1,721,124 research outputs found
How did the planktonic foraminifera respond to the extreme environmental stress induced by the OAE2 (Bonarelli Level) in the Bottaccione section (Gubbio, Italy)?
No full textRevets S. A. (Ed.), Forams 2002, International Symposium on Foraminifers, The University of Westrern Austarlia, Perth, 4-8 February 2002
Posadia feroniensis n. gen., n. sp (Lituolida, Hormosinidae) from the Bathonian of Sardinia, Italy
No full textDetailed stratigraphical and paleobiological studies on
the Mesozoic carbonate platform of eastern Sardinia (Italy)
revealed the occurrence of an unknown foraminifer
in the Bathonian (Middle Jurassic) Dorgali Dolostone
cropping out in the Posada hill. Posadia feroniensis n.
gen., n. sp., a new distinctive agglutinated foraminifer
referable to the family Hormosinidae Haeckel, 1894, is
formally described and figured. Posadia is morphologically
characterized by an uniserial, roughly finished test
with inverted ‘‘V’’-like chambers in longitudinal section
Peculiar architectures in the Cretaceous planktonic foraminifera: links to oceanic anoxic events and major global changes
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Integrated stratigraphy (biostratigraphy and geochronology) of the Early Miocene sequence from the Emilia Apennines (Italy)
No full textVolcaniclastic layers interlayered within marine sediments of Early Miocene age have been reported from many sections of the Emilia and Marche Apennines. Ten sections are considered by Borsetti et al. (1979a, 1979b) who emphasize the common explosive volcanic activity ‘at the Oligocene/Miocene boundary’. These volcaniclastic layers were studied during elaboration of doctoral theses dealing with the sedimentology (Amorosi, 1993) and petrography (Tateo, 1992) of Oligocene and Miocene deposits in northern Italy. The presence of volcanic layers within a marine sedimentary sequence and the general goals of the Miocene Columbus Project (Integrated Stratigraphy with particular emphasis on the geochronological—biostratigraphical connection) led us to focus on gathering information on selected sections relevant for integrated stratigraphy
Guembelitria irregularis bloom at the K-T boudary: morphological abnormalities induced in planktonic foraminifera by impact-related extreme environmental stress?
No full textThe planktonic foraminiferal species Guembelitria irregularis displays an aberrant test due to the irregular disposition and growth of the chambers which suggest a morphological malformation. Available data across the Cretaceous-Tertiary (K-T) transition from three Tunisian sections (El Kef II, Elles II, Ain Settara) and Kazakstan (Koshak) and new data from Spain (Caravaca), and Italy (Erto), show a dramatic and remarkable increase in abundance of G. irregularis (up to 93% at El Kef II) in the small 38-63 μm fraction of the assemblages from the lower Danian planktonic foraminiferal Zones P0-P1a. Positive peaks in the abundance of this form are also recorded in the latest Maastrichtian, even though with minor percentages (up to 16% at El Kef II). Fossil and Recent foraminiferal tests showing morphological abnormalities have long been reported from stressed environments. Accordingly, we speculate that the morphological abnormalities shown by the G. irregularis test across the K-T boundary are the result of the extremely stressful environmental conditions related to the complex interplay of different events (rapid and extreme climate fluctuactions, sea-level changes, intense volcanism, and impact events, which characterize the last hundreds of thousand of years of the Cretaceous and the beginning of the Danian. In particular, the post-K-T morphological abnormality of G. irregularis may be related to high stress conditions induced by the K-T impact
Shocked diamonds in agglutinated foraminifera from the Cretaceous/Paleogene Boundary, Italy - a preliminary report
No full textWashed acid residues from rock samples taken at measured intervals across the Cretaceous/Paleogene boundary (KPB) section at Monte Cònero, Italy, were examined for agglutinated foraminifera to assess their ability to select heavy mineral phases. Examination with scanning electron microscopy (SEM) and electron microprobe has enabled us to identify minerals comprising the outer walls of several agglutinated foraminiferal species, including Psammosphaera fusca, and Reophax cf. parvulus. Modern representatives of these genera are known to preferentially agglutinate heavy minerals. Because of this curious behaviour, we postulated that heavy detrital minerals, including impact ejecta, would have been scavenged by these organisms and incorporated into their tests. We have identified microdiamond likely formed by impact, together with distinctive Ni-Co-rich mineral residues in agglutinated foraminifera from the KPB clay, and also from specimens sampled both above and below the boundary clay. This is the first reported occurrence of impact-related microdiamond associated with the KPB discovered outside North America. We conclude that scavenging of ejecta grains by agglutinated foraminifera is an important process for subsequent bioturbation and redistribution of the ejecta material. The grain-size distribution of the microdiamond is consistent with impact diamond formed uniquely as ejecta from the Chicxulub Crater, but further work is needed
Evolutionary and paleoecological response of Cretaceous radially elongated chambered planktonic foraminfiera to the Oceanic Anoxic Event
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Timing and pattern of biotic changes across the Bonarelli Level of the Southern Alps (Italy).
