- Email: [email protected]
Lateral shifts of Apenninic foredeep depocentres reflecting detachment of subducted lithosphere
Earth and Planetary Science Letters 154 Ž1998. 203–219
Lateral shifts of Apenninic foredeep depocentres reflecting detachment of subducted lithosphere M.J. van der Meulen ) , J.E. Meulenkamp, M.J.R. Wortel Faculty of Earth Sciences, Vening Meinesz Research School of Geodynamics, PO Box 80021, 3508 TA Utrecht, The Netherlands Received 18 June 1997; revised 16 September 1997; accepted 16 September 1997
Abstract The hypothesis of lateral migration of slab detachment was formulated on the basis of seismic tomography results on the 3-D structure of subduction zones in the Mediterranean region wM.J.R. Wortel and W. Spakman, Structure and dynamics of subducted lithosphere in the Mediterranenan region, Proc. K. Ned. Akad. Wet. 95 Ž1992. 325–347x. The redistribution of slab pull forces associated with the tearing process is taken to affect foredeep development by adding a lateral component to internal–external depocentre migrations. In the case of the Apenninic Arc the direction of detachment and associated depocentre migration is expected to be southeast. This prediction has been confronted with the tectonostratigraphy of Oligocene to Recent Apenninic foredeeps. Results show there are two episodes marked by important lateral shifts of foredeep depocentres. During the early Late Miocene ŽTortonian. the depocentre of the Northern Apennines foredeep shifted towards the southeast. This is evidenced by the relative positions of the depocenters of the Burdigalian–Serravallian Marnoso Arenacea and the Tortonian Umbrian–Marchean and Lazian ‘‘Minor Basins’’. A further, stepwise southeastward migration can be inferred from the Plio-Pleistocene records of the Central and Southern Apennines. In a more general sense, our results indicate that slab detachment may play a significant role in the evolution of foredeeps along convergent plate boundaries. q 1998 Elsevier Science B.V. Keywords: Italy; Apennines; stratigraphy; geophysics; subduction; active margins; basin analysis; fore-arc basins
1. Introduction The Mediterranean region is the area of the convergent plate boundary zone of the African and European plates ŽFig. 1.. The western Mediterranean area includes the large extensional Balearic and Tyrrhenian Basins on the internal side of the Apenninic and Maghrebian Žp.p.. mountain belts. Since the extensional basin development occurred synchronously with the internal–external propagation of )
Corresponding author. E-mail: [email protected]
the adjacent fold and thrust belts w1–4x a genetic relation between the two processes is generally accepted w5,6x. The configuration of the western Mediterranean area is considered to be the result of the African–European collision in the Late Eocene and subsequent rollback, during the Oligocene to Recent time span. Recently new aspects of the structure of the upper mantle in the Alpine–Mediterranean region have been revealed by seismic tomography w7,8x, see also w9x. The seismic velocity structure of subducted lithosphere shows evidence for slab detachment under-
0012-821Xr98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 0 1 2 - 8 2 1 X Ž 9 7 . 0 0 1 6 6 - 0
204
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Fig. 1. Schematic map of the Central and Western Mediterranean.
neath the Dinarid–Hellenic and Apenninic Arcs. On the basis of this result Wortel and Spakman w10x formulated the hypothesis of lateral migration of slab detachment ŽFig. 2.. Since it is intrinsically impossible for seismic tomography to provide 100% confidence on the actual existence of slab detachment Žfor a contrasting view, see Amato et al. w11x., we follow the approach in which predictions of the tomography based hypothesis are tested against independent geological data. Slab detachment is considered to be a self-perpetuating process of lateral migration of a tear in the subducted lithosphere Žsee also w12x.. The present study focusses on the expected surface expression of the redistribution of slab pull forces associated with the tearing process. The transition from detached to continuous subducted lithosphere is marked by a zone of enhanced foredeep subsidence Žzone B in Fig. 2.. In the area which has undergone slab detachment the resulting decrease in slab pull forces leads to rebound Žzone C in Fig. 2.. When assuming that the excess subsidence is associated with increased
sedimentation rates, then slab detachment would introduce a lateral component to internal external foredeep depocentre migrations. The assumed relation between foredeep subsidence and sediment accumulation is in fact widely accepted and best illustrated by the well-known wedge shaped geometry of foredeep infillings in cross-sections perpendicular to the basin axis, reflecting the subsidence pattern inherent to the flexural deformation of the overridden plate. Meulenkamp et al. w13x tentatively invoked lateral migration of slab detachment to account for accelerating trends in rates of lateral depocentre migration as well as sediment accumulation for the Eastern AlpsrCarpathian foredeeps. In view of the higher resolution in the tomography results for the Apenninic region relative to those for the Carpathian region the former region is more suitable to serve as a test area for the hypothesis of lateral migration of slab detachment. Wortel and Spakman w10x hypothesised that the Adriatic lithosphere detached from northwest to southeast. If so, the surface effects of this tearing process should include a lateral compo-
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
205
Fig. 2. Graphical representation of the hypothesis of lateral migration of slab detachment w10x, and predicted surface effects.
nent towards the southeast in the migrations of Apenninic foredeep depocentres. This prediction will be confronted with the Oligocene–Recent tectonostratigraphic history of the Apenninic foredeeps. It must be kept in mind that throughout the Oligocene and most of the Miocene one can distinguish between a Northern and a Southern Apenninic tectono-stratigraphic history. The boundary between these two realms is the Anzio–Ancona line Že.g., w14x. which is shown in Fig. 4. If slab detachment has occurred, an overall trend in depocentre migrations can, however, be expected along the composite arc.
2. Apenninic foredeeps The studied Oligocene and Miocene Apenninic foredeeps have invariably been incorporated in the chain, and their depocentres have been located by the
analysis of published sediment accumulation data Žsee below.. The Plio-Pleistocene Apenninic foredeep, loosely defined in literature as the clastic wedge on the external side of the Apenninic chain w15x, has essentially been preserved as such, and its depocentres can be recognised from the seismic record w16x. The evolutionary history of the PlioPleistocene depocentres is inferred from sediment accumulation data from drillings w17x or from seismic stratigraphy w15,18x. In contrast to the OligoMiocene depocentres the Plio-Pleistocene depocentres often accommodate displaced extra- or intrabasinal units. The two sets of data allow a complete reconstruction of Oligocene to Recent depocentre migration patterns, because the top Miocene represents both the upper limit of Oligocene to Miocene foredeep sequences that can successfully be studied in outcrop within the chain, as well as an excellent seismic reflector at the base of large parts of the Plio-Pleistocene foredeep fill.
206 M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219 Fig. 3. Timetable used in this paper. Biozonationsrbioevents of Cita w20x, Crescenti w17x, Iaccarino w21x, and Lourens et al. w22x; converted to the Berggren et al. w23x timescale.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Depocenters have been incorporated in this analysis irrespective of their relative internal–external position within complex foredeep systems Žfor classifications, see e.g. w18,19x., because subsidence governed by deflection of the overridden plate may be reflected in sediment accommodation in any Žsub.basin within the subduction zone. So, in the context of this contribution foredeep must be read as foredeep sensu lato. In order to achieve coherency in the heterogenous set of data used, the most recent geological timescale has been used to attribute numerical ages to biostratigraphic events. The timetable used in this paper is given in Fig. 3, and shows the biozonationsrbioevents of Cita w20x, Crescenti w17x, Iaccarino w21x,
207
and Lourens w22x, converted to the Berggren et al. w23x timetable. 2.1. Oligo-Miocene foredeep sequences Fig. 4 shows the position of the Oligo-Miocene foredeeps and their depocentres d1 trough d5. In this figure basins have been combined in age groups because of complex stacking of the various units, as well as to facilitate the comparison between Northern and Southern Apenninic foredeeps. The subsidence of the Northern Apenninic foredeeps started in the Oligocene ŽRupelian., around 31 Ma B.P. when sedimentation began in the Macigno Basin, which now covers parts of Liguria, Tuscany
Fig. 4. Overview of Apenninic foredeeps. Compiled from many sources.
208 M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219 Fig. 5. Ža. Sedimentation rates for Northern Apenninic foredeep depocentres. Compiled from Boccaletti et al. w25x, Cantalamessa et al. w26x, Nardi and Nardi w24x, and Ricci Lucchi w18,27x. Žb. Maximum sedimentation rates for Southern Apenninic foredeeps. Compiled from Boenzi and Ciaranfi w28,29x, Palmentola w30x, Ciaranfi et al. w31x, Casnedi w32x, Pescatore et al. w33x, Lacasella et al. w34x, Loiacono w35x, Guerrera and Coccioni w36x, Ippolito et al. w37x, Pescatore w38x, Pescatore and Senatore w39x, Barbera et al. w40x, di Nocera et al. w41x, Santo w42x, Tortorici w43x, and De Pascale et al. w44x.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
fig. 5. Žc. Sedimentation rates for the ‘‘Minor Basins’’, sensu Centamore et al. w45x. Compiled from Angelucci w46x, Angelucci et al. w47x, Centamore et al. w45x, Bellotti et al. w48x, Boccaletti et al. w25x, and Cantalamessa et al. w26x. Depocentres are indicated in black Žsee text for explanation..
