Imp.Perilli& VILLAFRANCHIAN DEPOSITS OF THE BARGA AND CASTELNUOVO GARFAGNANA BASINS (TUSCANY, ITALY): LITHOSTRATIGRAPHY AND SEDIMENTARY FEATURES Nicola Perilli, Alberto Puccinelli, Giovanni Sarti & Giacomo D’Amato Avanzi Dipartimento di Scienze della Terra, Università di Pisa. Via S. Maria 53 – 56126 Pisa – Italy sarti@dst.unipi.it perilli@dst.unipi.it ABSTRACT: N. Perilli et al., Villafranchian deposits of the Barga and Castelnuovo Garfagnana basins (Tuscany, Italy): lithostratigraphy and sedimentary features. (IT ISSN 0394-3356, 2004). Based on a refined mapping of the sedimentary wedges accumulated in the so-called Barga and Castelnuovo Garfagnana basins and on a review of previous studies, the distinguished formations are here described. The “Argille, sabbie e conglomerati di Fornaci di Barga” mainly consists of fine grained lithofacies with organic-rich horizons and coarse grained conglomerate. The “Conglomerati di Barga”, dominated by coarse grained lithofacies, is also characterized by silty to sandy interbeds, whilst organic-rich levels and paleo- sol horizons are rare. Within this formation, the Mt. Alfonso member is also distinguished, albeit hardly mappable. Sedimented in two separated tectonic depressions, connected by the “Mt. Perpoli high”, this succession has been interpreted in previous studies as ran- ging from cohesive sediment anabranching (“Argille, sabbie e conglomerati di Fornaci di Barga”) to gravel bed-load braided river deposits (“Conglomerati di Barga”), roughly flowing from north to south. In the Castelnuovo Garfagnana area, the Mt. Alfonso member also records the development of a tributary river flowing from west to east and interpreted as a braided fluvial fan. In this frame, the “Mt. Perpoli high” acted as a sedimentary by-pass, since the beginning of the sedimentation. RIASSUNTO: N. Perilli et al., I depositi villafranchiani dei bacini di Barga e Castelnuovo Garfagnana (Toscana, Italia): litostratigrafia e caratteristiche sedimentarie. (IT ISSN 0394-3356, 2004). Sulla base di rilevamenti geologici di dettaglio effettuati nei depositi villafranchiani dei bacini di Barga e Castelnuovo Garfagnana e di una revisione della letteratura, vengono definite le caratteristiche litostratigrafiche delle due formazioni riconosciute. La formazione delle “Argille, sabbie e conglomerati di Fornaci di Barga” giace in discordanza sul substrato costituito da unità toscane metamorfiche (Nucleo Metamorfico Apuano) e non metamorfiche (Falda Toscana) e, subordinatamente, da unità liguri e subliguri (Unità Ottone e Unità Canetolo); essa è caratterizzata prevalentemente da litofacies fini, con livelli di accumulo organico e di orizzonti pedogenetici e intercalazioni di conglomerati. La formazione dei “Conglomerati di Barga” è invece costituita da litofacies conglomeratiche, con spora- diche intercalazioni siltoso-sabbiose, a cui talvolta si associano paleosuoli e rari livelli di accumulo organico. All’interno di questa for- mazione, è stato distinto nell’area di Castelnuovo Garfagnana il membro di M. Alfonso, costituito da conglomerati grossolani eterome- trici. La formazione dei “Conglomerati di Barga” giace in possibile discordanza sulle “Argille, sabbie e conglomerati di Fornaci di Barga”, anche se le cattive condizioni di affioramento non permettono di escludere a priori un possibile passaggio stratigrafico. Le due formazioni vengono attribuite a due sistemi fluviali riferibili rispettivamente a un cohesive sediment anabranching river (“Argille, sabbie e conglomerati di Fornaci di Barga”) e a un gravel bed-load braided river (“Conglomerati di Barga”), ambedue ad andamento circa nord–sud. Il membro di M. Alfonso registrerebbe invece la deposizione, nel bacino di Castelnuovo Garfagnana, di un sistema tributario attribuibile ad un braided fluvial fan a decorso circa ovest-est e alimentato dalle Alpi Apuane. In questo quadro, la soglia di Monte Perpoli avrebbe agito come by-pass sedimentario fin dall’inizio della deposizione villafranchiana. Keywords: Lithostratigraphy, Continental deposits, Villafranchian, Tuscany, Italy. Parole chiave: Litostratigrafia, Depositi continentali, Villafranchiano, Toscana, Italia. Il Quaternario Italian Journal of Quaternary Sciences 17(2/1), 2004, 313-322 1. INTRODUCTION Since the 19th century, the