Permian continental basins in the Southern Alps (Italy ... - Springer Link

Int J Earth Sci (Geol Rundsch) (2012) 101:129–157 DOI 10.1007/s00531-011-0642-6

REVIEW ARTICLE

Permian continental basins in the Southern Alps (Italy) and peri-mediterranean correlations Giuseppe Cassinis • Cesare R. Perotti Ausonio Ronchi

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Received: 22 June 2010 / Accepted: 22 January 2011 / Published online: 6 March 2011 Springer-Verlag 2011

Abstract The Late Carboniferous to Permian continental successions of the Southern Alps can be subdivided into two main tectono-sedimentary Cycles, separated by a marked unconformity sealing a Middle Permian time gap, generally estimated at over 10 Ma. The lower cycle (1), between the Variscan crystalline basement and the Early Permian, is mainly characterised by fluvio-lacustrine and volcanic deposits of calc-alkaline acidic-to-intermediate composition, which range up to a maximum thickness of more than 2,000 m. The upper cycle (2), which is devoid of volcanics, is mostly dominated through the Mid?–Late Permian by alluvial sedimentation which covered the previous basins and the surrounding highs, giving rise to the subaerial Verrucano Lombardo-Val Gardena (Gro¨den) redbeds, up to about 800 m thick. The palaeontological record from the terrigenous deposits of both the above cycles consists mainly of macro- and microfloras and tetrapod footprints. The age of the continental deposits is widely discussed because of the poor chronological significance of a large number of fossils which do not allow reliable datings; however, some sections are also controlled by radiometric calibrations. The comparison with some selected continental successions in southern Europe allows to determine their evolution and set up correlations. A marked stratigraphic gap shows everywhere between the above-mentioned Cycles 1 and 2. As in the Southern Alps, the gap reaches the greatest extent during the Mid-Permian, near the Illawarra Reversal geomagnetic event (265 Ma). In western Europe, however, such as in Provence and

G. Cassinis (&) C. R. Perotti A. Ronchi Earth Science Department, Pavia University, Via Ferrata 1, 27100 Pavia, Italy e-mail: [email protected]

Sardinia, the discussed gap persists upwardly to Late Permian and Early Triassic or slightly younger times, i.e. to the onset of the ‘‘Alpine sedimentary Cycle’’, even though in northeastern Spain (Iberian Ranges, Balearic Islands) this gap results clearly interrupted by late Guadalupian– Lopingian deposits. The above two major tectonosedimentary cycles reflect, in our view, two main geodynamic events that affected the southern Europe after the Variscan orogenesis: the Late Carboniferous–Early Permian transformation of the Gondwana–Eurasia collisional margin into a diffuse dextral transform margin and the Middle– Late Permian opening of the Neotethys Ocean, with the onset of a generalised extensional tectonic regime and the progressive westward marine ingression. Keywords Southern Alps Late Carboniferous Permian Triassic Chronostratigraphy Interregional correlation Geodynamics

General outline The Late Palaeozoic, post-Variscan stratigraphic record of the Southern Alps consists of continental and marine deposits. The latter, however, are subordinate and occur only between the Adige Valley and Slovenia. In this area, the marine sediments, known as the Bellerophon Formation, are Late Permian in age, but in the Carnic Alps they also extend back, as the Pontebba Supergroup (Nassfeld Schichten), to the Early Permian and Carboniferous (Fig. 1). The continental deposits consist of both igneous and siliciclastic rocks. The former mostly include volcanic rocks, with ignimbrites, tuffs and lava flows of calc-alkaline acidic and intermediate composition, locally reaching

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Int J Earth Sci (Geol Rundsch) (2012) 101:129–157

Fig. 1 General and simplified distribution of the Late Carboniferous to Early Permian rocks in the Southern Alps, North Italy, and location of some main basins. The small Westphalian to Stephanian outcrops of the Lugano area and environs have been represented, for major

evidence, into the inset larger-scale map. The radiometric ages (in Ma) related to intrusive bodies are in agreement with the most reliable data of the literature cited in the text

a maximum thickness of more than 2,000 m, such as in the ‘‘Bozen Volcanite Complex’’ where the volcanism was very intense. These extrusive rocks generally pertain to the Early Permian, along with a number of interspersed subvolcanic bodies. Also the well-known Biella-Valsessera, Alzo-Roccapietra, Mottarone-Baveno, Montorfano, Val Ganna, Val Biandino, M. Sabion, M. Croce-Bressanone and Cima d’Asta intrusives, thanks to radiometric ages, are in tune with the above dating (Fig. 1 and references below). The Late Carboniferous and Early Permian continental sedimentary rocks are composed of fluvio-lacustrine, and in some places also fluvio-palustrine, generally varicoloured deposits. To the west of the Adige Valley, where these clastics are widespread, they infilled some depressions (such as the Collio and Orobic Basins), locally alternating with or passing laterally into volcanics (Fig. 1). Thus, their thickness shows very marked changes, from 0 to over 1,000–1,500 m. In contrast, during Mid?–Late Permian times, the Southern Alpine palaeogeographical domain was mostly dominated by alluvial sedimentation, which covered the previous basins and the surrounding highs giving rise to the subaerial Verrucano Lombardo-Val

Gardena (Gro¨den) red-beds. Generally these deposits, compared with the Early Permian succession, appear more widely distributed although less thick, up to a maximum of about 800 m.

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Geological setting As emphasised in a large number of papers (e.g. Italian IGCP 203 Group 1986; Cassinis et al. 1988; Massari et al. 1994), two main well-differentiated tectonosedimentary Cycles (Fig. 2), separated by a very distinct unconformity which marks a gap of still-imprecise duration, are clearly evident in the Late Carboniferous to early Middle Triassic succession of the Southern Alpine domain (Massari and Neri 1997). Nevertheless, a further third Cycle could also be suggested, at least in western Lombardy—Canton Ticino (near Lugano), from the Middle Carboniferous up to perhaps the earliest Permian sequences. In this area, however, the transition between these systems has not been studied carefully, and thus the establishment of another basal cycle, starting from the Variscan crystalline basement, is still hypothetical.


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from each other by metamorphic and igneous structural paleo-highs. The boundary faults normally show SSW– NNE and E–W trends, and often coincide with long-lived tectonic lineaments (such as the Val Trompia, Giudicarie and Valsugana Lines). In this geological scenario, the aforementioned magmatic bodies (Biella, Baveno, etc.), again calc-alkaline intermediate and acidic in composition, also occur. Generally, the beginning of the post-Variscan continental succession in the Southern Alps is marked by polygenic conglomerates, interbedded with sandstones and finer-grained clastics (Basal Conglomerate, Ponte Gardena Conglomerate), which unconformably overlie the Variscan crystalline basement. The climate, up to Early Permian times, changed from humid to moderately semi-arid conditions (Dal Cin 1972; Krainer 1993), the latter with alternating wet and dry periods (Roscher and Schneider 2006). According to the literature, palaeontological studies of the macroflora (e.g. Geinitz 1869; Venzo and Maglia 1947; Jongmans 1951; Remy and Remy 1978; Kozur 1980a; Visscher et al. 2001), palynomorphs (e.g. Cassinis and Doubinger 1992; Barth and Mohr 1994; Pittau 1999a, b, c, Pittau 2001; Pittau et al. 2008) and tetrapod footprints (e.g. Conti et al. 1991, 1997; Nicosia et al. 2000; Cassinis and Santi 2005) suggest that the aforementioned cycle began in some places during the Late Carboniferous (‘‘Westphalian’’), but generally developed during the Early Permian times. Radiometric investigations on intrusive and extrusive rocks by Hunziker and Zingg (1980: Rb–Sr 276 ± 5), Bakos et al. (1990: Rb–Sr 281 ± 9 and 275 ± 8), Barth et al. (1993, 1994: All 275.5 ± 1.5 and 276.3 ± 2.2), Klo¨tzli et al. (2003: Zr 284.9 ± 1.6 and 274.1 ± 1.4), Bargossi et al. (2004: Zr 277-274), Schaltegger and Brack (2007: from Zr 283.1 ± 0.6 to Zr 277 ± 5), Visona` et al. (2007: Zr 290.7 ± 3), and other researchers generally agree with an Early Permian interpretation (Fig. 3). Fig. 2 Isopach maps a of the Lower Permian succession and b the ?Mid to Late Permian Verrucano Lombardo from the typical Collio Basin and surroundings areas. c Palinspastic cross sections of the Permian succession showing the two main tectono-sedimentary cycles of this region (From Perotti and Siletto 1996)

Lower Cycle As previously stated, in the Southern Alps this early Cycle 1, or lower tectono-stratigraphic unit (TSU), consists of calc-alkaline acidic (rhyolite/rhyodacite) to intermediate (andesite) volcanic rocks, and alluvial to lacustrine continental deposits (such as Collio and Tregiovo Fms., Ponteranica and Dosso dei Galli Cgls.), both infilling intramontane fault-bounded, transtensional subsiding basins, isolated

Lugano area and surroundings In the aforementioned geological context, it must be remembered that in western Lombardy, such as in the Logone continental deposits (west of Lake Como) (Fig. 1), Venzo and Maglia (1947) identified Calamites spp., Pecopteris plumosa, Linopteris neuropteroides, Lepidodendron weltheimi, L. aculeatum, Lepidodendron majus, abundant Sigillariae and other forms (Westphalian C), whereas Jongmans (1951, 1960) pointed out in the Manno molasse (Lugano) (Fig. 1) the presence of Linopteris neuropteroides, Pecopteridium, Sigillariaephyllum and Cordaites cf. borassifolius (probably Westphalian B–C). Lastly, Pittau et al. (2008) also recognised in the same basal clastics that the palynoflora of Brezzo di Be´dero (near

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Fig. 3 Early Permian radiometric ages from upper crustal intrusive and volcanic rocks of the Southern Alps, from Lake Maggiore area to the east of the Adige Valley. This scheme shows only reliable data, with: U–Pb ages on zircons (blank and black dots imply intrusive and volcanic rocks, respectively), Th–Pb allanite (intrusive and volcanic

rocks derive from Barth et al. 1994) and other selected Rb–Sr-ages (blank and black dots indicate intrusive and volcanic rocks, respectively). The listed numerical ages are from ‘‘A Geologic Time Scale’’ by Gradstein et al. (2004)

Luino, Lake Maggiore) (Figs. 1, 4) shows strong affinities with those of Western Europe. The most abundant forms are trilete spores known to be characteristic of late Westphalian and early Stephanian assemblages. They exhibit the remarkable presence of Florinites and subordinately Wilsonites species, low numbers of Potonieisporites, rare Limitosporites and Vesicaspora, and very rare LatensinaCordaitina pollen. From the above data, however, we point out that the age of several macro- microflora assemblages in the Late Carboniferous–Early Permian time interval is common to most of the SW Europe basins (e.g. Broutin et al. 1999), and a strong palaeoclimatic control is now accepted. These Late Carboniferous detrital bodies (Manno and Logone conglomerates, etc.) occur only from Lake Maggiore to Lake Como. In contrast, eastwards, above the Variscan crystalline basement locally in Lombardy (Basal Conglomerate) and from the Adige Valley up to the Carnia region (Ponte Gardena Conglomerate), are found ruditic and arenitic alluvial deposits, from zero thickness up to a maximum of 200 m (Sesto), lacking in fossils but generally interpreted as Early Permian in age, from the inclusion of volcanic clasts related to this period (Figs. 5, 6). However, the lithic fragments mainly seem to be derived from the metamorphic substrate.

