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Home , Assoro, Barrafranca, Butera, Caltagirone, Caltanissetta, Centuripe

EGU Stephan Mueller Special Publication Series, 1, 211–221, 2002 c European Geosciences Union 2002

Plio- sedimentary facies and their evolution in centre-south-eastern : a working hypothesis

A. Di Grande and V. Giandinoto Dipartimento di Scienze Geologiche, Sezione di Geologia e Geofisica, Universita` di , Corso Italia 55, 95 127 – Catania, Received: 14 December 2000 – Revised: 26 April 2001 – Accepted: 12 June 2001

Abstract. This paper examines the distribution and evo- The lithostratigraphic, geometric and tectonic elements lution of the Plio-Pleistocene sedimentary facies in centre- suggest that the Plio-Pleistocene geological evolution in the south-eastern Sicily, especially around , and area examined is mainly tied to a large sedimentary episode . Sectors occur in this region (- which developed between the and the Selinuntian Enna-, --- with facies progradation to the South and South-East. A pos- , S. Michele di Ganzaria-Caltagirone-, Licata- sible scheme of interpretation could be the one proposed by ) where, in relation to the late Zanclean- / Grasso et al. (1997, 1998) and Lickorish et al. (1999) for the Selinuntian period, the sedimentary succession has different Licata area, which predicted the southward tectonic migra- lithostratigraphic characteristics. tion of the sedimentary basins without particular emergence. The area studied belongs to the Caltanissetta Basin, which In this development the eustatic variations of the sea level is a paleogeographical-sedimentary unit. From the Late Mio- show a clear effect on the borders of the basins. cene to the period it consisted of a dynamic fore- The peculiarities of the first two areas mentioned deep basin between the Hyblean Foreland and the Apennine- (Caltanissetta-Enna-Centuripe, Pietraperzia-Barrafranca- Maghrebian Trust front. Between the Early and Piazza Armerina-Butera) belong to two episodes of the periods this front advanced about 50 km sedimentary basin during its southward migration between southwards and south-eastwards. late Zanclean and Selinuntian times. The other two areas, The Plio-Quaternary lithostratigraphic sequence is mainly between Caltagirone and Licata, lying close to the front of represented by 11 units: Zanclean Trubi Fm, Pliocene Argille the Gela Nappe, record a further movement of the basin Brecciate Fm. (Pliocene Brecciated Clays-AB IV, V), Enna towards the South and South-East. Marls of the late Zanclean-Piacenzian, Centuripe Sandstones and Capodarso Calcarenites of the late Zanclean-Piacenzian, Geracello Clayey Marls of the Piacenzian-Selinuntian, Pi- 1 Introduction azza Armerina Sands of the Piacenzian-Selinuntian, Mt. S. Giorgio Marly Clays of the Selinuntian, Caltagirone-Niscemi In the south-eastern area of central Sicily (Fig. 1), up to the Sands of the Selinuntian, Terraced sediments of the Middle- western Hyblean border, prevalently Plio-Quaternary sedi- , Present day sediments. ments outcrop. The paleogeographical evolution has been There are three clear unconformities in the sequence, ex- characterised, since the , by the emergence of both cluding the one at the base of the quaternary terraced de- the Madonie-Nebrodi-Peloritani ranges and the central part posits. The first, of late Zanclean , is located above the of the Hyblean mountains. The first corresponds to the Trubi Fm., and developed immediately after the beginning of Miocene Apennine-Maghrebian thrust belt, the second to the the Enna Marls sedimentation; it has a synsedimentary char- northern sector of the Pelagian Foreland (Ben Avraham et al., acter and developed in a marine environment without emer- 1990). gence. The second, of late Piacenzian age, lies at the base of After evaporite deposition, there was a return the Geracello Clayey Marls, while the third (Selinuntian), is to fully marine conditions with the sedimentation of Zan- located at the base of the Mt. S. Giorgio Marly Clays. Mi- clean pelagic carbonates. This unit, in the main part of nor unconformities, probably of glacio-eustatic origin, are the Mediterranean area, presents a homogeneous lithology locally present. (marly limestones and calcareous marls containing an Zan- clean planktonic foraminifer association) showing condi- Correspondence to: A. Di Grande ([email protected]) tions of variable bathymetry but becoming deeper with time. 212 A. Di Grande and V. Giandinoto: Plio-Pleistocene sedimentary facies in centre-south-eastern Sicily

13E 14E 15E Sea Peloritani Mts. 38N Madonie-Nebrodi Mts.

