1,720,989 research outputs found
Calcareous nannofossil quantitative data from the Tithonian-Berriasian interval: implications for the Jurassic/Cretaceous boundary
No full textThe Jurassic/Cretaceous (J/K) boundary time interval is characterized by a major calcareous nannofossil speciation episode: several Cretaceous genera and species appear and rapidly evolve. Nannoliths, and especially nannoconids, show a progressive increase in diversity, abundance and degree of calcification through time, which have been documented in both Atlantic and Tethys oceans (Nannofossil Calcification Event – NCE, Bornemann et al., 2003; NCEs, Casellato, 2009).
Calcareous nannofossil biostratigraphy, relative and absolute abundances have been investigated on selected Tethyan land sections (Southern Alps, Northern Italy) in order to integrate calcareous nannofossil events with the polarity chron sequence and, partly, with calpionellid biostratigraphy. Analyses have been performed on un-heated magneto-core end-pieces, using both simple smear slides and ultra-thin sections (7-8μm thick). Calcareous nannofossil absolute abundances, performed on ultra-thin sections, have been also investigated on the DSDP Site 534 from Central Atlantic Ocean, in order to compare nannofossil patterns in different paleogeographic settings and to point out their supraregional importance. All calcareous nannofossil zones and subzones proposed for the Tithonian-Berriasian interval (NJ-19; NJ-20a, NJ-20b; NJK-A, NJK-B, NJK-C, NJK-D; NK-1, Bralower et al. 1989) have been recognized.
Quantitative studies indicate that nannolith taxa (firstly F.multicolumnatus, then C.mexicana, finally P.beckmannii) increase significantly in abundance, size and calcification degree gaining lithogenetic proportion (NCE1, Casellato 2009): the abundance acmes are reached in discrete steps between calcareous nannofossil Zones NJ-20 and NJK-A. Nannoconids rapidly evolve across the J/K boundary, reaching lithogenetic abundances from calcareous nannofossil Subzone NJK-C upward (NCE2, Casellato 2009), when highly calcified conical morphotypes (N.wintereri, N.steinmannii minor, N.kamptneri minor) appear. This event correlates with the middle CM19n to the CM18r interval and the ‘explosive’ appearance of small globular Calpionella alpina (C.alpina “acme”).
Calcareous nannofossil quantitative studies permit to identify additional potential events, characterized by an increase in size, calcification degree and abundance of nannoliths. Calibration with magnetostratigraphy indicates that these trends could be very useful as new bio-horizons in identifying the lower Upper Tithonian and for locating the J/K boundary. The speciation of highly calcified nannoconids and their remarkable increase in volume and abundance, increase the stratigraphic resolution of the J/K boundary time interval.
Bornemann, A., Aschwer, U. and Mutterlose, J., 2003. The impact of calcareous nannofossils on the pelagic carbonate accumulation across the Jurassic-Cretaceous boundary. Palaeogeography Palaeoclimatology Palaeoecology, 199(3-4): 187-228.
Bralower, T.J., Monechi, S. and Thierstein, H.R., 1989. Calcareous nannofossil Zonation of the Jurassic-Cretaceous Boundary Interval and Correlation with the Geomagnetic Polarity Timescale. Marine Micropaleontology, 14: 153-235.
Casellato C.E. (2009) - Causes and consequences of calcareous nannoplankton evolution in the Late Jurassic: implications for biogeochronology, biocalcification and ocean chemistry. PhD Thesis, 116 pp., Università degli Studi di Milano, Scuola di Dottorato “Terra, Ambiente e Biodiversità”, Dottorato di ricerca in Scienze della Terra, Ciclo XXI
Change in the earth system and calcareous nannofossil evolution: does any linkage exist? An example from the Late Jurassic Tethys Ocean
Full text linkIn the Late Jurassic calcareous nannoplankton experienced a progressive increase in diversity, abundance and degree of calcification, culminating in the Middle Tithonian – Berriasian interval (Calcareous Nannofossils Zone NJK and NK1 – Bralower et al., 1989). Were there any linkages between calcareous nannoplankton evolution and geologic, palaeoceanographic or palaeoclimatic events?
