Campanian Apennines - Studi Geologici e Ambientali

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SGI Bollettino Dgs09 142
Boll.Soc.Geol.It. (Ital.J.Geosci.), Vol. 126, No. 2 (2007), pp. 397-409, 11 figs., 1 tab.
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Tectonic significance of geomorphological features in the Telesina Valley
(Campanian Apennines)
PAOLO MAGLIULO (*), FILIPPO RUSSO (*) & ALESSIO VALENTE (*)
ABSTRACT
In this paper, the results of a geomorphological study carried
out in the Telesina Valley, a morphostructural depression located in
the axial sector of the Campanian Apennine chain, are presented.
The aim of this paper is to check morphological features which highlight the tectonic significance of some Quaternary landforms occurring in the valley. This area, according to many authors, is characterised by active tectonics, as pointed out by many catastrophic
earthquakes, also occurred in historical times.
The study has been based on a detailed geomorphological survey, performed concurrently with the analysis of aerial photographs
and topographic maps, also supported by literature data. It pointed
out that some escarpments, nowadays rather degraded, display morphological features and field evidence of faulting, which allow us to
hypothesize a tectonic origin for such escarpments. A tectonic control has been also highlighted by displacements of alluvial terraces,
simultaneous increases of both the riverbed gradient and sinuosity
of the channel, anomalous geometry of the meander belt and rectangular pattern of the general hydrographic network. By means of a
combination of such data, a map of the frame of faulting interesting
the study area has been obtained as a final result.
The inferred morphotectonic framework of the Telesina Valley
confirms the presence of tectonic activity which could have played,
at least from the Middle Pleistocene, a significant role in the geomorphological evolution of the valley.
KEY WORDS: Morphotectonics, Campanian Apennines,
Benevento Province, Quaternary.
RIASSUNTO
Significato tettonico degli elementi geomorfologici nella
Valle Telesina (Appennino campano).
Nel presente lavoro, vengono presentati i risultati di uno studio
geomorfologico condotto nella Valle Telesina (Appennino campano).
L’area in studio, che corrisponde alla bassa valle del Fiume Calore, è
una depressione morfostrutturale ubicata nel settore assiale della catena sud-appenninica. Quest’ultima è geologicamente caratterizzata
da una serie di unità tettoniche meso-cenozoiche impilate che sono
state profondamente erose ed incise durante il Quaternario. Su tale
substrato tettonicamente deformato, giacciono in discordanza depositi quaternari interessati da tettonica prevalentemente distensiva.
Tali depositi risultano per la maggior parte di natura alluvionale e
costituiscono anche il principale riempimento della Valle Telesina.
Obiettivo del presente lavoro è il riconoscimento e l’interpretazione di elementi geomorfologici indicativi di un controllo tettonico
nella genesi e/o nell’evoluzione di alcune forme del paesaggio presenti nell’area in studio. Quest’area, come precedentemente evidenziato da vari autori, è interessata da tettonica attiva, testimoniata tra
l’altro da numerosi terremoti catastrofici, verificatisi anche in tempi
storici (ad esempio, nel 1456, nel 1688 e nel 1732). Lo studio è stato
eseguito mediante un dettagliato rilevamento geologico e geomorfologico condotto parallelamente all’analisi di foto aeree e di carte to-
(*) Department of Geological and Environmental Studies,
University of Sannio, Via Port’Arsa, 11 - 82100, Benevento, Italy.
[email protected]
pografiche in scala 1:5000. I risultati sono stati confrontati con dati
di letteratura.
L’analisi geomorfologica è stata prevalentemente incentrata
sulle forme maggiormente indicative e/o sensibili ad un eventuale
controllo tettonico. In particolare, sono state analizzate: 1) scarpate,
2) terrazzi, 3) pattern del reticolo idrografico, 4) geometria del canale
del corso d’acqua principale e 5) conoidi alluvionali.
Più specificamente, è stato evidenziato come alcune delle scarpate analizzate, attualmente piuttosto degradate, mostrino caratteristiche morfologiche ed evidenze di campagna (ad esempio, tiltaggio e dislocazione degli strati) che consentono di ipotizzare una loro origine
tettonica. Un controllo tettonico è stato inoltre evidenziato dall’analisi
geometrica del canale del corso d’acqua principale, che è risultato interessato da improvvisi e localizzati incrementi del gradiente fluviale
associati ad aumenti della sinuosità. Evidenze di tettonica sono inoltre
rappresentate dal pattern di tipo rettangolare del reticolo idrografico e
dall’anomala geometria e distribuzione delle tracce dei meandri abbandonati del corso d’acqua principale. Quest’ultima, unitamente ad
altri elementi geologici e geomorfologici (tiltaggio dei depositi alluvionali, geometria dei corpi di conoide, asimmetria nella distribuzione
dei terrazzi sui due versanti vallivi), suggerisce un generalizzato processo di basculamento dell’intera valle verso sud o sud-est. Un’eccezione è rappresentata dal settore centrale dell’area investigata che mostra, al contrario, evidenze di tiltaggio verso nord o nord-ovest.
Il risultato finale del presente studio è rappresentato da una
carta delle faglie, ottenuta combinando i dati in precedenza descritti. Le faglie sono state riconosciute e tracciate sulla base dei
principali allineamenti di elementi geomorfologici indicativi di
controllo tettonico. Le faglie ipotizzate risultano spesso in accordo
con quelle riconosciute da altri autori sulla base di dati ottenuti
utilizzando metodologie differenti.
In conclusione, è possibile affermare che il quadro tettonico della Valle Telesina ricostruito in questo studio conferma la presenza di
un’attività tettonica che potrebbe aver giocato, a partire almeno dal
Pleistocene medio, un ruolo significativo nell’evoluzione geomorfologica della valle.
TERMINI CHIAVE: Morfotettonica, Appennino campano,
Provincia di Benevento, Quaternario.
INTRODUCTION
The Southern Apennines are characterized by active
tectonics and large damaging earthquakes are common
(ASCIONE & CINQUE, 2003). Seismic events are mainly
located along the chain axis and show extensional or
transcurrent focal mechanisms. The hypocentres are at a
depth generally ranging from 10 to 12 km from the surface (VANNUCCI et alii, 2004). Most of the catastrophic
earthquakes in the Southern Apennines have probably
ruptured along NW-SE trending and NE dipping faults
(VILARDO et alii, 2003). To mitigate earthquake damage,
the knowledge of the distribution of potentially seismogenetic faults is fundamental. In this framework, studies of
tectonic geomorphology (sensu KELLER & PINTER, 2002)
have been proven very useful in terms of recognising and
interpreting surface evidence of faulting.
