Tectonic history of the Lagonegro Domain and Southern Apennine thrust belt evolution

TECTONOPHYSICS ELSEVIER

Tectonophysics 252 (1995) 307-330

Tectonic history of the Lagonegro Domain and Southern Apennine thrust belt evolution Ennio Marsella a’* , Albert0 W. Bally b, Giuseppe Cippitelli ‘, Bruno D’Argenio d, Gerard0 Papponed a Geomare Sud, Istituto di Geologia b Department of Geology and Geophysics, ’ Via Jannozzi 38, S. Donuto ’ Dip.

Scienze

della

Terra,

Marina de1 CNR, Napoli, Rice University, Houston, Milanese, Milano, Italy

Universitir

Federico

II, Napoli.

Italy Texas,

USA

Italy

Received 24 August 1994; accepted 15 March I995

Abstract The tectonic history of the Lagonegro Domain in Southern Italy is an intriguing topic for the Mesozoic Mediterranean paleogeography and is important for reconstructions of the Tethys. Previous interpretations postulate the paleogeographic position of a deep Lagonegro-Molise-(Sicilide) basinal domain between the external Apulia carbonate platform to the east, and the internal Apenninic carbonate platform (i.e. the Albumo-Cervati-Maddalena Mountains) to the west. A second and separate deep basin more to the west was the home of the Liguride units which cover extensive areas of the Southern Apennines. Following an extensive review of previously published concepts and on the base of the structural interpretation of the Southern Apennines thrust belt using additional subsurface data and extensive field mapping, the authors now suggest that all deep basinal units of the Southern Apennines, i.e. the Ligurides, the Lagonegro units and the Molise-Sicilide units, derive from internal areas located to the west with respect to a coeval wide carbonate platform-slope-shallow-basin complex which, in its pre-Middle Miocene reconstruction, extended from Apulia well beyond the present-day Tyrrhenian coast of Southern Italy. The basinal units were first assembled as an accretionary wedge and overthrusted during the Late Miocene over the carbonate platform-slope-shallow-basin complex. The Liguride-Lagonegro-Molise-(Sicilide) accretionary wedge was later cut by an envelopment thrust which overthrust the previously underlying platform complex over the previously emplaced complex accretionary wedge. Our hypothesis in part revives an old concept proposed by Selli (1962) and requires further testing and research. We conclude that paleogeographic reconstructions of the Southern Apennines and the Mediterranean Tethys are still in a state of flux. 1. Introduction

The reconstructed position of the Lagonegro Domain of the Southern Apennines has been in con* Corresponding author. OGK- 19.5 l/95/$09.50 SSDI

0040.195

0 1995 Elsevier 1(95)00097-6

Science

B.V.

All rights

reserved

tention for many years. D’Argenio (1984) has vividly described the vicissitudes of the Lagonegro over the last one hundred years. D’Argenio et al. (1993) have updated the record by detailing some of the new concepts for the Southern Apennines. It is only fitting to remind the reader that this year (1994) is

E. Marsello

I;*& 4.3. - hiunc ,~rolog~rn ~-I~cmnIic.~ Pollino (Scala 1:2oO.ooO). Fig. I Two geologic section by De Lorenzo Mt. Alpi and the Mt. Pollino.

(1896)

et (II./

7‘ectonophysic.s

dcl II.>P;IIO Jcl I;un~c SIIIII;, across

the Lagonegro

the centennial of the classic ‘Le Montagne Mesozoiche di Lagonegro’ of De Lorenzo (1894). For this reason we begin this paper with two cross-sections (Fig. 1) and a tectonic map (Fig. 2) published somewhat later by De Lorenzo (1896).

Fig. 2. Tectonic map by De Lorenzo direction of axial planes of the folds

in

252 (1995)

(I 896) showing the main the Lagonegro nappe.

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~ticlla I,~u~.~,,~,,, trn II Al. Alpc

area in the Southern

Apennines.

c II g’“,‘,“’

Note the structural

Jcl ,\l position

of the

During the first half of this century the Lagonegro series was the subject of intensive controversy between autochthonists and allochthonists which culminated with the memoir of Selli (1962) who proposed the widespread allochthoneity of the internal Lagonegro series which, together with other units, where part of a large gravitational thrust complex (see also Scandone, 1967; D’Argenio and Scandone, 1970). Subsequent papers (e.g., Scandone, 1972; D’Argenio et al., 1973; Catalano et al., 1976; Sgrosso, 1983, Sgrosso, 1986) attempted to develop a number of paleogeographic schemes which all placed the Lagonegro unit in a more external (i.e. eastern) position as one and/or part of several basins that were located between carbonate platforms (for details see D’Argenio et al., 1993). An interesting reconstruction that shows the Lagonegro as a southeast-facing embayment of the eastern margin of the Apulian promontory is offered by ClermontC (1982). A very recent and most significant contribution by Mostardini and Merlini ( 1986) presented for the first time a set of deep regional geological cross-sections across the Southern Apennines, based on magnetic surveys, seismic reflection profiles and numerous wells drilled in the context of the exploration for hydrocarbons. The authors of that synthesis suggest that an igneous and metamorphic Paleozoic base-

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et ul./Tectonophy.sics

ment is not involved in the deformation of the Southern Apennines. Most importantly, Mostardini and Merlini suggest that all the deep basinal allochthonous units (i.e. Lagonegro, Molise-Sicilide units) form part of a large allochthonous mass that was originally located between an internal Apenninic platform and an external Apulian platform (itself subdivided into a mostly outcropping eastern platform and a western platform in the subsurface) (see also: Pieri, 1966; Ogniben, 1969; Pescatore and Tramutoli, 1980). Two variations on the overall theme introduced by Mostardini and Merlini were published later. Casero et al. (1988) proposed that the basement may be involved in an ‘out of sequence’ manner, without actually offering any direct evidence for basement involvement. Hill and Hayward (1988) include some crude!y balanced cross-sections across the area and follow the progressive emplacement of a Liguride accretionary prism over the Southern Apennines. More recently, Marsella et al. (1992) re-evaluated the previous work and concluded that the combined Lagonegro-Molise-Sicilide originated in a deep water basin located to the west of the combined calcareous Apennines-Apulia platform complex. In this perspective the basinal units were ‘enveloped’ or ‘involved’ by the allochthonous western carbonate units after their emplacement as a complex accretionary wedge over much of the carbonate complex. This concept re-emphasizes that basinal ‘Lagonegro-Molise-Sicilide-Liguride’ type units can be found both under (e.g., Ietto, 1963, Ietto, 1965; Scandone, 1967, 1972; D’Argenio et al., 1973; Turco, 1976; Mostardini and Merlini, 1986) and over the western platform units (e.g., Ferranti and Pappone, 1992; Marsella et al., 1992; see also Ietto and Barilaro, 1993). Note that in effect Marsella et al. (1992) return to the position originally proposed by Selli (1962) without, however, invoking gravitational gliding as a tectonic emplacement mechanism. A more internal position of the Lagonegro Domain is now also accepted by Patacca et al. (1992b) and by P. Scandone (pers. commun., 1993) on the base of partly different arguments. The wider importance of the Lagonegro problem is illustrated by various reconstructions of the Tethys. Early reconstructions by Laubscher and Bernoulli 11977) and Bernoulli et al. (1990) positioned the

252 (1995)