Upper Oxfordian - Berriasian selected sections from the Southern Alps (N Italy) have been analyzed for calcareous nannofossil biostratigraphy, relative and absolute abundances and palaeofluxes. Data were compared with litho-magneto-chemostratigraphy and available information on the tectonic, palaeoceanographic and palaeoclimatic regime.
A calcareous nannofossil increase in diversity, abundance and calcification occurred, inducing a major change in pelagic sedimentation from predominantly siliceous (Radiolarite fm. and lower part of the Rosso ad Aptici fm.) to mostly calcareous (upper part fo Rosso ad Aptici fm. and Maiolica fm.). In particular, an impressive speciation started in the Tithonian, including the first occurrence and early diversification of nannoliths and nannoconids. The increase in abundance of coccoliths and nannoliths affected the ocean carbonate system, especially because of the high rates of some nannolith calcification.
These nannoplankton evolutionary events occurred during times of low spreading rates, low pCO2, low Mg/Ca ratio, cool climatic conditions and relatively oligotrophic oceans. Available data suggest that calcareous phytoplankton was stimulated by environmental stability rather than perturbations. This is consistent with modern coccolithophorid distribution, showing highest diversity and abundance as well as calcification in stable oligotrophic oceanic areas.
A precise stratigraphic control allows to model the Late Jurassic nannofossil speciation episode and the abundance increase of high-calcified genera (Conusphaera, Polycostella, Faviconus, Nannoconus), evaluating environmental causes and consequences of evolution.
Preliminary results suggest that the Late Jurassic nannoplankton evolution was mostly controlled by the following factors: A) a decrease in pCO2 due to decreased spreading rate and/or increased weathering rate (87Sr/86Sr); B) a decrease in oceanic Mg/Ca ratio values promoting low Mg-CaCO3 and CaCO3 biomineralization (nannofossils fertilization sensu Stanley, 2006); C) cool climatic condition (Price, 1999)
Causes and consequences of calcareous nannoplankton evolution in the Late Jurassic : implications for biogeochronology, biocalcification and ocean chemistry.
Full text linkAbstract
The Jurassic was a time of important changes in the ocean/continent configuration: important reorganization of oceanic and climatic condition are underlined by a most remarkable widespread shift from mostly siliceous to mainly calcareous sedimentation. The beginning of Late Jurassic was a time of exceptionally low carbonate accumulation rates, while the uppermost Jurassic is characterized by high sedimentation rates and the deposition of calcareous nannofossil oozes. During the Late Jurassic calcareous nannoplankton experienced a progressive increase in diversity, abundance and degree of calcification, culminating in the Middle Tithonian – Lower Berriasian interval.
Upper Callovian – Lower Berriasian sections from the Southern Alps (Northern Italy) have been analyzed for calcareous nannofossil biostratigraphy; selected sections (Southern Alps )and the DSDP Site 534 A (Atlantic Ocean) were investigated for calcareous nannofossil relative and absolute abundances and to derive paleo-fluxes. Data were compared with litho-magnetostratigraphy, calpionellid biostratigraphy, where available, and information on the tectonic, palaeoceanographic and palaeoclimatic regime.