Later, the development of vigorous intrusive and extrusive igneous activity and a tectonic pulse led to the onset of some major, subsiding intracontinental troughs (such as, among the best known, the Orobic, Collio, Tione and Tregiovo basins), which were filled by volcanic and alluvial-to-lacustrine deposits, in places rich in macro- and microfloras and tetrapod footprints.

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Orobic Basin Towards the east, the Orobic Basin (Figs. 1, 5), which extends from Lake Como to the western spurs of the Alpine Adamello intrusion, shows a stratigraphic succession generally characterised in ascending order by a ‘‘Basal Conglomerate’’ (BC) Fm., of which the clastic sediments are described in the literature (e.g. Dozy and Timmermans 1935; Cadel et al. 1996). The formation is mainly composed of quartz pebble conglomerates, derived from the metamorphic basement. Small volcanic fragments are very rare and occur in sandstones from the lower and uppermost part of the unit. Although the centre(s) of this igneous activity remains unknown, it may be related to the Early Permian, as isotopically documented at the base of the Navazze uranium mine in the upper Val Seriana (Philippe et al. 1987: Zr ca. 280 Ma). Purple-red siltstones, locally


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Fig. 4 The Brezzo di Be´dero stratigraphic section of the Late Carboniferous in the Varese area (at the eastern side of Lake Maggiore) and close-up of beds sampled for palynology in the upper fine-grained portion. (From Pittau et al. 2008, slightly modified)

affected by intense bioturbation, which has been interpreted as characteristic of shallow ephemeral lake environments, are commonly interbedded with coarser BC sediments. Moreover, the presence of calcrete-bearing mudstones is consistent with dry-climate alluvial plain deposits. Both in Val Seriana and Val Brembana (Fig. 1), which run through the discussed Orobic Basin area, the conformably overlying Collio Group Auct. may be subdivided into two parts or informal units. The lower one (referred to as the ‘‘Vulcanite del Monte Cabianca’’, corresponding to the ‘‘Collio vulcanico’’ Auct.) consists of acidic to minor intermediate (andesite) volcanic rocks belonging to two volcanic cycles (Cadel 1986; Cadel et al. 1987), interbedded with subordinate siliciclastic deposits, while the upper

part (namely ‘‘Formazione del Pizzo del Diavolo’’) is essentially made up of a thick sequence of lacustrine and alluvial fan terrigenous sediments with intercalations of minor volumes of evaporites, lacustrine carbonates and volcanics. According to Cadel (1986), the two informal units were deposited in superimposed basins with different depocentres, which reached up to about 2,000 m in thickness, and are interrupted by a weak unconformity linked to a deformational, possibly transpressional, phase. The lack of significant palaeontological data from the Orobic Collio prevents any detailed age-interpretation of this unit. However, Hunziker (in Cadel 1986) and Philippe et al. (1987) obtained U–Pb age determinations (Fig. 3) on zircons from the Novazza mine, i.e. from the volcanic rocks beneath the Pizzo del Diavolo Fm. (of which the

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Fig. 5 Selected and simplified Permian stratigraphic columns of the central and eastern Southern Alps, from Lake Como (W) to the western Dolomites (E). Lithostratigraphic units (from bottom)— Lombardy-Canton Ticino (Varese/Lugano area, Orobic and Collio Basins): BC basal conglomerate, V undifferentiated volcanics, GG Val Ganna granite, CO Collio Formation, PC Ponteranica Conglomerate, DGC Dosso dei Galli Conglomerate (S, Pietra Simona Member), AV Auccia Volcanics, VL Verrucano Lombardo. Trentino and Alto Adige (Val Rendena, Tregiovo-Monte Luco, BolzanoTrento areas and western Dolomites): PGC Ponte Gardena Conglomerate, BV undifferentiated Bolzano (Bozen) volcanics, ML Mt. Luco Formation, TF Tregiovo Formation, VDC Val Daone conglomerate, VL Verrucano Lombardo, VGS Val Gardena (Gro¨den) Sandstone, BE Bellerophon Formation, WF Werfen Formation. In the above context,

the succession of the Varesotto/Luganese area is strongly incomplete, because of the great number of lithological changes affecting the region which prevent a careful stratigraphic reconstruction. In the related scheme, only the Westphalian—Stephanian ‘‘Basal Conglomerate’’ (BC) and the overlying shallow intrusive (‘‘granophyre’’) known as ‘‘Ganna Granite’’ (GG) of 281.3 ± 0.5 Ma obtained by Schaltegger and Brack (2007) on zircon age have been introduced. Lithology—(1) conglomerates and breccias; (2) sandstones and siltstones; (3) pelites, siltstones and marlstones; (4) limestones; (5) fossiliferous limestones; (6) oolitic limestones; (7) dolostones; (8) volcanic rocks. Other symbols—(9) unconformity, (10) erosional surface, (11) stratigraphic gap. Geologic Time Scale by Gradstein et al. (2004)

lithological characteristics reflect those of the typical Collio Fm. in the homonymous basin), yielding relevant age estimates of 287 and 280 Ma (late Sakmarian and early Artinskian, respectively, according to Gradstein et al. 2004), reliably consistent with an Early Permian age. Lastly, new U–Pb radiometric dates on zircon deriving

from the same, so-called Monte Cabianca Volcanite, which is about 700 m thick, led Berra et al. (2008) to interpret for a basal sample (collected in the first pyroclastic flow above the Basal Conglomerate) a weighted-mean concordia age of about 279 Ma (i.e. middle Artinskian). In contrast, the zircons from the uppermost part of the Monte Cabianca

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Fig. 6 Permian global stratigraphic scale (by Gradstein et al. 2004) and regional stratigraphic scales (by Menning et al. 2006, p. 334, modified), showing some Permian stratigraphical terms used in the text

volcanics would seem to pertain, again according to the same authors, to a younger age estimated at approximately 270 Ma (about the Cisuralian/Guadalupian or Early/Middle Permian boundary). This date, however, appears clearly in contrast to the stratigraphical arrangement of the Pizzo del Diavolo Fm. in the basin, because the unit starts and is greatly developed upwards for more than 600 m (Ronchi et al. 2005), and includes also some presumed airfall tuffs interbedded in the lacustrine deposits which might be derived from the Lugano area, according to Cadel (1986), where the rhyolites have an average age of 278 ± 3 Ma (Hunziker, again in Cadel 1986). In this context, we also record that Schaltegger and Brack (2007) suggested a Zr age of 281.3 ± 0.5 Ma for the Varesotto (Valganna)/Luganese area (Fig. 3), in good agreement with the indicated earlier dating. Therefore, on the basis of the preliminary radiometric data recently obtained from the Permian volcanics of the Orobic Basin, Berra et al. (2008) suggested that this activity generally implies a duration of about 10 Ma, which, if compared with that of the Collio Basin (Val Trompia) (3.5 Ma) and other South-Alpine areas, could generally testify to a space-and-time change of late Variscan volcanism. However, owing to the previous discussion, the Permian Orobic igneous complex deserves further research for a more plausible interpretation. Apart from the radiometric ages, the Pizzo del Diavolo Fm. (‘‘Collio sedimentario’’ Auct.) of the Orobic Alps seems, at least so far, devoid of any palaeontological

evidence of good biostratigraphic resolution for fixing a well-established age. In recent years, the Ponteranica Conglomerate near Gerola Alta (Orobic Basin) has yielded a conifer species that was described as Cassinisia orobica (Kerp et al. 1996). Other unspecified Walchia remains occur in the basin. Moreover, research carried out in the same area by Pavia and Roma Universities (e.g. Ceoloni et al. 1987; Nicosia et al. 2000; Santi 2001; etc.) uncovered a large number of tetrapod footprints. These forms were mainly collected in the proximity of the Rifugio FALC, NE of Pizzo Varrone, a little below the major angular unconformity between the Pizzo del Diavolo Fm. and the overlying Verrucano Lombardo. The Pizzo del Diavolo Fm., which is locally characterised by thin, finegrained, arenitic, siltitic and subordinate shaly sediments, blackish to grey in colour, passing in the uppermost 20 m (i.e. near the discontinuity) to dark red layers, yielded Amphisauropus latus, A. imminutus, Dromopus lacertoides and Varanopus curvidactylus along with reddish silicified woods (Nicosia et al. 2000). This association, which is generally comparable to that from the typical Collio Fm. in the Brescian Prealps, undoubtedly belongs to the Early Permian. Based on the palaeontological and radiometric dates from the latter area, the age-assessment of these Orobic footprints could be generally ascribed to an Artinskian–Kungurian interval. The affinity of this Orobic ichnoassociation with that of the Brescian Collio Basin is also confirmed by the discovery of other forms within the Collio Fm. Auct. (or its

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equivalent) of the nearby Brembana Valley (Santi and Krieger 2001). Rare and poorly preserved foraminifera (cf. Agathammina sp., cf. Hemigordius sp.) with both calcareous and agglutinated tests, along with small gastropod fragments and spheroidal phosphate nodules, were found in the western part of the basin (Orobic Anticline), within the finegrained sandstones to siltstones of the uppermost Pizzo del Diavolo Fm., 30 m below the pronounced unconformity with the late Guadalupian? to Lopingian red-beds of the Verrucano Lombardo (Sciunnach 2001). According to this author, a temporary seaway, necessary for the foraminifera to spread into a continental basin, implies that (1) the Orobic Basin was not only an intramontane but also a coastal lake and (2) its altitude did not exceed the amplitude of a first-order sea-level rise, which is about 100 m. However, in our opinion, the above interpretation is still uncertain and deserves further research across the Western Mediterranean. Collio Basin Across the continental Southern Alps, the best-preserved trough is the Early Permian Collio Basin, in eastern Lombardy. The deposits rest unconformably above the Variscan crystalline basement (Figs. 1, 5, 7) and can range up to a maximum thickness of more than 1,200 m. Its succession, along the Maniva-Giogo della Bala road, shows from base to top (Cassinis 1966): a calc-alkaline rhyolitic Fig. 7 Synthetic stratigraphic columns in central Southern Alps, from the typical Early Permian Collio Basin (E), in the Val Dasdana-Passo Maniva area, and the close small Boario Basin (W), in the Lower Val Camonica. TSU Tectonostratigraphic unit (according to Virgili et al. 2006) Vertical distances are not time- or thickness-related. Geologic time scale by Gradstein et al. (2004)

