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1.
In the Beni Issef Massif, nearly 30 km west of Chefchaouen (Morocco), the thickest post-nappe succession within the Rifian sector of the Maghrebian Chain seals the tectonic contact between the Intrarifian External Tanger and Loukkos Units, related to the Rifian External Domain. This succession is very important for the reconstruction of the deformation timing of the Rifian Maghrebids. The age of its base, in fact, is an important constraint for defining an upper boundary to the stacking of both the Intrarifian and Maghrebian Flysch Basin Units, because clasts fed by the Melloussa and Numidian Flysch Nappes are abundant in the conglomerate layers. Field and biostratigraphic analyses pointed out the presence of a Lower Beni Issef Fm, unconformable on the Intrarifian External Tanger and Loukkos Units, and an Upper Beni Issef Fm, unconformable on both the Intrarifian Units and the Lower Beni Issef Fm. The Lower Beni Issef Fm, 150 m thick, consists of lenticular conglomerates with huge blocks in a marly-clayey matrix, followed by marls and minor sandstones. It deposited in a siliciclastic platform, shows a fining upward trend and is affected by metre- to hectometre-sized, locally reversed, folds. Samples collected 45–50 m above the base of the formation resulted not older than Late Tortonian in age, but an older age for the base of the formation cannot be excluded. The Upper Beni Issef Fm, up to 550 m thick, starts with coarse conglomerates followed by medium- to coarse-grained well-bedded sandstones and by grey-blue marls and mudrocks. It indicates deposition in a channelized marine delta, with evolution towards pro-delta pelites, and shows sub-horizontal or gently dipping beds towards the east. Biostratigraphic data indicate a probable Messinian age for this formation. The composition of the arenites of both Lower Beni Issef and Upper Beni Issef Fms is quartzolithic and all samples show a notable content of monocrystalline well-rounded quartz and sedimentary lithic fragments. Detrital modes, all falling in the Quartzose Recycled and Transitional Recycled fields, suggest a provenance from recycling of sedimentary successions, easily recognizable in the Flysch Basin and External Units, mainly the Numidian Nappe sandstones. A Tortonian age of the Lower Beni Issef Fm would agree with the Late Serravallian age of the uppermost beds of the External Tanger Unit and indicate that the most probable age for the stacking of the Intrarifian Units falls in the Late Serravallian-Middle Tortonian time span. The Lower Beni Issef Fm was involved in a compressive tectonic phase testified by north-south striking folds. Later, probably during Messinian, the Upper Beni Issef Fm deposited in a younger intramontane basin, resting on both the Intrarifian Units and the Lower Beni Issef Fm. Successively, the Upper Beni Issef Fm was passively transported piggyback on top of the fold and thrust belt during later tectonic evolution of the Rifian Maghrebids. This tectonic evolution results quite similar to that recognized in the Tellian and Sicilian Maghrebids and also in the southern Apennines.  相似文献   

2.
Abstract

In the Northern Apennines, the External Liguride (EL) units are interpreted as derived from the domain that joined the Ligure–Piemontese oceanic basin to the Adriatic plate continental margin. The EL units can be divided into two different groups according to the lithostratigraphic features of the basal complexes underlying the Upper Cretaceous–Lower Tertiary carbonate flysch (e.g. Helminthoid flysch). The first group includes the western successions characterized by Santonian–Campanian sedimentary melanges where slide blocks of lherzolitic mantle, gabbros, basalts, granulites, continental granitoids are represented. The second group is represented by the eastern successions where the Cenomanian–Campanian basal complexes mainly consist of sandstones and conglomerates where the mafic and ultramafic rocks are scarce or completely lacking. Their original substrate is represented by the Middle Triassic to Lower Cretaceous, mainly platform carbonate deposits, found as slices at the base of the eastern successions.