Mt. Etna Mts. Enna Catania Caltanissetta G e la N ap Siracusa N pe Thrust Front Hyblean 37N Plateau 0 50 km

Caltanissetta Basin Fig. 1. Geographical map and location of the study area (Fig. 2). Figure 1. Geographical map and location of the study area (Fig. 2.) Afterwards, between the late Zanclean-Piacenzian and the els for the Italian area (C. N. R., 1975), this unit was consid- Selinuntian, the evolution of the sedimentary facies is associ- ered as a postorogenic sedimentation association following ated with tectonic-eustatic influence. These changes caused the Miocene paroxystic phase responsible for the formation the space-time alternation of pelitic and arenitic facies. The of the thrust belts in the Mediterranean area. evolution of these facies is sometimes interpreted as due to the occurrence of different sedimentary cycles correlated also In contrast, since the early 1980’s (Catalano and to tectonic events (Roda, 1966, 1967a, 1967b, 1968). Among D’Argenio, 1982; C.N.R., 1983; Bianchi et al., 1989; Ben these events, the south-east translation of the sediments with Avraham et al., 1990; et al., 1990, 1996; Butler et the substratum via movement of the Gela Nappe had impor- al., 1992, 1995; Catalano et al., 1993, 1996; Lickorish et tant consequences for the evolution of the succession. al., 1999), as previously suggested by Beneo (1958), Rocco The aim of this study is to propose a working hypothe- (1959), Roda (1967a), the orogenesis in the Sicilian area has sis on the basis of field analysis and already published data, considered as persisting until the Quaternary (Gela Nappe), synthetically outlining the lithological characteristics, the although with a lesser intensity than during the previous stratigraphic-geological setting and the tectonic-structural phases, with compressive-translative and synchronous rota- evolution of the Plio-Quaternary succession, in the area be- tional movements (Catalano et al., 1977; Grasso et al., 1987). tween Enna-Caltanissetta-Licata and Caltagirone-Niscemi. The consequence is that the foredeep basin area between Also for the chrono-biostratigraphic aspects we referred to the Maghrebian-Apennine Chain and the Hyblean Foreland, some published studies, integrating with the direct check. evolved in time and space with the advancing Chain front. The results of the analysis show some areas characterised According to literature, this front is located a few kilometers by almost uniform lithostratigraphic elements and structural north of Caltanissetta-Enna-Centuripe (Figs. 1, 2) in the Late evidence. The sedimentary series, the vertical and lateral mi- . In the Early Quaternary it is located near the Gela- gration of the facies and the paleogeographical evolution of Caltagirone- alignment (Fig. 2); a forward move- each area, have been reconstructed. We also attempt a pre- ment of about 50 km to the south-east is therefore recognised, liminary correlation of the different areas and their evolution with a consequent reduction of the foreland domain. in time.

It seems that this forward movement did not occur contin- 2 Geological and Structural setting uously but through several events which brought about the gradual reduction of the foredeep. From the to The study area, located between the southern part of the the Quaternary therefore, different paleogeographical struc- Maghrebian-Apennine Chain and the western part of the Hy- tural units (Satellite Basins) sometimes considered “piggy- blean Foreland, belongs to the Caltanissetta Basin (Fig. 1). back” basins (Catalano et al., 1993; Vitale, 1996; Lentini et In geological literature, the dynamic-structural interpretation al., 1991) often complexly interrelated, interacted together of this basin, which represents a Late Miocene-Quaternary in the centre-eastern Sicilian area. Their location is often paleogeographical unit, has changed in time. From about the only approximate because it is difficult to define the precise 1960’s (Ogniben, 1960, 1969) until the first structural mod- boundaries. A. Di Grande and V. Giandinoto: Plio-Pleistocene sedimentary facies in centre-south-eastern Sicily 213

Nissoria

Villapriolo Centuripe

ENNA

CALTANISSETTA Mt. Capodarso S. Cataldo

Geracello

Pietraperzia

Barrafranca Piazza Armerina Ramacca

Terraced - Present day marine and continental deposits Mid. Pleist.- Unconformity (Middle Pleist.) Mazzarino Caltagirone Sands Selinuntian S. Michele di Ganzaria Mt. S. Giorgio Marly Clays Mt. S Giorgio Selinuntian Mt. della Scala Caltagirone Unconformity (Selinuntian ) Piazza Armerina Sands Piacenzian-Selinuntian Butera Geracello Clayey Marls Piacenzian-Selinuntian Mt. S. Nicola Niscemi Unconformity (late Piacenzian) Mt. dell’Apa Licata Centuripe Sandstone and Capodarso Calcarenites late Zanclean-Piacenzian Enna Marls Gela late Zanclean-Piacenzian N

01020km Argille Brecciate Fm. (AB IV, AB V Brecciated Clays) Unconformity (late Zanclean) Location of the stratigraphic sections of figure 3. Trubi Fm. Zanclean Axis of anticline a or anticlinorium a Faults: Overthrust and reverse faults b a) surface b) subsurface - Miocene Axis of syncline b Gela Nappe boundary or sinclinorium substratum Figure 2. Geological schematic map of the plio-pleistocenic lithostratigrafic units in the examined area. The tectonic elements are partially fromLentini et al. (1996) mod.. Fig. 2. Geological schematic map of the Plio-Pleistocenic lithostratigraphic units in the examined area. The tectonic elements are partially from Lentini et al. (1996) mod.

