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The Permian–Triassic boundary in the continental series of Eurasia
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Palaeogeography, Palaeoclimatology, Palaeoecology 143 (1998) 273–283
The Permian–Triassic boundary in the continental series of Eurasia Vladlen R. Lozovsky * Geological Prospecting Institute, Miklucho-Maklay Street, 117873 Moscow, Russia Received 15 April 1997; accepted 1 December 1997
Abstract The most important Eurasian sections, where the transitional Permian=Triassic boundary beds are characterized palaeontologically, are found in the Germanic Basin (West European platform), Moscow Basin (East European platform), Tungusska Basin (Siberian platform), Jimsar Basin, Dalongkou area (Tianshan Mountains), and Noyan Somon depression (Mongolia). Usually the Permian and Triassic continental formations formed under distinct palaeogeographic (especially climatic) and palaeotectonic conditions, so the lithological and sedimentological differences between them are pronounced. Difficult problems appear in those regions where the sedimentation at this level proceeded under very similar conditions (Tungusska Basin, Jimsar Basin) across the Permo–Triassic boundary (PTB). Among palaeontological data, the most important for correlation of these continental beds is the tetrapod fauna. Broad interchange between the tetrapod fauna of the Old World continents resulted in the wide distribution during the Late Permian and Early Triassic of common or closely related forms, which enables distant correlations. The PTB is marked by the change of the Late Permian tetrapod communities, dominated by the large herbivore Dicynodon (or closely allied forms), to assemblages that include Lystrosaurus as the most common form. This is recorded in Lower Triassic beds of Eastern Europe, China, Mongolia, India and Siberia. The Upper Permian sporomorph associations (sa) are dominated by striate bissacate pollen, whereas the early Lower Triassic ones are distinguished by the very important role of spores, primarily by cavate trilete (Lundbladispora, Densoisporites) and also by non-striate dissacate (Klausipollenites) and teniate pollen (Lunatisporites). In the oldest horizons of the Triassic, very distinctive species of conchostracans (Falsisca eotriassica Kozur or the closely related form F. verhojanica Molin) appear. The PTB is within a normal polarity zone, formerly considered the lowest palaeomagnetic zone of the Triassic. The boundary beds of two sections (Moscow Basin and Jimsar Basin) may be equally worthy as candidates for the PTB GSSP in the continental series. The preference should be given to the section better characterized and internationally accessible to scientists. The PTB generally accepted for the continental series coincides more or less with the base of the Otoceras concavum ammonite zone of the Boreal province, and with the base of the boundary clay in Tethys. At the same time, it lies clearly below the traditionally adopted PTB in marine sequences at the base of the Otoceras woodwardi zone and also below the First Appearance Datum (FAD) of I. parva in the Meishan section, proposed now as the PTB GSSP (Yin, 1996, The Palaeozoic–Mesozoic Boundary Candidate of Global Stratotype Section and Point of the Permian–Triassic Boundary, China University Geoscience Press, Wuhan, 137 pp.). This demonstrates that the FAD of I. parva can be asynchronous (see Baud, 1996, Albertiana 18, pp. 6–9). That is why in the choice of the PTB GSSP in the marine series it is necessary to take into consideration the generally accepted point of view on the position of PTB in the continental series. 1998 Elsevier Science B.V. All rights reserved. Keywords: Permian; Triassic; conchostracans; continental series; tetrapods; sporomorphs
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1. Introduction One of the characteristic features of the historical stratotype sections of the Permian and Triassic is that their boundary beds are represented by continental deposits. Von Alberti in 1834 began the Trias with the Buntsanstein redbeds, which lie on saliferous Zechstein (Fig. 1). Seven years later, R. Murchison included in the upper part of the Permian the continental redbeds of central Russia, later named the Tatarian by S. Nikitin. Later it was demonstrated that the upper part of Nikitin’s Tatarian (or Vetlugian and Yarenskian in the modern nomenclature) is synchronous with the European Buntsandstein, while the lower part, keeping the name Tatarian until today, is actually of Late Permian age. After the work of Mojsisovics et al. (1895), which placed the lower boundary of the Trias at the base of the Otoceras woodwardi zone of the Himalayas, it was assumed without any fossil evidence, that this boundary in the marine facies corresponds almost exactly to the base of the German Buntsandstein. At present in Eurasia, some regions are known, where the transitional continental PTB beds are characterized palaeontologically. Besides the type areas of the Perm and Trias in Western and Eastern Europe, the sections of the Timano–Petchorian Basin (Eastern Europe), Tungusska Basin (Siberia), Jungar
Basin (Dalongkou area, western China) can be cited. The very important Gondwanan sections of South Africa, India and Antarctica are outside of the scope of this review, but some problems concerning the distribution of the tetrapod fauna in these regions will be touched upon briefly.
2. Methods used for subdividing and correlating continental PTB formations 2.1. Lithological methods Different methods are used for subdividing and correlating continental PTB formations. Lithological methods were the first to be applied because they were basic for the establishment of the first lithostratigraphic units. These are best exemplified by the European Zechstein and Buntsandstein. Recently, it has been demonstrated that the boundary between these two units is diachronous (Wagner, 1987; Kozur, 1989a, 1993a, 1994): in the marginal part of the Germanic Basin there is a gap of differing length, and the asynchronous appearance of the Germanic-looking facies is simultaneous with the disappearance of the saliferous Zechstein Permian facies. This was a case of uninterrupted sedimentation between the Perm and Trias, when the lithological
Fig. 1. The position of the P=T boundary in the historical type areas of the Permian and Triassic systems. Data from: von Alberti, 1834; Murchison, 1841.
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differences near the boundary under question were caused by tectonic and palaeogeographic (including climatic) factors. Lasting a very short time, they should occur asynchronously to some extent in different parts of the sedimentary basin. For this reason, it is difficult to trace the PTB in these regions based on lithological criteria alone. In other regions where there are discontinuities (breaks) in sedimentation at this boundary, the lithological differences between the Triassic and underlying beds of Permian age are very distinctive. For example, in the Lithuanian Basin, a marginal part of the Germanic Basin, the Nyamunskayan suite lies unconformably on the middle horizons of the Zechstein (Z3) and sometimes on the older Palaeozoic to metamorphic Precambrian rocks (Kisnerus and Saidakovsky, 1972). In the Moscow Basin, a clear break in sedimentation can be observed at the PTB. Here, the Vetlugian lies on different horizons of the Tatarian (Lozovsky, 1992), and the lithological differences between them are very distinctive. 2.2. Biostratigraphic methods Biostratigraphic methods are best suited for defining the PTB. Because the broad interchange between the tetrapod communities of the former continents resulted in the wide distribution of common or closely related tetrapods during the Late Permian and Early Triassic, long-distance correlations are possible, and tetrapods are the best fossils for biostratigraphic correlation (Shishkin and Ochev, 1993). The particular importance of this group is linked with the fact that some Lower Triassic amphibian genera are known from both continental and nearshore marine deposits that contain ammonites. This provides a basis for direct correlation between the marine and continental scales. It is commonly believed (Ochev, 1993; Rubidge, 1995; Lucas, 1996) that the boundary under discussion in the continental series is characterized by the change of the Upper Permian tetrapod communities, dominated by the large herbivore Dicynodon, to Lower Triassic assemblages that include the small, hippopotamus-like semi-aquatic Lystrosaurus as the most common form (Fig. 2). Dicynodon and closely allied genera were found in the youngest Upper Permian beds of South Africa,
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China and Russia (Rubidge, 1995; Lucas, 1996), while Lystrosaurus is known to have spread much more broadly. Besides South Africa, China and Russia, it has also been found in India, Antarctica, Mongolia and Siberia. In China, Dicynodon coexisted for some time with Lystrosaurus (Lucas, 1993), but soon after went extinct. Apart from Lystrosaurus, the important linking forms are Proterosuchus, Lidekkerina and related genera (Sennikov, 1992; Shishkin and Ochev, 1993; Rubidge, 1995). The PTB vertebrate transition is recorded most completely in the Moscow Basin of East Europe. As was noted by Ochev, here change did not proceed in the catastrophic way, and he shows the different patterns at particular stratigraphic levels (lower=upper Tatarian, within the upper Tatarian). The lowest of the Upper Permian levels is in the middle part of the Vyatskian horizon, where the Vyasnikovskian fauna appears (Shishkin, 1990). Besides the abovementioned Dicynodon, the small pareiasaurs of the Elginiidae (Ivachnenko, 1992) and the cynodont Nanocynodon seductus Tatarinov (Tatarinov, 1968), it shows the first appearance of Archosauria, a group playing a dominant role in Triassic communities, and Bystrowianidae, now found to extend into the Triassic (Shishkin and Novikov, 1992). Let us examine the change of other groups at the boundary, where the Dicynodon fauna is replaced by the Lystrosaurus fauna, which we believe marks the PTB in the continental series (Lozovsky, 1995). After tetrapods, sporomorph assemblages (sa) are the most efficient for interfacial correlations. The correlation of the sporomorph zonations is shown in Fig. 3. Usually, the Late Permian sa are dominated by striate bissacate pollen, whereas the Lower Triassic ones are characterized by the very important role of spores, primarily by cavate trilete (Lundbladispora, Densoisporites) and also by non-striate dissacate (Klausipollenites) and teniate (Lunatisporites) pollen (Tiwari, 1993; Lozovsky and Yaroshenko, 1994). The PTB sporomorph transition was recently well recorded in the Moscow Basin (Yaroshenko and Lozovsky, 1997). Along with this, it is clearly indicated that the appearance of the typical Lower Triassic taxa and the disappearance of the Upper Permian taxa occurred at different levels
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Fig. 2. Correlation of the P=T boundary beds based on tetrapod assemblages. Data from: Sadovnikov and Orlova, 1994, 1995, Lozovsky, 1995, 1996; (all for Siberian platform) Rubidge, 1995; Cheng et al., 1996.