209
210
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
and Umbria. The thickness of the Macigno sequences varies along the Apenninic strike, and perpendicular to it Že.g., w24,25x.. The depocentre d1 of the basin is represented by the Macigno sequence of the Chianti mountains with a thickness of ; 3000 m w25x, yielding a Žuncorrected. sedimentation rate of ; 62 cmrky ŽFig. 5a.. In the Southern Apennines the Cilento basin and part of the Numidian basin developed w4x in response to the beginning of Apenninic tectogenesis. In the literature large discrepancies exist with respect to the dating of both these basins. The Cilento flysch has been attributed to the Cretaceous w39x, to the Eocene–Oligocene, and even to the Early Miocene w44x. The oldest datings would put it even before the start of the development of the Apennines; for that reason the Cilento flysch is not included in Fig. 5b. The Numidian flysch has been dated as Chattian to Burdigalian Že.g., w36x., and as Chattian to Langhian Že.g., w4,31x.. The present study does not aim to contribute to a discussion on the ages of the Numidian and Cilento flysches: in this context it is sufficient to establish the fact that any of the proposed ages for each of the flysches yield a lower sedimentation rate than that for the Northern Apenninic Macigno Basin. During the next stage in Northern Apennine foredeep evolution turbiditic sediments were deposited in the latest Chattian–earliest Langhian Cerverola Basin Ž24.0–16.1 Ma B.P.., which is now incorporated in the Ligurian, the Tuscan–Emilian and the Umbro– Marchean Apennines. The sediments of the Cerverola Basin have approximately the same lateral extent as the Macigno fill. The basin prograded over the former ramp of the Macigno Basin during and after the incorporation of the latter basin in the evolving Apenninic thrust belt. The greatest thickness Ž; 1100 m. of the Cerverola sequence has been observed in the Prato Magno area Žd2., yielding a maximum sedimentation rate of ; 10 cmrky Že.g., w25x.. Nardi and Nardi w24x, however, report a maximum thickness in approximately the same area Ž2000 m., which would yield a sedimentation rate of 18 cmrky. In the Southern Apennines the Numidian basin continues to exist up to the Burdigalian or Middle Langhian Žsee above., with sedimentation rates of ; 22 cmrky. The Marnoso Arenacea Basin Ž16–7.2 Ma B.P., Langhian–Tortonian., of which the sediments are
found in the Emilia–Romagnan part of the Apennines and in Umbria, was the next basin to develop in front of the advancing Apenninic nappes during and after the disruption of the Cerverola Basin by thrust activity. It has maximum sedimentation rates in the Emilian–Tuscan Apennines of ; 75 cmrky Žaveraged., with peak values of ) 100 cmrky Žd3. w26,27x. Southeast of the depocentre sedimentation rates vary between 40 and 60 cmrky w25x. North of the depocentre the Marnoso Arenacea was progressively invaded by the gravitationally displaced Ligurian allochthon w49x. In the Southern Apennines the Gorgoglione, Castelvetere, and Serra Palazzo flysches filled in various realms within the Irpinian basin, the new foredeep established after the disruption of the Numidian basin w38x. The Irpinian basin is contemporary with the Marnoso Arenacea Basin although there are some discrepancies with respect to its age. It started either in the Burdigalian w39x or in the Middle Langhian w4x. The disruption of the Irpinian basin has been dated at the Tortonian–Messinian transition by Patacca et al. w7x; Tortorici w43x presents biostratigraphical evidence for a Tortonian age of this event. Any of these datings, however, yield lower sedimentation rates for Irpinian formations than for the Marnoso Arenacea flysch in its depocentre. Pronounced reorganisations took place in the Central Apennines during the Tortonian, i.e. between about 11 and 7 Ma B.P. The southern Marnoso Arenacea Basin became disrupted and subsequently flysch sedimentation took place in narrow troughs w45,50x, the Umbro–Marchean ‘‘Minor Basins’’, sensu Centamore w50x. The depocentral area of the Marnoso Arenacea Basin does not undergo the same segmentation. However, a shallowing in this part of the foreland, preceded by a drop in sedimentation rate Žsee Fig. 5a and c. can be inferred from a facies change at ; 8 Ma. Turbiditic sediments with a fan lobe facies are overlain by marls w6x forming the top of the Marnoso Arenacea sequence with an upper fan to slope facies. These marls are in turn overlain by the Messinian shallow ‘‘Ghioli di Letto’’ marls w6x. The above-mentioned modifications in the Central Apenninic foreland basins are interpreted as the result of east verging thrust activity along the Anzio– Ancona line. At the external side of this renewed and now emerging segment of the Central Apenninic
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Fig. 6. Isopach map of the Plio-Pleistocene Apenninic foredeep. Modified from Ambrosetti et al. w16x.
211
212
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Chain small turbiditic fans developed in small, elongated Lazian ‘‘Minor Basins’’ Žsensu Centamore w50x.. The highest sedimentation rates, of ; 50 cmrky in these elongated basins are observed close to the thrust front in the Tagliacozzo Basin Ždepocentre d4 in Fig. 4.. The sedimentation rates in this basin exceed the rates in the contemporary Umbrian–Marchean Minor Basins, as well as in the remaining Lazian Minor Basins Žsee Fig. 5c.. In the Southern Apennines ambiguity in datings of the Late Miocene foredeep sequences does not allow a clear comparison with the Northern and Central Apennines Žsee Fig. 5b.. Either the top sequences of the Irpinian basin or the post-Irpinian successions are coeval with the Minor Basins sequences. Both possibilities would put the Apenninic depocentre Žindicated in black in Fig. 5c. in the Central Apennines, so age uncertainties do not seriously hamper this depocentre analysis. The Tortonian configuration formed the prelude to the next important stage in the development of the Apennines: the establishment of the Laga Basin Žde-
pocentre d5, indicated in black in Fig. 4. in the Messinian. Its 3000 m thick w25x fill is now to be found in the Abruzzi area. The considerable thickness of the Laga Basin fill yields a very high sedimentation rate of up to 200 cmrky, exceeding Žclastic. sedimentation rates in any other Messinian foreland basin. The Laga Basin is partly contemporary with the Minor Umbrian–Marchean basins, where sequences shallow and reach evaporitic conditions in response to the Messinian salinity crisis w4,25,26x. In the Lazian Minor Basins Early Messinian sandstones overlie the Tortonian turbidites w6,46–48x. The bathymetry and sedimentation rate in the Laga Basin apparently were so high that the effects of the Messinian salinity crisis were almost completely overprinted. Only a level of gypsum-arenitic turbidites is indicative of evaporitic conditions in the source area w3,26,45x. In the Southern Apennines marine evaporitic conditions are reached within the foredeep and clastic sedimentation was suspended for the duration of the salinity crisis Že.g., w4x..
Fig. 7. Sedimentation rates for Plio-Pleistocene depocentres. Compiled from Crescenti w17x, Ricci Lucchi w18x, and Ori et al. w15x. Central and Southern depocentres indicated in black Žsee text for explanation.. Thick black lines indicate the last occurrence of basin-modifying thrusts.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
2.2. The Plio-Pleistocene foredeep system The Plio-Pleistocene Apenninic foredeep shows four different depocenters, as recognised by the depth of the base of its infilling. In Fig. 6 these depocentres ŽA–D. are shown on a map and in a profile constructed through Žthe tipline of. the most external Apenninic thrusts. The depocentres have been num-
213
bered A through D. The northernmost, composite depocentre ŽA., has approximately the same lateral extent as the pre-Tortonian Northern Apenninic foredeeps. At this site the base of the Pliocene is located at a depth of up to 9 km. In front of the Central Apennines depocentre B occupies the same along-arc position as the Messinian Laga Basin. In the Southern Apennines two other depocentres ŽC and D. are
Fig. 8. Location of drillings used in this paper Žmodified from Crescenti w17x., to elaborate Plio-Pleistocene depocentre evolution.
214
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
present. The thickness of Plio-Pleistocene sequences at these locations is ) 6 km. Sedimentation rates ŽFig. 7. have been inferred from seismic stratigraphy of the Northern Apenninic w18x and for the Central Apenninic foredeep w15x, and from drilling data ŽFig. 8. for the Southern Apennines w17x. Sedimentation rates in depocentre A are consistently the highest observed. Local depocentres C, B and D develop successively, as indicated in black in Fig. 7. The Central Apenninic depocentre ŽB., positioned externally with respect to the Messinian Laga Basin had its main phase of infill in the Early Pliocene Ž) 3.3 Ma.. Depression C is mainly filled during the Late Pliocenerearliest Pleistocene Ž3.3–1.43 Ma., whereas the southernmost depocentre is essentially Pleistocene of age Ž1.43–0.8 Ma.. The age of the last occurrence of major, basinmodifying thrust events affecting Žsee w17x. PlioPleistocene depocentres B–D Žindicated with black lines in Fig. 7. shows the same southeastward shifting as the one observed for sedimentation rates. It should be noted that each of these events led to the displacement of intra- or extrabasinal units, which have to be accommodated by subsequent deflection of the foredeep substratum.
