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Late Pleistocene–Holocene landscape evolution in Fossa Bradanica, Basilicata (southern Italy)
Geomorphology 102 (2008) 297–306
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Geomorphology j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / g e o m o r p h
Late Pleistocene–Holocene landscape evolution in Fossa Bradanica, Basilicata (southern Italy) F. Boenzi a,⁎, M. Caldara a, D. Capolongo a, P. Dellino b, M. Piccarreta a, O. Simone a a b
Dipartimento di Geologia e Geofisica, Università di Bari, via Orabona 4, Bari, Italy Dipartimento Geomineralogico, Università di Bari, via Orabona 4, Bari, Italy
A R T I C L E
I N F O
Article history: Received 24 September 2007 Received in revised form 13 March 2008 Accepted 28 March 2008 Available online 11 April 2008 Keywords: Gullies Valley fills Late Pleistocene–Holocene Fossa Bradanica Southern Italy
A B S T R A C T Studies in the middle Basento river basin supported by reliable chronological data (tephra layers and a number of absolute datings) have allowed the reconstruction of Late Pleistocene–Holocene geomorphological evolution of the middle to low Fossa Bradanica area (Basilicata, southern Italy). The original Upper Pleistocene hillslope has been dissected by deep gullies leaving relict slope pediments. Holocene filling of the Basento river valley and gullies occurred as a succession of downcut and fill episodes. A first phase of accumulation occurred in the Late Neolithic, which was followed by a downcutting between 4500 and 3700 cal. yr BP. A second deposition phase took place in the Greek–Roman period between 2800 and 1620 cal. yr BP, which was interrupted at around 2500 cal. yr BP. Another downcutting phase took place between 1620 and 1500 cal. yr BP, followed by a deposition phase between 1440 and 1000 cal. yr BP. After 1000 cal. yr BP a deep downcutting took place. Evidence collected with this study, coupled with climate data recorded in other Italian and European locations, suggests that filling and downcutting episodes in Fossa Bradanica were predominantly climate-driven. Anthropogenic impact only intensified or weakened these processes. © 2008 Elsevier B.V. All rights reserved.
1. Introduction The landscape of Fossa Bradanica in Basilicata, southern Italy, reflects a long history of tectonic activity, sea-level changes and climate shifts. Drainage systems respond to such events by changing valley erosion and deposition patterns. Channel gradients, stream discharge, and sediment flux may respond rapidly to tectonic or eustatic movements, to changes of precipitation regime, to deforestation and agricultural practices. Anthropogenic activity has been considered by some authors as a significant factor for the landscape evolution. Nonetheless, it is always difficult to state which of the two factors (climatic versus human) is to be considered as the driving mechanism behind the valley fill accumulation or downcutting. Some sedimentary sequences also show that during the Holocene, the deposition style must have shifted abruptly from one cause to another (Wilkinson, 1999). The first investigations on the Holocene evolution in Basilicata were carried out by Neboit (1977, 1980, 1983), Brückner (1982, 1983, 1986, 1990), Brückner and Hoffman (1992), Boenzi et al. (1986) and Abbott and Velastro (1995). They studied both the deposits filling the incisions and those forming the Upper Holocene terraces in
⁎ Corresponding author. Fax: +39 080 5442526. E-mail addresses: [email protected] (F. Boenzi), [email protected] (M. Caldara), [email protected] (D. Capolongo), [email protected] (P. Dellino), [email protected] (M. Piccarreta), [email protected] (O. Simone). 0169-555X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2008.03.013
the Bradano, Basento and Cavone river basins. Neboit (1977, 1980, 1983), Brückner (1982, 1983, 1986, 1990) and Brückner and Hoffman (1992) suggest that valley bottom deposition in the main rivers mostly occurred during the Greek–Roman period, when the extensive land use caused accelerated erosion processes within basin areas. Neboit rules out the influence of climate-driven processes, since during the Holocene no arid or semi-arid climatic phases have been recorded. Abbott and Velastro (1995) suggest that in southern Italy two significant accumulation phases occurred throughout the Middle to Late Holocene: one during the Neolithic, the other during the Iron Age. The latter, could have been caused by the intense land use that occurred during the Greek colonization period (Adamasteanu, 1974). Grove (2001) favoured the climatic forcing mechanism by hypothesizing that in Mediterranean areas many of the recent Holocene accumulations (sensu Vita-Finzi, 1969) could have been produced during cold–wet periods, as happened during the Little Ice Age. Grove (1988) and Grove and Rackham (2001) state that valley fills in Mediterranean countries are contemporaneous with Alpine glacier growth. The goal of this work is to highlight the Late Pleistocene and Holocene evolution of Fossa Bradanica, focusing on a small area of the middle valley of the Basento river basin. In particular, we reconstructed the Quaternary evolution of this area by means of analyses of both terrace deposits and valley fills, with the aim of stressing the relative role of climate conditions versus anthropogenic activities. We consider this area as a good test site because of the contemporaneous occurrence of: well exposed Pleistocene and Holocene
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deposits; tephra marker layers, whose chemical and mineralogical composition and stratigraphic position allow a precise correlation with well known explosive eruptions of the Campanian volcanic districts (Phlegrean Fields and Vesuvius); well-preserved artifacts useful for sediment dating and paleo-landscape reconstruction. The combined analysis of these data allowed interpretation of the chronological sequence of the morphogenetic processes that occurred in the study area through the Late Pleistocene and Holocene. 2. Study area and methods The study area is located south-west of Pomarico, between Masseria Glionne (40°28′49″N, 16°31′06″E) and Masseria Trincicanaro di Capo (40°27′07″N,16°33′30″E) on the north side of the Basento river (Fig. 1). It is characterized by a modified Mediterranean climate, with a mean annual precipitation of 750 mm, mean July temperature of 22 °C and a mean January temperature of 7 °C (Piccarreta et al., 2004, 2005). The vegetation cover is a man-modified, scrub oak-pine woodland with a mixed shrub understory. A general geological and morphological analysis has been carried out using stereoscopic aerial photographs (scale 1:30,000) and topographic maps (scale 1:25,000). Detailed field survey has been carried out to reconstruct the stratigraphic sequence of terrace and fluvial deposits and to collect samples for successive laboratory analyses. In
particular, we sampled in detail three stratigraphic successions (CAP 1, CAP 2 and CAP 3). They were chosen because of their good exposure, easy correlation through marker horizons, and the presence of features highly indicative of paleoenvironmental conditions. For each sequence we analysed sediment grain size, structures and composition. Gravelly beds and sets of lenses made of cross-laminated sand alternating with fine gravel material have been interpreted as channel deposits. Finer loamy material in massive continuous beds, showing laminations or ripple marks, has been interpreted as overbank deposits. Brownish and dark-brownish layers yielding charcoals, land snails, root marks and calcium carbonate concretions have been interpreted as palaeosols. A reliable chronological dataset, consisting of several 14C datings (see Table 1), tephra horizons (related to known eruptions that occurred in the Campanian region) and a few preserved artifacts (mainly potshards and a burial), allowed a detailed reconstruction of the events that occurred in the study area, particularly during the Middle to Late Holocene. Tephra layers were analysed for their characteristic chemical, mineralogical compositional, and glass particle morphology, which helped attribute them to well known explosive eruptions. The archaeological material has been studied by Dr. A. De Siena, from Soprintendenza Archeologica della Basilicata. Radiocarbon-dated material has been processed at CEDAD — CEnter for DAting and Diagnostics (laboratory code LTL), University of Salento (Lecce, Italy),
Fig. 1. Study area location (a) and its 3D oblique aerial view (b).
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Table 1 Radiocarbon dates on sediments and soils, Fosso La Capriola Laboratory code
Sample name
Succession
Position above modern channel (m)
Material
14
δ13C (‰)
Calibrated 2 σ
UGAMS 01910 LTL1816A LTL1817A UGAMS 01911 LTL1815A UGAMS 01912 UGAMS 01914 UGAMS 01913
cap2_233 cap2 c2.1 cap2ps cap2_966 cap1 r1 cap6_170 cap5_140 cap6_770
CAP 1 CAP 1 CAP 1 CAP 1 CAP 2 CAP 3 CAP 3 CAP 3
2.33 4.80 4.10 9.66 1.40 1.70 6.70 7.70
Charcoal Charcoal Charcoal Charcoal Charcoal Charcoal Ox bone Charcoal
3470 ± 50 1553 ± 60 3059 ± 95 1130 ± 40 4340 ± 50 4340 ± 50 1710 ± 40 1090 ± 40
−23.6 −27.6 ± 0.2 −31.7 ± 0.2 −22.4 −23.5 ± 0.6 −27.0 −20.7 −23.2
3616–3870 1318–1555 2976–3454 958–1147 3066–3582 4835–5041 1536–1708 928–1070
and the Center for Applied Isotope Studies (laboratory code UG), Athens (Georgia, USA). Finally, landforms have been interpreted and mapped on the basis of their spatial position and age. 3. Geological and geomorphological setting The Fossa Bradanica is a narrow Pliocene–Pleistocene sedimentary basin with a NW-SE trend, located between the southern Apennines and the Apulian foreland (Ricchetti, 1981; Pieri et al., 1996). Two main successions can be recognized, which are composed of clay and sandy-conglomerates, respectively (Fig. 2). The former is the basal unit and corresponds to the more than 1000 m of thick clayey “Argille Subappennine” Formation (Ricchetti, 1981), while the latter, about 50 m thick, is the closing unit of the Fossa Bradanica sedimentary cycle. It is made up by the sandy “Sabbie di Monte Marano” and the conglomeratic “Conglomerato di Irsina” formations (Ricchetti, 1981). In the Middle Pleistocene the Fossa Bradanica began to uplift, allowing both the ancestral rivers (Bradano, Basento and Cavone) to cut deep valleys perpendicularly to the coast and the lateral erosion to attack the hillslopes. The result was an increased dissection and exposure of the highly erodible clayey bedrock. The uplift is evidenced by fluvial terraces and, in the Ionian hinterland, by a complex system of coastal marine terraces (Boenzi et al., 1971; Brückner, 1980). A sequence of slightly tilted relict slope pediments occurs in the middle and high parts of the hillslope, while well-preserved remains of a Pleistocene fluvial terrace (T1) are present in the lower parts. Towards the valley bottom two levels of Holocene fluvial terraces (T2 and T3) as well as the modern floodplain of the Basento river are present (Fig. 3). The hillslopes are cut by deep gullies (fossi), which often erode up to their upper parts making them susceptible to landsliding. Where clays crop out, the gully heads and sides exhibit patterns of badland erosion (calanchi). 4. Main geomorphological features 4.1. Hillslope processes and slope pediment The hillslope has been incised and dissected by deep gullies (Fosso del Pantano La Foggia, Fosso del Castello, Fosso La Capriola and others). At an elevation between 300 and 150 m, a sequence of relict slope pediments tilted 15° towards the valley bottom is present (Fig. 2). The pediment surfaces are made of landslide detritus and consist of heterometric arenaceous and conglomeratic blocks from the upslope caprock. In many cases surfaces have been reworked and smoothed by subaerial erosion processes. They have been covered by sandy colluvial material and are correlated with the alluvial deposits at the top of the Pleistocene fluvial terraces to form multiple slope pediments (Fig. 2). At the valley bottom, the gullies are filled by up to 15 m of silty–sandy alluvial deposit, which exhibit erosional surfaces and create a typical gullies-in-valley-fills morphology (Campbell, 1989).