(Tatarian=Astashichian, Astashichian=Ryabynskian, Ryabinskian=Krasnobakovskian). This is similar to the above-mentioned changes of the tetrapod communities near the PTB. The sa of the lower part of the Vokhmian horizon (beginning with the Astashichian Member, where Lystrosaurus was found) is well correlated with others in the continental facies usually dated as Lower Triassic, i.e., with the Lundbladispora obsoleta–Lunatisporites noviaulensis sa from the lower parts of the Baltic Formation of Poland (Orlowska-Zwolinska, 1984), the sa from the Nyamunskaya suite of Lithuania, and the sa from the upper Guodikieng Formation, western China (Permian and Triassic strata, 1986; Cheng, 1993). Some observable differences between these complexes are closely related to the facial peculiarities of their burial. The characteristic features of the PTB beds consist of the mass expansion of the fungal fossils Tympanicysta stoschiana and other forms (microfloral event of Wood and Mangerud, 1994).
The role of conchostracans is very important, because they are present in fresh- to mesohaline brackish-water deposits, and are sometimes associated with marine facies. This makes them suitable for intercontinental correlations (Kozur, 1993b). For the Permian, some conchostracan zonations are known. Kozur and Seidel (1983) and Kozur (1993b) proposed a zonation for the Germanic Buntsandstein. Fig. 4 shows the correlation of conchostracan zonations. A very distinctive zone (Polygrapta, Megasitum, diverse Leaiida) can be traced in the middle part of the Tatarian (Luptugian Member of the Vyatskian horizon, Russia), the lower part of the Bugariktinskaya suite (Exinian beds), the Lebedevskian horizon, Siberia, the upper part of the Wutonggou Formation and the lower part of the Guodikeng Formation, western China, as well as the Belmont Shale, Australia (Novojilov, 1970; Cheng, 1993; Liu, 1994). The same conchostracans were found in Hungary in pre-Zechstein beds (Kozur, 1989a). In the upper part of the Permian, the genus
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Fig. 3. Correlation of the P=T boundary beds based on sporomorph assemblages.
Falsisca appears (Kozur, 1989b). This event evidently preceded the first record of Lystrosaurus and the L. obsoleta–L. noviaulensis sa. The basal Lower Triassic beds are well correlated by the very distinctive species of Falsisca–F. eotriassica (upper Brockelschiefer, upper Guodikeng) (fide Kozur) and closely related F. verchojanica (Astachishian Member, Russia; Putoranian and Marininskian horizons, Siberia) (Lozovsky, 1995). The role of other animal groups is subordinate. For example, the ostracods, often used for local zonations, are very dependent on facial conditions. For example, at the PTB in the Moscow Basin the large forms of Darwinula and Darwinuloides were replaced by the small and elongate species of Darwinula and Gerdalia, a stenobiont freshwater form (Kuchtinov, 1976). But, the first Gerdalia appears in the upper part of the Tatarian; at the base of the Early Triassic they become predominant. The stratigraphic role of macroflora is exaggerated by some investigators. It should be kept in mind,
as stressed by Meyen (1973), that the transition between palaeophyte and mesophyte floras occurred asynchronously in different regions of the world. Palaeomagnetic methods play a very important role in the subdivision and correlation of the continental redbeds facies, but their application should be checked by palaeontological data.
3. Sections in Eurasia — candidates for the GSSP in the continental series The more interesting sections of Eurasia where the PTB GSSP in continental sequences can be traced are as follows. The Jimsar Basin, Dalongkou area (western China) is characterized by diverse groups (tetrapods, conchostracans, sa, ostracods, etc.) (Cheng, 1993; Cheng et al., 1996). The base of bed 54 of the Dalongkou section was proposed as a candidate for the nonmarine PTB GSSP by Cheng and Lu-
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Fig. 4. Conchostracan zonation of the P=T boundary beds. Data from: Kozur and Seidel, 1983; Kozur, 1993b; Liu, 1994; Sadovnikov and Orlova, 1995.