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Fig. 1 - (a) Geological sketch map of CampanianLucanian Apennines (SCANDONE, 1983; modified
by ASCIONE & CINQUE, 2003). LEGEND: 1) Pleistocene sedimentary deposits; 2) Pleistocene volcanoclastic deposits; 3) Pliocene deposits; 4) internal nappes; 5) Mesozoic carbonate platform
successions; 6) Mesozoic basin successions;
7) Apulia platform; 8) thrusts; 9) buried thrust
front; 10) main faults; 11) syncline axis; 12) location of the Telesina Valley. (b) Location of the
Telesina Valley in the framework of the largest
earthquakes of the Benevento Province (Campanian Apennines) (from: MAGLIULO et alii, 2004,
modified. Seismic data after GRUPPO DI LAVORO
CPTI, 1999; VALENSISE & PANTOSTI, 2001; BOLLETTINO SISMICO DELL’ISTITUTO NAZIONALE DI
GEOFISICA E VULCANOLOGIA-CENTRO NAZIONALE
TERREMOTI, 2004).
– (a) Schema strutturale dell’Appennino Campano-Lucano (SCANDONE, 1983; modificato da
ASCIONE & CINQUE, 2003). LEGENDA: 1) depositi
sedimentari pleistocenici; 2) vulcaniti pleistoceniche; 3) depositi pliocenici; 4) coltri interne; 5) successioni mesozoiche di piattaforma carbonatica;
6) successioni mesozoiche di bacino; 7) Piattaforma Apula; 8) sovrascorrimenti; 9) fronte sepolto
dell’alloctono; 10) principali faglie; 11) asse di sinclinale; 12) ubicazione della Valle Telesina. (b) Localizzazione della Valle Telesina nel quadro dei
maggiori terremoti occorsi nella Provincia di Benevento (Appennino meridionale) (da: MAGLIULO
et alii, 2004, modificato. Dati sismici: GRUPPO DI
LAVORO CPTI, 1999; VALENSISE & PANTOSTI,
2001; BOLLETTINO SISMICO DELL’ISTITUTO NAZIONALE DI GEOFISICA E VULCANOLOGIA-CENTRO
NAZIONALE TERREMOTI, 2004).
In this paper, we present the results of a geomorphological study designed to elucidate the tectonic landforms
of the Telesina Valley. This latter is an important morphostructural depression of the Campanian sector of the
Southern Apennines (fig. 1a) characterized by active
extension and associated severe seismicity (DI BUCCI et
alii, 2005b). The Telesina Valley is crossed by the low
course of the Calore River. This location has experienced
many catastrophic earthquakes also in historical times
(i.e. 1456, 1688, 1732; fig. 1b), which have completely
destroyed many villages in the study area and killed or
injured thousands of people. In particular, the 1688 earthquake completely destroyed the villages of Guardia Sanframondi and Cerreto Sannita, leaving also clear evidence
in the local landscape (SERVA, 1981; BOSCHI et alii, 1997).
GEOLOGICAL AND GEOMORPHOLOGICAL SETTING
The Telesina Valley is a E-W oriented basin, elongated
for ~15 km between the villages of Ponte and Solopaca
Scalo in the Calore River valley. It falls within the axis of
the Campanian sector of Southern Apennines fold-andthrust belt (fig. 1a), which is the result of compressional
tectonics mainly active during Tertiary (ROURE et alii,
1991; DI BUCCI et alii, 1999). In the study area, Apenninic
carbonate platform units overthrust the Molise-SannioLagonegro pelagic basin successions (MOSTARDINI &
MERLINI, 1986). The Apenninic carbonate units extensively crop out on the Camposauro Mt. which borders the
study area to the south, while the basinal successions
mainly outcrop on the northern side of the Telesina Valley
(DI NOCERA et alii, 1993; MAGLIULO, 2005) (fig. 2). On
such tectonically deformed Meso-cenozoic substratum,
several Quaternary deposits uncomformably rest. After the
Tertiary mainly-compressional tectonic phases, the Campanian Apennines have been affected, chiefly during the
Quaternary age, by an extensional phase, still active at the
present and generating normal fault systems. This extensional regime is presently acting also in the study area
(MASSA et alii, 2004). BOUSQUET et alii (1993) found ESEWNW and W-E trending normal fault systems. DI BUCCI et
alii (2005b) suggest the occurrence of a NE-dipping main
fault located at the foothill of the Camposauro Mount.
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399
Fig. 2 - Schematic geo-lithological map of the study area (from: MAGLIULO, 2005; modified). LEGEND: 1) alluvial sand and poorly sorted
calcareous gravel (Present); 2) Calcareous coarse-gravelly colluvial deposits (Holocene); 3) Alluvial silty-sand and gravel (Holocene); 4) Grey
tuff (Ignimbrite Campana, Auct.; ~39 ka BP); 5) Brownish ignimbrite (Ignimbrite of Guardia Sanframondi; ~560 ka BP); 6) Alluvial polygenic
and poorly sorted gravel, yellowish sand, greenish palustrine pelite (Middle Pleistocene): a) gravelly member; b) sandy-gravelly-pelitic member;
c) silty-clayey member; 7) Conglomerate, sand and clay (Altavilla Unit; Messinian-Lower Pliocene); 8) Calcareous breccia, calcarenite,
multi-coloured pelite, marl and sandstone (Caiazzo Unit; Tortonian-Lower Messinian): a) arenaceous member; b) calcareous-pelitic member;
9) Multi-coloured clay and marl (Argille Varicolori Unit; Upper Cretaceous?-Miocene); 10) Calcarenite with reddish marly interbeddings
(«Flysch Rosso» Unit; Upper Cretaceous-Oligocene); 11) Main faults.
– Carta geolitologica schematica dell’area di studio (da MAGLIULO, 2005; modificato). LEGENDA: 1) sabbie e ghiaie calcaree alluvionali (Attuale);
2) Depositi colluviali di versante costituiti da ghiaie calcaree (Olocene); 3) Sabbie limose e ghiaie alluvionali (Olocene); 4) Ignimbrite Campana
Auct. (~39 ka BP); 5) Tufo brunastro (Ignimbrite di Guardia Sanframondi; ~560 ka BP); 6) Ghiaie e sabbie alluvionali e peliti palustri (Pleistocene
medio); 7) Conglomerati, sabbie ed argille (Unità di Altavilla; Messiniano-Pliocene inferiore); 8) Brecce calcaree, calcareniti, peliti policrome,
marne ed arenarie (Unità di Caiazzo; Tortoniano-Messiniano inferiore): a) membro arenaceo, b) membro calcareo-pelitico; 9) Marne ed argille
policrome (Unità delle Argille Varicolori; Cretaceo superiore?-Miocene); 10) Calcareniti con intercalazioni marnose (Unità del «Flysch Rosso»;
Cretaceo superiore-Oligocene); 11) Principali faglie.
MASSA et alii (2005) hypothesize W-E, NW-SE and SW-NE
oriented normal faults.
According to the existing literature (BERGOMI et alii,
1975; DI NOCERA et alii, 1995; MAGLIULO, 2005), the oldest outcropping Quaternary deposits consist of cemented
calcareous breccias. These deposits crop out just outside
the study area, in the intermediate part of the Mt. Camposauro slopes, and directly overlie the Mesozoic limestone. The calcareous breccias have been tentatively
dated back to Mindel by BERGOMI et alii (1975) and to the
Lower Pleistocene by MAGLIULO (2005). The breccias are
unconformably overlaid by alluvial fan deposits. These
latter mainly consist of poorly sorted, subangular calcareous pebbles in a silty-sandy matrix, locally of volcanoclastic origin (MAGLIULO et alii, 2004a; MASSA et alii, 2005).