Biostratigraphic investigations led to revise the biostratigraphic schemes available for Late Jurassic, and a new scheme is proposed for Tethyan Realm. Quantitative investigations and derived paleo-fluxes show a calcareous nannofossil increase in diversity, abundance and calcification, inducing a major change in pelagic sedimentation from predominantly siliceous (lower part of the Rosso ad Aptici) to mostly calcareous (Rosso ad Aptici – Maiolica transition and Maiolica). In particular, an impressive speciation started in the Tithonian, including the first occurrence and early diversification of nannoliths and nannoconids. The increase in abundance of coccoliths and nannoliths affected the ocean carbonate system, especially because of the high rates of some nannolith calcification. These nannoplankton evolutionary events (NCEs) occurred during times of low spreading rates, low pCO2, low Mg/Ca ratio, cool climatic conditions and relatively oligotrophic oceans. Available data suggest that calcareous phytoplankton was stimulated by environmental stability rather than perturbations. This is consistent with modern coccolithophorid distribution, showing highest diversity and abundance as well as calcification in stable oligotrophic oceanic areas. A precise stratigraphic control allows to model the Late Jurassic nannofossil speciation episode and the abundance increase of high-calcified genera (Conusphaera, Polycostella, Faviconus, Nannoconus), evaluating environmental causes and consequences of evolution. The results suggest that the Late Jurassic nannoplankton evolution was mostly controlled by the following factors: A) a decrease in pCO2 due to decreased spreading rate and/or increased weathering rate (87Sr/86Sr); B) a decrease in oceanic Mg/Ca ratio values promoting low Mg-CaCO3 and CaCO3 biomineralization (nannofossils fertilization sensu Stanley, 2006); C) cool climatic condition (Price, 1999).
The Tithonian time interval provides examples of accelerated intra- and inter-generic evolutionary rates (a speciation event) during a time period of environmental stability, in absence of coeval environmental change evidences. It provides an excellent opportunity to investigate nannoplankton evolutionary behaviour, and on the basis on the achieved stratigraphic and time framework, evolutionary trends of calcareous nannoplankton were quantified: example of Philetic Gradualism, Punctuated Equilibrium and Punctuated Gradualisms as well were described
Does environmental stability stimulate species renovation?
No full textThe Tithonian-Berriasian time interval is characterized by a major calcareous nannoplankton speciation episode: several coccolith and nannolith genera and species first appear and rapidly evolve, reaching a high diversity, abundance, and calcification degree.
The history of calcareous nannoplankton indicates that times of accelerated rates of radiations (or extinctions) generally correlate with global changes in the geosphere, hydrosphere and atmosphere suggesting that evolutionary patterns are intimately linked to environmental modifications (Roth, 1989; Bown et al., 2004; Erba, 2006). Nevertheless, the Tithonian-Berriasian interval provides examples of intra- and intergeneric accelerated evolutionary rates (an origination event) during a time period of general environmental stability, in absence of coeval environmental change evidence. The Tithonian - Early Berriasian can be regarded as a “quiet” interval as far as the C cycle is concerned; the δ13C curve shows a gradual minor decline after the Oxfordian anomalies and prior to the Valanginian event.
The Tithonian-Berriasian speciation episode provides an excellent opportunity to study modo and tempo of calcareous nannoplankton evolution relative to absent environmental change, which is believed to be instrumental for driving biological evolution. Nannofossils have been investigated in sections from the Tethys and Atlantic oceans in order to discriminate among local, regional or global causes, and to verify possible diachroneity in calcareous phytoplankton evolution and/or in response to global changes. Calcareous nannofossil species richness, first and last occurrences and relative abundance were achieved.
Different evolution modes have been proposed since Darwin’s Evolutionary Theory: Phyletic Gradualism (Darwin, 1859), Punctuated Equilibrium (Gould & Eldredge, 1977) and Punctuated Gradualism (Malmgren et al., 1984). Phyletic gradualism holds that new species arise from slow, steady transformation of populations providing gradational fossil series linking separate phylogenetic species. Punctuated gradualism implies long-lasting evolutionary stasis interrupted by rapid, but gradual phyletic transformation without lineage splitting. Punctuated equilibrium explains the appearance of new species by rapid speciation occurring in small peripheral isolated populations, followed by migration to other areas where fossil sequence usually shows a series of sharp morphological breaks. The Tithonian-Berriasian nannoplankton speciation episode is characterized by the first occurrence of several new nannolith genera (Conusphaera, Polycostella, Pseudolithraphidites and Lithraphidites, Nannoconus, Assipetra, Braarudoaphaera and Micrantolithus), few new coccoliths genera (Umbria, Rhagodiscus, Cruciellipsis) and several coccoliths and nannolith new species. Most new species rapidly evolved generating related new species or subspecies, often in a time interval shorter than two millions of years, providing examples of all speciation modes.
