LATE QUATERNARY EVOLUTION OF THE TERNI BASIN, CENTRAL ITALY: NEW GEOARCHAEOLOGICAL DATA Milena Bertacchini Dipartimento di Scienze della Terra, Università di Modena e Reggio Emilia, Modena e-mail: milena.bertacchini@unimore.it ABSTRACT: Bertacchini M., New geoarchaeological data on the recent evolution of the Terni basin, Central Italy. (IT ISSN 0394-3356, 2009). Because of an archaeological find of part of a Hellenistic city wall (ca 5th -3rd century BCE) a well-preserved 10 m thick fluvial sequence was studied close to the centre of the town of Terni, in an area of Central Italy (Umbria) where the geological outcrops are generally scarce. This study was made in a large excavation for a building that permitted direct observation of the sediments that filled the Terni basin and provided a step forward in our knowledge of its geoenvironmental evolution. The sedimentary sequence was deposited by a segment of the ancient Nera river-course (paleo-Nera) in the Late Pleistocene-Early Holocene and its presence is correlated with the development of the first human settlements in the town of Terni. This fluvial sequence shows evidence of a low-sinuosity gravel mean- der system consisting of transverse gravel bars and gravel sheets in its lower part, that are capped by a 5 m thick levee unit and over- bank deposits interbedded with incipient paleosols and a crevasse channel unit. The floristic composition contents in the paleosols of the overbank sequence provide important information on the climatic transition from the Late Glacial to the Holocene. The upper part of the sequence, a paleosol dated with archaeological remains to Roman times, contains important elements that aid in understanding the development of the first phases of urbanisation of the ancient town of Terni. RIASSUNTO: Bertacchini M., Nuovi dati sull’evoluzione recente della piana di Terni (Italia centrale). (IT ISSN 0394-3356, 2009). Lo scavo ad uso civile realizzato nel sito di Corso del Popolo, nei pressi del centro storico di Terni, ha permesso la diretta osservazione di una potente successione sedimentaria di ambiente fluviale deposta a partire dal Tardo Pleistocene da un antico tratto del fiume Nera (paleo-Nera). Lo studio di dettaglio condotto sulla successione esposta ha rappresentato una importante opportunità per la raccolta di nuove informazioni sull’evoluzione geologico-ambientale recente del bacino di Terni, attraverso indagini di tipo geologico-sedimentolo- gico, mineralogico-petrografico, paleontologico e pollinico, affiancate da dati archeologici. La base della successione è rappresentata da sedimenti ghiaiosi di canale attivo passanti a depositi di esondazione con sequenze di argine, di canale di rotta e di canale di cre- vasse, intervallati da paleosuoli interessati da una pedogenesi poco evoluta. La variazione del contenuto pollinico registrata all’interno dei depositi di esondazione è da imputare al cambiamento climatico legato alla fine del Tardi-Glaciale ed all’inizio dell’Olocene. L’abbandono del canale fluviale favorisce la formazione di un lago poco profondo o acquitrino e la deposizione di sedimenti carbonatici fini interrotti a tetto da un paleosuolo archeologicamente riferibile al I sec. a.C. I dati stratigrafici e cronologici ottenuti dallo studio della sequenza investigata concorrono a ricostruire con maggior puntualità la situazione geo-ambientale che accompagnò le prime fasi di urbanizzazione della città di Terni. Keywords: fluvial deposits, paleosols, Holocene, Terni, Central Italy. Parole chiave: depositi fluviali, paleosuoli, Olocene, Terni, Italia Centrale. Il Quaternario Italian Journal of Quaternary Sciences 22(2), 2009 - 249-256 INTRODUCTION The Terni plain is located in the southern part of the Umbria region, within the central and terminal sec- tors of the Nera river basin (fig. 1). It is a transition area between the inner Apennine chain and the hills and plains of the western regions of Italy in the Tiber Valley (southern and northern Etruria). The stratigraphy of the continental deposits filling the Terni basin is not well-known because of the scarci- ty of useful outcrops. The entire continental succession, which characterises the recent sedimentary deposition of the plain, is largely hidden below the surface. Most of the detailed subsurface geological data collected has come from archaeological or civil excavations and the results of recent studies of the sediments in the Terni basin (BE R T A C C H I N I et al., 2006; FA Z Z I N I & MA F F E I, 2006) have