IS THERE ANY EVIDENCE OF AN OCEANIC ANOXIC EVENT?

Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2014
GEOCHEMICAL CHARACTERIZATION OF THE NORIAN-RHAETIAN TRANSITION:
IS THERE ANY EVIDENCE OF AN OCEANIC ANOXIC EVENT?
Ph.D. candidate: MARIACHIARA ZAFFANI, I course
Tutor: Dr. MANUEL RIGO
Co-advisor: Dr. CLAUDIA AGNINI
Cycle: XXIX
Abstract
The Pignola-Abriola section (southern Italy) provides geochemical evidence of anoxic conditions around the Norian-Rhaetian
boundary, such as high Total Organic Carbon (TOC) values and a prominent negative δ13Corg excursion. The latter also has
been recognized in the North America realm, suggesting that the Pignola-Abriola anoxic conditions could be indicative of a
global anoxic state of the ocean, that is an Oceanic Anoxic Event (OAE). Geochemical proxy records (e.g., TOC, δ13C, δ15N,
87
Sr/86Sr, 187Os/186Os) of different paleogeographic areas are required to prove this hypothesis. The TOC and δ13Corg data
obtained from four Tethyan sections appear to support this supposition and, moreover, highlight the onset of pulsed NorianRhaetian volcanic activity. Further analyses are necessary to demonstrate the global extension of the OAE and the occurrence
of the Norian-Rhaetian volcanic activity. If they are proved to be true, these phenomena might offer us a new insight on the
end Triassic mass extinction.
Introduction
The End-Triassic mass extinction (ETE) is one of the five most important and studied extinction of
the Phanerozoic (e.g., Ward et al., 2001; Hallam, 2002; Tanner et al., 2004). Nevertheless, its mode,
tempo and causes are still debated. Different authors agree that the ETE is the result of stepped and
prolonged episodes of biotic crises throughout the Late Triassic that eventually culminated in the
Triassic-Jurassic boundary (TJB, 201.3±0.2 Ma) mass extinction (e.g., Hallam, 2002; Tanner et al., 2004),
which appears to be associated with the emplacement of the Central Atlantic Magmatic Province (CAMP)
(Palfy et al., 2001; Hesselbo et al., 2002; Marzoli et al., 2004; Dal Corso et al., 2013) that, in turn, implies
a severe perturbation of the carbon cycle (Ward et al., 2004; Van de Schootbrugge et al., 2008; Tanner,
2010). In particular, a negative carbon isotope excursion has been recognized at the TJB worldwide (Palfy
et al., 2001; Hesselbo et al., 2002). Preceding this main excursion, a less intense δ13Corg negative shift has
been reported from the North America realm at the Norian-Rhaetian boundary (NRB, ≈208.5 Ma) (Ward
et al., 2001; Sephton et al., 2002; Whiteside & Ward; 2011).
Notably, a δ13Corg negative excursion paired with an increase in the Total Organic Carbon (TOC)
content and a negative shift in the nitrogen isotope record (δ15N) has been recognized at the NRB also in
the Tethys realm at the Pignola-Abriola section (Lagonegro Basin, southern Italy), suggesting the
occurrence of anoxic conditions (Zaffani, 2013). If these modifications of paleoenviromental conditions
are proved to be recorded worldwide, they could be indicative of global anoxic conditions (e.g., Jenkyns,
2010) or, in other words, of an Oceanic Anoxic Event (OAE). The occurrence of such an important
perturbation of the carbon cycle is in perfect agreement with the scenario expected during the ETE. In
fact, OAEs are related to profound changes in the climate and paleoceanographic conditions and are thus
able to induce/control the fractionation of many isotope systems (e.g., C, N, S, Fe, Mo, and U) and the
mobilization and incorporation of certain trace elements into minerals and organic matter (e.g., Jenkyns,
2010).
Aim of the project
The aim of this PhD project is to perform geochemical analyses on Late Triassic geological sections
located in different paleogeographic areas and depositional settings in order to verify the occurrence of a
global perturbation of the carbon cycle and the possible consequent development of globally expanded
anoxic conditions at the NRB. These results will be eventually integrated with T/J datasets to allow a
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2014
long-term geochemical record, which is crucial to understand the detailed biotic and abiotic evolution
during the ETE.
