Pennsylvanian floras from Italy : an overview of the main sites and historical collections

The Pennsylvanian was one of the most important times for coal formation in Earth history. The lowland areas of Eura­ merica and China were covered by extensive wetland forests dominated by arborescent lycopsids and tree ferns (OP LUŠ­ TIL & CLEAL, 2007). Extensive floras are known from Up­ per Silesia, the Intra Sudetic Basin, Central and Western Bo­ hemia, South Wales and from the Pennines (for more details see OPLUŠTIL & CLEAL, 2007). In Italy (Southern Alps, Tuscany, Sardinia, Liguria), se­ veral outcrops of terrestrial sediments have also yielded Pennsylvanian floras. Although the Carboniferous sections are mostly scattered and of limited extent, these Pennsylva­ nian occurrences are fundamental for regional correlations and palaeogeographic reconstructions. Therefore the goal of this paper is to provide an updated review on the main sections which have yielded rich Penn­ sylvanian plant megafossils and palynofloras, hoping that a future taxonomic revision of them can provide a better pic­ ture of the Pennsylvanian floras of Italy.


INTRODUCTION
The Pennsylvanian was one of the most important times for coal formation in Earth history. The lowland areas of Eura merica and China were covered by extensive wetland forests dominated by arborescent lycopsids and tree ferns (OP LUŠ TIL & CLEAL, 2007). Extensive floras are known from Up per Silesia, the Intra Sudetic Basin, Central and Western Bo hemia, South Wales and from the Pennines (for more details see OPLUŠTIL & CLEAL, 2007).
In Italy (Southern Alps, Tuscany, Sardinia, Liguria), se veral outcrops of terrestrial sediments have also yielded Pennsylvanian floras. Although the Carboniferous sections are mostly scattered and of limited extent, these Pennsylva nian occurrences are fundamental for regional correlations and palaeogeographic reconstructions.
Therefore the goal of this paper is to provide an updated review on the main sections which have yielded rich Penn sylvanian plant megafossils and palynofloras, hoping that a future taxonomic revision of them can provide a better pic ture of the Pennsylvanian floras of Italy.
The successions, called by many authors the "Basal Con glomerate", are alternations of conglomerates, sandstones and siltstones composed of metamorphic and veintype quartz clastics. These units were also name "nonporphyric" conglo merates (e.g., BAGGIO & DE MARCO, 1960), in order to distinguish them from younger deposits where volcanoclastic deposits occur. The bedding of these generally coarsegrained sediments is often irregular and some crude channelling is ob served. Deposits occur generally pinched along major tectonic lines or in stratigraphic nonconformities above the metamor phic basement, and represent the "Southern Alps sedimentary front". These sediments are the product of the erosion of the Variscan mountain chain, and the contact with the crystalline   (from PITTAU et al., 2008a, mod.) A -Italian/Swiss sector between Lake Maggiore and Lake Lugano; B -Italian/Swiss sector between Lake Lugano and Lake Como. Bold line is the Italian-Swiss border. basement is marked by a gap of unknown time (BERTOTTI, 1991). The thickness varies from 0-15 m in the Val Sanagra (VENzO & MAGLIA, 1947), to 20-30 m in the Val Rezzo (Fig. 3) and in the upper Val Colla, and to about 100 m beneath the Denti della Vecchia (LEHNER, 1952).
The finer greytoreddish clastic sediments structurally de veloped in a basin situated south of the Marzio Lineament, (or BrusimpianoCabiaglio Lineament). They generically follow the initial deposition of volcanicrich conglomerate, and are called the Mesenzana Formation (CASATI, 1978;see Fig. 5).

SECTOR B
To the East, between the Lugano and Como lakes, some small outcrops with fine to coarse grained clastic deposits occur (Fig. 2B), including Alpe Logone, which has yielded a rich macrofloral association. The first report on Carbonife rous macrofloras from this locality is from MAGNANI (1946) Mariopteris, Neuropteris, Linopteris). Poorly preserved banded fragments of Sigillaria were also reported from the arenaceous layers. The rich collection, housed in the Museo Civico di Storia Naturale of Milan, is currently under revi sion (Fig. 4).
The flora was ascribed to the late Westphalian (Westpha lian C) by VENzO & MAGLIA (1947) and VENzO (1951). These authors consider the flora of the Alpe Logone to be slightly older than the flora from the Manno Conglomerate in Ticino (see below), even if both show close affinities. Accor ding to PITTAU et al. (2008a), the very rich Logone and Man no's macrofloristic assemblages allow assignment to the Bol sovian (Westphalian C) or to the DuckmantianBolsovian (Westphalian B-C) transition.