cas (1993). Subsequently, Liu (1994) lowered the PTB to coincide with the first appearance of the conchostracan Falsisca, but this level evidently lay below the first appearance of Lystrosaurus. It is logical to continue detailed studies of this section with a variety of experts, incorporating especially magnetostratigraphy, palynology and conchostracan palaeontology. The PTB sections of Western Europe are rich in conchostracans, ostracods and sa, but are unsuitable as potential GSSP’s because of the absence of the tetrapod fauna. The very interesting sections in central Russia are in the Moscow Basin, Eastern Europe. One of them is on the Vetluga River, where in the series of exposures the full succession of the PTB beds can be observed. Near the
town of Voskresenskoye, Nyzhegorodskaya district, the youngest Tatarian sandstones of the Molomskaya Member, Vyatskian horizon are exposed, in which a complete cranium of Dicynodon was found (Blom, 1968). Here, these Tatarian beds are overlain by the Vetlugian redbeds, well exposed in the series of exposures upstream on the right bank of the Vetluga River. Near the village Astashicha, in the red clay of the stratotype section of the Astashichian Member, Vokhmian horizon, the complete skeleton of Lystrosaurus georgi Kalandadze was found with the typical complexes of ostracods and Falsisca verchojanica Molin (Kalandadze, 1975; Lozovsky, 1983). In overlying conglomerates of the Ryabinskian Member, Vokhmian horizon (Znamenskoye locality near Astashicha), Tupilakosaurus sp.,
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Contritosaurus sp. and Lystrosauria, genus indeterminate, were found. The second section, which was recently discovered by the author, is situated on the right bank of the Volga River near the town Putcheg (Ivanovskaya district). In the lower part of the exposure variegated marls and clays of the upper Tatarian, considered to have been deposited in brackish water lakes, are exposed. A rich fauna of upper Tatarian ostracods and gastropods was found in these rocks. Above them lies the brown-green sand with a lens of sandstone and conglomerate of the Astashichian Member, in which the canine of a dicynodont (a little larger than the Vetlugian Lystrosaurus according to the conclusion of M.F. Ivachnenko) and the bone of a Lower Triassic labyrinthodont (definition of M.A. Shishkin) were found. The overlying red clays contain Lower Triassic ostracods and conchostracans (Falsisca sp.). At the PTB there is a small break in sedimentation, exemplified by the very small erosional canals and traces of weathering in the underlying marls, etc. A very interesting region for the development of the PTB beds is situated in the Tungusska Basin, Siberia. Here, flood basalt, tuff, and tuffaceous siltstones, sandstones and argilites about 3 km thick accumulated. Some investigators (Dobruskina, 1980; Mogutcheva, 1989; and others) trace the PTB at the base of the volcanogene series where the Mesophyte flora appears. Sadovnikov and Orlova (1994, 1995) go to the other extreme and date all of the tuff-lava beds as Permian, supposing that the upper part of this succession is younger than the Russian Tatarian, being formed during the break in sedimentation in Eastern Europe, which corresponds to the specific Taimyrian stage. In general, the Tungusska succession can be divided into two parts. The lower (tuffogene series), now subdivided by Sadovnikov into Tutontchanian, Lebedevskian and Hungtukunskian horizons, and the upper part formed essentially by lava (Putoranian horizon). The Triquitrites proratus–Lueckisporites virkkiae sa (Yaroshenko, 1990), close to the youngest sa of the Permian Zechstein of Western Europe (Kozur, 1989a), was found in the upper part of the tuffogene series of the Nizhnia Tunguska Basin (Hungtukunskian horizon). These beds are overlain by lava of the Nidymskaya suite (Putoranian hori-
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zon), which are correlated easily with the upper part of the lava flow of the Norilsk region (northwest of the Tunguskaya Basin). This correlation is based on tracing the marker basalt beds (Delutchinskyi, Dagtaliiskyi, Agitkanskyi, Jambukanskyi) and is adopted in all the stratigraphic schemes of the Siberian region. The upper Norilskian basalt, beginning at the Morongovskaya suite, lies discordantly on the underlying Nadezdinskaia suite (Lebedevsky horizon) (G.N. Sadovnikov, pers. commun.). The following arguments can be presented in support of an Early Triassic age for the Norilsky basalt. (1) The presence of Lystrosaurus (?) sp. (Shishkin et al., 1986) in the lower horizons of the Norilskian basalts (Verchnemokulaevskaia suite). (2) The affinities of the conchostracans of Putoranian and overlying Marininskian suites containing Falsisca verchojanica Molin (G.N. Sadovnikov, pers. commun.). The later suite contains also the charophyte Vladimirella karpinskyi (Demin) Said., typical of the lowest horizons of the Eastern European Trias (Saidakovskii, 1990). (3) The definition of the radiometric age of the intrusive rocks of the Norilsky region, correlated with the Mokulaevskyi basalt (248 š 4 Ma) (Campbell et al., 1992), very close to the one of volcanic ash origin (white clay near the PTB boundary, Meishan section: Yin, 1996). The normal polarity of these basalts, which indicate the palaeomagnetic zone of the latest Permian and oldest Trias (Campbell et al., 1992), is not contradictory to this conclusion. The absence of good exposures of the boundary beds is the principal reason for not recommending this region as the stratotype for establishment of the PTB GSSP. Besides the Eurasian regions there are the Gondwanan regions (South Africa, India, Antarctica), where sections with the potential PTB GSSP could be established. At present, the boundary beds of two sections (Moscow Basin and Dalongkou area) may be equally considered as candidates for the PTB GSSP in the continental series. The preference should be given to the section better characterized and accessible for visitation and investigation (including unrestricted sample transport to abroad) by foreign scientists. But, in any case, the final decision can be made only after the establishment of the PTB GSSP in the marine scale.
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4. Correlation of the Permian–Triassic continental and marine scales Before the mutual correlation of the continental and marine scales it is necessary to emphasize that the PTB problem, dating back at least one century, is still far from being resolved. Either of the proposed variants of the PTB placement and consequently a choice of the PTB GSSP in the marine series — traditionally at the base of the Otoceras woodwardi zone (Mojsisovics et al., 1895), at the base of the boreal O. concavum zone (Tozer, 1988; Dagys, 1994), supported by the author, at the base of the conodont zone I. parva (Kozur, 1989b; Yin, 1996 etc.) or at the base of an assemblage conodont zone (Neogondolella meishanensis, N. taylorae, N. carinata and N. orchardi) (Orchard, 1996; Baud, 1996) — has its own shortcoming, and encounters considerable difficulties, when tracing across the diverse biogeographical provinces. At present, Kozur’s view on the partial correspondence of the Changxingian stage (Tethyan province) and Griesbachian stage (Boreal province) (see Kozur, 1989b) is broadly accepted (Krystin and Orchard, 1996). It is confirmed, in particular, by the palynological data which enable the direct correlation of the marine and continental series. The typical L. obsoleta–L. noviaulensis sa from the lower part of the Vokhmian horizon, Moscow Basin and its equivalents (as stated above) are very close, on one hand, to the sa’s (Protohaploxypinus and Taeniaesporites) from the Otoceras beds of Greenland (Balme, 1979), Lower Griesbachian of western Canada (Jansonius, 1962), Sverdrup Basin, Canadian Arctic Archipelago (Fisher, 1979; Utting, 1994) (see Lozovsky and Yaroshenko, 1994; Yaroshenko and Lozovsky, 1997), on the other hand to the sa, determined by Kozur (1989b) from the Lower Tesero-oolites above the event clay with the typical Changxingian conodont H. latidentatus praeparvus, Paleofusulina and mass occurrences of marine fungi. Besides the sa, used for direct correlation between the continental and marine scales, the one proposed by the author for these purposes is the ecotonal method. It is based on S. Meyen’s principle of mutual substitution of indications. It uses the Amphibia, found in the continental facies as well as in the marine, with the ammonites. Such correlation allows
us to correlate the Moscow Basin continental section with the marginal marine one of East Greenland. The amphibian genus Tupilakosaurus, known from the lower Glyptophiceras martini beds up to Proptychites (interval corresponding to the Otoceras boreale–Ophiceras commune zones) was found in the Ryabinskian and Krasnobakovskian Members of the Vokhmian horizon. Right from the base of the Krasnobakovskian Member (Moscow Basin) and the zone of O. commune (Greenland) the amphibian genus Luzocephalus is present (Shishkin, 1980). This correlation (Lozovsky, 1983) is supported by palaeomagnetic data. The lower part of the continental Vetlugian of the Moscow Basin (Astashichian and Ryabinskian Members), as well as the lower part of the Baltic Formation of Poland, has normal polarity (zone N1T) (Lozovsky and Molostovsky, 1993; Nawrocki et al., 1993). Above, it was shown that these beds correlate with the Otoceras beds of East Greenland. Normal magnetization of the zones of O. concavum–O. boreale of the sections of the Arctic Archipelago (Ogg and Steiner, 1989) gives strong support for the former conclusion. The change of polarity from normal to reversed observed at the Ryabinskian=Krasnobakovskian boundary in the Moscow Basin is also marked at the lower boundary of the Ophiceras commune zone of Arctic Canada, which was already correlated by the presence of Luzocephalus. As there is a break below the Otoceras concavum zone in the Canadian section (Tozer, 1988), it remained unclear what was the polarity of the youngest Permian rocks. The palaeomagnetic study of the Meishan section shows that the polarity of Mixed bed 1 (black clay), corresponding to the Otoceras genozone, as well as the underlying boundary clay and uppermost part of the Changxingian stage, is normal (Yin, 1996). This fact provides a perfect analogy with the continental sequence of Poland, where the normal polarity zone embraces not only the lower horizons of the Baltic Formation but also the youngest ones of the Zechstein (Nawrocki et al., 1993). The underlying part of the Changxingian stage in the Meishan section as well as the upper part of the Zechstein have mainly a reversed polarity with a small interval of normal polarity zones This correlation between the continental and marine series is confirmed by the data of Kozur and
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Mock (1993) based on the study of conchostracans. In the Nadaskut Dolomite Member of Hungary, the time equivalent of the lowermost part of the Tesero-oolites of South Alpine sections, the conchostracan Falsisca eotriassica was found, a very important form of the lowest horizons of the continental European Buntsandstein, as well as of the upper Guodikieng Formation of China. F. verchojanica, closely similar morphologically to F. eotriassica, was found in the lowermost Triassic beds of the western slope of West Verchoianian, correlated by Molin (1965) with the Otoceras zone. Above these beds in this region lies the Ustkelterskaia suite with the conchostracan Wetlugites pronus, which was found together with ammonites of the Ophiceras zone (Ophiceras sp., Wordieoceras wordie Spath, etc.) at the eastern slope of the same region (Dagys et al., 1979).