3 Plio-Pleistocene lithostratigraphic units arenaceous conglomeratic level is present (Arenazzolo). – Argille Brecciate Fm. (Brecciated Clays-AB IV, V ac- The stratigraphic succession exposed in centre-eastern Sicily cording to Ogniben, 1953, 1954). Grey-dark brown (Fig. 2) consists, from bottom to top, of the following infor- brecciated clays with diverse clasts including rare lenses mal lithostratigraphic units: a few meters thick of marly limestones or calcare- ous marls similar to Trubi Fm., and white marls. – Trubi Fm. Marly limestones and calcareous marls with These blocks are considered olistostromes of tectono- Globigerinidae prevalently of pelagic-neritic environ- gravitational (Ogniben, 1953, 1954; Rigo De Righi, ment, white, heavily fractured normal to the bedding. 1957) or tectono-diapiric (Monaco and Tortorici, 1996) They often contain yellow-reddish ferruginous concre- origin. They are considered marine, but, for the top lev- tions, and grade upwards into an alternation of grey els, it is not possible to exclude a continental genesis. marls and white marly limestones. Their age is Zan- clean, the upper part may sometimes (Mt. S. Nicola-Rio – Enna Marls. Marls and grey-blue clayey marls, cal- et al., 1994) extend into early Piacenzian. Locally, be- careous, white towards the base and yellow silt to- tween this Formation and the Messinian terms, a sandy- wards the top. Southwards their age gradually changes 214 A. Di Grande and V. Giandinoto: Plio-Pleistocene sedimentary facies in centre-south-eastern Sicily