C date
4.2. Fluvial terraces The Pleistocene fluvial terrace T1 occurs at an elevation between 120 and 170 m and is well preserved, especially at Masseria Glionne, Masseria La Capriola and Trincicanaro di Capo (Fig. 2). It is characterized by two well defined lithological units. The basal one consists of conglomerate layers made of medium-sized pebbles which were emplaced under relatively high-energy conditions in a braided channel (Boenzi et al., 1986). The upper unit is made up of silts and thin sub-horizontal beds of sands. At several locations, on top of the upper unit, a more than 1 mthick tephra sequence is found. The first 0.3 m is made of two ash layers in continuous stratigraphic contact that show features of primary deposition. The basal layer is pinkish and is made of fine- and medium-grained ash, the upper layer is grey and made of fine ash. The upper part of the tephra sequence (0.7 m) is made of grey ash and is interpreted as material that accumulated after reworking of the basal layer. Pyroclastic material is mainly made of irregular pumice fragments characterized by broken gas bubbles; its composition is alkali-trachytic. Thickness, grain size and glass particle morphology is indicative of a large scale explosive eruption which formed a tall eruptive “Plinian” column and spread material over a long distance from the source area. The only active volcanic area capable of producing such an eruption is the Campanian volcanic district, located about 260 km west of the study area. In particular, the only big scale event characterized by alkali-trachytic magma and forming a typical pinkishgrey sequence is the Campanian Ignimbrite eruption of Phlegrean Fields, dated to about 39 ka BP (Civetta et al., 1997; Pappalardo et al., 2002). In the same unit, chaotic and heterogeneous caprock arenaceous and conglomeratic materials are interbedded in the silty-sand sediments. According to Boenzi et al. (1978) these deposits are a relic of paleo-landslides contemporaneous with T1 terrace formation. The Upper Holocene terrace T2 consists of a sequence of alternating silty-sand deposits with thin intercalations of conglomerate lenses that occur at elevations of 15–25 m above the present-day channel. At about 2 m from the base, a 50 cm-thick tephra layer lies. It is made of fine grey ash of tephritic–phonolitic composition, which components are mainly represented by highly to moderately vesicular pumices with a subordinate amount of pyroxene and feldspar crystals. Lithological features, mineralogical and chemical composition and morphological characteristics of the ash fragments suggest that this layer is linked to the fallout phase of the Plinian 3700 yr BP Avellino eruption of Vesuvius (Cioni et al., 2000; Sulpizio et al., in press). The basal unit of the T2 sediment is not exposed at this location, though surveys in adjacent areas indicate that it is composed primarily of conglomerate layers. The more recent Holocene terrace T3 formed as the result of intense floods that occurred between the 14th and 18th centuries AD in all the Basilicata rivers (i.e. during the Little Ice Age; Brückner, 1986; Brückner and Hoffman, 1992). 5. Late Pleistocene geomorphological evolution The T1 terrace formation started in the Late Pleistocene, and the analysis of its stratigraphy allows the reconstruction of the Late
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Fig. 2. Geomorphological map of the study area (a) and schematic geomorphological profile (b).
Pleistocene evolution of the Basento river. Deposit features show that: a) in a first phase, sediments were deposited under high-energy conditions by a braided channel; and b) in a second period, loamysand material started to accumulate, indicating a change in solid
transport capacity and stream power. These can be classified as overbank deposits. At several locations (in particular in Masseria Glionne area) upper terrace deposits are intercalated with poorlysorted slope materials that Boenzi et al. (1978) interpreted as being
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Fig. 3. Stratigraphic sequence of the T1 fluvial terrace at Masseria Glionne.
formed by large landslides, which occurred during T1 sediment accumulation (Fig. 4). Finally, in Masseria Glionne and Masseria La Capriola areas, several decimeters-thick tephra layers have been found at the top of the T1 terrace (Fig. 5). Analysis of the tephra sequence suggests that the pyroclastic material accumulated in a calm waterbody far from the main stream flow. This sequence correlates with the Campanian Ignimbrite eruption of Campi Flegrei (39 ka BP). The climate conditions dominating the T1 accumulation timespan can be inferred from pollen successions obtained from Lago Grande di Monticchio, a Pleistocene crater lake about 90 km north of the study area. Several authors described there a succession of pollen zones showing several climatic shifts (Watts et al., 1996a,b; Allen et al., 1999; Huntley et al., 1999; Table 2). According to these studies, in Basilicata forests developed under wet conditions between 50,000 and 42,500 yr BP. Drier conditions occurred between 42,500 and 40,700 yr BP. A new wetter phase characterized the timespan of 40,700–37,600 yr BP. In this period the sandy-conglomeratic caprock topping the higher areas bordering the Basento valley were subjected to extensive mass movements. Landslide material reached the Basento valley and intermixed with fluvial sediments. At the end of this phase the landslide material was mantled by the 39,000 yr BP pyroclastic layer. Monticchio pollen records suggest that arid conditions dominated during the period of 37,600–36,300 yr BP. Afterward, wetter conditions established, and were followed by cold–dry conditions that continued until 18,000 yr BP. In higher areas of Basilicata, e.g. Monte Pollino and Monte Sirino, the cold climate caused the formation of small glaciers (Boenzi and Palmentola, 1972; Palmentola et al., 1990; Jaurand, 1994). In our study area the barren landscape probably favoured erosive processes, which produced the slope pediment connecting the hilltops to the T1 terrace.
At the peak of the last glacial maximum, sea level was approximately 150 m lower than today (Lambeck and Chappell, 2001; Lambeck et al., 2002). Sea regression produced a marked river channel downcutting. In the study area, the Basento channel underwent a downcutting of about 20 m, as revealed by several drillings under the Pisticci Scalo industrial plants (Boenzi et al., 1987). The tributary streams deeply excavated the substrate beds, triggering paleopediment dissection processes. 6. Holocene evolution 6.1. Fosso La Capriola valley fills We have analysed in detail several sediment exposures along the fluvial downcutting Fosso La Capriola, a tributary of the Basento river (Fig. 2a). The infilling sediments cut by Fosso La Capriola are mainly characterized by alternating fine sand, silt and palaeosol beds. The bedding pattern is often affected by irregular erosion surfaces defining lenses of coarser and fine material. At the junctions between the tributary valleys and the main channel, the ancient slope angle showed an abrupt decrease, which caused coarse gravel accumulation. Among the many available exposures along the flanks of the narrow Fosso La Capriola valley, three stratigraphic successions have been investigated (CAP 1, CAP 2 and CAP 3 in Fig. 2a). 6.1.1. CAP 1 succession This exposure is located on the east side of the main channel of Fosso La Capriola (Fig. 6). The first 2 m of the succession show a sequence of pale brown plane and cross-laminated sand layers, sparse in organic matter.
Fig. 4. Tephra layers in the T1 fluvial terrace at Masseria Glionne (i) and Masseria La Capriola (ii).
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Fig. 5. Fosso La Capriola successions.