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ignimbrite plateau; tuffs and intercalated alluvial fan bodies; shallow alluvial to lacustrine finegrained sediments with several episodes of emersion and desiccation as indicated by tetrapod footprints, mud-cracks and raindrop impressions (Pian delle Baste member of the Collio Fm.); volcaniclastic mass-flow deposits and pyroclastic units (‘‘Dasdana beds’’; Breitkreuz et al. 2001); stratified sandstones and siltstones, again intercalated with the aforementioned thin volcaniclastic key beds (Val Dorizzo member of the Collio Fm.); the alluvial red-brown Dosso dei Galli Conglomerate, including at the base or in the middle part the sandy-shaley ‘‘Pietra Simona’’ Member; and, at the top, the calc-alkaline rhyolitic/rhyodacitic Auccia Ignimbrites. Through a marked unconformity, the aforementioned succession is covered by the red Verrucano Lombardo of generally Late Permian age. However, above the Collio Fm., the onset of the Dosso dei Galli Conglomerate is defined by another minor unconformity. This is mainly evident along the southern margin of the basin, in the upper Val Trompia and nearby, and westwards also in the small Boario Terme Basin, beside the lower Camonica Valley (Figs. 1, 7). In the former region, we can locally observe that the boundary between the two formations is strikingly discontinuous, as in the Monte Colombine area, and marked by incised channelled surfaces; moreover, the intermediate wellstratified Pietra Simona Member of the nearby upper Val Dasdana stratotype is locally eroded and reworked along the Maniva-Croce Domini road, by coarse polygenic


conglomerates, and disappears southwards; finally, near the Passo delle Sette Crocette and up to the extreme western boundary of the Collio Basin (from the Cigoleto to Bozzoline valleys) ‘‘the Conglomerate’’ consists only of its upper typical member which rests step by step unconformably on the ‘‘lower Collio’’ and the underlying volcanics. In the Boario Terme Basin, the Dosso dei Galli Conglomerate is essentially characterised by the Pietra Simona Member (which could be interpreted for its typical features and the conspicuous development as a ‘‘Scoyenia ichnofacies’’; Cassinis and Schirolli 2008; Ronchi 2008), about 300 m thick, which includes thin volcaniclastic deposits (Fig. 7). Within the same basin, a few basal conglomerates of the formation directly overlie the Permian basal volcanics (ignimbrites and tuffs), which mark the transition to the east of the typical Collio Basin. The Dosso dei Galli Formation, which is so far devoid of fossils, can be interpreted as a complex of amalgamated and irregular alluvial fan bodies prograding into, and sealing, the Collio Basin. It mainly consists of metamorphic, quartz-vein and intra- and extra-basinal igneous lithoclasts, transported by mass-flow or debris-flow mechanisms triggered in a rejuvenated tectonic phase. Thus, such a deformation event led to regional uplift which caused denudation of underlying Permian and pre-Permian rock units. In continental Italy, these pulses could be also connected with those generating the Asciano Breccias in the Pisan Mountains (Rau and Tongiorgi 1976) and the Torri Conglomerates in the Iano inlier, situated in northwestern and central Tuscany, respectively. Furthermore, belief in the existence of a hiatus between the Dosso dei Galli Conglomerate and the Auccia Volcanics (Ori et al. 1988) may be justified. This event was suggested by Ori and Dalla, having observed an erosional surface between the two units, probably due to the normal (autocyclic) evolution of the fan systems and not directly linked to tectonic movements. The uppermost unconformity of the Auccia ignimbrites, which in the Camonica, Trompia and Giudicarie areas represent the last event of the Permian volcanics just on the top of the Collio Basin, in many places shows erosion surfaces and palaeosol deposits (e.g. Wopfner 1981). It marks the end of the Permian first megasequence (TSU 1 or early Cycle 1; Fig. 7) and the onset of the Verrucano red clastics of the second megasequence (TSU 2 or late Cycle 2; Fig. 7). This unconformity, at the base of the Verrucano Lombardo/Val Gardena Sandstone lithosome, was preliminarily related by some Italian authors to the ‘‘Saalian phase’’ (Cassinis 1964; Vai and Elter 1976; etc.). Later, however, it was related by Kozur (1980a, b) to the ‘‘Palatine phase’’, between Early and Middle Permian times. Following the first study by Geinitz (1869) of the plant remains collected in the lower member of ‘‘the Collio’’,

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which led to the correlation of this unit with the German Rotliegend, and other research, a recent review by Visscher et al. (2001) based on the flora examined by Remy and Remy (1978) confirmed the presence of Sphenopteris suessii, S. kukukiana. S. patens, ‘‘Sphenopteris’’ cf. interrupte-pinnata, Hermitia (al. Walchia) geinitzii and Walchiostrobus sp. However, according to Visscher et al. (2001), none of the sphenopterids is reported from the classical Rotliegend, in contrast to the associated conifer foliage types which are normally found. In any case, for a reliable macrofloral dating of the Val Trompia Collio Fm., Visscher et al. (2001) came to the conclusion that the taxonomic assignments suggested are only tentative because no cuticles are known. Some palynological research carried out by ClementWesterhoff et al. (1974), Doubinger (in Cassinis and Doubinger 1991, 1992), as well as Pittau (1999a) allowed these authors to suggest a late Artinskian, Kungurian or early Ufimian age (according to the Cis Ural/Russian standard scale). In particular, the discovery of Lundbladispora simoni, Cordaitina sp., Potonieisporites sp., Nuskoisporites sp., Playfordiaspora crenulata, Vestigisporites minutus, Lueckisporites microgranulatus, Falcisporites cf. zapfei, Vittatina foveolata, Vittatina costabilis and Vittatina sp. ‘‘A’’ sensu Hochuli (1985) led Doubinger to ascribe the Collio Fm. to a presumed late Early Permian age (post-early Artinskian). In contrast, Haubold (in Haubold and Katzung 1975) first related the tetrapod footprint assemblage (?Antichnium salamandroides, Amphisauropus imminutus, A. latus, Dromopus lacertoides, cf. Gilmoreichnus brachidactilus) from the Val Trompia Collio Fm. to the Mid-European late Autunian, more or less coeval with the ‘‘Oberhof beds’’ (c. early Sakmarian) of Thuringia. Later, after a re-examination (Conti et al. 1991, 1997, 1999) of the above specimens, the Collio ichnotaxa of the Brescian Prealps consisted only of Amphisauropus latus, A. imminutus, Ichniotherium cottae, Dromopus lacertoides, ‘‘D.’’ didactylus (Moodie 1930) and Batrachichnus sp. The presence of Camunipes cassinisi remains questionable. From the literature (e.g. Voigt 2005; Lucas and Hunt 2006), all these footprints can be generally interpreted as belonging to an unsubdivided Early Permian, even though Conti et al. (1997) seem to be in favour of approximately Kungurian and Ufimian p.p. times. Furthermore, radiometric investigations by Schaltegger and Brack (2007) ascribed the rhyolitic/rhyodacitic volcanic rocks at the base and the top of the lower cycle clastic succession, which infilled the Collio Basin, to previous Early Permian times. A 206Pb/238U age of 283.1 ± 0.6 Ma has been calculated from U–Pb zircon analyses of a sample from the ‘‘Lower Ignimbrites’’, while an age of 279.8 ± 1.1 Ma resulted from zircon analyses of the

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uppermost ignimbrites (Auccia Volcanics), both based on outcrops exposed along the Maniva-Giogo della Bala road (Figs. 3, 7). Thus, according to the geological timescale (Cisuralian) from Gradstein et al. (2004), the age values of the described lower megasequence or cycle of the Collio Basin, implying a time span of about 3.5 Ma, range predominantly throughout the Artinskian. Consequently, as also pointed out by the aforementioned authors, the radiometric dates ascribe the examined Permian succession to older ages than those generally based on palaeontological data (palynomorphs, tetrapod footprints), as earlier suggested by the Haubold estimate for the Val Trompia ichnofossils. Tregiovo Basin and surroundings The Tregiovo Basin, which is located in the upper Val-diNon (between the Bolzano and Trento provinces) and bounded by the Giudicarie Line to the west and the Foiana Line to the east, is a small sedimentary basin infilled with siliciclastics and minor freshwater carbonates. It has been investigated since the nineteenth century by several authors (e.g. Vacek 1882, 1894; Vacek and Hammer 1911; Giannotti 1963; Mostler 1965, 1966; Bargossi et al. 1983; Klau and Mostler 1983; Astl and Brezina 1986; Cassinis and Neri 1990, 1992; and others), mainly from palaeontological, stratigraphical and petrographical points of view (Figs. 1, 5). The typical Tregiovo Fm., which is deposited exclusively in the southeastern sector of a wider Early Permian basin, i.e. the Monte Luco volcanic district, overlies rhyolite ignimbrites and agglomerates and consists at its base of chaotic conglomerates, followed above by trough crossbedded gravels and coarse sandstone, and subsequently by ‘‘varved’’ lacustrine mudstones with thin (mm- to cmthick) sandstone intercalations. Freshwater limestones with cyanobacterial laminites (stromatolites) occur locally. Pb– Zn mineralisation is quite widespread. Thickness, ranging from a few dozen metres to about 200 m, along with facies, seems to have been strongly controlled by synsedimentary tectonics, interpreted as transtensional by some authors (Cassinis and Perotti 1994; Bampi et al. 1996). The great importance of the Tregiovo Formation is essentially due to the fossil content, represented by plant remains, palynomorph assemblages and tetrapod footprints. A list of macrofloras is reported from the literature, but their exact provenance is however quite uncertain. For instance, Remy and Remy (1978) recognised Ullmannia frumentaria and Lesleya (al. Taeniopteris) eckardtii, which, according to Visscher et al. (2001), is a typical Zechstein element; they also highlighted other plant remains, such as Lodevia (al. Callipteris) cf. nicklesii originally described from the Lower Permian of Lode`ve

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(southern France). Later, bearing in mind the previous discovery of ‘‘Ullmannia bronni, U. frumentaria, Lebachia laxifolia, L. piniformis, Ernestiodendron filiciforme, Quadrocladus orobiformis and Pseudovoltzia liebeana’’, Kozur (1980a) suggested that the Tregiovo beds were younger than Artinskian and older than the Late Permian. A specimen of Ulmannia frumentaria, collected by Cassinis and Doubinger along the road running below the Tregiovo village, has also been determined by Broutin (pers. comm.). Lastly, Visscher et al. (2001) pointed out the presence of isolated conifer leaves showing similarities with those related to Ortiseia leonardii. However, all the above authors shrink from making any clear age interpretation of the discussed formation, due to the lack of reliable macrofloral data. As regards the palynological research on the Tregiovo Fm., after the preliminary investigations carried out by Klaus (in Visscher 1973) and Klau (in Kozur 1980a), a large number of pre-pollen and pollen grains has been reported from papers by Cassinis and Doubinger (1991, 1992), Barth and Mohr (1994), and Pittau (1999b). In particular, Pittau suggested that the data obtained might be in favour of the Kungurian–(?)Ufimian age advanced by previous palynological investigations on the Tregiovo Fm. (Klau 1965; Doubinger in Cassinis and Neri 1990; Cassinis and Doubinger 1991, 1992; Barth and Mohr 1994). However, a younger age may be hypothesised, at least for the uppermost part of the type-sequence, since the lowest occurrence of Lueckisporites virrkiae has been confirmed in the lower Kazanian (i.e. Roadian) of the type area (Utting et al. 1997). Furthermore, Pittau (1999b) pointed out that comparisons with the assemblages of the overlying Val Gardena (Gro¨den) Sandstone reveal remarkable differences in the qualitative and quantitative composition, although the suite affinity of non-taeniate disaccate pollen and the presence of Nuskoisporites dulhuntyi are impressive. In this sense, again according to Pittau (1999b), the upper part of the Tregiovo succession is, in the former two-fold subdivision of the Permian system, towards the Late Permian (now corresponding to Guadalupian–Lopingian) rather than the Early Permian (Cisuralian). Tetrapod footprints were discovered in the lower part of the Tregiovo Formation, but in contrast with the Collio unit, they seem to pertain only to a monotypic assemblage, dominated by ‘‘Dromopus’’ didactylus (Conti et al. 1999). Recently, the Permian sediments of the nearby small Monte Luco Basin (Fig. 5) also yielded an interesting tetrapod footprint assemblage, with cf. Amphisauropus, Dromopus lacertoides, Dromopus cf. D. didacyilus and cf. Batrachichnus (Avanzini et al. 2008). However, because the ages of the confining volcanic rocks above and below are 279.6 ± 1.5 and 278.4 ± 1.5 Ma (Fig. 3), respectively, this ichnocoenosis should be considered as clearly older