not permitted a recognition of the continuous stratigraphic succession, mainly formed by lacustrine and fluvial-lacustrine sediments, deposited from the VII century BCE until Roman times. In this framework the sequence here studied is fundamental for the knowl- edge of the sediments filling the Terni basin and for better understanding both the geoenvironmental evolu- tion of the plain and the development of the first human occupation in the centre of Terni. The Terni plain has continuously been a major communication and trade passageway since the Bronze Age, because of its mor- ph o lo gi cal an d s t ra t egi c g eo g ra ph ic al lo cat i on (GIONTELLA, 2006). The town of Terni was formally founded in the 672 BCE (BONOMI PONZI, 2006), even though the oldest sig- nificant phase of its urban development was in the 3 rd century BCE, in coincidence with the Roman expansion in the Umbria region (PE R I S S I N O T T O, 2006). The ancient name of Terni, Interamna Nahars, means “between two rivers”, was given because its position at a confluence of the Nera river with the Serra-Tescino stream sug- gesting a different hydrographic layout at that time. Several authors have hypothesized that both streams have probably changed their courses through time (GRASSINI, 1947; FONTAINE, 1990; FAZZINI & MAFFEI, 2006), on the basis of archaeological data (fig. 1). This paper presents the data obtained of a verti- 250 M. Bertacchini cal s eq u en ce o f s ed ime n t s exposed by a civil excavation (over 50 m wide) conducted in summer 2006 along Corso del Popolo road, close to the centre of Terni, which has given us an insight as to the morphologic grounding of this newly founded city in its earliest days. GEOLOGICAL SETTING The Terni plain is one of the fault-bounded intermontane basins formed during the Plio- Quaternary succession of tec- tonic phases in an extensional regime, which affected the cen- tr al po rt ion of t h e n ort h ern Apennine chain (BA R C H I et al. , 1991; CA T T U T O et al., 1992; CA V I- N A T O et al., 1993; BR O Z Z E T T I & LA- V E C C H I A, 1995). Accordingly, the elongated NNE-SSW shape of the Terni basin results from the complex in te ract ion o f th e Martani, Sabini and Val di Serra fault systems boardering the plain (BO N I N I, 1997; GI R O T T I & MA N C I N I, 2003). The Terni basin is consid- ered to be the western elongation of the Tiber basin, an intermontane Apenninic depression that was gradually filled with fluvial and lacustrine deposits (LO T T I, 1917; LI P P I BO N C A M B I, 1960; AM B R O S E T T I et al., 1978; BA S I L I C I, 1993; AM B R O S E T T I et al., 1995; CO N T I & GI R O T T I, 1977; GIROTTI & MANCINI, 2003). A shallow lake or pond system occupied the Terni basin up to earliest historical times that gradually disappeared due to the alluvial infill from the Nera, Serra and Tescino streams (BERTACCHINI et al., 2006; FAZZINI & MAFFEI, 2006). The Terni basin is flanked by Martani-Reatini Mountains to the east and Amerini-Narnesi-Sabini Mountains to the west. These higher areas consist of calcareous Meso-Cenozoic units of the Umbria-Marche marine succession, where the headwaters of the Nera river and its main tributaries are located (the Aia and Serra-Tescino streams and the Bianco-Caldaro brook). The predominance of carbonate rocks in this Apennine area greatly control the composition of the sediments transported by the watercourses into the Terni basin as well as the groundwater composition of the region. METHODS Preliminary data here presented results from a sedimentological and physical study of the sediments in order to integrate the detailed visual inspection of the deposits and define the lithostratigraphical sequence. These data are a combination of: lithology, grain size, sedimentary structures, colour and any other possible diagnostic element. Colour definitions, such as 2.5 Y 5/4, are referred to Munsell Colour Soil Chart and con- sists of hue (2.5 Y), lightness (5), and chroma (4). AMS (Accelerator Mass Spectrometry, Nelson et al. 1977; BENNETT et al. 1977) radiocarbon datings have been car- ried out from carbon organic remains in the Beta Analytic Inc. Laboratory in Miami, Florida. The datings refer to the IntCal04 calibration data set for terrestrial samples (REIMER et al., 2004). The first results on pale- ontological (macro and micro) and pollen characters cited in this paper have been supplied by personal communications respectively from A. Russo and S. Marvelli. The paleontological samples have been