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Lagonegro Domain during the Early Mesozoic between the Apulian platform and the Central Apennine carbonate platform. The recent reconstructions of Dercourt et al. (1992) suggest that the Lagonegro basin developed from a minor appendix of the Permo-Triassic Tethys (see Fig. 3) w h’ic h cu t s into the ApeMines across the present position of the Gargano Peninsula. During the Late Jurassic and Early Cretaceous this trough eventually links with the Liguride basin. In alternative reconstructions, Stampfli et al. (1991) and Stampfli and Pillevuit (1992) still depict the Lagonegro as a Paleotethys appendix during the Late Permian, this time however with a Neothetys already forming in the Eastern Mediterranean. In this conception the Late Permian deep-water faunas reported by Catalano et al. (1988, Catalano et al. (1991) would correlate directly with the Lagonegro trough. D. Bernoulli (written commun., 1994) emphasizes the overall similarity of the Lagonegro with other sequences reported from the Eastern Mediterranean (e.g., Pindos, M ammonia units and Hawasina unit of Oman). Thus a review of the structural setting of the Lagonegro series should help to evaluate the many published reconstructions of Tethys. In the context of this introduction, it must also be mentioned that Boccaletti et al. (1990) have offered some valuable maps that depict the progressive Neogene development of the Apennine foredeep which was emplaced on the extension of the Apulian and Apennine carbonate platforms. More specific reconstructions of the development of the Southern Apennine foredeep are proposed by Patacca et al. (1990) Finally, a few words about extensional tectonics are in order because recent studies emphasize its importance (D’Argenio et al., 1987; Oldow et al., 1993). It turns out that in this segment of the Apennines, low-angle normal faults (LANFs in D’Argenio et al., 1987) commonly are responsible for a structural omission of stratigraphic units up to few kilometers. Associated with the LANFs are tilted blocks due to rotational displacement which are frequently observed together with widespread cataclastic textures that suggest deformation under low-confining pressure. In many instances, a strong structural discordance also characterizes thrust surfaces reactivated in extension.

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In addition to the previously known (e.g., De Lorenzo, 1896) extension, the above-cited authors now observe substantial longitudinal pre-Quatemary extension in the Southern Apennines. Kinematics and geologic relationships are best explained with the longitudinal extension of the Late Cenozoic arc of the Southern Apennines (Oldow et al., 1993).

te Anisian 237 - 234 M.A.

Late Cenomanian

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In this process, regions close to the thrust front were subjected to foreland-directed shortening, while the more internal parts, that were incorporated earlier in the folded belt, were first extended longitudinally, thus increasing the length of the arc prior to much of the Pleistocene high-angle normal faulting (HANF). Consequently, both high- and low-angle normal faults

’

94 - 92 M.A.

Fig. 3. In these recontructions by Dercourt et al. (I 992), the Lagonegro trough (Z,nT) is positioned between the Apulian platform (A) and the Central Apennine carbonate platform (AU). It develops from a minor appendix of the Permo-Triassic Tcthys, into a significant trough which eventually links up with the Liguride basin during the Cretaceous.

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have played an important role in the tectogenetic processes that dissect previously stacked masses of allochthonous thrust sheets (D’Argenio et al., 1987; Oldow et al., 1993). We have also to mention the recent studies on paleomagnetically determined rotations (Incoronato and Nardi, 1987; Channel1 et al., 1990; Oldow et al., 1990) and strike-slip tectonics (Ghisetti and Vezzani, 1983; Russo and Schiattarella, 1992; Cinque et al., 1993; Monaco and Tortorici, 1994) which provide an interesting scenario for the most recent evolution of the Southern Apennines. Despite the large amount of stratigraphic and structural data collected in the last 20 years, we admit that we do not yet have detailed sections illustrating the structural setting of the Southern Apennines at an adequate scale. New information is expected to be published in the near future from the deep seismic sounding performed in the context of CROP (Deep Crust Project), a joint venture of the CNR (National Research Council), AGIP, ENEA and ENEL. In the last years the Mesozoic carbonate and basinal sequence (Wood, 1981; Miconnet, 1983; Marsella, 1988; Ciarapica et al., 1990; Pappone, 1990; Amodeo et al., 1991) as well as the elastic Tertiary and Quaternary deposits, have been defined or redefined (e.g., Sgrosso, 198 1, 1988; Perrone and Sgrosso, 1982; Bonardi et al., 1985, Bonardi et al., 1988a; Santo and Sgrosso, 1987; Amore et al., 1988; Patacca et al., 1990, Patacca et al., 1992a). Of special interest for the tectogenetic models are the papers on the Tertiary and Quatemary elastic deposits. The Tertiary sedimentary basins and the ages of their often syntectonic depositional sequences need to be analyzed to understand the progressive development of both foredeep and satellite (piggy-back) basins. Typically, the most recent papers (e.g., Santo and Sgrosso, 1987; Amore et al., 1988; Patacca et al., 1990, Patacca et al., 1992a) provide data which tend to assign a younger age to the Late Tertiary carbonates and the elastic deposits that directly overlie the Mesozoic platform sequences. This does not only post-date the Neogene compressional development of the Apennine Chain, but also has an impact on the regional structural revision. In a nutshell this paper attempts to sum up the

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present status of the Lagonegro basin in the perspective of Marsella et al. (1992). Rather than proposing yet another solution, this paper is to be viewed as a progress report and an attempt to redefine some of the problems that need to be addressed.

2. Structural

units of the Southern Apennines

Traditional ‘stratigraphic-structural’ subdivisions are based on a concept which assumes that structural units ought to be characterized and defined by their own stratigraphic facies (e.g., the ‘isopic zones’ of earlier geologists, the ‘cylindristic’ elements of alpine geologists and the ‘terranes’ of younger generations). Perhaps the term ‘lithotectonic assemblage’ may be more appropriate, but we prefer not to engage in a semantic discussion of the ‘true’ meaning of various terms and here we simply will refer to ‘units’ of the Campania-Lucania Apennines. We are acutely aware that the definition of a regional structural unit by its facies is geologically unrealistic and that it would be better to define units as fault-bounded entities which may or may not involve different facies. Our experience is that structural trends (i.e. thrust and folds trends) are often strongly oblique to facies trends. On the other hand, it is also clear that different structural styles often reflect facies-controlled ductility distribution changes within the stratigraphic column. Because the whole thrust of geologic work in the Southern Apennines was mostly based on facies models we have little choice but to rely in this review on the traditional units. This state of affairs may change in the future with a more focused structural analysis of the area. A greatly simplified lithostratigraphy of the basic units of the Southern Apennines is graphically summarized on the clearly self-explanatory Table 1. Of course the reader of the voluminous geological literature will find numerous divergent opinions and therefore the table is meant to serve only as a guide that reflects an approximate consensus. A very problematic point in describing the Neogene units of the Southern Apennines is when deposits, which could be considered as belonging to the ‘true’ foredeep sequence, begin to onlap the already

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er al. / Trctonophy.sic.s

r

AGE

a

lithostratigraphy

ilento and Satellite Basins

of the basic

units

of the Southern

Apennines

BASIN Ligurides *

Hialus Marl or argillaceous carbonate

307-330

nomenclature. In this paper all the Neogene formations will be reported in Section 3 (Foredeep and piggy-back basins) in the perspective of the current work of the researchers of the Southern Apennines. Fig. 4 is a schematic tectonic map showing the location and distribution of the main columns shown in Table 1. Fig. 5 shows the location of our structural sections and relevant wells on the background of Fig. 4. The map is a simplified version of the relevant portion of Sheet 4 of the recently issued Structural Model of Italy (Bigi et al., 1992). Fig. 6 is a set of cross-sections, which will be discussed later but which may also help the reader follow the description of the various tectonic units that follow.