3. Analysis and discussion 3.1. Depocentre migrations Depocentre migration patterns for the entire Apenninic evolution have been reconstructed from the integrated study of the Oligo-Miocene and PlioPleistocene foredeeps ŽFigs. 8–10.. Depocentres of the Northern Apenninic Macigno, Cerverola and Marnoso–Arenacea Basins occupy approximately the same along-arc position: there is no lateral, but a clear internal–external component in depocentre migrations from the Middle Oligocene till the early Late Miocene ŽTortonian., i.e. from about 31 to 11 Ma B.P. In the course of the early Late Miocene the pattern of internal–external depocentre migration became interrupted. A major deformational event w45x led to the partial disruption of the Marnoso Arenacea Basin as well as to the formation of the ‘‘Minor
Basins’’ Žsensu Centamore w50x.. At the same time the locus of maximum deposition shifted laterally from the Marnoso Arenacea Basin Žd3. to the Tagliacozzo Basin Žd4 in Fig. 4.. During the latest Miocene ŽMessinian. the locus of maximum deposition was present in the Laga Basin Žd5 in Fig. 4. situated externally of the Tagliacozzo Basin. Thus, in the early Late Miocene the depocentre shifted to the Central Apennines and remained there throughout the Late Miocene, although internal–external propagation did occur. At the beginning of the Pliocene depocentre A ŽFig. 9. developed at approximately the same position along the Northern Apennines as occupied by the pre-Tortonian depocentres Žd1–3., and depocentre B Žsee Fig. 9. developed externally with respect to the Late Miocene depocentres d4–5. Depocentre A remained the locus of maximum deposition throughout the Plio-Pleistocene in the Northern Apennines, whereas in the Southern Apennines depocentre B was succeeded by the Late Pliocene depocentre C in the central part of the Southern Apennines. In the Early Pleistocene the maximum accumulation rates are found in the southernmost part of the Southern Apennines. Thus, the pattern of Rupelian–Serravallian internal–external as well as the Tortonian–Messinian lateral depocentre migrations appear to persist after the Messinian. It must be kept in mind, however, that the primary goal of this study was to identify zones of maximum subsidence. Local, excess subsidence Žas in Fig. 2, zone B. cannot be considered an exclusive mechanism to create foredeep depocentres, since accommodation space is not a limiting factor for sediment accumulation in deep turbiditic basins. Nevertheless, when taking into account the reconstructed basin configuration for the Late Miocene Northern Apennines, and the preserved configuration of the Southern Apenninic Plio-Pleistocene foredeep Žsee above., the laterally migrating depocentres appear to mark a laterally migrating zone of maximum subsidence. The residence time of the laterally migrating depocentres decreased in time from 7.6 Ma for the Central Apenninic depocentre Žcomposed of Late Miocene depocentres d4–5 and Early Pliocene depocentre B., to 2.2 Ma Ždepocentre C., and to 0.6 Ma Ždepocentre D.. This accelerating pattern is in
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Fig. 9. Longitudinal profile constructed along the tipline of the most external Apenninic thrusts, showing lateral depocentre migrations. For further explanation, see text.
215
216
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
qualitative agreement with the nature of the detachment process w10,12x. 3.2. Rebound It has been demonstrated that the approach chosen reveals a lateral variation of foredeep depocentres and tectonic activity which is in good accordance with the predictions from the hypothesis of lateral migration of slab detachment. In addition to lateral migration of foredeep depocentres, the hypothesis of slab detachment predicts dynamic rebound in areas
which have undergone detachment ŽFig. 2, zone C.. Evidence for the latter phenomenon can be inferred from sedimentary facies changes superimposed on the accumulation patterns as shown in Figs. 5 and 7. In the Northern Apennines late Tortonian regressive sequences of the Marnoso Arenacea foredeep in its depocentral area Žsee above., as well as in piggyback basins on the Ligurian allochthon w18x could indicate rebound after the depocentre shift to the Central Apennines. A early Late Pliocene Ž3.6 Ma B.P.. shallowing in the area of depocentre B can be inferred by the compartimentation of this part of the
Fig. 10. Map showing Oligocene to Recent depocentre migrations.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
basin by the emergence of previously submerged crests of blind thrusts w15x. This shallowing event is coeval with the depocentre shift from the Central Apennines towards the southeast. Marine sedimentation continues up to the earliest Pleistocene in depocentre C and up to the Middle Pleistocene in depocentre D Žsee Fig. 7.. These preliminary relations between depocentre migrations and uplift are shown in Fig. 11. When assessing the present configuration of he Apenninic foreland it is tempting to consider the deep depression of the Ionian basin Ž) 3000 m. to be the culmination of the surface effects of the detachment process Žas indicated tentatively in Fig. 9a, migration 3.. However, the Plio-Pleistocene fossil foredeeps are seated on the continental lithosphere of the ApulianrAdriatic platform, whereas the basement of the Ionian foreland consists of old ŽMesogean. oceanic crust: the differences in the properties of the foredeep basement are considerable and, without any doubt, their effect on the present configuration accordingly. Nevertheless, one cannot exclude that the great water depths in the Ionian basin can partly be attributed to the transferred weight of detached subducted lithosphere.
217
4. Conclusions This first order attempt to assess the role of slab detachment in the evolution of the Apennines showed that a clear pattern of lateral Žalong strike. migration of depocentres and associated tectonic activity exists from the early Late Miocene ŽTortonian. onwards. After a depocentre has shifted to a new locus, the previous locus is subjected to uplift. The combination of these patterns is good agreement with the predictions from the hypothesis of lateral migration of slab detachment. The Apenninic depocentres show punctuated in stead of gradual migrations, and may be the reflection of a punctuated tearing process at depth, or a punctuated surface response to a smooth tear propagation at depth. Whereas the good agreement between predictions and observations is obviously in support of the hypothesis of lateral migration of slab detachment, this does not imply that no alternative mechanisms are possible. If alternative mechanisms would appear to explain the observations equally well, further tests to discriminate between competing hypotheses will have to be developed to discriminate between them. The recognised axial trend in the development of
Fig. 11. Tentative scheme showing the relation between depocentre shifting, and uplift. Uplift after depocentre development is evidenced by: Ž A. regressive sequence w7x; Ž B . compartimentation of foredeep by blind thrust emergence w15x; Ž C . unconformity Žtop of sequence, see Fig. 8.; and Ž D . unconformity Žtop of sequence, see Fig. 8..
218
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
the Apennines can contribute to the understanding of aspects in the evolution of individual segments of the arc. The time frame provided can be used for specific further elaboration of the surface effects of the detachment of subducted lithosphere. Future research will focus on the reconstruction of vertical motions for selected parts of the Apenninic foreland, in order to refine our understanding of the relation between upper mantle and geological processes at the Earth surface. Since our approach has been process-oriented our results implicitly indicate that slab detachment is to be considered as a possible element in the evolution of foredeep systems along convergent plate boundaries, in general.
w6x
w7x
w8x
w9x
w10x
w11x
Acknowledgements E. Carminati, W. Spakman, P.Th. Meijer, J.H. ten Veen, M. Boccaletti and S.J.H. Buiter are acknowledged for discussion and suggestions. A.J. van der Meulen is acknowledged for critically reading the manuscript. We wish to thank the reviewers L. Jolivet and W.B.F. Ryan for helpful suggestions. This work was conducted under the programme of the Dutch national research school, the Vening Meinesz Research School of Geodynamics. MJvdM is financed by the Geosciences Foundation ŽGOA. of the Netherlands Organization for Scientific Research ŽNWO.. [RV] References w1x J.-P. Rehault, G. Boillot, A. Mauffret, The western Mediter´ ranean Basin geological evolution, Mar. Geol. 55 Ž1984. 447–477. w2x J.-P. Rehault, E. Moussat, A. Fabri, Structural evolution of ´ the Tyrrhenian back-arc basin, Mar. Geol. 74 Ž1987. 123– 150. w3x M. Boccaletti, F. Calamita, G. Deianan, R. Gelati, F. Massari, G. Moratti, F. Ricci Lucchi, Migrating foredeep–thrust belt system in the northern Apennines and Southern Alps, Palaeogeogr., Palaeoclimatol., Palaeoecol. 77 Ž1990. 3–14. w4x M. Boccaletti, N. Ciaranfi, D. Cosentino, G. Deiana, R. Gelati, F. Lentini, F. Massari, G. Moratti, T. Pescatore, F. Ricci Lucchi, L. Tortorici, Palinspastic restoration and paleogeographic reconstruction of the peri-Tyrrhenian area during the Neogene, Palaeogeogr., Palaeoclimatol., Palaeoecol. 77 Ž1990. 41–50. w5x A. Malinverno, W.B.F. Ryan, Extension in the Tyrrhenian