The stratigraphic features shown by the basal complexes allow the reconstruction of their source area that is assumed to be also representative for the pre-Upper Cretaceous setting. The proposed reconstruction suggests the occurrence in the EL domain of two distinct domains. The eastern domain was characterized by a thinned and faulted continental crust belonging to the Adriatic continental margin. The western domain was instead floored by subcontinental mantle associated with lower and upper continental crust, representing the ocean–continent transition. This setting is interpreted as the result of the opening of the Ligure–Piemontese oceanic basin by passive rifting, mainly developed by simple shear, asymmetric extension of the continental crust. © 2001 Éditions scientifiques et médicales Elsevier SAS  相似文献   

3.
《Geodinamica Acta》2001,14(5):307-320
In the Northern Apennines, the External Liguride (EL) units are interpreted as derived from the domain that joined the Ligure–Piemontese oceanic basin to the Adriatic plate continental margin. The EL units can be divided into two different groups according to the lithostratigraphic features of the basal complexes underlying the Upper Cretaceous–Lower Tertiary carbonate flysch (e.g. Helminthoid flysch). The first group includes the western successions characterized by Santonian–Campanian sedimentary melanges where slide blocks of lherzolitic mantle, gabbros, basalts, granulites, continental granitoids are represented. The second group is represented by the eastern successions where the Cenomanian–Campanian basal complexes mainly consist of sandstones and conglomerates where the mafic and ultramafic rocks are scarce or completely lacking. Their original substrate is represented by the Middle Triassic to Lower Cretaceous, mainly platform carbonate deposits, found as slices at the base of the eastern successions.The stratigraphic features shown by the basal complexes allow the reconstruction of their source area that is assumed to be also representative for the pre-Upper Cretaceous setting. The proposed reconstruction suggests the occurrence in the EL domain of two distinct domains. The eastern domain was characterized by a thinned and faulted continental crust belonging to the Adriatic continental margin. The western domain was instead floored by subcontinental mantle associated with lower and upper continental crust, representing the ocean–continent transition. This setting is interpreted as the result of the opening of the Ligure–Piemontese oceanic basin by passive rifting, mainly developed by simple shear, asymmetric extension of the continental crust.  相似文献   

4.
A series of 8 new seismic refraction profiles were computed as extensions of the borehole controlled reflection profiles of the Po plain into the northern Apennines and the Ligurian Alps. They help to more clearly define the subsurface structure of this intricate ‘Ligurian knot’. In particular, it has been possible to identify a number of high velocity bodies, and they may be correlated with such geological entities as the Adriatic Mesozoic, ophiolites of the Apenninic Liguride nappes, and ophiolites or Mesozoic carbonates underlying the Antola flysch in the Alpine part of the knot. When combining the refraction and reflection lines, these bodies appear to be bounded by important dislocation surfaces, such as the Padanide sole thrust (Plio-Pleistocene), the Villalvernia Varzi line (Oligo-Miocene), the Ottone-Levanto line (Oligo-Miocene), and the Volpedo-Valle Salimbene fault (Oligo-Miocene; reactivated as a transfer fault in the Plio-Pleistocene). The 3D geometry may be interpreted in terms of regional kinematics and is compatible with a model that envisages an Oligo-Early Miocene NW translation of the Adriatic indenter, coupled with collapse in the Provençal-Ligurian sea and rotation of the Sardinia-Liguria complex into the roll-back of the Adriatic subduction zone. The refraction interpretations, extending to a depth of 15 km, are supplemented by data on the Moho configuration obtained for the European Geotraverse. The Moho appears to be dissected into a series of patches which may be interpreted in terms of the shallow crustal configuration and its history. In particular, the deepest patch appears to be terminated by the Volpedo-Valle Salimbene fault, which consequently would displace the entire crust.  相似文献   

