Traditionally, the Permian-Triassic boundary in the Tunguska Basin has been placed at the base of the Tutonchanian RS because of the most drastic sedimentologic and biotic change in the Permian-Triassic of Siberia (Vladimirovich, 1967; Prinada, 1970; Betekhtina et al., 1984; Betekhtina et al., 1986; Dobruskina, 1994; Sadovnikov, 2008; Mogucheva, 2016). This position of the boundary was utilized in the all of the official geologic maps in the Tunguska Basin of Russia (Kovrigina, 2000; Permyakov et al., 2012; Paderin et al., 2016; Lipenkov et al., 2018; Varganov et al., 2018).

The CA-IDTIMS U-Pb dates were obtained from the layered intrusions and sills in Tunguska Basin and Taymir (Figures 1–3). Seventeen sill/intrusion samples within the Tunguska Basin yielded dates ranging from 251.813 ± 0.065 to 251.354 ± 0.088 Ma (Burgess and Bowring, 2015). Although Burgess and Bowring (2015) claimed that the eruptions were before and during the mass extinction, most of the obtained ages with the uncertainties postdate the onset of the extinction at 251.941 Ma established in South China (Burgess et al., 2014). The oldest range of the uncertainty from the sample G22-63 from the Norilsk intrusion 251.907 ± 0.067 Ma slightly overlaps the onset of the extinction determined in South China (Burgess 2014). Two U-Pb dates, sample KZ1799-1195, 251.801 ± 0.088 Ma from the Talnakh intrusion and sample G22-65, 251.813 ± 0.065 Ma from the Norilsk intrusion, (Distler et al., 1999) slightly overlap the cessation of the extinction as determined in South China (Burgess et al., 2014). In addition to the lack of the Permian radioisotopic ages for the Tunguska Basin sills and intrusions, the relationship of the intrusive rock with the Triassic volcano-sedimentary succession in the region was assumed but has never been precisely constrained. (Paderin et al., 2016; Rad'ko, 2016). According to the data of Burgess and Bowring (2015), most of the studied sills and intrusions are of Induan (Early Triassic) in age, whereas all traps were placed in the Permian (Figure 2, column 2, see also Figure 3 in Burgess and Bowring, 2015). The latter would mean that an extensive pre-extrusive feeder intrusive-sills system of the of Permian age must be existed in the region, but that one is unknown. Only the small Ergalakh intrusive complex, which is developed around the Norilsk area, has been proposed to be a potential feeder for the latest Permian Ivakin Fm, because of the cross-cutting relationship with the Paleozoic rocks only (Kovrigina, 2000; Ryabov et al., 2001). The scale of the Ergalakh intrusive complex within the entire Tunguska Basin is minimal.

The cross-cutting relationships, petrology, and geochemistry of most of the intrusions in the Norilsk region suggest co-magmatic relationships of the intrusive and extrusive rocks (Zolotukhin et al., 1986; Zolotukhin and Al'Mukhamedov, 1991; Ryabov et al., 2014; Krivolutskaya, 2016). Therefore, according to these data most of the traps are supposed to be Triassic in age. A recent study of the mean geomagnetic directions of the Norilsk group layered intrusions (Norilsk 1, Norilsk 2, and Chernogorsky; Figures 1–3) and Talnakh group of layered intrusions (Talnakh, Oganer, and Zayachiy Creek) disclose their similarity to the geomagnetic signature of the upper Olenekian – lower Anisian Mokulaev (4.3°–5.9°) and Kharaelakh formations (2.9°–4.9°) of Anisian age (Figure 2). At the same time paleomagnetic directions of the intrusions of the Talnakh group of layered intrusions (Talnakh, Oganer, and Zayachiy Creek) reveal the lowest angular differences with the Olenekian Moronga-Mokulaev formations (2.1°–3.5°) (Figure 2) (Latyshev et al., 2020). This difference between formations and intrusions suggest the comagmatic emplacement of these lavas and intrusions as previously suggested by the cross-cutting relationship and the geochemistry (Ryabov et al., 2014; Krivolutskaya, 2016) (Figure 2).