Moving upwards, the sediment (still sandy) becomes richer in loam and the bedding is marked by thin clayey horizons. Between 2 m and 3 m the deposit is loamy, finely laminated and with a higher amount in organic matter. In particular, between 2.25 and 2.4 m, the deposit, which is red-brownish in colour, is rich in charcoal, and shows the typical features of a palaeosol. A charcoal sample from this layer has been 14C dated, and the obtained calendar age is 3740 yr BP. The succession continues upwards with some 0.9 m of alternating beds made of fine cross-laminated sand and laminated silt with ripple structures. These deposits are capped by a thin pyroclastic horizon. As discussed in the previous section, this marker bed can be related to the
Table 2 Characterization of the pollen assemblage zones at Lago Grande di Monticchio (modified from Watts et al., 1996a) Pollen Age (calendar zone years BP)
Characterisation
4
14,300–26,100
5a 5b
26,100–29,500 29,500–31,700
6
31,700–34,900
7
34,900–36,300
8 9 10 11
36,300–37,600 37,600–40,700 40,700–42,500 42,500–50,000
Mainly herbaceous pollen. Juniperus type and Pinus frequent; few other trees; frequent Helianthemum type Decreasing Juniperus type, Helianthemum type. Small percentages of Quercus, Fagus in 5a, increasing in 5b with Abies, Ulmus, Carpinus betulus Mainly herbaceous pollen (Artemisia, Chenopodiaceae, Helianthemum type frequent), with decrease of tree pollen abundance to about 20% 50% trees with frequent Quercus, Betula, Abies, Fagus. Decrease in Artemisia, Chenopodiaceae Recession in tree percentages. Artemisia abundant once more 70% trees. Succession of Betula, Quercus, Acer, Fagus, Abies Recession in tree percentages, herbs rise to 80% of pollen sum Long forest succession with broad-level deciduous trees including Betula, Quercus, Tilia, Ulmus, Corylus. Trees to 60%. An “Interstadial”
Avellino eruption of Vesuvius (3700 yr BP). Above the “Avellino” tephra, there is 0.85 m of pale brown laminated silt. The bedding planes are often marked by millimeter-thick horizons made of dark organic matter or reddish oxidised material. In this interval a discontinuous palaeosol level is also present. A radiocarbon-dated charcoal gave the calibrated age of 3215 yr BP. Another thin tephra horizon lies at about 4.7 m from the ground. It is composed of grey ash of tephritic–phonolitic composition, which main components are highly vesicular pumice fragments and subordinate feldspar and pyroxene crystals. The geochemical features suggest that this bed can be attributed to the AP3 eruption of Vesuvius (Andronico and Cioni, 2002; Santacroce et al., submitted for publication). This eruption occurred between the “Avellino” and “Pompeii” events, at about 2800 cal. yr BP. The AP3 tephra is capped by 1.3 m of massive loam, greyish in colour, rich in organic material. A 1.45 m sequence of three palaeosols alternating with thin sand levels (5 to 10 cm thick) lies on the massive loam. The palaeosols are brown in colour, massive, rich in calcareous lumps and root marks. Several landsnails have also been found. The palaeosol succession is capped by a 0.7 m-thick layer of reddish coarse, partially pedogenized sand, bearing pebbles (mainly concentrated in its lower part). An erosional surface cuts part of the sequence, defining a several meters thick channel. The deposit filling the channel contains a set of lenses mainly made of cross-laminated coarse sand. Thick lenses of gravel, laminated loam and thin horizons bearing dark organic matter (mainly tiny pieces of charcoal) have also been observed. One of the layers is rich in charcoal, whose samples gave a calibrated age of 1435 yr BP. The channel deposit is buried by a pale brown massive sand layer whose top is at 8.5 m above the ground. Above the massive sand, a 1.4 m-thick palaeosol developed, bearing scattered tiny pieces of charcoal whose fragments yielded a calibrated 14C age of 1050 yr BP. The succession is topped by 1.3 m of fine pale brown sand with plane and cross-laminations.
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Fig. 6. Holocene tephra layers in Fosso La Capriola (CAP 2 succession).
6.1.2. CAP 2 succession This exposure is situated on the west side of the main channel; it is about 11 m thick and can be subdivided into several parts according to its main lithological features (Fig. 6). The lower part of the succession (about 2 m) is made up of laminated loamy sands. The lamination is generally plane to parallel, although sets of ripples have been observed. The stratigraphic continuity of this sandy part is interrupted by the occurrence of the two Holocene Vesuvius tephra horizons; Avellino and AP3 tephra, respectively (Fig. 7). The former is found at about 0.6 m above the modern channel bed and has a maximum thickness of 10 cm; the latter lies at the top of the sand interval, it is thinner and less continuous. At about 1.4 m from the ground a charcoal sample was radiocarbon dated to 3325 cal. yr BP. The second interval is a succession of two thick palaeosols, separated by a sand layer. The first palaeosol is 1.2 m thick, massive and rich in calcareous lumps and scattered large landsnails (Helicidae). At about 0.25 m from its base, several flat and discontinuous reddish sand lenses (3 to 5 cm thick) have been observed, they are locally rich in tiny charcoal pieces. The laminated sand layer separating the two palaeosols is 0.4 m thick and shows ripple structures. The second palaeosol is 0.7 m thick. It is characterized by a sandy grain size, crudely laminated and rich in calcareous lumps. The top of the palaeosol section is cut by a paleochannel
which incised the substratum for several meters. The base of the erosional surface is marked by a thick gravel deposit. The material filling the paleochannel is an alternation of coarse cross-laminated sand and gravel lenses with a coarse sand matrix. The paleochannel is capped by 0.7 m of plane plane-laminated sand, with intercalated organic remains (charcoal and landsnails) and scattered pebbles. The succession continues with a poorly developed palaeosol, pale brown in colour, rich in calcareous lumps with a few scattered tiny charcoal pieces. On top of the palaeosol, a plane- to cross-laminated sand layer lies, which is 3.5 m thick. It is pale brown in colour and lacks in organic matter. The topmost part of the sequence is made up of 1.2 m of loose to poorly consolidated gravel. The top of the succession is at about 11 m from the modern channel bed. 6.1.3. CAP 3 succession This is a 10 m-thick succession, the nearest one to the Basento river. It is situated on the east side of Fosso La Capriola, near the unpaved road crossing the stream (Fig. 6). Here the oldest Holocene sediments have been found. The lower part of the exposure (1.6 m thick) is made up of an irregular alternation of well-sorted coarse sand, massive loamy sand and finely laminated silt, followed by 0.3 m of massive silty-sand layer bearing many pottery fragments and charcoal. The
Fig. 7. Relation between deposition and erosion stages in Fossa Bradanica and main climatic epochs during the Holocene in Europe.
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potshards have been sampled and analysed by archaeologists from Soprintendenza Archeologica della Basilicata, and are referred to the Neolithic cultural phase known as “Diana” (Bianco, 1985). An AMS radiocarbon date obtained from a charcoal fragment gave an age of 4940 cal. yr BP. An erosive surface separates these levels from the rest of the succession and defines a small channel whose filling started shortly before the deposition of the “Avellino” tephra, which is here 2– 4 cm thick. Above the “Avellino” marker there is a 0.5 m thick sequence made up of: massive fine sand with a high organic content (15 cm thick), a palaeosol (20 cm thick), and a layer of fine plane-laminated sand (15 cm thick). The deposition continued with the “AP3” tephra, here about 5–6 cm thick. A 1.8 m succession of two palaeosols, separated by a 0.25 m sand layer, lies on the top of the “AP3” horizon. The palaeosols are brown and characterized by scattered centimetric calcareous lumps, charcoal and some landsnails (mostly Helicidae). Several scattered charcoal pieces have also been observed within the sand. The palaeosol is topped by a 0.70 m of brown-reddish, partially pedogenised sand with scattered pebbles. Within this layer a pot about 20 cm wide and 30 cm high has been found. Archaeologists from Soprintendenza Archeologica della Basilicata interpret the pot as the burial receptacle of a child dating back to around 2500 BP. The grave was excavated in the reddish sand deposit, which at that time represented the ground surface. On this layer a 2.4 m thick succession of pale brown fine sand lies. These deposits are either laminated (plane- and cross-lamination) or massive. The top of the sequence is characterized by a 4.0 m thick succession of three palaeosols separated by laminated fine sand layers showing both planar lamination and ripple structures. A radiocarbon date obtained from an ox bone collected from the first palaeosol gave a calibrated age of 1620 yr BP; while a charcoal from the sand layer separating the first palaeosol from the second gave an age of 1000 cal. yr BP. 6.2. Discussion One of the main goals in the study of Holocene valley filling/ downcutting sequences is to define their climatic or anthropogenic origin. Several researchers advocate the anthropogenic cause (Butzer, 1980; Davidson, 1980; van Andel et al., 1990; Barker and Hunt, 1995, 2003), whereas others do not exclude that in some cases climate must have played an important role (Bintliff, 1975; Ballais, 1995; GutiérrezElorza and Peña-Monné, 1998). From the succession of Fosso La Capriola area several main deposition/erosion phases can be inferred (Fig. 7). They are well defined from a chronological point of view and allow a comparison with major climate changes recorded in other European areas. 6.2.1. Phase A A first phase of deposition started in a yet unknown period and ended after 4500 yr BP (‘Diana’ potshards in CAP 3) during the Late Neolithic. Our hypothesis is that this stage could be linked to the Rotmoos Alpine glaciers advance (Grove 1988). 6.2.2. Phase B The subsequent downcutting phase took place after 4500 yr BP and before 3700 yr BP. We do not know how intense the erosional activity was. We are only able to state that the small channel at the base of the CAP 3 had been carved before 3700 yr BP (“Avellino” tephra). Detailed pollen studies can give an idea about climate characterizing this period. In particular, there is an apparent abrupt collapse in the concentration of tree pollen recorded in many Mediterranean areas at that time. In central Italy an evident arboreal pollen decline has been found at Lago di Mezzano (Sadori et al., 2004) after 3820 ± 40 14C yr BP (unpublished radiocarbon age, Sadori, personal communication), at Lagaccione around 3750 ± 80 14C yr BP (Magri, 1999), at Lago di Vico around 3710 ± 50 14C yr BP (Magri and Sadori, 1999) and at Valle di Castiglione after 3480 ± 50 14C yr BP (Follieri et al., 1988). In Apulia