treat- ed with H2O2 (2% vol.) and the observations have been carried out on a dry residue, sieved and desiccated in oven at 105 °C. The pollen analysis have been carried out following the standard procedure described by Lowe et al. (1996) in the Archaeoenvironmental Giorgio Nicoli Laboratory in Bologna. The micromorphological study on paleosol thin sections have been examined under the optical micro- scope applying the methods of Stoops (2003) and some terminology of BU L L O C K et al. (1985) and BR E W E R ( 1 9 7 6 ) . M in eralo gic al an aly ses on pebbl e coat in gs observed in the sequence have been conducted by Energy-dispersive X-ray (EDX) technique coupled with an environmental scanning electron microscope ESEM Quanta-200 in the Modena University CIGS Laboratory. THE SEDIMENTARY SEQUENCE OF THE CORSO DEL POPOLO SITE This study is based on observations made during the excavation of the Corso del Popolo car park located Fig. 1 - Morphological and geographical location of the town of Terni. This map contains the present-day hydrographic system and the stream-course changes both of the Nera River, according to this study and that of Fontaine (1990), together with data concerning the Serra- Tescino stream, according to GRASSINI (1947), FONTAINE (1990) and FAZZINI & MAFFEI (2006). The confluence of the Serra-Tescino stream with the Nera River during medieval times has been suggested by GRASSINI (1947) and FONTAINE (1990). Ubicazione geografica della città di Terni e rappresentazione cartografica semplificata del suo territorio. Nella mappa è ricostruita la paleoidrografia dei principali corsi d’acqua dell’area: il Fiume Nera, sulla base dei risultati presentati in questa ricerca e dei dati pubblicati da FONTAINE (1990); e i torrenti Serra e Tescino, come riportato da GRASSINI (1947), FONTAINE (1990) e FAZZINI & MAFFEI (2006). near the centre of Terni, not far from the present-day course of the Nera River. The examined section has permitted the reconstruction of a 10 m thick sedimenta- ry succession, which was deposited by the water- course antecedent to the modern Nera. A detailed multidisciplinary stratigraphical investi- gation has been carried out based on geological, miner- alo g ica l, pet r og r aph i cal - micr o mor ph o lo g ica l an d paleontological evidences alo n g wi t h p ol len an d archaeological data. Four main different un it s h ave been re cog n i zed in t h e investigated sequence. Unit A, at the base of the excavation, consists of a 3 m t h ic k s e dime n t ary sequence mainly composed of gravel with subordinate pebbly-sand and sand. This unit, whose lower limit is not exposed, abruptly passes to a finer deposit of the overly- ing Unit B. The sedimentary structures observed in these deposits are mainly repre- sented by t rough -sh aped an d pla n ar cr os s - be ds , which develop in a meter- long continuous sets. The gravels are generally moder- ately sorted. They are com- posed of rounded to sub- ro u n ded cal car eo u s an d ch er t y, med iu m t o l arg e pebbles , rang ing 1 ÷3 cm (mean diameter). Unit s of single depositional events are in sets about 40 cm thick and an angle of about 20°, suggesting a main water- course flow from NE to SW. The gravels are clast- su ppo rt ed w it h les s t han 10% smaller sized clasts of san d an d mu d as matr ix. Peb ble s a re c oa t ed by a reddish-black thin iron-man- ganese film and there is very lit t l e mat r ix bet w een t h e clasts. Horizontally bedded gravel sheets are present in the upper portion of Unit A. They are formed of rounded medium to very large peb- bles and subordinate cob- bles , s li gh t ly imbr ica te d. They appear as moderately sorted, graded, clast-sup- ported deposits with subor- dinate sand and mud. Unit B overlies Unit A and is formed by a 5 m thick 251Late Quaternary evolution of the Terni basin, Central Italy: ... sequence consisting of a well-developed cyclicity, which is cadenced by dark brown levels presenting pedogenic modification. Each cycle is characterized by a basal sandy unit overlain by a pedogenised horizon of coarser-grained sediment (B1) or of finer-grained sedi- ment (B2). Each simple pedofacies sequence (KR A U S, Fig. 2 - Stratigraphic section studied in the Corso del Popolo site of the Terni basin. The different units are described in text. A: Unit A, related to coarse-grained point bar deposits; B: Unit B, an overbank sequence formed of levee (B1) and crevasse-splay (B2) sediments interbedded with floodplain deposits; Unit C, a crevasse channel deposit; C: Unit D, sequence due to a cut-off event. Ricostruzione della successione stratigrafica del sito di Corso del Popolo a Terni. Sono indicate le diverse unità come descritte nel testo. A: Unità A, caratterizzata da sedimenti ghiaiosi di canale attivo; B: Unità B, depositi di esondazione con sequenze di argine (B1) e di canale di rotta (B2) intervallati da paleosuoli interessati da una pedogenesi poco evoluta; C: Unità C: deposito di canale di crevasse; D: Unità D, depositi dovuti alla formazione di un lago poco profondo o acquitri - no conseguente all’abbandono del canale fluviale. 