Imp.Girotti PPLLIIOO--PPLLEEIISSTTOOCCEENNEE SSTTRRAATTIIGGRRAAPPHHYY AANNDD RREELLAATTIIOONNSS BBEETTWWEEEENN MMAARRIINNEE AANNDD NNOONN--MMAARRIINNEE SSUUCCCCEESSSSIIOONNSS IINN TTHHEE MMIIDDDDLLEE VVAALLLLEEYY OOFF TTHHEE TTIIBBEERR RRIIVVEERR ((LLAATTIIUUMM,, UUMMBBRRIIAA)) OOddooaarrddoo GGiirroottttii11--22 && MMaarrccoo MMaanncciinnii11 1 Dipartimento di Scienze della Terra, Università degli Studi di Roma “La Sapienza” - Piazzale Aldo Moro 5, 00185 Roma odoardo.girotti@uniroma1.it; marco.mancini@uniroma1.it 2 CNR IGAG - co Dipartimento di Scienze della Terra, Università degli Studi di Roma “La Sapienza”. ABSTRACT The Middle Valley of the Tiber River (MVT) corresponds to the “Paglia-Tevere Graben”, a “neoautochthonous” basin developed since the latest Early Pliocene. The basin is in part linked with the intrapenninic Tiberino and Rieti Basins to the east, and with the Roman Basin to the south. The filling is mostly made up of Plio-Pleistocene marine deposits, unconformably overlaying the meso-cenozoic sub- stratum. Two outcropping 3rd order depositional sequences have been recognised: 1) the older is composed of Lower Pliocene-earliest Upper Pliocene shelfal clays and sands (G. puncticulata and G. aemiliana Chronozones) and rarer continental deposits; 2) the younger is late Gelasian-Santernian in age (G. inflata and G. cariacoensis-B. elegans marginata Chronozones) and mostly corresponds to the “Chiani-Tevere formation”, composed of neritic clayey-sandy sediments interfingered with fluvial-deltaic gravelly-sandy deposits. The correlation between marine and non-marine deposits is based both on physical-stratigraphic observations and data (lithostrati- graphy, facies analysis, sequence stratigraphy) and on their integration with biostratigraphic (foraminifera) and magnetostratigraphic data and with the numerical values of the 87Sr/86Sr ratio measured on mollusc shells, for the marine deposits, and with biochronological data (fresh- and brackish-water molluscs and ostracods, mammals) for the non-marine and transitional deposits. As for the younger successions from the latest Early Pleistocene to Holocene, which are characterised by travertines and gravelly flu- vial terraced deposits, the correlation with the marine successions of the Roman Basin is indirect and mostly based on biochronology and on relations between sedimentary and volcanic units. RIASSUNTO La media valle del Fiume Tevere (MVT) tra Orvieto e Fiano rappresenta un’area ideale per lo studio delle correlazioni tra depositi marini e continentali Plio-Pleistocenici. Infatti essa corrisponde al “Bacino del Paglia-Tevere”, a prevalente sedimentazione marina, parzial- mente contiguo ad Est ai bacini intrappenninici di Rieti e Tiberino e al bacino romano a Sud. Viene intodotto un nuovo schema stratigra- fico, che aggiorna il precedente di Ambrosetti et al. (1987) e pone in evidenza la presenza di cicli sedimentari di III e IV ordine controlla- ti dall’evoluzione tettonico-regionale tramite fasi di subsidenza e di sollevamento. La correlabilità tra bacini si basa su: 1) dati stratigrafi- co-fisici ottenuti mediante rilevamenti litostratigrafici e analisi di facies; 2) biostratigrafia a foraminiferi; 3) biocronologia a mammiferi e molluschi continentali; 4) magnetostratigrafia delle successioni marine e datazioni Ar/Ar e K/Ar di unità vulcaniche; 5) nuovi dati strati- grafico-isotopici ottenuti mediante misure del rapporto 87Sr/86Sr su gusci di molluschi e idrozoi. La fase di subsidenza è caratterizzata da due cicli sedimentari marino-continentali di III ordine. Il primo ciclo (tardo Zancleano- Gelasiano iniziale) è composto dai depositi terrigeni marini delle “unità di Fabro”, “formazione di Tenaglie-Fosso San Martino” e “unità di Città della Pieve”, cui localmente si intercalano sedimenti fluvio-lacustri. Il secondo ciclo (tardo Gelasiano-Santerniano) è caratteriz- zato dalla eteropia tra i depositi marini di piattaforma e transizionali della “formazione del Chiani-Tevere” e i depositi fluviali della “for- mazione di Santa Maria di Ciciliano” e della “formazione di Poggio Mirteto”. In particolare all’interno della formazione marina, sono stati riconosciuti tre grandi episodi progradazionali intercalati a fasi trasgressive ed evidenziati dai sedimenti ghiaiosi deltizi dei “membri di Civitella San Paolo”, “Torrita Tiberina”, “Vasanello”. Il primo episodio progradazionale ricade al passaggio Gelasiano-Santerniano, men- tre i successivi sono di età Santerniana. La fase regionale di sollevamento (Emiliano-Olocene) è caratterizzata dai depositi misti carbonatico-terrigeni della “unità di Giove” (Pleistocene Inferiore pp.), da vulcaniti, e dai depositi terrazzati fluviali ghiaioso-sabbiosi delle “unità di Civita Castellana” (Pleistocene Inferiore pp.-Pleistocene Medio pp.), “Graffignano” (Pleistocene Medio), “Rio Fratta” (tardo Pleistocene Medio) e “Sipicciano”(Pleistocene Superiore). Sulla base dei dati di terreno (biocronologia, rapporti con unità vulcaniche) e di interpretazioni paleogeografiche si ipotizzano correlazioni tra le unità continentali della MVT e le unità marino-transizionali dell’area romana, per il tardo Pleistocene Inferiore e l’inizio del Pleistocene Medio. Keywords: Late Pliocene, Early Pleistocene, Latium, Umbria, stratigraphy, paleogeography, Sr isotope stratigraphy. Parole chiave: Pliocene Superiore, Pleistocene Inferiore, Lazio, Umbria, stratigrafia, paleogeografia, stratigrafia isotopica dello Sr Il Quaternario Italian Journal of Quaternary Sciences 1166(1Bis), 2003, 89-106 11.. IINNTTRROODDUUCCTTIIOONN The middle Valley of the Tiber River (MVT) repre- sents a good example of how to correlate marine with non-marine successions, using both direct field observa- tions and analytical techniques like facies analysis, paleontologic and isotope-stratigraphic analyses and their integration, for chronologic and paleoevironmental purposes. The MVT is located at the border between Latium and Umbria and widens up to 60 km, between the Orvieto and Fiano towns (Fig. 1). Structurally it corre- sponds to the “Paglia-Tevere Graben” (Funiciello et al., 1981), a NNW-SSE trending extensional basin develo- ped since the late Early Pliocene, in concomitance with the Globorotalia puncticulata Chronozone (Barberi et al., 90 O. Girotti & M. Mancini Fig. 1 - Geological map of the MVT. Legend: A) RReecceenntt aalllluuvviiaall ddeeppoossiittss (Holocene). B) SSiippiicccciiaannoo uunniitt: IV order fluvial terrace of the Tiber River (Late Pleistocene). C) RRiioo FFrraattttaa uunniitt:: III order fluvial terrace (Middle Pleistocene). D) GGrraaffffiiggnnaannoo uunniitt: II order fluvial terrace (Middle Pleistocene). E) VVoollccaanniicc aanndd vvoollccaannoo--sseeddiimmeennttaarryy ssuucccceessssiioonnss ooff tthhee 22nndd vvoollccaanniicc pphhaassee (Middle Pleistocene). F) CCiivviittaa CCaasstteellllaannaa uunniitt:: I order fluvial terrace (Early-Middle Pleistocene). G) PPyyrrooccllaassttiitteess aanndd llaavvaass ooff tthhee 11sstt vvoollccaanniicc