5.
The External Tanger Unit represents one of the most complete Cretaceous-Miocene successions in the central areas of the Internal Intrarif sub-Domain (External Rif Zones, Morocco). An interdisciplinary study has been carried out to propose a new characterization of this unit which would allow a better comprehension of the confused and complex relationships among different units of the same sub-domain. The results achieved can be summarized as follows: (1) redefinition of the stratigraphic (litho-, bio-, and chrono-) record and introduction of a new, informal lithostratigraphic terminology; (2) recognition of two main depositional sequences (lower-middle Eocene p.p. and lower Oligocene p.p.-lower Miocene p.p.) separated by extended gaps (latest Cretaceous-early Eocene p.p. and middle Eocene p.p.-early Oligocene p.p.); (3) reconstruction of the evolution of the sedimentary realm, and of the relationships between tectonics and sedimentation; and (4) comparison between the upper Cretaceous-Miocene stratigraphic record and tectonic events of the Intrarif, which is located in the western external portion of the Maghrebian Flysch Basin, and the equivalent sedimentary record of the eastern portion of this basin in the Tunisian Tell. More in general, our results allowed (i) a first reconstruction of the Cretaceous-Miocene main tectono-sedimentary events; (ii) a more detailed location of the sedimentary suite in the external African Margin in the context of a wider palaeogeographic framework; and (iii) the definition of the main stages of the geological evolution of the area.  相似文献   

6.
The evolution of the oceanic Maghrebian Flysch Basin and its continuation in the Southern Apennines was studied by reconstructing mainly representative stratigraphic successions. In all sectors a common evolution has been identified. Rifting and drifting phases are indicated by remnants of oceanic crust, Jurassic limestones, Cretaceous–Palaeogene turbiditic and pelagic deposits. The pre-orogenic sedimentation was mainly controlled by extensional tectonics and sea-level changes. The occurrence of a generalized foredeep stage since the Early Miocene is testified by thick siliciclastic and volcaniclastic syn-orogenic flysch successions. The deformation of the oceanic areas began in the Burdigalian and the resulting nappes were stacked in the growing chains. During the Middle Miocene, piggy-back basins developed and the building of the chains was accomplished in the Late Tortonian. Areal distribution and ages of flysch deposits represent an important tool for the study of the diachronous growth of the accretionary wedges.  相似文献   

7.
Rheology and seismotectonic regime in the northern central Mediterranean   总被引：4，自引：0，他引：4  
The connection between thermal field and mechanical properties is analysed in the northern central Mediterranean region, extending from the Ligurian-Provençal basin to the Adriatic foredeep. As the thermal regime is still far from equilibrium in most of the tectonic units, transient thermal models are used. The temperature-depth distribution is estimated in four areas affected by the volcanic activity, which from the Neogene to the Present shifted from Corsica to the Apenninic arc. In the Adriatic foredeep, the thermal effects of the recent thrust-faulting phase in the buried sectors of the northern Apennines are taken into account.

The general context consists of convergence involving westward subduction of the Adriatic plate. This process caused anti-clockwise rotation of Corsica and Sardinia, which led to formation of the Ligurian marginal basin, and also resulted in crustal doubling and overthrusting in the northern Apennines and rifting in the northern Tyrrhenian.

Seismic activity is focused in the internal and external zones of the Apenninic arc, where low surface heat flux is observed, and in the western margin of the Ligurian-Provençal basin. This is a consequence not only of lateral variations in the thermal field but also of the different tectonic settings. Regional extensional patterns in the shallow crust, with minimum principal stress axes trending N60°E and E-W, are observed in the northern and in the southern sectors of the Apenninic arc, respectively. A compressional regime at depths greater than 30 km is observed below the northern sector of the arc, while to the south a change in the structure of the lithosphere is marked by a decrease in deeper seismic activity. Thrust faults and strike-slip faults with a thrust component support a compressional regime along the western margin of the Ligurian basin with maximum principal stress axis oriented N120°E.