5. Conclusions The lower boundary of the continental series of the Triassic accepted now for Europe and Asia (which corresponds with the appearance of Lystrosaurus, the conchostracan Falsisca eotriassica ( D F. verchojanica), L. obsoleta–Lunatisporites noviaulensis sa), more or less coincides with the base of the O. concavum zone in the Boreal regions and with the base of the boundary clay in the Tethys. It lies clearly below the traditionally adopted PTB in marine sequences at the base of the Otoceras woodwardi zone and also below the first appearance of I. parva in the Meishan section, proposed now as the PTB GSSP by Yin (1996). With this it is possible that the first appearance of I. parva can be asynchronous (see Baud, 1996). That is why in the choice of the PTB GSSP in the marine series it is necessary to take into consideration the generally accepted point of view on its position in the continental series.
References Balme, B.E., 1979. Palynology of Permian–Triassic boundary at Kap Stosch, East Greenland. Medd. Groenl. 200 (6), 1–37. Baud, A., 1996. The Permian–Triassic boundary: recent developments, discussion and proposals. Albertiana 18, 6–9.
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Blom, G.I., 1968. Catalogue the Localities of the Faunistic Remains in the Lower Triassic Deposits of the Middle Povolgie and Prikamie (in Russian). Kazanian University, Kazan, 375 pp. Campbell, Y.H., Czamanske, G.K., Fedorenko, V.A., Hill, R.J., Stepanov, V.D., 1992. Synchronism of the Siberian Traps and the Permian–Triassic boundary. Science 258, 1760–1763. Cheng, Z., 1993. On the discovery and significance of the nonmarine Permo–Triassic transition zone at Dalongkou in Jimsar, Xinjiang, China. N.M. Mus. Nat. Hist. Sci. Bull. 3, 65–67. Cheng, Z., Lucas, S.G., 1993. A possible nonmarine GSSP for the Permian–Triassic boundary. Albertiana 12, 30–44. Cheng, Z., Wu, S., Feng, X., 1996. The Permian–Triassic sequences in the southern margin of the Jungar basin and the Turpan basin, Xinjiang, China. Geological Publishing House, Beijing, 25 pp. Dagys, A.S., 1994. Correlation of the lowermost Triassic. Albertiana 14, 38–44. Dagys, A.S., Archipov, Y.V., Bychkov, Y.M., 1979. Stratigraphyof the Triassic System of North-Eastern Asia (in Russian). Nauka, Moscow, 245 pp. Dobruskina, I.A., 1980. Stratigraphic position of Triassic plantbearing beds of Eurasia (in Russian). Academy of Sciences USSR Order of the Red Banner of Labour Geological Institute, Trans. 346, 163 pp. Fisher, M.J., 1979. The Triassic palynofloral succession in the Canadian Arctic Archipelago. Am. Assoc. Stratigr. Palynol. Contrib. B5, 83–100. Ivachnenko, M.F., 1992. Late Permian faunistic complexes of tetrapods of East Europe and its Gondwanan analogues. In: Paleontology and Stratigraphy of the Continental Permian and Triassic Deposits of Northern Eurasia, Abstracts, Moscow, pp. 14–15. Jansonius, J., 1962. Palynology of Permian and Triassic sediments, Peace River area, Western Canada. Paleontographica B110, 35–98. Kalandadze, N.N., 1975. The first find of Lystrosaurus in the European part of the USSR. Paleontol. J. 4, 140–142. Kisnerus, J.L., Saidakovsky, L.Y., 1972. Stratigraphie der TriasAblagerungen der westlichen und su¨dwestlichen Osteuropa¨ischen Tafel (in Russian). Arbeiten, Vol. 16, Vilnius, 124 pp. Kozur, H.W., 1989a. Biostratigraphic zonation in the Rotliegendes and their correlations. Acta Mus. Reginaehradecensis S.A., Sci. Nat. 22, 15–30. Kozur, H.W., 1989b. The Permian–Triassic boundary in marine and continental sediments. Zentralbl. Geol. Palaeontol. 1, 1245–1277. Kozur, H.W., 1993a. Annotated correlation tables of the Germanic Buntsandstein and Keuper. In: Lucas, S.G., Morales, M. (Eds.), The Nonmarine Triassic. N.M. Mus. Nat. Hist. Sci. Bull. 3, 243–248. Kozur, H.W., 1993b. Range charts of the conchostracans in the Germanic Buntsandstein. N.M. Mus. Nat. Hist. Sci. Bull. 3, 249–253. Kozur, H.W., 1994. The correlation of the Zechstein with the marine standard. Zentralbl. Geol. Bundesanst. 137 (1), 85– 103.
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Kozur, H.W., Mock, R., 1993. The importance of conchostracans for the correlation of continental and marine beds. In: Lucas, S., Morales, M. (Eds.), The Nonmarine Triassic 3, N.M. Mus. Nat. Hist. Sci. Bull. 3, 261. Kozur, H.W., Seidel, G., 1983. Revision der Conchostracen– Faunen des unteren und mittleren Buntsandsteins, Teil 1. Z. Geol. Wiss. 11 (3), 289–417. Krystin, L., Orchard, M.J., 1996. Lowermost Triassic ammonoid and conodont stratigraphy of Spiti, India. Albertiana 17, 10–21. Kuchtinov, D.A., 1976. Biostratigraphy of the Triassic Deposits of the Pre-Caspian Syneclise on the Base of Ostracods (in Russian). Nedra, Moscow, 99 pp. Liu, S., 1994. The nonmarine Permian–Triassic boundary and Triassic conchostracan fossils in China. Albertiana 13, 12–24. Lozovsky, V.R., 1983. About the age of beds with Lystrosaurus in Moscow syneclise. Dokl. Akad. Nauk USSR 272 (6), 1433– 1437. Lozovsky, V.R., 1992. The Permian–Triassic boundary in the continental series of Laurasia and its correlation with the marine scale. Int. Geol. Rev. 34 (10), 1008–1014. Lozovsky, V.R., 1995. The Permian–Triassic boundary in continental sequences. 13th Int. Congr. Carboniferous–Permian, August 28–September 2 1995, Krakow, Abstr., pp. 91–92. Lozovsky, V.R., 1996. The Permian–Triassic boundary in the continental series of Eurasia. 30th Int. Geol. Congr., Abstr. 2, p. 55. Lozovsky, V.R., Molostovsky, E.A., 1993. Constructing the Early Triassic magnetic polarity time scale. N.M. Mus. Nat. Hist. Sci. Bull. 3, 297–300. Lozovsky, V.R., Yaroshenko, O.P., 1994. The Permian=Triassic boundary in the continental series of the Moscow syneclise: recent achievements. Permophiles 24, 54–59. Lucas, S.G., 1993. Vertebrate biochronology of the Triassic of China. N.M. Mus. Nat. Hist. Sci. Bull. 3, 361–366. Lucas, S.G., 1996. The Dicynodon biochron and the unity of Late Permian Pangaea. 30th Int. Geol. Congr. Abstr. 2, p. 94. Meyen, S.V., 1973. The Permian and Triassic systems and its relation to the Paleophyte–Mesophyte flora boundary. Mem. Can. Soc. Pet. Geol. 2, 662–667. Mogutcheva, L., 1989. The change of the flora at the Permian=Triassic boundary in Angarida (in Russian). In: Dagys, A.S., Dubatolov, V. (Eds.), Upper Paleozoic and Trias of Siberia. Nauka, Novosibirsk, pp. 4–12. Mojsisovics, E., Waagen, W., Diener, C., 1895. Entwurf einer Gliederung der pelagischen Sediments der Trias-Systems. Sitzungsber. Akad. Wiss. Wien, Math. Naturwiss. Kl. 104, 1–32. Molin, V.A., 1965. The Lower Triassic conchostracans from northern Yakutia (in Russian). In: Conchostraca of the Northern Part of USSR. Nauka, Moscow, pp. 62–73. Murchison, R., 1841. Geological Investigations in Russia (in Russian). Govn. J., 11–12, 160–170. Nawrocki, J., Wagner, R., Grabowski, J., 1993. The Permian– Triassic boundary in the Polish basin in the light of paleomagnetic data. Geol. Q. 37 (4), 565–578. Novojilov, N.I., 1970. The Extinct Limnadioidea (in Russian). Nauka, Moscow, 237 pp.