Villafranchian succes- sion cropping out in the Barga and Castelnuovo Garfagnana tectonic depressions (Tuscany) was investi- gated due to its fossil record, mainly represented by vegetable and mammal remains. The paleontological data increased as a consequence of the lignite and clay mining, that ended during the first and last decades of the 20th century, respectively. On the basis of few paleontological studies and limited number of vertebra- te remains (De Stefani, 1887 and 1889; Ugolini, 1902; Zaccagna, 1932 and Masini, 1936), the Villafranchian age of this succession is accepted. The main lithological features of these deposits have been described, among the others, by Nardi (1961) and Calistri (1974), and mapped at 1:10,000 scale by Nardi et al. (1986 and 1987). Unfortunately, these papers were not supported by detailed lithostrati- graphic and sedimentological studies. Nevertheless, based on the significant lignite contents of the fine grai- ned basal sediments and the dominant coarse grained overlying deposits, the whole succession was interpre- ted as a fluvial-lacustrine cycle. Recently, lithostrati- graphy and facies analysis of these deposits were inve- stigated by Puccinelli et al. (in press, a) and Landi et al. (2002-2003), respectively. On the basis of these stu- dies, the main lithostratigraphic and sedimentary featu- res of the Villafranchian formations, discontinuously exposed in the Barga and Castelnuovo Garfagnana areas, will be described in this paper. A similar succession, dividable in two formations, crops out north-westward in the Aulla-Olivola and Pontremoli tectonic depressions (Bertoldi, 1997 and 314 N. Perilli et al. Bernini et al., 1990). Mainly consisting of fine grained lithofacies with medium to thick coarse grained inter- beddings, the “Argille, sabbie e conglomerati di Aulla” (Puccinelli et al., in press, b) is characterized by a varia- ble amount of centimetric to decimetric lignite frag- ments and organic-rich horizons. It is overlain by the coarse grained “Conglomerati di Olivola” (Puccinelli et al., in press, b), characterized by subordinate fine grai- ned interbeddings. 2. GEOLOGICAL SETTING The investigated area (Fig. 1) is one of the conti- nental intermontane tectonic depressions, that opened as a consequence of the counter-clockwise migration of the chain-foredeep-foreland system and of the extension of the Northern Apenninic Tyrrhenian margin (Meletti et al., 1995 and references therein) during the Late Ruscinian/Early Villafranchian time interval (Bernini et al., 1990; Bertoldi, 1995 and 1997). Roughly comprised between the Apuan Alps and the Apenninic watershed, the studied area includes two tectonic depressions, 5 Km wide and 10 (Barga) to 15 Km (Castelnuovo Garfagnana) long, separated by the so-called “Mt. Perpoli high” (Soglia di Monte Perpoli of Puccinelli, 1987). These depressions are related to the movement of tectonic blocks collapsed and rotated along antithetical faults and interpreted as half-graben, with the master faults plunging towards the Tyrrhenian border (Martini & Sagri, 1973; Eva et al., 1978). The Villafranchian succession laid down in the Barga and Castelnuovo Garfagnana depressions unconformably overlies sedimentary successions of the Apennine thrust- and-fold belt, here represented by the Falda Toscana (mainly with the Macigno Formation), Canetolo and Ottone Units. Along the western sides of both depressions, the Falda Toscana in turn tectonically overlies the Methamorphic Core Complex of the Apuan Alps. 3. PREVIOUS STUDIES AND INFERRED AGE The sedimentary succession, cropping out in the Barga and Castelnuovo Garfagnana areas, was investi- gated entirely by few authors. Among them, De Stefani (1887 and 1889), Zaccagna (1917 and 1932), Ugolini (1902), Masini (1932 and 1936), Tongiorgi & Trevisan (1953), Azzaroli (1955), Nardi (1961) and Calistri (1974) focused on stratigraphy, even if only this latter studied the entire Villafranchian sedimentary succession. The papers of Bartolini & Bortolotti (1971), Nardi (1961 and 1965), Nardi et al. (1986 and 1987), D’Amato Avanzi & Puccinelli (1988), Puccinelli (1987), Dallan et al. (1991) and Moretti (1990) mainly deal with neotectonics and/or landslide hazard. Fig. 1 - Tectonic sketch of the Northern Apennines and location of the main intermontane tectonic depressions nearby the study area (within the square). Schema strutturale dell’Appennino settentrionale con la localizzazione delle principali depressioni tettoniche limitrofe all’area di studio (nel riquadro). 