pphhaassee (Early Pleistocene). H) GGiioovvee aanndd AAccqquuaassppaarrttaa ffoorrmmaattiioonnss: travertines (Early Pleistocene). I) CChhiiaannii--TTeevveerree ffoorrmmaattiioonn: marine, fine-grained terrigenous deposits (Late Pliocene-Early Pleistocene). J) CChhiiaannii--TTeevveerree ffoorrmmaattiioonn: transitional, coarse-grained terrigenous (CCiivviitteellllaa SS.. PPaaoolloo,, TToorrrriittaa TTiibbeerriinnaa and VVaassaanneelllloo mmeemmbbeerrss) and carbonatic deposits (Late Pliocene-Early Pleistocene). K) PPooggggiioo MMiirrtteettoo ffoorrmmaattiioonn: fluvial deposits (Late Pliocene-Early Pleistocene). L) IInnttrraammoonnttaannee llaaccuussttrriinnee aanndd aalllluuvviiaall ddeeppoossiittss (Middle Pliocene-Early Pleistocene). M) TTeennaagglliiee--FFoossssoo SS.. MMaarrttiinnoo ffoorrmmaattiioonn: marine deposits (Middle-Late Pliocene). N) CCaarrbboonnaattiicc aanndd ssiilliicciiccllaassttiicc ssuucccceess-- ssiioonnss (Trias-Miocene). O) Normal fault. P) Thrust. Q) Stratigraphic log. 1994). It is bordered to the east by the Mt Peglia- Amerini-Narni-Sabini-Lucretili Mts ridge, where Triassic to Miocene marine, carbonatic and siliciclastic succes- sions crop out. The western borders of the basin are the Castell’Azzara-Mt Razzano ridge (Barberi et al., 1994), almost totally overlain by the Quaternary volcanites of the Vulsini, Cimini and Sabatini Mts volcanic districts, and the Mt Soratte horst. The basin is prevalently filled with Plio-Pleistocene marine terrigenous deposits. However, coeval non-marine and transitional terrige- nous and carbonatic deposits extensively crop out along the western margin of the Mt Peglia-Lucretili Mts ridge (Ambrosetti et al., 1987; Barberi et al., 1994; Girotti & Piccardi, 1994), while Pleistocene volcano-sedimentary successions are well exposed west of the Tiber River (Fig. 1). The present paper represents an update on the information about the Neogene-Quaternary stratigraphy of the MVT, both derived from the re-examinations of previously collected and published data and from new geological mapping and stratigraphic, sedimentologic and paleontologic analyses (Mancini, 2000; Mancini et al., 2001). In particular this work deals with: 1) the intro- duction of a new stratigraphic scheme; 2) detailed analyses of the relationships among Late Pliocene-Early Pleistocene marine, transitional and non-marine depo- sits; 3) paleogeographic reconstructions of the MVT and surrounding areas during the Late Pliocene-earliest Middle Pleistocene. 22.. PPRREEVVIIOOUUSS WWOORRKKSS The study of the relations between Plio- Pleistocene marine and non-marine deposits in the Umbria-Latium region was a topic for geologists since the late XIX century, with particular interest in the strati- graphic, paleontologic and geomorphic features (Tuccimei 1888; 1889; 1891; 1895; Clerici 1895; 1929). In fact the “Villafranchiano” stage was introduced for the first time in central Italy just in the MVT, near Poggio Mirteto (Tuccimei, 1889), after the discovery of a rich mammalian and molluscan fauna characterising that period (1). The non-marine deposits bearing such an assemblage were considered Pliocene in age and over- laying, with angular unconformity, “Astian” marine depo- sits (Tuccimei, 1888; 1895). On the other hand, Clerici (1895) disproved the angular unconformity proposing the lateral continuity between the Villafranchian and the marine deposits. The heteropic relations between non-marine and marine deposits were recurrently considered in order to understand the geology of the Tiber River’s valley and its surrounding areas. In particular, discoveries of mari- ne and transitional sediments within fluvial and lacustri- ne successions near Terni (Terrenzi, 1886) and Todi (Principi, 1922), based on malacological observations, should be mentioned. Therefore, the possibility of corre- lating marine and non-marine deposits was later put in evidence by discoveries of fresh-water molluscs and mammals within marine and nearshore successions and of brackish-water assemblages into non-marine succes- sions, in particular in the roman area (Bonadonna, 1968; Girotti, 1972) and in the south-western Tiberino Basin (Ippolito 1947; Girotti, 1967; Conti & Girotti, 1977; Ambrosetti et al., 1987), which are laterally continuous to the MVT southward and eastward respectively. Progress in the stratigraphical knowledge of the MVT, mainly due to micropaleontological studies (Ambrosetti et al., 1987; Buonasorte et al., 1991), led to the introduction of two marine sedimentary cycles (Fig. 2): 1) the first cycle developed during the latest Early Pliocene and the earliest Late Pliocene, between the G. puncticulata and G. aemiliana zones. It includes the “Argille di Fabro”, the “Sabbie a Flabellipecten” and the “Conglomerato di Città della Pieve” units (Ambrosetti et al., 1987). 2) The second cycle is chronologically limited to the Santernian and corresponds to the “Argille sab- biose del Chiani-Tevere” unit (asCT), which indicates marine and brackish-water environments, laterally conti- nuous with the “Complesso argilloso-sabbioso” unit 91Plio-Pleistocene stratigraphy ... (cas), of fluvial and lacustrine environment (Ambrosetti et al., 1987). The two cycles are separated by an unconformity of regional importance known as the “Fase erosiva dell’Acquatraversa” (Bonadonna, 1968) coinci- ding with the G. inflata zone. As a result of the new stratigraphic setting and mapping, most of the marine deposits, previously thou- ght of Pliocene age, are actually Early Pleistocene, while the heteropic relations among fully marine, transi- tional and non-marine units were detected only within the second sedimentary cycle (Ambrosetti et al., 1987; Piccardi, 1993). 33.. MMEETTHHOODDOOLLOOGGYY Thirty surface stratigraphic sections (Fig. 1) have been analysed using the standard methods of field geo- logy and facies analysis (Miall, 2000), examining in par- ticular their lithologic, textural and paleontologic featu- res. Micropaleontologic data have been obtained by collecting 73 samples of pelite or sand (Mancini, 2000), for qualitative analyses on micro-molluscs and forams, and have been added to the bibliographic data about the same topic (Ambrosetti et al., 1987; Carboni et al., 1993; Piccardi, 1993; Di Bella, 1994; Carboni & Di Bella, 1994; Carboni & Di Bella, 1996; Ciangherotti et al., 1998). Each sample, having a 200 cm3 volume, was treated with a H2O and H2O2 solution, and washed through a 125 µm sieve. The >125 µm size fraction of the wash residue was considered for the collection and recognition of the microfauna; up to 300 specimens for sample were counted. The biostratigraphic scheme used is from Cita (1975) and Iaccarino (1985), while the chronostratigraphic scheme is based on Sprovieri (1993) and Cita & Castradori (1995). Twelve measures of the 87Sr/86Sr ratio on frag- ments of marine molluscs and hydrozoa have been car- ried out by Prof. Mario Barbieri, at the “Istituto di Geologia Ambientale e Geoingegneria” (CNR-Rome), for chronostratigraphic purposes; the analytical method is described in Barbieri et al. (1998). Several radiometric (Arias et al., 1980; Borghetti et al., 1981; Sollevanti, 1983; Laurenzi & Villa, 1987; Cioni et al., 1993; Barberi et al., 1994; Perini et al., 1997) and magnetostratigraphic (Florindo & Sagnotti, 1995; Borzi et al., 1998) data were used to directly date several vol- canic and sedimentary units. 