w12x
w13x
w14x
w15x
w16x
w17x
w18x
w19x
w20x
w21x
sea and shortening in the Apennines as a result of arc migration driven by sinking of the lithosphere, Tectonics 5 Ž1986. 227–245. E. Patacca, R. Sartori, P. Scandone, Tyrrhenian Basin and Apenninic arcs, kinematic relations since Late Tortonian times, Mem. Soc. Geol. Ital. 45 Ž1990. 425–451. W. Spakman, M.J.R. Wortel, N.J. Vlaar, The Hellenic subduction zone: a tomographic image and its geodynamic implications, Geophys. Res. Lett. 15 Ž1988. 60–63. W. Spakman, Delay-time tomography of the upper mantle below Europe, the Mediterranean, and Asia Minor, Geophys. J. Int. 107 Ž1991. 309–332. W. Spakman, S. van der Lee, R. van der Hilst, Travel-time tomography of the European-Mediterranean mantle down to 1400 km, Phys. Earth. Planet. Inter. 79 Ž1993. 3–74. M.J.R. Wortel, W. Spakman, Structure and dynamics of subducted lithosphere in the Mediterranean region, Proc. K. Ned. Akad. Wet. 95 Ž1992. 325–347. A. Amato, B. Alessandrini, G.B. Cimini, Teleseismic wave tomography of Italy, in: H.M. Iyer, K. Hirara ŽEds.., Seismic Tomography: Theory and Practice, Chapman and Hall, London, 1993, pp. 361–396. S. Yoshioka, M.J.R. Wortel, Three-dimensional numerical modeling of detachment of subducted lithosphere, J. Geophys. Res. 100 ŽB10. Ž1995. 20223–20244. J.E. Meulenkamp, M. Kovac, ´ˇ I. Cicha, On late Oligocene to Pliocene depocenter migrations and the evolution of the Carpathian–Pannonian system, Tectonophysics 266 Ž1996. 301–318. A. Castellarin, R. Colacicchi, A. Praturlon, Fasi distensive trascorrente e sovrascorrimenti lungo ‘‘linea Ancona–Anzio’’ dal Lias al Pliocene, Geol. Rom. 17 Ž1978. 161–189. G.G. Ori, G. Serafini, C. Visentin, F. Ricci Lucchi, R. Casnedi, M.L. Colalongo, S. Mosna, The Pliocene–Pleistocene Adriatic Foredeep ŽMarche and Abruzzo, Italy., an integrated approach to surface and subsurface geology, in: Adriatic Foredeep Field Trip Guide Book, 3rd E.A.P.G. Conf., Firenze, 1991, pp. 5–52. P. Ambrosetti, C. Bosi, F. Carraro, N. Ciaranfi, M. Panizza, G. Papani, L. Vezzani, A. Zanferrari, Neotectonic map of Italy, C.N.R., Quad. Ric. Sci. 4 Ž114. Ž1983. . U. Crescenti, Sul substrato Pre-Pliocenico dell’avanfossa Appenninica dalle Marche allo Jonio, Boll. Soc. Geol. Ital. 94 Ž1975. 583–634. F.R. Lucchi, The Oligocene to Recent foreland basins of the Northern Apennines, Spec. Publ. Int. Assoc. Sedimentol. 8 Ž1986. 105–139. G.G. Ori, P.F. Friend, Sedimentary basins formed and carried piggyback on active thrust sheets, Geology 122 Ž1984. 475– 478. M.B. Cita, Planktonic foraminiferal biozonation of the mediterranean Pliocene deep sea record: a revision, Riv. Ital. Paleontol. Stratigr. 81 Ž1975. 527–544. S. Iaccarino, Mediterranean Miocene, Pliocene planktic foraminifera, in: H.M. Bolli, J.B. Saunders, K. Perch-Nielsen ŽEds.., Plankton Stratigraphy, Cambridge University Press, Cambridge, 1985, pp. 283–314.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219 w22x L.J. Lourens, F.J. Hilgen, W.J. Zachariasse, A.A.M. van Hoof, A. Antonarakou, C. Vergnaud-Grazzini, Evaluation of the Pliocene to Early Pleistocene astronomical timescale, in: L.J. Lourens, Astronomical forcing of Mediterranean climate during the last 5.3 million years. Ph.D. Thesis, Utrecht University, Utrecht, 1994. w23x W.A. Berggren, D.V. Kent, C.C. Swisher, M.P. Aubry, A revised Cenozoic geochronology and chronostratigraphy, Soc. Econ. Paleontol. Mineral., Spec. Publ. 54 Ž1995. 129–212. w24x L.D. Nardi, R. Nardi, Schema stratigrafico e strutturale dell’Apennino settentrionale, Mem. Accad. Lunig. Sci. 42 Ž1972. 1–212. w25x M. Boccaletti, F. Calamita, E. Centamore, U. Chiocini, G. Deiana, A. Micarelli, G. Moratti, M. Potetti, Evoluzione dell’Appennino Tosco–Umbro–Marchigiano durante il Neogene, G. Geol. 48 Ž1986. 227–233. w26x G. Cantalamessa, E. Centamore, U. Chiocchini, A. Micarelli, M. Potetti, L. Lorito, Il miocene delle Marche, in: E. Centamore, G. Deiana ŽEds.., La Geologia delle Marche, Stud. Geol. Camerti, Vol. Spec., 1986. w27x F. Ricci Lucchi, Recherches stratonomique et sedimentol´ giques sur le flysch Miocene ` de la Romagne ŽFormation ‘‘Marnoso–Arenacea’’., G. Geol. 35 Ž4. Ž1969. 163–198. w28x F. Boenzi, N. Ciaranfi, Sulla presenza di depositi da frane sottomarine nelle argille varicolori dell’Appennino Lucano, Boll. Soc. Geol. Ital. 87 Ž1968. 505–509. w29x F. Boenzi, N. Ciaranfi, Stratigrafia di dettaglio del ‘‘flysch di Gorgoglione’’ ŽLucania., Mem. Soc. Geol. Ital. 9 Ž1970. 65–79. w30x G. Palmentola, Nuovi dati e considerazioni sulla formazione di Serro Palazzo in Lucania, Mem. Soc. Geol. Ital. 9 Ž1970. 81–90. w31x N. Ciaranfi, L. Dazzaro, P. Pieri, L. Rapisardi, A. Sardella, Geologia della zona compresa fra Bisaccia ŽAvellino. ed il T. Olivento, Presso Lavello ŽPotenza., Mem. Soc. Geol. Ital. 12 Ž1973. 279–315. w32x R. Casnedi, Sedimentazione e tettonica pliocenica nel sottosuolo della bassa Valle del Fortore ŽFoggia., Mem. Soc. Geol. Ital. 19 Ž1978. 605–612. w33x T. Pescatore, G. Salvati, M. Tramutoli, Regressive depositional cycles in the Gorgoglione flysch, Irpinids, ŽSouthern Italy., Geol. Rom. 19 Ž1980. 51–61. w34x M. Lacasella, B. Lops, G. Piccarreta, L’Arco CalabroPeloritano e il Bacino Irpino nell’area Gorgoglione–Cirigliano, Rend. Soc. Geol. Ital. 4 Ž1981. 359–361. w35x F. Loiacono, Contributo alla ricostruzione paleografica del bacino di sedimentazione del flysch di Gorgoglione ŽLucania., Boll. Soc. Geol. Ital. 100 Ž1981. 193–211. w36x F. Guerrera, R. Coccioni, Caratteristiche sedimentologiche e micropaleontologiche di successioni ‘‘tripolacee’’ plioceniche dell’Appennino Lucano, Boll. Soc. Geol. Ital. 103 Ž1984. 205–223.
219
w37x F. Ippolito, B. D’Argenio, T. Pescatore, P. Scandone, Structuralstratigraphic units and tectonic framework of Southern Apennines, in: C.H. Squyres ŽEd.., The Geology of Italy, Earth Sci. Soc., Tripoli, 1975, pp. 317–327. w38x T. Pescatore, Evolution of the Irpinian Basin ŽMiocene. in the Southern Apennines, Rend. Soc. Geol. Ital. 9 Ž1986. 225–228. w39x T. Pescatore, M.R. Senatore, A comparison between a present-day ŽTaranto Gulf. and a Miocene ŽIrpinian Basin. foredeep of the Southern Apennines ŽItaly., Spec. Publ. Int. Assoc. Sedimentol. 8 Ž1986. 169–182. w40x C. Barbera, A. Ietto, G. Pappone, Le faune ad inocerami del Flysch del Cilento: Paleontologia ad interpretazione cronostratigrafica, Boll. Soc. Geol. Ital. 106 Ž1987. 621–632. w41x S. di Nocera, C. Pagano, B. Russo, M. Torre, Successioni del Bacino Irpino nei Dintorni di Celenza Valfortore ŽAppennino Dauno., Mem. Soc. Geol. Ital. 41 Ž1988. 423–430. w42x A. Santo, La successione stratigrafica dell’unita Dauna a Monte Sidone ŽCastelluccio Valmaggiore–Foggia., Mem. Soc. Geol. Ital. 41 Ž1988. 431–438. w43x L. Tortorici, Osservazioni geologiche sul flysch di S.Bartolomeo nell’area compresa tra il fiume Trigno e Benevento ŽItalia Meridionale., Boll. Soc. Geol. Ital. 94 Ž1975. 1791– 1809. w44x B. de Pascale, J.P. Bouillin, H. Feinberg, Le probleme ` de l’age ˆ des flyschs de San Mauro et d’Albidona ŽCilento et ´ confins Calabro–Lucaniens, Italie.: Etude de leur nanoflore, C.R. Acad. Sci. Paris 310 Ž1990. 633–638. w45x E. Centamore, U. Chiocchini, N. Cipriani, G. Deiana, A. Micarelli, Analisi dell’evoluzione tettonico–sedimentaria dei ‘‘Bacini Minori’’ torbiditici del Miocene medio-superiore nell’Apennino umbro-marchigiano e lazialeabbruzzese: 5. Resultati degli studi in corso, Mem. Soc. Geol. Ital. 18 Ž1978. 135–170. w46x A. Angelucci, La serie Miocenica nella media Valle Latina ŽFrosinone., Geol. Rom. 5 Ž1966. 425–452. w47x A. Angelucci, P. Bellotti, P. Valeri, Analisi di facies dei sedimenti terrigeni Tortoniani nella zona di Frosinone, Geol. Rom. 18 Ž1979. 127–135. w48x P. Bellotti, B. Landini, P. Valeri, Complesso torbiditico Altomiocenico Laziale–Abruzzese, Boll. Soc. Geol. Ital. 103 Ž1984. 311–326. w49x J. de Jager, The relation between tectonics and sedimentation along the ‘‘Sillaro Line’’, Ph.D. Thesis, Utrecht University, Utrecht, 98 pp. ŽGeol. Ultraiectina, 19 Ž1979... w50x E. Centamore, U. Chiocchini, N. Cipriani, G. Deiana, A. Micarelli, The ‘‘Minor Basins’’ in the context of the Umbro-Marchean region tectonic — Tectonic–sedimentary evolution during Middle–Upper Miocene, Ann. Geol. ´ Pays Hell., Tome ˆ hors ser. ´ fasc. 1 Ž1979. 247–251.