SECTOR A
To the West, between the Maggiore and Lugano lakes ( Fig.  2A), several small outcrops of the Manno conglomerate are known. The type section crops out in the homonymous vil lage in Ticino (Switzerland). The fossiliferous successions are characterized by alternations of fine layered sandstones and conglomerates of lightgrey colour. Locally they bear anthracitetype rock layers with poorly preserved plant re mains. As in Manno, these deposits occur in very scattered outcrops, generally pinched along tectonic lines. They rep resent the oldest sedimentary units in the Western Southern Alps. The Manno conglomerates likely filled a faultbounded intracontinental basin characterized by fluviolacustrine and fluviopalustrine environments. These deposits represent the base of an initial tectonosedimentary cycle developed mainly during the Early to Middle Permian throughout the Southern Alpine domain (e.g., GAETANI et al., 1986;CAS SINIS & PEROTTI, 2007).
From the Manno typelocality, HEER (1876) listed Calamites cisti, Sigillaria elongata and S. elegans. ESCHER (1911), confirmed Calamites cisti, and Sigillaria elonga , but attributed the last species to S. tessellata. SORDELLI (1896), recognized 13 species; ten are common with the flora from the Alpe Logone, including five species of Sigillaria, and another five species among the genera Calamites, Lepidodendron and Cordaites. He attributed the Manno flora to the early Stephanian, but with many Westphalian elements (SORDELLI, 1896). VENzO (1951) attributed the flora from Manno to the transition between the Westphalian B and Westphalian C, suggesting it to be slightly older than the flora from Alpe Logone (see above). JONGMANS (1950), related the floras of various Swiss localities (including Manno), first to the Westphalian B-C due to the presence of some elements such as Linopteris neuropteroides, cf. Pecopteridium, Sigillariaephyllum, Cordaites cf. borassifolius, but later considered it to be slightly younger, most likely West phalian ("Mittleres Westphalen", JONGMANS, 1960, p. 95).
Along the GermignagaBèdero road on the eastern side of Lake Maggiore, some light grey coloured layers of sand stones and conglomerates also occur. Locally, they bear an thracite with badly preserved plant remains including Sigillaria, which is putatively attributed to the Stephanian (VENzO & MAGLIA, 1947). Clasts of this succession show an origin from the metamorphic basement alone, but at the top of the Bèdero section, and in the very nearby outcrop, (i.e. along the LuinoLaveno railwayline), volcanicrich conglomerates are also reported by these authors and thus suggesting a younger (Permian?) age for these latter sedi ments (Fig. 6).
More recently, the Bèdero section (Lake Maggiore, Fig.  2A and Fig. 7) yielded a rich palynoflora, which allowed as signment of these sediments to the late Westphalianearly Stephanian (PITTAU et al., 2008a). In the sporomorphs, 42 genera and 76 species with one new genus (Cassinisporites) and ten new species have been distinguished. The Bèdero assemblages are suggested as being younger than the suc cessions studied from NorthEastern Italy, and to be more or less of the same age as the flora of San Giorgio (SouthWest ern Sardinia). The dominance of trilete spores, with a pro nounced taxonomic diversity, and Florinites pollen (over 70%), is indicative of a welldeveloped flora dominated by ferns, pteridosperms and Cordaitales, typical of a lowland flora (PITTAU et al., 2008a).