deformed Lagonegro unit and the adjacent carbonate platform units. Perhaps it would be useful in a near future to distinguish (as suggested by C. Doglioni, written commun., 1995) the Mesozoic Lagonegro passive margin related sequence, from a Lagonegro Tertiary active margin related sequence, which may overlap, besides the Mesozoic pelagic sequence, also the eastern Mesozoic carbonate platform. So far most of the deposits related to this aspect are very well known with consolidated names in the geological literature of Southern Italy. For this reason, at this time, we prefer not to confuse this already complicated argument by introducing a new

Table 1 Simplified

252 ( 1995)

FORELANO

PLATFORM

S. Donalo *

w

Clay, shale Resedimenlcd carbonate

li;

Shallow water carbonate

DolornIle

E. Marsella

LEGEND

BASINAL

m

;~~;~liocene

0

Pliocene-Holocene “nd,“erent,a,d cO”tl”*ntal an* marine deposits

m

Miocene Satellite Basins 0rade.asa”dsto”eo. conglomera,er and tnYdsto”es. locally with r.sedimen,ad carbona,es B”d o,,stostromes

- Pleistocene

Base of Salellite Basins

m B.!

et al. /Tectonophysics

Lower M,ocene Numidian Reredimen;edq”arzareni,e

a

313

307-330

PLATFORM

UNITS

Molise (Upper Cretaceous ? - Upper Miocene) Variegatedclays and LiliCeO”Ssediment* werlaln by ca,carec.“s rere*im.“,~and Shales

Es

UNITS

Lower Miocene ca,caremtes and sllicIc1astIcsediments Calcareous Apennines Triassic-Paleogene Shallow water llmes,ones and re%dimen,ed caIcare”tte*

owty ,,mes,ones,rmtio,ari,e*,SiliCeLwS sediments, *hater and carbonat* r*sedime”tS 0

Flysch

(/I Fig. the LAG V =

252 (1995)

Ligurides (cretaceous - Late Oligocene) Ophioli,e.beer(ngmetaplite~ an* quatiiter with metatim**toneS Stratigraphic contacts

El

Do,cml,,erand *hallow water limeStOneS

Extensional faults

4. Schematic tectonic map showing the location and distribution of the main columns shown in Table text: A = Albidona; AA = Altavilla-Ariano; AC = Albumo-Cewati; B = Bulgheria; BR = Bradano; San Mauro; = Lagonegro; LIG = Ligurides; MA = Mt. Alpi; MS, P, SM = Mt. Sacro, Pollica, Verbicaro.

1 and rock local names quoted in C = Calvello; G = Gorgoglione; P = Pollino; SD = San Donato;

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Tecronophysics

2.1. External carbonate platform units The herein described units (see left half of Table 1) are in our view all parts of a large ‘carbonateplatform-and-basin-system’ domain that formed part of the Adriatic Promontory of the southern margin of the Tethys (e.g., Laubscher and Bernoulli, 1977; D’Argenio et al., 1980 and Dercourt et al., 1992). It may help to briefly discuss the notion of a ‘basinal’ unit that is merged within a single ‘carbonate platform and basin’ context. As elsewhere in the world most Mesozoic carbonate platforms have detrital aprons derived from the platform, and these often interfinger with pelagic basinal carbonates. In Italy the ‘transitional’ facies and their relation to the basinal facies had been

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described since the basic work of Renz (1936). Most recently such a transition has been described by D’ Argenio (1970, D’ Argenio (19741, Bernoulli (19721, Pappone (19901, Vecsei (199 11, Graziano (19921, de Alteris and Aiello (19931, Bosellini et al. (1993) and Eberli et al. (1993). It is difficult, however, to draw a clear line that separates these transitional and basinal carbonate facies from other presumably much deeper basinal facies that are represented by the reddish and varicolored argille scagliose and the radiolarites-ftanites and chert-rich sediments of the Molise and Lagonegro units of the Southern Apennines. In other words the term ‘basinal’ within a carbonate-platform-to-deep-slope oceanic context includes many different kinds of basinal associations with

Tyrrhenian Sea

Marina di Maratei

1

20KM

Fig. 5. Location of the structural portion of Sheet 4 of the recently

sections and relevant wells in the background of Fig. 4. The map is a simplified issued Structural Model of Italy (Bigi et al., 1992).

version

of the relevant

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transitions that are not always well defined. On the other hand, if one would include all deep-water series initiated during the Permo-Triassic and dominated by radiolarian series such as the Lagonegro, the Pindos of Greece and the Hawasina of Oman, a definition of a clearly oceanic domain becomes more obvious. With this understanding and knowing that, excluding the Apulian platform, most of our Mesozoic-Cenozoic units have been seriously deformed by widespread thrusting and later extension, we will briefly list the main units proceeding from east to west. 2.1.1. Murge-Gargano or the Apulian platjTonn unit This is the easternmost unit (D’Argenio, 1970, D’Argenio, 1974; Graziano, 1992; de Alteris and Aiello, 1993; Bosellini et al., 1993; Zappaterra, 1994). Its western subsurface extension is the lowermost unit of the area which in effect represents the autochthonous foreland of the Southern Apennines. Wells drilled in this unit are reported to have penetrated ‘Permian-Triassic’ red beds. The Mesozoic is represented by shallow platform to basinal carbonate deposits, at least 5 km thick, which outcrop for approximately 300 km from the Gargano Peninsula to the Salento area. Thick Triassic to Early Jurassic evaporites underlie much of this platform. A small Triassic evaporite and marly limestones outcrop at the Punta delle Pietre Nere (north of Gargano Peninsula) and are intruded by basic dykes of Eocene age. Much of the Jurassic and Cretaceous is in platform, slope and base-of-slope facies. Thin Paleogene and Late to Middle Miocene shallow-water calcarenites overlie this sequence. To the east and northeast (i.e. eastern Gargano) scarp deposits and basinal deposits have been reported, e.g., from the Aquila field offshore Brindisi (Schlumberger, 1987) and by de Alteris and Aiello (1993). This basinal facies eventually may merge with the ‘Ionian zone’ (southern Adriatic Sea) of Albania, while the platform zone would have an equivalent in the Sazana platform in that country. To the southwest, in the subsurface, the MurgeGargano platform passes into a scarp and basin realm (the Apulo basin, Mostardini and Merlini, 1986) which is overlain by the Early to Late Pliocene foredeep deposits of the Bradano trough (Casnedi et

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315

al., 1982; Casnedi, 1988). These deposits consist of several hundred to thousand meters of clays and conglomerates, which are interbedded with some olistrostromes. The Murge-Gargano platform and its western downdip subsurface extension has been affected by numerous tensional and/or transcurrent faults (see Mostardini and Merlini, 1986). The western downdip extension of the platform has been illustrated by Mostardini and Merlini (1986) on the base of numerous wells and the seismic information that was available to these authors (see also Fig. 6). In their interpretation the subsurface Apulian platform extends all the way to the Tyrrhennian coast with several duplex-type structures involving the downdip continuation of the platform. These structures include the hydrocarbon accumulation of Costa Molina (Schlumberger, 1987) which encountered Serravalian-Langhian calcarenites of the platform in overlying with Upper Paleocene to Upper Cretaceous calcirudites. Farther north similar duplex structures are found extending from the Monte Forcuso area to the Casoli-Bomba area of the Molise zone. The downdip westward prolongation of the Apulian platform and its Neogene duplex structures as proposed by Mostardini and Merlini has been accepted by most subsequent authors (Casero et al., 1988; Hill and Hayward, 1988; Cello et al., 1989; Patacca and Scandone, 1989; Lentini et al., 1990; Marsella et al., 1992). On its western margin the top of that platform would be found at a depth of approximately 7-8 km. 2.1.2. Monte Alpi unit This unit (Ortolani and Torre, 1971; D’Argenio et al., 1973) forms a mountainous outcrop area in the Basilicata (Lucania) region. It consists of approximately IOOO-m-thick Jurassic carbonates, overlain by a few meters of Early Cretaceous platform carbonates which in turn are overlain by a few meters of Paleogene and Miocene calcilutites and calcarenites that are unconformably followed by alternating conglomerates, sandy calcarenites and clays of Langhian to Messinian age (Miiller et al., 1988; Sgrosso, 1988; Patacca et al., 1992a; Taddei and Siano, 1992). 2.1.3. Monte Pollino unit This unit is lumped together by many authors with the Albumo-Cervati unit (D’Argenio et al., 1973; Bousquet, 1973; Ghisetti and Vezzani, 1983;