315Villafranchian deposits of the Barga ... 4. LITHOSTRATIGRAPHY AND SEDIMENTARY FEATURES OF THE MAPPED FORMATIONS As it is well known, the continental successions cropping out in the intermontane, post-collisional basins are usually badly exposed, due to both the large diffusion of the anthropic activities (e.g. agriculture, urbanization) and vegetation cover. Consequently, the vertical and/or lateral outcrop extension is often limited, and the geometric and stratigraphic relationships between formations overshadowed. However, based on some well exposed sections, the entire succession has been rather well reconstructed. In the study areas, most significant sections are located in the Barga area, where the mapped forma- tions and the boundary between them are also well exposed. According to previous papers (Nardi et al., 1986 and 1987; Dallan et al., 1991), in the investigated area two formations have been recognized, and named by Puccinelli et al. (in press, a): “Argille, sabbie and conglomerati di Fornaci di Barga” (AFB) and “Conglomerati di Barga” (PLB). In the Castelnuovo Garfagnana area, within PLB, the Mt. Alfonso mem- ber is distinguishable. The exten- sion of both formations (AFB+PLB) is represented in Fig. 2. 4.1. Argille, sabbie e conglome- rati di Fornaci di Barga (Puc- cinelli et al., in press, a) Synonymies Argille azzurre lignitifere e sabbie ocracee (Nardi, 1961) Argille di Fornaci di Barga pro parte (Calistri, 1974) Sabbie e argille lignitifere (Nardi et al., 1986) Argille e sabbie lignitifere (Nardi et al., 1987) Formazione di Fornaci di Barga (Catanzariti et al., 2002) Lithostratigraphic Unit 1 (Landi et al., 2002-2003) Significant outcrops (see Tab. 2) Barga: Rio Secco, Fornaci di Barga, T. Loppora, Rio Zanesi, Rio Cavo, T. Giuvicchia, Rio Val di Lago, Le Palmente and Corsonna. Castelnuovo Garfagnana: Rio la Fossa, Rio Dezza, Bamborino, Rio Valardino, La Bottegaccia, Villa Collemandina, Gamberone, Antisciana and Belvedere. Tab. 1 - List of vertebrate fossils remains from the “Argille, sabbie e conglomerati di Fornaci di Barga” and “Conglomerati di Barga” formations. Elenco dei resti dei vertebrati fossili provenienti dalle formazioni delle “Argille, sabbie e con- glomerati di Fornaci di Barga” e dei “Conglomerati di Barga”. Authors Localities Fossil remains Formations De Stefani (1889) Barga Equus stenonis Conglomerati di Barga Meneghini (1880) Ghivizzano Tapirus Hystrix De Stefani (1889) Fornaci di Barga Rhinoceros etruscus Rhinoceros etruscus Sus arvernensis Cervus sp. De Stefani (1889) T. Loppora Felis cfr. isdiorensis Meganthereon nestii Histrix sp. Tapirus sp. Mastodon arvernensis Ugolini (1902) Fornaci di Barga Tapirus arvernensis Cervus pardinensis Masini (1936) Fornaci di Barga Mastodon arvernensis Emys sp. Tapirus sp. La Fossa Sus sp. Felis cfr. isdiorensis Cervus sp. Mastodon arvernensis De Stefani (1887) Custia Mastodon arvernensis Cervus sp. Fornaci del Ponte Mastodon arvernensis Castiglione Tapirus sp. Machiarodus eultridens Fornaci del Bianchi Tapirus sp. Sus arvernensis Ugolini (1902) T. Loppora Tapirus arvernensis Cervus pardinensis Masini (1932) Mastodon arvernensis A rg ill e , s a b b ie e c o n g lo m e ra ti d i F o rn a c i d i B a rg a Unfortunately, the paleontological data as well as the age-significant fossil remains are scarce (Tab. 1). However, the mammal fragments and the presen- ce (Landi et al . 2002-2003) of some molluscs (Laminifera villafranchiana, Prososthenia paulae, Theodoxus cf. groyanus) and characean species (Nitellopsis cf. Megarensis - Carnevale et al., 2003) point to (according to Azzaroli, 1977 and De Giuli & Masini, 1983) a Lower-Middle Villafranchian age for the “Argille, sabbie e conglomerati di Fornaci di Barga” and allow to assign the overlying “Conglomerati di Barga” to Late Villafranchian. 