from late Zanclean to -Selinuntian and they oc- – Caltagirone Sands (Selinuntian). Littoral yellow silty cupy the lithostratigraphic interval known elsewhere as sands with arenaceous lenses, in stratigraphic continuity Monte Narbone Formation, with reference to a deep with the Mt. St. Giorgio Marly Clays, passing in the up- marine environment of 500–1300 meters according to per part to sands, gravels and red conglomerates, proba- Rio et al. (1994). They often lie unconformably above bly of continental origin, associated to travertine levels. Trubi Fm. and sometimes on the older units. East of The thickness ranges from between 100 and 270 m in Enna (Assoro-Centuripe) they tend to be less calcare- the Caltagirone-Niscemi area to more than 400 m near ous. North of Centuripe they lie above Oligo-Miocenic St. Michele di Ganzaria, with a marked reduction to- terrains with transgressive arenitic-ruditic basal level wards the area of Gela (less than 40 m in Mt. dell’Apa). (0–70 m). Close to the old coast line they gradually de- Such variations in thickness, together with their age, velop into Centuripe-Capodarso arenites. suggest relationships of lateral heteropy with the Mt. St. Giorgio argillaceous sediments. – Centuripe Sandstones and Capodarso Calcarenites (Late Zanclean-Piacenzian). They show stratigraphic conti- – Terraced sediments. Near the present day coastline ma- nuity with the Enna Marls and quick heteropy, often rine arenites and rudites of the Middle-Late Pleistocene within very small distances, among themselves. On occur. These belong to various levels of terraces located the northern slope of the Centuripe hill these pliocenic up to a height of 80 m. Between Gela and Niscemi vari- sandstones and quartz sands are superimposed with ous levels of continental terraces are present, at the same stratigraphic continuity on the Enna Marls, while on the height as the marine ones. The series closes with marine southern slope there is a big lens (0–400 meters) of a and continental Present day sediments. clayey marly and silty-arenaceous interbedded alterna- tion. In the western part there are yellow bioclastic cal- carenites (Capodarso Calcarenites) on the Enna Marls. 4 Plio-Pleistocene facies areal distribution These two littoral units outcrop together along a curved area, about 4 km wide, extending from Centuripe to Cal- In the area examined, relatively to the late Zan- tanissetta and also in other areas. Immediately to the clean/Selinuntian interval, four sectors with different li- south of Caltanissetta-Enna--Regalbuto (Fig. 2) thostratigraphic characteristics were observed. These give they have a regressive attitude, while northwards they precise temporal and space information on the facies evolu- are superimposed transgressively on the oligo-miocenic tion. Some of them correspond to paleogeographical units. terms. This unit shows a maximum thickness of 300 m The relative lithostratigraphic sequences are illustrated in decreasing to the South and South-East. In the Capo- Fig. 3 which also shows, as in Fig. 4, the correlation ele- darso area this formation is referred to Middle Pliocene, ments. In the whole area the Mio-Early Pliocene substratum because of the heteropy with the upper level of the Enna shows constant lithostratigraphic and structural characteris- Marls, by Roda (1967b), to the same age by Catalano et tics and almost everywhere, except the area of Mt. St. Nicola, al. (1993) and to Early Gelasian by Vitale (1996). to the north of Gela, (Channel et al., 1992; Rio et al., 1994), the late Zanclean unconformity between Trubi Fm. and Enna – Geracello Clayey Marls. Clayey marls, marly clays and Marls is observable. silty marls. They are considered transgressive by Roda (1968) because they present a basal sand-gravelly level 4.1 Caltanissetta-Enna-Centuripe (First Area) and sometimes lie unconformably on older units. They are Piacenzian in age to the north, while southwards In the late Zanclean this area corresponded to the north- they are Selinuntian in age, belonging to the Mt. Nar- ern margin of the Caltanissetta Basin and was located be- bone Fm. (Rio et al., 1994). Sometimes they exceed a tween the southern front of the Maghrebian-Apennine Chain, thickness of 300 m. mainly characterized by uplift in the Pliocene age, and the foredeep, where subsidence prevailed at the same time. – Piazza Armerina Sands (Piacenzian-Selinuntian). Yel- The outcropping lithostratigraphic pliocenic sequence low sands with arenaceous levels, locally conglom- presents a complete sedimentary cycle which was involved erates, in stratigraphic continuity with the Geracello during the late Zanclean in a tectonic event responsible for Clayey Marls and showing a diachronous relationship the aforesaid unconformity between Enna Marls and Trubi of heteropy with the same. Their maximum thickness is Fm. It probably represents a synsedimentary event because it over 250 m (Piazza Armerina). is not possible to observe any coeval emergence in the zone. – Mt. St. Giorgio Marly Clays (Selinuntian). They out- Locally, the same event, controlled in places by submarine el- crop from Mt. St. Giorgio (Caltagirone) to Licata, along evated structures, influenced the direct superposition of Enna the valley of the Maroglio river and along the present Marls on the Miocene substratum. Sometimes the geometry day coastal area. In outcrops they rest unconformably, of the facies is altered by this tectonic event, with a consid- through a sandy silty level (50–200 cm), on marly clays erable variation in thickness. or on clayey marls referable to the Mt. Narbone Fm. The Leonforte-Centuripe area is characterised by a Plio- (Rio et al., 1994) aged from Piacenzian to Selinuntian. cene lithostratigraphic sequence with frequent lateral het- A. Di Grande and V. Giandinoto: Plio-Pleistocene sedimentary facies in centre-south-eastern Sicily 215 0 250 500 750 1250 1500 1000 ? Mt. dell’Apa Fourth Area Thickness (meters) (Di Geronimo, and Costa, 1978) Mt. S. Nicola Selinuntian unconformity ? ? ? ? C (Channel et al., 1992) Gela (Rocco, 1959) A B A B Niscemi (Roda, 1967 a) A B (Frazzetta, 1971) Mt. della Scala Third Area Early-Pleistocene “GELA NAPPE” alloctonous sediments A (Roda, 1967 a) Caltagirone

S. Michele di Ganzaria (Wezel, 1964) A

B

C

late Piacenzian unconformity hemicycle sedimentary Selinuntian B Butera (Roda, 1967 a) A A Barrafranca (Di Geronimo, 1969) Second Area (Roda, 1967 a) A late Zanclean unconformity Piazza Armerina A (Roda, 1968)

?

B Pietraperzia hemicycle sedimentary Piacenzian-Selinuntian (Roda, 1967 b) Caltanissetta Enna (Casale, 1969) ? Assoro First Area Prevalently not affected by “Gela Nappe” sediments? Nissoria (Di Grande et al., 1976) Regalbuto Unconformity (late Piacenzian) Unconformity (Selinuntian) Unconformity (late Zanclean) Piazza Armerina Sands Piacenzian-Selinuntian Miocene deposits Caltagirone Sands Selinuntian Centuripe Sandstone and Capodarso Calcarenites late Zanclean-Piacenzian Enna Marls late Zanclean-Piacenzian Trubi Fm. Zanclean Mt. S. Giorgio Marly ClaysSelinuntian with a sandy level (a) C B Argille Brecciate Fm. (AB IV, AB V - Brecciated Clays) A Geracello Clayey Marls Piacenzian-Selinuntian (a)

Centuripe

A

cycle sedimentary Zanclean-Piacenzian Correlation between stratigraphic sections known in literature correlated with the main Plio-Pleistocenic unconformities (A, B, C). Fig. 3. 216 A. Di Grande and V. Giandinoto: Plio-Pleistocene sedimentary facies in centre-south-eastern Sicily