The alluvial fan deposits are interfingered with terraced
fluvial and fluvio-lacustrine deposits of Calore River,
mainly consisting of gravels and sands, locally with siltyclayey interbeddings. These deposits are interpreted by
MAGLIULO (2005) as the product of a single, prolonged
depositional event. The same author dated back such
deposits to the Middle Pleistocene on the basis of the
39
Ar/40Ar radiometric age of a brownish ignimbrite
(Ignimbrite of Guardia Sanframondi, hereafter referred
as IGS) interbedded in the upper part of the succession:
the radiometric age of IGS is 560±2 ka BP (fig. 3). On the
contrary, DI BUCCI et alii (2005a, b) and MASSA et alii
(2005) interpret the fluvial and fluvio-lacustrine deposits
as products of different depositional events. According to
these authors, the age of the event accounting for the
deposits below the order C2 terraces is early Upper Pleistocene (namely, >0.097 Ma BP). However, they do not
exclude the possibility of a Middle Pleistocene fluvial
depositional event on the basis of a 674 ka BP aged pyroclastic layer interbedded in the fluvial succession.
On both the Quaternary deposits and pre-Quaternary
substratum, an Upper Pleistocene grey tuff (Ignimbrite
Campana Auct., ~39 ka BP aged according to DE VIVO et
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Fig. 3 - Schematic morphostratigraphic cross
section, not to scale, of the different terrace
orders (I-V) in the Telesina Valley and main
geochronological constraints according to
MAGLIULO (2005).
– Sezione morfostratigrafica schematica, non in
scala, dei diversi ordini (I-V) di terrazzi nella
Valle Telesina e dei relativi, principali vincoli
geocronologici secondo MAGLIULO (2005).
alii, 2001) unconformably rests. The lithological succession characterizing the Telesina Valley is completed by
Holocene alluvial deposits of the Calore River, consisting
of silty sands and gravels (BERGOMI et alii, 1975), which
represent the product of the last depositional cycle of the
Calore River (DI BUCCI et alii, 2005a, b; MAGLIULO, 2005;
MASSA et alii, 2005).
From a geomorphological point of view, previous
studies highlight that the Telesina Valley is characterized by a clear asimmetry (DI NOCERA et alii, 1995). In
the southernmost part of the valley, two (MASSA et alii,
2005; DI BUCCI et alii, 2005a) or three (MAGLIULO, 2005)
generations of entrenched alluvial fans occur (fig. 4). In
the central part of the area, five orders of terraces have
been observed. The highest and oldest terrace is morphologically connected with a glacis, which occurs in
the northernmost sector of the Telesina Valley (DI
NOCERA et alii, 1995). However, the origin and the ages
of these landforms and especially of the river terraces
are still debated. Because fluvial terraces represent a
powerful tool in recognizing and possibly dating geomorphological evidence of tectonics, which is the main
topic of this paper, the different interpretations concerning the terraces of the Calore River will be briefly summarized below.
According to MAGLIULO (2005), the I-IV orders of terraces are formed on the Middle Pleistocene fluvial and
fluvio-lacustrine deposits of Calore River, while the V
order formed on Holocene alluvial deposits (fig. 3). The
top surfaces of the I and V order are depositional, while
those of the II, IV and, probably, III order are erosional.
The age of the I order is constrained by the 39Ar/40Ar
radiometric age of the IGS, which is 560±2 ka BP. The
IGS is overlaid by few meters of alluvial deposits witnessing a reprise of the fluvial aggradation after the emplacement of the ignimbrite (fig. 3). The aggradation probably
stopped at the end of the cold climatic phase during
which the IGS emplaced (MIS-14: ~540-580 ka BP,
according to KARNER et alii, 1999). Thus, the age of the I
order terrace is probably ~540 ka B.P. (Middle Pleistocene). The age of the II order terrace is >200 ka BP
(Middle Pleistocene) as suggested by Early Musterian
cherty artefacts found at the top of this terrace (pers.
com. of Prof. F. Fedele). The age of the III order terrace is
>>39 ka BP as highlighted by the fact that the incisions
which deeply dissect this terrace are completely filled by
Ignimbrite Campana Auct. (hereafter referred as IC),
which is ~39 ka BP aged (DE VIVO et alii, 2001). The IV
order terrace formed after a phase of deep fluvial downcutting which interested the IC, clearly witnessed by more
than 15 m high fluvial scarps occurring just outside the
study area (namely to the south of Amorosi village),
which was followed by lateral planation of the Calore
River. Thus, the age of the IV order is probably late Upper
Pleistocene-early Holocene, even if the excellent degree of
preservation and the wide extension of IV order terraces
leads to prefer an early Holocene age. Finally, the wide
and very well preserved V order terraces are Middle-(?)
late Holocene in age.
Contrasting interpretations have been given by DI
BUCCI et alii (2005a, 2005b). These authors observe: 1) a
first river terrace (referred as C1), Middle Pleistocene aged;
Fig. 4 - Map of the terraces (Roman numerals
indicate the relative order), alluvial fans and
escarpments in the Telesina Valley. See text for
details.
– Rappresentazione cartografica dei terrazzi (i
numeri romani indicano l’ordine), delle conoidi
alluvionali e delle scarpate della Valle Telesina.
Per ulteriori dettagli, si veda il testo.
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2) a C2 terrace, whose forming deposits are >0.097 Ma
aged (early Upper Pleistocene); 3) a C3 terrace, formed on
deposits 0.097 Ma aged on the basis of 40Ar/39Ar radiometric dating of a pyroclastic level uncomformably overlying
the top of this terrace; 4) a C4 terrace, whose underlying
deposits are Holocene-early Upper Pleistocene (namely
<0.007 Ma-0.039 Ma) aged; 5) a C5 terrace, formed on
deposits Holocene aged as containing reworked terracotta
fragments (whose oldest age is <7 ka BP; BARKER, 1984).
Regarding different interpretations about the ages of
the terraces, worthy to note is the fact that the 0.097 Ma
aged pyroclastic layer found by DI BUCCI et alii (2005a) at
the top of the C3 terrace has been sampled at a locality
called Masseria Piana, which is located on a III order
remnant sensu MAGLIULO (2005) (fig. 4). Furthermore,
the 0.097 Ma age suggested by DI BUCCI et alii (2005a)
does not contrast with the time span (~200 - ~39 ka BP)
hypothesized by MAGLIULO (2005) for the III order.
The age of ~540 ka BP for the I order and the age
>200 ka BP for the II order suggested by MAGLIULO
(2005) does not strikingly contrast with the age proposed
by DI BUCCI et alii (2005a) for the C2 terrace (mainly
embracing both I and II order sensu MAGLIULO, 2005)
which is generically >0.097 Ma BP.
Finally, a (?)late Upper Pleistocene-early Holocene
and a middle-(?)upper Holocene can be suggested,
respectively, for the IV and V order of terraces.