316

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Bigi et al., 1992; Ietto et al., 1992; Ietto and Barilaro, 1993; Monaco, 1993). In the context of this paper we prefer to identify this as a separate unit which may have a tectonic position between the nearby Monte Alpi unit and the Albumo-Cervati unit. The unit consists of some 2500 m of Mesozoic platform carbonates spanning from Late Triassic dolomites to Late Cretaceous platform carbonates overlain by a condensed sequence of a few meters of Paleogene calcilutites and calcirudites which underlie Early Miocene calcarenites. An unconformity separates this lower sequence from a < 50-m-thick sequence of marls and clays with intercalated silicielastics of Burdigalian to Langhian age. In the Mount Pollino area, the age of the upper portion of the elastic sediments (Civita Sandstone Fm.) is Serravallian (Patacca et al., 1992a). 2.1.4. Maddalena-Marzano unit This is the first platform unit of the calcareous Apennines which clearly overthrusts and overlies the allochthonous basinal Lagonegro-Molise complex (Ietto, 1963, Ietto, 1965; Scandone, 1967; Turco, 1976). The unit is prevalently formed by lOOO1500-m-thick Late Triassic-Liassic shallow-water carbonates which, according to most authors, are overlain by thin limestone breccias, calcirudites and calcarenites with reported ages ranging from Middle Jurassic to Maastrichtian and Paleogene. Major hiatuses are suggested (Scandone and Bonardi, 1967). (There are considerable doubts in our mind as to whether at least some of these hiatuses, besides being due to a slope environment, could be due to Late Neogene extensional omission.) Recent studies attribute the siliciclastic sediments, found at the top of the carbonate sequences, to the Late Tortonian (I. Sgrosso, pers. commun., 1992). 2.1.5. Alburno-Ceruati unit This unit (Scandone, 1972; D’Argenio et al., 1973; Bonardi et al., 1988b; Bigi et al., 1992) includes extended outcrops in the mountains from the Lattari ridge of the Sorrento Peninsula to the north, to include the Albumi and Cervati mountains to the south. Traditionally, the unit was believed to be the median part of a large carbonate-platform-and-basin system as it shows facies variations (shallow water, slope to basin) at different stratigraphic levels begin-

252 f 1995)

307-330.

317

ning since the Triassic. The typical sequence is formed by over 4500 m of carbonates ranging from the Late Triassic to the Late Cretaceous, whereby the Paleogene is less than 100 m thick. Discordantly overlying this unit is a thin formation of Early Miocene calcarenites, which still corresponds to the platform cover. Recent work (Sgrosso, 198 1; Perrone and Sgrosso, 1982; Santo and Sgrosso, 1987; Santo, 1988) have substantially postdated to the Late Miocene the age of the overlying siliciclastic deposits which form the sedimentary cover of the carbonate sequences. Thus in the Albumi sector, the Piaggine Flysch is of Tortonian age (Sgrosso, 1981; I. Sgrosso, pers. commun., 1992). 2.1.6. Capri-Bulgheria-Verbicaro unit This unit outcrops along the Tyrrhenian coast at the northern Calabria border, at Monte Bulgheria and on the Island of Capri and consists of over 2000 m of Triassic to Cretaceous platform, slope and baseof-slope sequences grading into thin Tertiary calcareous-dolomitic sequences either belonging to scarp and basin facies or to carbonate platform facies. Some of the sequences (M. Foraporta) are considered of restricted basin origin (Boni et al., 1974; De Alfieri et al., 1987) while others clearly show slope facies (Ietto et al., 1992; Ietto and Barilaro, 1993; Iannace et al., 1994). 2.2. Internal deep basinal units The following units, in our working hypothesis, were all originally located to the west of the previously described carbonate platform units, i.e. between the northern and southern margins of the Tethys realm. Some of them may have been deposited on attenuated transitional continental margin crust, others on oceanic crust. Our description proceeds from the present east to west. 2.2.1. Molise-Sicilide unit The definition and subdivision of this unit is complex and often confusing (Selli, 1962; Pescatore, 1965; D’ Argenio et al., 1973; Sgrosso, 1986; Sgrosso et al., 1988; Mostardini and Merlini, 1986; Casero et al., 1988; Amore, 1990; Patacca et al., 1992a, Patacca et al., 1992~). A good basic description of the

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northern part of this unit was given by ClermontC (1982). The unit occupies much of the Molise province and coincides with the Irpinian basin of Cocco et al. (19721, Pescatore (1978, Pescatore (1988), Perrone and Sgrosso (19821, Pescatore and Senatore (1986), who view this unit as a basin that was located in front and to the east of an already deformed stack of thrust sheets involving the Lagonegro, the Campania-Lucania platform and higher units. Note, however, that this in effect is also the unit which Mostardini and Merlini (1986) like to merge into a single basin that also includes the Lagonegro basin to the west. These authors, however, do not detail the precise stratigraphic relations between the Lagonegro and the Molise units. Patacca et al. (1992~) reviewed the stratigraphy of the northem portion of this basin in an extensive paper that summarizes the relationship of the Central and Southern Apennines. As we sense that the Sicilide units of Ogniben (1969) and the Molise unit are basically the same, we treat them as one entity. In the following we follow in part the description of Patacca et al. (1992~) which primarily concerns a region located to the north of the area represented on our map (i.e. the northern Molise). The Molise units (including the Daunia, Tufillo and Agnone units of Patacca et al., 1992~) are all underlain by chaotic, red to variegated clays with thin interbeds of radiolarian-rich sediments, partly with manganese nodules. The age of this unit is uncertain but Patacca et al. (1992c), much like Clermonte (1982), point out that the clays are overlain by Late Oligocene to Burdigalian red marls and resedimented calcirudites. Thus there is an informal consensus that the variegated clays including minor Upper Cretaceous and Paleogene calcarenites probably range in age from Late Cretaceous to Eocene. Earlier authors frequently mention the local occurrence of ftanites (i.e. radiolarian cherts) within the variegated clays of the Molise zone. Farther north in the Sangro valley one of these outcrops was described by Bally (1952, Bally (1954) under the name of the series of Taranta. Recent studies of these rocks suggest an Early Cretaceous age (F. Roure, oral commun., 1988). The point here is to emphasize that future studies may have to renew focus on the paleontology of all radiolarian rocks in the Molise zone. In this context note also that ‘coaly’ layers associated with these ftanites are