252 1987) is capped by the base of the ensuing cycle with little or no erosion; except the top of Unit B, which was truncated by the erosive deposition of Unit C (Fig. 2). The simple pedofacies sequence (B1) is made of coarsening-upward cycles of fine sandstones and silt- stones showing weakly identifiable ripple-cross lamina- tion and matrix-supported graded gravel deposits formed of brown-reddish pebbles and cobbles. The gravel levels have been affected by pedogenic modifi- cation including root structures, scattered desiccation cracks and mottling. These pedofeatures have also been examined in a thin section where, when mottling is present, there is a clearly visible considerable scat- tered enrichment in interstitial oxides of iron and man- ganese. This weakly developed pedogenic modification has been observed in the gravel layers of B1 in associa- tion with unaltered parent material characterized by sandstones, siltstones and lithic fragments. The lowest gravel layer in B1 has been studied in greater detail to obtain a better understanding of the relations between Unit B and the underlying Unit A. The finer sediment in the lower part of this horizon is dark brown (7.5 YR 3/2-4) and yellow brown mottled (10 YR 5/6), passing to yellow-reddish brown mottled (7.5 YR 5/6) in the upper part. The second and relative younger dark brown (10 YR 4/2) gravel layer in B1 (fig. 2) is indi- cated by prevalent amounts of pedogenic modification that is, however, more immaturely developed; mottling is observed but desiccation cracks are not present. A determination of the absolute age through ASM radiocarbon dating has yielded a value of 9310±50 BP (10660-10310 cal BP; Beta-238366). The pollen data of the base of B1 have revealed a moderate presence of deciduous oaks with F r a x i n u s in an open landscape and a high content of non-arboreal pollen (Cicho- rioideae). At the top of B1, arboreal vegetation u n d e r- went a clear reduction, without disappearing completely. The simple pedofacies sequence B2 overlies B1; it is formed by fining upward cycles of laterally discon- tinuous exposure sheet-like siltstones and very-fine sandstones, interspersed with dark-coloured pedo- genised mudstones (10 YR 5/2; 4/2). Each cycle of sandy layers capped by a single paleosol is repeated at least six times moving upward B2, with a range in thick- ness of each one from 0.4 to 1 m. No erosional surfaces are observed between two subsequent cycles, passing upward B2. The last cycle at the top of B2, and corresponding to the top of Unit B, is truncated and eroded by a channelized-shape gravel deposit (Unit C). In general, the sediment forming the base of each series consists of a beige-coloured (10 YR 6/4; 7/2-4; 8/4-6) calcareous sandy siltstone or fine sandstone that passes upwards to a fine siltstone. The primary structures are generally not preserved but, where identifiable, they present cross and horizontal lamination. The top of each cycle is dominated by crumbly calcareous mudstones on which a single paleosol pro- file (FREYTET, 1973), with an immature pedogenic evolu- tion, develops. These paleosols present dark brown coloured zones with burrowing, root traces, rare calcite nodules, and bacterial concretions. The micromorpho- logical data confirm the pedofeatures observed in out- cropping and show the correlation between root traces and calcite nodules, when the nodules are present. The paleosol of the uppermost cycle B2 was not truncated, and lies at the base of the gravel channelized-shape deposit. It is the only horizon to show rare papulae ped- ofeatures (BREWER, 1976) in a thin section. This deposit has a radiometric age of 8010±40 BP (9010-8730 cal BP; Beta-238365). An appreciable vegetation change occurred at the beginning of the deposition of the simple pedofacies sequence B2, mainly due to the early appearance of Tilia and Salix, while the landscape was still fairly open. Moving