44.. SSTTAATTIIGGRRAAPPHHIICC SSEETTTTIINNGG OOFF TTHHEE MMVVTT The sedimentary units decribed below are of the lithostratigraphic and of the UBSU type (Salvador, 1994). In part they have already been introduced, while the others are presented here for the first time; in both cases they are going to be formalised. Such units are separated on the basis of their ages, also considering the sedimentary cyclicity previously introduced (Ambrosetti et al., 1987; Bossio et al., 1998) and the regional geological evolution with reference to the Latial volcanism and its cyclicity (Barberi et al., 1994; Mancini, 2000). Consequently, these units are grouped into: late- st Early Pliocene-earliest Late Pliocene units, latest Late 92 O. Girotti & M. Mancini F ig . 2 - S tr a tig ra p h ic s ch e m e o f th e M V T 93 Pliocene-earliest Early Pleistocene units, middle Early Pleistocene-earliest Middle Pleistocene units, Middle Pleistocene-Holocene units. 44..11.. LLaatteesstt EEaarrllyy PPlliioocceennee--eeaarrlliieesstt LLaattee PPlliioocceennee uunniittss These units crop out along the western margin of the Mt Peglia and of the northern Amerini Mts, south of Orvieto, and near the Mt Soratte (Fig. 1). They constitu- te the first MVT “neoautochthonous” sedimentary cycle and are: the Fabro formation, the Tenaglie-Fosso San Martino formation and the Città della Pieve unit. 44..11..11.. TThhee FFaabbrroo ffoorrmmaattiioonn The Fabro formation, already known as Argille di Fabro (Ambrosetti et al., 1987), crops out in the northernmost MVT along the Paglia River banks. It is composed of blue-grey, marine, sandy clays, mostly massive or tabular bedded. The strata, which are tecto- nically tilted, gently dip toward east, 8-10°. The thick- ness of the formation is up to 100 metres. The malaco- logic content, which was fully detailed by Malatesta (1974), indicates the neritic circalittoral stage. The pre- sence of G. puncticulata and G. aemiliana is indicative of the Early-Middle Pliocene age. Non-marine and presumably transitional deposits were recently discovered near Orvieto, in the Camorena site (Barberi et al., 1994), and near Fabro (Petronio et al., in press). These deposits are interlayered with the marine ones, at the base of the G. aemiliana zone (about 3.0 Ma). The malacologic content suggests that such sediments are of fluvial and lacustrine environ- ments and of Early Villafranchian age (2) (Ciangherotti et al., 1998; Petronio et al., in press). 44..11..22.. TThhee TTeennaagglliiee--FFoossssoo SSaann MMaarrttiinnoo ffoorrmmaattiioonn The Tenaglie-Fosso San Martino formation crops out in the Mt Peglia and northern Amerini Mts areas, where it corresponds to the Sabbie a Flabellipecten for- mation (Ambrosetti et al., 1987), and west of Mt Soratte. It unconformably overlays the Meso-Cenozoic substra- tum, vertically continuous above the Fabro formation. Its maximum thickness is up to 200 m. The formation is commonly composed of massive or tabular stratified sands, in some cases well cemented by calcium carbonate. Structures like hummocky and swaley cross stratification and gravelly lenses, few metres thick, are common. In the Mt Soratte area the sands laterally pass to well cemented, oligomittic, poorly sorted conglomerates and breccias, almost exclusively calcareous. The clast size ranges from a few centime- tres up to 1 metre. The paleontologic content is very rich and compo- sed of Pecten (Flabellipecten) flabelliformis, Chlamys (Gigantopecten) latissima, Terebratula ampulla, Ostrea spp., Balanidae, Bryozoa and Rhodophyceae. The fora- minifer assemblage is characterised by G. aemiliana, Bulimina marginata and Amphistegina spp., typical of the late Middle Pliocene and of the earliest Late Pliocene. The sedimentologic and paleontologic data indicate the shoreface and the offshore-shoreface tran- sition environments. 44..11..33.. TThhee CCiittttàà ddeellllaa PPiieevvee uunniitt This unit, already known as Conglomerato di Città della Pieve (Ambrosetti et al., 1987), crops out in few sites of the northern MVT. It is composed of well cemen- ted cobblestones, up to 10 metres thick, conformably overlaying the Tenaglie-Fosso San Martino formation. These rudites are interpreted as gravelly beach deposits (Ambrosetti et al., 1987). 44..22.. TThhee llaatteesstt LLaattee PPlliioocceennee--eeaarrlliieesstt EEaarrllyy PPlleeiissttoo--cceennee uunniittss Such units, which form the second “neoautochtho- nous” marine and non-marine cycle, widely crop out in the entire MVT. The units described below are: the Chiani-Tevere formation, the Poggio Mirteto formation and the Santa Maria di Ciciliano formation. 44..22..11.. TThhee CChhiiaannii--TTeevveerree ffoorrmmaattiioonn The Chiani-Tevere formation, which corresponds to the Argille sabbiose del Chiani-Tevere (Ambrosetti et al., 1987), is composed of marine, transitional and more limited non-marine deposits. It unconformably overlays the Tenaglie-Fosso San Martino formation and the Meso-Cenozoic substratum (Fig. 3). Its maximum thick- ness in outcrop is up to 350 m, but as the base rarely crops out the formation may be thicker. The marine deposits are composed of blue-grey sandy clays, commonly massive or planar bedded, verti- cally passing to massive sandy silts and fine silty sands, where structures like hummocky cross stratification and turbiditic beds are common. Such fine lithofacies verti- cally pass to coarse grained sands, with frequent amal- gamated hummocky and swaley cross stratifications and trace fossils like Scolicia and Thalassinoides. Strata are commonly sub-horizontal. The entire succession of lithofacies described above, which is well exposed in the northern MVT, indicates a regressive trend from inner shelf to shoreface deposits (Mancini, 2000). East of Mt Soratte a few metres thick, bioclastic calcarenitic level (Fig. 4), almost totally composed of chaotically amalgamated nearshore molluscs, echinids and corals, and well rounded pebbles, covers the under- laying coastal and fluvial deposits (see the discussion below). It is interpreted as a transgressive lag deposit, which is laterally continuous to the cemented sands, very rich in forams, that crop out at Vallericca (Carboni et al., 1993) few km far from the MVT southward (Fig. 4). Still in the Vallericca section, a several decimetres thick horizon of resedimented pyroclastites also crops out (Arias et al., 1980) (Fig. 4), which is placed within the B. marginata zone (Carboni et al., 1993). This level is dated 2.1 ± 0.2 Ma by fission track analyses on volca- nic glass shards (Arias et al., 1980), and 1.8 ± 0.3 Ma by analyses on zircons (Arias et al., 1990). Furthermore, recent magneto-stratigraphic analyses (Florindo & Sagnotti, 1995; Borzi et al. 1998), carried out several metres above and below the volcanoclastic level, sug- gest that the investigated section may be placed at the C2r.1r polarity subchron of the Geomagnetic Polarity Time Scale (Cande & Kent, 1992), between the Reunion and Olduvai subchrons. This horizon is the only dated layer and one of the lowermost outcropping beds of the formation. The microfauna is abundant and contains: Bulimina marginata and Globorotalia inflata, only found in the lower part of the formation (Piccardi, 1993; Carboni & Di Bella, 1996), and Bulimina elegans marginata, Bulimina etnea, Cassidulina carinata, Valvulinerina bradyana, Bolivina alata, Uvigerina peregrina, Globigerina caria- coensis, Globigerinoides tenellus, Globigerina calabra, Plio-Pleistocene stratigraphy ... 