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some of the richest petroleum source beds analysed in the laboratory and that their organic metamorphism is practically in a ‘lignite’ stage, i.e. they had little overburden throughout their history. Overlying the variegated clays are widespread Miocene sequences which include prominent turbiditic calcarenites and calcirudites alternating with marls which typically range in age from Burdigalian to Tortonian. Patacca et al. (1992a) also point out that Numidian-type quarz-arenites of Langhian age occur in this sequence. Finally and still according to Patacca et al. (1992~1, the northern Molise units are discordantly overlain by a pre-evaporitic early Messinian flysch sequence. In the specific area shown on our map (Fig. 41, the Molise zone corresponds to what many authors include in their Sicilide units. Here these are made up by a group of sequences, Middle Cretaceous to Early Miocene in age, generally discontinuous and poorly outcropping. The complete sequence is formed by: more than 500 m of varicolored clays, argillaceous marlstones and calcarenites; approximately 1000 m of marlstones, argillaceous marlstones and calcarenites passing upward to sandstones and calcarenites (Corleto-Perticara Fm., A.A.); approximately 500 m of varicolored clays and calcarenites; more than 300 m of tuffites, marlstones and limestones (Tusa Tuffites Fm., A.A.) (see also: Ogniben, 1969; Pescatore and Tramutoli, 1980; Carbone et al., 1988). Based on their stratigraphic positions, a large part of these sequences has been correlated in recent years to the Upper Cretaceous-Lower Miocene portion of the Lagonegro units and attributed to Lagonegro Flysch Rosso Formation (Geological map of Southern Apermines, by Bonardi et al., 1988b; Pescatore et al., 1988). 2.2.2. Lagonegro unit Classically, six main intervals have been distinguished in the Lagonegro sequence (Scandone, 1967, Scandone, 1972; Wood, 198 1; Miconnet, 1983; Marsella, 1988; Ciarapica et al., 1990; Marsella et al., 1991; Amodeo et al., 19911, spanning from Triassic to Cretaceous and Early Tertiary. From bottom to top: The Monte Facito Formation consists of terrigenous deposits, fine to coarse re-sedimented carbon-

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ates associated with large limestone blocks, nodular limestones, radiolarites, tuffites, and partly of resedimented terrigenous material of Permian age. The age ranges from middle Scythian-Anisian to middle Carnian. The thickness of this formation is not easy to establish, but it is probably not less than 300 m (Scandone, 1967; Wood, 1981; Miconnet, 1983; Ciarapica et al., 1990; Marsella et al., 1991). The Cherty Limestone Formation is made of limestones and dolostones with chert levels and nodules, resedimented micro-breccias, slumping and slump breccias (middle Carnian to Rhaetian). The overall thickness varies from 200 m to 500 m. Slumps and debris-flow deposits become dominant at the top of the Cherty Limestone Formation and help to define a ‘transition zone’ (Marsella, 1988; Amodeo et al., 1991). The Radiolarite Formation consists of silicified marlstones and shales, radiolarites and resedimented interbeds of silicified carbonates of deep-water origin. At the present time, the age of this interval is not clearly defined, even though it is generally believed to be Jurassic p.p. (Lias-Malm, Scandone, 1967, Scandone, 1972; Miconnet, 1983; Marsella, 1988). The Flysch Galestrino Formation consists of sometimes graded limestones, siliceous marlstones, shales as well as calcarenites and calcilutites, with rare quartz-arenite beds (Upper Jurassic-Lower Cretaceous). The thickness is variable and may reach some hundred meters. The Flysch Rosso Formation is represented by two members: a lower, siliceous-calcareous marly member, about 250 m thick, of Late Cretaceous to Late Oligocene age, and an upper, marly-argillaceous member, 100 m thick, of Late Oligocene to Langhian age (Scandone, 1967, Scandone, 1972). The Lagonegro is topped by Numidian Flysch with quartz-arenites, at times reaching a thickness of several hundred metres. These sediments are regionally present in the study area. Patacca et al. (1992a), recently attributed these sediments to a Langhian large-scale depositional event, which also occurred in the foredeep basin. 2.2.3. San Donato unit The San Donato unit (Amodio Morelli et al., 1976; Ietto and Barilaro, 1993) outcrops in the coastal

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chain of northern Calabria and to the southwest of Monte Pollino. The formation consists of metamorphosed (greenschist facies) Middle Triassic terrigenous deposits with massive organogenic limestone lenses overlain by undifferentiated limestones. The stratigraphic thickness is about 2000 m. A few meters of Neogene siliciclastics overlie the uppermost part of the sequence (Patacca et al., 1992a). We share in this paper part of the concept of Ietto et al. (1992) and Ietto and Barilaro (1993) who suggest that this unit is formed dominantly by Triassic sediments showing striking similarities to the less metamorphosed Lagonegro sequence and that it belongs to the same paleogeographic domain. 2.2.4. Liguride units These are due to the deformation of paleogeographic domains that in our view were probably located in zones that were originally still more ‘internal’ relative to the Lagonegro Domain (Ietto et al., 1965, Ietto et al., 1983, Ietto et al., 1985; Vezzani, 1968a, Vezzani, 1968b, Vezzani, 1968c, Vezzani, 1970; Ogniben, 1969; Amodio Morelli et al., 1976; Zuppetta et al., 1984; Bonardi et al., 1985, Bonardi et al., 1988a, Bonardi et al., 1993; Amore et al., 1988). No doubt the Ligurides are the most controversial unit of the Southern Apennines. Parts of the Liguride units are locally known as ‘Cilento flysch’ (Ietto et al., 1965). Most of the authors believe that these units originally formed on an oceanic crust, from which, at times, shreds of the original basement were preserved in the form of ophiolitic fragments. The lithologies of these units are prevalently black shales, siliciclastic and carbonate sediments, partly affected by low-grade metamorphism. Their age is between the Late Jurassic and the Early Tertiary. Among the most important formations we only mention here: Frido Fm., Episcopia-S. Severino Melange, Timpa delle Murge ophiolites; Crete Nere Fm., Saraceno Fm., and other sequences whose lithologies are strongly reminiscent of Sicilide units and of the Liguride units of the Northern Apennines. Note that the Ligurides are unconformably overlain by sedimentary sequences which are described by Amore et al. (1988) as the turbiditic Cilento group which has yielded Late Burdigalian to Langhian faunas at its base. We share, in this paper, the point of view which

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considers the Ligurides as part of an accretionary wedge overthrusted above the carbonate units (see Cello et al., 1989; Knott and Turco, 1991; Monaco and Tortorici, 1994). 3. Foredeep and piggy-back basins Resting on the previous units are a variety of more or less deformed elastic deposits which were involved in the thrusting process. These sequences include elastic sediments as well as subordinate carbonates and evaporites which were deposited in foredeep and/or piggy-back basins of a Late TertiaryPleistocene age. In our description we describe only the major units, proceeding from west to east. 3.1. Cilento basin Up to 2000-m-thick turbiditic siliciclastic and catbonate sequences outcrop in the Cilento area (Torrente Bruca Fm., Pollica Fm., and S. Mauro Fm.) and at the Calabria-Lucania boundary (Albidona Fm.) (Ietto et al., 1965, Ietto et al., 1983, Ietto et al., 1985; Bonardi et al., 1985, Bonardi et al., 1988a). The age of these units ranges from late Burdigalian to Langhian-Serravalian. The Cilento is a satellite basin which unconformably overlies the Ligurides (Bonardi et al., 1985, Bonardi et al., 1988a; Amore et al., 1988) and part of the Lagonegro units. The unconformable contact is marked by a basal conglomerate which contains pebbles derived from crystalline rocks, carbonate platform deposits and from the Lagonegro domain. 3.2. Irpinian basin Two main groups are described in this paper in the Irpinian basin (sensu Cocco et al., 1972; Pescatore, 1978; Pescatore and Senatore, 1986). A first group is represented by the ‘Gorgoglione Flysch’ with its approximately 1500-2000 m of non-stratified conglomerates, clays and pelitic-arenaceous and arenaceous-conglomeratic deposits (Selli, 1962; Boenzi and Ciaranfi, 1970; Pescatore, 1978; Patacca et al., 1990; Catalan0 et al., 1994). The ‘Gorgoglione Flysch’ stratigraphically overlies both the Cilento (Albidona Fm.) and the Lagonegro units (see Geological Map of the Southern Apennines, edited by Bonardi et al., 1988b). In the past the age of the