Lateral shifts of Apenninic foredeep depocentres reflecting detachment of subducted lithosphere M.J. van der Meulen ) , J.E. Meulenkamp, M.J.R. Wortel Faculty of Earth Sciences, Vening Meinesz Research School of Geodynamics, PO Box 80021, 3508 TA Utrecht, The Netherlands Received 18 June 1997; revised 16 September 1997; accepted 16 September 1997
Abstract The hypothesis of lateral migration of slab detachment was formulated on the basis of seismic tomography results on the 3-D structure of subduction zones in the Mediterranean region wM.J.R. Wortel and W. Spakman, Structure and dynamics of subducted lithosphere in the Mediterranenan region, Proc. K. Ned. Akad. Wet. 95 Ž1992. 325–347x. The redistribution of slab pull forces associated with the tearing process is taken to affect foredeep development by adding a lateral component to internal–external depocentre migrations. In the case of the Apenninic Arc the direction of detachment and associated depocentre migration is expected to be southeast. This prediction has been confronted with the tectonostratigraphy of Oligocene to Recent Apenninic foredeeps. Results show there are two episodes marked by important lateral shifts of foredeep depocentres. During the early Late Miocene ŽTortonian. the depocentre of the Northern Apennines foredeep shifted towards the southeast. This is evidenced by the relative positions of the depocenters of the Burdigalian–Serravallian Marnoso Arenacea and the Tortonian Umbrian–Marchean and Lazian ‘‘Minor Basins’’. A further, stepwise southeastward migration can be inferred from the Plio-Pleistocene records of the Central and Southern Apennines. In a more general sense, our results indicate that slab detachment may play a significant role in the evolution of foredeeps along convergent plate boundaries. q 1998 Elsevier Science B.V. Keywords: Italy; Apennines; stratigraphy; geophysics; subduction; active margins; basin analysis; fore-arc basins
1. Introduction The Mediterranean region is the area of the convergent plate boundary zone of the African and European plates ŽFig. 1.. The western Mediterranean area includes the large extensional Balearic and Tyrrhenian Basins on the internal side of the Apenninic and Maghrebian Žp.p.. mountain belts. Since the extensional basin development occurred synchronously with the internal–external propagation of )
Corresponding author. E-mail: [email protected]
the adjacent fold and thrust belts w1–4x a genetic relation between the two processes is generally accepted w5,6x. The configuration of the western Mediterranean area is considered to be the result of the African–European collision in the Late Eocene and subsequent rollback, during the Oligocene to Recent time span. Recently new aspects of the structure of the upper mantle in the Alpine–Mediterranean region have been revealed by seismic tomography w7,8x, see also w9x. The seismic velocity structure of subducted lithosphere shows evidence for slab detachment under-
0012-821Xr98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 0 1 2 - 8 2 1 X Ž 9 7 . 0 0 1 6 6 - 0
204
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Fig. 1. Schematic map of the Central and Western Mediterranean.
neath the Dinarid–Hellenic and Apenninic Arcs. On the basis of this result Wortel and Spakman w10x formulated the hypothesis of lateral migration of slab detachment ŽFig. 2.. Since it is intrinsically impossible for seismic tomography to provide 100% confidence on the actual existence of slab detachment Žfor a contrasting view, see Amato et al. w11x., we follow the approach in which predictions of the tomography based hypothesis are tested against independent geological data. Slab detachment is considered to be a self-perpetuating process of lateral migration of a tear in the subducted lithosphere Žsee also w12x.. The present study focusses on the expected surface expression of the redistribution of slab pull forces associated with the tearing process. The transition from detached to continuous subducted lithosphere is marked by a zone of enhanced foredeep subsidence Žzone B in Fig. 2.. In the area which has undergone slab detachment the resulting decrease in slab pull forces leads to rebound Žzone C in Fig. 2.. When assuming that the excess subsidence is associated with increased
sedimentation rates, then slab detachment would introduce a lateral component to internal external foredeep depocentre migrations. The assumed relation between foredeep subsidence and sediment accumulation is in fact widely accepted and best illustrated by the well-known wedge shaped geometry of foredeep infillings in cross-sections perpendicular to the basin axis, reflecting the subsidence pattern inherent to the flexural deformation of the overridden plate. Meulenkamp et al. w13x tentatively invoked lateral migration of slab detachment to account for accelerating trends in rates of lateral depocentre migration as well as sediment accumulation for the Eastern AlpsrCarpathian foredeeps. In view of the higher resolution in the tomography results for the Apenninic region relative to those for the Carpathian region the former region is more suitable to serve as a test area for the hypothesis of lateral migration of slab detachment. Wortel and Spakman w10x hypothesised that the Adriatic lithosphere detached from northwest to southeast. If so, the surface effects of this tearing process should include a lateral compo-
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
205
Fig. 2. Graphical representation of the hypothesis of lateral migration of slab detachment w10x, and predicted surface effects.
nent towards the southeast in the migrations of Apenninic foredeep depocentres. This prediction will be confronted with the Oligocene–Recent tectonostratigraphic history of the Apenninic foredeeps. It must be kept in mind that throughout the Oligocene and most of the Miocene one can distinguish between a Northern and a Southern Apenninic tectono-stratigraphic history. The boundary between these two realms is the Anzio–Ancona line Že.g., w14x. which is shown in Fig. 4. If slab detachment has occurred, an overall trend in depocentre migrations can, however, be expected along the composite arc.
2. Apenninic foredeeps The studied Oligocene and Miocene Apenninic foredeeps have invariably been incorporated in the chain, and their depocentres have been located by the
analysis of published sediment accumulation data Žsee below.. The Plio-Pleistocene Apenninic foredeep, loosely defined in literature as the clastic wedge on the external side of the Apenninic chain w15x, has essentially been preserved as such, and its depocentres can be recognised from the seismic record w16x. The evolutionary history of the PlioPleistocene depocentres is inferred from sediment accumulation data from drillings w17x or from seismic stratigraphy w15,18x. In contrast to the OligoMiocene depocentres the Plio-Pleistocene depocentres often accommodate displaced extra- or intrabasinal units. The two sets of data allow a complete reconstruction of Oligocene to Recent depocentre migration patterns, because the top Miocene represents both the upper limit of Oligocene to Miocene foredeep sequences that can successfully be studied in outcrop within the chain, as well as an excellent seismic reflector at the base of large parts of the Plio-Pleistocene foredeep fill.
206 M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219 Fig. 3. Timetable used in this paper. Biozonationsrbioevents of Cita w20x, Crescenti w17x, Iaccarino w21x, and Lourens et al. w22x; converted to the Berggren et al. w23x timescale.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Depocenters have been incorporated in this analysis irrespective of their relative internal–external position within complex foredeep systems Žfor classifications, see e.g. w18,19x., because subsidence governed by deflection of the overridden plate may be reflected in sediment accommodation in any Žsub.basin within the subduction zone. So, in the context of this contribution foredeep must be read as foredeep sensu lato. In order to achieve coherency in the heterogenous set of data used, the most recent geological timescale has been used to attribute numerical ages to biostratigraphic events. The timetable used in this paper is given in Fig. 3, and shows the biozonationsrbioevents of Cita w20x, Crescenti w17x, Iaccarino w21x,
207
and Lourens w22x, converted to the Berggren et al. w23x timetable. 2.1. Oligo-Miocene foredeep sequences Fig. 4 shows the position of the Oligo-Miocene foredeeps and their depocentres d1 trough d5. In this figure basins have been combined in age groups because of complex stacking of the various units, as well as to facilitate the comparison between Northern and Southern Apenninic foredeeps. The subsidence of the Northern Apenninic foredeeps started in the Oligocene ŽRupelian., around 31 Ma B.P. when sedimentation began in the Macigno Basin, which now covers parts of Liguria, Tuscany
Fig. 4. Overview of Apenninic foredeeps. Compiled from many sources.
208 M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219 Fig. 5. Ža. Sedimentation rates for Northern Apenninic foredeep depocentres. Compiled from Boccaletti et al. w25x, Cantalamessa et al. w26x, Nardi and Nardi w24x, and Ricci Lucchi w18,27x. Žb. Maximum sedimentation rates for Southern Apenninic foredeeps. Compiled from Boenzi and Ciaranfi w28,29x, Palmentola w30x, Ciaranfi et al. w31x, Casnedi w32x, Pescatore et al. w33x, Lacasella et al. w34x, Loiacono w35x, Guerrera and Coccioni w36x, Ippolito et al. w37x, Pescatore w38x, Pescatore and Senatore w39x, Barbera et al. w40x, di Nocera et al. w41x, Santo w42x, Tortorici w43x, and De Pascale et al. w44x.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
fig. 5. Žc. Sedimentation rates for the ‘‘Minor Basins’’, sensu Centamore et al. w45x. Compiled from Angelucci w46x, Angelucci et al. w47x, Centamore et al. w45x, Bellotti et al. w48x, Boccaletti et al. w25x, and Cantalamessa et al. w26x. Depocentres are indicated in black Žsee text for explanation..