(southern Italy), at Lago Battaglia in the coastal Gargano area (Caroli and Caldara, 2007), a sharp collapse of arboreal pollen and a considerable increase in fire frequencies occurred approximately 4200 cal. yr BP (age estimated through the interpolation of other radiocarbon dates). All these studies suggest that a dry phase should have taken place around 4000 cal. yr BP. According to Jalut et al. (2000), in coastal areas in south-eastern France and south-eastern Spain, pollen records suggest that the dry period should have occurred between 4500 and 4000 yr BP (5300–4200 cal. yr BP). By combining the evidence is it possible to suggest that the downcutting phase recorded in the Fosso La Capriola area between 4500 and 3700 yr BP took place during a dry climate period. 6.2.3. Phase C A new deposition period started shortly before the “Avellino” tephra; from 3700 to 2800 yr BP, a timespan including the Bronze Age. Deposition processes were rather slow (accumulation was around 1 m or little more); this is in agreement with the data published by Neboit (1977, 1980, 1983), Brückner (1982, 1983, 1986, 1990) and Brückner and Hoffman (1992). This period could have been characterized by hydrogeological unsteadiness. Proof is that, due to recurrent flooding events and to the rising up of the groundwater table, around 2500– 2300 cal. yr BP, the inhabitants of Metaponto (coastal Basilicata) moved towards higher areas and built an artificial drainage network (Boenzi et al., 1987; De Siena, 2001). The Lago Battaglia (Gargano coast, Apulia) pollen record shows a relatively wetter climate from around 2700 to 2190 cal. BP (Caroli and Caldara, 2007). In the same period severe alluvial and erosive phenomena occurred at many places in northern Italy (Veggiani, 1987) and in the Mediterranean basin (e.g. in Spain) where large amounts of sediments accumulated on the hillslopes (Gutiérrez-Elorza and Peña-Monné, 1998; Gutiérrez Elorza and Sesé Martínez, 2001; Gutiérrez et al., 2006). All these phenomena seem to be connected to a cool–wet climate coinciding with the Alpine glacier advance (Orombelli and Porter, 1982; Orombelli and Pelfini, 1985; Baroni and Carton, 1991) during the Göschenen I glaciation (Patzelt, 1974). The deposition rate increased between 2800 and 1620 cal. yr BP, between Greek colonization and the Roman Age (about 6 m of sediments in CAP 3). There is evidence that at least one deposition stasis occurred around 2500 yr BP, as suggested by the grave found in CAP 3. When sediments started again to accumulate, the sedimentation continued at higher rates until 1620 cal. yr BP. At that time anthropogenic pressure on the environment would have been considerable. The exploitation of the region by the Romans was intense, as suggested by the many small farms and villas scattered all over the region (Racioppi, 1889). 6.2.4. Phase D A new erosional phase started after 1620 cal. yr BP (CAP 3) and ended before 1435 cal. yr BP (CAP 1). We have not been able to find any useful elements to date the channel in CAP 2. Nevertheless, from its stratigraphic position, similar to the channel in CAP 1 (above the “AP3” tephra and between the two palaeosol sequences), we hypothesize that it was incised in the same period. 6.2.5. Phase E Fosso La Capriola sediment accumulation started again shortly before 1435 cal. yr BP (material filling the channel in CAP 1) and continued until an unknown date after 1000 cal. yr BP (CAP 3). This phase of deposition lasted almost the whole of the early Middle Ages, when Byzantine and Longobard populations began to compete for regional supremacy. In Basilicata most of the population settled near monasteries or fortified places on the hilltops (Guillou, 1983). Given the low settlement density we believe that the anthropogenic pressure on the environment was rather low; this leads us to exclude humans as the main cause of geomorphological changes. Thus, the erosion/deposition phenomena should have been driven by climatic
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factors. Information about the climate condition that characterized this period could be inferred from Alpine glacier behaviour. In the same period the Alps underwent the Göschenen II glaciation (Patzelt, 1974). Glacial advances are known for the Brenva glacier on Monte Bianco, where a log found within a moraine gave the radiocarbon age 1179 ± 55 14C yr BP (Orombelli and Porter, 1982), and for the Lys glacier on Monte Rosa, where a palaeosol buried by moraine deposits dates to 1185 ± 80 14C yr BP (Strumia, 1997). Advancing Alpine glaciers could mean a wetter climate in southern Italy. 6.2.6. Phase F After 1000 cal. yr BP a new erosional period began. Fosso La Capriola and also other Basilicata streams strongly deepened their channels; the fluvial terrace T2 was formed along the middle to low reaches of the main regional rivers. The start of this new downcutting phase is also documented by archaeological and historical data. In particular, near the old Pisticci train station, the ruins of an XI century AD Benedictine monastery lay on the T2 Basento terrace, at around 15 m above the modern floodplain. Thus, the Basento river incised its alluvial deposits before the monastery was built (Caputo and Bubbico, 1983). A similar situation has been observed in the Bradano river basin, between S. Giuliano lake and Masseria S. Lucia, where a XII century subterranean church (La Scaletta, 1966) was dug in the Plio-Pleistocene calcarenite at 12 m above the present floodplain. However, downcutting of the Basilicata rivers was not triggered by tectonic uplift. According to recent studies (Westaway,1993; Schiattarella et al., 2003), from the Middle Pleistocene until the present, this part of southern Italy was characterized by a 0.5 mm/yr mean tectonic uplift, and the uplift rate was even lower in the Bradanic Trough in Fossa Bradanica. Therefore, the recent regional tectonic movements were too slow to justify such a deep downcutting in less than one thousand years. We believe that the erosion began towards the end of the early Middle Ages and that it was accelerated around 1000 yr BP, during the socalled Medieval warm period. Starting from 800–700 cal. yr BP, flood phenomena affecting the Basilicata rivers (e.g. Bradano and Basento) suggest a new period of geomorphological instability (Tanzi, 1746; Giustiniani, 1797). Similar events occurred also in the upper valley of the nearly Sinni river, where remains of a monastery settlement built in 700 yr BP (Giganti, 1978) are today buried under alluvial sediments. In conclusion, data collected with this study do not show a direct connection between climate shifts and landscape evolution. The only evidence is that incision/accumulation states shift almost contemporaneously with climate changes (recorded in several other Italian and European areas). This leads us to consider climatic causes as the main factor ruling the evolution of study area during the Mid- to Late Holocene. The function of fires in shaping the landscape also seems uncertain. In fact, the low amount of charcoal found in several levels of the investigated exposures lead us to rule out the occurrence of wild fires as a factor affecting the erosion/deposition processes. In addition, archaeological studies carried out in the surrounding areas suggest that charcoal might instead be related to local anthropogenic activity (De Siena, personal communication). 7. Conclusion This study has added new elements to our knowledge of the geomorphological evolution of the Fossa Bradanica from the Late Pleistocene and over the entire Holocene, in relation to climatic shifts. The starting point was the Pleistocene fluvial terrace T1, mainly preserved on the north side of the middle Basento river and chronologically referable to 39,000 yr BP (Campanian Ignimbrite tephra). On the most elevated parts of the hillslopes, pediment remains are present, which are stratigraphically linked to the fluvial terrace T1. The pediment genesis began shortly after the Campanian Ignimbrite deposition in relation to a cold-arid climate with steppe vegetation. The Late Pleistocene sea-level retreat triggered fluvial incision,
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pediment dissection and the formation of deep gullies. River valley bottom infilling occurred gradually during the Holocene. Sedimentation started due to postglacial sea-level rise (Brückner, 1983); subsequently the accumulation processes have been mostly controlled by climatic and anthropic causes. The study of Fosso La Capriola filling sediments showed a Holocene alternation of different phases of erosion and deposition: 1) The first phase of deposition occurred in the Late Neolithic and was followed by a downcutting phase; 2) A second accumulation phase took place in the Greek period between 2800 and 2500 yr BP. In Basilicata, this timespan was characterized by floods and erosive phenomena, which also influenced human settlements. Similar phenomena occurred in areas of central-northern Italy (Veggiani, 1987) and in the Mediterranean basin and is well connected to a cool–wet period coinciding with glacial advance in the Alps. After a period of stasis that occurred about 2500 yr BP, a new deposition phase occurred continuing until 1600 BP, probably in relation to remarkable land-use pressure by the Romans; 3) A new erosional period occurred from 1620 to 1435 yr BP and was followed by a sedimentation phase between about 1435 and 1000 yr BP; 4) After 1000 yr BP a downcutting occurred, creating the fluvial terrace T2 and the stream channel deepening. This downcutting phase coincides with the Medieval warm period; 5) From 750–700 until 400–300 yr BP flooding phenomena took place in the river valley bottoms. These phenomena coincide with the Little Ice Age. The results of this study support the idea that climatic changes were the main controlling factor in the rapid and varied geomorphologic transformation of the Fossa Bradanica during both the Late Pleistocene and the Holocene, with anthropogenic factors playing a presumably minor role during modern times. This paper also demonstrates that a detailed field study, coupled with analyses of tephra layers, absolute 14C dating and archaeological characterization of artefacts, which result in independent and coherent chronological data, is very helpful in unravelling the complex evolution of recent sedimentary basins of the Mediterranean area. Acknowledgements This research was supported by the PRIN-COFIN 2005 (Coordinator: Federico Boenzi). Dr. Antonio De Siena from Soprintendenza Archeologica della Basilicata and Katia Straziuso are gratefully thanked for their constructive contribution. We thank the Editor and three anonymous reviewers for their constructive revision of the original manuscript. References Abbott, J., Velastro, S., 1995. The Holocene alluvial records of the chorai of Metapontum, Basilicata and Croton, Calabria, Italy. In: Lewin, J., Macklin, M.G., Woodward, J.C. (Eds.), Mediterranean Quaternary River Environments. A.A.Balkema, Rotterdam, pp.195–205. Adamasteanu, D., 1974. La Basilicata antica. Storia e monumenti. Ed. Di Mauro, Cava dei Tirreni, 230 pp. Allen, J.R.M., Brandt, U., Brauer, A., Hubberten, H.W., Huntley, B., Keller, J., Kraml, M., Mackensen, A., Mingram, J., Negendank, J.F.W., Nowaczyk, N.R., Oberhänsli, H., Watts, W.A., Wulf, S., Zolitschka, B., 1999. Rapid environmental changes in southern Europe during the last glacial period. Nature 400, 740–743. Andronico, D., Cioni, R., 2002. Contrasting styles of Mt Vesuvius activity in the period between Avellino and Pompeii plinian eruptions, and some implications for assessments of future hazards. Bulletin of Volcanology 64, 372–391. Ballais, J.L., 1995. Alluvial Holocene terraces in eastern Maghreb: climate and anthropogenica controls. In: Lewin, J., Macklin, M.G., Woodward, J.C. (Eds.), Mediterranean Quaternary River Environments. Balkema, Rotterdam, pp. 183–194. Barker, G.W., Hunt, C.O., 1995. Quaternary valley floor erosion and alluviation in the Biferno valley, Molise, Italy: the role of tectonics, climate, sea level change and human activity. In: Lewin, J., Macklin, M.G., Woodward, J.C. (Eds.), Mediterranean Quaternary River Environments. Balkema, Rotterdam, pp. 145–157. Barker, G.W., Hunt, C.O., 2003. The role of climate and human settlement in the evolution of the Biferno Valley (Molise, Central Italy). In: Livadie, C.A., Ortolani, F.