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‘Gorgoglione Flysch’ was considered Langhian-Tortonian (Boenzi and Ciaranfi, 1970; Pescatore, 1978) but it has recently been assigned a younger, Tortonian age (Patacca et al., 1990). A second group, the ‘Castelvetere Flysch’, is formed by a few hundred meter thick sequence of Tortoniar-Messinian age (Patacca et al., 1990) which is characterized by large limestone boulders and blocks (at times reaching dimensions of millions of cubic meters) embedded in arenaceous and conglomeratic deposits which may well rest unconformably on carbonate platform units (Maddalena-Marzano or Albumo-Cervati) or other basinal units (see Bonardi et al., 1988b). 3.3. Altavilla-Ariano

basins

The Altavilla satellite basin (Formazione Gessoso-Solfifera Auct.) developed after latest Tortonian-Messinian tectonic phases and includes two sedimentary cycles. The lower cycle is formed by clayey sandstones, diatomites and evaporitic limestones of lagoonal to brackish marine facies, reaching some hundred meters of thickness. The upper cycle is separated from the lower one by clayey olistostromes derived from internal tectonic elements, and is characterized by clays and evaporites, sandy conglomerates and sands of shallow marine to deltaic facies (some hundred meters in thickness). The Ariano basin also includes two sedimentary cycles formed by clays, sands and conglomerates of regressive marine to continental facies, several hundred meters in thickness. These were deposited during the Early-Middle Pliocene in large interconnected basins, extending over partly emerged Apenninic structures. A large part of the above-described sediments are equivalent to the Torrente Braneta and Ariano sedimentary cycles, of latest MessiniarZanclean age, of Patacca et al. (1990). 3.4. The Sant Arcangelo, Caluello, Potenza basins These basins include terrigenous deposits (clays, sands and conglomerates) that are some hundred meters thick and fill an intramontane depression of Middle-Late Pliocene to Early Pleistocene age (Caldara et al., 1988). Most of these sediments corre-

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spond to the Atessa sedimentary sequence, Piacenzian-Quaternary in age, of Patacca et al. (1990). 3.5. Bradano

trough

This unit developed during the Pliocene-Early Pleistocene in the updip part of the foredeep. It is formed by several hundred to a few thousand meters of clays, sandstones, conglomerates and interbedded olistostromes (Casnedi, 1988; Casnedi et al., 1982).

4. Structural

cross-sections

The structural cross-sections of Fig. 6 are a modified version of three sections previously published by Mostardini and Merlini (1986). We decided to use these sections as a starting point because we share with these authors the idea that the basement is not involved in the Neogene deformation of the Southern Apennines, a point supported by the published magnetic maps of Italy which suggest a very deep basement that has no obvious relationship to the surface and near-surface geology of the area. Note that an ‘igneous-metamorphic’ magnetic basement of either Paleozoic or Precambrian age has never been encountered in wells in Southern Italy (see also a similar discussion about the basement of the Central Apermines in Bally et al., 1986). We re-interpreted the sections of Mostardini and Merlini (1986) using additional subsurface data published in the last years and our extensive field mapping in the Lagonegro area. Mostardini and Merlini (1986) did not balance their cross-sections because the paucity and mediocre quality of seismic data did not justify such an effort. We agree with their judgement but nevertheless we made a ‘symbolic’ effort to crudely balance at least the lower platform-involving structures on our cross-sections. We also agree with these authors that for all practical purposes the Molise (Sicilide and/ or I rpinian units) were formed in the same basinal area as the Lagonegro units. The palinspastic restorations of our re-interpreted cross-sections, however, imply, other than in Mostardini and Merlini (1986), that both the Molise and the Lagonegro units were originally located to the west of the Albumo-Cervati-Bulgheria platform in the same deep sea that was also the home of the Lig-

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uride units. Thus, we visualize that basinal units which included the Molise, the Lagonegro and the Liguride units, were involved in a complex accretionary wedge which during the Late Miocene-Early Pliocene was emplaced over the Apulian-Albumi platform and its downdip western continuation. In this perspective, outcrops and wells that show overthrusts of platform facies over basinal facies are typically interpreted as envelopments of basinal units by originally deeper platform units. Note that some geologists would consider the term ‘out of sequence’ to be equivalent to our use of the term ‘envelopment’. For some terminological comments on this topic see also Ghisetti et al. (1993). Specifically our sections, like their predecessors (Mostardini and Merlini, 1986), show the Apulian platform and its basement (the Adriatic promontory of various authors) dipping gently westward under the Southern ApeMines. Overlying it is an accretionary wedge involving the basinal sediments of the combined Molise-Sicilide, Lagonegro and Liguride units which in fact fills the foredeep. In other words, the same foredeep which is filled with thick Neogene sediments all the way from the latitude of Pescara to the PO Plain, farther to the south is mostly filled with an accretionary wedge! Note that on our sections the downdip extension of the Apulian platform is shown with a uniform stratigraphy showing a constant thickness. This is only a convenient but unrealistic simplification based on very few wells. In fact some seismic profiles suggest that the Apulian platform sequences may thin towards the west into a slope facies farther downdip. In other words, facies changes such as those recently described by Eberli et al. (1993) from the Maiella area to thwe north may well occur in the downdip Apulian subsurface. Also farther downdip and underlying the accretionary Lagonegro-Molise complex, a number of duplex-type structures are shown of which Costa Molina is a prominent hydrocarbon accumulation. We are aware that these structures are only vaguely recognizable on reflection seismic profiles, because like in the Northern Apemrines, the surface areas underlain by the chaotic and structurally complex basinal units do not easily yield good deep reflections that may be used for an interpretation. Note

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also on our sections that we accepted the assumption of a basal evaporitic dCcollement of probable Triassic age that underlies the whole system. Needless to say if the present d&collement level is most unlikely to maintain its thickness, we would expect evaporites to flow into the core of anticlines but, alas, the lack of good seismic data is not likely to give a good image of the dCcollement level. Poor seismic mappability in the Southern Apennines is one of the main reasons that prevents us from drawing more elaborate balanced cross-sections with their restorations. Unfortunately the industry is not using a combination of reflection seismic profiling with broadside refraction and wide-angle reflection techniques which was for many years used quite successfully in the Canadian Rocky Mountains (Keating, 1966). The combination of the techniques allows for a better determination of the top of highvelocity carbonate structures. Note that on our sections and in contrast to Mostardini and Merlini (1986) we ‘pinch’ off the Lagonegro unit at about 5-6 km depth below the Maddalena-Albumi-Cervati units. This unit itself overthrusts and envelops the combined LagonegroMolise accretionary wedge. Farther west and overlying the Albumo-Cervati unit we find a Liguride sequence of unknown thickness, that is overlain by the Cilento-flysch basin. Thus, on our section we see parts of the accretionary wedge overthrust by and therefore underlying the Maddalena-Albumi-Cervati unit, while other parts of the accretionary wedge are overlying the same unit. We are driven to that suggestion not only by the field work done in the Lagonegro area but also by the work of Ghisetti and Vezzani (1983), Bonardi et al, (198.5, Bonardi et al. (1988a), Amore et al. (19881, and Ietto and Barilaro (19931, in the western and southwestern portion of our map area. These authors, as well as the compilers of the Structural Model of Italy (Bigi et al., 1992) have inspired us with the idea that the combined Liguride-Frido units overlie the calcareous Apennines of the Albumi Mountains and their supposed continuation in the Mount Pollino area to merge farther east with the Molise (i.e. Sicilide) units. This picture is also shared by many authors for the Calabro-Lucano ApeMines as recently proposed, e.g., by Monaco and Tortorici (1994).