209
210
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
and Umbria. The thickness of the Macigno sequences varies along the Apenninic strike, and perpendicular to it Že.g., w24,25x.. The depocentre d1 of the basin is represented by the Macigno sequence of the Chianti mountains with a thickness of ; 3000 m w25x, yielding a Žuncorrected. sedimentation rate of ; 62 cmrky ŽFig. 5a.. In the Southern Apennines the Cilento basin and part of the Numidian basin developed w4x in response to the beginning of Apenninic tectogenesis. In the literature large discrepancies exist with respect to the dating of both these basins. The Cilento flysch has been attributed to the Cretaceous w39x, to the Eocene–Oligocene, and even to the Early Miocene w44x. The oldest datings would put it even before the start of the development of the Apennines; for that reason the Cilento flysch is not included in Fig. 5b. The Numidian flysch has been dated as Chattian to Burdigalian Že.g., w36x., and as Chattian to Langhian Že.g., w4,31x.. The present study does not aim to contribute to a discussion on the ages of the Numidian and Cilento flysches: in this context it is sufficient to establish the fact that any of the proposed ages for each of the flysches yield a lower sedimentation rate than that for the Northern Apenninic Macigno Basin. During the next stage in Northern Apennine foredeep evolution turbiditic sediments were deposited in the latest Chattian–earliest Langhian Cerverola Basin Ž24.0–16.1 Ma B.P.., which is now incorporated in the Ligurian, the Tuscan–Emilian and the Umbro– Marchean Apennines. The sediments of the Cerverola Basin have approximately the same lateral extent as the Macigno fill. The basin prograded over the former ramp of the Macigno Basin during and after the incorporation of the latter basin in the evolving Apenninic thrust belt. The greatest thickness Ž; 1100 m. of the Cerverola sequence has been observed in the Prato Magno area Žd2., yielding a maximum sedimentation rate of ; 10 cmrky Že.g., w25x.. Nardi and Nardi w24x, however, report a maximum thickness in approximately the same area Ž2000 m., which would yield a sedimentation rate of 18 cmrky. In the Southern Apennines the Numidian basin continues to exist up to the Burdigalian or Middle Langhian Žsee above., with sedimentation rates of ; 22 cmrky. The Marnoso Arenacea Basin Ž16–7.2 Ma B.P., Langhian–Tortonian., of which the sediments are
found in the Emilia–Romagnan part of the Apennines and in Umbria, was the next basin to develop in front of the advancing Apenninic nappes during and after the disruption of the Cerverola Basin by thrust activity. It has maximum sedimentation rates in the Emilian–Tuscan Apennines of ; 75 cmrky Žaveraged., with peak values of ) 100 cmrky Žd3. w26,27x. Southeast of the depocentre sedimentation rates vary between 40 and 60 cmrky w25x. North of the depocentre the Marnoso Arenacea was progressively invaded by the gravitationally displaced Ligurian allochthon w49x. In the Southern Apennines the Gorgoglione, Castelvetere, and Serra Palazzo flysches filled in various realms within the Irpinian basin, the new foredeep established after the disruption of the Numidian basin w38x. The Irpinian basin is contemporary with the Marnoso Arenacea Basin although there are some discrepancies with respect to its age. It started either in the Burdigalian w39x or in the Middle Langhian w4x. The disruption of the Irpinian basin has been dated at the Tortonian–Messinian transition by Patacca et al. w7x; Tortorici w43x presents biostratigraphical evidence for a Tortonian age of this event. Any of these datings, however, yield lower sedimentation rates for Irpinian formations than for the Marnoso Arenacea flysch in its depocentre. Pronounced reorganisations took place in the Central Apennines during the Tortonian, i.e. between about 11 and 7 Ma B.P. The southern Marnoso Arenacea Basin became disrupted and subsequently flysch sedimentation took place in narrow troughs w45,50x, the Umbro–Marchean ‘‘Minor Basins’’, sensu Centamore w50x. The depocentral area of the Marnoso Arenacea Basin does not undergo the same segmentation. However, a shallowing in this part of the foreland, preceded by a drop in sedimentation rate Žsee Fig. 5a and c. can be inferred from a facies change at ; 8 Ma. Turbiditic sediments with a fan lobe facies are overlain by marls w6x forming the top of the Marnoso Arenacea sequence with an upper fan to slope facies. These marls are in turn overlain by the Messinian shallow ‘‘Ghioli di Letto’’ marls w6x. The above-mentioned modifications in the Central Apenninic foreland basins are interpreted as the result of east verging thrust activity along the Anzio– Ancona line. At the external side of this renewed and now emerging segment of the Central Apenninic
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Fig. 6. Isopach map of the Plio-Pleistocene Apenninic foredeep. Modified from Ambrosetti et al. w16x.
211
212
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Chain small turbiditic fans developed in small, elongated Lazian ‘‘Minor Basins’’ Žsensu Centamore w50x.. The highest sedimentation rates, of ; 50 cmrky in these elongated basins are observed close to the thrust front in the Tagliacozzo Basin Ždepocentre d4 in Fig. 4.. The sedimentation rates in this basin exceed the rates in the contemporary Umbrian–Marchean Minor Basins, as well as in the remaining Lazian Minor Basins Žsee Fig. 5c.. In the Southern Apennines ambiguity in datings of the Late Miocene foredeep sequences does not allow a clear comparison with the Northern and Central Apennines Žsee Fig. 5b.. Either the top sequences of the Irpinian basin or the post-Irpinian successions are coeval with the Minor Basins sequences. Both possibilities would put the Apenninic depocentre Žindicated in black in Fig. 5c. in the Central Apennines, so age uncertainties do not seriously hamper this depocentre analysis. The Tortonian configuration formed the prelude to the next important stage in the development of the Apennines: the establishment of the Laga Basin Žde-
pocentre d5, indicated in black in Fig. 4. in the Messinian. Its 3000 m thick w25x fill is now to be found in the Abruzzi area. The considerable thickness of the Laga Basin fill yields a very high sedimentation rate of up to 200 cmrky, exceeding Žclastic. sedimentation rates in any other Messinian foreland basin. The Laga Basin is partly contemporary with the Minor Umbrian–Marchean basins, where sequences shallow and reach evaporitic conditions in response to the Messinian salinity crisis w4,25,26x. In the Lazian Minor Basins Early Messinian sandstones overlie the Tortonian turbidites w6,46–48x. The bathymetry and sedimentation rate in the Laga Basin apparently were so high that the effects of the Messinian salinity crisis were almost completely overprinted. Only a level of gypsum-arenitic turbidites is indicative of evaporitic conditions in the source area w3,26,45x. In the Southern Apennines marine evaporitic conditions are reached within the foredeep and clastic sedimentation was suspended for the duration of the salinity crisis Že.g., w4x..
Fig. 7. Sedimentation rates for Plio-Pleistocene depocentres. Compiled from Crescenti w17x, Ricci Lucchi w18x, and Ori et al. w15x. Central and Southern depocentres indicated in black Žsee text for explanation.. Thick black lines indicate the last occurrence of basin-modifying thrusts.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
2.2. The Plio-Pleistocene foredeep system The Plio-Pleistocene Apenninic foredeep shows four different depocenters, as recognised by the depth of the base of its infilling. In Fig. 6 these depocentres ŽA–D. are shown on a map and in a profile constructed through Žthe tipline of. the most external Apenninic thrusts. The depocentres have been num-
213
bered A through D. The northernmost, composite depocentre ŽA., has approximately the same lateral extent as the pre-Tortonian Northern Apenninic foredeeps. At this site the base of the Pliocene is located at a depth of up to 9 km. In front of the Central Apennines depocentre B occupies the same along-arc position as the Messinian Laga Basin. In the Southern Apennines two other depocentres ŽC and D. are
Fig. 8. Location of drillings used in this paper Žmodified from Crescenti w17x., to elaborate Plio-Pleistocene depocentre evolution.
214
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
present. The thickness of Plio-Pleistocene sequences at these locations is ) 6 km. Sedimentation rates ŽFig. 7. have been inferred from seismic stratigraphy of the Northern Apenninic w18x and for the Central Apenninic foredeep w15x, and from drilling data ŽFig. 8. for the Southern Apennines w17x. Sedimentation rates in depocentre A are consistently the highest observed. Local depocentres C, B and D develop successively, as indicated in black in Fig. 7. The Central Apenninic depocentre ŽB., positioned externally with respect to the Messinian Laga Basin had its main phase of infill in the Early Pliocene Ž) 3.3 Ma.. Depression C is mainly filled during the Late Pliocenerearliest Pleistocene Ž3.3–1.43 Ma., whereas the southernmost depocentre is essentially Pleistocene of age Ž1.43–0.8 Ma.. The age of the last occurrence of major, basinmodifying thrust events affecting Žsee w17x. PlioPleistocene depocentres B–D Žindicated with black lines in Fig. 7. shows the same southeastward shifting as the one observed for sedimentation rates. It should be noted that each of these events led to the displacement of intra- or extrabasinal units, which have to be accommodated by subsequent deflection of the foredeep substratum.