94 O. Girotti & M. Mancini F ig . 3 – S tr a tig ra p h ic a n d s e d im e n to lo g ic r e la tio n sh ip s a m o n g p lio -p le is to ce n e m a ri n e , tr a n si tio n a l a n d n o n -m a ri n e d e p o si ts a lo n g t h e w e st e rn m a rg in o f th e A m e ri n i M ts . L e g e n d ( sy m b o ls a re th e s a m e a s in f ig u re s 4 a n d 5 ): 1 = t ra n si tio n o ff sh o re -s h o re fa ce s a n d y si lts a n d o ff sh o re c la ys ; 2 = u p p e r a n d lo w e r sh o re fa ce s a n d s; 3 = p ro g ra d in g b e a ch g ra ve ls ; 4 = b io cl a st ic c a lc a re n iti c le ve l; 5 = c e m e n te d c a rb o n a tic s a n d s; 6 = l a g o o n a l a n d d e lta -f ro n t sa n d y cl a ys ; 7 = t ra ve rt in e s; 8 = l a cu st ri n e a n d f lo o d p la in c la ys ; 9 = f lu vi a l cr o ss b e d d e d g ra ve ls ; 1 0 = f lu vi a l cr o ss b e d d e d sa n d s; 1 1 = l ig n ite ; 1 2 = p yr o cl a st ite s; 1 3 = m o llu sc s sa m p le d f o r is o to p ic a n a ly se s; 1 4 = s e ct io n i n ve st ig a te d f o r m a g n e to -s tr a tig ra p h ic a n a ly se s; 1 5 = L ith o p h a g a b o ri n g s; 1 6 = m a ri n e m o llu - sc s; 1 7 = b ra ck is h w a te r m o llu sc s; 1 8 = f re sh w a te r m o llu sc s; 1 9 = la n d s n a ils ; 2 0 = v e rt e b ra te r e m a in s. 95Plio-Pleistocene stratigraphy ... Fig. 4 - Stratigraphic and sedimentologic relationships among marine, transitional and fluvial deposits in the central and southern part of the MVT. (1) = data after Arias et al. (1980); (2) = Arias et al. (1990); (3) = Florindo & Sagnotti (1995). Globigerina aff. calida calida (Carboni et al., 1993; Di Bella, 1994; Carboni & Di Bella, 1994; Mancini, 2000). It indicates the late Gelasian-Santernian age, in concomi- tance with the G. inflata-G. cariacoensis and the B. mar- ginata-B elegans marginata zones. The macrofauna is characterised by Corbula (Vericorbula) gibba, Natica tigri- na, Archimediella spirata, Amyclina semistriata, Sinodia brocchii, Panopaea glycimeris, Venus (Ventricoloidaea) multilamella, Pinna tetragona, Cladocora coespitosa (Piccardi, 1993; Mancini, 2000). The analysis of the 87Sr/86Sr ratio carried out on several fragments of molluscs and hydrozoa (Mancini, 2000) provided numerical values between 0.709068 and 0.709083 (Tab. 1), which correspond to 1.5 and 1.7 Ma. The Chiani-Tevere formation’s transitional and non-marine deposits extensively crop out along the eastern sector of the basin and are represented by the lithofacies assemblages described below. 1) Fine clayey sands of brackish-water environment. These deposits are widespread along the western margin of the Amerini-Narni Mts and correspond to the “facies salmastra” of the “asCT” (Am-brosetti et al., 1987). They are mainly composed of tabular stra- tified sands, which are laterally continuous westward to marine pelitic sands, and to the sandy fluvial deposits of the Santa Ma-ria di Ciciliano formation (see below) to the east. A rich brackish water fauna has been found: Cera-stoderma glaucum, Bittium deshayesi, Potamides tricinctus, Thericium vulga- tum, Anadara darwini, Trunculariopsis truncula con- globata, Ammonia tepida. Such deposits may be considered of the delta front environment (Mancini, 2000). 2) Travertines and c a l c a r e o u s silts. These n o n - m a r i n e deposits crop out near the top of the for- mation and c o m m o n l y overlay the car- bonatic sub- stratum. They constitute tabu- lar or lenticular bodies, few metres to seve- ral decametres thick (Fig. 3), that are alter- nated with the brackish-water clayey sands. These lithofa- cies are rich in L a t e Villafranchian fresh water molluscs and pulmonates like M e l a n o p s i s a f f i n i s , T h e o d o x u s g r o y a n u s , Viviparus belluccii, Emmericia umbra, Neumayria priscillae, Bithynia tentaculata, B. leachi, Micromelania (Goniochilus) zitteli, Prososthenia meneghiniana, Valvata cristata. 3) Cross bedded coarse grained sands alternated with clinostratified gravels. They are coarsening-up alter- nances of sands and gravels interpreted as parase- quences, marked at the base by a flooding surface. Each parasequence is generally 2 to 10 metres thick. The lower sands are cross bedded and of the shoreface environment; they vertically and landward pass to clinostratified, westward prograding gravels, overlain by planar bedded gravels of the beachface environment (Massari & Parea, 1988). Rarely at the top, thin horizons of massive clay bearing brackish water molluscs have been found. The gravels are commonly well sorted, rich in sandy matrix and com- posed of well rounded calcareous, cherty and arena- ceous cobbles and pebbles; in many cases the cla- sts are perforated by Lithophaga. Balanids, Anomia ephippium, and Ostrea spp. are the most frequent fossils. Three, very thick (50 to 100 metres), gravelly-sandy bodies, composed of several vertically stacked para- sequences, crop out in the Orte-Amelia area and east of Mt Soratte. Each of them represents a set of parasequences that interfingers with the nearshore marine deposits to the west and with fluvial deposits to the east. They correspond to the Civitella San Paolo member, the Torrita Tiberina member and the Vasanello member (Figs. 2, 4). 4) Cross bedded talus. These deposits crop out at the 96 O. Girotti & M. Mancini Tab. 1 top of the formation in several sites along the western margin of the Amerini-Lucretili Mts, where they ovelay the Mesozoic substratum and are in part covered by nearshore sands. This lithofacies is com- posed of poorly sorted rudites, rich in sandy and clayey matrix, and subangular clasts. The depositio- nal architecture is characterised by alternated chan- nelized and tabular bodies, seaward interfingering with the marine and transitional sands. The total thickness ranges between 50 and 80 metres. Such deposits are interpreted as fan-delta deposits (Girotti & Piccardi, 1994; Mancini et al., 2001). 