Ochev, V.G., 1993. On the relationship between the history of Triassic tetrapods from Eastern Europe and climate evolution. In: Sun, A., Wang, Y. (Eds.), Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota. Short Papers. China Ocean Press, Beijing, pp. 43–46. Ogg, J.G., Steiner, M.B., 1989. Early Triassic magnetic polarity time scale . Earth Planet. Sci. Lett. 21, 305–311. Orchard, M.J., 1996. Conodont succession about the Permian– Triassic boundary. Guadalupian II Conference, Alpine (Texas), Abstr. Vol., p. 18. Orlowska-Zwolinska, T., 1984. Palynostratigraphy of the Buntsandstein in the sections of western Poland. Acta Palaeontol. Pol. 29, 161–194. Rubidge, B.S. (Ed.), 1995. Biostratigraphy of the Beaufort Group (Karoo Supergroup), South Africa. S. Afr. Committee Stratigr. Biostratigr. Ser. 1, 1–46. Sadovnikov, G.N., Orlova, E.F., 1994. Taimyrian stage—the terminal stage of the continental Permian (in Russian). Dokl. Akad. Nauk SSSR 338 (5), 658–661. Sadovnikov, G.N., Orlova, E.F., 1995. The news in the stratigraphy of the P=T volcanogene series of the central part of Tungusskaia syneclise (in Russian). Stratigr. Geol. Correlat. 3 (1), 34–42. Saidakovskii, L.J., 1990. Biostratigraphic correlation of the Triassic deposits of Eurasia on the base of Charophytes (in Russian). Tesisy Dokladov XXXVI Vsesoyuznogo Paleontologicheskogo Obschestva, pp. 60–61. Sennikov, A.G., 1992. The earliest Triassic archosaurs of eastern Europe (in Russian). Dokl. Akad. Nauk SSSR 326 (5), 896– 899. Shishkin, M.A., 1980. New family of Triassic Labyrinthodontia Luzocephalidae (in Russian). Paleontol. J. 1, 104–119. Shishkin, M.A., 1990. About the threefold-division of the Upper Tatarian of Upper Permian on the basis of tetrapod fauna (in Russian). Bull. MOIP 65 (2), 117. Shishkin, M.A., Novikov, I.V., 1992. Relict Anthracosaurus in the early Mesozoic of East Europe (in Russian). Dokl. Akad. Nauk SSSR 325 (4), 829–832. Shishkin, M.S., Ochev, V.G., 1993. The Permian=Triassic transition and the Early Triassic history of the Euramerican tetrapod fauna. N.M. Mus. Nat. Hist. Sci. Bull. 3, 435–437. Shishkin, M.S., Lozovsky, V.R., Ochev, V.G., 1986. Review of Triassic land vertebrate localities in the Asiatic part of USSR (in Russian). Bull. MOIP 61 (6), 51–63. Tatarinov, L.P., 1968. New theriodonts from the Upper Permian of the USSR. In: Upper Paleozoic and Mesozoic Reptiles and Amphibia of the USSR. Nauka, Moscow, pp. 32–46. Tiwari, R.S., 1993. Evolutionary shifts in Triassic palynofloras and palynoevent stratigraphy. N.M. Mus. Nat. Hist. Sci. Bull. 3, 465–470. Tozer, E.T., 1988. Towards a definition of the Permian–Triassic boundary. Episodes 11 (3), 251–255. Utting, J., 1994. Palynostratigraphy of Permian and Lower Triassic rocks in the Sverdrup Basin, Canadian Arctic Archipelago. Geol. Surv. Can. Bull. 478, 107 pp. von Alberti, F., 1834. Beitrag zu einer Monographie des Bunten
V.R. Lozovsky / Palaeogeography, Palaeoclimatology, Palaeoecology 143 (1998) 273–283 Sandsteins, Muschelkalks und Keupers und die Verbinding dieser Gebilde zu einer Formation. Cotta, Stuttgart, 366 pp. Wagner, R., 1987. Stratigraphy of the uppermost Zechstein in northwestern Poland. Bull. Pol. Acad. Sci., Earth Sci. 35 (3), 265–273. Wood, G.D., Mangerud, G., 1994. The Permo–Triassic (mycofloral-spike: palynological evidence of a possible crisis event. Int. Symp. Permian Stratigraphy, Environments and Resources, Guiyang, Abstr., pp. 39–40. Yaroshenko, O.P., 1990. Miospore assemblages and age of tuffo-
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gene—sedimentary deposits of Tungusskaya basin (in Russian). In: Paleofloristica and Stratigraphy of the Phanerozoic. Nauka, Moscow, pp. 44–84. Yaroshenko, O.P., Lozovsky, V.R., 1997. Modification of palynoflora in the Moscow syneclise (in Russian). Stratigr. Geol. Correlat. 5 (3), 43–57. Yin, H. (Ed.), 1996. The Paleozoic–Mesozoic Boundary Candidate of Global Stratotype Section and Point of the Permian–Triassic Boundary. China University Geoscience Press, Wuhan, 137 pp.
