Stratigraphic significance of carbon isotope variations in the shallow-marine Seis/Siusi Permian-Triassic boundary section (Southern Alps, Italy)

Abstract

Carbonate carbon‐isotope values from the Permian–Triassic (P–T) boundary section at Seis/Siusi (Southern Alps, Italy) show a trend similar to that in numerous other P–T boundary sections worldwide. Values decrease from 3.2 ‰ (V‐PDB) in the upper Bellerophon Limestone Formation (Late Permian) to a minimum of –1.7 ‰ in the lower Mazzin Member. This minimum may represent the P–T boundary. The overall declining carbon‐isotope trend is interrupted by a ca. 1 ‰ positive excursion in the higher Tesero Oolite Horizon. This positive peak is located at a higher lithostratigraphic level than a comparable peak in the adjacent Pufels section, which suggests that the Tesero Oolite Horizon in the Seis section is stratigraphically slightly older than in the Pufels section, and this is also suggested by palaeomagnetic correlation. It is therefore concluded that the base of the Tesero Oolite Horizon does not reflect a synchronous “current event” but is slightly diachronous, a result that was previously shown by biostratigraphic correlation. Nevertheless, this suggestion should be verified by further detailed litho‐, magneto‐ and chemostratigraphic analysis of other P–T sections in the Southern Alps. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carbon isotope signatures of latest Permian marine successions of the Southern Alps suggest a continental runoff pulse enriched in land plant material

“…These shortterm positive d 13 C shifts represent a chemostratigraphic marker which occurs somewhat below the low-latitude marine event horizon (cf. Kraus et al 2009;Richoz et al 2010). Palynological data from Misci (Cirilli et al 1998) indicate that the event horizon (EH) occurs slightly above their sample S80 (indicated in Figure 4).…”

“…We include in the following discussion published carbonate and organic carbon isotope data for the PTB succession in Seis/Siusi (Kraus et al 2009;Siegert et al 2011;Figs 1, 4) for comparison (see also Horacek et al 2010). In general, it is difficult to biostratigraphically define precisely the PTB in the Southern Alps because the sediments are rare in conodonts.…”

“…The conodont Hindeodus, however, is reported from the Southern Alps at the Reppwand (Gartnerkofel core) and Pufels/Bula/Bulla (Schaenlaub 1991;Perri 1991;Farabegoli & Perri 1998), allowing the definition of the PTB and its correlation to the carbon isotope curve (see . This definition has been used to suggest the possible location of the stratigraphic horizon of the PTB at Seis (Kraus et al 2009;Siegert et al 2011) which can be applied for Misci, too. Following this line of reasoning, the biostratigraphic (conodontdefined) PTB in this section is drawn at the carbonate carbon isotope minimum (cf.…”

“…The negative carbon isotope excursion at the PTB is superimposed by additional positive and negative d 13 C events (e.g., Korte et al 2004bKorte et al , 2004cRichoz 2006;Algeo et al 2007Algeo et al , 2008Kraus et al 2009;Cao et al 2010;Richoz et al 2010;Takahashi et al 2010;Shen et al 2012aShen et al , 2012bShen et al , 2012c. A characteristic, abrupt, $ 1 ‰ positive d 13 C excursion, interrupting the general latest Permian negative trend, occurs just before the low-latitude marine event (mass extinction) horizon (Korte et al 2004b(Korte et al , 2004cRichoz 2006;Kraus et al 2009;Cao et al 2010;Richoz et al 2010;Takahashi et al 2010).…”

“…The negative carbon isotope excursion at the PTB is superimposed by additional positive and negative d 13 C events (e.g., Korte et al 2004bKorte et al , 2004cRichoz 2006;Algeo et al 2007Algeo et al , 2008Kraus et al 2009;Cao et al 2010;Richoz et al 2010;Takahashi et al 2010;Shen et al 2012aShen et al , 2012bShen et al , 2012c. A characteristic, abrupt, $ 1 ‰ positive d 13 C excursion, interrupting the general latest Permian negative trend, occurs just before the low-latitude marine event (mass extinction) horizon (Korte et al 2004b(Korte et al , 2004cRichoz 2006;Kraus et al 2009;Cao et al 2010;Richoz et al 2010;Takahashi et al 2010). This positive excursion has recently drawn attention, and authors argued that it might have been caused by enhanced nutrient availability, producing an algal and/or bacterial bloom (Payne & Kump 2007;Takahashi et al 2010), deposition of coaly fly ash from Trap volcanism (Grasby et al 2011), or enhanced terrestrial influx due to climatic perturbations (Krassilov & Karasev 2009;Takahashi et al 2010;Siegert et al 2011; see also Wacey et al 2007).…”