The appearance of highly calcified nannoplankton and its evolution in the Tithonian-Berriasian interval were possibly controlled by abiotic factors, such as seawater chemistry (Mg/Ca ratio and pCO2) and temperature (cool climatic episode). On the other hand this speciation episode corresponds to an interval of environmental stability, probably favoring diversification and expansion of calcareous nannoplankton, adapted to oligotrophic oceans.
Nannoliths seem to have experienced all three evolutionary modes, while coccoliths provide examples for only two of them. Evolutionary patterns in the studied interval permit the following considerations: at specific level both nannoliths and coccoliths gradually evolve in time intervals of more that 1 Ma, while at generic level a rapid speciation is most common.
Bown, P.R., Lees, J.A., Young, J.R. (2004). Calcareous nannoplankton evolution and diversity through time. In: Thierstein, H.R., Young, J.R. (Eds.), Coccolithophores. From Molecular Processes to Global Impact. Springer-Verlag, Berlin, pp. 481 – 508.
Darwin, C. (1859). L’Origine delle specie. In: L’Evoluzione. Newton, 1994
Erba, E. (2006). The first 150 million years history of calcareous nannoplankton: Biosphere - Geosphere interaction. Paleogeogr. Paleoclimatol.Paleoecol. 232, 237-250.
Gould, S.J. & Eldredge, N. (1977). Punctuated equilibria: the tempo and mode of evolution reconsidered. Paleobiology 3:115-151.
Malmgren, B.A., Berggren, W.A. & Lohmann, G.P. (1984). Species formation through Punctuated Gradualism in Planktonic Foraminifera. Science 225, 317-319.
Roth, P.H. (1989). Ocean circulation and calcareous nannoplankton evolution during the Jurassic and Cretaceous. Palaeogeogr. Palaeoclimatol. Palaeoecol. 74, 111 – 126.
Stenseth, N.C. & Maynard Smith, J. (1984). Coevolution in ecosystems: rred queen evolution or stasis? Evolution 38, 870-880.
Van Valen, L. (1973). A new evolutionary law. Evolutionary Theory 1:1-30
The Toarcian Oceanic Anoxic Event and the emplacement of the Karoo-Ferrar Large Igneous Province: calcareous nannoplankton evidence trace major climate and paleoceanographic changes
No full textCalcareous nannofossil biostratigraphy across the Toarcian Oceanic Anoxic Event (T-OAE) (Colle di Sogno section, Southern Alps) and their response to high CO2 concentration: preliminary results.
No full textTithonian Nannofossil Calcification Events and the Shatsky Rise Plateau emplacement: is there a relationship?
No full textReview of calcareous nannofossil events in the Late Tithonian-Early Berriasian time interval: implications for the definition of the base of the Cretaceous
No full textCalcareous nannofossils have been proved to be a powerful biostratigraphic tool for dating and for interregional correlations of Jurassic to Recent marine sequences. The latest Jurassic-earliest Cretaceous time interval was crucial for calcareous nannoplankton that experienced a major speciation episode, with the appearance of new taxa that persisted through the rest of the Mesozoic. The dramatic change in calcareous nannofloras, becoming rapidly dominated by highly calcified nannoconids across the J/K boundary interval provides the opportunity to achieve high-resolution biostratigraphic data, amplifying the possibility of dating and correlating.