Geochemical analyses, including isotope analyses of δ13Corg, δ13Ccarb, δ15N, 88Sr/86Sr, 87Sr/86Sr,
187
Os/186Os, Mo, and TOC content, will be performed in all the studied sections.
Analytical methods
The δ13Corg, δ13Ccarb and δ15N analyses are performed through a Delta V Advantage Mass
Spectrometer connected to a Flash HT Elementar Analyzer (σ=0.3‰) in the Spectrometry Laboratory of
the Department of Geosciences, University of Padova. All samples are washed in millipore water and a
representative portion of each sample is then analyzed. Few grams of sediment are reduced into a fine
powder using a Retsch RM0 grinder and dried overnight at 40°C. The powders are acid-washed overnight
with 10% HCl, neutralized in millipore water, dried at 40°C overnight and wrapped in tin capsules.
Voids, blanks (empty tin capsules), international (IAEA CH-6 = -10.45‰, IAEA CH-7 = -32.15‰,
Coplen et al., 2006) and in-house isotope standards are included in every set of analyses
The TOC analyses are performed in collaboration with Prof. G. Concheri (Department of Agricultural
Biotechnology, University of Padova) using a Vario Macro CNS Elementar Analyzer (relative standard
deviation σ=0.5%) in the Biotechnology Laboratory of the Department of Agronomy, Food, Natural
resources, Animals and Environment (DAFNAE), University of Padova. The powdered samples are
treated with a 10% HCl solution in silver capsules, dried on a hot plate at 50°C and analyzed against
Sulfanilamide standard (N=16.25%; C=41.81%; S=18.62%; H=4.65%).
The 88Sr/86Sr, 87Sr/86Sr and 187Os/186Os analyses will be performed in collaboration with Dr. J. Trotter
and Prof. M. McCulloch, studying biogenic apatite from conodonts using a Neptun Plus MC-ICPMS and
a Triton TIMS (σ=0.000017‰) in the Ocean Institute Laboratory of the School of Earth and
Environment, University of Western Australia, following the in-house methodologies for the preparation
and the treatment of the samples.
Part of the Pignola-Abriola δ13Corg and δ15N analyses were performed by Dr. L. Godfrey in
collaboration with Dr. M. Katz (Department of Earth and Environmental Science, Rensselaer Polytechnic
Institute, Troy, NY) in the Rutgers University Laboratory (Department of Earth and Planetary Science,
Rutgers University, Piscataway, NJ), using a GVI Isoprime CF-IRMS (σ²=0.2‰).
First-year results and preliminary conclusions
During the first year of my PhD program, the Lagonegro Basin has been further investigated at three
localities, Mt. Volturino, Mt. S. Enoc and Madonna del Sirino, where the Norian-Rhaetian transition is
well documented. These sections belong to the Calcari con Selce (cherty limestones) and Scisti Silicei
(cherts and radiolarites) Fms, displaying a good exposure and continuity (Giordano et al., 2010).
These three sections have been analyzed for δ13Corg and TOC content, while the Pignola-Abriola
section has been re-analyzed to improve the existing δ13Corg record. The correlation proposed for the
studied δ13Corg profiles is based on chemostratigraphy and biostratigraphy and highlights a general
negative trend throughout the Late Triassic in the Lagonegro Basin. This long-term trend could be further
subdivided into four short-lived perturbations of the carbon cycle, which age ranges from early Sevatian 1
(upper Norian) to early Hettangian. These δ13Corg short-lived perturbations are all characterized by a
negative shift followed by a recovery phase toward background values. Notably, each negative shift
predates the appearance of a conodont species and is accompanied by high TOC content. In particular, the
Pignola-Abriola δ13Corg profile nicely mimics the δ13Ccarb record reported for the same section by Preto et
al. (2013), thus further confirming that profound perturbations of the carbon cycle actually occurred in
this interval.