upward along the sequence, the pollen content increases, both in quantity and diversity of species; the deciduous oaks accompanied by several other arboreal taxa (Fraxinus, Tilia, Carpinus, Pinus, Salix, Alnus ecc.) define a forested landscape. The upper part of Unit B is engraved and eroded by a coarse-grained channelized-shape deposit, here indicated as Unit C (fig. 2). Unit C appears as a lens, a few meters wide and one meter thick, with gentle flanks and an erosive con- cave base. The channel-filling is formed by moderately sorted to well sorted graded coarse to pebbly sands up to pebble gravels. The finer sediments at the base of the channel present ooids and tubular bacterial struc- tures and show trough cross bedding (MI A L L, 1996). Penetrative rhizolite laminar calcretes are present, due to the calcification around roots (WR I G H T et al., 1995). These are 3-5 cm thick and 40 cm long and develop along the main cross-bedding surfaces. They corre- spond to beige calcareous cementation normally devel- oped around root mats and show alveolar septal struc- tures in a thin section (WRIGHT et al., 1995). A pebble to cobble gravel sheet closes the coars- ening upward channel-filling and exhibits a slightly con- vex shape. Unit D constitutes a 4 m thick sequence charac- terized by calcareous, gold-coloured (10 YR 8/2-3), fine siltstones with faintly planar lamination at the base. This deposit continues at the base of the upper section examined at the Corso del Popolo site. In about two meters of thickness it is possible to observe siltstones or mu d st o n es w it h Os t r aco ds a n d p u lmo n at e Gastropods (in course of determination), bioturbation, root tubules and carbonate concretions. At the top of the sequence there is a yellow brown (2.5 Y 5/4) mottled paleosol containing archaeological remains that accumulated before the 1s t century BCE (Superinten dence to Archaeological properties of Umbria, personal communication). An important structure, part of a huge wall of Hellenistic age (5t h- 3r d century BCE) has been found above the muddy sandstones with ripple lamination on the northern side of the site excavation. The presence of significant human exploitation of the Corso del Popolo area since that time has probably contributed to erase all other parts of that wall. INTERPRETATION Integrating lithological, sedimentological, miner- alogical aspects with physical evidence and paleonto- logical and pollen data, allows us to reconstruct a rea- sonable picture of the alluvial environment where the continental studied succession accumulated. Each unit is related to characteristic depositional processes. M. Bertacchini 253 Unit A shows sediments and sedimentary struc- tures deposited by fluvial processes in an alluvial plain, probably due to the accumulation of lag deposits within transverse gravel bars and horizontal beds (lithofacies Gp, Gt and Gh of MI A L L, 1996). According to Jackson (1 9 7 6 ) , GU S T A V S O N (1 9 7 8 ) a n d M I A L L ( 1 99 6 ) , t h is sequence is probably related to a coarse-grained point bar deposit characterized by lateral accretion and grav- el bedform elements. Extensive continuous sets of trough cross-strata are interpretable as due to a moder- ately stable bar related to a gravel-bed wandering flu- vial system (AS H M O R E, 1991; WO O L D R I D G E & HI C K I N, 2005). Such an important supply of coarse-grained grav- elly sediments requires the effects of intense physical weathering processes and extreme ranges in fluvial dis- charge to favour their deposition. Post-depositional movement of fluids through the sediments also caused intense fluid washing with a concomitant removal of most fine-grained sediment, therefore little matrix remains. Unit B shows a coarsening-upward simple pedo- facies sequence at the bottom (B1), which is overlaid by a fining-upward simple pedofacies sequence (B2), both are interbedded with incipient paleosols. Unit B devel- oped in a floodplain area proximal to the active chan- nel. It corresponds to a vertical sequence of overbank environments constituted by progressive sandy levee (B1) and crevasse-splay (B2) sediments associated with finer-grained floodplain deposits. The passage between unaltered fluvial sediments and paleosols is apparently related to an alternating succession between periods of flood events and peri- ods of quiescence without fluvial sedimentation. The sequence B1 suggests relatively rapid accretion rates on the basis of poorly developed pedogenic modifica- tion. The