316 Fig. 2 - Schematic geological map of the Barga and Castelnuovo depressions and nearby areas, based on the Geological Map at 1:50,000 - Sheet 250 Castelnuovo Garfagnana (Puccinelli et al., in press, a) and on some geological maps at 1:10,000 scale (Nardi et al., 1986 and 1987; Dallan et al., 1991). Carta geologica schematica dei bacini di Castelnuovo Garfagnana e Barga e delle aree limitrofe, basata sulla Carta Geologica a scala 1:50.000 – Foglio 250 Castelnuovo Garfagnana (Puccinelli et al., in press, a) e su alcune carte geologiche a scala 1:10.000 (Nardi et al., 1986 and 1987; Dallan et al., 1991). N. Perilli et al. 317 AFB mainly consists of fine (clayey to sandy) grai- ned lithofacies interbedded by medium to coarse con- glomerate (from channel to wedge or sheetlike shaped), that sometimes can be dominant. The formation is also Localities Member (Mb.) Lithofacies (Lt.) Formations Barga area T. Loppora Lenticular-shaped conglomerate (Lt.) channel-shaped conglomerate (Lt.) Rio Latrani Sheet-like conglomerate (Lt.) Rio Zanesi Sheet-like conglomerate (Lt.) Corsonna Fine grained (Lt.) & channel-shaped conglomerate (Lt.) Le Palmente Lenticular-shaped conglomerate (Lt.) & sandy (Lt.) Casa Volpaia Fine grained (Lt.) and organic-rich horizons & channel-shaped conglomerate (Lt.) Pieve di Loppia-Barga road Lenticular-shaped conglomerate (Lt.) & sandy (Lt.) Barga Lenticular-shaped conglomerate (Lt.) & sandy (Lt.) Castelnuovo G. area Rio Dezza Mt. Alfonso (Mb.). Poorly sorted conglomerate Il Colle Mt. Alfonso (Mb.). Poorly sorted conglomerate Mt. Alfonso Mt. Alfonso (Mb.). Poorly sorted conglomerate S. Lucia Lenticular-shaped conglomerate (Lt.) & sandy (Lt.) Castegni Lenticular-shaped conglomerate (Lt.) & sandy (Lt.) Soffiana Sand and silty (Lt.) & rare organic-rich horizons Bamborino Lenticular-shaped conglomerate (Lt.) & sandy (Lt.) Liana Sandy (Lt.) & lenticular shaped conglomerate (Lt.) Barga area Rio Secco Fine grained (Lt.) & channel-shaped conglomerate (Lt.) Cava Fornaci Fine grained (Lt.) T. Loppora Channel-shaped conglomerate (Lt.) & fine grained (Lt.) Le Palmente Fine grained (Lt.) Rio Cavo Fine grained (Lt.) & channel-shaped conglomerate (Lt.) Rio Zanesi Fine grained (Lt.) & channel-shaped conglomerate (Lt.) Rio Val di Lago Fine grained (Lt.) and organic-rich horizons & channel-shaped conglomerate (Lt.) Corsonna Fine grained (Lt.) & channel-shaped conglomerate (Lt.) Rio della Giuvicchia Fine grained (Lt.) and organic-rich horizons & channel-shaped conglomerate (Lt.) Casa Volpaia Fine grained (Lt.) & channel-shaped conglomerate (Lt.) Castelnuovo G. area Rio Dezza Fine grained (Lt.) & channel-shaped conglomerate (Lt.) Rio la Fossa Fine grained (Lt.) and organic-rich horizons & channel-shaped conglomerate (Lt.) Collemandina Fine grained (Lt.) & sandy (Lt.) Bamborino Fine grained (Lt.) La Bottegaccia Fine grained (Lt.) & organic-rich horizons Gamberone Fine grained (Lt.), organic-rich horizons & sandy (Lt.) Antisciana Fine grained (Lt.) & channel-shaped conglomerate (Lt.) Belvedere Fine grained (Lt.) & channel-shaped conglomerate (Lt.) Rio Valardino Fine grained (Lt.) & channel-shaped conglomerate (Lt.) C o n g lo m e ra ti d i B a rg a A rg ill e , s a b b ie e c o n g lo m e ra ti d i F o rn a c i d i B a rg a Tab. 2 - Most significant outcrops in the Barga and Castelnuovo Garfagnana depressions of the “Argille, sabbie e conglomerati di Fornaci di Barga” and “Conglomerati di Barga” formations. Exposed lithofacies are also synthetically described. Affioramenti maggiormente significativi nelle aree di Barga e Castelnuovo Garfagnana delle formazioni delle “Argille, sabbie e conglo- merati di Fornaci di Barga” e dei “Conglomerati di Barga”. Sono anche descritte in modo sintetico le litofacies caratteristiche affioranti. characterized by a variable amount of centimetric to decimetric lignite fragments, that in places are abundant and concentrated in organic-rich horizons (Fig. 3a). The fine grained deposits, ranging from 0.5 to 3-7 Villafranchian deposits of the Barga ... 