A possible explanation for the δ13Corg negative trend recognized in the Lagonegro Basin is the release
of 12C-enriched carbon from a volcanogenic source (e.g., Jenkyns, 2010; Tanner, 2010). This is because
the repeated carbon negative shifts, as well as their durations, are consistent with the pulsed-mode and the
long times typical of a magmatic activity. However, a fundamental difference is invoked between these
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2014
negative carbon shifts: the first three short-term perturbations are suggested to be related to a NorianRhaetian volcanic activity, while the fourth short-term perturbation, known as the “initial negative CIE”
(Palfy et al., 2001, 2007; Hesselbo et al., 2002; Dal Corso et al., 2013), is related to the CAMP volcanic
activity (e.g., Dal Corso et al., 2013). The volcanic origin of the 12C-enriched carbon released during the
younger δ13Corg perturbations is confirmed by the strontium and osmium isotope stratigraphy as illustrated
by Callegaro et al. (2012).
One of the main outcomes of this first year is that the prominent negative δ13Corg shift observed close
to the NRB in the Lagonegro Basin is correlative to negative δ13Corg excursions reported from the North
America realm, suggesting a global extension of this perturbation. Moreover, unlike the other short-term
perturbations, the NRB δ13Corg excursion in the Lagonegro Basin is associated with a decrease in the
87
Sr/86Sr and 187Os/186Os values (high volcanic activity) and by an increase in the TOC content even
during the δ13Corg recovery phase. This peculiar behavior suggests that the input of 12C-enriched carbon,
likely due to magmatic activity, is completely blurred by the effect of an anomalous storage of organic
matter in the sediments. In other words, the presence of organic-rich black shales in the Pignola-Abriola
section is suggestive of high primary productivity and/or preservation of organic matter as well as of
anoxic conditions that results in more positive δ13Corg values. This overwhelms the volcanic effect
(decrease in δ13Corg values) and provides a further recovery mechanism. If anoxic conditions are a global
feature at NRB, the presence of an OAE could also be inferred.
The Pignola-Abriola section, one of the studied section, meets all the requirements for serving as the
Global Stratotype Section and Point (GSSP) for the base of the Rhaetian stage: the section is continuously
outcropping, well accessible and framed in a detailed magnetostratigraphy and biostratigraphy. The
presence of a likely global negative δ13Corg excursion is suggested as the criteria to define the base of the
stage. For these reasons, we proposed the Pignola-Abriola section as GSSP candidate for the base of the
Rhaetian stage.
Next future
I am going to spend some months at the Ocean Institute Laboratory of the School of Earth and
Environment (UWA) collaborating with Dr. J. Trotter and Prof. M. McCulloch. The main motive for this
scientific stay is to acquire the know-out to perform 88Sr/86Sr, 87Sr/86Sr and Sr/Ca analyses on biogenic
apatite of conodonts. The strontium isotopes will provide a further support to the volcanic origin of the
carbon short-term perturbations, possibly assessing the occurrence of Norian-Rhaetian magmatic activity.
Moreover, the Kastelli section (north-western Peloponnese, Greece), recently sampled by Dr. M.
Rigo, and Wombat Basin samples will be analyzed for the δ13Corg, δ13Ccarb, δ15N and TOC content and
compared to the Lagonegro Basin profiles in order to verify the occurrence of the Norian-Rhaetian
magmatic activity and/or NRB OAE. Further Upper Triassic samples from the Lombard Basin will be
collected next September.
All the collected samples will be probably analyzed for the molybdenum isotope composition at the
Rutgers University Laboratory in collaboration with Dr. L. Godfrey (Department of Earth and Planet
Science, Rutgers University, Piscataway, NJ). These analyses are crucial since the concentration and the
isotopic composition of the molybdenum are used as proxies for paleo-ocean redox state.
References
CALLEGARO, S., RIGO, M., CHIARADIA, M., MARZOLI, A., 2012. Latest Triassic marine Sr
isotopic variations, possible causes and implications. Terra Nova, 24, 130–135.