paleosol at the base of this unit can be inter- preted as an entisol that, even though immature, testi- fies to a slight decrease in the sedimentation rate (KRAUS, 1987). The strong presence of burrowing, root- ing and calcite nodules as pedogenic features in the paleosols observed in the sequence B2, hints that the deposition of new sediments were relatively frequent over a period of time but sufficiently infrequent as to permit the triggering of such aspects of pedogenic modification. The pollen assemblage of the lowest part of B1 is interpreted as representing a semi-arid and cool phase where moderate deciduous oaks dominated the open landscapes. The marked vegetational reduction record- ed at the top of B1 suggests a worsening of the severe climatic conditions. Moving upward B2, a significant vegetational change is marked. The appearance of Tilia and Salix at the base and a significant expansion of Tilia and various other tree taxa at the top of the sequence, evidence a more temperate and humid climate than in the previous phase. Unit C marks a limited erosive event, which cut the top of Unit B sequence. It is characterized by a coarse-grained lens deposited by a crevasse channel, which probably is correlated to the sediments of the cut-off event of Unit D. The penetrative rhizolite laminar calcretes, which occurred as calcareous cementation around root mats, suggest a carbonate-rich groundwater environment ass ociated to an in crease of t emperature, wh ich favoured the calcium-carbonate precipitation. Unit D is associated with a shallow lake, pond or marshy environment overlies a structure that represents a probable cut-off process from the active stream- channel (SM I T H et al., 1989; WI L L I S & BE H R E N S M E Y E R, 1994; MIALL, 1996). Unit D represents the beginning of a new geoenvironmental situation favouring the develop- ment of a shallow carbonate lacustrine-palustrine envi- ronment related to a shallow, fresh-water lake (PLATT & WRIGHT, 1992) and a more humid climate. This interpre- tation is also based on the first results obtained from fossil species present in the sediments at the bottom of Unit D. The degree of pedogenic modification increases upwards in the sequence. DISCUSSION OF THE RESULTS T h e s ed imen t s an d se dime nt ar y s t r u ct u res observed in the Corso del Popolo fluvial succession on the Terni plain are representative of an ancient stream course, flowing on the eastern side of the present-day town of Terni. The collected data suggest that this stream acted as an ancient segment of a paleo-Nera river located close to the west of the present-day course of the Nera river. This geological result proves the change in the Nera river-course originally hypothe- sised by FONTAINE (1990) on the basis of archaeological speculations (fig. 1). The studied sequence represents a rare example of a continuous succession deposited from the Late Ple is t o cen e- Ear ly Ho lo ce n e u p t o R om an t imes observed in the Terni basin. Fig. 3 - Hypothesis of reconstruction of the oldest defensive wall built around the centre of Terni during the 5th-3rd century BCE (mod. ZAMPOLINI FAUSTINI, 2006) Schema ricostruttivo della cinta muraria a difesa dell’antica città di Terni tracciato sulla base del rinvenimento del tratto di muro ascrivibile al V-III sec. a.C. citato nel testo (mod. ZAMPOLINI FAUSTINI, 2006). Late Quaternary evolution of the Terni basin, Central Italy: ... 254 The detailed analysis of the sedimentary succes- sion show an interesting geoenvironmental evolution of the basin, passing from a coarse-grained point bar sequence deposited by a low-sinuosity fluvial system (Unit A), grading to an overbank succession composed of levee deposits (B1) and crevasse-splays (B2), cycli- cally interrupted by immature paleosols. A crevasse channel (Unit C) truncates the overbank deposits and marks the transition to a shallow lacustrine-palustrine environment related to a cut-off event. The AMS radiometric dating determined at the base of Unit B links the visible part of Unit A to the effects of the final phases of the last glacial portion of Late Pleisto cene (BU S S C H E R S et al., 20 07) , wh ich favoured the large supply of the coarse-grained sedi- ments forming Unit A. A Late Glacial climatic situation which is comparable with the last glacier advance of the Gran Sasso Massif in the Central Apennines dated by GIRAUDI & FREZZOTTI (1997) at ca. 11000 yr B.P. The sequence of the overbank deposits (Unit B), in spite of their laterally