Eastern Southern Alps and border with Austria (Carnian Alps)
The Carboniferous successions of the Eastern Southern Alps crop out in several localities of the Carnian Alps, near the border with Austria and in Carinthia (Fig. 8). They represent the lower part of the more than 200 metrethick terrestrial transitionalmarine PermoCarboniferous sequence ( Fig. 9).
The Corona Formation is characterized by its almost complete lack of carbonatic levels (so far only one has been identified, see Krainer in VENTURINI, 1990b). It consists mainly of alternations of fine quartzose conglomerates, sand stones and siltstones corresponding to subaerial or paralic environments (VENTURINI, 1990a, b). There also exist, two transgressional acmes with fine siltstone, hummocky structures and a high abundance of marine fauna (brachio pods, crinoids, marine ichnofossils). Plant megafossils occur in the fine sandstones and pelitic levels (Fig. 10), and several sphenophyte trunks have been found in situ (with a diameter of up to 20 cm). Coalrich levels of up to 30 cm have also been recorded from these horizons (SELLI, 1963 (Fig. 11), are currently stored at the Museo Friulano di Sto ria Naturale of Udine ( Fig. 12; courtesy of Udine Museum), at the University of Innsbruck (Austria) and at the Landes museum Klagenfurt (Germany).
The floras of the Austrian side of the border have been mostly studied since the 1980's. Grouping the floras stratigra phically (Fig. 13), the following information can be given (for more details see FRITz & KRAINER, 2006. The Bom baso Formation crops out near Passo Pramollo (FRITz & KRAINER, 1995, 2006, Tomritsch (layers 1, 2, 5, 6) and Rudniggraben (KRAINER in VENTURINI, 1990b;FRITz & KRAINER, 2006). According to the authors, typical ele ments of the floras include Linopteris neuropteroides, Neuropteris cordata, N. scheuchzeri and N. ovata. Tomritsch 6 has been attributed to the Odontopteris cantabricazone, due to the presence of Sphenophyllum oblongifolium and Neuropteris scheuchzeri (moved to Macroneuropteris) following the mega florazonation of WAGNER (1984). This translates to a Can tabrian age (late Pennsylvanian; FRITz & KRAINER, 1995). The fossiliferous horizons of Malga (Alm) Straniger, Wai degger Alm, zollner See, Passo del Cason di Lanza and Tom ritsch 3 belong to the Meledis Formation. Tomritsch 3 has been attributed, due to the presence of Sphenophyllum angus-  tifolium and Pseudomariopteris busquetii, to the Sphenophyllum angustifolium zone, which according to WAGNER (1984), corresponds to a lower to middle Stephanian C age. One of the most prominent elements of this flora is Linopteris neuropteroides var. major, as well as a high abundance in frag ments of the Neuropteris cordata and N. ovata (FRITz, 1990;FRITz & KRAINER, 2006 STACHE, 1874;FRECH, 1894;GEyER, 1897;FRITz, 1980FRITz, , 1990FRITz, et al. 1990;KRAINER, 1992;FRITz & KRAINER, 1993). The presence of Pseudomariopteris busquetii attributes these floras to the Sphenophyllum angustifolium zone, (lower to middle Stephanian C; FRITz & KRA INER, 1993). Linopteris neuropteroides and Neuropteris cordata seem to disappear in the upper part of the formation. The appearance of the genus Lebachia, an important conifer genus during the Permian, is of particular interest, and not described from any of the other Carboniferous floras of the Carnian Alps (FRITz & KRAINER, 1993, 2006 So far, there has been only one study of the palynoflora of this area (FRANCAVILLA, 1966). According to the au thor, the microflora is characterized by the spores Densosporites, Dictyotriletes, Lycospora and Verrucosisporites. Very interesting regional correlations and comparison between the Italian/Austrian Carboniferous and Permian flo ras could be also done in the future with neighboring countries such as Slovenia (KOLARJURKOVŠEK & JURKOVŠEK, 2012).

Pisani Mountains
The Pisani Mountains are located along the socalled Mid dleTuscan Ridge, a regional morphostructural high extend ing from the Apuan Alps to the Leoni Mountain (Fig. 14).
The stratigraphic sections of the Pisani Mountains, near San Lorenzo of Vaccoli in NorthWestern Tuscany (Valle del Guappero), can be subdivided into two main sedimentary cy cles (RAU & TONGIORGI, 1974). The first is represented by the alluvial to lacustrine San Lorenzo Schists (Fig. 15), very rich in megafloras of Pennsylvanian to Cisuralian age. The overlying fluvial Asciano red breccias and conglomerates, are attributed to the Early Permian for regional correlations.   Fig. 17 shows a biostratigraphic and lithostratigraphic subdivision of the PennsylvanianAutunian succession, on the basis of different fossil floras found at various localities in the Valle del Guappero (from TRE VISAN, 1955and RAU & TONGIORGI, 1974in LANDI DEGLI INNOCENTI et al., 2008mod.).
It is suggested that these floras are similar to the Sardi nian flora of the San Giorgio basin described by COCOzzA (1967). The genera Annularia, Asterophyllites, Calamites, Callipteridium, Cordaites, Pecopteris, and Walchia, occur in both floras (LANDI DEGLI INNOCENTI et al., 2008;CIOPPI in MONECHI & ROOK, 2010;see Fig. 18). TONGIORGI unsuccessfully attempted to collect micropalaeontological data in the area of the Pisani Mountains (LANDI DEGLI INNOCENTI et al., 2008). Marine fossils of inferred Penn sylvanian age, were recently discovered in the lower part of the San Lorenzo Schists at Montuolo . These discoveries indicate strong palaeoenvironmen tal analogies between this part of the San Lorenzo Schists and the coeval, coastalneritic Iano Schists and sandstones  (From RAU & TONGIORGI, 1974;TONGIORGI et al., 1977).
cropping out near Volterra (COSTANTINI et al., 1998) and the Rio Marina Formation on Elba Island .