Gela 0

Caltagirone

250 Caltagirone Sands

Mt. S. Giorgio Marly Clays Barrafranca 500 Thickness (meters) Piazza Armerina Sands Gela Nappe

Pietraperzia Geracello Clayey Marls

Enna Caltanissetta Capodarso Calcarenites AB V Enna Marls Enna AB V Marls AB V

Trubi Fm. Trubi Fm. AB IV Miocene deposits Miocene deposits

Fig. 4. CorrelationFigure 4. amongCorrelation the plio-pleistocenic among the plio-pleistocenic lithostratigraphic units lithostratigrafic on the basis of units Fig. on 3 elements. the basis In of agreement Figure 3 with elements. Ogniben, In 1953, agreement withOgniben 1953, 1954, the abbreviationAB corresponds to the Argille Brecciate Fm. 1954 the abbreviation AB corresponds to the Argille Brecciate Fm. (Brecciated Clays) and similarly AB IV corresponds to those associated (Brecciated Clays ) e similarlyAB IV corresponds to those associated with the Trubi Fm. and AB V to with the Trubi Fm., and AB V to those associated with Enna marls. those associated withEnna marls . eropies. The succession, emerging along the southern flank The Pliocene sequence shows a single complete sedi- (Di Grande et al., 1978; Carbone et al., 1990; Lentini et mentary cycle and the regressive hemicycle is generally al., 1991), consists of Trubi Fm. (0–70 m) sometimes over- strongly represented. Possible smaller unconformities ob- lapped by Argille Brecciate Fm. (Brecciated Clays-AB IV served within it (Catalano S., pers. comm.) suggest sec- according to Ogniben, 1953, 1954), Enna Marls (50–400 m), ondary sedimentary episodes. superimposed with unconformity and containing thin lev- Between Enna and beyond Caltanissetta, the Pliocene suc- els of Argille Brecciate Fm. (Brecciated Clays-AB V ac- cession shows a sedimentological and structural setting simi- cording to Ogniben, 1953, 1954), and Centuripe Sandstones lar to the Leonforte-Centuripe one, but with a larger calcare- (100–300 m). In the eastern part an additional argillaceous- ous sedimentary component. Besides the late Zanclean un- marly-arenaceous-silty alternation is present (Di Grande et conformity, smaller unconformities are observable at various al., 1978; Carbone et al., 1990). To the north, the Enna Marls levels, especially in the Capodarso Fm. (Vitale, 1996). At are replaced by the Centuripe Sandstones, and are superim- M. Sabbucina some lenses of Brecciated Clays are interbed- posed, directly or through a basal conglomerate, on Oligo- ded in the Capodarso Fm. It is not possible to exclude that Miocenic units. in this area the Piacenzian marine regression was quite com- plex with local transgressive episodes in a general regressive The distribution of the Pliocene units along the Leonforte- tendency. Centuripe ridge therefore suggests the presence, up to the late Zanclean-Piacenzian, of a paleocoastline with East-West direction close to Nissoria-Regalbuto and a rapidly deep 4.2 Pietraperzia-Barrafranca-Piazza Armerina-Butera basin, as is shown by the quick heteropy between arenitic (Second Area) and argillaceous sediments and by the thickness of the lat- ter. The synsedimentary unconformity between Trubi Fm. Located in the centre of the study area, it is characterised by and Enna Marls (Fig. 3: A unconformity) is associated with arenitic facies (Piazza Armerina-Butera Sands), prevalently erosion and the deformation of the Trubi Fm., increase of superimposed with stratigraphic continuity on pelitic facies the bathymetry of the basin and, moreover, a depression of (Geracello Clayey Marls). The age of the arenites here is all the ridge with consequent “transgressive” northward pro- Piacenzian-Selinuntian and the underlying argillaceous sedi- graded position of the Centuripe and Capodarso Fms. basal ments are more recent than in the previous area. The thick- levels. ness and the correlations are indicated in Figs. 3, 4. A. Di Grande and V. Giandinoto: Plio-Pleistocene sedimentary facies in centre-south-eastern Sicily 217

Near Barrafranca and Piazza Armerina two synsedimen- Terraced marine deposits of the Middle-Late Pleistocene tary unconformities are present, associated with two hia- are also present in this area. They are not affected by any tuses. The older, sometimes covered by Argille Brecciate tectonic movements. Fm. (Brecciated Clays-AB IV), is late Zanclean in age. The An important stratigraphic and structural element, for their younger lies between Piacenzian and Piacenzian-Gelasian bulk and rapid formation (Ogniben, 1 954; Monaco and Tor- sediments. Also in this area the pelitic sediments are more torici, 1996), are the considerable bodies of Argille Brecciate widespread towards the South and East, with considerable Fm. (AB IV-Brecciated Clays) at the level of the late Zan- variations and deepening of the facies in the same direction. clean unconformity (Grasso et al., 1997, 1998).