318 m in thickness, are usually organized in centimetric to decimetric rhythmical alternance of grey-dark, grey to bluish or violet clay to silty-clay and yellowish silty or sandy beds, with horizontal to cross or through lamina- tion, in places well evidenced by small lignite frag- ments. They can be associated with 0.5 to 3.5 m thick massive to horizontal laminated organic-rich clay or silty to sandy interbeddings, that somewhere show soft deformation structures. The organic-rich levels, more abundant in the lower portion of the formation, contain scattered lignite fragments, that can concentrate in 20 to 40 cm thick horizons, with limited (10-15 m) lateral extent. The sandy intervals, usually 10-20 cm thick and up to 1.5-2 m wide, can be up to 1.5 m thick and 10 m wide. In the thickest sandy levels, thin to medium thick lens-shaped conglomerate can be present. At different levels, and mainly within the clay and silty-clay intervals centimetric to decimetric (20-30 cm), dark grey paleosols containing land fossils (Landi et al., 2002-2003) are present. Unfortunately, the lateral extent of these horizons is limited and their correlation unreliable. The scarce fossil remains of the fine grained lithofacies include ostracods and gastropods, along with extremely rare teeth of fish and charophites oogo- nia (genus and species names in Landi et al., 2002- 2003). Fragments of leaves and chunks of trees are also present and in few places the latter are still obser- vable in life position (Rio Dezza). The isolated channel-shaped, clast-supported poly- mictic conglomerate, from grey/dark grey to brownish, consist of sub-rounded to well rounded clasts, in places imbricated. This medium to coarse grained massive and well sorted conglomerate shows a low percentage of silt to fine matrix, not always present. This deposit, with weak to strong erosive basal surface and limited (3-5 to 15-20 m) lateral extent, ranges from 1 to 3 m in thickness. The coarse grained lithofacies can also be repre- sented by an alternance of clast-supported, wedge- to sheet-like conglomerate or sandy conglomerate, and medium to coarse sand. This conglomerate, from 1 to 3 m thick and up to 20-40 m wide, lacks any evidence of basal erosive surface. The pebbles and cobbles range from sub-angular to sub-rounded/rounded. The medium to coarse sandy matrix is present in variable amount, that can vary in percentage at metric scale. The sandy interbeds range from massive to cross laminated. In both types of conglomerate, the clasts are mainly represented by unmetamorphosed lithotypes, with the arenaceous clasts (referable to the Macigno Fm.) slightly more abundant than the carbonatic ones. In places, the arenaceous clasts can be dominant. The metamorphic (Landi et al. 2002-2003) ones are more abundant in the Barga (up to 15-20%) than in the Castelnuovo Garfagnana area, where they are extre- mely rare (below 1%). Scattered along the Apenninic border, AFB is interbedded, at different levels, with medium/coarse to very coarse grained, monomictic, massive conglomerate, mainly made of clasts referable to the Macigno Fm. (i.e. Units 3 and 4 of Landi et al., 2002-2003). This unsorted to poorly sorted, matrix- to clast-supported conglomera- te is nicely exposed at Colle Buvicchia and Mologno. It chiefly consists of sub-angular to rounded cobbles and boulders, in places well imbricated. The medium to coar- se sandy matrix is furnished by the Macigno Fm. weathering. Ranging in thickness from few metres up to 100 m, such coarse clastic wedges (in places) can represent the entire Villafranchian sedimentary record. According to Landi et al. (2002-2003), the asso- ciation of fine and coarse grained lithofacies with in situ accumulated organic matter (mainly represented by lignite) was sedimented in a braided fluvial system, referable to an anabranching organo-clastic substage (sensu Nanson & Knighton, 1996), flowing from Castelnuovo Garfagnana to Barga. It interfingers with the alluvial fan deposits (dominated by debris-flow pro- cesses), cropping out along the Apenninic border (i.e. Units 3 and 4 of Landi et al., 2002-2003), and develops transversally to the tectonic depression axis. The thickest exposures range from 10-40 to 80 m in the Barga area and from 10 to 30-40 m in the Castelnuovo Garfagnana area. The maximum thickness of this formation measured near Castelnuovo Garfagnana, including a drilled portion, can reach 200 m (De Marco & Caielli, 1995; Cancelli et al., 2002). Usually, the outcrops are not thicker than 10-30 m in Barga as well as in Castelnuovo Garfagnana areas. The unconformable contact with the underlying formations is exposed in few localities, with bad expo- sure conditions and very limited lateral extent. Along the eastern border of the Barga depression, the