SARDINIA
Transtensional tectonics, which deeply affected the disman tling of the Variscan orogen, led to the opening of a number of intramontane basins, filled with lacustrine to alluvial sedi ments (RONCHI et al., 2008 and ref. therein;see Fig. 21).

South-western Sardinia
Clear evidence of the first postorogenic clastic deposition on the island is represented by the reduced San Giorgio Ba sin sequence, which crops out in the Iglesiente subregion The flora shows several endemic species, suggesting onset of a regional characterized Sardinian flora resulting from the isolation of Sardinia from southern Europe during the Penn sylvanian, (for more details see PITTAU et al., 2008b).
From a palynological point of view, the Montarbu mi croflora is framed in the Potonieisporites Phase (PITTAU et al., 2008b), being represented by high numbers of Potonie isporites and Florinites and with a minor component rep resented by Plicatipollenites, Costapollenites and Vittatina pollen types. Thus, Voltziales, Cordaitales and, to a lesser extent, Peltaspermales appear to characterize the flora grow ing on dry or drained areas and slopes, in the surroundings of the lacustrine basin of Montarbu, at Seui and Seulo, whereas a hygrophillous flora of licophytes, sphenophytes and pterophytes, covered shorelake, banks, ponds and the alluvial plain.
According to the authors (e.g. VANOSSI et al., 1986), during the Pennsylvanian (Stephanian-?Autunian), lacu strine shales and siltstones (Murialdo Formation) or conti nental arenites (Viola and Gorra Schists) were deposited Figure 19: Generalized geological map of Iano (after COSTANTINI et al., 1998 andPANDELI, 1998).    In contrast with such accepted agedeterminations, and with all the former stratigraphic interpretations (see e.g., VANOSSI et al., 1986), the Pennsylvanian volcanic and sedi mentary clas tic deposits, which unconformably overlie a Namurian crystal line basement, have recently been related to Permian ages (DALLAGIOVANNA et al., 2009). New radioisotopic dates on the Case Lisetto rhyolites (285.6 ±2.6 Ma concordant age), ascribed these volcanic rocks to the late Sakmarian-?Artinskian timespan. Therefore the Ollano Formation should be placed in the Early Permian, in firm conflict with its palaeontological con tent, as reported in earlier literature.

CONCLUSIONS
The Italian Pennsylvanian continental successions are scat tered across the country in the following places: 1) In the western Southern Alps (Lombardy/Switzer land) sparse sections occur pitched in tectonic slices at the front of the metamorphic basement. The rich macroflora from the Alpe Logone has been dated to the Bolsovian (West phalian C), or DuckmantianBolsovian (Westphalian B-C transition). Between the Maggiore and Lugano lakes, the outcrops are less rich in plant remains, and perhaps slightly older than these of Logone.
2) In the eastern Southern Alps (Carnic Alps) the Car boniferous successions crop out in several localities near the border with Austria, such as Passo Pramollo, Cason di Lanza, 3) In Tuscany, the floras mostly come from the Pisani Mountains and the surroundings of Iano. The San Lorenzo Schists, from which the specimens of the historic collections were collected, have been attributed to a Pennsylvanian to Cisuralian age.
4) Several small basins in Sardinia yield megafossils and/or palynomorphs respectively of WestphalianStepha  nian, StephanoAutunian or Autunian age, suggesting the differentiated onset of basins in Late Palaeozoic times in re lation to the Hercynian and moreover postHercynian tec tonic events.
5) The floras of Liguria mostly come from Pietratagliata (Genoa). This flora has a Late Westphalian-Stephanian age.