Joachimski et al. carried out geochemical investigations to study seawater temperature changes and their potential triggers across the Permian-Triassic Boundary (PTB). Unfortunately, in our opinion, an incorrect biochronology was applied to define the PTB, and the existing alternative was not considered, nor the reasoning explained. As a consequence, Joachimski et al. report diachronous temperature changes for the investigated Chanakhchi section with respect to the global stratotype section and point (GSSP) in Meishan, China. This discrepancy disappears when the, in our view, correct position of the PTB is adopted by using the proper biochronology.

Permian-Triassic boundary (PTB) sections have been intensively investigated since Abich (1878), and this event boundary has been identified as the severest extinction in the Phanerozoic (Sepkoski, 1989). The PTB section in Meishan, China was proposed as a GSSP (global stratotype section and point; Yin et al., 1996) and was finally voted for and ratified in 2001 (Yin et al., 2001). Within this process, the conodont Hindeodus parvus was selected as the index fossil for the base of the Triassic. The reasons for the catastrophic turnover of flora and fauna are currently still not completely revealed and are the topic of ongoing research.

The Chanakhchi (former Sovetashen) section in Armenia, Transcaucasia region, refers to a section in an area that has been studied from the nineteenth century (Abich, 1878; Arthaber, 1900; Bonnet, 1912a, 1912b, 1919; Bonnet and Bonnet, 1947; Noethling, 1905; Stoyanow, 1910, 1942) and since then more or less continuously investigated (e.g., Rostovtsev and Azaryan, 1973; Aslanian, 1984; Kotlyar et al., 1983; Baud et al., 1989; Grigoryan, 1990; among others; also see literature in Rostovtsev and Azaryan, 1973). The latest studies on the PTB are: Zakharov et al. (2005), performing a stratigraphical update of Chanakhchi aiming to improve correlation between the various Armenian sections; Friesenbichler et al. (2018), concentrating on the microbial sediments in the immediate boundary interval and basalmost Triassic; and Joachimski et al. (2020), performing a seawater temperature investigation from the Upper Permian to Lower Triassic. Their first results were published by Grigoryan et al. (2015). All of these latest studies base their stratigraphy either on the conodont investigation of the Chanakhchi section by Grigoryan (1990), or on its revision and reinterpretation by Zakharov et al. (2005).

Grigoryan (1990) identified the first Hindeodus parvus on top of the basal microbialites (in the same position and in agreement with Rostovtsev and Azaryan [1973], based on their reporting of the first occurrence of the bivalve Claraia). Zakharov et al. (2005), restudied Gregorian's materials and moved the PTB ∼3 m below to the base of the microbial limestone above the boundary clay due to identifying Hindeodus parvus at that location, thereby shifting the boundary downward with respect to Grigoryan (1990). Interestingly, already in 1983, the PTB in Chanakhchi was identified there by Kotlyar et al., 1983. Friesenbichler et al. (2018) place the PTB by following Zakharov et al. (2005), whereas Grigoryan et al. (2015) persistently draw the boundary “…in the uppermost stromatolitic limestones…”, and Joachimski et al. (2020) find “…Hindeodus parvus in sample CH44 from the topmost basal calcimicrobial buildup…” (placing the PTB ∼2 m above the base of the microbial limestone, according to their fig. 3). Further confuses the fact that Joachimski et al. (2020) document Hindeodus parvus in their fig. 6 from sample CH43, almost 1 m below their PTB.

As the revision of conodonts in Zakharov et al. (2005) was carried out by H. Kozur, who has defined and published most of the relevant conodont species around the PTB (e.g., Hindeodus parvus, identified in the nearby Dorasham section, Hindeodus praeparvus, Hindeodus magnus, etc.) we have no doubt that his determinations are correct. Zakharov et al. (2005) further explain the discrepancies between their and Grigoryan's interpretation. It is therefore unclear to us, why this revision has not been considered and adopted by Joachimski et al. (2020), as the authors knew about it, judging from their citation of the respective articles. The reporting of Hindeodus parvus from CH43, below their sample CH44, also contradicts the positioning of the PTB by Joachimski et al. (2020), unless this is a typing error. Furthermore, we deem it very problematic not to address such an existing stratigraphic discrepancy (with respect to the other studies) and not to explain why a differing biochronology is applied, as in the present situation, the reader is misled to assume that the position of the boundary is unequivocal and undisputed. For example, this deviating position of the PTB in Chanakhchi by Joachimski et al. (2020) potentially might have motivated Chen et al. (2020) to search for a “…conservative option…” to present results in agreement with them. Though speculative, this is an attempt to find an explanation for the, in our opinion, incorrect and illogical placement of the PTB in Abadeh by Chen et al. (2020; see Horacek et al., 2021).

Additional evidence concerning the wrong placement of the PTB in the Chanakhchi section provides the δ13C-curve, as its minimum usually occurs significantly above the PTB (with the exception of results of clay samples that might contain diagenetic calcite) in the upper Hindeodus parvus and/or Isarcicella isarcica Zone (e.g., Horacek et al., 2010; Richoz et al., 2010; Korn et al., 2021).

The consequences of the erroneous placement of the PTB in Chanakhchi result in an incorrect duration of the seawater warming event, which does not only occur from the iranica to the base of praeparvus Zones, but reaches to or even straddles the PTB (also see Horacek et al., 2021). Following the underestimated duration of the temperature change in the Chanakhchi section, Joachimski et al. (2020) wondered about the discrepancies with the Meishan section, where the temperature change occurs over a longer period. Considering the corrected PTB position in the Chanakhchi section, this discrepancy disappears.

We thank the editors B.S. Singer and B. Cramer for their skillful handling. This is a contribution to International Geoscience Programme (IGCP) projects 630 and 710.

Science Editor: Brad S. Singer
Associate Editor: Bradley Cramer
Gold Open Access: This paper is published under the terms of the CC-BY license.