The U-Pb dates from the intrusions (Burgess and Bowring, 2015) integrated with the geomagnetic secular variation data (Figure 2, column 1), manifest the discrepancy between these two datasets especially with regards to the succession of the extrusive rocks and radioisotopically dated intrusives (Davydov, 2021 in press). The geomagnetic secular variation was measured in the open pit (Medvezhyi Creek), the underground Skalistyi and Oktyabrskyi mines and on several natural outcrops (Figure 1C) (Latyshev et al., 2020), whereas U-Pb dates were obtained from the wells at different location (Figure 1C) (Burgess 2014), and the correlation between these two datasets (geomagnetic secular variation and U-Pb dates), except when that they were collected from several multi-layered intrusive bodies, is not possible (Figure 1C).

Radioisotopic U-Pb ages in well G22 in the Norilsk-1 intrusion occur in the opposite direction of the supposed stratigraphy in the well, i.e. the oldest age from sample G22-63-5 occurs near the top and the youngest age from sample G22-105-2 is near the bottom (Davydov, 2021 in press). This suggests a complicated internal structure of the multilayers and their different origin during at least a half-million or more years (Figure 3A). A similar case was reported recently in the Norilsk region, where the Norilsk-type layered intrusive has been intruded into the Ergalakh intrusive complex (considered to be late Permian) and thus the latter is interlayered with the former timewise in an upside-down position (Figure 3C) (Sereda et al., 2020). All this suggests that to recognize the true age of the geomagnetic secular variation, their measurements and the radioisotopic dating must be obtained from the same samples.

The layered intrusions from the other regions are similar in their internal structure, i.e. Precambrian layered intrusions of southern Montana (Figure 3B), where some layers were constructed out of stratigraphic superposition (Wall et al., 2018). This is certainly similar to the 0.3–0.4 Myr case in the Norilsk-1 cross-cut layered intrusive, which was crystallized in multiple phases over a timeframe of about half a million years, and the timing and nature of interaction with the surrounding sedimentary rocks was much more complicated than proposed in recent models (Svensen et al., 2018). A comprehensive radioisotopic calibration in the main multi-layered intrusive complexes in Tunguska Basin is required to prove the link between intrusive magmatism in the region with the end-Permian mass extinction in South China and elsewhere.

Three more CA-ID-TIMS dates from the intrusions in the Taymir Peninsula, northern Siberia, were reported recently. All of them are yielded the Triassic ages: TP-55 - 251.64 ± 0.11; TP-42 - 251.46 ± 0.13 and TP-43 - 250.60 ± 0.22 (Augland et al., 2019). The latter sample reveals a non-overlapping clustering in the age distribution, whereas the older cluster possessing a large uncertainty 251.67 ± 0.41, the maximum age of which slightly overlapped with the end-Permian extinction. This cluster is interpreted to represent initial crystallization in the magma system and probably emplacement of an early pulse of magma. The younger cluster represent the final emplacement and crystallization of the monzonite-diorite horizon within the Dumtalei layered intrusive complex (Augland et al., 2019). These data are quite consistent with the data from the Tunguska Basin (Burgess and Bowring, 2015), but also suggest generally a post-extinction age of the intrusive magmatism in Taymir. Besides, at least two (or more) magmatic crystallization events (magma pulses) are proposed in the Dumtalei layered intrusive complex, like multiple crystallization events in the Norilsk-1 layered intrusion (see discussion regarding G-22 well, Figures 3A,C). The extrusive volcanism in Taymir also appears in the late Changhsingian Syradasai and Shaitan formations with the late Permian flora Cordaites candalepensis (Zalesskyi), Zamiopteris schmalhausenii Schwedov, Nephropsis ingenta Schwedov (Proskurin et al., 2015). This age is consistent with the Changhsingian volcanism in the Ivakin Fm of the Tunguska Basin.