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Geomorphology j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / g e o m o r p h
Late Pleistocene–Holocene landscape evolution in Fossa Bradanica, Basilicata (southern Italy) F. Boenzi a,⁎, M. Caldara a, D. Capolongo a, P. Dellino b, M. Piccarreta a, O. Simone a a b
Dipartimento di Geologia e Geofisica, Università di Bari, via Orabona 4, Bari, Italy Dipartimento Geomineralogico, Università di Bari, via Orabona 4, Bari, Italy
A R T I C L E
I N F O
Article history: Received 24 September 2007 Received in revised form 13 March 2008 Accepted 28 March 2008 Available online 11 April 2008 Keywords: Gullies Valley fills Late Pleistocene–Holocene Fossa Bradanica Southern Italy
A B S T R A C T Studies in the middle Basento river basin supported by reliable chronological data (tephra layers and a number of absolute datings) have allowed the reconstruction of Late Pleistocene–Holocene geomorphological evolution of the middle to low Fossa Bradanica area (Basilicata, southern Italy). The original Upper Pleistocene hillslope has been dissected by deep gullies leaving relict slope pediments. Holocene filling of the Basento river valley and gullies occurred as a succession of downcut and fill episodes. A first phase of accumulation occurred in the Late Neolithic, which was followed by a downcutting between 4500 and 3700 cal. yr BP. A second deposition phase took place in the Greek–Roman period between 2800 and 1620 cal. yr BP, which was interrupted at around 2500 cal. yr BP. Another downcutting phase took place between 1620 and 1500 cal. yr BP, followed by a deposition phase between 1440 and 1000 cal. yr BP. After 1000 cal. yr BP a deep downcutting took place. Evidence collected with this study, coupled with climate data recorded in other Italian and European locations, suggests that filling and downcutting episodes in Fossa Bradanica were predominantly climate-driven. Anthropogenic impact only intensified or weakened these processes. © 2008 Elsevier B.V. All rights reserved.
1. Introduction The landscape of Fossa Bradanica in Basilicata, southern Italy, reflects a long history of tectonic activity, sea-level changes and climate shifts. Drainage systems respond to such events by changing valley erosion and deposition patterns. Channel gradients, stream discharge, and sediment flux may respond rapidly to tectonic or eustatic movements, to changes of precipitation regime, to deforestation and agricultural practices. Anthropogenic activity has been considered by some authors as a significant factor for the landscape evolution. Nonetheless, it is always difficult to state which of the two factors (climatic versus human) is to be considered as the driving mechanism behind the valley fill accumulation or downcutting. Some sedimentary sequences also show that during the Holocene, the deposition style must have shifted abruptly from one cause to another (Wilkinson, 1999). The first investigations on the Holocene evolution in Basilicata were carried out by Neboit (1977, 1980, 1983), Brückner (1982, 1983, 1986, 1990), Brückner and Hoffman (1992), Boenzi et al. (1986) and Abbott and Velastro (1995). They studied both the deposits filling the incisions and those forming the Upper Holocene terraces in
⁎ Corresponding author. Fax: +39 080 5442526. E-mail addresses: [email protected] (F. Boenzi), [email protected] (M. Caldara), [email protected] (D. Capolongo), [email protected] (P. Dellino), [email protected] (M. Piccarreta), [email protected] (O. Simone). 0169-555X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2008.03.013
the Bradano, Basento and Cavone river basins. Neboit (1977, 1980, 1983), Brückner (1982, 1983, 1986, 1990) and Brückner and Hoffman (1992) suggest that valley bottom deposition in the main rivers mostly occurred during the Greek–Roman period, when the extensive land use caused accelerated erosion processes within basin areas. Neboit rules out the influence of climate-driven processes, since during the Holocene no arid or semi-arid climatic phases have been recorded. Abbott and Velastro (1995) suggest that in southern Italy two significant accumulation phases occurred throughout the Middle to Late Holocene: one during the Neolithic, the other during the Iron Age. The latter, could have been caused by the intense land use that occurred during the Greek colonization period (Adamasteanu, 1974). Grove (2001) favoured the climatic forcing mechanism by hypothesizing that in Mediterranean areas many of the recent Holocene accumulations (sensu Vita-Finzi, 1969) could have been produced during cold–wet periods, as happened during the Little Ice Age. Grove (1988) and Grove and Rackham (2001) state that valley fills in Mediterranean countries are contemporaneous with Alpine glacier growth. The goal of this work is to highlight the Late Pleistocene and Holocene evolution of Fossa Bradanica, focusing on a small area of the middle valley of the Basento river basin. In particular, we reconstructed the Quaternary evolution of this area by means of analyses of both terrace deposits and valley fills, with the aim of stressing the relative role of climate conditions versus anthropogenic activities. We consider this area as a good test site because of the contemporaneous occurrence of: well exposed Pleistocene and Holocene
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deposits; tephra marker layers, whose chemical and mineralogical composition and stratigraphic position allow a precise correlation with well known explosive eruptions of the Campanian volcanic districts (Phlegrean Fields and Vesuvius); well-preserved artifacts useful for sediment dating and paleo-landscape reconstruction. The combined analysis of these data allowed interpretation of the chronological sequence of the morphogenetic processes that occurred in the study area through the Late Pleistocene and Holocene. 2. Study area and methods The study area is located south-west of Pomarico, between Masseria Glionne (40°28′49″N, 16°31′06″E) and Masseria Trincicanaro di Capo (40°27′07″N,16°33′30″E) on the north side of the Basento river (Fig. 1). It is characterized by a modified Mediterranean climate, with a mean annual precipitation of 750 mm, mean July temperature of 22 °C and a mean January temperature of 7 °C (Piccarreta et al., 2004, 2005). The vegetation cover is a man-modified, scrub oak-pine woodland with a mixed shrub understory. A general geological and morphological analysis has been carried out using stereoscopic aerial photographs (scale 1:30,000) and topographic maps (scale 1:25,000). Detailed field survey has been carried out to reconstruct the stratigraphic sequence of terrace and fluvial deposits and to collect samples for successive laboratory analyses. In
particular, we sampled in detail three stratigraphic successions (CAP 1, CAP 2 and CAP 3). They were chosen because of their good exposure, easy correlation through marker horizons, and the presence of features highly indicative of paleoenvironmental conditions. For each sequence we analysed sediment grain size, structures and composition. Gravelly beds and sets of lenses made of cross-laminated sand alternating with fine gravel material have been interpreted as channel deposits. Finer loamy material in massive continuous beds, showing laminations or ripple marks, has been interpreted as overbank deposits. Brownish and dark-brownish layers yielding charcoals, land snails, root marks and calcium carbonate concretions have been interpreted as palaeosols. A reliable chronological dataset, consisting of several 14C datings (see Table 1), tephra horizons (related to known eruptions that occurred in the Campanian region) and a few preserved artifacts (mainly potshards and a burial), allowed a detailed reconstruction of the events that occurred in the study area, particularly during the Middle to Late Holocene. Tephra layers were analysed for their characteristic chemical, mineralogical compositional, and glass particle morphology, which helped attribute them to well known explosive eruptions. The archaeological material has been studied by Dr. A. De Siena, from Soprintendenza Archeologica della Basilicata. Radiocarbon-dated material has been processed at CEDAD — CEnter for DAting and Diagnostics (laboratory code LTL), University of Salento (Lecce, Italy),
Fig. 1. Study area location (a) and its 3D oblique aerial view (b).
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Table 1 Radiocarbon dates on sediments and soils, Fosso La Capriola Laboratory code
Sample name
Succession
Position above modern channel (m)
Material
14
δ13C (‰)
Calibrated 2 σ
UGAMS 01910 LTL1816A LTL1817A UGAMS 01911 LTL1815A UGAMS 01912 UGAMS 01914 UGAMS 01913
cap2_233 cap2 c2.1 cap2ps cap2_966 cap1 r1 cap6_170 cap5_140 cap6_770
CAP 1 CAP 1 CAP 1 CAP 1 CAP 2 CAP 3 CAP 3 CAP 3
2.33 4.80 4.10 9.66 1.40 1.70 6.70 7.70
Charcoal Charcoal Charcoal Charcoal Charcoal Charcoal Ox bone Charcoal
3470 ± 50 1553 ± 60 3059 ± 95 1130 ± 40 4340 ± 50 4340 ± 50 1710 ± 40 1090 ± 40
−23.6 −27.6 ± 0.2 −31.7 ± 0.2 −22.4 −23.5 ± 0.6 −27.0 −20.7 −23.2
3616–3870 1318–1555 2976–3454 958–1147 3066–3582 4835–5041 1536–1708 928–1070
and the Center for Applied Isotope Studies (laboratory code UG), Athens (Georgia, USA). Finally, landforms have been interpreted and mapped on the basis of their spatial position and age. 3. Geological and geomorphological setting The Fossa Bradanica is a narrow Pliocene–Pleistocene sedimentary basin with a NW-SE trend, located between the southern Apennines and the Apulian foreland (Ricchetti, 1981; Pieri et al., 1996). Two main successions can be recognized, which are composed of clay and sandy-conglomerates, respectively (Fig. 2). The former is the basal unit and corresponds to the more than 1000 m of thick clayey “Argille Subappennine” Formation (Ricchetti, 1981), while the latter, about 50 m thick, is the closing unit of the Fossa Bradanica sedimentary cycle. It is made up by the sandy “Sabbie di Monte Marano” and the conglomeratic “Conglomerato di Irsina” formations (Ricchetti, 1981). In the Middle Pleistocene the Fossa Bradanica began to uplift, allowing both the ancestral rivers (Bradano, Basento and Cavone) to cut deep valleys perpendicularly to the coast and the lateral erosion to attack the hillslopes. The result was an increased dissection and exposure of the highly erodible clayey bedrock. The uplift is evidenced by fluvial terraces and, in the Ionian hinterland, by a complex system of coastal marine terraces (Boenzi et al., 1971; Brückner, 1980). A sequence of slightly tilted relict slope pediments occurs in the middle and high parts of the hillslope, while well-preserved remains of a Pleistocene fluvial terrace (T1) are present in the lower parts. Towards the valley bottom two levels of Holocene fluvial terraces (T2 and T3) as well as the modern floodplain of the Basento river are present (Fig. 3). The hillslopes are cut by deep gullies (fossi), which often erode up to their upper parts making them susceptible to landsliding. Where clays crop out, the gully heads and sides exhibit patterns of badland erosion (calanchi). 4. Main geomorphological features 4.1. Hillslope processes and slope pediment The hillslope has been incised and dissected by deep gullies (Fosso del Pantano La Foggia, Fosso del Castello, Fosso La Capriola and others). At an elevation between 300 and 150 m, a sequence of relict slope pediments tilted 15° towards the valley bottom is present (Fig. 2). The pediment surfaces are made of landslide detritus and consist of heterometric arenaceous and conglomeratic blocks from the upslope caprock. In many cases surfaces have been reworked and smoothed by subaerial erosion processes. They have been covered by sandy colluvial material and are correlated with the alluvial deposits at the top of the Pleistocene fluvial terraces to form multiple slope pediments (Fig. 2). At the valley bottom, the gullies are filled by up to 15 m of silty–sandy alluvial deposit, which exhibit erosional surfaces and create a typical gullies-in-valley-fills morphology (Campbell, 1989).