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Fig. 8 Age-assessment of some well-known and debated lithostratigraphic units (oblique lines) in the central Southern Alps, based on palynological research, radiometric data and regional correlation. Vertical distances are not time- or thickness-related. Geologic time scales: by Gradstein et al. (2004) (International Stratigraphic Chart); Menning et al. (2006, modified) (Central Europe); Kotlyar and ProninaNestell (2005) (East-Europe). The Vjaznikovian Gorizont, late Tatarian (Lopingian), has been recently proposed in the East European platform by Kukhtinov et al. (2008)

than that of the Tregiovo Basin and younger than the Collio Basin (Figs. 5, 8). From the above discussion of palaeontological data (macro- and microfloras, ichnofaunas), it seems very difficult to draw a common conclusion on the age of the discussed formation, due to the uncertain provenance of some plants so far collected (which could also derive from other sedimentary units occurring underneath or within the Bolzano volcanics or from other regional stratigraphic contexts) and the poor knowledge of their key ageassessment. Generally, however, a Kungurian age seems to be more reliable after a comparison with the fossil content of the already-examined continental basins of central Southern Alps. In addition, radiometric analyses of the rhyolitic tuffs of the Ora Formation (Figs. 1, 3, 5, 8), which crop out in Val d’Adige on top of the Tregiovo beds and closes the cycle of the ‘‘Athesian Volcanic Group’’ (AVG), indicate that the

discussed unit dates to about 277–274 Ma (Bargossi et al. 2004; Morelli et al. 2006; Schaltegger and Brack 2007; Marocchi et al. 2008), i.e., according to the Permian timescale by Gradstein et al. (2004), between a latest Artinskian–early Kungurian interval. Moreover, again from the aforementioned palaeontological data, a slightly younger Permian age for the Tregiovo Fm. than that for the Collio Fm. appears unquestionable (Figs. 3, 5, 8). As regards this age-assessment, however, Visscher et al. (2001) recorded that the palynological assemblages of ‘‘Tregiovo’’ seem to be younger than those from the marine Amanda Fm. present in boreholes in the northern Adriatic Sea and probably corresponding to the Neoschwagerina (fusulinid) Zone (Sartorio and Rozza 1991). This hypothetical correlation could also tentatively support the Kazanian (i.e. Roadian) age suggested by some authors (e.g. Conti et al. 1997) for the uppermost sediments of the Tregiovo Fm. and the

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overlying volcanics. But, on the grounds of our stratigraphical data used to classify the unit, both these dates (i.e. for Tregiovo and the volcanics on the top) should be rejected. Upper Cycle This Permian younger Cycle 2, or upper tectono-stratigraphic unit (TSU), marks the onset of widespread erosion and the cessation of volcanic activity in the whole Southern Alpine domain. It is generally represented by the fluvial red clastics of the Verrucano Lombardo and Val Gardena (Gro¨den) Sandstone, which is in part laterally and upwardly replaced, east of the Adige Valley, by the sulphate evaporite to shallow-marine carbonate sequences of the Bellerophon Formation (Figs. 5, 8). As previously pointed out, the former deposits, locally through the presence of basal ruditic bodies (such as the Val Daone and Sesto Conglomerates, as well as the Tarvisio Breccia), give rise to an almost continuous blanket, up to a max. of about 800 m thick, from Lake Como to Carnia and Slovenia, which covers both the basins of the lower cycle and the surrounding paleo-highs (Figs. 2, 5, 8). In the Southern Alps, the boundary between Cycles 1 and 2 is marked by a regional unconformity associated with a gap of doubtful and variable duration. Towards the east, according to Massari et al. (1994) and Massari and Neri (1997), the Late Permian Cycle continues up to the overlying Triassic, including the Werfen Fm. (Induan–Olenekian p.p.) up to the Lower Serla Fm. (latest Olenekian–early Anisian). Orobic and Brescian Alps Owing to the lack of fossils, the age of the Verrucano Lombardo is still the subject of uncertainty and debate. However, as the unit generally rests above Early Permian volcanic and sedimentary deposits and below Early Triassic fossiliferous marine sediments, its attribution to the Mid?–Late Permian is very plausible. In detail, taking into account the ages suggested for the underlying units from which it is separated by a remarkable gap, the Verrucano Lombardo probably developed diachronously during Tatarian times, i.e. in the Middle p.p.—Late Permian, reaching up to about the Permian–Triassic boundary (Figs. 5, 6, 8). Recent research by Cassinis et al. (2007), from Lake Como to the Brescian Prealps, pointed out the presence of a presumed small hiatus between the latest Lopingian and the earliest Induan, probably affected by a different development. Giudicarie and Rendena valleys On the eastern side of the Val Trompia Basin, along the Giudicarie Belt (western Trentino), the Early Permian

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Cycle is in some places unconformably capped by the socalled Val Daone Conglomerate (VDC), from zero to more than 100 m thick, which has been recently related to a presumed Middle Permian age (Cassinis et al. 2008b) (Figs. 5, 8). The unit is characterised by whitish to greyish alluvial fan and braided river deposits, composed predominantly of vein quartz and volcanic fragments, and passes upwards, probably through a small (?) stratigraphic gap, to the Verrucano Lombardo red-beds, which are generally related to the Late Permian. In Val Daone (W of the South Giudicarie Line), a thin grey siltstone layer included in the coarser fluvial bodies of the unit has yielded an abundant and significant palynological assemblage. According to Pittau et al. (2006), this microflora shows a close similarity with that found by Visscher (1973) and Visscher et al. (1974) in the continental red-beds of the well-known ‘‘Saxonian or SaxonoThuringian Leóuve´ facies’’ cropping out in the Doˆme de Barrot (French Maritime-Alps), bearing a miospore assemblage characterised by Lueckisporites virrkiae, Corisaccites sp., Crucisaccites (closely resembling Crucisaccites variosulcatus Djupina 1971) and a large number of other palynomorphs. Therefore, according again to Pittau et al. (2006), the similarity of these species suggests the extension of the stratigraphic potential of this Crucisaccites variosulcatus-Lueckisporites virrkiae zone to Western Europe. Furthermore, due to a careful review by the last authors (pers. comm.), on the whole the discovered microfossils seem to span, in Europe, from latest Kazanian to slightly younger Permian times. Based on geological evaluations and timescale correlation, Cassinis et al. (2008b) have ascribed the Val Daone Conglomerate possibly to the Wordian, obviously prior to deposition of the overlying Mid?–Late Permian Verrucano Lombardo/Val Gardena Sandstone red-beds (Figs. 5, 8). From the Val d’Adige to Dolomites Notably in the eastern Southern Alps, i.e. to the east of the Adige Valley (western Dolomites), the Val Gardena Sandstone drew great attention for the presence of macrofloral, palynological and tetrapod footprint assemblages, as well as marine organisms in the interbedded and overlying Bellerophon beds (Figs. 5, 8). Visscher et al. (2001) recognised among the macrofloras, through detailed comparative cuticle analysis, three species within the coniferous form-genus Ortiseia (ClementWesterhof 1984), viz. O. leonardii, O. visscheri and O. jonkeri. Other dominant conifers are Majonica, Dolomitia and Pseudovoltzia, rather than Walchia, Ullmannia and Voltzia of the earlier literature. The most prominent pteridosperm fragments correspond to the species formerly known from the Zechstein Basin of NW Europe as


Callipteris martinsii, now included in the natural genus Peltaspermum (P. martinsii; Poort and Kerp 1990). Palynological studies have been published by a number of authors (Klaus 1963; Clement-Westerhof et al. 1974; Italian IGCP 203 Group 1986; Visscher and Brugman 1988; Massari et al. 1988, 1994; Conti et al. 1997; Cirilli et al. 1998; Pittau 1999c; etc.). The large quantity of palynomorphs in the Bletterbach section would firstly give rise, according to Pittau (in Massari et al. 1988), to three informal associations: (A) not defined by particular taxa; (B) identified by the concurrent presence of Protohaploxypinus microcorpus and Playfordiaspora crenulata; and (C) characterised by the occurrence of Lunatisporites noviaulensis, Inaperturopollenites dolomiticus n. sp. and Lueckisporites sp. However, this biostratigraphical scheme has not been extended to all the studied sections of the Val Gardena area, due to the unsatisfactory control of some taxa used. Therefore, in a more general paper on the Late Permian deposits of the Dolomites and Carnia (Massari et al. 1994), several sets of taxa, beside the presence/absence of Protohaploxypinus microcorpus and Endosporites exareticulatus, have been successfully used to correlate the lower and central parts of the succession (respectively corresponding to the A and B associations of the Bletterbach section); other stratigraphically relevant taxa, like Lueckisporites parvus and Guttulapollenites sp., have been used to correlate the upper part of the succession (equivalent to the C association of the Bletterbach section). Pittau (2001) discussed and compared the investigated Southern Alpine microfloras of the Val Gardena Fm. with those of the Late Permian Tatarian (Koloda and Kanev 1996) in the Volga-Urals type-area. A moderate taxonomic affinity is indicated for the Urzhumsky Horizon (lower Tatarian; Kotlyar and Pronina-Nestell 2005); the occurrence of Lunatisporites and Klausipollenites schaubergeri pollen grains, and the smaller number of Costati, enhances the similarity between the Severodvinsky Horizon and the basal Gardena red-beds (cycle 1). Based on the presence of Protohaploxypinus microcorpus in the Viatsky Horizon and the very high degree of taxonomic similarity of their assemblages, a correlation is proposed between the microflora of this late Tatarian Horizon and those of the overlying Val Gardena and Bellerophon Fms. (cycles 2 and 3). The appearance of Lunatisporites noviaulensis at the top of the Viatsky Horizon, as well as the absence of Lueckisporites parvus from the Tatarian stratotype, which are observed stratigraphically later in the Southern Alps, might suggest a very limited hiatus between the Tatarian and the Triassic, probably coinciding with only part of the Changhsingian. According again to Pittau (2001), the strong taxonomic similarity also

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indicates that the Late Permian vegetation of the aforementioned areas formed part of a single Euro-Cisuralian palaeobotanical province. Tetrapod footprint assemblages are very common and well known in the Bletterbach-Butterloch outcrops. According to Conti et al. (1999), typical Permian genera, such as Ichniotherium and Hyloidichnus, have been found in association with taxa displaying a clearly Triassic affinity. In fact, the whole ichnofauna is characterised by an extreme ‘‘modernity’’ in comparison with other known Permian faunas, as witnessed by the presence of Rhyncosauroides and Dicynodontipus which are elsewhere known as typical Triassic ichnogenera. For this reason, the Bletterbach ichnofauna is really unique, and probably represents the youngest Permian assemblage known in the world. The most typical element of this ichnofauna is Pachipes dolomiticus, which is ubiquitous and can be regarded as a biochronological marker. From the given palaeontological data, the Val Gardena Sandstone is generally related to Late Permian times, even though its boundaries are not yet well defined (Fig. 5). In fact, a large number of authors (e.g. Italian IGCP 203 Group 1986; Massari et al. 1988) suppose that the unit could include part of the Middle Permian (late Guadalupian?). Therefore, further studies are necessary to refine the age of the formation across its full extent. For instance, in Carnia and to the east the age assessment of the Gardena (Gro¨den) beds is mainly in tune with the Middle Permian. Very likely the respective siliciclastic sediments, moving towards the west, rise to progressively younger time levels, along with the lateral and overlain marine Bellerophon carbonates (Figs. 5, 8). In conclusion, the Val Gardena Sandstone in the South-Alpine domain should be interpreted as a Permian diachronic unit.