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Note that the three cross-sections on Fig. 6 appear to be incompatible with the relatively steep subduction postulated for this area by many authors (Boccaletti and Guazzone, 1974; Gasparini et al., 1982; Royden et al., 1987; Moretti and Royden, 1988). This problem is implicit in the cross-sections of Mostardini and Merlini (1986) and farther north in the regional profiles of Bally et al. (1986). A reconciliation of a steep westward-dipping subducted slab could imply widespread basement-involved deformation underlying the Apennines (see Casero et al., 1988) for which there is no support from the magnetic data (Arisi Rota et al., 1986). Another alternative would be a complex wedging mechanism by which the observed overall eastwardvergent ApeMines would be linked to the postulated westward-dipping subducted slab by an hypothetical, i.e. sofar unobserved, westward-verging decoupling system, that would have to override an actively spreading Tyrrhenian microplate.

5. Discussion and conclusions One of the main issues discussed in this paper is the position of the Lagonegro-Molise units with respect to the Apulian and other Apennine carbonate platforms. This position can be depicted from the palinspastic restoration which our cross-sections imPlY. A new paleogeographic map is not presented at this time, because the authors are still in the process of evaluating the surface and subsurface data to the north and south of the study area presented in Fig. 5 Most of the models proposed by different authors in recent years (Mostardini and Merlini, 1986; Casero et al., 1988; Hill and Hayward, 1988; Patacca and Scandone, 1989) accept the external (i.e. relatively more eastern) paleogeographic position of the Lagonegro basin suggested by the Neapolitan School from the early 70’s (D’Argenio et al., 19731, which considered the Lagonegro basin placed between a Campania-Lucania carbonate platform to the west and an Abruzzi-Campania carbonate platform to the east. Moreover the above scheme suggested a Molise basin even farther east that separated the AbruzziCampania carbonate platform from the Apulia carbonate platform.

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Marsella et al. (1992) propose significant modifications of the above models and place the Lagonegro basin farther west, i.e in a relative more internal position and to the west of the Campania-Lucania carbonate platform, a solution which is similar (at least in a gross palinspastic restoration) to that proposed by Selli (1962). The modification is based on field-research in areas where the carbonate platform and basin system units are in tectonic contact with the Lagonegro units (numbers on the Geological Map of Italy: 185 Salerno; 186 S. Angelo dei Lombardi; 187 Melfi; 199 Potenza; 210 Lauria). The authors did have limited access to seismic data which in their minds justified a re-evaluation of the past models. Important additional evidence is also derived from the evolution of terrigenous deposits that are contemporaneous with the shortening and which yield the age relations for the tectonic emplacement of the various units. The recent general assignment of younger ages to these deposits by many authors (Bonardi et al., 1985, Bonardi et al., 1988a; Amore et al., 1988; Patacca et al., 1990, Patacca et al., 1992a) also influenced us. Note in this context that the siliciclastic deposits of the Cilento units of late Burdigalian-Langhian (Serravallian?) age seal the tectonic contact between Liguride units and Lagonegro units (Bonardi et al., 1985, Bonardi et al., 1988a; Amore et al., 19881, e.g., in the Molitemo area. Moreover the Gorgoglione Flysch deposits (Irpinian basin domain of Pescatore, 1978; Pescatore and Tramutoli, 1980; Perrone and Sgrosso, 1982; Pescatore et al., 1988) of Tortonian age lay irregularly on the Cilento basin units (Albidona Formation) and on those stratigraphically higher portions of the Lagonegro units which were at that time already deformed. If we consider that the age of deformation of the Campania-Lucania carbonate platform units, outcropping west of the Lagonegro units, ranges from Tortonian (Album0 Cervati unit) to late Tortonian (Monti della Maddalena-Monte Marzano unit) (Santo and Sgrosso, 1987; Santo, 1988; Patacca et al., 1992a), it does not seem possible to deduct that the Liguride units (of accepted internal origin) overlapped the Lagonegro units (of supposed external origin) since late Burdigalian-Langhian times, skipping the Album0 Cervati and Monti della Mad-

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dalena-Monte Marzano units (of supposed intermediate origin), taking into account that the latter will be taken by deformation later on, in the late Tortonian. As previously reported (Marsella et al., 1992), we believe that the overthrust of the internal basinal nappes over the Apulian platform units and the downdip subsurface extension occurred after the Langhian-Serravallian and, in this segment of the chain, was completed in Messinian time during the deposition of the Castelvetere Flysch. The envelopment thrust that subsequently broke through the allochthonous and brought the Albumo-Cervati and other platform units on top of the accretionary wedge, took place after the Messinian and most likely before the Middle Pliocene. This coincides with the lack of Pliocene deposits in this sector of the chain in contrast to the extensive Pliocene outcrops in more external sectors (e.g., Ofanto valley, Bradano trough). In a nutshell, the most significant aspect of our model, which differs from previous propositions, is the contention that the Lagonegro-Molise units were first thrust over the Albumo-Cervati, the Maddalena-Marzano unit (at the time part of the foreland) and the internal parts of the Apulia foreland. Subsequently, envelopment thrust systems displaced the Albumo-Cervati unit into its present structural position in post-early Messinian times. We realize that ours is only one of many altemative proposals and hope that, at best, it may serve as a working hypothesis for further research. In this context we would like to first discuss some of the weaknesses we perceived with previous models and some of the very significant problems that we see with our own model. Traditional paleogeographies of the Napoli school-type that separate one or two basin areas for the Lagonegro-Molise units were focussed on the search for transitional and slope facies between platforms and on the separate location of a Liguride basin to the west. In this context relatively few regional or other detailed structural studies were made (Mauro and Schiattarella, 1988; Lentini et al., 1990; Torrente, 1990; Mazzoli, 1993; Sacchi et al., 1993; Pappone and Ferranti, 1995). While the traditional approach may have been reasonable, today it is most difficult to escape the impression given by Mostardini and Merlini’s (1986) section that these

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basinal units are now presenting themselves as a highly deformed complex accretionary wedge, the leading edge of which is visible on seismic profiles in the Bradano trough and across the Gulf of Taranto and farther south (e.g., Finetti, 1976; Cello et al., 1981; Rossi et al., 1983; Pescatore and Senatore, 1986). Assuming that the varicolored clays of the Molise zone, and the deep water assemblages of the Lagonegro were originally deposited on a much attenuated continental or even an oceanic crust, it remains difficult to visualize a single subduction zone which would involve first subduction of the oceanic Liguride substratum, then subduction of the more continental substratum of the Albumo-Cervati-Maddalena platform and finally subduction of the attenuated substratum of the Lagonegro Molise zone (as proposed by Pescatore and Senatore, 1986). An alternative which involves separate subduction zones for each basinal unit is also difficult to justify because it would have a complexity derived entirely from paleogeographic models that are not supplemented by structural studies (see also Malinvemo and Ryan, 1986; Royden et al., 1987). An apparent strength of the traditional models is that the calcareous components of turbidites deposited in various Neogene satellite basins that are superposed on the Lagonegro-Molisano may be derived from co-eval carbonates. Presumably these would have outcropped to the west (e.g., the paleogeographic scheme proposed by Pescatore and Senatore, 19861. We plan to further pursue the viability of our model because we realize that the new model may be structurally easier to grasp and because it allows to visualize the emplacement of a single - albeit very complex - accretionary wedge associated with a single subduction zone that first involved the subduction of oceanic crust and later the subduction of a limited amount of attenuated continental crust. We are aware of the fact that perhaps the greatest weakness of our proposed model is the enormous amount of detailed work done in the Southern Apennines which has resulted in an incredible proliferation of over five hundred formation names with fossil assemblages with ever-changing age assignments with various (often not specified) ranges of uncertainty. Some may sense that our quest for a

