“Chaotic Carbon Interval”: New Clues from the Δ13c
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Research Paper GEOSPHERE 13 The Norian “chaotic carbon interval”: New clues from the δ Corg GEOSPHERE; v. 13, no. 4 record of the Lagonegro Basin (southern Italy) 1 1,6 2 3 4 1,5 1,6 doi:10.1130/GES01459.1 Mariachiara Zaffani , Claudia Agnini , Giuseppe Concheri , Linda Godfrey , Miriam Katz , Matteo Maron , and Manuel Rigo 1Department of Geosciences, University of Padova, via Gradenigo 6, 35131 Padova, Italy 2Department of Agronomy, Food, Natural Resources, Animals and the Environment (DAFNAE), University of Padova, Viale dell’Università 16, 35020 Legnaro (PD), Italy 3 figures; 1 supplemental file 3Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey 08854, USA 4Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, 110 8th St., Troy, New York 12180, USA CORRESPONDENCE: 5Department of Earth Sciences “Ardito Desio,” University of Milan, via Mangiagalli, 34, 20133 Milan, Italy mariachiara .zaffani@ studenti .unipd.it 6Institute of Geosciences and Earth Resources–Consiglio Nazionale delle Ricerche (CNR), Via G. Gradenigo 6, 35131 Padova, Italy CITATION: Zaffani, M., Agnini, C., Concheri, G., Godfrey, L., Katz, M., Maron, M., and Rigo, M., 2017, ABSTRACT (e.g., Lucas, 1999; Benton and Twitchett, 2003; Lucas and Orchard, 2004; The Norian “chaotic carbon interval”: New clues from Erwin, 2006); and (2) the end-Triassic mass extinction (e.g., Hallam, 2002; 13 the d Corg record of the Lagonegro Basin (south A global carbon-isotope curve for the Late Triassic has the potential for Tanner et al., 2004; Richoz et al., 2007). The Triassic is also characterized by ern Italy): Geosphere, v. 13, no. 4, p. 1133–1148, doi:10.1130/GES01459.1. global correlations and new insights on the complex and extreme environ- a dynamic climate regime (e.g., Preto et al., 2010; Rigo et al., 2012b; Trotter mental changes that took place in this time interval. We reconstruct the global et al., 2015) and widespread geological and paleontological events, includ- 13 Received 28 November 2016 δ Corg profile for the late Norian, improving on sparse published data from ing humid and warm episodes (e.g., Carnian Pluvial Event, Upper Triassic, Revision received 3 March 2017 North American successions that depict a “chaotic carbon-isotope interval” Simms and Ruffell, 1989, 1990; Simms et al., 1995; Ruffell et al., 2015), vol- Accepted 14 April 2017 with rapid oscillations. In this context, we studied three sections outcrop- canism, and changes in the biosphere (e.g., Raup and Sepkoski, 1982; McEl- Published online 9 June 2017 ping in the Lagonegro Basin (southern Italy), originally located in the western wain et al., 1999; Hallam, 2002; Marzoli et al., 2004; McRoberts et al., 2008; Tethys. The carbon-isotope profiles show four negative excursions correlat- Lucas, 2010; Rigo and Joachimski, 2010; Rigo et al., 2012b; Dal Corso et al., able within the Lagonegro Basin. In particular, a negative shift close to the 2012, 2014; Trotter et al., 2015). Stable isotopes play a critical role in biogeo- Norian/Rhaetian boundary (NRB) appears to correlate with that observed in chemical cycles and therefore can provide important clues of ocean-water 13 the North American δ Corg record, documenting the widespread occurrence chemistry, oxygenation, and productivity of marine environments during the 87 86 187 188 13 of this carbon cycle perturbation. The Sr/ Sr and Os/ Os profiles sug- Triassic. Among these tools, one of the most widely applied is d Corg. This gest that this negative shift was possibly caused by emplacement of a large isotopic system varies in time as a function of productivity, organic carbon 13 igneous province (LIP). The release of greenhouse gases (CO2) to the atmo- burial, and C assimilation pathway (C3 or C4). Therefore, d Corg can provide sphere-ocean system is supported by the 12C enrichment observed, as well essential clues on the evolution of ocean-water chemistry, oxygenation, and as by the increase of atmospheric pCO2 inferred by different models for the productivity of past marine environments (e.g., Hayes et al., 1999; Veizer Norian/Rhaetian interval. The trigger of this strongly perturbed interval could et al., 1999; Payne et al., 2004; Korte et al., 2005; Lucas, 2010; Preto et al., 13 thus be enhanced magmatic activity that could be ascribed to the Angayu- 2012). In particular, excursions in marine d Corg records that can be correlated cham province (Alaska, North America), a large oceanic plateau active ca. globally are often thought to be related to global changes in the carbon cycle, 214 ± 7 Ma, which has an estimated volume comparable to the Wrangellia such as those induced by marine and terrestrial extinction episodes (Berner, and the Central Atlantic Magmatic Province (CAMP) LIPs. In fact, these three 2002; Galli et al., 2005; Payne and Kump, 2007; Korte and Kozur, 2010), which 13 Late Triassic igneous provinces may have caused extreme environmental and are often marked by negative d Corg anomalies. climate