Two lithospheric cross-sections across the study region are constructed, based on structural, thermal, gravity, rheological and seismic data. There is clear evidence of the presence of the subducting slab of the Adriatic plate, corresponding to a thickening of the uppermost brittle layer. The crustal seismicity cut-off corresponds to temperatures of 320–390°C. A brittle layer of considerable thickness is present in the uppermost mantle beneath Variscan Corsica and the Adriatic foredeep, with estimated seismic cut-off temperature of about 550 ± 50°C.  相似文献   


8.
The different segments of the tectonic boundary between external (European) and internal (Penninic) units in the Western Alps, the so-called Penninic Front (PF), formed at different times and according to different kinematic scenarios. During a first episode (Eocene), the PF corresponds to a transpressive suture zone between Penninic and European units. North- to NNW-trending stretching lineations, found along internal nappe contacts within the Penninic units, are related to this episode. This subduction zone was sealed by the Priabonian flysch of the Aiguilles d'Arves, a detrital trench formation that formed during the final stages of subduction. During a second episode, starting in mid-Oligocene times, the PF, imaged along the ECORS-CROP profile, acted as a WNW-directed thrust. This thrust, the Roselend Thrust (RT), only partially coincides with the PF. South of Moûtiers, the RT propagates into the Dauphinois units, carrying the former Eocene PF (including the Priabonian flysch) passively in its hangingwall. South of the Pelvoux massif the RT finds its continuation along the "Briançonnais Front", an out-of-sequence thrust behind the Embrunais-Ubaye nappes. On a larger scale, our findings indicate oblique (sinistral) collision within the future Western Alps during the Eocene, followed by westward indentation of the Adriatic block.  相似文献   

9.
《Geodinamica Acta》2013,26(1-2):71-97
Most of the tectonic units cropping out in Western Tuscany are fragments of the Jurassic oceanic crust, ophiolitic successions, overlaid diachronously by Upper Cretaceous-middle Eocene carbonate and siliciclastic flysch successions with their Cenomanian-lower Eocene shalycalcareous basal complexes. These units, so called Ligurian, have been emplaced during the closure of the Ligurian-Piedmont Ocean. Ophiolite bearing debris flows are common in the flysch basins and their relationship with ophiolitic tectonic slices points to a strong relation between tectonics and sedimentation from the early compressive events of the Late Cretaceous. The tectonic activity reflects in a rough morphology of the ocean floor. It progressively influences the distribution and sedimentology of the turbidites. During middle Eocene this relationship begun very important and a paleogeographic reconstruction with prominent linear ophiolitic reliefs that bounded some turbiditic basins can be done. In our reconstruction the sedimentary and structural evolution can be framed in the context of strain partitioning, developed during the ocean closure, between subduction processes and ancient weakness zones crosscutting both the ocean and the Adria continental margin and reactivated in compressive regime. These weakness zones can be interpreted as transform faults of the Ligurian-Piedmont Ocean with prolongations in the Adria passive margin.

The weakness zones crosscut the oceanic lithosphere and the Adria continental margin and interfered with the subduction processes. The activity of the weakness zones is reflected in the Ligurian Units architecture where two main structural strike trends of thrusts and folds axial planes occur. The first trend is WSW-ENE oriented and it is connected with the reactivation of the weaknesses zones. This first orientation developed progressively from Late Cretaceous to Pliocene, from oceanic to ensialic convergence (D1, D2, and D4 deformation phases). The second trend is NNE-SSW oriented and is related to the late Eocene continental collision and the subsequent translation to the NE of the oceanic units onto the Adria continental margin (D3 deformation phase).  相似文献   

10.
The Lagonegro Units are a part of the southern Apennines orogenic wedge. The age of the Lagonegro successions ranges from lower–middle Triassic to Oligo-Miocene. During late Cretaceous and Oligocene the deposition of calcareous-clastic sediments occurred interbedded with shales (Flysch Rosso Fm). During Oligocene and early Miocene, in the Mediterranean area, an important variation of the tectonic regime occurred, and siliciclastic sediments of the Numidian Basin unconformably lay on the Meso-Cenozoic units of the Lagonegro Basin. In the Lucanian Apennine, the Aquitanian–Langhian Numidian Flysch Fm overlies the Flysch rosso Fm. The shales of the Flysch rosso Fm have a peculiar geochemical fingerprint relative to typical shales of post-Archean age. The abundance of Ni and Cr is significantly higher and the HREE chondrite-normalized patterns are steep with a (Gd/Yb)ch>2. A supply of material from the African Archean terranes could be the cause. The palaeo-weathering indices record changes at the source, reflecting variations in the tectonic regime. The oldest samples are derived from an environment in which steady-state weathering conditions prevailed, whereas the youngest samples are related to non-steady-state weathering conditions. This difference could record deformational events that affected the Mediterranean area during the Oligocene and early Miocene. The sample at the top of the studied log has very high silica content and an abundant coarse grain-sized fraction. This suggests that this sample belongs to the Numidian Flysch Fm. The geochemical proxies of this sample are different from those associated with samples from the Flysch rosso Fm, indicating that the source-area of the Numidian Flysch Fm did not include the Archean terranes.  相似文献   