Thus, although the U-Pb dates from the intrusions of the Norilsk and Taymir regions only roughly constrain the onset of the SLIP, what we can conclude at this point is that SLIP generally postdates the end-Permian extinction. Furthermore, inferences about the volcanic, biotic, environmental, and climatic events associated with SLIP need to be reconsidered and better and more directly documented. The layered intrusive rocks in the Tunguska Basin and Taymir regions represent a complex multi-stadial crystallization within an intrusive body and cannot be employed for the evaluation of the sedimentary, and biotic processes during Permian-Triassic transition until their crystallization history can be precisely calibrated with the CA-IDTIMS method. The minimal influence of the intrusive rocks on the surrounding pre-Triassic sedimentary succession and especially on the Carboniferous-Permian coals in the Tunguska Basin is documented in the recent review paper (Davydov, 2021 in press).

The only coal gap in the Earth history lasted from approximately 252.94 (the extinction event in South China) through the late Anisian-Ladinian and is known to be of global scale (Retallack et al., 1996). The very last coal in the Permian of the Norilsk region is documented in the upper Ivakin Fm (Paderin et al., 2016; Rad'ko, 2016). No coals are known or ever been documented in the Tutonchanian, Dvurogian and Putoranian RS in the entire Tunguska Basin (Cherepovskiy, 2001). The first thin, cm-scale coal layers are documented in the volcaniclastic upper Anisian and Ladinian. The coals are getting more frequent in the Upper Triassic (Kazakov, 2002). This coal record in the Tunguska Basin is consistent with the Triassic age of the trap’s succession in the Tunguska Basin.

According to the Burgess and Bowring (2015) model, the pyroclastic eruption started sometime around 255.58 Ma or even earlier, but this hypothesis requires additional confirmation. Only acidic volcanism has been documented in the coal-bearing successions of the Tunguska Basin (Cherepovskiy, 2001; Paderin et al., 2016). Burgess and Bowring (2015) suggested that almost the entire sedimentary-traps succession, except the Samoed Formation in the Norilsk region is Permian in age (Figure 2, column 2, see Figure 3 in Burgess and Bowring, 2015), although none of the Permian plant fossils ever been found in the traps (Radchenko and Schwedov, 1940; Mogucheva, 1973; Gor, 1985; Mogucheva and Krugovykh, 2009).

Flora is one of the most sensitive indicators of environments and hence of climate change (Taylor et al., 2009). The abnormally large Siberian LIP volcanism at the Permian-Triassic transition that caused, as proposed, the most severe of global extinctions (Svensen et al., 2009; Hinojosa et al., 2012; Clapham, 2013; Retallack, 2013; Black et al., 2014; Bond and Wignall 2014; Burgess et al., 2014; Chu et al., 2016; Svensen et al., 2018; Clapham and Renne, 2019; Shen et al., 2019; Feng et al., 2020; Vajda et al., 2020) is supposed to have caused even stronger extinction in the region of this LIP, i.e. in Tunguska Basin (Jones, 2015; Black et al., 2021, in press; Mather and Schmidt 2021, in press). The reality, at least with the flora in the Tunguska Basin, is the opposite of what most people proposed.

The Permian and Triassic flora record in the Tunguska Basin and surrounding regions (Kuznetsk Basin, East Kazakhstan, Taymir, Verkhoyanie) and has been well studied for more than 100 years, because it is the primary correlation tool in these commercially important regions (coal, oil, gas, diamonds) (Zalessky, 1912, Zalessky, 1918; Zalessky and Tchirkova, 1935; Radchenko and Schwedov, 1940; Neiburg, 1948; Andreeva et al., 1956; Neiburg, 1958; Meyen, 1966; Sadovnikov, 1967; Vladimirovich, 1967; Radchenko, 1969; Mogucheva, 1973; Radchenko, 1973; Orlova and Sadovnikov, 1974; Vladimirovich, 1980, Vladimirovich, 1981; Meyen, 1982; Betekhtina et al., 1984; Betekhtina et al., 1986; Sadovnikov, 1987b; Dobruskina, 1994; Dobruskina and Durante, 2004; Sadovnikov, 2008; Mogucheva and Krugovykh, 2009; Mogucheva, 2016; Sadovnikov, 2016).

