
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