changes during the Late Triassic. The carbon-isotope record of the Triassic has been studied in some de- tail, but its interpretation is complex because of the multiple ecological and geochemical controls on this proxy (e.g., Hayes et al., 1999; Veizer et al., 1999; INTRODUCTION Muttoni et al., 2004, 2010, 2014; Payne et al., 2004; Galli et al., 2005, 2007; Korte et al., 2005; Lucas, 2010; Mazza et al., 2010; Preto et al., 2012). A pronounced neg- The Triassic is a key period in Earth’s history, characterized by breakup ative excursion is recorded at the Permian/Triassic boundary with oscillations of the supercontinent Pangea, episodes of biotic crises, and climate fluctu- in the lowermost Triassic, which is characterized by strong isotopic instability For permission to copy, contact Copyright ations (e.g., Ogg, 2012). This period is constrained by: (1) the end-Permian (e.g., Payne et al., 2004; Lucas, 2010). This is followed by a more stable period Permissions, GSA, or [email protected]. mass extinction—the most extensive biotic decimation of the Phanerozoic in the Middle Triassic (Payne et al., 2004; Tanner, 2010) and early Late Triassic © 2017 Geological Society of America GEOSPHERE Volume 13 Number 4 13 | | Zaffani et al. | Norian d Corg record of the Lagonegro Basin (southern Italy) Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/13/4/1133/3995120/1133.pdf 1133 by guest on 27 September 2021 Research Paper 13 13 (Julian, lower Carnian), with steadily rising values of d Corg and d Ccarb likely GEOLOGIC SETTING related to environmental recovery after the Late Permian mass extinction and increasing storage of organic carbon in terrestrial environments (e.g., Lucas, The Lagonegro Basin is located in the Southern Apennines (Italy) and is 2010). The Late Triassic is bracketed by two significant negative shifts, both interpreted as part of the Ionian Sea, a branch of the western Tethys Ocean linked to a large igneous province (LIP). The first occurred in the Carnian and (Ş engör et al., 1984; Catalano et al., 2001; Stampfli and Marchant, 1995; Ciara- is associated with the Carnian Pluvial Event and emplacement of the Wrangel- pica and Passeri, 1998, 2002; Stampfli et al., 2003). The Lagonegro Basin is lia igneous province (e.g., Furin et al., 2006; Dal Corso et al., 2012, 2015). The interpreted as an oceanic basin based on the available seismic lines and mag- second is at the Triassic/Jurassic transition associated with the end-Triassic netic anomaly pattern of the Ionian Sea, which show that the sedimentary suc- mass extinction and emplacement of the Central Atlantic Magmatic Province cession of this area lies upon oceanic crust (e.g., Finetti, 1982; Finetti et al., (CAMP) (e.g., Marzoli et al., 2004; Whiteside et al., 2010; Schaller et al., 2012; 1996; Catalano et al., 2001; Argnani, 2005; Rigo et al., 2007, 2012a; Speranza Dal Corso et al., 2014). The causes of the Triassic carbon-isotope excursions et al., 2012). It consists of shallow to deep basinal pelagic successions, Permian remain a topic of much debate, with the most likely trigger mechanisms be- to Miocene in age (Scandone, 1967; Rigo et al., 2005, 2012a, 2012b; Gior- ing outgassing during volcanic activity, changes in productivity, ocean anoxia, dano et al., 2010). The Lagonegro sequence is subdivided into many tectonic and/or seafloor methane release (e.g., Richoz et al., 2007; Lucas, 2010). These units, accumulated between the Apenninic and Apulian carbonate platforms processes evidently perturbed the global carbon cycle and caused episodes (Mostar dini and Merlini, 1986) during the Apenninic orogenesis and formation of biotic crises (e.g., Rampino and Stothers, 1988; Jones and Jenkyns, 2001; of a part of the Southern Apennines chain (southern Italy). The Upper Triassic Wignall, 2001; Ward et al., 2004; Richoz et al., 2007; van de Schootbrugge et al., in the Lagonegro Basin is represented by the Calcari con Selce and the Scisti 2008; Jenkyns, 2010; Tanner, 2010; Pálfy and Kocsis, 2014, Trotter et al., 2015). Silicei Formations. The Calcari con Selce consists of calcilutites bearing cono- Therefore, a global carbon-isotope curve for the Triassic would have the po- donts, radiolarians, and thin-shelled bivalves (e.g., Halobia), intercalated with tential for global correlation and would provide new insights on the environ- marls, siltstones, and calcarenites (Rigo et al., 2005, 2012a; Giordano et al., mental changes that took place in this period. Muttoni et al. (2014) provide a 2010). Nodules and layers of chert are present throughout this unit, and lime- 13 composite d Ccarb record from the Ladinian (ca. 242 Ma) to present, but the stones show varying degrees of dolomitization. The Scisti Silicei is character- construction of a Triassic organic carbon-isotope record is still in progress. ized by centimeter-thick multicolored cherts, radiolarites, and often siliceous 13 Published d Corg data are especially focused on mass extinction events (i.e., shales (Amodeo, 1999; Bertinelli et al., 2005a; Giordano et al., 2010).