11.
We present a comprehensive study of the recent and active tectonics of the external part of the Northern Apennines (Italy) by using morphotectonic, geological–structural, and stratigraphic analysis, compared with the current seismicity of the region. This analysis suggests that the external part of the Northern Apennines is characterised by presence of three major systems of Quaternary compressive structures corresponding to (1) the Apenninic watershed, (2) the Apennines–Po Plain margin (pede-Apenninic thrust front), and (3) the Emilia, Ferrara, and Adriatic Fold systems buried below the Po Plain. Geological data and interpreted seismic sections indicate a roughly N–S Quaternary deformation direction, with rates <2.5 mm/year. The shortening decreased since the Pliocene, when our data indicate compression in a NNW–SSE direction and rates up to 7 mm/year. The trend and kinematics of the structures affecting the Apennines–Po Plain margin and the Po Plain subsoil fit well the pattern of the current seismicity of the area, as well as recent GPS and geodetic levelling data, pointing to a current activity of these thrust systems controlled by an overall compressive stress field. Close to the Apenninic watershed, earthquake focal mechanisms indicate that shallow extension is associated to deep compression. The extensional events may be related to a secondary extensional stress field developing on the hangingwall of the thrust system affecting the Apenninic watershed; alternatively, this thrust system may have been recently deactivated and overprinted by active normal faulting. Deeper compressive events are related to the activity of both a major basement thrust that connects at surface with the pede-Apenninic thrust front and a major Moho structure.  相似文献   

12.
The identification of syn- and late-orogenic flysch deposits, extending from the Betic Cordillera to the Southern Apennines, assists in the reconstruction of the tectonic-sedimentary evolution of the perimediterranean chains. A microplate was located between the European and African Plates during the Late Jurassic–Early Cretaceous, bordered northwards by the Piemontese Ocean and southwards by another (North Africa ‘Flysch’ Basin or Maghrebian) Ocean. The Piemontese Ocean and the northern margin of the microplate were structured from the Late Cretaceous to the Eocene to create an Eo-alpine Chain. The southern margin of the microplate was deformed in the Aquitanian, when the internal areas of the Maghrebian Ocean were characterized by syn-orogenic flysch deposits. This episode culminated with metamorphism (25–22 Ma) and nappe emplacement, which destroyed the former palaeogeography and created an orogenic belt (AlKaPeCa). Afterwards, a lower Burdigalian late-orogenic cycle started in the deformed area, which as a result of the opening of the Algero-Provençal Basin, caused the fragmentation of the AlKaPeCa, its thrusting on the ‘Flysch’ Basin and the collision with the North Africa and South Iberia Margins. These latter were folded and thrusted, the ‘Flysch’ Units pushed over the External Domain and also back-thrusted. Langhian late-orogenic deposits suture the new tectonic features. Finally, the whole orogen was thrust onto the foredeep during the Middle–Late Miocene.  相似文献   