Late Carboniferous to Permian stratigraphic framework of Southern Europe: an overview The Permian stratigraphic and tectonic architecture of the Southern Alps is herewith briefly compared with selected continental sequences of the Mediterranean (Fig. 9), which have been investigated by the present authors, for better evaluation of their affinities in a wider geological context. (a)

Bulgaria—According to syntheses by Yanev and Cassinis (1998) and Cassinis and Yanev (2001), in the northern part of this country the stratigraphic Permian restoration of Moesia displays a Rotliegend succession which is made up of varicoloured fluvio-lacustrine sedimentary and calc-alkaline volcanic deposits (the latter mainly developed in the lower part)

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generally related to undefined Early Permian ages (Fig. 9, no. 9). The so-called Taˆrgovishte Fm., which consists of alluvial, partly deltaic massive siliciclastic red-beds, over 1,000 m thick, follows unconformably above. Locally, such as in the Provadia syncline, it is intercalated with evaporites and carbonate fossiliferous bodies (Vetrino Fm.), which seem consistent with the presence of marine conditions towards the east, in the position of the present-day Black Sea. The discovery of palynomorphs (Schirmer and Kurze 1960; Pozemova et al. 1976, in Yanev 1993) in some

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basal pelites (Mirovo Fm.), such as Lueckisporites virrkiae, L. platysaccoides, Klausipollenites schaubergeri and Falcisporites zapfei, suggests that this younger cycle generally developed during late Guadalupian?–Lopingian times. These deposits are more widely distributed than those of the Early Permian Cycle. In some places, however, they lack evidence. Over a large part of Moesia, the Taˆrgovishte Fm. is overlain by well-bedded varicoloured, finegrained sediments, yielding later Permian palynomorphs (in part equivalent, according to Pozemova et al. (1976),

Int J Earth Sci (Geol Rundsch) (2012) 101:129–157 b Fig. 9 Chronostratigraphical correlation and comparison between

Permian–Triassic continental sections of Southern Europe. Lithostratigraphic units (in alphabetic order)- AB Asciano Breccia, AF Ambon Fm., ALF Alcotas Fm., AM Aimoni Mb. (Melogno Fm.), AMF Anageniti Minute Fm., ASA Asa´ Fm., AV Auccia Volcanics, A7R Rhyolite, B Buntsandstein, BC Bric Crose Tuffs, BCO Basal Conglomerate, BF Bayonne Fm., BG Borda Granodiorites, BOF Boniches Fm., BRF Bron Fm., B1 ANT Buntsandstein del Penãl del Antechristo, B2 CR Buntsandstein di Cala Rotja, CA Angolo Limestone, CAF Can˜izar (=Rillo de Gallo) Fm., CBO Bovegno Carnieule, CC Chequilla Conglomerate, CdV Cala del Vino Fm., CF Collio Fm., Cl C lithozone (Melogno Fm.), CL Case Lisetto Metarhyolites, CMF Civitella Marittima Fm., CP Case Pollaio Mb. (Melogno Fm.), CRF Carpineta Fm., CSV Case Satta Volcanics, CVS Cala Viola Sandstones, DGC Dosso dei Galli Conglomerate, Dl D lithozone (Melogno Fm.), EC Port d’es Canonge Fm., EF Eze Fm., ESF Eslida Fm., FAF Fabregas Fm., FF Farma Fm., FPC Fosso Pianaccia Conglomerate, G Grezzoni, GF Graissessac Fm., GG Gonfaron Sandstones, GS Sollie`s Sandstones, HG Hoz del Gallo Conglomerate, LAV L’Avellan Fm., LF Lisio Fm., LI Lower Ignimbrites, LLF La Lieude Fm., LMF La Motte Fm., LP Les Playes Fm., LPE Les Pellegrins Fm., LPF Les Pradinaux Fm., LSF Les Salettes Fm., M Muschelkalk, MF Mirovo Fm., MIF Le Mitan Fm., MM Merifons Mb. (Salagou Fm.), MP Melogno Porphyroids, MQF Monte Quoio Fm., MUF Le Muy Fm., OF Ollano Fm., OM Octon Mb. (Salagou Fm.), PC Porticciolo Conglomerate, PF Porto Ferro Fm., PLC Punta Lu Caparoni Fm., PNQ Ponte di Nava Quartzites, PPF Poggio alle Pigne Fm., PPI Port-Issol Conglomerate, PRF Prados Fm., PS Pietra Simona Mb. (Conglomerato del Dosso dei Galli Fm.), PSI Pedru Siligu Fm., PT Plan de la Tour Fm., P1, P2, P3, ‘‘Saxonian facies’’, RF Rabejac Fm., RT Rotliegend, S Servino Fm., SAL Sant’Antonio Limestone, SF Salagou Fm., SLS San Lorenzo Schists, SMF St-Mandrier Fm., SPM San Pietro dei Monti Fm., SQ Mt. Serra Quartzites, SS Spirifer-bearing Schists, SSE Son Serralta Fm., T-L Tuilie`res-Loiras Fms., TAF Taˆrgovishte Fm., TBF Tabarrenã Fm., TCF Tocchi Fm., TF Transy Fm., TOF Totleben Fm., U-SP Usclas-St Privat Fms., VB Verrucano Brianzonese, VE Verrucano Fm., VEF Vetrino Fm., VF Viala Fm., VL Verrucano Lombardo, VMP Val Marenca Pelites, VS Viola Schists. Lithology: see Fig. 5 for the symbols. Other symbols—(1) unconformity, (2) erosional surface, (3) stratigraphic gap, (4) IR: Illawarra Reversal geomagnetic event (ca. 265 Ma; Menning 2001). Geologic time scale by Gradstein et al. (2004) (ISC 2009)

to the upper Tatarian of the Russian Platform), known as the Totleben Fm. From the above Permian stratigraphic framework, we point out some affinities with the second Southern Alpine cycle, in particular as regards the continental Val Gardena Sandstone and the evaporitic-marine Bellerophon Fm. of the Dolomites. The underlying unconformity marks a gap probably in part coeval with the already signalled ‘‘Mid– Permian Episode’’. In Moesia, the Totleben Fm. is unconformably capped by the Lower Triassic Buntsandstein red clastics (known also as the Petrohan Group), which are widespread across the country and gave rise to a new sedimentary cycle. This regional discontinuity marks a time gap of imprecise duration, which, according to some authors (e.g. Yanev 1981), seals the Permian–Triassic boundary.

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In this context, it is also worth mentioning that, in the Noevtzi section of the Kraishte Unit (SW Bulgaria), the basal part of the Petrohan Group includes some white wind-worn quartz phenoclasts (‘‘ventifacts’’), which are indicative of a hyper-arid climate and generally assigned to Dienerian–Smithian times (Durand 2006). (b)

Tuscany—In Italy, according to Rau and Tongiorgi (1974), the Mts. Pisani section (Fig. 9, no. 7 left) in northwestern Tuscany can be subdivided into two main sedimentary cycles. In our opinion, the basal Late Carboniferous to Early Permian alluvial-tolacustrine S. Lorenzo Schists Fm., very rich in megafloras, undoubtedly belongs to the Lower Cycle, as well as the overlying fluvial Asciano breccias and conglomerates. This red unit, which resembles the Dosso dei Galli Conglomerate of the Collio Basin in eastern Lombardy, rests unconformably on the above formation, which in the Valle del Guappero type-area displays in the lower part marine fossils (?brachiopods, bivalves, bryozoans, crinoids; Pandeli et al. 2008) and was on the whole related, according to the pristine chronostratigraphical classification, to a ?Westphalian D–Stephanian–Autunian time interval (Rau and Tongiorgi 1974). The presence of younger volcanic manifestations has been argued from the discovery of red rhyolitic rock fragments at the base of the Triassic Verrucano (the name of which is derived from this Pisan area), which indicates that volcanism occurred after the Asciano red-beds, but before the Triassic Verrucano. Therefore, it seems possible to suggest that such post-Variscan igneous activity in Tuscany, as in many other countries of Europe (Germany, Italy, France, Sardinia, Corsica, etc.), took place mainly throughout the Early Permian.