5) Breccias and conglomerates with abundant sandy- clayey matrix. They are poorly sorted rudites, with subangular clasts commonly borrowed by Lithophaga. Such rudites crop out in many sites of the Amerini-Lucretili Mts western margin, directly onlapping the Meso-Cenozoic substratum, and late- rally continuous seaward to shoreface sands. They are interpreted as transgressive beach deposits and cliff breccias (Girotti & Piccardi, 1994). 44..22..22.. TThhee PPooggggiioo MMiirrtteettoo ffoorrmmaattiioonn The Poggio Mirteto formation is heteropic to the Chiani-Tevere formation’s transitional deposits. It crops out in the south-eastern MVT along the western margin of the Sabini Mts and in the lower Farfa River valley, areas historically known as Valli sabine (Tuccimei, 1889). The formation is up to 300 m thick and is compo- sed of cross bedded, well sorted gravels, alternated with lenses of trough cross stratified silty sands. At a large scale the gravels and sands are arranged into multisto- rey-multilateral channel-bodies and are interpreted as fluvial deposits filling active channels. They are also interbedded with tabular bodies of massive or thinly laminated clays, the thickness of which ranges between 1 and 20 m. The clays, which commonly contain lignite, may be interpreted as fluvial-overbank or lacustrine deposits. Such fine sediments are rich in fresh water mollu- scs like M. affinis, T. groyanus, Viviparus ampullaceus, Prososthenia etrusca, P. meneghiniana, Negulus villa- franchianus, E. umbra, M. (G.) zitteli, Belgrandia sp. (Ciangherotti et al., 1998; Mancini, 2000; Petronio et al., in press); in several cases sandy and clayey horizons that bear brackish water molluscs have been found (see logs 28 and 29 in Fig. 4). Vertebrate fossils are rarer: few remains of Equus stenonis were discovered at Filacciano (Di Bella, 1995) (Fig. 4), Bocchignano and Castel S. Pietro (Tuccimei, 1891, 1893), and bones of Anancus arvernensis and Stephanorinus etruscus at Castel S. Pietro (Tuccimei, 1891; Petronio et al., in press). The malacologic and mammal content indicates the Olivola-Tasso Faunal Units (Ciangherotti et al., 1998; Petronio et al., in press). 44..22..33.. SSaannttaa MMaarriiaa ddii CCiicciilliiaannoo ffoorrmmaattiioonn The Santa Maria di Ciciliano formation (Basilici, 1993) crops out very limitedly in the Amelia-Narni area, where the MVT basin is directly linked with the south- western branch of the Tiberino Basin. This formation is composed of cross bedded silty sands, that laterally pass to the transitional sands of the Chiani-Tevere for- mation. More detailed data are dealt with in Ambrosetti et al. (1995). 44..33.. TThhee mmiiddddllee EEaarrllyy PPlleeiissttoocceennee ––eeaarrlliieesstt MMiiddddllee PPlleeiissttoocceennee uunniittss The units of this period are in the chronological order: the Giove formation, the Mt Cimino volcanic and volcano-sedimentary successions, the Civita Castellana unit. 44..33..11.. TThhee GGiioovvee ffoorrmmaattiioonn The Giove formation limitedly crops out along the western margin of the Amerini Mts, where it corre- sponds to the travertini antichi (Ambrosetti et al., 1987). It unconformably overlays the Chiani-Tevere formation and laterally rests on the Meso-Cenozoic substratum. Its base is generally subplanar, although it is local- ly incised for a few tens of metres into the Chiani-Tevere formation (see logs 4, 5 and 9, in Fig. 3). Its planar top surface gently dips toward SW from 350 to 280 metres a.s.l., providing a terraced appearence to the formation. The maximum thickness is 60 m. The lower part of the Giove formation, which is 25 m thick, is composed of cross bedded, calcareous or quartz-bearing sands and gravels, commonly cemented by calcium carbonate and interspersed with lenses of travertines. Such mixed carbonatic and silicilcastic facies vertically pass to thick layers of well cemented travertines or, more rarely (see log 11, Fig. 3), to planar bedded calcareous silts bearing V. belluccii, M. affinis, T. groyanus, Carychium minimum, E. umbra, Hauffenia minuta, Bithynia spp., Lymnaea spp. (Piccardi, 1993). At Bandita di Giove (see log 8, Fig. 3) several remains of Late Villafranchian mammals have been found (Petronio et al., in press): Stephanorhinus etruscus, Leptobos sp., Elephantidae indet.. The sedimentologic and paleontologic data indica- te that the Giove formation deposited firstly in a fluvial environment of relatively high energy, and successively in little lakes and swamps dominated by carbonatic pro- duction. The probable age is middle Early Pleistocene. 44..33..22.. TThhee MMtt CCiimmiinnoo vvoollccaanniicc aanndd vvoollccaannoo--sseeddiimmeennttaarryy ssuucccceessssiioonnss These deposits crop out in the western bank of the Tiber River near Orte and Viterbo. They form a wide tabular body with undulate base placed at 200 to 220 metres a.s.l., about 150 m above the modern Tiber River’s plain. They are mostly riodacitic pyroclastic flow deposits, locally interlayered with lavas and travertines. The maximum thickness exceedes 100 m. The activity of the Mt Cimino Complex ranges between 1.35 and 0.95 Ma (Borghetti et al., 1981; Sollevanti, 1983), and the most widespread formation is the “Peperino” formation Auct., a 1.30 Ma old latitic ignimbrite (Barberi et al., 1994). 44..33..33.. TThhee CCiivviittaa CCaasstteellllaannaa uunniitt The Civita Castellana unit partly corresponds to the Paleotiber gravels (Alvarez 1972; 1973). It is an unconformity-bounded unit, mostly composed of fluvial gravels (Mancini, 2000) overlaying the Chiani-Tevere formation; its unconformable base may be correlated to the “Cassia erosional phase” (Bonadonna, 1968; Alvarez, 1972). No direct stratigraphic relationships with the Giove formation and the Mt Cimino volcanites are evident. In the northern MVT as far as Orte, this unit forms the highest fluvial terraced deposits, which represents 97Plio-Pleistocene stratigraphy ... the I order terrace of the Tiber River. Its tread gently decreases southward from 280 to 170 metres a.s.l., while the thickness is up to 80 m. South of Orte and west of the Mt Soratte the Civita Castellana unit fills a deep incision carved into the Chiani-Tevere formation (Fig. 5); there, the base is at 50 metres a.s.l. and the thickness reaches 120 m. The most frequent lithofacies are tabular and cross bedded gravels (Gh, Gt and Gp facies sensu Miall (1996)), while trough cross-bedded sands are rarer. The gravels, in general well rounded and lamellar or discoi- dal in shape, are mainly of calcareous nature, although arenaceous and siliceous clasts are also present. Frequent imbricate structures indicate prevalent southward-directed flows. The sandy matrix is abundant and rich in quartz and muscovite, although the calcite may locally dominate. In some cases the sandy lenses are rich in biotite and sanidine, probably supplied after the erosion of the Mt Cimino volcanites; furthermore vol- canic clasts belonging to the Peperino formation were also found (Brandi et al., 1970). The textural data and the depositional architecture, which shows multistorey-multilateral channel bodies, suggest that the Civita Castellana unit was deposited in a braidplain environment. The gravels and sands are rarely interbedded with few metres thick, tabular or lenti- cular, pelitic beds of the floodplain environment (Fig. 5), and with travertines, lignites and buried paleosols. The pelitic levels are rich in fresh water molluscs like Valvata piscinalis, Bithynia spp., Planorbis planorbis and more rarely M. affinis and T. groyanus (logs 18 and 21, Fig. 5), characteristic of the Early Pleistocene. In the lowermost part of the formation few remains of Bison cfr. B. degiulii, which indicates the Farneta and Pirro Faunal Units (late- st Late Villafranchian) (Gliozzi et al., 1997; Di Stefano et al., 1998), have been discovered (log 18, Fig. 5). This unit is late Early Pleistocene-earliest Middle Pleistocene in age, as it is overlain by the initial products of the Vulsini and Sabatini Mts volcanic complexes, pla- ced at around 600-500 ka (Barberi et al., 1994). 