C date
4.2. Fluvial terraces The Pleistocene fluvial terrace T1 occurs at an elevation between 120 and 170 m and is well preserved, especially at Masseria Glionne, Masseria La Capriola and Trincicanaro di Capo (Fig. 2). It is characterized by two well defined lithological units. The basal one consists of conglomerate layers made of medium-sized pebbles which were emplaced under relatively high-energy conditions in a braided channel (Boenzi et al., 1986). The upper unit is made up of silts and thin sub-horizontal beds of sands. At several locations, on top of the upper unit, a more than 1 mthick tephra sequence is found. The first 0.3 m is made of two ash layers in continuous stratigraphic contact that show features of primary deposition. The basal layer is pinkish and is made of fine- and medium-grained ash, the upper layer is grey and made of fine ash. The upper part of the tephra sequence (0.7 m) is made of grey ash and is interpreted as material that accumulated after reworking of the basal layer. Pyroclastic material is mainly made of irregular pumice fragments characterized by broken gas bubbles; its composition is alkali-trachytic. Thickness, grain size and glass particle morphology is indicative of a large scale explosive eruption which formed a tall eruptive “Plinian” column and spread material over a long distance from the source area. The only active volcanic area capable of producing such an eruption is the Campanian volcanic district, located about 260 km west of the study area. In particular, the only big scale event characterized by alkali-trachytic magma and forming a typical pinkishgrey sequence is the Campanian Ignimbrite eruption of Phlegrean Fields, dated to about 39 ka BP (Civetta et al., 1997; Pappalardo et al., 2002). In the same unit, chaotic and heterogeneous caprock arenaceous and conglomeratic materials are interbedded in the silty-sand sediments. According to Boenzi et al. (1978) these deposits are a relic of paleo-landslides contemporaneous with T1 terrace formation. The Upper Holocene terrace T2 consists of a sequence of alternating silty-sand deposits with thin intercalations of conglomerate lenses that occur at elevations of 15–25 m above the present-day channel. At about 2 m from the base, a 50 cm-thick tephra layer lies. It is made of fine grey ash of tephritic–phonolitic composition, which components are mainly represented by highly to moderately vesicular pumices with a subordinate amount of pyroxene and feldspar crystals. Lithological features, mineralogical and chemical composition and morphological characteristics of the ash fragments suggest that this layer is linked to the fallout phase of the Plinian 3700 yr BP Avellino eruption of Vesuvius (Cioni et al., 2000; Sulpizio et al., in press). The basal unit of the T2 sediment is not exposed at this location, though surveys in adjacent areas indicate that it is composed primarily of conglomerate layers. The more recent Holocene terrace T3 formed as the result of intense floods that occurred between the 14th and 18th centuries AD in all the Basilicata rivers (i.e. during the Little Ice Age; Brückner, 1986; Brückner and Hoffman, 1992). 5. Late Pleistocene geomorphological evolution The T1 terrace formation started in the Late Pleistocene, and the analysis of its stratigraphy allows the reconstruction of the Late
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Fig. 2. Geomorphological map of the study area (a) and schematic geomorphological profile (b).
Pleistocene evolution of the Basento river. Deposit features show that: a) in a first phase, sediments were deposited under high-energy conditions by a braided channel; and b) in a second period, loamysand material started to accumulate, indicating a change in solid
transport capacity and stream power. These can be classified as overbank deposits. At several locations (in particular in Masseria Glionne area) upper terrace deposits are intercalated with poorlysorted slope materials that Boenzi et al. (1978) interpreted as being
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Fig. 3. Stratigraphic sequence of the T1 fluvial terrace at Masseria Glionne.
formed by large landslides, which occurred during T1 sediment accumulation (Fig. 4). Finally, in Masseria Glionne and Masseria La Capriola areas, several decimeters-thick tephra layers have been found at the top of the T1 terrace (Fig. 5). Analysis of the tephra sequence suggests that the pyroclastic material accumulated in a calm waterbody far from the main stream flow. This sequence correlates with the Campanian Ignimbrite eruption of Campi Flegrei (39 ka BP). The climate conditions dominating the T1 accumulation timespan can be inferred from pollen successions obtained from Lago Grande di Monticchio, a Pleistocene crater lake about 90 km north of the study area. Several authors described there a succession of pollen zones showing several climatic shifts (Watts et al., 1996a,b; Allen et al., 1999; Huntley et al., 1999; Table 2). According to these studies, in Basilicata forests developed under wet conditions between 50,000 and 42,500 yr BP. Drier conditions occurred between 42,500 and 40,700 yr BP. A new wetter phase characterized the timespan of 40,700–37,600 yr BP. In this period the sandy-conglomeratic caprock topping the higher areas bordering the Basento valley were subjected to extensive mass movements. Landslide material reached the Basento valley and intermixed with fluvial sediments. At the end of this phase the landslide material was mantled by the 39,000 yr BP pyroclastic layer. Monticchio pollen records suggest that arid conditions dominated during the period of 37,600–36,300 yr BP. Afterward, wetter conditions established, and were followed by cold–dry conditions that continued until 18,000 yr BP. In higher areas of Basilicata, e.g. Monte Pollino and Monte Sirino, the cold climate caused the formation of small glaciers (Boenzi and Palmentola, 1972; Palmentola et al., 1990; Jaurand, 1994). In our study area the barren landscape probably favoured erosive processes, which produced the slope pediment connecting the hilltops to the T1 terrace.
At the peak of the last glacial maximum, sea level was approximately 150 m lower than today (Lambeck and Chappell, 2001; Lambeck et al., 2002). Sea regression produced a marked river channel downcutting. In the study area, the Basento channel underwent a downcutting of about 20 m, as revealed by several drillings under the Pisticci Scalo industrial plants (Boenzi et al., 1987). The tributary streams deeply excavated the substrate beds, triggering paleopediment dissection processes. 6. Holocene evolution 6.1. Fosso La Capriola valley fills We have analysed in detail several sediment exposures along the fluvial downcutting Fosso La Capriola, a tributary of the Basento river (Fig. 2a). The infilling sediments cut by Fosso La Capriola are mainly characterized by alternating fine sand, silt and palaeosol beds. The bedding pattern is often affected by irregular erosion surfaces defining lenses of coarser and fine material. At the junctions between the tributary valleys and the main channel, the ancient slope angle showed an abrupt decrease, which caused coarse gravel accumulation. Among the many available exposures along the flanks of the narrow Fosso La Capriola valley, three stratigraphic successions have been investigated (CAP 1, CAP 2 and CAP 3 in Fig. 2a). 6.1.1. CAP 1 succession This exposure is located on the east side of the main channel of Fosso La Capriola (Fig. 6). The first 2 m of the succession show a sequence of pale brown plane and cross-laminated sand layers, sparse in organic matter.
Fig. 4. Tephra layers in the T1 fluvial terrace at Masseria Glionne (i) and Masseria La Capriola (ii).
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Fig. 5. Fosso La Capriola successions.