The Verrucano Group (which also comprises the superjacent Mt. Serra Quartzites) steps down unconformably on older sedimentary units and the metamorphic basement, marked by a very extensive gap. It corresponds to a fluvio-deltaic shelf complex (Tongiorgi et al. 1977), generally interpreted as (?)late Ladinian–Carnian in age, which is capped by Norian carbonates known as ‘‘Grezzoni’’. Its dating was supported by broader research (Rau and Tongiorgi 1974; Rau et al. 1988) which led to consider the Verrucano of Mts. Pisani to be linked to the second sedimentary cycle, probably belonging to the ?late Ladinian–Carnian of the La Spezia Triassic aborted rift. However, if compared with the same Tuscan siliciclastic outcrops, the very different age of the Pisan Verrucano could also be due to other geological causes, such as local tectonic activity and the influence of an irregular landscape. Eastward, south of the Arno River, in the

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neighbourhood of the village of Iano (near Volterra), the basal sedimentary succession includes, according to Vai and Francavilla (1974), the presence in some pelitic beds of Stephanian plants, as well as of rare crinoids, bivalves and probable brachiopods, which generally suggested a deltaicneritic environment for these deposits. From the section in Fig. 9, the onset of the very long stratigraphic gap between the Late Carboniferous–Early Permian rocks and the Middle–Late Triassic Verrucanotype was probably caused by Mid–Permian tectonics. During the latter times, the Verrucano Group diachronously eroded the previous deposits ending in a peneplane suitable for the ingression of carbonate marine conditions. In southern Tuscany, the post-Variscan stratigraphic record (Fig. 8, no. 7 right) seems mainly dominated, in the Mt. Leoni–Farma stream area, by Late Carboniferous and Late Permian/earliest Triassic shallow-water deposits, which are separated by a gap of approximately 35 Ma (Aldinucci et al. 2008a, b). In our opinion, however, this peculiar geological scenario could have itself been involved in the ‘‘Mid–Permian Tectonic Event’’, locally enhanced by the erosion of relatively older rocks and/or the lack of sedimentation. Above the P/T transition, which is still subject to discussion, appeared the Verrucano Group cycle. Its first unit, known as the Civitella Marittima Formation, has been until now ascribed by some authors (Lazzarotto et al. 2003; Aldinucci et al. 2008a) to the Early?–Middle Triassic (Anisian pp.). Instead, the overlain Verrucano sensu stricto (Mt. Quoio, Anageniti Minute, Tocchi Fms.), which rests unconformably on previous units, belongs to Ladinian– Carnian times. In this context, it is also noteworthy that the lower part of the last formation, with the presence of Carnian foraminifers, marks the beginning of the Late Triassic marine transgression. Marine conditions in other Tuscan areas affected Elba Island, where Bodechtel (1964) collected in the Rio Marina Fm. (about 50 m below the Verrucano) a sample yielding fusulinids referable to Parafusulina sp., which seems to belong to the Artinskian Praeparafusulina lutiginiP. pseudo-japonica zones (Khaler and Khaler 1969; Pasini 1991). Marine influences have been also recorded from SE of Mt. Amiata, in the Piancastagnaio geothermal field, with the discovery of Kubergandinian fusulinids ascribed to the Cancellina Zone (Pandeli and Pasini 1990; Pasini 1991). (c)

Ligurian Alps—Recently, the Briançonnais domain of the Ligurian Alps (Fig. 9, no. 6) was the topic of a review (Dallagiovanna et al. 2009). In contrast with former stratigraphic interpretations, the Late Carboniferous volcanic and sedimentary clastic deposits, which unconformably overlie a Namurian crystalline basement, have now been related only to Permian

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ages. This new dating, based on radioisotopic research, place the rocks within an Asselian–?Artinskian time-span, in firm conflict with the Westphalian– Stephanian macrofloras of the Ollano Fm. suggested by the past literature (Portis 1887; Bloch 1966). Moreover, the overlying Melogno porphyroids (MP) surprisingly highlighted two distinct dates: the lower calc-alkaline lithozone C pertains to the Early Permian (mainly Kungurian), whereas the uppermost lithozone D, which is sub-alkaline in nature, displays a Late Permian (Wuchiapingian) age. Consequently, an intermediate gap of about 14 Ma, extending for the entire Middle Permian, has been inferred. If similar interpretations are newly supported, this gap could be clear evidence of a ‘‘Mid–Permian Episode’’. Through a Late Permian unconformity, the Verrucano conglomerates and the Early Triassic quartzites follow upwards, capped by finer-grained clastic and carbonate deposits. (d) Sardinia—In northwestern Sardinia (Nurra), the region of the island where the Permian and Lower– Middle Triassic units are best exposed (Fig. 9, no. 4), the stacking of three main tectonosedimentary cycles or sequences, separated by regional unconformities, can be wonderfully observed (Cassinis and Ronchi 2002; Cassinis et al. 2003). The 1st small sequence, which is made up of late Autunian (i.e. late Asselian– early Sakmarian, see also Ronchi et al. 1998, 2008; Werneburg et al. 2007) plant-bearing sediments and volcanic rocks, rests directly on the Variscan crystalline basement and is discordantly overlain by a thick detrital megasequence (2nd cycle), mainly consisting of fluvial unfossiliferous red-beds with interspersed volcanic rocks in the lower part. However, the recent and significant find in the last formation of this cycle (Cala del Vino Fm.), below the Triassic Buntsandstein deposits, of large vertebrate bones (Ronchi et al. 2009), seems to support a late Early Permian to early Mid-Permian transitional age. Therefore, this datum would imply the presence of a Mid–Late Permian gap, probably interpreted as the local equivalent of the discussed ‘‘Episode’’ at a larger timescale. The uppermost siliciclastic 3rd cycle (‘‘Conglomerato del Porticciolo’’ and Arenarie di Cala Viola), as almost everywhere in the selected southern European sections, gave rise to a new sedimentary cycle, ?late Induan–Olenekian to Anisian in age, which lies unconformably on previous rocks. According to Pittau and Del Rio (2002), in the subsurface siliciclastics (i.e. the Cuggiareddu well), which are similar to those cropping out in the Cala Viola coastal area, two differing sporomorph assemblages occur. The older one bears Olenekian?–early Anisian taxa,


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standard for the continental Permian, due to the great number of diversified and careful studies, mainly concentrated on palaeontological subjects. The annexed stratigraphic section (Fig. 9, no. 3) shows a lower cycle, about 700 m thick, characterised by wellbedded fluvio-deltaic and lacustrine varicoloured formations (Usclas-St Privat, Tuillie`res-Loiras, Viala), known as the ‘‘Autunian Group’’ sensu Gand et al. 1997, which have been related to the early Cisuralian (Asselian ? Sakmarian) mainly based on abundant macro- and microfloral assemblages (Galtier and Broutin 1995, 2008; Schneider et al. 2006) and the occurrence of two ichnoassociations (Gand and Durand 2006). Cinerite key beds also crop out.

whereas the younger association yields typical forms from late Anisian times. This fluvial unit was progressively drowned by the marine Muschelkalk. (e)

Southern Provence—The Toulon-Cuers Basin of southwestern Provence (Fig. 9, no. 5 left) displays peculiar similarities with the Nurra succession of Sardinia, owing to the Permian proximity of these regions (Cassinis et al. 2003). The most distinct difference, at the top of Les Salettes Fm., is the Bau Rouge Mb., which is partly characterised by fluviolacustrine, macro- microfloral bearing sediments of as-yet imprecise correlation (post-Kungurian to preTatarian age by Broutin and Durand 1995; Broutin et al. 2002; latest Artinskian to early Kungurian in the opinion of the present authors). The volcanic activity, apart from the calc-alkaline products in the Avellan Basin, is much better represented than in Nurra and marked by repeated alkaline ignimbrites, pyroclastics and lava flows.

In contrast with the previous French basin, the BasArgens and Este´rel area (Fig. 9, no. 5 right) of southeastern Provence is characterised by a very different history. In particular, it was dominated by intense volcanic activity, which led to some isotopic and geochemical data of vital importance for interregional correlation, and based also on the discovery of a great number of fossiliferous sites (vertebrate footprints, macro- and microfloral assemblages, ostracods) throughout the entire section, allowing some key beds to be fixed, for the purposes of the reliable restoration of Permian regional stratigraphy. Among these are the dating by the 40Ar–39Ar method of the A7 Rhyolite to 272.5 ± 03 Ma (Zheng et al. 1992), i.e. to a late Early Permian (Kungurian) age, and the attribution of the Les Pradinaux, Le Mitan and Le Muy Fms., as well as the overlying La Motte (or Fabregas) Fm., to the early–mid Middle Permian (Roadian–Wordian: Durand 2006, 2008; Gand and Durand 2006; Bourquin et al. 2007). In contrast, on the basis of tetrapod associations, the cited formations have been ascribed by Lucas and Hunt (2006) to Guadalupian (Wordian, Capitanian) and Lopingian (Wuchiapingian) times, but this age attribution needs further research. Upwards, the Buntsandstein facies crops out unconformably, yielding early Anisian palynomorphs (Adloff in Durand et al. 1988). After this review, it follows that the ‘‘Middle Permian Episode’’ was overwhelmed, in Provence, by a younger event, marked by a gap generally running from the Late Permian to the Early Triassic, which could also be interpreted as the prelude of the subsequent Alpine sedimentation. (f)

Languedoc—Westwards in southern France, near Montpellier, the Lode`ve Basin is considered a

Above follows, from late Cisuralian (Artinskian– Kungurian) up to middle Guadalupian times, a second cycle of ca. 2,000 m thickness (‘‘Saxonian Group’’ sensu Gand et al. 1997), which was defined by a regional unconformity and by an overall southward thickening of deposits. Rare tuffaceous markers also occur (Nmila et al. 1992). The lower fluvial Rabejac Fm., yielding Supaia sp. and other floras, evolves in a dry, tropical and semi-arid climate to the silty red mudstones and thin playa-lake dolomites of the Salagou Fm. At the top, the base of the La Lieude unit, which starts with sheetflood and braided river conglomerates, as well as large-scale cross-bedded, pebbly channel sandstones, is supposed to be adjacent to the Illawarra Reversal (Bachtadse, in Roscher and Schneider 2006), i.e. at about 265 Ma. However, a careful regional calibration of the uppermost ichnoassociation IV (La Lieude) with Dromopus didactylus, Brontopus giganteus, Merifontichnus thalerius, Lunaepes ollierorum, Planipes brachydactylus, as well as of Batrachichnus salamandroides, Hyloidichnus major, Varanopus rigidus taxa found in few levels below, in the Salagou Fm. (Gand and Durand 2006), stressed by the regular stratigraphical position of these forms over the Association III with Varanopus curvidactylus/Microsauripus acutipes, Dromopus didactylus and Hyloidichnus major of the Rabejac Fm., which has been recently ascribed to late Artinskian–Kungurian owing to a macrofloral review by Galtier and Broutin (2008), allow the present authors to ascribe both La Lieude and Salagou Fms. to a late Cisuralian–early/mid Guadalapian interval, i.e. beneath the Illawarra Reversal geomagnetic event. In this context, as in Provence, the overlying middle Anisian Buntsandstein generally seals a gap of Late Permian to Early and younger Triassic age, which clearly increased the ‘‘Mid–Permian Episode’’ indicated in the literature. (g)

SE Iberian Ranges—The long and complex extensional story of the Iberian Basin, which is

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geographically subdivided into the Aragonese and Castillian branches of the Iberian Ranges, started during the Early Permian with the extensional collapse of the Variscan orogen and westward propagation of Neotethys, and continued during the Late Permian and the Triassic (e.g. Sopenã et al. 1988). According to Arche and Lo´pez-Go´mez (1996), Lo´pezGo´mez et al. (2002) and Arche et al. (2004), the continental facies in central to NE sectors of the Iberian microplate have been subdivided into three unconformity-bounded units or major sedimentary cycles: Autunian (mainly Early Permian), ‘‘Saxonian–Thuringian’’ (late Middle to Late Permian) and Buntsandstein (Late Permian–Early Triassic). As regards the first succession, the Iberian Ranges (Fig. 9, no. 1) contain a number of small outcrops of volcanic and/or sedimentary rocks, such as Retiendas, Valdesotos, Molina de Aragoń, etc. Some of them have been ascribed to the Early Permian (Autunian) by rich macroand microfloristic assemblages and absolute dating of volcanic rocks (Lago et al. 2004 and references therein). The general development of Middle–Late Permian to Triassic continental basins in Spain was not coeval with those in the rest of Europe (see chronostratigraphic chart of Fig. 9); in fact, in the Iberian Ranges the post-Autunian sedimentation is divided into two main pulses of rifting separated by an unconformity. The late Middle Permian to Late Permian sediments (‘‘second succession’’ of Arche and Lo´pez-Go´mez 1996) are represented in SE Iberian ranges by the Boniches and Alcotas Fms., which lie unconformably over the Lower Permian successions (Lo´pez-Go´mez and Arche 1993; Benito et al. 2005; Die´guez et al. 2007). This 2nd succession, in our view, could represent the true beginning of the ‘‘Alpine’’ cycle in this area. Recent detailed mineralogical-petrological, palaeontological and paleosol profile analyses of alluvial sediments of the Alcotas Fm. (lower Lopingian) has allowed us to infer that significant environmental changes occurred during this time period (Benito et al. 2005; Arche and Lo´pez-Go´mez 1996; Die´guez et al. 2007; De la Horra et al. 2008). Finally, the latest Permian–Middle Triassic deposition (third succession) follows unconformably, representing the second pulse of rifting (De La Horra et al. 2008): it is represented by the continental Buntsandstein facies (starting with the Hoz del Gallo and Can˜izar Fms. in the Iberian Ranges) and the shallow-marine Ro¨t, as well as a lower part of the Muschelkalk facies, deposited in a single rift basin (Sopenã et al. 1988; Lo´pez-Go´mez and Arche 1993). It should be borne in mind that in Spain the term Buntsandstein is attributed to continental and coastal

