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Palaeoecological significance of coral-encrusting foraminiferan associations: a case-study from the Upper Eocene of Northern Italy

100%

Bosellini F. R., Papazzoni C. A.

Acta Palaeontologica Polonica

2003

tom 48

nr 2

Encrusting foraminiferans, although representing an important component of the so−called cryptic assemblages in both modern and ancient reef environments, are in general poorly described and little is known as regards their association with corals.In this paper, we describe coral−encrusting foraminiferan associations in the different facies that characterize the shallowing upward parasequences of the Nago Limestone (Upper Eocene, Trentino, northern Italy).From a relatively deep reef slope up to the shallow shelf−edge, corals have been recognized to be encrusted by different types of foraminiferan assemblages that differ on the basis of relative abundance of species, growth form and type of encrusted coral surface.The succession of encrusting foraminiferan assemblages is interpreted as controlled mainly by light, competition with coralline algae, hydrodynamic energy, and coral growth fabric.

The middle to Late Eocene evolution of nummulitid foraminifer Heterostegina in the Western Tethys

80%

Less G., Ozcan E., Papazzoni C. A., Stockar R.

Acta Palaeontologica Polonica

2008

tom 53

nr 2

Megalospheric forms of Western Tethyan late Bartonian to late Priabonian involute Heterostegina from numerous localities, marking different ecological conditions, were morphometrically investigated. They belong to three species, H. armenica, H. reticulata, and H. gracilis based on the presence/absence of granulation, on the chamberlet characteristics and on the relative size of proloculus. Within these species a very rapid evolution could be observed in the reduction of the number of operculinid chambers, in the increase of the number of chamberlets and partially in the increase of the proloculus size. This evolution is demonstrated by stratigraphic superpositions in several localities (especially in the Mossano section), and is supported also by the change of co−occurring fossils, starting with the disappearance of large−sized Nummulites, then followed by the appearance of the genus Spiroclypeus and then by the disappearance of orthophragmines of middle Eocene acme. Based on the reduction of operculinid chambers, two chronosubspecies of Heterostegina armenica and seven of H. reticulata are defined biometrically (four of them: H. armenica tigrisensis, H. reticulata tronensis, H. r. hungarica, and H. r. mossanensis are introduced here). This allows to subdivide the Shallow Benthic Zone (SBZ) 18 into three and SBZ 19 into two subzones. The extremely rapid evolution of H. reticulata allows to calibrate larger foraminiferal events around the middle/late Eocene boundary. The extinction of large−sizedNummulitesseems to be heterochronous in the late Bartonian in having migrated eastward, while the first appearance of Spiroclypeus is shown to be synchronous at the base of the Priabonian. The middle/upper Eocene (= Bartonian/Priabonian) boundary is to be placed at the base of the Priabona marls in the Mossano section corresponding to the SBZ 18/19 limit, to the first appearance of genus Spiroclypeus, to that of Nummulites fabianii and of Heterostegina reticulata mossanensis. It falls into the upper part of both the P 15 and NP 18 planktic zones. The Western Tethyan Eocene involute Heterostegina became extinct, apparently with no Oligocene successors.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

2 Papazzoni C. A.

1 Bosellini F. R.

1 Less G.

1 Ozcan E.

1 Stockar R.

1 2008

1 2003

Wyniki wyszukiwania

Palaeoecological significance of coral-encrusting foraminiferan associations: a case-study from the Upper Eocene of Northern Italy

The middle to Late Eocene evolution of nummulitid foraminifer Heterostegina in the Western Tethys