Moving upwards, the sediment (still sandy) becomes richer in loam and the bedding is marked by thin clayey horizons. Between 2 m and 3 m the deposit is loamy, finely laminated and with a higher amount in organic matter. In particular, between 2.25 and 2.4 m, the deposit, which is red-brownish in colour, is rich in charcoal, and shows the typical features of a palaeosol. A charcoal sample from this layer has been 14C dated, and the obtained calendar age is 3740 yr BP. The succession continues upwards with some 0.9 m of alternating beds made of fine cross-laminated sand and laminated silt with ripple structures. These deposits are capped by a thin pyroclastic horizon. As discussed in the previous section, this marker bed can be related to the
Table 2 Characterization of the pollen assemblage zones at Lago Grande di Monticchio (modified from Watts et al., 1996a) Pollen Age (calendar zone years BP)
Characterisation
4
14,300–26,100
5a 5b
26,100–29,500 29,500–31,700
6
31,700–34,900
7
34,900–36,300
8 9 10 11
36,300–37,600 37,600–40,700 40,700–42,500 42,500–50,000
Mainly herbaceous pollen. Juniperus type and Pinus frequent; few other trees; frequent Helianthemum type Decreasing Juniperus type, Helianthemum type. Small percentages of Quercus, Fagus in 5a, increasing in 5b with Abies, Ulmus, Carpinus betulus Mainly herbaceous pollen (Artemisia, Chenopodiaceae, Helianthemum type frequent), with decrease of tree pollen abundance to about 20% 50% trees with frequent Quercus, Betula, Abies, Fagus. Decrease in Artemisia, Chenopodiaceae Recession in tree percentages. Artemisia abundant once more 70% trees. Succession of Betula, Quercus, Acer, Fagus, Abies Recession in tree percentages, herbs rise to 80% of pollen sum Long forest succession with broad-level deciduous trees including Betula, Quercus, Tilia, Ulmus, Corylus. Trees to 60%. An “Interstadial”
Avellino eruption of Vesuvius (3700 yr BP). Above the “Avellino” tephra, there is 0.85 m of pale brown laminated silt. The bedding planes are often marked by millimeter-thick horizons made of dark organic matter or reddish oxidised material. In this interval a discontinuous palaeosol level is also present. A radiocarbon-dated charcoal gave the calibrated age of 3215 yr BP. Another thin tephra horizon lies at about 4.7 m from the ground. It is composed of grey ash of tephritic–phonolitic composition, which main components are highly vesicular pumice fragments and subordinate feldspar and pyroxene crystals. The geochemical features suggest that this bed can be attributed to the AP3 eruption of Vesuvius (Andronico and Cioni, 2002; Santacroce et al., submitted for publication). This eruption occurred between the “Avellino” and “Pompeii” events, at about 2800 cal. yr BP. The AP3 tephra is capped by 1.3 m of massive loam, greyish in colour, rich in organic material. A 1.45 m sequence of three palaeosols alternating with thin sand levels (5 to 10 cm thick) lies on the massive loam. The palaeosols are brown in colour, massive, rich in calcareous lumps and root marks. Several landsnails have also been found. The palaeosol succession is capped by a 0.7 m-thick layer of reddish coarse, partially pedogenized sand, bearing pebbles (mainly concentrated in its lower part). An erosional surface cuts part of the sequence, defining a several meters thick channel. The deposit filling the channel contains a set of lenses mainly made of cross-laminated coarse sand. Thick lenses of gravel, laminated loam and thin horizons bearing dark organic matter (mainly tiny pieces of charcoal) have also been observed. One of the layers is rich in charcoal, whose samples gave a calibrated age of 1435 yr BP. The channel deposit is buried by a pale brown massive sand layer whose top is at 8.5 m above the ground. Above the massive sand, a 1.4 m-thick palaeosol developed, bearing scattered tiny pieces of charcoal whose fragments yielded a calibrated 14C age of 1050 yr BP. The succession is topped by 1.3 m of fine pale brown sand with plane and cross-laminations.
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Fig. 6. Holocene tephra layers in Fosso La Capriola (CAP 2 succession).
6.1.2. CAP 2 succession This exposure is situated on the west side of the main channel; it is about 11 m thick and can be subdivided into several parts according to its main lithological features (Fig. 6). The lower part of the succession (about 2 m) is made up of laminated loamy sands. The lamination is generally plane to parallel, although sets of ripples have been observed. The stratigraphic continuity of this sandy part is interrupted by the occurrence of the two Holocene Vesuvius tephra horizons; Avellino and AP3 tephra, respectively (Fig. 7). The former is found at about 0.6 m above the modern channel bed and has a maximum thickness of 10 cm; the latter lies at the top of the sand interval, it is thinner and less continuous. At about 1.4 m from the ground a charcoal sample was radiocarbon dated to 3325 cal. yr BP. The second interval is a succession of two thick palaeosols, separated by a sand layer. The first palaeosol is 1.2 m thick, massive and rich in calcareous lumps and scattered large landsnails (Helicidae). At about 0.25 m from its base, several flat and discontinuous reddish sand lenses (3 to 5 cm thick) have been observed, they are locally rich in tiny charcoal pieces. The laminated sand layer separating the two palaeosols is 0.4 m thick and shows ripple structures. The second palaeosol is 0.7 m thick. It is characterized by a sandy grain size, crudely laminated and rich in calcareous lumps. The top of the palaeosol section is cut by a paleochannel
which incised the substratum for several meters. The base of the erosional surface is marked by a thick gravel deposit. The material filling the paleochannel is an alternation of coarse cross-laminated sand and gravel lenses with a coarse sand matrix. The paleochannel is capped by 0.7 m of plane plane-laminated sand, with intercalated organic remains (charcoal and landsnails) and scattered pebbles. The succession continues with a poorly developed palaeosol, pale brown in colour, rich in calcareous lumps with a few scattered tiny charcoal pieces. On top of the palaeosol, a plane- to cross-laminated sand layer lies, which is 3.5 m thick. It is pale brown in colour and lacks in organic matter. The topmost part of the sequence is made up of 1.2 m of loose to poorly consolidated gravel. The top of the succession is at about 11 m from the modern channel bed. 6.1.3. CAP 3 succession This is a 10 m-thick succession, the nearest one to the Basento river. It is situated on the east side of Fosso La Capriola, near the unpaved road crossing the stream (Fig. 6). Here the oldest Holocene sediments have been found. The lower part of the exposure (1.6 m thick) is made up of an irregular alternation of well-sorted coarse sand, massive loamy sand and finely laminated silt, followed by 0.3 m of massive silty-sand layer bearing many pottery fragments and charcoal. The
Fig. 7. Relation between deposition and erosion stages in Fossa Bradanica and main climatic epochs during the Holocene in Europe.
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potshards have been sampled and analysed by archaeologists from Soprintendenza Archeologica della Basilicata, and are referred to the Neolithic cultural phase known as “Diana” (Bianco, 1985). An AMS radiocarbon date obtained from a charcoal fragment gave an age of 4940 cal. yr BP. An erosive surface separates these levels from the rest of the succession and defines a small channel whose filling started shortly before the deposition of the “Avellino” tephra, which is here 2– 4 cm thick. Above the “Avellino” marker there is a 0.5 m thick sequence made up of: massive fine sand with a high organic content (15 cm thick), a palaeosol (20 cm thick), and a layer of fine plane-laminated sand (15 cm thick). The deposition continued with the “AP3” tephra, here about 5–6 cm thick. A 1.8 m succession of two palaeosols, separated by a 0.25 m sand layer, lies on the top of the “AP3” horizon. The palaeosols are brown and characterized by scattered centimetric calcareous lumps, charcoal and some landsnails (mostly Helicidae). Several scattered charcoal pieces have also been observed within the sand. The palaeosol is topped by a 0.70 m of brown-reddish, partially pedogenised sand with scattered pebbles. Within this layer a pot about 20 cm wide and 30 cm high has been found. Archaeologists from Soprintendenza Archeologica della Basilicata interpret the pot as the burial receptacle of a child dating back to around 2500 BP. The grave was excavated in the reddish sand deposit, which at that time represented the ground surface. On this layer a 2.4 m thick succession of pale brown fine sand lies. These deposits are either laminated (plane- and cross-lamination) or massive. The top of the sequence is characterized by a 4.0 m thick succession of three palaeosols separated by laminated fine sand layers showing both planar lamination and ripple structures. A radiocarbon date obtained from an ox bone collected from the first palaeosol gave a calibrated age of 1620 yr BP; while a charcoal from the sand layer separating the first palaeosol from the second gave an age of 1000 cal. yr BP. 6.2. Discussion One of the main goals in the study of Holocene valley filling/ downcutting sequences is to define their climatic or anthropogenic origin. Several researchers advocate the anthropogenic cause (Butzer, 1980; Davidson, 1980; van Andel et al., 1990; Barker and Hunt, 1995, 2003), whereas others do not exclude that in some cases climate must have played an important role (Bintliff, 1975; Ballais, 1995; GutiérrezElorza and Peña-Monné, 1998). From the succession of Fosso La Capriola area several main deposition/erosion phases can be inferred (Fig. 7). They are well defined from a chronological point of view and allow a comparison with major climate changes recorded in other European areas. 6.2.1. Phase A A first phase of deposition started in a yet unknown period and ended after 4500 yr BP (‘Diana’ potshards in CAP 3) during the Late Neolithic. Our hypothesis is that this stage could be linked to the Rotmoos Alpine glaciers advance (Grove 1988). 6.2.2. Phase B The subsequent downcutting phase took place after 4500 yr BP and before 3700 yr BP. We do not know how intense the erosional activity was. We are only able to state that the small channel at the base of the CAP 3 had been carved before 3700 yr BP (“Avellino” tephra). Detailed pollen studies can give an idea about climate characterizing this period. In particular, there is an apparent abrupt collapse in the concentration of tree pollen recorded in many Mediterranean areas at that time. In central Italy an evident arboreal pollen decline has been found at Lago di Mezzano (Sadori et al., 2004) after 3820 ± 40 14C yr BP (unpublished radiocarbon age, Sadori, personal communication), at Lagaccione around 3750 ± 80 14C yr BP (Magri, 1999), at Lago di Vico around 3710 ± 50 14C yr BP (Magri and Sadori, 1999) and at Valle di Castiglione after 3480 ± 50 14C yr BP (Follieri et al., 1988). In Apulia