401
Fig. 5 - Tilted alluvial fan strata (southern side of Telesina Valley, SW
of Ponte). The maximum height of the outcrop is approximately 10 m.
– Evidenze di tiltaggio tettonico della successione di conoide alluvionale
(sinistra orografica, SW di Ponte). La massima altezza dell’affioramento
è circa 10 m.
MATERIALS AND METHODS
The study of geomorphological evidence of tectonics
has been performed using classical techniques of geomorphic analysis of the relief. A preliminary analysis of
aerial photographs at 1:33,000 nominal scale was carried
out. It has been followed by a 1:5,000 geological and geomorphological field survey, mainly focused on Quaternary deposits and landforms and on field evidence of tectonics (figs. 5 and 6). The surveyed data have been
integrated with the results of cartographic analysis performed on 1:5,000 scale maps. In some cases, cartographic analysis has been performed using GIS softwares. Such analysis allowed to reconstruct a projected
longitudinal profile of the fluvial terraces of the Calore
River (fig. 7). In this profile, each terrace remnant has
been represented as a parallelogram on a Cartesian
plane. The ordinates of the upper and lower side of each
parallelogram indicate the altitude (in m a.s.l.) of the
inner and outer edge of each terrace remnant, respectively. Some authors maintain that the most reliable
method to detect tectonic features analysing river terraces profiles consists in considering the change in elevation of the unconformities where the terrace deposits sit
on the bedrock. Unfortunately, such unconformities
never outcrop in the study area, so it was not possible to
use this method. However, the stratigraphic boundary
between the Middle Pleistocene fluvial deposits and the
substratum has been surveyed in the field and the relative elevation has been reported on the profile (fig. 7).
Other authors (e.g. VANNOLI et alii, 2004) obtain good
results in recognizing tectonic features by means of
analysis of terraces profiles using changes in elevations
of the inner edges of each terrace remnant. Such method
has been used also in this paper, even if much caution
has been taken in interpreting results.
Fig. 6 - Conjugate faults in the alluvial fan conglomeratic succession
(southern side of Telesina Valley, SW of Ponte). The displacements,
highlighted by the sandy layer in the upper part of the outcrop, are
of few decimetres.
– Faglie coniugate interessanti la successione conglomeratica di conoide
alluvionale (sinistra orografica, SW di Ponte). I rigetti, evidenziati
dal livello sabbioso nella parte alta della scarpata, sono dell’ordine di
alcuni decimetri.
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Fig. 7 - Longitudinal projected profile of the Calore River terraces. Each parallelogram represent a terrace remnant. The ordinates of the upper and lower side of each parallelogram
indicate the altitude (m a.s.l.) of the inner and
outer edge of each terrace remnant, respectively. Correlated remnants are marked with the
same symbol. Faults parallel to the Calore River
are not shown. LEGEND: a) upper lithological
boundary of Middle Pleistocene alluvial deposits and relative altitude (m a.s.l.); b) maximum
elevation of the inner edge of terrace remnant
(m a.s.l.); c) well preserved remnant; d) badly
preserved remnant; e) very badly preserved
remnant; f) main certain and uncertain faults
elongated sideways to the Calore River. (From:
MAGLIULO 2005, modified).
– Profilo longitudinale dei terrazzi del Fiume Calore. Ciascun parallelogramma rappresenta un
lembo di terrazzo. Le ordinate del lato superiore
ed inferiore di ciascun parallelogramma indicano
rispettivamente la quota del bordo interno e la
quota del bordo esterno di ciascun lembo. Lembi
correlabili sono contrassegnati dalla medesima
campitura. Non sono riportate le faglie longitudinali al corso del Fiume Calore. LEGENDA: a) limite
litologico superiore delle alluvioni medio-pleistoceniche e relativa quota in metri s.l.m.; b) quota
massima del bordo interno di lembo di terrazzo;
c) lembo di terrazzo ben conservato; d) lembo
di terrazzo rimodellato; e) lembo di terrazzo fortemente rimodellato; f) principali faglie (certe
ed incerte) trasversali all’alveo del Fiume Calore
(da: MAGLIULO 2005, modificato).
The sinuosity of the best preserved edges of the terraces has also been determined analysing the 1:5,000
scale maps using GIS softwares. Sinuosity has not been
determined for those edges partly buried by alluvial fans
deposits.
Anomalies in the hydrographic network (mainly
subsequent reaches of streams) have also been investigated by means of cartographic analysis and validated
by field data. Faults have been inferred along the main
alignments of subsequent reaches of streams and/or
where these reaches were aligned with escarpments
showing field evidence of, at least partly, tectonic origin (fig. 8).
To recognise tectonic deformation by means of Calore
River responses, a detailed projected profile of the channel
has been reconstructed from a 1:5,000 scale map. Then,
the channel has been subdivided into segments comprised
between points of known elevation. For each segment,
the projected channel slope and the Sinuosity Index
(SCHUMM, 1963) has been calculated. The parameters
needed to calculate the Sinuosity Index (i.e. channel
length and valley length along each segment) have been
Fig. 8 - Map of the Degraded Fault Scarps
(DFS) and hydrographic network anomalies in
the Telesina Valley. LEGEND: (1) DFS; (2) subsequent reach of stream; (3) abandoned meander scar; (4) main alignments of subsequent
reaches of streams and/or DFS; (5) toponyms
of the main tributary streams of Calore River
cited in the text: a) Vallone Ariola, b) Rio
Stream, c) Ratello Stream, d) Acquafredda
Stream, e) Vallone Codacchio, f) Vallone del
Lago, g) Vallone del Corpo. Note the wide
meander in the central sector of the valley (evidenced by «Calore River» label).
– Rappresentazione cartografica delle Degraded
Fault Scarps (DFS) e delle anomalie del reticolo idrografico nella Valle Telesina. L EGENDA :
(1) DFS; (2) tratto susseguente di corso d’acqua;
(3) traccia di meandro abbandonato; (4) principali allineamenti di tratti susseguenti di corsi
d’acqua e/o DFS; (5) toponimi dei principali tributari del Fiume Calore citati nel testo: a) Vallone Ariola, b) Torrente Rio, c) Torrente Ratello,
d) Torrente Acquafredda, e) Vallone Codacchio,
f) Vallone del Lago, g) Vallone del Corpo. Si noti
l’ampio meandro nel settore centrale della valle
(evidenziato dalla dicitura «Calore River»).
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TECTONIC SIGNIFICANCE OF GEOMORPHOLOGICAL FEATURES IN THE TELESINA VALLEY
403
measured by means of GIS softwares. Following a method
proposed by OUCHI (1985), the channel slope curve has
been overlaid to the Sinuosity Index curve. According to
this method, faults have been inferred in those points of
the river channel where an increase of both the projected
channel slope and of Sinuosity Index occurred (fig. 9). The
presence of such inferred faults has been confirmed only
in those points of the river channel where aerial photographs analysis and field survey pointed out evidence of
change in elevation of the riverbed (e.g. fluvial rapids) not
due to changes of lithology.
RESULTS
The main results provided by this geomorphological
study could be summarized as follows.
a) The escarpments.