discontinuous exposure, sug- gests that deposition occurred in a relatively proximal position with respect to the paleo-Nera river-channel, starting from 9310±50 BP (10660-10310 cal BP). The overbank sequence was generated by sporadic flood events followed by pedogenesis, which was periodical- ly in terrupted by crev as se- splay depos ition un til 8010±40 BP (9010-8730 cal BP), when a crevasse channel (Unit C) cut the sequence and ended the over- bank deposition. The pollen assemblage and the forest reduction recorded in the lower part of Unit B is related to a semi- arid and cool phase. This was successive the marked vegetational fluctuation proved at Rieti Basin (RI C C I LU C C H I et al., 2000) and at Lagaccione, near Lago di Bolsena, until a few centuries after 10850±105 yr B.P. (MAGRI, 1996), and which the Authors consider related to the Younger Dryas event. The vegetation associated to the upper part of Unit B suggests a progressive considerable forest expansion, which is interpretable as due to a more tem- perate and humid climate. The increase of arboreal plants marks the transition to Holocene as observed in oth er s ites of Cen t ral I taly (F O L L I E R I et al., 19 89 ; CALDERONI et al., 1994; WATTS et al., 1996; MAGRI, 1999; MAGRI and SADORI, 1999; RICCI LUCCHI et al., 2000). Palustrine-shallow lacustrine and calcareous sedi- ments close the Corso del Popolo sequence (Unit D) were deposited in a cut-off shallow lake or pond envi- ronment related to a temperate wet climate, where the rising temperature was favourable to the deposition of the calcium-carbonate. Similar environmental condi- tions are documented at Rieti Basin (RICCI LUCCHI et al., 2000), Lagaccione (MA G R I, 1999) and Lago di Vico (MAGRI & SANDORI, 1999) during the interval 8000-7000 yr BP. The environmental changes recorded in the sedi- ments of the Terni sequence from the middle Holocene were a consequence of climatic changes affected by regional and local factors. It is more difficult to put forward a reconstruction hypothesis based on the scarce remains of the wall of Hellenistic age (ca 5t h - 3r d century BCE) found at the Corso del Popolo site. This wall apparently represented a portion of the eastern side of the oldest defensive wall built around the town of Terni, at the beginning of its Roman political organization (fig. 3). CONCLUSIONS Fluvial systems may contain important archives for improving the understanding of present and past landscape stability. The wide fluvial sequence of the Corso del Popolo site on the Terni plain is an u nus ual occas ion t o observe a well-preserved sediment record of an ancient course of Nera River starting from the Late Pleistocene. Detailed analyses of the geometry and internal lithological variation of the fluvial succession, as well as the pedogenic features and pollen assemblages of allu- vial paleosols in the overbank deposits, have permitted a more detailed reconstruction of the recent geoenvi- ronmental evolution of the Terni plain to be improved and, meanwhile, some historical and archaeological speculations concerning the ancient hydrographic sys- tem of the town of Terni to be addressed, even in a humble site such as a future car-park. Considering the vertical evolution of the sedimen- tary sequence recorded in Terni, it is possible to relate the sedimentological and ecological evidences obser- ved to significant changes in climatc conditions due to the transition between the last phases of Late Glacial times and the more temperate and humid beginning of the Holocene. These results are in agreement with the records from ot her sites in Central Italy: Valle di Cas t ig li on e ( F O L L I E R I e t a l. , 1 9 8 9 ) , L ag o L u n g o (CALDERONI et al., 1994), Lago Albano (LOWE et al., 1996), Lagaccione (MA G R I , 19 99), Lago di Vico (MA G R I & SADORi, 1999), Rieti (RICCI LUCCHI et al., 2000). The Terni site can be considered an important archive of paleoenvironmental and paleoclimate record for the global climatic transition from the end of the Last Glacial times to the beginning of Holocene, while the ensuing climatic changes recorded in the sediments were progressively affected by regional and local envi- ronmental factors. ACKNOWLEDGEMENTS I wi s h t o t h an k L a u ra B o n om i Po n zi o f t h e Su perintendence to Arch aeological propert ies of Umbria who made this research possible, and Terni Corso del Popolo SpA which supported the work. I am grateful to B.C. 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