44..44.. TThhee MMiiddddllee PPlleeiissttoocceennee--HHoolloocceennee uunniittss A staircase of fluvial terraced deposits borders the modern course of the Tiber River. The Graffignano unit (Middle Pleistocene), Rio Fratta unit (late Middle Pleistocene), Sipicciano unit (Late Pleistocene) and the recent alluvial deposits (Holocene) (Figs 1 and 2) repre- sent the II, III and IV order terraces. Their respective treads decrease southward: 1) from 210 to 65 m a.s.l.; 2) from 150 to 40 m a.s.l.; 3) from 100 to 35 m a.s.l.; 4) 98 O. Girotti & M. Mancini Fig. 5 - Stratigraphic relationships among Pleistocene fluvial deposits in the western part of the MVT. G.u. = Graffignano unit; R.F.u. = Rio Fratta unit. from 70 to 25 m a.s.l. All the terraced deposits are mostly composed of cross bedded gravels and sands of the braided river environment; overbank deposits, paleosols and travertines are less frequent. The volcanic and volcano-sedimentary succes- sions of the Vulsini Mts, Vico and Sabatini Mts are widely exposed along the western bank of the Tiber, and are mainly composed of pyroclastites interbedded with lavas and travertines. The stratigraphic relationships between some dated volcanic formations and the terraced depo- sits provide a fairly precise chronological framework for the fluvial units (Mancini, 2000) (Fig. 2). The Graffignano unit, indeed, is more recent than the Tufo giallo della Via Tiberina formation, dated 550 ± 10 ka (Cioni et al., 1993), but it precedes the Lake Vico lava Formation (Perini et al., 1997), with ages between 305 ± 9 e 258 ± 2 ka. The Rio Fratta unit is younger than the above men- tioned lavas, but it is older than the Tufo rosso a scorie nere vicano formation, 151 ± 3 ka old (Laurenzi & Villa, 1987). Finally, the Sipicciano unit is younger than the Tufo rosso a scorie nere vicano formation. 55.. DDIISSCCUUSSSSIIOONN 55..11.. IInnffeerreenncceess oonn sseeddiimmeennttaarryy ccyycclliicciittyy dduurriinngg tthhee PPlliioocceennee aanndd tthhee eeaarrlliieesstt EEaarrllyy PPlleeiissttoocceennee.. The sedimentary units of the MVT are separated into two main groups. 1) The first group spans from late Zanclean to Santernian and is characterised by the pre- ponderance of marine deposits on transitional and conti- nental ones. It represents a subsidence-dominated stra- tigraphic domain as the basin fill occurred during phases of subsidence (Ambrosetti et al., 1987; Barberi et al., 1994; Bossio et al., 1998). 2) The second group, which ranges from middle Early Pleistocene to Holocene, is solely characterized by terraced continental deposits interlayered with volcanic and volcano-sedimentary suc- cessions, and indicates an uplift-dominated stratigraphic domain. The subsidence-dominated domain is composed of the two main marine-non-marine cycles described above (Fig. 2): 1) the first cycle (late Zanclean-early Gelasian), which started at about 3.6 Ma, corresponds to the I and II sedimentary cycles described in Barberi et al. (1994) and to the P2 and P3 units of Bossio et al. (1998), spanning 1.2-1.3 Ma; 2) the second cycle corre- sponds to the III cycle of Barberi et al. (1994) and to the unit Q1 (Bossio et al., 1998). It spans 0.65 Ma (Bossio et al., 1998) and probably began at 2.1 Ma. The first cycle is up to 300 m thick, while the second cycle is 350 m thick. The time spans and thicknesses therefore sug- gest that the two cycles may be considered as III order depositional sequences (Vail et al., 1990). The Acquatraversa erosional phase, which sepa- rates the two cycles, spans 0.2-0.3 Ma (Bossio et al., 1998). The related unconformable surface indicates a sea level drop probably due to local infra-Gelasian tec- tonism, that caused the emersion and the eastward til- ting of I cycle’s units, in the northern MVT and near Mt Soratte. The Acquatraversa erosional phase may also be correlated to the global eustatic sea level fall that occurred at 2.4 Ma, when a major event of cooling was recorded (Haq et al., 1987; Bossio et al., 1998). Similarly, the older fluvial and lacustrine deposits inter- fingered with marine sediments at Camorena (Barberi et al., 1994) and Fabro (Fig. 2) may be interpreted as a sedimentary response to the global cooling event that occurred at about 3.0 Ma (Channel et al., 1992; Bossio et al., 1998). In the central MVT, the Acquatraversa unconformable surface may be present in the subsoil, below the lowermost outcropping levels of the II sedi- mentary cycle. It may be possible that the unconformity laterally passes to a conformable surface as well. The few subsurface data from the MVT do not verify any hypotheses, as the drilled sediments only belong to the II cycle (Di Bella, 1994; Carboni & Di Bella, 1994). Nevertheless, subsurface data from the bordering Sabatini Mts area, at Bracciano (Carboni & Palagi, 1998)), and from Vallericca (Arias et al., 1990; Carboni et al., 1993) in the lower Tiber Valley indicate the strati- graphic continuity from late Zanclaean to Santernian (Figs 6 and 7). 55..22.. RReellaattiioonnss bbeettwweeeenn mmaarriinnee aanndd nnoonn--mmaarriinnee ssuucccceess-- ssiioonnss aanndd llaattee GGeellaassiiaann--SSaanntteerrnniiaann ppaalleeooggeeooggrraapphhyy The MVT II sedimentary cycle is characterized by the heteropic relations between the Chiani-Tevere and Poggio Mirteto formations, east of Mt Soratte, and between the Chiani-Tevere and Santa Maria di Ciciliano formations near Amelia. The main architectural feature is represented by three large clastic wedges interfinge- ring with the Chiani-Tevere formation’s shelf deposits. The clastic wedges are composed of the gravelly-sandy beach deposits of the Civitella San Paolo, Torrita Tiberina and Vasanello members, and of their laterally continuous fluvial deposits (Figs 2-4). Each wedge indi- cates a phase of basinward progradation of fluvial, del- taic and coastal sediments alternated with transgressive phases, that are evidenced by the shelf deposits (Fig. 4). The first prograding wedge may have developed at the Gelasian-Santernian transition; this is suggested by the correlation with