3. Analysis and discussion 3.1. Depocentre migrations Depocentre migration patterns for the entire Apenninic evolution have been reconstructed from the integrated study of the Oligo-Miocene and PlioPleistocene foredeeps ŽFigs. 8–10.. Depocentres of the Northern Apenninic Macigno, Cerverola and Marnoso–Arenacea Basins occupy approximately the same along-arc position: there is no lateral, but a clear internal–external component in depocentre migrations from the Middle Oligocene till the early Late Miocene ŽTortonian., i.e. from about 31 to 11 Ma B.P. In the course of the early Late Miocene the pattern of internal–external depocentre migration became interrupted. A major deformational event w45x led to the partial disruption of the Marnoso Arenacea Basin as well as to the formation of the ‘‘Minor
Basins’’ Žsensu Centamore w50x.. At the same time the locus of maximum deposition shifted laterally from the Marnoso Arenacea Basin Žd3. to the Tagliacozzo Basin Žd4 in Fig. 4.. During the latest Miocene ŽMessinian. the locus of maximum deposition was present in the Laga Basin Žd5 in Fig. 4. situated externally of the Tagliacozzo Basin. Thus, in the early Late Miocene the depocentre shifted to the Central Apennines and remained there throughout the Late Miocene, although internal–external propagation did occur. At the beginning of the Pliocene depocentre A ŽFig. 9. developed at approximately the same position along the Northern Apennines as occupied by the pre-Tortonian depocentres Žd1–3., and depocentre B Žsee Fig. 9. developed externally with respect to the Late Miocene depocentres d4–5. Depocentre A remained the locus of maximum deposition throughout the Plio-Pleistocene in the Northern Apennines, whereas in the Southern Apennines depocentre B was succeeded by the Late Pliocene depocentre C in the central part of the Southern Apennines. In the Early Pleistocene the maximum accumulation rates are found in the southernmost part of the Southern Apennines. Thus, the pattern of Rupelian–Serravallian internal–external as well as the Tortonian–Messinian lateral depocentre migrations appear to persist after the Messinian. It must be kept in mind, however, that the primary goal of this study was to identify zones of maximum subsidence. Local, excess subsidence Žas in Fig. 2, zone B. cannot be considered an exclusive mechanism to create foredeep depocentres, since accommodation space is not a limiting factor for sediment accumulation in deep turbiditic basins. Nevertheless, when taking into account the reconstructed basin configuration for the Late Miocene Northern Apennines, and the preserved configuration of the Southern Apenninic Plio-Pleistocene foredeep Žsee above., the laterally migrating depocentres appear to mark a laterally migrating zone of maximum subsidence. The residence time of the laterally migrating depocentres decreased in time from 7.6 Ma for the Central Apenninic depocentre Žcomposed of Late Miocene depocentres d4–5 and Early Pliocene depocentre B., to 2.2 Ma Ždepocentre C., and to 0.6 Ma Ždepocentre D.. This accelerating pattern is in
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
Fig. 9. Longitudinal profile constructed along the tipline of the most external Apenninic thrusts, showing lateral depocentre migrations. For further explanation, see text.
215
216
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
qualitative agreement with the nature of the detachment process w10,12x. 3.2. Rebound It has been demonstrated that the approach chosen reveals a lateral variation of foredeep depocentres and tectonic activity which is in good accordance with the predictions from the hypothesis of lateral migration of slab detachment. In addition to lateral migration of foredeep depocentres, the hypothesis of slab detachment predicts dynamic rebound in areas
which have undergone detachment ŽFig. 2, zone C.. Evidence for the latter phenomenon can be inferred from sedimentary facies changes superimposed on the accumulation patterns as shown in Figs. 5 and 7. In the Northern Apennines late Tortonian regressive sequences of the Marnoso Arenacea foredeep in its depocentral area Žsee above., as well as in piggyback basins on the Ligurian allochthon w18x could indicate rebound after the depocentre shift to the Central Apennines. A early Late Pliocene Ž3.6 Ma B.P.. shallowing in the area of depocentre B can be inferred by the compartimentation of this part of the
Fig. 10. Map showing Oligocene to Recent depocentre migrations.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
basin by the emergence of previously submerged crests of blind thrusts w15x. This shallowing event is coeval with the depocentre shift from the Central Apennines towards the southeast. Marine sedimentation continues up to the earliest Pleistocene in depocentre C and up to the Middle Pleistocene in depocentre D Žsee Fig. 7.. These preliminary relations between depocentre migrations and uplift are shown in Fig. 11. When assessing the present configuration of he Apenninic foreland it is tempting to consider the deep depression of the Ionian basin Ž) 3000 m. to be the culmination of the surface effects of the detachment process Žas indicated tentatively in Fig. 9a, migration 3.. However, the Plio-Pleistocene fossil foredeeps are seated on the continental lithosphere of the ApulianrAdriatic platform, whereas the basement of the Ionian foreland consists of old ŽMesogean. oceanic crust: the differences in the properties of the foredeep basement are considerable and, without any doubt, their effect on the present configuration accordingly. Nevertheless, one cannot exclude that the great water depths in the Ionian basin can partly be attributed to the transferred weight of detached subducted lithosphere.
217
4. Conclusions This first order attempt to assess the role of slab detachment in the evolution of the Apennines showed that a clear pattern of lateral Žalong strike. migration of depocentres and associated tectonic activity exists from the early Late Miocene ŽTortonian. onwards. After a depocentre has shifted to a new locus, the previous locus is subjected to uplift. The combination of these patterns is good agreement with the predictions from the hypothesis of lateral migration of slab detachment. The Apenninic depocentres show punctuated in stead of gradual migrations, and may be the reflection of a punctuated tearing process at depth, or a punctuated surface response to a smooth tear propagation at depth. Whereas the good agreement between predictions and observations is obviously in support of the hypothesis of lateral migration of slab detachment, this does not imply that no alternative mechanisms are possible. If alternative mechanisms would appear to explain the observations equally well, further tests to discriminate between competing hypotheses will have to be developed to discriminate between them. The recognised axial trend in the development of
Fig. 11. Tentative scheme showing the relation between depocentre shifting, and uplift. Uplift after depocentre development is evidenced by: Ž A. regressive sequence w7x; Ž B . compartimentation of foredeep by blind thrust emergence w15x; Ž C . unconformity Žtop of sequence, see Fig. 8.; and Ž D . unconformity Žtop of sequence, see Fig. 8..
218
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219
the Apennines can contribute to the understanding of aspects in the evolution of individual segments of the arc. The time frame provided can be used for specific further elaboration of the surface effects of the detachment of subducted lithosphere. Future research will focus on the reconstruction of vertical motions for selected parts of the Apenninic foreland, in order to refine our understanding of the relation between upper mantle and geological processes at the Earth surface. Since our approach has been process-oriented our results implicitly indicate that slab detachment is to be considered as a possible element in the evolution of foredeep systems along convergent plate boundaries, in general.
w6x
w7x
w8x
w9x
w10x
w11x
Acknowledgements E. Carminati, W. Spakman, P.Th. Meijer, J.H. ten Veen, M. Boccaletti and S.J.H. Buiter are acknowledged for discussion and suggestions. A.J. van der Meulen is acknowledged for critically reading the manuscript. We wish to thank the reviewers L. Jolivet and W.B.F. Ryan for helpful suggestions. This work was conducted under the programme of the Dutch national research school, the Vening Meinesz Research School of Geodynamics. MJvdM is financed by the Geosciences Foundation ŽGOA. of the Netherlands Organization for Scientific Research ŽNWO.. [RV] References w1x J.-P. Rehault, G. Boillot, A. Mauffret, The western Mediter´ ranean Basin geological evolution, Mar. Geol. 55 Ž1984. 447–477. w2x J.-P. Rehault, E. Moussat, A. Fabri, Structural evolution of ´ the Tyrrhenian back-arc basin, Mar. Geol. 74 Ž1987. 123– 150. w3x M. Boccaletti, F. Calamita, G. Deianan, R. Gelati, F. Massari, G. Moratti, F. Ricci Lucchi, Migrating foredeep–thrust belt system in the northern Apennines and Southern Alps, Palaeogeogr., Palaeoclimatol., Palaeoecol. 77 Ž1990. 3–14. w4x M. Boccaletti, N. Ciaranfi, D. Cosentino, G. Deiana, R. Gelati, F. Lentini, F. Massari, G. Moratti, T. Pescatore, F. Ricci Lucchi, L. Tortorici, Palinspastic restoration and paleogeographic reconstruction of the peri-Tyrrhenian area during the Neogene, Palaeogeogr., Palaeoclimatol., Palaeoecol. 77 Ž1990. 41–50. w5x A. Malinverno, W.B.F. Ryan, Extension in the Tyrrhenian
w12x
w13x
w14x
w15x
w16x
w17x
w18x
w19x
w20x
w21x
sea and shortening in the Apennines as a result of arc migration driven by sinking of the lithosphere, Tectonics 5 Ž1986. 227–245. E. Patacca, R. Sartori, P. Scandone, Tyrrhenian Basin and Apenninic arcs, kinematic relations since Late Tortonian times, Mem. Soc. Geol. Ital. 45 Ž1990. 425–451. W. Spakman, M.J.R. Wortel, N.J. Vlaar, The Hellenic subduction zone: a tomographic image and its geodynamic implications, Geophys. Res. Lett. 15 Ž1988. 60–63. W. Spakman, Delay-time tomography of the upper mantle below Europe, the Mediterranean, and Asia Minor, Geophys. J. Int. 107 Ž1991. 309–332. W. Spakman, S. van der Lee, R. van der Hilst, Travel-time tomography of the European-Mediterranean mantle down to 1400 km, Phys. Earth. Planet. Inter. 79 Ž1993. 3–74. M.J.R. Wortel, W. Spakman, Structure and dynamics of subducted lithosphere in the Mediterranean region, Proc. K. Ned. Akad. Wet. 95 Ž1992. 325–347. A. Amato, B. Alessandrini, G.B. Cimini, Teleseismic wave tomography of Italy, in: H.M. Iyer, K. Hirara ŽEds.., Seismic Tomography: Theory and Practice, Chapman and Hall, London, 1993, pp. 361–396. S. Yoshioka, M.J.R. Wortel, Three-dimensional numerical modeling of detachment of subducted lithosphere, J. Geophys. Res. 100 ŽB10. Ž1995. 20223–20244. J.E. Meulenkamp, M. Kovac, ´ˇ I. Cicha, On late Oligocene to Pliocene depocenter migrations and the evolution of the Carpathian–Pannonian system, Tectonophysics 266 Ž1996. 301–318. A. Castellarin, R. Colacicchi, A. Praturlon, Fasi distensive trascorrente e sovrascorrimenti lungo ‘‘linea Ancona–Anzio’’ dal Lias al Pliocene, Geol. Rom. 17 Ž1978. 161–189. G.G. Ori, G. Serafini, C. Visentin, F. Ricci Lucchi, R. Casnedi, M.L. Colalongo, S. Mosna, The Pliocene–Pleistocene Adriatic Foredeep ŽMarche and Abruzzo, Italy., an integrated approach to surface and subsurface geology, in: Adriatic Foredeep Field Trip Guide Book, 3rd E.A.P.G. Conf., Firenze, 1991, pp. 5–52. P. Ambrosetti, C. Bosi, F. Carraro, N. Ciaranfi, M. Panizza, G. Papani, L. Vezzani, A. Zanferrari, Neotectonic map of Italy, C.N.R., Quad. Ric. Sci. 4 Ž114. Ž1983. . U. Crescenti, Sul substrato Pre-Pliocenico dell’avanfossa Appenninica dalle Marche allo Jonio, Boll. Soc. Geol. Ital. 94 Ž1975. 583–634. F.R. Lucchi, The Oligocene to Recent foreland basins of the Northern Apennines, Spec. Publ. Int. Assoc. Sedimentol. 8 Ž1986. 105–139. G.G. Ori, P.F. Friend, Sedimentary basins formed and carried piggyback on active thrust sheets, Geology 122 Ž1984. 475– 478. M.B. Cita, Planktonic foraminiferal biozonation of the mediterranean Pliocene deep sea record: a revision, Riv. Ital. Paleontol. Stratigr. 81 Ž1975. 527–544. S. Iaccarino, Mediterranean Miocene, Pliocene planktic foraminifera, in: H.M. Bolli, J.B. Saunders, K. Perch-Nielsen ŽEds.., Plankton Stratigraphy, Cambridge University Press, Cambridge, 1985, pp. 283–314.