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VERKOUTEREN, R.M., 2006. After two decades a second anchor for the VPDB d13C scale. Rapid
Commun. Mass Spectrom., 20, 3165–3166.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2014
DAL CORSO, J., MARZOLI, A., TATEO, F., JENKYNS, H.C., BERTRAND, H., YOUBI, N.,
MAHMOUDI, A., FONT, E., BURATTI, N., CIRILLI, S., 2014. The dawn of the CAMP volcanism
and its bearing on the end-Triassic carbon cycle disruption. Journal of the Geological Society, 171, 153164.
GIORDANO, N., RIGO, M., CIARAPICA, G., BERTINELLI, A., 2010. New biostratigraphical
constraints for the Norian⁄Rhaetian boundary: data from Lagonegro Basin, Southern Apennines, Italy.
Lethaia, 43, 573-586.
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HESSELBO, S.P., ROBINSON S.A., SURLYK, F., PIASECKI, S., 2002. Terrestrial and marine
extinction at the Triassic-Jurassic boundary synchronized with major carbon-cycle perturbation: A link
to initiation of massive volcanism? Geology, 30, 251-254.
JENKYNS, H.C., 2010. Geochemistry of oceanic anoxic events. Geochem. Geophys. Geosyst., 11, 1-30.
MARZOLI, A., BERTRAND, H., KNIGHT, K.B., CIRILLI, S., BURATTI, N., VERATI, C., NOMADE,
S., RENNE, P.R., YOUBI, N., MARTINI, R., ALLENBACH, K., NEUWERTH, R., RAPAILLE, C.,
ZANINETTI, L., BELLIENI, G., 2004. Synchrony of the Central Atlantic magmatic province and the
Triassic-Jurassic boundary climatic and biotic crisis. Geology, 32, 973-976.
MCELWAIN, J.C., BEERLING, D.J., WOODWARD F.I., 1999. Fossil plants and global warming at the
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PALFY, J., DEMENY, A., HAAS, J., HETENYI, M., ORCHARD, M.J., VETO, I., 2001. Carbon isotope
anomaly and other geochemical changes at the Triassic-Jurassic boundary from a marine section in
Hungary. Geology, 29, 1047-1050.
PRETO, N., AGNINI, C., RIGO, M., SPROVIERI, M., WESTPHAL, H., 2013. The calcareous
nannofossil Prinsiosphaera achieved rock-forming abundances in the latest Triassic of western Tethys:
consequences for the d13C of bulk carbonate. Biogeosciences, 10, 6053–6068.
SEPHTON, M.A., AMOR, K., FRANCHI, I.A., WIGNALL, P.B., NEWTON, R., AND ZONNEVELD,
J.-P., 2002. Carbon and nitrogen isotope disturbances and an end-Norian (Late Triassic) extinction
event. Geology, 30, 1119-1122.
TANNER, L.H., LUCAS, S.G., CHAPMAN, M.G., 2004. Assessing the record and causes of Late
Triassic extinctions. Earth-Science Reviews, 65, 103–139.
TANNER, L.H., 2010. The Triassic isotope record. Geological Society Special Publication, 334, 119138.
VAN DE SCHOOTBRUGGE, B., PAYNE, J.L., TOMASOVYCH, A., PROSS, J., FIEBIG, J.,
BENBRAHIM, M., FOLLMI, K.B., QUAN, T.M., 2008. Carbon cycle perturbation and stabilization in
the wake of the Triassic-Jurassic boundary mass-extinction event. Geochem. Geophys. Geosyst., 9, 1-16.
WARD, P.D., HAGGART, J.W., CARTER, E.S., WILBUR, D., TIPPER, H.W., EVANS, T., 2001.
Sudden productivity collapse associated with the Triassic–Jurassic boundary mass extinction. Science,
292, 1148-1151.
WHITESIDE, J.H., WARD, P.D., 2011. Ammonoid diversity and disparity track episodes of chaotic
carbon cycling. Geology, 39, 99-102.