those marine successions where the Plio-Pleistocene boundary is present or inferred, like Lugnano, Orte Scalo, Vallericca (Carboni et al. 1993; Carboni & Di Bella 1994; Borzi et al. 1998) (Fig. 4). The younger wedges are Santernian in age. Such prograda- tional phases are also evidenced by other transitional and continental lithofacies: 1) the “fine clayey sands of brackish water environment” and the “travertines and calcareous silts” are related to the II and III progradatio- nal episodes (Fig. 3); 2) the fan deltas occurring at Fosso Marutana, Camartana, Montasola, Poggio Catino and Marcellina (Fig. 7) are only related to the III episode. The transgressive phases are evidenced not only by the rapid deepenig of facies, but also by the progres- sive onlap of the “breccias and conglomerates with abundant matrix” above the substratum, and by aligne- ments of Lithophaga borings and notches (Fig. 7a). Such depositional and erosive elements indicate short- term sea level stands that punctuated the transgres- sions. The latter also caused an eastward shifting of the transitional facies, that reached the southwestern Tiberino Basin, as it is indicated by the discovery of brackish water molluscs (Fig. 7a). The paleogeographic thresholds linking the MVT and the Tiberino Basin were located east of Amelia at the San Pellegrino pass and, perhaps, at the Forello gorge near Todi and at Configni in Sabina (Fig. 7); they are considered as outlets of ancient fluvial systems (Ambrosetti et al., 1987; Girotti & Piccardi, 1994; D’Agostino et al., 2001). The Rieti Basin 99Plio-Pleistocene stratigraphy ... 100 O. Girotti & M. Mancini F ig . 6 - C o rr e la tio n b e tw e e n t h e M V T a n d s u rr o u n d in g s b a si n s (d a ta p a rt ly m o d ifi e d a ft e r B o n a d o n n a ( 1 9 6 8 ), B a si lic i ( 1 9 9 3 ), C a rb o n i e t a l. (1 9 9 3 ), B a rb e ri e t a l. (1 9 9 5 ), M a rr a e t a l. (1 9 9 5 ), M ill i (1 9 9 7 ), C a rb o n i & P a la g i ( 1 9 9 8 ), B e rg a m in e t a l. (2 0 0 0 ). 101Plio-Pleistocene stratigraphy ... F ig . 7 - P a le o g e o g ra p h y o f th e L a tiu m -U m b ri a r e g io n d u ri n g t h e l a te G e la si a n -S a n te rn ia n : (A ) tr a n sg re ss iv e a n d ( B ) p ro g ra d a tio n a l p h a se s. L e g e n d : a ) ca rb o n a tic a n d s ili ci cl a st ic m e so -c e n o - zo ic s u b st ra tu m , b ) a llu vi a l a n d l a cu st ri n e d e p o si ts , c) p lio -q u a te rn a ry n o n -m a ri n e d e p o si ts s u b je ct e d t o e ro si o n , d ) d e lta ic a n d c o a st a l d e p o si ts , e ) e m e rg e d m a ri n e d e p o si ts , f) t ra ve rt in e s, g ) vo lc a n ite s, h ) ve rt e b ra te r e m a in s, i ) b ra ck is h -w a te r m o llu sc s, j ) o lig o h a lin e o st ra co d s, k ) L ith o p h a g a b o ri n g s (w ith a lti tu d e a .s .l. ), l ) fa n -d e lta a n d a llu vi a ll- fa n , m ) d ir e ct io n o f a n ci e n t ri ve r, n ) d ir e ct io n o f d e lta ic p ro g ra d a tio n , o ) d ir e ct io n o f p yr o cl a st ic f lo w , p ) n o rm a l f a u lt, q ) st ri ke -s lip f a u lt, r ) m a in c ra te r. was probably affected indirectly by transgessions too, as it is evidenced by the presence of olighoaline ostra- cods in its northern sector, at Fosso Filundici and Madonna della Torricella (Barberi et al., 1995; Gliozzi & Mazzini, 1998) (Fig. 7a). It would be likely that the Rieti Basin was linked with the MVT basin through the Terni sub-basin and/or the Farfa valley (Figs 1 and 7). On the other hand, the paleocoastline’s seaward shiftings, which occurred at the progradational phases, may be estimated at 12-15 km with respect to the western margin of Mt Peglia-Lucretili Mts ridge. Such progradations are clearly evident in the Vasanello-Orte- Amelia and Mt Soratte-Sabini Mts areas in front of the deltaic systems of the Paleo-Nera and Paleo-Farfa rivers, that respectively drained the Tiberino and Rieti Basins (Fig. 7b). Each progradation is related to periods of increased sedimentary supply coming down from the intramontane basins and their surrounding mountainous areas. This increment may be due to: 1) tectonics, that caused differential uplifts of the inner areas with respect to the subsiding marine basin. This twofold movement may have led to an increment of relief energy and con- sequent erosion in the emerged areas, and to an increa- se of accomodation space in the MVT basin. 2) Climate changes, that may have been characterised by alterna- tions between temperate and cold phases. In fact coo- ling episodes, if coupled with rainy periods and limited vegetation covers, may produce a great amount of ero- ded sediments and facilitate their transport. Furthermore, they are in general associated with eusta- tic sea level falls. In the Chiani-Tevere formation the effects of clima- tically-induced sea level falls have been detected only within the fan-delta deposits (III progradational episode). The related base level drop is estimated at 70 m, althou- gh neither the tectonic nor the eustatic component have been fully distinguished (Girotti & Piccardi, 1994). As for the older progradational episodes, no erosive or deposi- tional elements linked to sea level falls, like incisions or downward shifts of coastal facies, have been observed. In fact, it seems likely that the progradational and tran- sgressive deposits progressively filled the basin in con- comitance with the subsidence throughout the entire late Gelasian-Santernian. Therefore, negative eustatic movements have not been recorded by erosive surfa- ces, as their rates were of the same magnitude or slower than the subsidence rate. On the other hand, the sedimentologic and erosive effects of periodical sea level rises and transgressions are clearly evident, as it is discussed above. Although the triggering mechanism that control the alternating progradational and transgressive phases is not clear at all, each couple of main progradation-tran- sgression may suggest a IV order cyclicity within the main III order cycle. 