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siliciclastic sediments of Late Permian (Wuchiapingian) to Early Triassic age (Sopenã et al. 1988; Arche and Lo´pezGo´mez 1996; Lo´pez-Go´mez and Arche 1993; Arche et al. 2004). The P/T boundary (PTB) in Spain lies somewhere in a continental red-bed succession, and thus, it is difficult to separate the two systems, or establish with accuracy a regional correlation in the sedimentary record. In the SE Iberian Ranges (Fig. 8, no. 1), the PTB is probably located at the unconformable contact between the lower and upper conglomerate subunits of the Hoz de Gallo Fm. The latter, in the lower part of the Can˜izar (=Rillo de Gallo) Fm., is also termed the Chequilla Conglomerate (Lo´pez-Go´mez et al. 2005; Durand 2006; Bourquin et al. 2007). Only the lower part of the Hoz del Gallo Formation contains Thuringian (Late Permian–Chanshingian?) microflora. In our opinion, as indicated in a paper on the regional stratigraphy of NE Spain (Iberian, Ebro and Catalan Basins) by Arche et al. (2004), a powerful correlation tool to be combined with lithostratigraphic and biostratigraphic data is the analysis of angular unconformities and hiatuses that subdivide the sedimentary record into unconformity-bounded units. A major difference between the Iberian Peninsula and the rest of Europe is that in Spain it is not easy to detect which could be the hiatus-unconformity which marks almost everywhere the ‘‘Middle Permian event’’, because three different angular unconformities occur, as stated above. (h)

Balearic Islands—The Late Palaeozoic sedimentary evolution of Majorca and Minorca seems to follow an analogous pattern to that of the Iberian Ranges, apart from the first ‘‘Autunian’’ succession which in the islands is totally absent (Lo´pez-Go´mez and Arche 1993). In the former area (Fig. 9, no. 2 left), the Permian deposits start with the Port d’Es Canonge Fm. which consists of a basal conglomerate overlain at first by a thick claystone unit and later by the Asa´ Sandstones, yielding near the base pollen and spores, such as Lueckisporites virrkiae, Nuskoisporites dulhuntyi, Paravesicaspora splendens, Klausipollenites schaubergeri, Crucisaccites variosulcatus, etc. (Ramos and Doubinger 1989), generally ascribed to a Late Permian (Thuringian) age. According to other authors (Bourquin et al. 2007), the Port d’Es Canonge deposits are correlated to the St-Mandrier (Provence) and Cala del Vino (Sardinia) fms. and separated by an unconformity from the Asa´ Fm. More recently, for Linol et al. (2009), the Port d’Es Canonge and Asa´ fms. may correspond to a complete sedimentary cycle (i.e. retrogradation/progradation), identical to the one described in Minorca and ascribed to Late Permian times.

In Minorca the Middle?–Upper Permian fms. are represented, respectively by P1-P2-P3 (‘‘Saxonian facies’’),


respectively (Broutin et al. 1992). The Late Permian age of the top of this succession was very recently confirmed by a rich and diverse ‘‘Thuringian’’ palynoflora and several megafloral taxa found at Cala del Pilar (Fig. 9, no. 2 right) by Bercovici et al. (2009). As for most continental Late Palaeozoic deposits of western Europe, the top of the Permian succession in both the islands is marked by a major unconformity (Bourquin et al. 2007; Linol et al. 2009). In Minorca, above this unconformity, the beginning of Triassic sedimentation is characterised by azoic braided river systems: the B1 clastic deposits (Buntsandstein) of Antechristo locality were recently ascribed to the Early Triassic by Bercovici et al. (2009) and show at their base a quartz-conglomerate considered by the authors to be very similar to that of Provence and NW Sardinia (Olenekian: Bourquin et al. 2007; Linol et al. 2009; Bercovici et al. 2009). The overlying Cala Roja deposits bear the first palaeontological data, which relate them to the Anisian. In Majorca, in contrast, the P/T gap seems longer, because the first Triassic sediments are the overlying claystones and sandstones of Son Serralta, which have yielded some microfloras with typical Anisian assemblages. On top, in the two islands, marine deposits of Muschelkalk facies crop out, starting from mid–late Anisian times.

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•

•

Late Palaeozoic geodynamic setting and evolution of Southern Europe Late Palaeozoic–Early Triassic times marked the transition from the Variscan orogenesis to the Alpine depositional cycle, which was induced by the opening of the Neotethys ocean. In the examined regions, the Alpine sedimentary cycle is delimited at its base by a marked unconformity that has been observed everywhere. However, the stratigraphic gap related to this unconformity, even if it developed around the Middle Permian, is not completely synchronous and does not have the same duration in all the areas: in particular, the base of the Alpine cycle has an age that probably ranges from the Late Permian (Bulgaria, Southern Alps, Ligurian Alps, S Tuscany, Iberian Ranges and Balearic Islands) to the Early (Sardinia, SW Provence) or Middle Triassic (SE Provence, N Tuscany and Languedoc). The beginning of the Alpine sedimentary cycle shows, in every considered sector, typical and common features which characterise and confirm such correlations; they can be synthesised as follows: •

the onset of a generalised and large-scale molassic sedimentation. The Alpine cycle begins everywhere with clastic deposits (generally conglomerates or

•

•

•

sandstones), rich in quartz, deriving from the erosion of the residual Variscan relief. The different ages of the sediments—Late Permian in northeastern Bulgaria (Taˆrgovishte Fm.), the Southern Alps (Verrucano Lombardo and Val Gardena Sandstone), Ligurian Alps, Iberian Ranges and Balearic Islands (Boniches, Alcotas and related formations), and Triassic in Tuscany (Verrucano), Sardinia, Southern Provence and Languedoc—are related to the local palaeogeographic domains and do not alter the meaning of this sedimentary record; the onset of marine ingression. In all the examined regions, the continental clastic deposition that characterises the base of the Alpine cycle is progressively replaced by marine sediments representing the ingression of Neotethys. The age of the first marine formations indicates that the transgression was proceeding, from east to west, from the Late Permian (Bellerophon Fm., in part a lateral equivalent of the Val Gardena Sandstone in the eastern Southern Alps) to Early (ServinoWerfen Fms. in the Southern Alps) and Middle Triassic (Ligurian Briançonnais, Sardinia, France, Spain and other western regions); the change in subsidence. During the periods preceding the Alpine sedimentary cycle, subsidence was concentrated in tectonic basins, where it reached the highest values (e.g. over 1,200 m of deposits in about 5 Ma in the Collio Basin, and up to 2,500 m in the Lode`ve Basin); in contrast, at the start of the Alpine deposition, a recovery of the isotherms occurred and a general minor and uniform subsidence took place in enlarged sedimentary basins; the transition from continental sedimentation, in fluvial-lacustrine intramontane basins (ephemeral to perennial and deep lakes), which characterised the earlier Permian successions, to a regional widespread deposition, indicating progressive peneplanation of the emerged lands, that promote the aforementioned marine transgression; the transition from discontinuous and localised sedimentation of the older sedimentary cycles, characterised by several unconformities, hiatuses and changes in sedimentary facies, to a more or less continuous succession, without major unconformities and hiatuses; the end of volcanism. The Late Palaeozoic volcanic activity, of which the bulk is concentrated in the Early Permian, seems not to develop later than the ?middle Guadalupian (Provence and Languedoc). In fact, generally, the onset of the Alpine depositional cycle is almost everywhere (except the Ligurian Alps which seem to go against this trend) devoid of any volcanic event and represents the conclusion of the preceding volcanism that affected all the examined regions and that was strictly linked to tectonic events. In the

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Southern Alps, a new volcanic episode took place consistently during the Ladinian and Carnian, but its geodynamic meaning was completely different (Gaggero, in Cassinis et al. 2008a) as it was linked, at least in part, to the beginning of the rifting in the Alps; the climate change. The Alpine sedimentary succession indicates that the climate was progressively becoming drier across Europe, with warm and semi-arid to arid conditions, whereas before it was characterised by rapidly alternating and locally varying wet monsoonal and dry periods (Schneider et al. 2006; Kutzbach and Ziegler 1993). The southern Variscan relief, which in the Early Permian was probably not higher than 2 km (Fluteau et al. 2001) or even much lower (Roscher and Schneider 2006), was completely peneplanated during the Late Permian. An arid belt in the subtropics over the western side of Gondwana and Laurussia has been postulated by many authors. The global aridisation trend of northern Pangaea throughout the Permian, indicated by playa and sabkha red-beds, aeolianites and evaporites, was interrupted by several short phases of increased humidity, indicated by wet red-beds, lake sediments and coal deposits (Roscher and Schneider 2006). A maximum of aridity in the Kungurian-toCapitanian time-span is postulated by the same authors and ascribed to a reorganisation of the major ocean currents. A global cooling event (Kamura Event: Isozaki et al. 2007) ended shortly before the Guadalupian–Lopingian (Middle–Late Permian) boundary (ca. 260 Ma). According to the above authors, this 3–4 million years long unique cooling event occurred clearly after the Gondwana glaciation period (Late Carboniferous to Early Permian) in the middle of the long-term warming trend towards the Mesozoic. This cooling may have been a direct cause of the endGuadalupian extinction of low latitudes.