4.3 St. Michele di Ganzaria-Caltagirone-Niscemi (Third Area) 5 Plio-Pleistocene tectonics The Pliocene terrains distribution and their vertical and lat- This area is characterised by the superposition of Selinuntian eral relationships make it possible to recognise compressive, sediments (Mt. St. Giorgio Marly Clays and Caltagirone- extensive and transcurrent tectonic structures in the exam- Niscemi Sand) on the more southerly advanced front of the ined area (Fig. 2). The areas described correspond to zones Plio-Quaternary Allochthon (Gela Nappe). Around Calta- with a different stratigraphic and structural significance. girone this basal surface with unconformity is seen to lie After normal marine conditions resumed in the Zanclean, upon different levels of the Piacenzian-Gelasian (Malatesta the first tectonic episode, common to every area, involved and Torrente, 1954; Ruggieri, 1958; Roda, 1967a), by the the development of a general unconformity at the contact of absence of continental erosion and by the lack of recognis- the same Trubi Fm. with the Enna Marls. It was a synsed- able transgressive facies at the contact. The local outcrop- imentary episode, which caused basin deepening and early ping succession is shown in Figs. 3, 4. postdepositional sediment dislocation. Also in this area the generalised absence of some strati- In general the overthrusts (Fig. 2), which are a signal of graphic levels, recognised within the Piacenzian-Gelasian the southerly migration of the Apennine-Maghrebian front, sediments, and a marked unconformity, confirm (according mainly involve terrains older than the Piacenzian. Their to Beneo, 1958; Ogniben, 1960; Roda, 1967a, 1971; Lickor- outcrops are prevalently covered by younger Piacenzian- ish et al., 1999) a translation of the Mio-Pliocene sediments Quaternary formations. They have an East-West trend in to the East and South, with a revival of deep sedimentation the northern part and NE-SW in the southern one. Close in the Selinuntian. to the Hyblean area the latter orientation still prevails. It To the south-west of Caltagirone, in the areas with de- shows a possible evolutionary link between the Apennine- pressed morphology, terraced fluvial deposits lie above a va- Maghrebian Chain and the Hyblean Foreland. riety of sediments of the sequence. These are at the same Such tectonic episodes, which could be ascribed to the height as the Middle-Late Pleistocene terraced marine de- early Piacenzian, have remarkable intensity in the whole posits of the Gela-Licata coastal zone. Other portions of the area and their reactivation episodes are mainly responsible Pleistocene marine terraces are present in the depression of for the structural set around the Plio-quaternary sedimentary Caltagirone river. basins. In the contiguous foreland area (Hyblean Plateau) the tensional evolution became most intense during the Piacen- 4.4 Licata-Gela (Fourth Area) zian tectonic phase (Ghisetti e Vezzani, 1981; Grasso, 1993; Di Grande, 1997) and is linked to extensive basic eruptive Near Licata-Gela the youngest sedimentary levels involved activity (Beccaluva et al., 1993; Schmincke et al., 1997). in the Apennine-Maghrebian Front are present. In compari- In the first area (Caltanissetta-Centuripe) the most re- son with the previous area, this is characterised by the incre- cent outcropping terrains involved in the tectonics are of ment of pleistocenic argillaceous facies and by the presence the late Zanclean-Piacenzian age, so the respective struc- of Quaternary compressive structures which involve also the tures are younger. The upper chronological limit is uncer- postorogenic deposits of the Gela Nappe. Current official tain. The compressive tectonic controlled the development cartography (Carta Geol. d’Italia, 1955), Di Grande and in this area, from East to West (Fig. 2), of the Leonforte- Muzzicato (1986), Grasso et al. (1995) recognised the con- Centuripe Sinclinorium, which shows an axis made of three tinuity over 20 km of a reverse fault, which immediately to tracts sharply aligned East-West, the Villapriolo Sinclino- the north of Gela leads the Miocene over Selinuntian units. rium (Mt. Giulfo – Mt. Corvo) with the same axial direction, Considering the sediments involved and not involved, they the Capodarso Monocline with East-West orientated axis, can be dated as late as about the terminal Selinuntian age. and the Caltanissetta-S. Cataldo Sinclinorium with NE-SW In the Mt. dell’Apa area, Di Geronimo and Costa (1978) orientation. There are 5 major anticlinal structures with a observe a regressive sandy- sequence with a thickness mainly NE-SW axial orientation. of 150 m. Alloctonous Messinian evaporitic deposits are in- In the same Caltanissetta-Centuripe area there are nor- terbedded between clays and sands. This situation can be mal, reverse and transcurrent faults (Lentini et al., 1996) linked to a revival of the Gela