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The Permian–Triassic boundary in the continental series of Eurasia Vladlen R. Lozovsky * Geological Prospecting Institute, Miklucho-Maklay Street, 117873 Moscow, Russia Received 15 April 1997; accepted 1 December 1997
Abstract The most important Eurasian sections, where the transitional Permian=Triassic boundary beds are characterized palaeontologically, are found in the Germanic Basin (West European platform), Moscow Basin (East European platform), Tungusska Basin (Siberian platform), Jimsar Basin, Dalongkou area (Tianshan Mountains), and Noyan Somon depression (Mongolia). Usually the Permian and Triassic continental formations formed under distinct palaeogeographic (especially climatic) and palaeotectonic conditions, so the lithological and sedimentological differences between them are pronounced. Difficult problems appear in those regions where the sedimentation at this level proceeded under very similar conditions (Tungusska Basin, Jimsar Basin) across the Permo–Triassic boundary (PTB). Among palaeontological data, the most important for correlation of these continental beds is the tetrapod fauna. Broad interchange between the tetrapod fauna of the Old World continents resulted in the wide distribution during the Late Permian and Early Triassic of common or closely related forms, which enables distant correlations. The PTB is marked by the change of the Late Permian tetrapod communities, dominated by the large herbivore Dicynodon (or closely allied forms), to assemblages that include Lystrosaurus as the most common form. This is recorded in Lower Triassic beds of Eastern Europe, China, Mongolia, India and Siberia. The Upper Permian sporomorph associations (sa) are dominated by striate bissacate pollen, whereas the early Lower Triassic ones are distinguished by the very important role of spores, primarily by cavate trilete (Lundbladispora, Densoisporites) and also by non-striate dissacate (Klausipollenites) and teniate pollen (Lunatisporites). In the oldest horizons of the Triassic, very distinctive species of conchostracans (Falsisca eotriassica Kozur or the closely related form F. verhojanica Molin) appear. The PTB is within a normal polarity zone, formerly considered the lowest palaeomagnetic zone of the Triassic. The boundary beds of two sections (Moscow Basin and Jimsar Basin) may be equally worthy as candidates for the PTB GSSP in the continental series. The preference should be given to the section better characterized and internationally accessible to scientists. The PTB generally accepted for the continental series coincides more or less with the base of the Otoceras concavum ammonite zone of the Boreal province, and with the base of the boundary clay in Tethys. At the same time, it lies clearly below the traditionally adopted PTB in marine sequences at the base of the Otoceras woodwardi zone and also below the First Appearance Datum (FAD) of I. parva in the Meishan section, proposed now as the PTB GSSP (Yin, 1996, The Palaeozoic–Mesozoic Boundary Candidate of Global Stratotype Section and Point of the Permian–Triassic Boundary, China University Geoscience Press, Wuhan, 137 pp.). This demonstrates that the FAD of I. parva can be asynchronous (see Baud, 1996, Albertiana 18, pp. 6–9). That is why in the choice of the PTB GSSP in the marine series it is necessary to take into consideration the generally accepted point of view on the position of PTB in the continental series. 1998 Elsevier Science B.V. All rights reserved. Keywords: Permian; Triassic; conchostracans; continental series; tetrapods; sporomorphs
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1. Introduction One of the characteristic features of the historical stratotype sections of the Permian and Triassic is that their boundary beds are represented by continental deposits. Von Alberti in 1834 began the Trias with the Buntsanstein redbeds, which lie on saliferous Zechstein (Fig. 1). Seven years later, R. Murchison included in the upper part of the Permian the continental redbeds of central Russia, later named the Tatarian by S. Nikitin. Later it was demonstrated that the upper part of Nikitin’s Tatarian (or Vetlugian and Yarenskian in the modern nomenclature) is synchronous with the European Buntsandstein, while the lower part, keeping the name Tatarian until today, is actually of Late Permian age. After the work of Mojsisovics et al. (1895), which placed the lower boundary of the Trias at the base of the Otoceras woodwardi zone of the Himalayas, it was assumed without any fossil evidence, that this boundary in the marine facies corresponds almost exactly to the base of the German Buntsandstein. At present in Eurasia, some regions are known, where the transitional continental PTB beds are characterized palaeontologically. Besides the type areas of the Perm and Trias in Western and Eastern Europe, the sections of the Timano–Petchorian Basin (Eastern Europe), Tungusska Basin (Siberia), Jungar
Basin (Dalongkou area, western China) can be cited. The very important Gondwanan sections of South Africa, India and Antarctica are outside of the scope of this review, but some problems concerning the distribution of the tetrapod fauna in these regions will be touched upon briefly.
2. Methods used for subdividing and correlating continental PTB formations 2.1. Lithological methods Different methods are used for subdividing and correlating continental PTB formations. Lithological methods were the first to be applied because they were basic for the establishment of the first lithostratigraphic units. These are best exemplified by the European Zechstein and Buntsandstein. Recently, it has been demonstrated that the boundary between these two units is diachronous (Wagner, 1987; Kozur, 1989a, 1993a, 1994): in the marginal part of the Germanic Basin there is a gap of differing length, and the asynchronous appearance of the Germanic-looking facies is simultaneous with the disappearance of the saliferous Zechstein Permian facies. This was a case of uninterrupted sedimentation between the Perm and Trias, when the lithological
Fig. 1. The position of the P=T boundary in the historical type areas of the Permian and Triassic systems. Data from: von Alberti, 1834; Murchison, 1841.
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differences near the boundary under question were caused by tectonic and palaeogeographic (including climatic) factors. Lasting a very short time, they should occur asynchronously to some extent in different parts of the sedimentary basin. For this reason, it is difficult to trace the PTB in these regions based on lithological criteria alone. In other regions where there are discontinuities (breaks) in sedimentation at this boundary, the lithological differences between the Triassic and underlying beds of Permian age are very distinctive. For example, in the Lithuanian Basin, a marginal part of the Germanic Basin, the Nyamunskayan suite lies unconformably on the middle horizons of the Zechstein (Z3) and sometimes on the older Palaeozoic to metamorphic Precambrian rocks (Kisnerus and Saidakovsky, 1972). In the Moscow Basin, a clear break in sedimentation can be observed at the PTB. Here, the Vetlugian lies on different horizons of the Tatarian (Lozovsky, 1992), and the lithological differences between them are very distinctive. 2.2. Biostratigraphic methods Biostratigraphic methods are best suited for defining the PTB. Because the broad interchange between the tetrapod communities of the former continents resulted in the wide distribution of common or closely related tetrapods during the Late Permian and Early Triassic, long-distance correlations are possible, and tetrapods are the best fossils for biostratigraphic correlation (Shishkin and Ochev, 1993). The particular importance of this group is linked with the fact that some Lower Triassic amphibian genera are known from both continental and nearshore marine deposits that contain ammonites. This provides a basis for direct correlation between the marine and continental scales. It is commonly believed (Ochev, 1993; Rubidge, 1995; Lucas, 1996) that the boundary under discussion in the continental series is characterized by the change of the Upper Permian tetrapod communities, dominated by the large herbivore Dicynodon, to Lower Triassic assemblages that include the small, hippopotamus-like semi-aquatic Lystrosaurus as the most common form (Fig. 2). Dicynodon and closely allied genera were found in the youngest Upper Permian beds of South Africa,
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China and Russia (Rubidge, 1995; Lucas, 1996), while Lystrosaurus is known to have spread much more broadly. Besides South Africa, China and Russia, it has also been found in India, Antarctica, Mongolia and Siberia. In China, Dicynodon coexisted for some time with Lystrosaurus (Lucas, 1993), but soon after went extinct. Apart from Lystrosaurus, the important linking forms are Proterosuchus, Lidekkerina and related genera (Sennikov, 1992; Shishkin and Ochev, 1993; Rubidge, 1995). The PTB vertebrate transition is recorded most completely in the Moscow Basin of East Europe. As was noted by Ochev, here change did not proceed in the catastrophic way, and he shows the different patterns at particular stratigraphic levels (lower=upper Tatarian, within the upper Tatarian). The lowest of the Upper Permian levels is in the middle part of the Vyatskian horizon, where the Vyasnikovskian fauna appears (Shishkin, 1990). Besides the abovementioned Dicynodon, the small pareiasaurs of the Elginiidae (Ivachnenko, 1992) and the cynodont Nanocynodon seductus Tatarinov (Tatarinov, 1968), it shows the first appearance of Archosauria, a group playing a dominant role in Triassic communities, and Bystrowianidae, now found to extend into the Triassic (Shishkin and Novikov, 1992). Let us examine the change of other groups at the boundary, where the Dicynodon fauna is replaced by the Lystrosaurus fauna, which we believe marks the PTB in the continental series (Lozovsky, 1995). After tetrapods, sporomorph assemblages (sa) are the most efficient for interfacial correlations. The correlation of the sporomorph zonations is shown in Fig. 3. Usually, the Late Permian sa are dominated by striate bissacate pollen, whereas the Lower Triassic ones are characterized by the very important role of spores, primarily by cavate trilete (Lundbladispora, Densoisporites) and also by non-striate dissacate (Klausipollenites) and teniate (Lunatisporites) pollen (Tiwari, 1993; Lozovsky and Yaroshenko, 1994). The PTB sporomorph transition was recently well recorded in the Moscow Basin (Yaroshenko and Lozovsky, 1997). Along with this, it is clearly indicated that the appearance of the typical Lower Triassic taxa and the disappearance of the Upper Permian taxa occurred at different levels
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Fig. 2. Correlation of the P=T boundary beds based on tetrapod assemblages. Data from: Sadovnikov and Orlova, 1994, 1995, Lozovsky, 1995, 1996; (all for Siberian platform) Rubidge, 1995; Cheng et al., 1996.