All the above features of the Alpine sedimentary cycle, and the marked unconformity localised at its base, point to a geodynamic and plate reorganisation source, whose meaning is not yet entirely clear. The geodynamic event that marks the base of the Alpine cycle would be positioned very close to or strictly connected with the onset of the geomagnetic signal known by the name ‘‘Illawarra Reversal’’ (I.R.). It generally developed according to the authors (such as Menning 1995, 2001; Steiner 2006; others) between the Mid-Wordian and the basal Capitanian, i.e. during the Middle Permian (Guadalupian), and ended the ‘‘Carboniferous–Permian reversed polarity superchron’’ (also named the ‘‘Kiaman superchron’’) after ca. 50 Ma. From a palaeogeographic point of view, in Late Palaeozoic times, the South-Alpine and other examined regions were part of the southern border of the European Variscan

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chain. This orogen was the product of the final collision between the Laurussia and Gondwana continents, which was preceded by the collision of Laurussia with the Avalonia and Armorica microplates (Scotese and McKerrow 1990). Variscan deformation and metamorphism reached their acme during the Early Carboniferous (Laüfer et al. 2001), and the metamorphic temperature peak was presumably reached between 340 and 320 Ma (Schaltegger and Brack 2007). At the end of the orogenesis, the belt had a direction presumably ranging from E–W to WSW–ENE (e.g. Ziegler et al. 1997; Matte 2001) and extending from central and northeastern America to Asia. The plate reconstructions show (Ziegler and Stampfli 2001; Stampfli and Borel 2002; Vai 2003; Torsvik and Cocks 2004): a continent–continent collision zone in the western and central Mediterranean area; another collision zone to the west, deriving from the oblique subduction of the west Africa and GuaiananAmazonian platform beneath Laurussia (AlleghenianMauritanides orogens); at the southeastern side, an oceanic plate (Palaeotethys) in subduction towards the N and NW, beneath the Laurussia plate; and finally, to the NE, the Urals orogen caused by the convergence between Laurussia and Siberia. From the mid part of the Carboniferous, the Pangaea supercontinent was completely assembled; it was partially surrounded by subducting oceanic plates and enclosed the large eastward-opening ocean of Palaeotethys. This wedge-shaped ocean was divided into two plates by an active ridge: the northern plate of oceanic lithosphere in subduction to the north, beneath northern Pangaea, and a plate comprising the southern part of Palaeotethys and continental Pangaea. Two main geodynamic events affected this scenario: (1) the beginning of the north-directed subduction of the Palaeotethys oceanic ridge beneath Eurasia and the alreadyformed Variscan chain; and (2) the progressive opening of the Neotethys Ocean, after which the Cimmerian continent rifted from the northern margin of southern Pangaea, essentially during the Middle Permian (270–265 Ma; Gutie´rrez-Alonso et al. 2008; Muttoni et al. 2009). In our view, the subduction of the still-active Palaeotethys oceanic ridge beneath Eurasia created a triple junction among the ridge and two convergent margins (the Variscan collisional chain to the west and Palaeotethys subduction zone to the east; Fig. 10), and due to its instability, the western convergent margin progressively changed into a diffuse dextral transform margin. So the unstable TTR triple point transformed in a stable transform–trench–ridge junction, progressively migrating towards the ENE owing to the subduction and subsequent closure of the Palaeotethys ocean. The Palaeotethys, Laurasia and Gondwana junction (FTR triple point) lasted throughout Permo-Carboniferous and Early Permian times as the substantial


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Fig. 10 Palaeotectonic and palaeogeographic reconstruction of the Pangaea during Early Permian times. The subduction of the Palaeotethys ridge beneath Eurasia progressively transformed the western collisional Variscan margin in a diffuse dextral transform margin and created a stable transformtrench-ridge junction (indicated by the star in the figure), gradually migrating towards ENE

alignment of the new transform and the preceding trench margins took place, as in the case presently observed at the southern end of the Gulf of California. The progressive transformation of the western Variscan chain from a collisional to a dextral shear margin led to the deposition in many European regions, and especially in Spain, France, Germany and Italy, of thick piles of fluvial-lacustrine sediments in narrow strike-slip or tectonic basins. The Permo-Carboniferous inception of the subduction of the Palaeotethys active oceanic ridge beneath Eurasia, and the transformation of the western and central Mediterranean sector of the Variscan collisional chain in a dextral strike-slip orogen evolving towards a dextral transform diffuse margin, progressively affected by transtension and crustal thinning, is suggested by many elements. Continental deposition into strike-slip basins was coupled with widespread magmatic activity, both extrusive and intrusive, of a highly variable chemistry, indicating lithospheric surge and uplift, probably favoured and conditioned by the subduction of the active Palaeotethys oceanic ridge and the presence of active deep-rooted transcurrent faults which involved a weakened crust. In general, these basins show common typical features such as a distinctive elongate morphology (locally sigmoid) caused by bordering marginal faults, strong lateral and longitudinal asymmetries with abrupt lateral and vertical changes of sedimentary facies, and tectonically induced irregular subsidence. For these reasons, many of them have been considered as pullapart or strike-slip basins connected to a regional shear zone that affected southern Europe after the end of the Variscan orogeny (Arthaud and Matte 1977; Cassinis and Perotti 1994; Burg et al. 1994; Schaltegger and Brack

2007). Also in the Southern Alps, the Collio, Tione, Tregiovo and Orobic basins formed under strike-slip to transtensional conditions (Bertoluzza and Perotti 1997) and the palinspastic reconstructions from palaeomagnetic data (Westphal 1976; Heller et al. 1989; Muttoni et al. 1996, 2003) indicate that many still recognisable Permian faults, like the Giudicarie Line for instance, had a formerly ESE–WNW orientation, which roughly coincides with the regional direction of the Variscan transform margin (Cassinis and Perotti 1994, 2007; Bertoluzza and Perotti 1997). The second main geodynamic event of the Late Palaeozoic period was the onset of the progressive opening of the Neotethys Ocean (Fig. 11). The transition from a dextral shear to an extensional tectonic regime caused the formation of the primary unconformity and the deposition of the overlying Alpine sedimentary cycle with its abovedescribed features. The birth of this ocean affected the study areas from the Middle Permian. The northwestward progressive propagation of the rifting, followed by marine ingression, caused the transition from a dextral shear to an extensional tectonic regime and the subsequent end of the transform movements. The Alpine tectonosedimentary cycle reveals a Late Permian structural reorganisation, marked by a diffuse and longer wavelength extensional regime. Magmatism changed abruptly at about the Middle Permian, from high-K calc-alkaline geochemistry to markedly alkaline compositions in southern and western Europe, and shortly after ceased. During this period, recovery of the isotherms occurred and general minor subsidence took place in a

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Fig. 11 Palaeotectonic and palaeogeographic reconstruction of the Pangaea during Late Permian times. The progressive opening of the Neotethys Ocean and the consequent drifting of the Cimmerian continent towards the NE caused the northwestward propagation of the rifting, followed by marine ingression, and the transition in Southern Europe from a dextral shear to an extensional tectonic regime

widespread sedimentary basin. This basin stretched for thousands of kilometres and engulfed the preceding pullapart basins. Stretching and extension were no longer concentrated in narrow or restricted areas, and influenced the entire Southern Alps and central-western Europe.

General conclusions On the basis of the chronostratigraphic correlations described above and synthesised in Fig. 9, it is possible to argue some general points which couple lithostratigraphicdepositional data and the main tectonic phases of the Late Palaeozoic period. In our view, what is clearly shown by Fig. 9 is that in the Southern Alps, which represent the main reference sector of this paper and, more generally, in most of the considered areas (i.e. in the selected south European or western Mediterranean sectors), two very different ‘‘worlds’’ in terms of tectonics and sedimentation occurred. The older one spans from Mid–Late Carboniferous and Early Permian times up to the middle part of the Guadalupian: it is represented by sometimes huge volcano-sedimentary sequences of alluvial-to-lacustrine clastics and extrusive rocks. These sediment piles, locally sourced and representing a large range of terrestrial palaeoenvironments, developed under both wet and dry climatic conditions. The basins which hosted the sedimentary deposits and the associated magmatic products were the expression of a transtensile tectonic regime, which largely affected the whole of Palaeoeurope and was induced by the N-directed

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subduction of the Palaeotethys active oceanic ridge and the transformation of the western Eurasian sector of the Variscan chain in a dextral strike-slip orogen and transform diffuse margin (Fig. 10). The existence of an intra-Pangaea dextral megashear system of Laurasia versus Gondwana during the PermoCarboniferous seems to favour the hypothesis of an Early Permian Pangaea ‘‘B’’ (Irving 1977; Morel and Irving 1981), successively evolving to Pangaea ‘‘A’’ during the Late Permian (Vai 2003; Muttoni et al. 2003, 2009 and reference therein). Even though a discussion on the configuration of Pangaea (Pangaea A, B and C) near the end of the Palaeozoic is beyond the purpose of this paper (see Torsvik and Cocks 2004, for an analysis of the problem), it must be outlined that in our reconstruction the dextral megashear between Gondwana and Laurasia should be due to the onset of the subduction of the Palaeotethys active oceanic ridge, and this shear does not imply a relative lateral displacement of 3,000 to 6,000 or more km between Gondwana and Laurussia, at a relative speed of more than 10 cm/year, with all the involved problems (Torsvik and Cocks 2004; Muttoni et al. 2009). The dextral shear would be induced and supplied by the nature of the triple junction itself, and is compatible also with the classical Pangaea A configuration. The succeeding geological setting (2nd Permian cycle) is first witnessed by the widespread deposition of a coarseto-fine blanket of red-beds which mirrors the final erosion and dismantling of the Variscan orogen. This new geological ‘‘world’’ was devoid of magmatic activity, the termination of which is to be considered as a major element of


a dramatic change in the geodynamic setting. This younger depositional cycle is linked to vigorous plate reorganisation, leading to the opening of the Neotethys ocean (Fig. 11) and culminating in the Middle Triassic and later times, and was controlled by a wider extensional tectonics with the development of large sedimentary basins which sutured the previous ones, and also spread over the remaining topographic highs of the Variscan basement. The major regional angular unconformity between the two Permian cycles was probably caused at least in part by a deformation pulse, which induced faulting, gentle folding, uplift and erosion or non-deposition. This tectonic event, connected to the transformation from a strike-slip to an extensional tectonic regime, and to another change of the relative plate directions, can be related to the so-called ‘‘Mid–Permian Episode’’ of Deroin and Bonin (2003), locally accompanied by (trans)compressional activity (e.g. Prost and Becq-Giraudon 1989; Cadel et al. 1996). The boundary between the two major tectonosedimentary cycles is also synchronous with the geomagnetic ‘‘Illawarra Reversal’’ (I.R.) event, which took place during the Middle Permian (Guadalupian) (Menning 1995, 2001; Steiner 2006; others) and is linked to the described Permian geodynamic change. Some authors (e.g. Isozaki 2009) have recently postulated as the trigger agent for the remarkable change in geomagnetism related to the I.R., as well as for the Pangaea breakup, a major change in the Earth’s geodynamo, with superplume activity. In any case, in several countries of Western Europe or in the Peri-Mediterranean area, these two aforementioned major successions, respectively ascribed to the closure of the Variscan movements and the onset of the Alpine cycle, are separated by a variable but long-lasting period of erosion or non-deposition generally beginning in the ‘‘Middle Permian’’ and locally extending up to Early Triassic times. Acknowledgments This paper benefited from several years of research by the authors, generally realised along with a large number of national and foreign colleagues. We are grateful to the referees (J.-P. Deroin and two others anonymous) for their critical comments and constructive criticism, which greatly improved a first drafting of the manuscript. Moreover, H. Lu¨tzner is warmly acknowledged for his helpful suggestions on the German Rotliegend. This work is a MIUR and CNR grant contribution.

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