In the study area, escarpments with different morphologic features have been surveyed. A first group of
escarpments (labelled with black squares on fig. 4) borders the treads of the five orders of terraces of the
Telesina Valley. Such escarpments cut the Middle Pleistocene sandy-gravelly fluvial deposits of the Calore River.
Particular attention has been given to define the morphometric features of each escarpment. The escarpments separating the IV and the V order of terraces are quite well
preserved and continuous, are 4-5 m high and have a
mean slope of 7%. The average sinuosity of such escarpments, measured along their upper edges, is 1.524. The
escarpments between IV and III order are 15-18 m high,
have a 15% mean slope and an average sinuosity of 1.250.
The escarpments between III and II order and between
the II and I order are much less preserved than the above
described ones and are less continuous because deeply
dissected by tributary streams. Both the bad preservation
and the discontinuity of these escarpments have made
much more problematic their morphometric analysis. In
particular, it has not been possible to determine their sinuosity. However, it has been possible to establish that the
escarpments between III and the II order are ~30 m high
and 18% sloping, while those between II and I order are
10-15 m high, are much declined and have a mean slope
of 9%. No field evidence of faulting (layer displacements,
pebbles dragged or realigned along fault planes, striations
on the pebbles surfaces, etc.) have been found associated
with these escarpments. These escarpments will be hereafter referred as Paleo-Fluvial Scarps, PFS (fig. 4).
A second group of escarpments (marked with dots on
fig. 4) displays very different features with respect to the
PFS described above. On the southern side of the valley,
these escarpments mainly cut alluvial fan deposits and
are mainly E-W or WSW-ENE oriented. On the contrary,
on the northern side of the valley they cut the Middle
Pleistocene sandy-gravelly fluvial deposits of the Calore
River and are mainly WNW-ESE or SW-NE oriented. The
scarps are generally 20-25 m high and incised to triangular facets. The triangular facets are particularly evident
on the northern side of the valley. The mean slope of
these scarps is 60%. In places, in the lower part of the
scarp the slope gradient strongly increases, reaching values of 90%. These sub-vertical parts of the escarpments
are only locally due to road cuttings. The average sinuosity of this second group of escarpments is 1.05, that is
Fig. 9 - Projected channel slope and sinuosity curves of the Calore
River in the study area. Stars indicate the location of points where
simultaneous increase of the two considered parameters, associated
with fluvial rapids, occur. See text for details.
– Curve del gradiente del profilo rettificato e della sinuosità del Fiume
Calore nell’area di studio. Le stelle indicano i punti in cui sono stati
registrati simultanei incrementi dei due parametri considerati associati
a rapide fluviali. Per ulteriori dettagli, si veda testo.
much lower than the sinuosity of the PFS. Locally, the
escarpments at issue are discontinuous because buried by
slope deposits. Thus, they appear on aerial photographs
and 1:5,000 topographic maps as composed of straight
segments (the sinuosity of each segment never exceeds
1.002). In places, such segments appears slightly shifted
upslope or downslope (fig. 4).
At the foot of this second group of escarpments, a
small scree talus deriving from the dismantling of the
escarpment itself is always present. The scree talus
deposits consist of reworked alluvial fan and fluvial
sandy-pebbly sediments.
Field evidence of faulting have been found associated
with these escarpments. Namely, along the escarpments the
fluvial and alluvial fan strata, which in the study area are
sub-horizontal or slightly dipping downslope respectively,
clearly dip upslope (fig. 5). The dipping never exceeds 7
degrees. Furthermore, small conjugate faults approximately
parallel to the surface of the escarpments have been
detected (fig. 6). Along the fault planes, displacements of
sandy layers and pebbles dragged and/or realigned have
been observed. The displacements are of few decimetres.
On the contrary, no evidence of faulting have been observed
on the exposed surface of the scarps, especially where they
are «refreshed» by road cuttings. These escarpments will be
hereafter referred as Degraded Fault Scarps, DFS (fig. 4).
On the northern side of the valley, the DFS mainly
occur between the III and the IV order of terraces, respectively dated back to the Upper Pleistocene and to the
(?)late Upper Pleistocene-early Holocene (DI BUCCI et alii,
2005a, b; MAGLIULO, 2005). In places, DFS also occur
between the III and II order, this latter Middle Pleistocene aged (MAGLIULO, 2005). Finally, a DFS has been
detected between two terrace remnants both belonging to
the II order. On the southern side of the valley, DFS cut
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the oldest alluvial fans generation (fig. 4), whose youngest
forming deposits are interfingered with the fluvial and
fluvio-lacustrine sediments which form the IV order terrace (MAGLIULO, 2005; MASSA et alii, 2005).
b) The longitudinal profile of the terraces
As pointed out, among others, by VANNOLI et alii
(2004) drainage systems respond very efficiently to the
vertical modifications of the ground surface induced by
faults. Analysing their associated geomorphic features
may return basic information on the geometry of faults.
Terraces are one of these geomorphic features.
In order to detect geomorphologic evidence of tectonics on the terraces in the study area, a projected longitudinal profile of the five orders of terraces has been
worked out (fig. 7). The projected profile clearly highlights that, while the lowest and youngest terraces (IV and
V order) are wide and very well preserved, the oldest terraces (especially II and I order) mainly occur as small,
badly preserved remnants.
The analysis of the longitudinal profile of the terraces suggests the occurrence of at least two faults transversal to the Calore River channel. The westernmost fault
is highlighted by a sudden changing in elevation from
160 m a.s.l. to 185 m a.s.l. of the upper stratigraphic
boundary of the Middle Pleistocene fluvial deposits forming the substratum of the oldest terraces. The possible
location of this fault is indicated with «a» in fig. 7. The
I order terraced surface located on the footwall is
presently almost completely eroded and, thus, is not
represented in the profile. The elevation of the remnants of the II order terrace, ~540 to ~200 ka BP aged
(MAGLIULO, 2005), change from 140 m a.s.l. on the hangingwall to 166 m on the footwall. Even if much caution is
needed in interpreting displacements using inner edges
elevations of the terraces, the fault at issue seems not
displacing neither the IV nor the V order, respectively
(?)late Upper Pleistocene-early Holocene and middle(?)upper Holocene aged.
The easternmost fault causes a down-throwing of
both the upper stratigraphic boundary of the Middle
Pleistocene fluvial deposits and of a I order terrace remnant from an elevation of 210 m a.s.l. to 185 m a.s.l. No
remnants of the II and III order occur along this fault,
while the IV and V orders seems not displaced. The likely
location of this fault is indicated with «b» in fig. 7 and
coincides with a reach of the Vallone del Lago Stream.
The projected profile of the terraces also points out
the occurrence of some small terrace remnants which
cannot be connected with any of the recognised terrace
orders on the basis of the elevation of their inner edges.
The remnants at issue are represented with empty parallelograms in fig. 7.
c) The hydrographic network pattern
The Calore River is the main river of the Telesina Valley (fig. 4). Because it flows between banks and on a bed
composed of sediment that is transported by the river
itself (fig. 2), it can be defined as an alluvial river
(SCHUMM, 1986).