Macigno Fm. is topped by the basal coarse grained and poorly sorted conglomeratic lithofacies of AFB. In the boreholes drilled near Villa Collemandina, the substra- tum (represented by Ligurian successions) has been reached below 90-100 m of AFB. The AFB/PLB contact is frequently well exposed and characterized by an abrupt facies change, sugge- sting a possible disconformity surface. Nevertheless, in some places (Gallicano and Barga areas) the heteropy between the two formations is not excluded. In fact, conglomeratic interbeddings are locally present in the uppermost part of AFB; they are similar to those inter- bedded in the lowermost part of PLB. In other areas, AFB is topped by the erosive post Villafranchian coarse grained terraced deposits. According to the quoted fos- sil remains, the lowermost portion of this formation could be assigned to the Lower Villafranchian, whilst its upper portion could reach the Middle Villafranchian. 4.2. Conglomerati di Barga (Puccinelli et al., in press, a) Synonymies Ghiaie con prevalenza di rocce mesozoiche e meta- morfiche (Nardi, 1961) Ciottoli e sabbie di Loppia (Calistri, 1974) Conglomerati a ciottoli prevalentemente calcarei (Nardi et al., 1986) Ghiaie e conglomerati calcarei (Nardi et al. 1987) Conglomerati di Barga (Catanzariti et al., 2002) Lithostratigraphic Unit 2 (Landi et al., 2002-2003) Significant outcrops (see Tab. 2) Barga: T. Loppora, Rio Latrani, Rio Zanesi, Le Pal- mente, Pieve di Loppia-Barga road, Barga and Casa Volpaia. Castelnuovo Garfagnana: Bamborino, Rio Dezza, Il Colle, S. Lucia, Castagni, Soffiana, Mt. Alfonso and Liana. N. Perilli et al. 319 Fig. 3 - Main litholological features of the “Argille, sabbie e conglomerati di Fornaci di Barga” Fm. (A) and of the “Conglomerati di Barga” Fm. (B). Colonne stratigrafiche mostranti le principali caratteristiche litologiche delle “Argille, sabbie e conglomerati di Fornaci di Barga” (A) e dei “Conglomerati di Barga” (B). Villafranchian deposits of the Barga ... PLB is characterized by the dominance of medium to coarse (from pebbles to cobbles) grained lithofacies, whilst sandy to silty-clayey levels, with very rare paleosols, are subordinate. Though texture, sedi- mentary structures and shapes of the conglomerate can change even at metric scale, two end-members can be described: one shows sheet-like geometry and significant presence of sand interbeddings, the other is lens-shaped and characterized by erosive basal surface and small amount of matrix (Fig. 3b). The sheet-like, clast-supported conglomerate, with massive to crude bedding is interbedded with thin (2-3 to 5-10 cm), massive to horizontally stratified, lenti- cular yellowish sand. These coarse grained intervals, with very rare sedimentary structures, mainly consist of poorly to moderately sorted conglomerate, with well rounded pebbles and cobbles, rarely imbricated and with a variable amount of sandy-silty to silty matrix; the matrix percentage may change even within the same interval. This disorganized to poorly organized conglo- merate, frequently ranging in thickness from 0.5 to 1 m, can be up to 3 m thick and 20-30 m wide. The lens-shaped, medium to coarse conglomera- te, is chiefly composed of well sorted clasts and small percentage of silty to sandy matrix. The sub-rounded to rounded clasts are frequently imbricated and the matrix can be, in places, either absent or significantly present. This conglomerate, sometimes channellized, shows weakly erosive basal surface and planar to through cross stratification. Ranging in thickness from 0.5 to 3 m, it can be up to 20-30 m wide. Within this conglome- rate, thin to thick (10-50 cm) interbeddings of massive, brownish to brown-reddish sand, with small lateral extension, are present. In both types of conglomerate, the clasts are chiefly represented by non-metamorphic or meta- morphic carbonatic lithotypes; whilst sandstone (refera- ble to the Macigno Fm.) is subordinate. Within the coar- se grained lithofacies, interbeddings of silt and fine to medium grained yellowish to reddish sand, up to 1 m thick, are present. More abundant in the sheet-like con- glomerate and sometimes bioturbated, silt and sand frequently show through and planar cross-bedding. In places, grey to dark-grey, millimetric to centimetric len- ses of