M.J. Õan der Meulen et al.r Earth and Planetary Science Letters 154 (1998) 203–219 w22x L.J. Lourens, F.J. Hilgen, W.J. Zachariasse, A.A.M. van Hoof, A. Antonarakou, C. Vergnaud-Grazzini, Evaluation of the Pliocene to Early Pleistocene astronomical timescale, in: L.J. Lourens, Astronomical forcing of Mediterranean climate during the last 5.3 million years. Ph.D. Thesis, Utrecht University, Utrecht, 1994. w23x W.A. Berggren, D.V. Kent, C.C. Swisher, M.P. Aubry, A revised Cenozoic geochronology and chronostratigraphy, Soc. Econ. Paleontol. Mineral., Spec. Publ. 54 Ž1995. 129–212. w24x L.D. Nardi, R. Nardi, Schema stratigrafico e strutturale dell’Apennino settentrionale, Mem. Accad. Lunig. Sci. 42 Ž1972. 1–212. w25x M. Boccaletti, F. Calamita, E. Centamore, U. Chiocini, G. Deiana, A. Micarelli, G. Moratti, M. Potetti, Evoluzione dell’Appennino Tosco–Umbro–Marchigiano durante il Neogene, G. Geol. 48 Ž1986. 227–233. w26x G. Cantalamessa, E. Centamore, U. Chiocchini, A. Micarelli, M. Potetti, L. Lorito, Il miocene delle Marche, in: E. Centamore, G. Deiana ŽEds.., La Geologia delle Marche, Stud. Geol. Camerti, Vol. Spec., 1986. w27x F. Ricci Lucchi, Recherches stratonomique et sedimentol´ giques sur le flysch Miocene ` de la Romagne ŽFormation ‘‘Marnoso–Arenacea’’., G. Geol. 35 Ž4. Ž1969. 163–198. w28x F. Boenzi, N. Ciaranfi, Sulla presenza di depositi da frane sottomarine nelle argille varicolori dell’Appennino Lucano, Boll. Soc. Geol. Ital. 87 Ž1968. 505–509. w29x F. Boenzi, N. Ciaranfi, Stratigrafia di dettaglio del ‘‘flysch di Gorgoglione’’ ŽLucania., Mem. Soc. Geol. Ital. 9 Ž1970. 65–79. w30x G. Palmentola, Nuovi dati e considerazioni sulla formazione di Serro Palazzo in Lucania, Mem. Soc. Geol. Ital. 9 Ž1970. 81–90. w31x N. Ciaranfi, L. Dazzaro, P. Pieri, L. Rapisardi, A. Sardella, Geologia della zona compresa fra Bisaccia ŽAvellino. ed il T. Olivento, Presso Lavello ŽPotenza., Mem. Soc. Geol. Ital. 12 Ž1973. 279–315. w32x R. Casnedi, Sedimentazione e tettonica pliocenica nel sottosuolo della bassa Valle del Fortore ŽFoggia., Mem. Soc. Geol. Ital. 19 Ž1978. 605–612. w33x T. Pescatore, G. Salvati, M. Tramutoli, Regressive depositional cycles in the Gorgoglione flysch, Irpinids, ŽSouthern Italy., Geol. Rom. 19 Ž1980. 51–61. w34x M. Lacasella, B. Lops, G. Piccarreta, L’Arco CalabroPeloritano e il Bacino Irpino nell’area Gorgoglione–Cirigliano, Rend. Soc. Geol. Ital. 4 Ž1981. 359–361. w35x F. Loiacono, Contributo alla ricostruzione paleografica del bacino di sedimentazione del flysch di Gorgoglione ŽLucania., Boll. Soc. Geol. Ital. 100 Ž1981. 193–211. w36x F. Guerrera, R. Coccioni, Caratteristiche sedimentologiche e micropaleontologiche di successioni ‘‘tripolacee’’ plioceniche dell’Appennino Lucano, Boll. Soc. Geol. Ital. 103 Ž1984. 205–223.
219
w37x F. Ippolito, B. D’Argenio, T. Pescatore, P. Scandone, Structuralstratigraphic units and tectonic framework of Southern Apennines, in: C.H. Squyres ŽEd.., The Geology of Italy, Earth Sci. Soc., Tripoli, 1975, pp. 317–327. w38x T. Pescatore, Evolution of the Irpinian Basin ŽMiocene. in the Southern Apennines, Rend. Soc. Geol. Ital. 9 Ž1986. 225–228. w39x T. Pescatore, M.R. Senatore, A comparison between a present-day ŽTaranto Gulf. and a Miocene ŽIrpinian Basin. foredeep of the Southern Apennines ŽItaly., Spec. Publ. Int. Assoc. Sedimentol. 8 Ž1986. 169–182. w40x C. Barbera, A. Ietto, G. Pappone, Le faune ad inocerami del Flysch del Cilento: Paleontologia ad interpretazione cronostratigrafica, Boll. Soc. Geol. Ital. 106 Ž1987. 621–632. w41x S. di Nocera, C. Pagano, B. Russo, M. Torre, Successioni del Bacino Irpino nei Dintorni di Celenza Valfortore ŽAppennino Dauno., Mem. Soc. Geol. Ital. 41 Ž1988. 423–430. w42x A. Santo, La successione stratigrafica dell’unita Dauna a Monte Sidone ŽCastelluccio Valmaggiore–Foggia., Mem. Soc. Geol. Ital. 41 Ž1988. 431–438. w43x L. Tortorici, Osservazioni geologiche sul flysch di S.Bartolomeo nell’area compresa tra il fiume Trigno e Benevento ŽItalia Meridionale., Boll. Soc. Geol. Ital. 94 Ž1975. 1791– 1809. w44x B. de Pascale, J.P. Bouillin, H. Feinberg, Le probleme ` de l’age ˆ des flyschs de San Mauro et d’Albidona ŽCilento et ´ confins Calabro–Lucaniens, Italie.: Etude de leur nanoflore, C.R. Acad. Sci. Paris 310 Ž1990. 633–638. w45x E. Centamore, U. Chiocchini, N. Cipriani, G. Deiana, A. Micarelli, Analisi dell’evoluzione tettonico–sedimentaria dei ‘‘Bacini Minori’’ torbiditici del Miocene medio-superiore nell’Apennino umbro-marchigiano e lazialeabbruzzese: 5. Resultati degli studi in corso, Mem. Soc. Geol. Ital. 18 Ž1978. 135–170. w46x A. Angelucci, La serie Miocenica nella media Valle Latina ŽFrosinone., Geol. Rom. 5 Ž1966. 425–452. w47x A. Angelucci, P. Bellotti, P. Valeri, Analisi di facies dei sedimenti terrigeni Tortoniani nella zona di Frosinone, Geol. Rom. 18 Ž1979. 127–135. w48x P. Bellotti, B. Landini, P. Valeri, Complesso torbiditico Altomiocenico Laziale–Abruzzese, Boll. Soc. Geol. Ital. 103 Ž1984. 311–326. w49x J. de Jager, The relation between tectonics and sedimentation along the ‘‘Sillaro Line’’, Ph.D. Thesis, Utrecht University, Utrecht, 98 pp. ŽGeol. Ultraiectina, 19 Ž1979... w50x E. Centamore, U. Chiocchini, N. Cipriani, G. Deiana, A. Micarelli, The ‘‘Minor Basins’’ in the context of the Umbro-Marchean region tectonic — Tectonic–sedimentary evolution during Middle–Upper Miocene, Ann. Geol. ´ Pays Hell., Tome ˆ hors ser. ´ fasc. 1 Ž1979. 247–251.