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simpler model may be naive but to us the complexities of the existing models remain unfathomable. Ietto and Barilaro (1993) have already pointed out the affinity of the somewhat metamorphic San Donato unit with the Lagonegro Series. They suggest that both units are overthrust by an allochthonous carbonate unit which extends from the calcareous Apennines to the north and includes the thick Monte Pollino carbonates. In this context we feel uncomfortable with the relatively thin Verbicaro unit which according to some authors represents slope facies tied directly to the much thicker Pollino carbonate platform sequence. We would like to suggest here that the influence of low-angle extensional faulting needs to be investigated. Furthermore in this context we do not quite understand the regional position of the Pollino unit which is commonly equated with the Albumi-Cervati unit. We simply wonder what relation the Monte Pollino unit may have to the projected downdip extension of Apulia. Perhaps we somewhat casually refer to the Lagonegro-Molise-Sicilide complex as an accretionary wedge, but actually we really do not fully understand the internal structural relation between the several Lagonegro sub-units, the Molisano (Sicilide) units and the Liguride units which to south of our area merge with the Molise (Sicilide) unit. The contrasting metamorphism between the Lagonegro and the San Donato needs to be addressed further. In our model the true structural nature of the many Neogene basins that are superposed on the Lagonegro-Molise accretionary wedge complex remains enigmatic. This may be in part a problem relating to nomenclature. Commonly, foredeeps or foreland basins elsewhere are directly superposed on the foreland platform without the intervention of an accretionary wedge between the platform and the overlying basin fill. Satellite basins (Boccaletti et al., 19901, i.e. the piggy-back basins of Ori and Friend (19841, are typically synorogenic basins that form within and on top of the folded belt. Some of these basins directly date the deformation of the decollement folds or thrust faults. Other satellite basins, however, appear to reflect the gravitational instability of the accretionary wedge (in excess of the critical taper) and effect the extensional system of the growth-fault type (e.g., Flinch, 1993). This type of basin in turn needs to be differentiated from

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post-erogenic extensional rifts which are already well-known from the Apermines. Finally, current nomenclature does not foresee extensive simple onlap of stratigraphic sequences on the accretionary wedge. A key nomenclatural question is whether one is to include an accretionary wedge as part of the foredeep basin fill or not. In any event we believe that the detailed local tectonic context of each individual satellite basin may need to be re-examined in an attempt to differentiate extensional, transtensional, compressional, transpressional, rooted or not-rooted satellite basins. In that context we particularly appreciate the paper by Patacca et al. (1990) which is an important attempt to address this problem area. The Neogene sequences associated with the satellite basin overlying the accretionary wedge often include re-sedimented carbonates, as well siliciclastic components. Our own model encounters difficulties with the origin of the carbonate components in these sequences and their area of origin. We admit that the traditional models with platforms interspersed between basins facilitate the conclusion that carbonate clasts are simply derived from the neighbouring platform. During an earlier life a similar proposition led one of us (Bally, 1952) to incorrectly assume that the whole Molise unit was essentially autochthonous! The problem we now have is to reconcile the paleobathymetry of an accretionary wedge with its relation to the paleobathymetry of foreland platforms which are in the process of ‘underthmsting’ the accretionary wedge. As mentioned earlier we have difficulties with one concept of the Albumi-Cervati-Maddalena platform carbonates sandwiched between a Liguride accretionary wedge and a Lagonegro-Molise-(Sicilide) accretionary wedge, whereby farther south to our area the Liguride wedge is directly superposed on the Molise-Sicilide units. Thus in the absence of platform carbonates incorporated within an accretionary wedge we have to search for other areas for the origin of the carbonate fragment in Neogene turbidites. We like to speculate that such an area may perhaps be available in a paleogeography which maintains a palinspastically reconstructed relatively undeformed Abruzzi-Lazio carbonate platform from where calcareous turbidites would originate and later were deposited in satellite

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basins overlying an accretionary wedge that is located to the south of that platform. Our discussion makes it obvious that a future generation of structural cross-sections on a larger scale will be needed to incorporate detailed surface observations, all subsurface data and the best possible reflection seismic profiles. In conclusion, we have difficulties with the traditional models but we also recognize substantial problems with our own model. This situation should provide fertile ground for new approaches. Among many of these, we see primarily the need for stratigraphic and structural work as follows: (1) While the stratigraphy of the Lagonegro units, the Molise-Sicilide units and the San Donato unit is already reasonably well described it would be desirable to evaluate a proposition that would in more detail correlate the stratigraphy of all three areas. Emphasis may be placed on the best possible dating of deep-water radiolarian faunas. (2) The often chaotic red and variegated clays are essentially undated. An attempt to obtain better dates of the radiolarian sequences and other pelagic sediments included in these clays may be most fruitful. (3) It is frequently not clear whether Neogene flysch formations that are either involved in or else overlying the basinal units of the accretionary wedge are pre- or synorogenic. As we and most other authors infer, these units are probably synorogenic. In this context it becomes important to carefully analyse the structural context of these basins, the nature of the basal discordance, the geometry of strata1 convergences and internal unconformities that may permit to evaluate the growth of compressional folds, extensional growth faults and possible diapiric structures. (4) We are keenly aware that during the Late Neogene much of our area has been extended in a longitudinal and a transverse sense (e.g., D’Argenio et al., 1987; Oldow et al., 1993). Some earlier authors have emphasized the possibility of strike-slip and oblique-slip faulting (e.g., Ghisetti and Vezzani, 1983; Russo and Schiattarella, 1992; Cinque et al., 1993; Monaco, 1993; Monaco and Tortorici, 1994). Its seems fairly obvious that widespread extensional tectonics are superposed on both basinal and platform units leading to stratigraphic omission and to

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structural thinning within many of the units here described. We therefore believe that detailed studies that attempt to unravel the importance of extensional tectonics are most important. (5) We have already mentioned the need for a new generation of large-scale (say 1:50,000 reduced to 1: 100,000) regional cross-sections based on detailed surface and subsurface data including the best possible reflection seismic data. Such a set of sections should be accompanied by longitudinal (i.e. strike) sections that would permit a better 3-dimensional understanding of the structures of the area. Of course many other approaches can be imagined! Most important however is that in our view the Southern Apennines offer a rich opportunity to document and test a number of different models. Our hypothesis is no more than a revived old concept (Selli, 1962) which we believe should be re-examined. The result of such a study may substantially modify paleogeographic reconstructions of the Tethys of the Central Mediterranean area. New reconstructions of the relative positions of the Paleotethys and the Neotethys during the Mesozoic will need to be based on the best possible regional structural profiles not only across the Southem Apennines but also across the Alpine system of Eastern Europe, the Eastern Mediterranean and adjacent Turkey. Acknowledgements This work was supported by CNR Geomare 1993 grants. We are particularly grateful for the support on the subsurface data acquisition we received from the Ente Nazionale Mine&o Idrocarburi Italiano, Sezione UMIG of Naples. We also wish to thank Ms. Chinjgu Liu for patiently and cheerfully redrawing most of our figures. We sincerely thank D. Bernoulli, M. Boccaletti, C. Doglioni and an anonymous reviewer for their comments which greatly improved the first version of this paper. References Amodeo, F., Molisso, F., Kozur, B., I99 I. Age of transitional

H., Marsella, E. and D’Argenio, interval beds from Cherty Lime-

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