The biostratigraphic and paleomagnetic data suggests that the Tutonchanian and lower Dvurogian RS belongs to the Induan and that the rest of the Dvurogian and lower Putoranian RS correlates with Olenekian, while the rest of the Putoranian and Uskelterian RS correlates with the Anisian (Figure 2) (Kazakov, 2002; Mogucheva, 2016). This correlation is generally consistent with the Ivakinian-Tutonchanian co-magmatism of the Ergalakh intrusive system and with the Putoranian co-magmatism of the Norilsk, Talnakh, Kharaelakh and most other intrusions in the Norilsk regions (Zolotukhin et al., 1986; Ivanov et al., 2013; Ryabov et al., 2014; Krivolutskaya, 2016; Rad'ko, 2016; Latyshev et al., 2020).

Two provinces are recognized within the Angarian paleofloristic Realm -- Siberian and Sub-Angarian that are divided into several subprovinces: Verkhoyanian, Tunguska-Verkhoyanian and Taymir-Kuznetsk (Figure 5C) (Meyen, 1990; Krassilov, 2003; Dobruskina and Durante, 2004). The Tunguska Basin is a part of the Tunguska-Verkhoyanian province, except for the Norilsk region, which belongs to the Taymir-Kuznetsk subprovince. The distinctive feature of the Tunguska-Verkhoyanie subprovince during the late Permian is the occurrence of the pteridosperms Comia, Callipteris and Compsopteris along with numerous ferns. The Tunguska-Verkhoyanie “cordaites” dominate in almost all localities and horsetails are found in greater numbers. We suggest including those into the Vojnovskyales order as a group of enigmatic gymnosperms. This assumption came from the fact that these “cordaites” are often associated with generative organs of Vojnovskya (Neiburg, 1955; Meyen, 1990).

The flora of the Taymir-Kuznetsk subprovince during this time is characterized by the voinovskian-peltasperms assemblage (Kaierkan and Ambarnaya Fms in Norilsk region), which comprises numerous voinovskians, including Rufloria, and abundant seeds of the genus Tungussocarpus, and the appearance of Samaropsis and Condomajella seeds (Gor, 1965; Gor, 1985). The ferns are rare, poor in diversity and include Pecopteris, Prynadaeopteris или Todites. The occurrence of Psygmophyllum foliage suggests similarity of the late Permian flora of Taymir and Norilsk with that of the Preuralian and Pechora basins (Pukhonto et al., 1998; Naugolnykh, 2007).

The late Permian Euromerian flora in the Northern arid belt along the northern slope of the Variscan orogenic belt (Germany, France, Caucasus) was predominantly xerophytic suggesting relatively warm and dry climate with no coal accumulation (Chumakov and Zharkov, 2003; Roscher and Schneider, 2006; Naugolnykh, 2007). The climate in the Angaran Realm was temperate and very wet with abundant coals that occur up to the top of the middle Changhsingian (Figure 2) (Cherepovskiy, 2001; Dobruskina and Durante, 2004; Davydov, 2021; Davydov et al., 2021). The upper Permian in the Kuznetsk Basin possessed the thickest coals (wet environments) in the entire Siberia (Cherepovskiy, 2001). The occurrence of the number of a late Permian provinces and subprovinces in the Angara Realm, suggests that the climate in the realm was also quite differentiated, similar to the current climate with a comparable differentiation of recent terrestrial biomes (Figure 5) (Foley et al., 2005; Dinerstein et al., 2019). Both the Taymir and Norilsk regions during late Permian – Early Triassic were located approximately at the latitude of the Kuznetsk Basin (Figure 4) and the flora from the Taymir and Norilsk regions directly correlates with the late Permian flora of the Kuznetsk Basin (Gor, 1965; Porokhovichenko, 2006; Mogucheva and Naugolnykh, 2010).