clay evidence the sedimentary structures of these fine grained interbeddings. PLB is also characterized by the occurrence of centimetric to decimetric rhythmical interbeddings of grey clay or silty-clay to sandy beds, with horizontal to cross or through lamination, similar to those described for the underlying formation. These fine grained lithofa- cies, usually ranging from few decimetres to 1-2 m (Rio Latrani, Rio Sartoiani, T. Giuvicchia and T. Corsonna), are up to 20 m thick at Casa Volpaia. In the silty-sandy or sandy beds micro and macro vegetable remains may concentrate and at different levels, centimetric to deci- metric dark grey or blackish paleosols are also present. In all quoted localities, the heteropic transitions with the coarse grained deposits are visible. As reported by Landi et al. (2002-2003), the described lithofacies association is dominated by con- glomerate together with sandy lenses and centimetric to decimetric alternance of fine grained deposits (cha- racterized by organic-rich horizons and paleosols). This association is referable to a gravel bed-load braided river system, flowing from NE to SW (i.e. from Castelnuovo Garfagnana to Barga). As described for AFB, along the Apenninic bor- der, also PLB, interfingers with coarse grained lithofa- cies (Unit 3 of Landi et al., 2002-2003), characterized by sub-angular to rounded (the boulders) clasts, chiefly consisting of sandstone (referable to the Macigno Fm.), and interpreted as coalescent alluvial fan deposits (dominated by debris-flow processes) developed tran- sversally to the tectonic depression axis. PLB is superbly exposed along the oriental side of the Serchio Valley, and ranges in thickness from 70 (Gallicano) to 170 m (Barga). The better exposures are located between Loppia and Barga and in the Villa Collemandina area. Usually, the outcrops can be 20-40 m thick and from 100 to 200 m wide. The clearly erosi- ve contact between the Conglomerati di Fornaci di Barga and the post Villafranchian coarse grained terra- ced deposits is frequently well exposed. According to the few listed paleontological remains, this formation could be assigned to the Middle to Late Villafranchian. West of the Castelnuovo Garfagnana area, PLB is represented by medium to coarse clast-supported con- glomerati of Mt. Alfonso member (Unit 5 of Landi et al., 2002-2003). Showing a tabular geometry with thickness ranging from 0.5 to 3 m, these deposits can vary even in a short distance from disorganized to organized sedi- mentary body. The poorly sorted clasts, with a diameter up to 50 cm, in places imbricated, are mainly compo- sed of carbonate, whilst the presence of sandstone is subordinate, though sometimes it can be significantly present. The 100 (westard) to 40 m (eastward) thick Mt. Alfonso member is interpreted as a braided fluvial fan, supplied by the Apuan Alps and developed transversal- ly to the basin axis (Landi et al. 2002-2003). 5. CONCLUSIVE REMARKS On the basis of the main lithostratigraphic and sedimentological features of the described Villafranchian succession, the following points should be emphasized. - In the Barga and Castelnuovo Garfagnana areas, AFB and PLB are characterized by distinctive lithofacies associations, and the boundary between the two for- mations is quite easily recognizable. - Within AFB, clay and conglomerate are subordinate and the formalized name points out the wide lithologi- cal spectrum, that characterizes this formation. Nevertheless, lateral and vertical variations between fine grained and coarse grained lithofacies are distin- guishable at outcrop scale, but hardly mappable, due to their limited thickness and lateral extent. - The clayey intervals of AFB are more widespread and thicker in the Castelnuovo Garfagnana than in the Barga depression, whilst sandy intervals are thicker and wider in the Barga than in the Castelnuovo Garfagnana area. Thin to very thin and well stratified, clayey-silty to sandy laminated (varve-like) intervals are peculiar of the Castelnuovo Garfagnana area. - The organic-rich horizons within AFB are relatively more abundant in the lower portion of the formation. They are usually represented by centimetric to deci- metric horizons within the fine grained portions. The largest fragments of lignite and the