We collected new data and critically revised published nannofossil biostratigraphies for the Tithonian-Berriasian interval to evaluate reproducibility and variability of individual biohorizons with the aim of determining primary, secondary and local events. We estimated the age of nannofossil events relative to magnetostratigraphy, calpionellid and ammonite zonations in the interval spanning magnetochrons (CM) CM20 to CM17. Our work intends to contribute to the Berriasian Working Group effort aimed at the improvement of a self-reinforcing stratigraphic matrix useful for the future choice of the GSSP of the base of the Cretaceous.
Our database comprises sites from different paleogeographic settings (Europe, America, Atlantic Ocean). We critically evaluated sampling rates, nannofossil preservation and abundance, and taxonomy applied by individual specialists. We privileged calibrations against magnetostratigraphy to highlight reproducibility of single nannofossil events against magnetochrons, and more specifically their time variability within CM19 and CM18. We also evaluated nannofossil events relative to ammonite and calpionellid biostratigraphies.
The main results of our critical revision, point out a sequence of several first occurrences (FO) and that some nannofossil events are more reproducible and reliable than others. We confirm the nannofossil potential as a stratigraphic tool for high-resolution dating and long-ranging correlations, a tool able to overcome paleoprovincialism often shown by ammonites.
The majority of the events characterizing the J/K boundary interval are the FOs of some Nannoconus species, specifically: N. globulus minor and N. erbae correlating with the topmost part of CM20N and lowermost part of CM19R, respectively. The FOs of N. globulus globulus and N. wintereri correlate with the middle part of CM19N, and the FOs of N. steinmannii minor and N. kamptneri minor correlate with the lowermost part of CM18R. Other events in the J/K boundary interval include the FOs of Rhagodiscus asper, Cretarhabdus surirellus, Cruciellipsis cuvillieri, Hexalithus geometricus, and Cretarhabdus octofenestratus.
The appearance and diversification of nannoconids are accompanied by a major increase in their total abundance. Consequently, the J/K boundary interval is also characterized by distinctive changes in “nannofacies” that are reproducible in the Tethys and Atlantic Oceans. Such assemblage changes further corroborate the nannofossil biostratigraphic characterization of the J/K boundary interval and might be used as additional marker levels.
Based on new and literature data, we propose the FO of N. steinmannii minor as the most robust and globally recognized event close to the J/K boundary, as documented in all available nannofossil biozonations of the past four decades. This bioevent correlates with the basal portion of CM18R.
If ammonite or calpionellid biohorizons are taken to define the base of the Cretaceous, the FOs of N. globulus globulus, H. geometricus, N. wintereri and C. cuvillieri approximate the base of both the Calpionella (B) Zone and ammonite jacobi-grandis Zone in the middle part of CM19N
Paleoceanografia del Giurassico nella Tetide occidentale : l’archivio geologico del Bacino Lombardo
No full textL’importanza litogenetica dei nannofossili calcarei del Triassico Superiore nella sezione di Pizzo Mondello
No full textI nannofossili calcarei (NC) sono parti micrometriche mineralizzate (coccoliti e nannoliti) dell’esoscheletro di alghe coccolitoforidi. Le forme più antiche sono carniche, e nel Triassico Sup. sono riconosciute ~12 specie. I NC acquistano significato lito-genetico nel Giurassico Inf., quindi l’origine della micrite pelagica pre-giurassica é ancora incerta.
La sezione del Triassico Sup. di Pizzo Mondello (M.ti Sicani, Sicilia – Muttoni et al. 2004; Balini et al. 2010), è selezionata per quantificare il reale contributo dei NC alla micrite pelagica, attraverso analisi qualitative e quantitative su 70 sezioni ultrasottili (spessore ~7 μm), usando un microscopio ottico polarizzatore a 1250 ingrandimenti. Le abbondanze assolute sono raccolte contando tutti gli esemplari in 1mm2 di sezione ultrasottile.