The major climate change occurs in Tunguska and in the Kuznetsk Basin sometimes during the second half of the Changhsingian, around 252.75 Ma (Davydov et al., 2021). At this time, the biomes differentiation is sharply decreased and the Euramerian -- Angaran Realms boundary shifted northward approximately to 15°. No provinces or subprovinces are recognized in the Angaran Realm at this time (Figure 5B). The provinciality decrease is distinguished by the distribution of Early Triassic plant associations known in all paleofloristic realms-provinces. For example, the widely distributed Early Triassic genus Pleuromeia and lycopsids with Annalepis-like scales have been found in both tropical and temperate (Siberia) climatic zones (Dobruskina, 1994; Retallack, 1997; Grauvogel-Stamm and Lugardon, 2001; Grauvogel-Stamm and Ash, 2005). The taxonomic composition of the Triassic conifer-fern flora testifies to the widest migration of plants to the central regions of Angarida both from the peripheral parts of the Angara kingdom and from the tropical belt (Mogucheva, 1996, Mogucheva, 2016). Such a migration, obviously, indicates a sharp weakening of floristic differentiation, and elimination of most paleofloristic barriers between different paleofloristic realms and the provinces-subprovinces that existed in the Late Paleozoic (Dobruskina and Durante, 2004). The latest-Permian - Early Triassic in the Angaran realm is associated with the climatic optimum, i. e. warmer and drier climate that is similar to the mid-Holocene climatic optimum in the region (Monserud et al., 1998). The current global climate warming is also resulting in a shift of the current temperate forest and boreal biomes northwards (D'Orangeville et al., 2016).

Progressive decline of the floral richness is observed in both basins during the late Permian (Figure 4). In the Tunguska Basin, the Wuchiapingian flora is quite diverse (94 species and 41 genera), but drastically reduced in richness in the Changhsingian to 38 species and 24 genera (Figure 4). The chronostratigraphy in the Tunguska Basin is not as precise as in Kuznetsk Basin and the turnover in the region occurs somewhere within the Ivakinian - Early Tutonchanian time (Changhsingian-Early Induan) (Figure 4). The floral richness (over 100 species) that is observed in the middle-late Tutonchanian is highest within the late Permian and Triassic in the region (Figure 4). The origination rate there is quite high, and the extinction rate is very low. Since the early Olenekian the extinction predominates over the origination and floral richness progressively declined towards the end of the Anisian. In the late Anisian only origination is observed in Tunguska Basin (Figure 4).

In the Kuznetsk Basin the floral richness is also declines, but slower and progressively towards the early Changhsingian. The essential taxonomic floral turnover in Kuznetsk Basin occurs in the mid-Changhsingian at approximately 252.75 Ma and ∼800 kyr before the Permian-Triassic boundary in South China (Davydov et al., 2021) (Figure 4). This level coincides with the boundary between the Tailugan and Maltsev formations and this is the former position of the regional Permian-Triassic boundary in Siberia that was utilized for many years and distinguished by the extinction of one small group of the wet-preferrable Vojnovskyales (“cordaites”) and by the appearance of many new taxa of ferns, cicades, pteridosperms, lycopsids, sphenopsids and other (Vladimirovich, 1967; Mogucheva, 1973; Betekhtina et al., 1986), All Paleozoic “cordaitian” (Vojnovskyales) at this time disappear and were replaced by more diverse new conifer-fern flora (46 species and 34 genera). The flora richness and origination in the Kuznetsk Basin in the Triassic progressively increased in Induan and Olenekian and no other extinction observed there (Figure 4). In the Kuznetsk Basin the floral origination in the region strongly predominates over extinction during Early Triassic and util early Anisian. Accordingly, the floral richness in Kuznetsk Basin in Triassic progressively increased and reaches the maximum in the early-middle Anisian, when it is stabilized. The volcanic activity in the Tunguska Basin ceased in the latest Putoranian (Naldrett et al., 1996; Fedorenko et al., 2000; Krivolutskaya, 2016; Paderin et al., 2016). The Late Triassic floral record overall is poor for the Tunguska Basin and in all of Siberia (Mogucheva, 2005).