(Tatarian=Astashichian, Astashichian=Ryabynskian, Ryabinskian=Krasnobakovskian). This is similar to the above-mentioned changes of the tetrapod communities near the PTB. The sa of the lower part of the Vokhmian horizon (beginning with the Astashichian Member, where Lystrosaurus was found) is well correlated with others in the continental facies usually dated as Lower Triassic, i.e., with the Lundbladispora obsoleta–Lunatisporites noviaulensis sa from the lower parts of the Baltic Formation of Poland (Orlowska-Zwolinska, 1984), the sa from the Nyamunskaya suite of Lithuania, and the sa from the upper Guodikieng Formation, western China (Permian and Triassic strata, 1986; Cheng, 1993). Some observable differences between these complexes are closely related to the facial peculiarities of their burial. The characteristic features of the PTB beds consist of the mass expansion of the fungal fossils Tympanicysta stoschiana and other forms (microfloral event of Wood and Mangerud, 1994).
The role of conchostracans is very important, because they are present in fresh- to mesohaline brackish-water deposits, and are sometimes associated with marine facies. This makes them suitable for intercontinental correlations (Kozur, 1993b). For the Permian, some conchostracan zonations are known. Kozur and Seidel (1983) and Kozur (1993b) proposed a zonation for the Germanic Buntsandstein. Fig. 4 shows the correlation of conchostracan zonations. A very distinctive zone (Polygrapta, Megasitum, diverse Leaiida) can be traced in the middle part of the Tatarian (Luptugian Member of the Vyatskian horizon, Russia), the lower part of the Bugariktinskaya suite (Exinian beds), the Lebedevskian horizon, Siberia, the upper part of the Wutonggou Formation and the lower part of the Guodikeng Formation, western China, as well as the Belmont Shale, Australia (Novojilov, 1970; Cheng, 1993; Liu, 1994). The same conchostracans were found in Hungary in pre-Zechstein beds (Kozur, 1989a). In the upper part of the Permian, the genus
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Fig. 3. Correlation of the P=T boundary beds based on sporomorph assemblages.
Falsisca appears (Kozur, 1989b). This event evidently preceded the first record of Lystrosaurus and the L. obsoleta–L. noviaulensis sa. The basal Lower Triassic beds are well correlated by the very distinctive species of Falsisca–F. eotriassica (upper Brockelschiefer, upper Guodikeng) (fide Kozur) and closely related F. verchojanica (Astachishian Member, Russia; Putoranian and Marininskian horizons, Siberia) (Lozovsky, 1995). The role of other animal groups is subordinate. For example, the ostracods, often used for local zonations, are very dependent on facial conditions. For example, at the PTB in the Moscow Basin the large forms of Darwinula and Darwinuloides were replaced by the small and elongate species of Darwinula and Gerdalia, a stenobiont freshwater form (Kuchtinov, 1976). But, the first Gerdalia appears in the upper part of the Tatarian; at the base of the Early Triassic they become predominant. The stratigraphic role of macroflora is exaggerated by some investigators. It should be kept in mind,
as stressed by Meyen (1973), that the transition between palaeophyte and mesophyte floras occurred asynchronously in different regions of the world. Palaeomagnetic methods play a very important role in the subdivision and correlation of the continental redbeds facies, but their application should be checked by palaeontological data.
3. Sections in Eurasia — candidates for the GSSP in the continental series The more interesting sections of Eurasia where the PTB GSSP in continental sequences can be traced are as follows. The Jimsar Basin, Dalongkou area (western China) is characterized by diverse groups (tetrapods, conchostracans, sa, ostracods, etc.) (Cheng, 1993; Cheng et al., 1996). The base of bed 54 of the Dalongkou section was proposed as a candidate for the nonmarine PTB GSSP by Cheng and Lu-
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Fig. 4. Conchostracan zonation of the P=T boundary beds. Data from: Kozur and Seidel, 1983; Kozur, 1993b; Liu, 1994; Sadovnikov and Orlova, 1995.
cas (1993). Subsequently, Liu (1994) lowered the PTB to coincide with the first appearance of the conchostracan Falsisca, but this level evidently lay below the first appearance of Lystrosaurus. It is logical to continue detailed studies of this section with a variety of experts, incorporating especially magnetostratigraphy, palynology and conchostracan palaeontology. The PTB sections of Western Europe are rich in conchostracans, ostracods and sa, but are unsuitable as potential GSSP’s because of the absence of the tetrapod fauna. The very interesting sections in central Russia are in the Moscow Basin, Eastern Europe. One of them is on the Vetluga River, where in the series of exposures the full succession of the PTB beds can be observed. Near the
town of Voskresenskoye, Nyzhegorodskaya district, the youngest Tatarian sandstones of the Molomskaya Member, Vyatskian horizon are exposed, in which a complete cranium of Dicynodon was found (Blom, 1968). Here, these Tatarian beds are overlain by the Vetlugian redbeds, well exposed in the series of exposures upstream on the right bank of the Vetluga River. Near the village Astashicha, in the red clay of the stratotype section of the Astashichian Member, Vokhmian horizon, the complete skeleton of Lystrosaurus georgi Kalandadze was found with the typical complexes of ostracods and Falsisca verchojanica Molin (Kalandadze, 1975; Lozovsky, 1983). In overlying conglomerates of the Ryabinskian Member, Vokhmian horizon (Znamenskoye locality near Astashicha), Tupilakosaurus sp.,
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Contritosaurus sp. and Lystrosauria, genus indeterminate, were found. The second section, which was recently discovered by the author, is situated on the right bank of the Volga River near the town Putcheg (Ivanovskaya district). In the lower part of the exposure variegated marls and clays of the upper Tatarian, considered to have been deposited in brackish water lakes, are exposed. A rich fauna of upper Tatarian ostracods and gastropods was found in these rocks. Above them lies the brown-green sand with a lens of sandstone and conglomerate of the Astashichian Member, in which the canine of a dicynodont (a little larger than the Vetlugian Lystrosaurus according to the conclusion of M.F. Ivachnenko) and the bone of a Lower Triassic labyrinthodont (definition of M.A. Shishkin) were found. The overlying red clays contain Lower Triassic ostracods and conchostracans (Falsisca sp.). At the PTB there is a small break in sedimentation, exemplified by the very small erosional canals and traces of weathering in the underlying marls, etc. A very interesting region for the development of the PTB beds is situated in the Tungusska Basin, Siberia. Here, flood basalt, tuff, and tuffaceous siltstones, sandstones and argilites about 3 km thick accumulated. Some investigators (Dobruskina, 1980; Mogutcheva, 1989; and others) trace the PTB at the base of the volcanogene series where the Mesophyte flora appears. Sadovnikov and Orlova (1994, 1995) go to the other extreme and date all of the tuff-lava beds as Permian, supposing that the upper part of this succession is younger than the Russian Tatarian, being formed during the break in sedimentation in Eastern Europe, which corresponds to the specific Taimyrian stage. In general, the Tungusska succession can be divided into two parts. The lower (tuffogene series), now subdivided by Sadovnikov into Tutontchanian, Lebedevskian and Hungtukunskian horizons, and the upper part formed essentially by lava (Putoranian horizon). The Triquitrites proratus–Lueckisporites virkkiae sa (Yaroshenko, 1990), close to the youngest sa of the Permian Zechstein of Western Europe (Kozur, 1989a), was found in the upper part of the tuffogene series of the Nizhnia Tunguska Basin (Hungtukunskian horizon). These beds are overlain by lava of the Nidymskaya suite (Putoranian hori-
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zon), which are correlated easily with the upper part of the lava flow of the Norilsk region (northwest of the Tunguskaya Basin). This correlation is based on tracing the marker basalt beds (Delutchinskyi, Dagtaliiskyi, Agitkanskyi, Jambukanskyi) and is adopted in all the stratigraphic schemes of the Siberian region. The upper Norilskian basalt, beginning at the Morongovskaya suite, lies discordantly on the underlying Nadezdinskaia suite (Lebedevsky horizon) (G.N. Sadovnikov, pers. commun.). The following arguments can be presented in support of an Early Triassic age for the Norilsky basalt. (1) The presence of Lystrosaurus (?) sp. (Shishkin et al., 1986) in the lower horizons of the Norilskian basalts (Verchnemokulaevskaia suite). (2) The affinities of the conchostracans of Putoranian and overlying Marininskian suites containing Falsisca verchojanica Molin (G.N. Sadovnikov, pers. commun.). The later suite contains also the charophyte Vladimirella karpinskyi (Demin) Said., typical of the lowest horizons of the Eastern European Trias (Saidakovskii, 1990). (3) The definition of the radiometric age of the intrusive rocks of the Norilsky region, correlated with the Mokulaevskyi basalt (248 š 4 Ma) (Campbell et al., 1992), very close to the one of volcanic ash origin (white clay near the PTB boundary, Meishan section: Yin, 1996). The normal polarity of these basalts, which indicate the palaeomagnetic zone of the latest Permian and oldest Trias (Campbell et al., 1992), is not contradictory to this conclusion. The absence of good exposures of the boundary beds is the principal reason for not recommending this region as the stratotype for establishment of the PTB GSSP. Besides the Eurasian regions there are the Gondwanan regions (South Africa, India, Antarctica), where sections with the potential PTB GSSP could be established. At present, the boundary beds of two sections (Moscow Basin and Dalongkou area) may be equally considered as candidates for the PTB GSSP in the continental series. The preference should be given to the section better characterized and accessible for visitation and investigation (including unrestricted sample transport to abroad) by foreign scientists. But, in any case, the final decision can be made only after the establishment of the PTB GSSP in the marine scale.