The analysis of aerial photographs and of 1:5,000
scale maps clearly highlighted abandoned meanders scars
of Calore River in the alluvial plain (fig. 8). These features
occur exclusively in the northern side of the valley and
are mainly concave to the SSE or to SE.
A different situation occurs in the central sector of the
alluvial plain, where a wide, active meander of the Calore
River is present (fig. 8). Such meander is characterized by
a small radius of curvature. Both to the north and to the
south of this meander, abandoned meander scars occur.
The presence of such scars to the north of the present-day
channel highlights that the Calore River channel was
located northernmost than today. The aerial photo analysis has pointed out that, moving northward, both the
degree of preservation and the sinuosity of the abandoned
meander scars progressively increases. The meander
scars incise the top surface of V order terrace remnants,
whose age is probably middle-(?)late Holocene (M A GLIULO, 2005). The northernmost meander scars are bordered by a ~15-20 m high scarp cut in the Middle Pleistocene deposits of Calore River. Such scarp directly
connects the III order terraces with the V order. Thus, IV
order remnants totally miss in this sector of the valley. To
the east, the fluvial strata outcropping along the scarp at
issue are tilted toward NW (immersion 310°N, 07°).
The geomorphological analysis of the study area
allowed to point out a series of anomalies also in the tributary hydrographic network pattern of the Telesina Valley,
which locally assumes the features of a rectangular pattern (ZERNITZ, 1932). The geological field survey allowed
to discriminate anomalous reaches of streams due to
their flowing on tectonic discontinuities («subsequent
streams») from ones due to the flowing on stratigraphic
boundaries between rocktypes with different erodibility.
In some cases, the subsequent reaches of streams are
aligned and/or parallel with respect to the DFS (fig. 8).
Particularly interesting is the case of the Vallone del
Lago Stream (indicated with «f» in fig. 8). At an elevation
of 120 m a.s.l., such stream changes its flow direction
from NNW-SSE to NE-SW and its channel becomes very
straight and perfectly aligned both with a subsequent
reach of Vallone del Corpo Stream (this latter indicated
with «g» in fig. 8) and with a straight segment of Calore
River. Furthermore, at the confluence between the Vallone del Lago Stream and the Calore River, the latter
describes a sharp angle of ~90°. Few decametres downstream, the Calore River is partially dammed by a small
alluvial fan. In such cases, SCHUMM (1977) points out
that rivers generally display an increase of sinuosity. In
this case, on the contrary, the Calore River keeps a very
straight course, which is typical of rivers flowing on tectonic discontinuities. We must keep in mind that, along
the Vallone del Lago Stream, a displacement of both the
stratigraphic boundary of the Middle Pleistocene fluvial
deposits and of the I order of terrace remnants has been
detected analysing the longitudinal projected profile of
the Calore River terraces (see section 4.b and fig. 7).
Another case is given by a subsequent reach of Acquafredda Stream (this latter indicated with «d» in fig. 8). The
Acquafredda Stream changes its flow direction from N-S to
E-W and lines up with: 1) a westernmost-located subsequent reach of a small tributary of Ratello Stream (this latter indicated with «c» in fig. 8); 2) an easternmost-located
DFS segment; and 3) with a subsequent reach of Vallone
Codacchio Stream (this latter indicated with «e» in fig. 8).
d) The geometry of the Calore River channel
The investigation devoted to the channel geometry of
the Calore River has revealed that the river course is
characterized by a sinuosity ranging from 1.0 to 1.258
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TECTONIC SIGNIFICANCE OF GEOMORPHOLOGICAL FEATURES IN THE TELESINA VALLEY
and by a slope gradient of the projected channel ranging
from 0.6‰ to 23.2‰ with frequent local steepenings.
These results are graphically shown in fig. 9, which has
been worked out following a method proposed by OUCHI
(1985). The figure highlights that simultaneous increases
both of projected channel slope and of sinuosity occur in
four points of the Calore River channel. The location of
such points is marked with stars in fig. 9. The aerial
photo analysis and the field survey pointed out the
occurrence in such points of fluvial rapids indicating a
change in elevation of the riverbed («knickpoints», sensu
BURBANK & ANDERSON, 2001). Because the Calore River
is an alluvial river and its riverbed is uniformly covered
by present-day alluvial deposits, such knickpoints may
not be well explained as the effect of the outcropping,
along the riverbed, of lithologies characterized by different erodibility.
A comparison between fig. 9 and fig. 8 highlights that
the first point in which both projected channel slope and
sinuosity increase (point «1» of fig. 9) is located at the
intersection of two alignments of subsequent reaches of
streams and/or DFS. The second point (point «2») is
located few decametres upstream with respect to subsequent reaches of Vallone del Lago Stream and Calore
River and downslope with respect to a DFS. As the previously described one, also the third point (point «3») occur
on a subsequent reach of stream of the Calore River and
downslope with respect to a DFS. Finally, the fourth
point (point «4») is aligned with point-2 and located
downslope with respect to the same DFS of point-2.
e) The alluvial fans
On the southern side of Telesina Valley, three generations of telescopically arranged alluvial fans occur (fig. 4).
The alluvial fans of the first generation are the largest
ones. They are very frequently interrupted downslope by
DFS. The alluvial fans of the second generation are
smaller than those of the first generation. Their fanheads
are perfectly aligned along the DFS. Among the alluvial
fans of the second generation, the one located to the
south of the wide active meander of Calore River experienced a major progradation than the others. Finally, the
third and youngest generation is represented by a single,
small alluvial fan body. Locally, both the second and
third alluvial fans generations are completely eroded by
Calore River.
On the northern side of the basin, the situation is
quite different. In fact, a single generation of superimposed and un-dissected alluvial fans occur. They are generally smaller than the first generation of alluvial fans
occurring on the opposite side of the valley. On the contrary, their dimensions are comparable with those of the
alluvial fans of second and third generations. Also on this
side of the valley, most part of the fanheads are aligned
along DFS.
DISCUSSION
The results of the geomorphological study carried out
in the Telesina Valley allow us to recognise various landforms and morphological features which could be interpreted as the effects of tectonic activity. For example,
among the escarpments previously described (see section
4.a) which have been distinguished in DFS and PFS (figs.
405
4 and 8), the DFS display clear geomorphological features
consistent with strongly degraded fault-scarps.
DFS show strongly contrasting features with respect
to PFS. In fact, PFS constantly border the terrace remnants, show a relatively high sinuosity (mean value:
1.524) and do not display field evidence of tectonic deformation. The mean slope gradient of PFS ranges from 7%
to 18%. These features suggest that PFS can be interpreted as declined paleo-fluvial scarps.