(southern Italy), at Lago Battaglia in the coastal Gargano area (Caroli and Caldara, 2007), a sharp collapse of arboreal pollen and a considerable increase in fire frequencies occurred approximately 4200 cal. yr BP (age estimated through the interpolation of other radiocarbon dates). All these studies suggest that a dry phase should have taken place around 4000 cal. yr BP. According to Jalut et al. (2000), in coastal areas in south-eastern France and south-eastern Spain, pollen records suggest that the dry period should have occurred between 4500 and 4000 yr BP (5300–4200 cal. yr BP). By combining the evidence is it possible to suggest that the downcutting phase recorded in the Fosso La Capriola area between 4500 and 3700 yr BP took place during a dry climate period. 6.2.3. Phase C A new deposition period started shortly before the “Avellino” tephra; from 3700 to 2800 yr BP, a timespan including the Bronze Age. Deposition processes were rather slow (accumulation was around 1 m or little more); this is in agreement with the data published by Neboit (1977, 1980, 1983), Brückner (1982, 1983, 1986, 1990) and Brückner and Hoffman (1992). This period could have been characterized by hydrogeological unsteadiness. Proof is that, due to recurrent flooding events and to the rising up of the groundwater table, around 2500– 2300 cal. yr BP, the inhabitants of Metaponto (coastal Basilicata) moved towards higher areas and built an artificial drainage network (Boenzi et al., 1987; De Siena, 2001). The Lago Battaglia (Gargano coast, Apulia) pollen record shows a relatively wetter climate from around 2700 to 2190 cal. BP (Caroli and Caldara, 2007). In the same period severe alluvial and erosive phenomena occurred at many places in northern Italy (Veggiani, 1987) and in the Mediterranean basin (e.g. in Spain) where large amounts of sediments accumulated on the hillslopes (Gutiérrez-Elorza and Peña-Monné, 1998; Gutiérrez Elorza and Sesé Martínez, 2001; Gutiérrez et al., 2006). All these phenomena seem to be connected to a cool–wet climate coinciding with the Alpine glacier advance (Orombelli and Porter, 1982; Orombelli and Pelfini, 1985; Baroni and Carton, 1991) during the Göschenen I glaciation (Patzelt, 1974). The deposition rate increased between 2800 and 1620 cal. yr BP, between Greek colonization and the Roman Age (about 6 m of sediments in CAP 3). There is evidence that at least one deposition stasis occurred around 2500 yr BP, as suggested by the grave found in CAP 3. When sediments started again to accumulate, the sedimentation continued at higher rates until 1620 cal. yr BP. At that time anthropogenic pressure on the environment would have been considerable. The exploitation of the region by the Romans was intense, as suggested by the many small farms and villas scattered all over the region (Racioppi, 1889). 6.2.4. Phase D A new erosional phase started after 1620 cal. yr BP (CAP 3) and ended before 1435 cal. yr BP (CAP 1). We have not been able to find any useful elements to date the channel in CAP 2. Nevertheless, from its stratigraphic position, similar to the channel in CAP 1 (above the “AP3” tephra and between the two palaeosol sequences), we hypothesize that it was incised in the same period. 6.2.5. Phase E Fosso La Capriola sediment accumulation started again shortly before 1435 cal. yr BP (material filling the channel in CAP 1) and continued until an unknown date after 1000 cal. yr BP (CAP 3). This phase of deposition lasted almost the whole of the early Middle Ages, when Byzantine and Longobard populations began to compete for regional supremacy. In Basilicata most of the population settled near monasteries or fortified places on the hilltops (Guillou, 1983). Given the low settlement density we believe that the anthropogenic pressure on the environment was rather low; this leads us to exclude humans as the main cause of geomorphological changes. Thus, the erosion/deposition phenomena should have been driven by climatic
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factors. Information about the climate condition that characterized this period could be inferred from Alpine glacier behaviour. In the same period the Alps underwent the Göschenen II glaciation (Patzelt, 1974). Glacial advances are known for the Brenva glacier on Monte Bianco, where a log found within a moraine gave the radiocarbon age 1179 ± 55 14C yr BP (Orombelli and Porter, 1982), and for the Lys glacier on Monte Rosa, where a palaeosol buried by moraine deposits dates to 1185 ± 80 14C yr BP (Strumia, 1997). Advancing Alpine glaciers could mean a wetter climate in southern Italy. 6.2.6. Phase F After 1000 cal. yr BP a new erosional period began. Fosso La Capriola and also other Basilicata streams strongly deepened their channels; the fluvial terrace T2 was formed along the middle to low reaches of the main regional rivers. The start of this new downcutting phase is also documented by archaeological and historical data. In particular, near the old Pisticci train station, the ruins of an XI century AD Benedictine monastery lay on the T2 Basento terrace, at around 15 m above the modern floodplain. Thus, the Basento river incised its alluvial deposits before the monastery was built (Caputo and Bubbico, 1983). A similar situation has been observed in the Bradano river basin, between S. Giuliano lake and Masseria S. Lucia, where a XII century subterranean church (La Scaletta, 1966) was dug in the Plio-Pleistocene calcarenite at 12 m above the present floodplain. However, downcutting of the Basilicata rivers was not triggered by tectonic uplift. According to recent studies (Westaway,1993; Schiattarella et al., 2003), from the Middle Pleistocene until the present, this part of southern Italy was characterized by a 0.5 mm/yr mean tectonic uplift, and the uplift rate was even lower in the Bradanic Trough in Fossa Bradanica. Therefore, the recent regional tectonic movements were too slow to justify such a deep downcutting in less than one thousand years. We believe that the erosion began towards the end of the early Middle Ages and that it was accelerated around 1000 yr BP, during the socalled Medieval warm period. Starting from 800–700 cal. yr BP, flood phenomena affecting the Basilicata rivers (e.g. Bradano and Basento) suggest a new period of geomorphological instability (Tanzi, 1746; Giustiniani, 1797). Similar events occurred also in the upper valley of the nearly Sinni river, where remains of a monastery settlement built in 700 yr BP (Giganti, 1978) are today buried under alluvial sediments. In conclusion, data collected with this study do not show a direct connection between climate shifts and landscape evolution. The only evidence is that incision/accumulation states shift almost contemporaneously with climate changes (recorded in several other Italian and European areas). This leads us to consider climatic causes as the main factor ruling the evolution of study area during the Mid- to Late Holocene. The function of fires in shaping the landscape also seems uncertain. In fact, the low amount of charcoal found in several levels of the investigated exposures lead us to rule out the occurrence of wild fires as a factor affecting the erosion/deposition processes. In addition, archaeological studies carried out in the surrounding areas suggest that charcoal might instead be related to local anthropogenic activity (De Siena, personal communication). 7. Conclusion This study has added new elements to our knowledge of the geomorphological evolution of the Fossa Bradanica from the Late Pleistocene and over the entire Holocene, in relation to climatic shifts. The starting point was the Pleistocene fluvial terrace T1, mainly preserved on the north side of the middle Basento river and chronologically referable to 39,000 yr BP (Campanian Ignimbrite tephra). On the most elevated parts of the hillslopes, pediment remains are present, which are stratigraphically linked to the fluvial terrace T1. The pediment genesis began shortly after the Campanian Ignimbrite deposition in relation to a cold-arid climate with steppe vegetation. The Late Pleistocene sea-level retreat triggered fluvial incision,
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pediment dissection and the formation of deep gullies. River valley bottom infilling occurred gradually during the Holocene. Sedimentation started due to postglacial sea-level rise (Brückner, 1983); subsequently the accumulation processes have been mostly controlled by climatic and anthropic causes. The study of Fosso La Capriola filling sediments showed a Holocene alternation of different phases of erosion and deposition: 1) The first phase of deposition occurred in the Late Neolithic and was followed by a downcutting phase; 2) A second accumulation phase took place in the Greek period between 2800 and 2500 yr BP. In Basilicata, this timespan was characterized by floods and erosive phenomena, which also influenced human settlements. Similar phenomena occurred in areas of central-northern Italy (Veggiani, 1987) and in the Mediterranean basin and is well connected to a cool–wet period coinciding with glacial advance in the Alps. After a period of stasis that occurred about 2500 yr BP, a new deposition phase occurred continuing until 1600 BP, probably in relation to remarkable land-use pressure by the Romans; 3) A new erosional period occurred from 1620 to 1435 yr BP and was followed by a sedimentation phase between about 1435 and 1000 yr BP; 4) After 1000 yr BP a downcutting occurred, creating the fluvial terrace T2 and the stream channel deepening. This downcutting phase coincides with the Medieval warm period; 5) From 750–700 until 400–300 yr BP flooding phenomena took place in the river valley bottoms. These phenomena coincide with the Little Ice Age. The results of this study support the idea that climatic changes were the main controlling factor in the rapid and varied geomorphologic transformation of the Fossa Bradanica during both the Late Pleistocene and the Holocene, with anthropogenic factors playing a presumably minor role during modern times. This paper also demonstrates that a detailed field study, coupled with analyses of tephra layers, absolute 14C dating and archaeological characterization of artefacts, which result in independent and coherent chronological data, is very helpful in unravelling the complex evolution of recent sedimentary basins of the Mediterranean area. Acknowledgements This research was supported by the PRIN-COFIN 2005 (Coordinator: Federico Boenzi). Dr. Antonio De Siena from Soprintendenza Archeologica della Basilicata and Katia Straziuso are gratefully thanked for their constructive contribution. We thank the Editor and three anonymous reviewers for their constructive revision of the original manuscript. References Abbott, J., Velastro, S., 1995. The Holocene alluvial records of the chorai of Metapontum, Basilicata and Croton, Calabria, Italy. In: Lewin, J., Macklin, M.G., Woodward, J.C. (Eds.), Mediterranean Quaternary River Environments. A.A.Balkema, Rotterdam, pp.195–205. Adamasteanu, D., 1974. La Basilicata antica. Storia e monumenti. Ed. Di Mauro, Cava dei Tirreni, 230 pp. Allen, J.R.M., Brandt, U., Brauer, A., Hubberten, H.W., Huntley, B., Keller, J., Kraml, M., Mackensen, A., Mingram, J., Negendank, J.F.W., Nowaczyk, N.R., Oberhänsli, H., Watts, W.A., Wulf, S., Zolitschka, B., 1999. Rapid environmental changes in southern Europe during the last glacial period. Nature 400, 740–743. Andronico, D., Cioni, R., 2002. Contrasting styles of Mt Vesuvius activity in the period between Avellino and Pompeii plinian eruptions, and some implications for assessments of future hazards. Bulletin of Volcanology 64, 372–391. Ballais, J.L., 1995. Alluvial Holocene terraces in eastern Maghreb: climate and anthropogenica controls. In: Lewin, J., Macklin, M.G., Woodward, J.C. (Eds.), Mediterranean Quaternary River Environments. Balkema, Rotterdam, pp. 183–194. Barker, G.W., Hunt, C.O., 1995. Quaternary valley floor erosion and alluviation in the Biferno valley, Molise, Italy: the role of tectonics, climate, sea level change and human activity. In: Lewin, J., Macklin, M.G., Woodward, J.C. (Eds.), Mediterranean Quaternary River Environments. Balkema, Rotterdam, pp. 145–157. Barker, G.W., Hunt, C.O., 2003. The role of climate and human settlement in the evolution of the Biferno Valley (Molise, Central Italy). In: Livadie, C.A., Ortolani, F.
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