chunks of trees 320 N. Perilli et al. are scattered throughout the formation, and some of these latter are sometimes still in life position. The lignite banks, including the mined ones, are thicker and more continuous than those cropping out or mined in the Barga area. - In AFB the coarse grained intervals are mainly repre- sented by channelized conglomerate interbedded by clayey-silty or sandy dominant lithofacies. Likewise, the sheetlike conglomerate (almost absent in the Castelnuovo Garfagnana area), present in the lower portion of the formation, is associated with clayey- silty or sandy lithofacies. - In spite of the lateral and vertical lithological variation of the different lithofacies, the dominance of the coar- se grained conglomerate allows the easy mapping of the PLB, also characterized by sandy interbeddings. Silty-clayey to sandy fine grained lithofacies (with thin organic-rich horizons similar to those present in AFB), with reduced thickness as well as lateral extent, are clearly in heteropy to the conglomerate. Also in the Castelnuovo Garfagnana area these lithofacies (including organic-rich horizons) are very limited in thickness and lateral extension. - Lignite fragments or other biogenic remains, as well as paleosols, are extremely rare and scattered within PLB. Indeed, large lignite fragments can be present within the coarse grained lithofacies, whilst millimetric to centimetric lignite flakes are relatively more fre- quent within the finest grained lithofacies. - In the Castelnuovo Garfagnana depression, within the PLB, the Mt. Alfonso member is distinguishable. Mainly consisting of polymictic, poorly sorted medium to coarse conglomerate and subordinate coarse grai- ned sand, it can be correlated with the conglomerate cropping out in the Gallicano area (D’Amato Avanzi & Puccinelli, 1988) and mapped within the PLB. - In spite of similar lithologies present in both forma- tions, the lithofacies assemblages point out the superposition of gravel bed-load braided river depo- sits (PLB) on cohesive sediment anabranching river deposits (AFB). Both successions interfinger with the alluvial fan conglomerate, that in places can represent the entire Villafranchian succession. - The abrupt facies change between these two clastic successions can be interpreted as a disconformity surface (Landi et al., 2002-2003). Unfortunately, it is neither supported by paleontological data nor confir- med by other field evidence. However, the conglome- ratic lithofacies interbedded within the AFB shows neither a polarity towards the top of the formation nor significant similarities with the coarse grained lithofa- cies of the PLB. - On the other hand, the erosive contact between AFB and PLB can be also interpreted as stratigraphic, because erosive surfaces are frequent within this type of deposits (from anabranching to gravel bed-load braided). Moreover, the presence of channellized con- glomeratic lenses within the uppermost part of the AFB, similar to those present in the overlying lower- most part of PLB, can support (at least in some pla- ces) a quite sharp but transitional boundary between AFB and PLB (Puccinelli et al., in press, a). - In summary, though the Villafranchian clastic wedges sedimented in two distinct tectonic depressions, con- nected by the sedimentary by-pass (Landi et al., 2002-2003) of the “Mt. Perpoli high”, active since the beginning of the Villafranchian deposition, the lithofa- cies associations characterizing AFB as well as PLB are quite similar in both areas. Furthermore, the boun- dary between AFB and PLB shows the same features in both depressions, even if the field evidence is not helpful to choose between the existence of a disconformity or a stratigraphic transition between AFB and PLB. - Although the correlation between continental clastic successions, not supported by sedimentological analysis and paleontological data is difficult, in our opinion the AFB and PLB can be correlated with the “Argille, sabbie e conglomerati di Aulla” and the “Conglomerati di Olivola”, respectively (Puccinelli et al., in press, b). Both crop out north-westward in the Magra Valley (Aulla-Olivola and Pontremoli tectonic depressions) and show strong affinities with AFB and PLB. 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