With respect to the PFS, DFS are almost straight (the
mean value of sinuosity is 1.05), are much steeper (mean
slope gradient is 60%) and are not always associated to
terrace treads. Furthermore, field evidence of tectonic
deformation have been surveyed along the incisions dissecting the DFS. In particular, the fluvial and alluvial fan
strata in which DFS are cut, which in the overall study
area are, respectively, sub-horizontal and gently dipping
downslope, slightly dip upslope along such incisions
(fig. 5). This strongly suggests the occurrence of tilting
processes. Another evidence of tectonic deformation
detected in the incisions at issue is given by systems of
small conjugate faults (fig. 6). Such faults are approximately parallel to the exposed surfaces of DFS. Both the
above described evidence of tilting and faulting and the
strongly contrasting morphometric features with respect
to the erosional paleo-fluvial scarps (PFS) suggest that
DFS are at least partly of tectonic origin. However, it
must be pointed out that no mesostructural field evidence
of faulting (e.g. faulted and/or striated pebbles, cataclastic
zones, deformed strata) have been found along the
exposed surfaces of DFS. Furthermore, the detected and
above described brittle deformation (conjugate faults),
detected along the incisions dissecting the DFS, seems
too weak to be explained with the activity of a main fault.
In fact, the displacements along the conjugate faults are
of few decimetres only. It seems more likely that such
brittle deformation could be the effect of the activity of
small subsidiary faults, generally associated to the main
fault (KELLER & PINTER, 2002). Therefore, our hypothesis
is that the DFS do not represent recently-formed faultscarps, but the products of degradational processes acting
on former fault-scarps (fig. 10). These processes probably
dismantled the most tectonically deformed area of the
footwall, in which evidence of deformation were much
clearer than those observed in the field. The hypothesis of
a degradation of fault-scarps is confirmed by the presence
of a scree talus at the foot of each DFS. Such scree talus
consists of the same deposits (obviously reworked) outcropping along the DFS. Thus, the scree talus can be confidentially interpreted as produced by the erosion of the
backwasting DFS. The aggradation of the scree talus progressively buried the main fault. The straight planform
geometry of the segments composing DFS is very probably inherited by the geometry of the former fault-scarp.
This suggests a prevailing retreat rather than a decline of
the original free-face of the fault-scarp. The outcropping
along the escarpments of sandy layers characterized by
higher erodibility than the overlying conglomeratic succession very probably induced undermining processes
which, in turn, favoured the retreat of the free-face. The
apparent «shifting» upslope or downslope of the segments composing the DFS could be therefore explained
with different rates of retreat of each segment.
The DFS are generally associated with subsequent
reaches of streams (fig. 8). These latter display a straight
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P. MAGLIULO ET ALII
Fig. 10 - Schematic morphostratigraphic cross sections illustrating a
possible evolution of the DFS. The figure refers to the DFS located
on the southern side of the Telesina Valley. On the northern side of
the valley, the tectonic displacement of the phase-1 mainly occurred
along the pre-existing paleo-fluvial scarp between III and IV order of
terraces. LEGEND: 1) alluvial fan sandy-conglomeratic succession
(straight lines indicate the rough stratification); 2) sandy-gravelly
fluvial deposits of Calore River; 3) scree talus deposits; 4) sandy-silty
alluvial deposits of Calore River; 5) main faults (hatched where
inferred); 6) subsidiary faults. IV and V indicate the terrace orders.
– Sezioni morfostratigrafiche schematiche illustranti una possibile evoluzione delle DFS. La figura si riferisce all’evoluzione delle DFS localizzate in sinistra orografica. In destra orografica, la dislocazione (fase-1)
interessò prevalentemente la preesistente paleo-scarpata di erosione fluviale tra il III ed il IV ordine di terrazzi. LEGENDA: 1) successione sabbioso-conglomeratica di conoide alluvionale (i tratti rettilinei indicano
la rozza stratificazione); 2) depositi fluviali sabbioso-ghiaiosi del Fiume Calore; 3) depositi di talus detritico; 4) alluvioni sabbioso-siltose
del Fiume Calore; 5) faglie principali (tratteggiate dove presunte); 6) faglie secondarie. «IV» e «V» indicano gli ordini di terrazzi.
course and flows approximately parallel to the foot of the
DFS. Such situation is particularly clear along the Vallone Ariola Stream (indicated with «a» in fig. 8) and along
some DFS located on the far southern border of the study
area. According to the evolution of DFS schematized in
fig. 10, subsequent reaches of streams probably flow
along the main fault located at the foot of the DFS. Therefore, the described linkage of DFS and subsequent
reaches of streams can be interpreted as a further proof
of the partly tectonic origin of DFS.
In some cases, subsequent reaches of streams are perfectly aligned each other. In turn, they are also aligned
with DFS remnants. A clear example is given in fig. 8: a
subsequent reach of Acquafredda Stream (indicated with
«d» in fig. 8), located to the south of Guardia Sanframondi, is aligned along a NW-SE trending straight line
both with other two subsequent reaches and with a DFS.
Because, as stated above, both subsequent reaches of
streams and DFS are associated with faults, we can infer
that the alignment at issue is probably due to the presence of a fault.
On the northern side of the basin, DFS are mainly
located along the inner edge of IV order of terraces.
On the southern side of the valley, DFS cut the alluvial
fan deposits, which are interfingered with the fluvial
deposits forming the IV order of terraces. Comparing
the data of DI BUCCI et alii (2005a, b) and MAGLIULO
(2005), a (?)late Upper Pleistocene-early Holocene age
can be inferred for such terraces. Thus, both the activity
of the generating faults and the following processes of
retreat of the fault-scarps are probably younger than
(?)late Upper Pleistocene-early Holocene. The former
and un-degraded fault-scarp was very probably much
lower than the present-day DFS. In fact, the upper surface of the footwall was dipping downslope, being the
surface of alluvial fans and/or declined paleo-fluvial
scarps. Thus, the erosional retreat of the free-face of the
former fault-scarp could have generated a progressively
higher scarp.
Various geomorphological evidence strongly suggest
the existence of an important NE-SW trending fault along
the Vallone del Lago Stream. Such evidence are: 1) a displacement of ~25 m both of the upper stratigraphic
boundary of the Middle Pleistocene fluvial deposits and
of a I order terrace remnant (see point «b» in fig. 7).
Because the I order is ~540 ka BP aged (MAGLIULO,
2005), this fault has been certainly active during the late
Middle Pleistocene; 2) perfectly aligned subsequent
reaches both of Calore River and Vallone del Lago Stream
(this latter indicated with «f» in fig. 8); 3) a simultaneous
increase of both the projected channel slope and sinuosity
of Calore River in a point located few decametres
upstream with respect to the inferred fault (point «2» in
fig. 9). In this point, the occurrence of fluvial rapids also
confirms the existence of a knickpoint (probably slightly
retreated) already suggested by the simultaneous
increases of channel slope and sinuosity (OUCHI, 1985;
SCHUMM et alii, 2000; BURBANK & ANDERSON, 2001;
KELLER & PINTER, 2002). Considering the high erodibility of the sediments in which the Calore River channel is
cut, the fact that such knickpoint is still clearly detectable
so close to the inferred fault suggests a recent activity of
the fault at issue. On the contrary, the projected long
profile of terraces seems to suggest that the most recent
terraces (IV and V order) are not displaced by the fault
(fig. 7). However, it is widely accepted that rivers are
much more sensible to tectonic deformations than their
terraces. Furthermore, data deriving from the analysis of
projected long profile of terraces based on the elevations
of the inner edges (such as the one presented in this
paper) must be interpreted with caution. Thus, the
hypothesis of a recent activity of the Vallone del Lago
fault, suggested by the simultaneous increase both of the
projected channel slope and sinuosity of Calore River,
looks probable.