55..33.. SSeeddiimmeennttaarryy aanndd ppaalleeooggeeooggrraapphhiicc eevvoolluuttiioonn dduurriinngg tthhee mmiiddddllee EEaarrllyy PPlleeiissttoocceennee--eeaarrlliieesstt MMiiddddllee PPlleeiissttoocceennee.. The regional uplift started at the earliest-middle Early Pleistocene between 1.5 and 1.3 Ma (Ambrosetti et al., 1987; Cavinato et al., 1994) and continued throu- ghout the rest of Quaternary, determining the alternance of erosional and depositional phases in concomitance with climate changes. Each sedimentary unit deposited during this period represents a cycle of degradation- aggradation. In particular, the late Middle Pleistocene- Holocene terraced units were cyclically deposited every 100 ka, with a recurrence due to global climatic changes related to variations of the orbital eccentricity (Imbrie, 1985). As for the middle Early Pleistocene-earliest Middle Pleistocene units, chronological data are less precise, so making uncertain the linkage between the alternances of depositional and erosional phases and the 100 ka spanning cyclicity. However, all the sedimen- tary units may indicate a IV order cyclicity, although the inferred time span of the Civita Castellana unit is about 600 ka, a bit longer than a IV order cycle. The most evident paleogeographic change after the early uplift was the south-westward shifting of the coastline for more than 30 km away from the Mt Peglia- Lucretili Mts ridge. In this way the Roman area was rea- ched, where coastal facies developed (Fig. 8a). During the Emilian, the developing juvenile Tiber River caused at first the incision of the just emerged Gelasian- Santernian sediments, and then the deposition of the Giove formation in concomitance with the Mt Cimino vol- canic activity. The ancient river flowed parallel to the axis of the Paglia-Tevere graben west of Mt Soratte (Alvarez, 1972; 1973). The ancient Tiber mouth may be represented by the transitional deposits of the “Sabbie gialle di Monte Mario” (Bonadonna, 1968); the latter crops out at Monte Mario in Rome, covers Santernian sediments and bears Late Villafranchian molluscs and vertebrates (Girotti, 1972; Caloi & Palombo, 1988; Petronio et al., in press) (Figs. 6 and 8a). The Tiber’s upper catchment was mainly affected by erosion, although local sedimentation persisted with the deposition of the lacustrine pelites of the “Case Strinati-Madonna della Torricella unit” in the northern Rieti Basin (Cavinato et al., 2000), and of the travertines of the “Acquasparta formation” in the southwestern Tiberino Basin (Basilici, 1992) (Figs. 6 and 8a). During the Sicilian-earliest Middle Pleistocene, the coastline continued to migrate westward reaching the Ponte Galeria area, where fluvial-deltaic sediments were deposited (Conato et al., 1980; Milli, 1997; Karner et al., 2000) (Figs 6 and 8b). In the MVT the ongoing uplift caused a renewal of the fluvial incision - the “Cassia erosional phase” Auct. – which may be estima- ted at more than 100 m (Mancini, 2000). Such an inci- sion cuts the Chiani-Tevere and Giove formations and caused the “cannibalization” of the oldest Tiber River’s deposits. This downcutting also affected the Meso- Cenozoic substratum at the Forello and Stifone gorges (Fig. 8b), where the activity of local antiapennic-trending faults may have caused captures and deviations of the Tiber and Nera river courses (Cattuto et al., 1997) (Figs. 8a-b). The erosional phase was followed by the aggra- ding Civita Castellana unit. This unit may be correlated with the fluvial deposits outcropping at Marcigliana in the lower Tiber valley (Basili, 1996), and with those fil- ling the small ongoing “Paleotiber graben” in the northern Roman area (Karner et al., 2001) (Fig. 8 b). The correlation is suggested by both the lateral conti- nuity between fluvial units, detected below the Middle Pleistocene Sabatini Mts volcanites (Funiciello et al., 1994), and by biochronological data after the discove- 102 O. Girotti & M. Mancini 103Plio-Pleistocene stratigraphy ... F ig . 8 - P a le o g e o g ra p h y o f th e L a tiu m -U m b ri a r e g io n d u ri n g : (A ) th e E m ili a n ; (B ) th e S ic ili a n -e a rl ie st M id d le P le is to ce n e . ries of vertebrates belonging to the Farneta-Pirro Faunal Units (late Early Pleistocene) in several sites as Rio Fratta, Capena, Redicicoli 1 (Di Stefano et al., 1998; Petronio et al., in press). 66.. CCOONNCCLLUUSSIIOONNSS The stratigraphic data and the consequent interpre- tation of the paleogeographic evolution of the MVT and surrounding basins delineate a Late Pliocene-earliest Early Pleistocene subsidence-dominated tectono-sedi- mentary phase and a middle Early Pleistocene-Holocene uplift-dominated phase. The first phase provides direct chronostratigraphic elements, based on biostratigraphic, biochronologic, physical-, isotopic- and magneto-strati- graphic analyses and observations which are of great relevance in correlating the interfingered marine, transi- tional and non-marine successions, widely outcropping at the borders of the MVT, Tiberino and Rieti Basins. For the second phase, the new biochronologic data, the rela- tions between fluvial and volcanic deposits and the infer- red regional paleogeography provide indirect tools for the correlation between the fully non-marine MVT basin and the Roman area, characterised by marine, transitional and fluvial successions, in particular for the Emilian-early Middle Pleistocene interval. NNootteess:: (1) Recent and exhaustive re-examinations of the ancient paleontologic findings in the Valli sabine are published in Kotsakis (1988), Esu & Girotti (1991), Gliozzi et al. (1997), Ciangherotti et al. (1998), Petronio et al. (in press). (2) Pareto (1865) introduced the Villafranchian Stage and attri- buted to it those non-marine sediments that were deposited above the Pliocene marine successions as a consequence of a general withdrawal of the sea. He applied the term Villafranchian to all the non-marine deposits of North- and Central-Italy and considered it as Quaternary in age. Hürzeler (1967) recognized a Pliocene age for the vertebrates of Villafranca d’Asti (the type locality of the stage) and Azzaroli (1977) subdivided the Villafranchian into Early (Middle Pliocene), Middle (Late Pliocene) and Late (Early Pleistocene). Most of the non-marine sediments ranging from Middle Pliocene to Early Pleistocene are actually mapped as Villafranchian on the Geologic Map of Italy. The succession of the type locality is Middle Pliocene. In recent times some doubt was expressed about the validity of the Villafranchian as chro- nostratigraphic unit (Carraro, 1996), whereas Gliozzi et al. (1997) introduced and defined the Villafranchian in the biochro- nological scale of the mammal ages. Nevertheless, the Plio- Pleistocene non-marine successions are so widespread in Italy that, in our opinion, they need to be classified in an indepen- dent chronostratigraphical scale; in fact, an attribution to the marine one is rarely possible. Therefore, we think that, in order to classify the huge amount of non-marine successions out- cropping in Italy, the Villafranchian should not be abandoned and a formalization is to be hoped for. The lower boundaries of Early and Late Villafranchian, at least, may be defined on sec- tions at Villafranca d’Asti and in the Upper Valdarno respecti- vely, where continuous sedimentation occured and litostrati- graphy as well as palaeontological and magnetostratigraphical data are available. AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS We would like to thank Prof. Mario Barbieri for the isotopic analyses and Dott. Carlo Bosi for the useful comments that have improved our manuscript. This research was supported by MURST (60%) and by CNR IGAG. RREEFFEERREENNCCEESS Alvarez W. (1972) - The Treia Valley north of Rome: vol- canic stratigraphy, topographic evolution, and geo- logical influences on human settlement. Geol. Romana, 1111, 153-176. Alvarez W. 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