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

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

Oligocene nearshore benthic assemblages and coral facies of the northern Gargano Promontory

Shallow water carbonate successions of Oligocene age are quite well distributed in the Apulia domain and are often associated with the development of luxuriant coral reef systems (Salento Peninsula, Maiella Mountain). The dominant biogenic components generally consist of rich associations of scleractinian corals and larger foraminifera. In the Gargano Promontory, the Oligocene has been recently reported for the first time and a new carbonate unit informally established and named as Grotta S.Michele limestone (Morsilli et al., 2005). The aim of the present study is thus to investigate the type locality of this unit in order to describe and interprete its lithologic composition and biotic content through facies analysis. The stratigraphic succession consists of grainstones-rudstones to wackestones-mudstones, reaches a maximum thickness of about 28 m and clearly shows a fining-upward trend. The fossil fauna is mainly characterized by abundant scleractinian corals, associated with benthic forams and coralline algae. Corals are represented by very few genera and basically consist of globose colonies of Goniopora near the base of the succession, followed by floatstones-rudstones rich in branched Acropora, Stylophora, Alveopora and phaceloid colonies of Caulastrea towards the top. Similarly, also the foraminiferal assemblages, dominated by miliolids and soritids, are rather poor, often with a small number of specimens and low taxonomic diversity. Some larger foraminifera such as Archaias, Austrotrillina, Nephrolepidina, and Nummulites also occur, thus indicating an Oligocene age (Chattian). Several facies types have been identified on the basis of macroscopic observations in the field and microfacies analysis. Data are provided in particular for the distribution and relative abundance of the main biotic components, including coralline algae, bivalve and gastropod fragments, together with textural features. The facies association suggests a nearshore, sheltered, shallow-water marine paleoenvironment with possible evidence of changes in hydrodynamic conditions from very low to moderate-high energy. Within this setting, the unusual low-diversified coral assemblages and the absence of a true framework can be interpreted as a response to stressed conditions probably controlled by the inherited paleotopography

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

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

The Colli Berici

The paper delas with the stratigraphical setting of the Colli Berici. After the geological and stratigraphical setting of the area, a detailed biostratigraphical setting of the Eocene successions is presented. The stops of the filed trips organised within the last meeting of the IGCP393 are also described and illustrated

The Varignano section (Trento Province, northern Italy): a chance to correlate shallow benthic zones and calcareous plankton zones near the Bartonian -Priabonian boundary

The GSSP for the base of the Priabonian stage has not yet been defined, but a candidate section has been recently proposed near Alano di Piave (Veneto region, northern Italy), some 50 km far from the historical stage stratotype of Priabona. The Alano section, deposited in a bathyal setting, has been investigated for the calcareous nannoplankton, planktic foraminifera, as well as magnetostratigraphy. Unfortunately, at Alano di Piave there is no way to directly correlate with the larger foraminiferal shallow-water biozones, namely the Shallow Benthic Zones (SBZ). We present the results of the calcareous plankton and SBZ data from the Varignano section (Trento Province, northern Italy), that provides a unique chance for a direct correlation between shallow- and deep-water environments across the Bartonina-Priabonian boundary

Correlation Between Shallow Benthic Zones and Calcareous Plankton Zones at the Bartonian–Priabonian Transition: Preliminary Results from the Varignano Section (Trento Province, Northern Italy)

The Varignano section (Trento province, northern Italy), the sediments of which were deposited in a bathyal palaeoenvironment, contains eight resedimented bioclastic levels with larger foraminifera, thus providing an excellent opportunity to directly correlate the shallow benthic zones (SBZs) with the standard calcareous planktonic zones around the Bartonian–Priabonian transition. Moreover, this section is located only 80 km from the Alano di Piave section (Veneto region), a candidate to host the GSSP of the base of Priabonian, where this direct correlation is hampered by the absence of resedimented levels across the critical interval. The preliminary results of the integrated study of calcareous plankton and larger foraminifera reveal that the extinction of morozovellids and large acarininids (E13–E14 boundary) occurs within SBZ18 and not at the SBZ18–SBZ19 boundary as usually considered

Dinosauri e dintorni

Pubblicazione divulgativa in occasione di una esposizione temporanea