Nappe, during the Selinuntian. (Fig. 2). The first are mainly present in the calcarenite 218 A. Di Grande and V. Giandinoto: Plio-Pleistocene sedimentary facies in centre-south-eastern Sicily blocks of the late Zanclean-Piacenzian; among the second with the base of the Geracello Clayey Marls in contact the M. Sacchitello reverse fault is very evident, connected to with the various underlying units; the third (C) is at the a overturned anticline, and located immediately SW of Enna, base of the Mt. S. Giorgio Marly Clays and is Selinun- where the Zanclean-Piacenzian terrains are also involved. In tian in age (Figs. 2, 3). this case too the chronological relationship between the two kinds of fault is not clear. The main dextral transcurrent – Minor discordances are visible in the whole series, first line, observed with an NW-SE direction, runs East from Enna in the upper part of the Enna Marls near Centuripe where it dislocates pre-Pliocene terrain. (Catalano S.: pers. comm.) and between Caltanissetta In the second area, apart from the overthrust described and Centuripe, in the Capodarso Calcarenites and Cen- above, the tectonic elements involve younger terrain, up to turipe Sandstones. In the Capodarso area, Catalano et the Selinuntian in age, and therefore their chronological lim- al. (1993) and Vitale (1996) report that the deposition of its (upper and lower) are more recent. The more impor- some beds was controlled by eustatic processes. Other tant compressive structures are the Butera Sinclinorium, with minor unconformities, with characteristics similar to the a NE-SW direction, and the Piazza Armerina Monocline, Caltanissetta-Centuripe ones, are located in the sands of which shows maybe a soft synclinal structure. There are nor- the Piazza Armerina-Butera area. mal, reverse and transcurrent faults (Lentini et al., 1996); the – During the entire period under consideration the area principal one is located between Piazza Armerina and Barra- studied shows a complete sedimentary cycle of the franca (Fig. 2). Zanclean-Piacenzian age, enhanced by a single synsed- Locally just to the North from Piazza Armerina, neptunean imentary tectonic event, and two regressive hemicy- dykes are present, aligned along pre-existing extensive fault cles could be detected, occurring respectively in the lines (Antolini, 1958). Piacenzian-Selinuntian and Selinuntian (Figs. 2, 3). In the third area the most important tectonic element is the buried front of the Gela Nappe and the corresponding – There is no field evidence of a true transgression, smaller structures. The Caltagirone-Niscemi highland and with continental erosion, among the three sedimentary the S. Michele di Ganzaria area are involved in intense and episodes referred to, while the start of the second and extensive tectonic movement. On the basis of the units in- third hemicycles is principally characterised by basal volved, the age of all the structures is Quaternary without discordances in marine environments. doubt. Around the Gela zone (the fourth area) the main structural – The Plio-Quaternary facies distributions have a NE-SW element, apart from the buried front of the Gela Nappe, is the trend, while they become gradually more recent towards wide overthrust, extending for about twenty kilometres and the South and South-East. overthrusting Mio-Pliocene terrains on to the Selinuntian. Its – The arenitic sediments remain prevalently on the age could be ascribed to the Selinuntian as it does not affect argillaceous ones, even if it is possible to observe re- the marine terraces of the Middle-Late Pleistocene (Grasso et ciprocal heteropies to the South. al., 1997, 1998). Another structural event is the reactivation of the Gela Nappe, which controlled the interfingering at Mt. – The only provable Plio-Pleistocene transgression rela- dell’Apa of Miocene deposits in the Pleistocene ones during tive to the Southern coastal stretch is demonstrated by the Selinuntian. terraced marine sediments of Middle-Late Pleistocene Along the western margin of the Hyblean area Plio- age. Quaternary tectonics are well developed. The activity is mainly linked to the Middle-Pliocene tectonic phase – In the Pliocene age, a production at various levels of (Ghisetti and Vezzani, 1980), showing a prevalently NE- clayey-breccia bodies (Argille Brecciate Fm.-AB III, SW direction, sometimes with transcurrent characteristics IV, V) of varying dimensions, must have modified the (Grasso, 1993; Di Grande, 1997). geometry of the sedimentary basins. – The bathyal facies of the more recent levels involved in 6 Elements for discussion the Gela Nappe are similar to the sediments lying on it. It is possible to assume a lowering of the basin towards The lithostratigraphic sequence and the geometric relation- East and South and a bathymetric reset by the translated ships between the formations show the following evolutive terrains. elements:

– There are three clear unconformities in the sequence (A, 7 Conclusions: paleogeographic evolution B, C in Fig. 3) excluding the one at the base of the qua- ternary terraced deposits. The first (A), of late Zanclean In conclusion a comparative study of the elements discussed age, is located on the Trubi Fm., and developed imme- suggests, as a working hypothesis, that the geological evolu- diately after the beginning of Enna Marl sedimentation. tion of the area examined is tied to a single large regressive The second (B), of late Piacenzian age, is associated sedimentary episode which occurred mainly from Piacenzian A. Di Grande and V. Giandinoto: Plio-Pleistocene sedimentary facies in centre-south-eastern Sicily 219

N Zanclean-Piacenzian foredeep S Piacenzian-Gelasian foredeep Caltanissetta- Enna Selinuntian foredeep Capodarso Fm.

Piazza Armerina- Pietraperzia

Enna Fm. Piazza Armerina Fm. S. Michele di Ganzaria- Caltagirone Geracello Fm. Caltagirone Fm. tatum Enna Fm. bs Su Gela ls ar Licata M M. S. Giorgio Fm. a B nn efore E Geracello Fm.

Enna Fm. M. S. Giorgio Fm. Plio-Pleistocene Folding Geracello Fm.

Enna Fm. Figure 5. Evolution hypotesis of the plio-pleistocenic sedimentary facies in the examined area using, with modifications, Fig. 5. Evolutionarythe schema hypothesis proposed of the Plio-Pleistocenic byGrasso et al. sedimentary (1997, 1998) facies and in the Lickorish examined et area al. (1999)using, with formodifications, the Licata area. the Theirschema proposed by Grassoprogradation et al. (1997, is 1998) related and to Lickorish the various et al. deformation (1999) for the events Licata area. which Their affected progradation the sedimentary is related to basin. the various The usedeformation of the events which affectedscheme the is sedimentary founded on basin. the facies The use and of age the of scheme the examined is founded area. on the facies and age of the examined units. to Selinuntian age with facies progradation towards the South – In the Piacenzian, in the southern and north-eastern part and South-East. A possible evolving scheme (Fig. 5), could of the basin, the arenitic facies (Centuripe Sandstones be the one proposed by Grasso et al. (1997, 1998) and Lick- and Capodarso Calcarenites) provide evidence of a ma- orish et al. (1999) for the Licata area, which foresees the tec- rine regression, while towards the North and North- tonic migration of the sedimentary basins to the South with- West the same facies, owing to eustatic and tectonic os- out substantial emergence. The glacio- eustatic variations of cillations, appear transgressive from late Zanclean. the sea level have a secondary character in this evolution but – These conditions remained till the Selinuntian, when show the clearest effects on the basin margins. The first two a sudden deepening of the southern and eastern mar- areas (Caltanissetta-Centuripe and Piazza Armerina-Butera) gin of the foredeep, together with orogenic reactivation developed two clear episodes of southward migration of the from the North, caused migration towards the South and sedimentary basin during Piacenzian-Selinuntian times. The East of the recently deposited terrains over the substra- other two areas, between Caltagirone and Licata, associated tum (Gela Nappe). The occasionally observed hiatus in with the front of the Gela Nappe, record a further movement the Late Pliocene argillaceous sediments (Di Geronimo, of the basin towards the South and South-East. 1969) may be an early signal of this event. The lithostratigraphic, geometric, tectonic and eustatic elements suggest an evolution summarised in the following – In the Selinuntian bathyal sedimentation recommenced episodes: intermittently and the Gela Nappe was reactivated; this event was followed, in the Selinuntian, by a general re- gression. – In the late Zanclean, at the end of the Trubi Fm. sedi- mentation, a tectonic episode resulted in the deepening – Just after the Selinuntian, the uplift commenced at of the sedimentary basin with deformation and synsed- a speed that can be calculated as about 0.2 mm/ imentary erosion. Bathyal sedimentation of the Enna (Cosentino and Gliozzi, 1988). Marls followed. In this context the direct superposition, with unconformity, of these marls on the units older than – During the Middle and Late Pleistocene there were var- Zanclean may be explained by sudden tectonism of the ious momentary sea level fluctuations with relative ef- bathyal environment and associated uplift. fects preserved up to the level of 80 m above the present day sea level. – Further marine withdrawals, linked to area uprising, – In the late Zanclean the production of a large body have continued up to the Present day. of clayey-breccia (Argille Brecciate Fm. (Brecciated Clays-AB IV), associated with the uplifting of the northern and north-western portion of the basin, con- tributed to the facies migration towards the South and South-East, with sedimentation of the Geracello Marly Acknowledgements. We wish to thank Martin Pedley and another Clays and the Piazza. anonymous reviewer for their useful comments and suggestions. 220 A. Di Grande and V. Giandinoto: Plio-Pleistocene sedimentary facies in centre-south-eastern Sicily

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