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4. Correlation of the Permian–Triassic continental and marine scales Before the mutual correlation of the continental and marine scales it is necessary to emphasize that the PTB problem, dating back at least one century, is still far from being resolved. Either of the proposed variants of the PTB placement and consequently a choice of the PTB GSSP in the marine series — traditionally at the base of the Otoceras woodwardi zone (Mojsisovics et al., 1895), at the base of the boreal O. concavum zone (Tozer, 1988; Dagys, 1994), supported by the author, at the base of the conodont zone I. parva (Kozur, 1989b; Yin, 1996 etc.) or at the base of an assemblage conodont zone (Neogondolella meishanensis, N. taylorae, N. carinata and N. orchardi) (Orchard, 1996; Baud, 1996) — has its own shortcoming, and encounters considerable difficulties, when tracing across the diverse biogeographical provinces. At present, Kozur’s view on the partial correspondence of the Changxingian stage (Tethyan province) and Griesbachian stage (Boreal province) (see Kozur, 1989b) is broadly accepted (Krystin and Orchard, 1996). It is confirmed, in particular, by the palynological data which enable the direct correlation of the marine and continental series. The typical L. obsoleta–L. noviaulensis sa from the lower part of the Vokhmian horizon, Moscow Basin and its equivalents (as stated above) are very close, on one hand, to the sa’s (Protohaploxypinus and Taeniaesporites) from the Otoceras beds of Greenland (Balme, 1979), Lower Griesbachian of western Canada (Jansonius, 1962), Sverdrup Basin, Canadian Arctic Archipelago (Fisher, 1979; Utting, 1994) (see Lozovsky and Yaroshenko, 1994; Yaroshenko and Lozovsky, 1997), on the other hand to the sa, determined by Kozur (1989b) from the Lower Tesero-oolites above the event clay with the typical Changxingian conodont H. latidentatus praeparvus, Paleofusulina and mass occurrences of marine fungi. Besides the sa, used for direct correlation between the continental and marine scales, the one proposed by the author for these purposes is the ecotonal method. It is based on S. Meyen’s principle of mutual substitution of indications. It uses the Amphibia, found in the continental facies as well as in the marine, with the ammonites. Such correlation allows
us to correlate the Moscow Basin continental section with the marginal marine one of East Greenland. The amphibian genus Tupilakosaurus, known from the lower Glyptophiceras martini beds up to Proptychites (interval corresponding to the Otoceras boreale–Ophiceras commune zones) was found in the Ryabinskian and Krasnobakovskian Members of the Vokhmian horizon. Right from the base of the Krasnobakovskian Member (Moscow Basin) and the zone of O. commune (Greenland) the amphibian genus Luzocephalus is present (Shishkin, 1980). This correlation (Lozovsky, 1983) is supported by palaeomagnetic data. The lower part of the continental Vetlugian of the Moscow Basin (Astashichian and Ryabinskian Members), as well as the lower part of the Baltic Formation of Poland, has normal polarity (zone N1T) (Lozovsky and Molostovsky, 1993; Nawrocki et al., 1993). Above, it was shown that these beds correlate with the Otoceras beds of East Greenland. Normal magnetization of the zones of O. concavum–O. boreale of the sections of the Arctic Archipelago (Ogg and Steiner, 1989) gives strong support for the former conclusion. The change of polarity from normal to reversed observed at the Ryabinskian=Krasnobakovskian boundary in the Moscow Basin is also marked at the lower boundary of the Ophiceras commune zone of Arctic Canada, which was already correlated by the presence of Luzocephalus. As there is a break below the Otoceras concavum zone in the Canadian section (Tozer, 1988), it remained unclear what was the polarity of the youngest Permian rocks. The palaeomagnetic study of the Meishan section shows that the polarity of Mixed bed 1 (black clay), corresponding to the Otoceras genozone, as well as the underlying boundary clay and uppermost part of the Changxingian stage, is normal (Yin, 1996). This fact provides a perfect analogy with the continental sequence of Poland, where the normal polarity zone embraces not only the lower horizons of the Baltic Formation but also the youngest ones of the Zechstein (Nawrocki et al., 1993). The underlying part of the Changxingian stage in the Meishan section as well as the upper part of the Zechstein have mainly a reversed polarity with a small interval of normal polarity zones This correlation between the continental and marine series is confirmed by the data of Kozur and
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Mock (1993) based on the study of conchostracans. In the Nadaskut Dolomite Member of Hungary, the time equivalent of the lowermost part of the Tesero-oolites of South Alpine sections, the conchostracan Falsisca eotriassica was found, a very important form of the lowest horizons of the continental European Buntsandstein, as well as of the upper Guodikieng Formation of China. F. verchojanica, closely similar morphologically to F. eotriassica, was found in the lowermost Triassic beds of the western slope of West Verchoianian, correlated by Molin (1965) with the Otoceras zone. Above these beds in this region lies the Ustkelterskaia suite with the conchostracan Wetlugites pronus, which was found together with ammonites of the Ophiceras zone (Ophiceras sp., Wordieoceras wordie Spath, etc.) at the eastern slope of the same region (Dagys et al., 1979).
5. Conclusions The lower boundary of the continental series of the Triassic accepted now for Europe and Asia (which corresponds with the appearance of Lystrosaurus, the conchostracan Falsisca eotriassica ( D F. verchojanica), L. obsoleta–Lunatisporites noviaulensis sa), more or less coincides with the base of the O. concavum zone in the Boreal regions and with the base of the boundary clay in the Tethys. It lies clearly below the traditionally adopted PTB in marine sequences at the base of the Otoceras woodwardi zone and also below the first appearance of I. parva in the Meishan section, proposed now as the PTB GSSP by Yin (1996). With this it is possible that the first appearance of I. parva can be asynchronous (see Baud, 1996). That is why in the choice of the PTB GSSP in the marine series it is necessary to take into consideration the generally accepted point of view on its position in the continental series.
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