13.
The nappe pile presently cropping out in the central sector of the Ligurian Alps, is represented by some principal groups of tectonic units. Starting from the foreland, the outer and lower, weakly metamorphic (up to 0.3 GPa) Briançonnais units support the high-pressure (up to 1.3 GPa) ensemble of inner Briançonnais nappes, in turn overridden by the Prepiedmont units, sourced from the European continental margin. Prepiedmont units form two superposed groups. The lower is composed only of a pre-Namurian basement (Alpine metamorphism up to 0.6 GPa); and the upper is mainly composed of a slightly metamorphic (greenschist facies) post-Namurian cover. At the top lie the high-pressure metamorphosed (up to 0.8 GPa in the sector here considered) ophiolitic units. The group of the non-metamorphic Helminthoid Flysch nappes (original stratigraphic cover of the ophiolitic units) has travelled the greatest distance and is presently mainly set onto the outer part of the chain. Only events up to the stacking of the nappe pile are discussed, disregarding late-stage deformation. As the examined sector is located at a considerable distance from the collisional zone, late processes did not change the overall order of superposition formerly acquired. The model proposes the development of two major, subhorizontal detachment surfaces. The first, shallower one confines at the base a very thin-skinned set of nappes, nearly totally made up of Prepiedmont sedimentary covers that are bounded at their top by the Helminthoid Flysch units. Both these groups underwent a mainly horizontal outwards transport. In contrast, the underlying Prepiedmont crust and the adjoining Briançonnais inner sector (separated by the second, deeper major detachment surface) were progressively dragged into the subduction zone under the ophiolitic units and duplexes were generated. Exhumation of the metamorphic units occurred along the subduction channel, as did stacking of the nappe pile.  相似文献   

14.
The ages obtained from planktonic foraminiferal assemblages retrieved from two exposures in the Gurnigel Flysch and from the re-examination of similar material gathered by previous researchers from the Voirons Flysch reveal only minor discrepancies with previous studies based on nannofossil biostratigraphy. In contrast, major divergences between this work and previous studies on the Voirons Flysch also based on planktonic foraminifera have been identified. They are generally related to distinct approaches in species classification and the use of different zonal schemes. Based on our data, the age of the Voirons Flysch extends from the Early Eocene (planktonic foraminiferal zone P7) to the Middle Eocene (planktonic foraminiferal zone P12). Contrasting with claims made in earlier studies, no specimen of Late Eocene or Early Oligocene age has been observed in the revised material. However, we cannot exclude a younger age (possibly Late Eocene) for the upper portion of this flysch from which we did not revise any sample. Thus, more research and sampling are needed to resolve this question. The palaeogeographic origin of the Voirons-Wägital complex as well as the sedimentation history of these flyschs need now to be re-evaluated in light of this revised biostratigraphic data.  相似文献   

15.
The Swiss Prealpine Dranse nappe consists of the badly known shaley Complexe de base series and the overlying Campanian to Maastrichtian Helminthoid Flysch. Our preliminary data from the shaley series indicate an Albian to Early Campanian age. It represents mid-slope to abyssal plain starved basin sediments. The occurrence of similar and coeval series in the Carpathians and Ligurian Alps suggest common tectonic and oceanographic conditions.  相似文献   

16.
F. Piana  R. Polino 《地学学报》1995,7(2):138-143
The relationship between the Alpine and Apenninic orogenic systems is concealed at the surface by Tertiary sediments of two main tectono-stratigraphic units: the 'Alpine-related' Torino Hill domain and the 'Apennines-related' Monferrato domain. Mapping and structural analyses carried out in the area behind the Mio-Pliocene Apenninic-Padane thrust front allow comparison of the kinematic history of the Torino Hill and Monferrato domains. These are separate by the transpressive Tlio Freddo Deformation Zone' (RFDZ), interpreted here as the superficial expression of a crustal discontinuity along which the Alpine metamorphic basement overrode the Apenninic Ligurian nappes during the Palaeogene.
The Western Monferrato structural setting is the result of: (i) Late Oligocene-Burdigalian transpressive tectonics due to lateral displacement between the Alps-related and the Apennines-related domains; and (ii) compressive post-Messinian tectonics related to northward transport along the main Padane thrust front. Post-Messinian tectonic events affected also the NW-vergent asymmetrical Torino Hill anticline.  相似文献   