ZAFFANI, M., 2013. Analisi geochimiche su materia organica (TOC e d15N) ed indagini
biostratigrafiche dell’intervallo Norico-Retico della sezione di Pignola-Abriola, Bacino di Lagonegro,
Potenza. Master thesis.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2014
SUMMARY OF ACTIVITY IN THIS YEAR
Courses:
L. WU, L. SALMASO, L. CORAIN: “Statistics for Engineers”. Department of Mechanical Engineering, University of Padova,
24/01 – 19/02/2014.
M. BORG: “Consolidating skills in English: a multimedial approach”, Department of Geosciences, University of Padova,
01/04 – 30/04/2014
L. GULICK: “Scientific English” Department of Geosciences, University of Padova, 26/05 – 30/05/2014
G. DE RUBEIS: “ArcGIS Online” Department of Mathematics, University of Padova, 30/09/2014
G. CAVAZZINI: “Geochimica isotopica dello Stronzio” Department of Geosciences, University of Padova, 03/10/2014 (still
in progress)
J. ANGEL: “Scientific Communication” Department of Geosciences, University of Padova, 21/10/2014 (still in progress)
Communications:
MARON, M., MUTTONI, G., RIGO, M., BERTINELLI, A., GODFREY, L., KATZ, M.E., ZAFFANI, M., 2014.
Magnetostratigraphic investigation of the Pignola-Abriola section (Southern Apennines, Italy): new constraints for the
Rhaetian chronology. In: 87° Congresso della Società Geologica Italiana e 90° Congresso della Società Italiana di
Mineralogia e Petrologia. Milano, Italy.
RIGO, M., AGNINI, C, BERTINELLI, A., CASACCI, M., CONCHERI, G., GATTOLIN, G., GIORDANO, N., GODFREY,
L., KATZ, M.E., MARON, M., MUTTONI, G., TATEO, F., SPROVIERI, M., STELLIN, F., ZAFFANI, M., New GSSP
candidate for the base of the Rhaetian: the Pignola-Abriola section. In: 87° Congresso della Società Geologica Italiana e 90°
Congresso della Società Italiana di Mineralogia e Petrologia. Milano, Italy.
Posters:
MARON, M., MUTTONI, G., KATZ, M.E., GODFREY, L., ZAFFANI, M., BERTINELLI, A., RIGO, M., 2014.
Magnetostratigraphic data from the Pignola-Abriola section (Southern Apennines, Italy): new constraints for the
Norian/Rhaetian boundary. In: European Geosciences Union General Assembly 2014. Vienna, Austria.
ZAFFANI, M., AGNINI, C., BERTINELLI, A., CONCHERI, G., GALATA’, F., GODFREY, L., KATZ, M.E., RIGO, M.,
STELLIN, F., 2014. Preliminary d13Corg and TOC data from the Lagonegro Basin (Southern Italy) across the NorianRhaetian boundary. In: 87° Congresso della Società Geologica Italiana e 90° Congresso della Società Italiana di
Mineralogia e Petrologia. Milano, Italy.
Publications:
MARON, M., RIGO, M., BERTINELLI, A., KATZ, M.E., GODFREY, L., ZAFFANI, M., AND MUTTONI, G., Editors
decision in progress. Magnetostratigraphy, biostratigraphy and chemostratigraphy of the Pignola-Abriola section: new
constraints for the Norian/Rhaetian boundary. Geological Society of America Bulletin.
RIGO, M., BERTINELLI, A., CONCHERI, G., GATTOLIN, G., GODFREY, L., KATZ, M.E., MARON, M., MUTTONI, G.,
SPROVIERI, M., STELLIN, F., ZAFFANI, M., submitted, The Pignola-Abriola section: a new GSSP candidate for the base
of the Rhaetian Stage. Lethaia.
Teaching activities:
Teaching assistant: 25 hours, “Geologia del Sedimentario”, Prof. C. Stefani, Laurea Triennale in Scienze Naturali (a.a.
2013/2014).
Teaching assistant: 24 hours, “Geologia del Sedimentario”, Dr. A. Breda, Laurea Triennale in Scienze Geologiche (a.a.
2014/2015) (still in progress).
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