Sono identificati otto morfotipi di NC (A, B, C, D, E, F, G, H), tutti nannoliti. Dal punto di vista tassonomico, E corrisponde certamente a P. triassica; F e B a Thoracosphaera; G è assimilabile a P. triassica, ma presenta una crosta esterna probabilmente diagenetica; A è documentato anche da Preto et al. (2012), ma non si riscontrano similitudini con taxa noti. Le altre forme osservate non sono assimilabili a specie note e sono previsti ulteriori studi per chiarirne la posizione. In generale i NC sono più abbondanti nella parte inferiore della sezione (0m-base del “Livello di Breccia”, 146,5m), dove l’abbondanza totale è doppia rispetto alla parte superiore (158m-424,65m). I morfotipi A, C e E sono i più comuni.
Analisi morfometriche su ogni esemplare contato permettono di calcolate l’area (A), volume (V) e le masse (m) di ogni nannolite riconosciuto. A e F sono i più grandi, quindi i più calcificati (A=24835 pg, F=45304 pg); D H e C sono i più piccoli e meno calcificati (D=740 pg, H=795 pg, C=1050 pg). Per quantificare il contributo dei NC alla micrite, sono calcolati i flussi di ogni taxon considerando abbondanze assolute e tasso di sedimentazione. A e F, presentando V, m e abbondanze maggiori, controllano le variazioni delle abbondanze assolute e dei flussi. Le altre tipologie contribuiscono meno alla micrite sia per le piccole dimensioni sia per la scarsa abbondanza. I risultati mostrano che i NC sono litogeneticamente importanti, rappresentando fino al 15% in area della micrite.
Nelle unità litostratigrafiche I e II (Muttoni et al. 2004), abbondanze assolute e flussi sono più alti che nell’unità IV (Muttoni et al. 2004). Considerando la suddivisione dell’unità II in Facies A, B e C (Balini et al. 2010), si nota corrispondenza tra abbondanze, flussi e Facies: valori maggiori corrispondono a Facies C, mentre valori minori corrispondono alle Facies B ed A. L’abbondanza totale qui presentata e quella relativa calcolata da Guaiumi (2010) sono confrontabili e mostrano valori doppi in corrispondenza della Facies C. Poichè l’abbondanza totale dei NC è proporzionale al grado di nodularità, forse abbondanze e flussi sono influenzati dalla condensazione, con dissoluzione preferenziale di coccoliti/nannoliti e della componente più minuta della micrite, concentrando le forme più robuste e resistenti.
I NC nel Triassico Sup. non avevano abbondanze tali da contribuire in modo determinante alla micrite, ma erano già componenti apprezzabili della sedimentazione pelagica.
BIBLIOGRAFIA
Balini M., Bertinelli A., Di Stefano P., Guaiumi C., Levera M., Mazza M., Nicora A., Preto N., Rigo M. (2010). The Late Carnian-Rhaetian succession at Pizzo Mondello (Sicani Mountains). Albertiana 39: 36-57.
Guaiumi C. (2010). Sedimentology of Upper Triassic hemipelagic micrites (Lagonero and Sicani Basins). Tesi di Dottorato. 91 pp., Università di Padova, Scuola di Dottorato di Ricerca in: Scienze della Terra, Ciclo XXI.
Muttoni G., Kent D.V., Olsen P.E., Di Stefano P., Lowrie W. Bernasconi S.M., Hernandez F.M. (2004). Thethyan magnetostratigraphy from Pizzo Mondello (Sicily) and correlation to the Late Triassic Newark astrochronological polarity time scale. GSA Bull. 116: 1034-1058.
Preto N., Rigo M., Agnini C., Bertinelli A., Guaiumi C., Borello S., Westphal H. (2012a). Triassic and Jurassic calcareous nannofossils of the Pizzo Mondello section: a sem study. Iiv. It. Strat. Paleont. 118 (1): 131-141.
Preto N., Willems H., Guaiumi C., Westphal H. (2012b). Onset of significant pelagic carbonate accumulation after the Carnian Pluvial Event (CPE) in the western Tethys. Facies. DOI 10.1007/s10347-012-0338-9
- …
