The Norian “chaotic carbon interval”: New clues from the δ ¹³ C _org record of the Lagonegro Basin (southern Italy)

Abstract

A global carbon-isotope curve for the Late Triassic has the potential for global correlations and new insights on the complex and extreme environmental changes that took place in this time interval. We reconstruct the global δ 13 C org profile for the late Norian, improving on sparse published data from North American successions that depict a "chaotic carbon-isotope interval" with rapid oscillations. In this context, we studied three sections outcropping in the Lagonegro Basin (southern Italy), originally located in the western Tethys. The carbon-isotope profiles show four negative excursions correlatable within the Lagonegro Basin. In particular, a negative shift close to the Norian/Rhaetian boundary (NRB) appears to correlate with that observed in the North American δ 13 C org record, documenting the widespread occurrence of this carbon cycle perturbation. The 87 Sr/ 86 Sr and 187 Os/ 188 Os profiles suggest that this negative shift was possibly caused by emplacement of a large igneous province (LIP). The release of greenhouse gases (CO 2) to the atmosphere-ocean system is supported by the 12 C enrichment observed, as well as by the increase of atmospheric pCO 2 inferred by different models for the Norian/Rhaetian interval. The trigger of this strongly perturbed interval could thus be enhanced magmatic activity that could be ascribed to the Angayucham province (Alaska, North America), a large oceanic plateau active ca. 214 ± 7 Ma, which has an estimated volume comparable to the Wrangellia and the Central Atlantic Magmatic Province (CAMP) LIPs. In fact, these three Late Triassic igneous provinces may have caused extreme environmental and climate changes during the Late Triassic.

New magnetobiostratigraphic results from the Ladinian of the Dolomites and implications for the Triassic geomagnetic polarity timescale

“…This age is coherent with the U-Pb age estimate of Wotzlaw et al (2014) for a level close to the last occurrence of the Norian bivalve Monotis subcircularis at the Levanto section in Peru (205.50 ± 0.35 Ma). The Norian/Rhaetian boundary at Pignola-Abriola is also approximated by a negative δ 13 C org excursion (Maron et al, 2015;Rigo et al, 2016;Bertinelli et al, 2016) that seems to be present in other marine sections (Zaffani et al, 2017). Previously, the Norian/Rhaetian boundary was placed in the Steinbergkogel section, GSSP candidate for the Rhaetian Stage, at the FO of M. posthernsteini sensu latu, and was magnetostratigraphically correlated to Newark levels at around 209 Ma (Krystyn et al, 2007a,b).…”

“…Carbon Isotopes Excursions (CIE) in Brumano and Italcementi Quarry sections are from Zaffani et al (2018); CIEs in St. Audrie's Bay section are from Hesselbo et al (2002Hesselbo et al ( , 2004. Base of Daxatina canadensis ammonoid Subzone is from Prati di Stuores, Italy (Ladinian base;Broglio Loriga et al, 1999;Mietto et al, 2012), FOs of conodonts Metapolygnathus parvus and Carnepigondolella gulloae are from Pizzo Mondello, Italy (Norian base; Mazza et al, 2012a), FO of conodont Misikella posthernsteini s.s. is from Pignola-Abriola, Italy (Rhaetian base; Maron et al, 2015;Rigo et al, 2016;Bertinelli et al, 2016;Zaffani et al, 2017), FO of Psiloceras spelae is from Levanto, Peru (Hettangian base; Schoene et al, 2010;Guex et al, 2012;Wotzlaw et al, 2014). See text for discussion.…”

“…Marzoli et al, 2004;Hesselbo et al, 2007;Deenen et al, 2010;Dal Corso et al, 2014;Davies et al, 2017) and associated with the end-Triassic extinction event (e.g. Hesselbo et al, 2002;Guex et al, 2004;Ward et al, 2004;Richoz et al, 2007;Van de Schootbrugge et al, 2008;Tanner, 2010;Whiteside and Ward, 2011;Hillebrandt et al, 2013;Zaffani et al, 2017;Lucas and Tanner, 2018), are located in the murky SA5n.2n-SA6n magnetostratigraphic interval of the St. Audrie's Bay section (Hesselbo et al, 2002(Hesselbo et al, , 2004Hounslow et al, 2004) and in the BIT2r-BIT5n interval of Brumano/Italcementi Quarry (Muttoni et al, 2010;Zaffani et al, 2018), which broadly correspond to the E22n-E24n interval in the Newark-APTS (Fig. 13).…”

Sedimentology and carbon isotope stratigraphy of the Rhaetian Hochalm section (Late Triassic, Austria)

“…13) might represent a new chemostratigraphic marker that was not identified clearly in previous low-resolution datasets (Korte et al, 2005) and could represent another carbon cycle perturbation of the Rhaetian preceding the ETME (see Ruhl & Kürschner, 2011;Mette et al, 2012). It remains unclear whether this marked increase in carbon isotopes is a feature that is essentially prescribed to the lower Rhaetian or whether it could represent the recovery part of a Norian/Rhaetian negative excursion previously identified by several authors (Preto et al, 2013;Muttoni et al, 2014;Maron et al, 2015;Zaffani et al, 2017). The longer lasting slight decrease of the carbonate carbon isotopes from the upper part of Unit 2 to the middle of Unit 3, as well as the > 1‰ increase in the upper part of Unit 3 and within Unit 4 is paralleled by trends in δ 13 C org .…”

BEGEOSCIENTIST a young network - I Congresso Nazionale dei Giovani Geoscienziati

“…The Norian-Rhaetian biotic crisis occurred in concomitance of a general d 13 C org perturbation that led to a negative carbon isotope excursion at the NRB, associated with the disappearance of bivalve Monotis and the first appearance of conodont Misikella posthernsteini. The chertylimestone sequence of Pignola-Abriola section, candidate GSSP for the Rhaetian Stage (Rigo et al, 2016), has been broadly studied for both biostratigraphy and carbon geochemistry (e.g., Giordano et al, 2010;Maron et al, 2015;Rigo et al, 2016;Zaffani et al, 2017;Rigo et al, 2020). The rock-magnetic data here presented (ARM, IRM, c, etc.)…”