Herb, R.; Hekel, H. (1975). Nummuliten aus dem Obereocaen von Possagno. Schweizerische Paläontologische Abhandlungen. 97: 113-135, 201-211.

385348

Herb, R.; Hekel, H.

1975

97: 113-135, 201-211

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In the Tertiary section of Possagno (Northern Italy) nummulites are restricted to the uppermost part of the Eocene. They occur in three lithologic units, the Marna di Possagno, the Calcare di S. Giustina and the overlying marne siltose. Within the Marna di Possagno the distribution of various groups of fossils (foraminifera, corals, molluscs) indicate a steady decrease of the water depth during deposition. The first occurrence of nummulites in the section is therefore related to water depth. The assemblages in this formation are characterized by the small size of the specimens, mainly the microspheric forms. The list of species includes N. incrassatus ramondiformis, N. cunialensis, N. chavannesi, N. stellatus, N. pulchellus, N. bouillei and N. garnieri. N. fabianii retiatus occurs very rarely in the silty clays, but is abundant and large in siltstones in the uppermost part of the formation. In the Calcare di S. Giustina N. fabianii fabianii is usually the most abundant species, followed in frequency by N. incrassatus ramondiformis and N. chavannesi. Many of the small forms found in the Marna di Possagno are missing in this formation. The assemblages of the marne siltose are dominated by N. fabianii retiatus and N. garnieri inaequalis. N. incrassatus ramondiformis occurs together with the less frequent, loosly coiled N. incrassatus incrassatus. The entire nummulite bearing part of the Possagno section belongs to the zone of Nummulites fabianii retiatus (uppermost Priabonian). This age is confirmed by the presence of Globorotalia cerroazulensis cunialensis below the first occurrence of nummulites. In the uppermost part of the section, the marne siltose, the nummulites of the fabianii-group (N. fabianii retiatus) partly show a more advanced development of the surface reticulation, but in their equatorial section they are clearly distinct from N. fichteli and are still considered to be of latest Eocene age, however, close to the Eocene/Oligocene boundary. In the Possagno section the nummulite occurrences represent a very short time interval, but in a variety of facies types. Their stratigraphic distribution within the section is dictated by environment. Water depth was probably one of the principal parameters, but others, such as the amount of detrital supply and the oxygen content of the water, may have been equally important. In the systematic part of the paper, the nummulite species of Possagno are described and figured, and biometric data are given. One new species, N. cunialensis, is defined.

Foraminifera

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