No full textCretaceous oceanic anoxic events and radially elongated chambered planktonic foraminifera: Paleoecological and paleoceanographic implications
No full textChamber elongation is a recurring morphological character in Cretaceous and Cenozoic planktonic foraminiferal evolution suggesting that the clavate body-plan takes advantage through particular environmental conditions. Cretaceous planktonic foraminifera bearing radially elongated chambers become repeatedly a consistent component of assemblages in correspondence with the deposition of remarkable organic layers that record the effects of oceanic anoxic events (OAEs). Due to this apparent
correspondence, chamber elongation has been recently interpreted as an adaptation to low oxygen levels in the upper water column. The paleoceanographic significance of planktonic foraminifera with radially elongated chambers remains however unclear. We investigated in great detail the distribution and abundance of elongated chambered planktonic foraminifera in an interval of about 40 myr across the Cretaceous OAEs in different well-dated sections. The increased abundance of planktonic foraminifera with elongated chambers can be a markedly evident feature across the Faraoni, the Selli and the Bonarelli OAEs. However each
event shows its own peculiarities. Remarkably, the first radiation of the Cretaceous elongated chambered morphotypes just predates the latest Hauterivian Faraoni Event. The Selli Event records the greatest diversification (number of species) of the group bearing elongated chambers. However, this was a period of great diversification in the planktonic foraminifera. This evidence may suggest that radiation of these forms was driven by more than upper water column anoxia per se (e.g., increased upper water column stratification, greater productivity, and/or greater seasonality).
The Albian OAE1b, OAE1c, and OAE1d display the lowest abundance and diversity of this group. Conversely, according to the available data, the first appearances of the species Muricohedbergella simplex and of the genus Schackoina occur close to the OAE1b and OAE1d, respectively. In the Italian record, the relative abundance of radially elongated chambered forms appears to be larger before the onset of the Bonarelli Event with respect to the Selli Event. The pattern involving this group across the Bonarelli Event appears more regular, thus indicating that the onset and the end of the OAE2 depend on very powerful global factors and are
less influenced by local aspects. We speculate that the relative abundance of planktonic foraminifera with radially elongated chambers may be proportional to the strength of the environmental perturbation related to the OAEs, thus reinforcing the idea that the ecological perturbation related to the OAE2 was more severe for the former.
Several lines of evidence suggest that water oxygenation could not have been the single controlling factor governing the development of elongate chambers. The role of availability of food and the nature of food has been so far probably underestimated. It is most likely that an interplay of several influential physical–chemical and ecological factors (i.e., dissolved oxygen concentration, temperature, salinity, nutrients, type of food, trace elements) was responsible for such a morphological adaptation.
We document linkages between the distribution, abundance, morphometric changes and evolution of the Cretaceous radially elongated chambered planktonic foraminifera and the major igneous, geological, geochemical, climate, nutrification and bioticevents and biocalcification trends
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