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TECTONIC SIGNIFICANCE OF GEOMORPHOLOGICAL FEATURES IN THE TELESINA VALLEY
407
Fig. 11 - Map of the faults of the Telesina
Valley as deduced from the geological and
geomorphological evidence of tectonics. Such
kinds of evidence are summarized and named
in tab. 1.
– Mappa delle faglie della Valle Telesina redatta
sulla base delle evidenze geologiche e geomorfologiche di tettonica. Tali tipi di evidenze sono
indicate e riassunte nella tab. 1.
An interesting geomorphologic evidence of tectonics is
represented by the particular distribution and geometry of
the abandoned meanders scars of Calore River (fig. 8). In
fact, such meander scars occur only on the northern side
of the valley and are mainly concave to the south or southeast. The data provided by several authors (MIKE, 1975;
ALEXANDER & LEEDER, 1987; LEEDER & GAWTHORPE,
1987; ALEXANDER et alii, 1994; SCHUMM et alii, 2000)
allow us to interpret such evidence as result of a generalized tilting process of the overall Telesina Valley toward
the south or south east. Furthermore, according to the
previously quoted authors, tilting processes also induce
TABLE 1
Summary of the geological and geomorphological evidence of tectonics observed in the study area which allowed to
reconstruct the map of the faults of fig. 11. For example, the fault n. 1 is deduced from the occurrence of the following
geomorphological evidence of tectonics: DFS, subsequent reaches of streams and anomalies in the channel geometry
of the Calore River; fault n. 1 is also reported in the literature data.
– Riepilogo delle evidenze geomorfologiche di tettonica riconosciute nell’area di studio che hanno consentito l’elaborazione
della carta delle faglie di fig. 11. Ad esempio, la faglia n. 1 è stata dedotta dai seguenti indizi geomorfologici di tettonica:
DFS, tratti susseguenti di corsi d’acqua ed anomalie nella geometria dell’alveo del Fiume Calore; la faglia n. 1 è inoltre
segnalata in letteratura.
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an asymmetric distribution of terraces on the opposite
sides of a valley. Such situation is particularly clear in the
study area (fig. 4). The hypothesis of a tilting of the entire
valley towards the south or south-east is also consistent
both with the hypothesis of a slow migration of the valley
axis suggested by MALATESTA (1959) and with the occurrence of the main fault of the Calore River active extensional system at the foothill of Camposauro Mt. (DI BUCCI
et alii, 2005a). However, some geomorphological features
suggest that the central sector of the valley very probably
experienced a tilting in the opposite direction (i.e. north
or north-west). Such evidence can be summarized as follows: 1) the meander scars in this sector are approximately parallel each other (fig. 8); 2) they are progressively best preserved moving northward. This suggests
that, moving northward, the meander scars are progressively younger, also because the meander scars at issue
cut the same substratum and, therefore, no different
erodibility of the substratum can be invoked to explain
their different degree of preservation; 3) the sinuosity of
the meander scars increases northward. PEAKALL (1996)
pointed out that when a river flows on a block which
experiences a downtilting transversal to its channel axis,
the sinuosity of the river at issue progressively increases;
4) among the alluvial fans of the second generation occurring on the southern side of the valley, the alluvial fan
occurring in this sector is the largest (fig. 4). According to
ROCKWELL et alii (1984) and ASCIONE & CINQUE (2003), a
major progradation of an alluvial fan with respect to the
adjacent ones in a subsiding area can be the effect of a
minor subsidence; 5) along the scarp which borders this
sector to the east, the alluvial strata display evidence of
tilting towards NW.
The meander scars in this sector of the valley incise
the top surface of the V order terrace. This latter is middle-(?)upper Holocene aged (MAGLIULO, 2005). This suggests a very recent age of the downtilting process. The
presence of meander scars to the north of the present-day
channel points out that the Calore River channel was
located northernmost than today. Probably, the channel
was following shifted to the present-day position by chute
cut-off processes.
The space distribution of single or combinated geological and geomorphological evidence of tectonics
allowed us to infer a possible distribution of the faults in
the study-area (fig. 11). The geomorphological features
which allowed to reconstruct the trending of the inferred
faults are: a) DFS; b) subsequent reaches of streams; c)
anomalies in the channel geometry of the Calore River
and d) displacements of terraces. Stratigraphic and literature data have also been considered. For each fault, the
evidence of tectonics are summarized in tab. 1.
CONCLUSIONS
The geomorphological survey carried out in the lower
reach of Calore River basin («Telesina Valley») allowed us
to highlight several morphological features with a tectonic significance. This confirms that the study area,
according to literature data, is characterised by active tectonics as witnessed by many catastrophic earthquakes
occurred also in historical times.
The investigated Quaternary landforms are: 1) escarpments, 2) hydrographic network pattern, 3) terraces,
4) channel of the main river (Calore River) and 5) alluvial fans.
The geomorphological analysis of the escarpments
has pointed out that, in the study area, degraded faultscarps (here referred as DFS) frequently occur. The
partly-tectonic origin of such escarpments has been confirmed both by field evidence of faulting and by morphometric features, these latter strongly contrasting with
those of the scarps of exclusively erosional origin (i.e.
paleo-fluvial scarps).
The analysis of the hydrographic network, which is
mainly of rectangular-type, has highlighted the occurrence
of several subsequent reaches of streams. These latter are
usually aligned and/or parallel to the DFS. This suggests
that subsequent reaches of streams probably flows on the
generating faults of DFS, nowadays buried by scree talus
deposits deriving from the dismantling of DFS.
The study of the geometry of the Calore River channel
has pointed out that, locally, sharp steepenings of the
riverbed are associated with increases of the sinuosity of
the channel. According to literature data, this is a typical
river response to longitudinal tectonic deformation.
The analysis of the terraces, performed by means of a
projected longitudinal profile, has highlighted displacements both of the I and II order terraces and of the upper
stratigraphic boundary of the Middle Pleistocene alluvial
deposits of Calore River. Along the inferred faults responsible of such displacements, subsequent reaches of
streams have been recognised.
For the entire valley, geological and geomorphological evidence (e.g. geometry and distribution of the abandoned meander scars, tilted alluvial strata, anomalies of
the geometry of the alluvial fans) strongly suggest a
downtilting towards the south or south-east, except for
the central sector which has been probably tilted towards
the north or north-west.
By means of a combination of such data, a map of the
frame of faulting interesting the study area has been
obtained as a final result. The resulting tectonic frame is
quite conformable with the one proposed by the other
authors, which have utilized different methodologies.
So, we can conclude that the morphotectonic framework of the Telesina Valley inferred in this paper confirms the presence of tectonic activity which could have
played, at least from the Middle Pleistocene, a significant
role in the geomorphological evolution of the valley outline.
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Received 26 July 2005; revised version accepted 7 December 2006.