17.
The boundary area between the Apenninic fold‐and‐thrust belt and the crystalline Calabrian Arc, located around Sangineto in northern Calabria, has been investigated. New geological mapping in the Sant'Agata area has been performed on the Triassic successions traditionally attributed to the metasedimentary San Donato Unit. This, coupled with a reappraisal of the stratigraphy and tectonics of coeval successions present more to the south in the Cetraro Unit, results in a new reconstruction of the Triassic evolution of all the metasedimentary successions found in the region. Four informal stratigraphic units have been distinguished in the S. Agata area. The lowest one (Unit A) consists of well‐bedded metalimestones and bioturbated marly limestones that correlate with Ladinian–Carnian carbonates in nearby areas. A second unit (Unit B), never recognized before, contains a complex alternation of dolomites, phyllites and some meta‐arenites containing several beds of Cavernoso facies, attributed to the Carnian. They grade upward to platform and platform‐margin dolomites of Norian–Rhaetian age (Unit C) that in turn are replaced upward and laterally by a fourth unit (Unit D) consisting of well‐bedded, dark dolomites and metalimestones with marly interlayers locally found as resedimented large blocks in slope conglomerates. Unit D correlates with Rhaetian–Liassic beds in nearby areas. Several pieces of evidence of post‐metamorphic contractional tectonics, with 140°N and 30°N trends, are found together with evidence of SW‐directed extension. The siliciclastic Carnian beds of Unit B are correlated with the phyllites of Cetraro, formerly believed to be Middle Triassic; moreover, it is suggested that in the Cetraro area Unit C is almost totally replaced by Unit D. This demonstrates that the former distinction between the two tectonic units in the whole area has to be discarded. We have made a general palaeoenvironmental reconstruction which progresses laterally, during Ladinian–Carnian times, from (i) a coastal, mixed siliciclastic–carbonate–evaporitic area at Cetraro to (ii) a transitional carbonate shelf where siliciclastic input was only episodic, and finally to (iii) a bioconstructed margin which was later replaced by a steepened margin created by tectonic instability. Starting from the Norian, subsidence shifted toward the former coastal area where an intraplatform, restricted basin developed. The proposed stratigraphy corresponds closely to the Alpujarride units of the Betic Cordillera, Spain. Moreover, it is shown that strong affinities also exist, in terms of the structural framework, with the metamorphic units of Tuscany and Liguria. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

18.
In the Variscan foreland of SW-Sardinia (Western Mediterranean sea), close to the leading edge of the nappe zone, nappe emplacement caused folding and repetition of stratigraphic successions, km-scale offset of stratigraphic boundaries and an extensive brittle-ductile shear zone. Thrusts assumed a significant role, accommodating a progressive change of shortening direction and forming complicated thrust triangle zones. During thrust emplacement of the nappes, strong penetrative deformation affected rocks beneath the basal thrust of the nappe stack and produced coeval structures with both foreland-directed and hinterland-directed (backthrusting) shear sense. Cross-cutting and overprinting relationships clearly show that the shortening direction changed progressively from N–S to E–W, producing in sequence: (1) E–W trending open folds contemporaneous with early nappe emplacement in the nearby nappe zone; (2) recumbent, quasi-isoclinal folds with axial plane foliation and widespread, “top-towards-the-SW”, penetrative shearing; (3) N–S trending folds with axial plane foliation, contemporaneous with late nappe emplacement; (4) backthrusts and related asymmetrical folds developed during the final stages of shortening, postdating foreland-verging structures. Structures at (3) and (4) occurred during the same tectonic transport “top-towards-the-E” of the nappe zone over the foreland. The several generations of folds, thrusts, and foliations with different orientations developed, result in a complex finite structural architecture, not completely explicable by the theoretical model proposed up to date.  相似文献   

19.
The Northern Apennines of Italy is a fold and thrust belt that resulted from the NE‐ward progressive overthrusting of a Mesoalpine stacking (the ocean‐derived Ligurian Units) onto the detached sedimentary cover of the Adria plate continental margin (Foredeep Units). The Futa Pass area represents a key sector for the reconstruction of the deformation history of two Foredeep Units (Acquerino and Carigiola Units). The tectonic evolution of this sector is characterized by the superposition of three main deformation stages, with a constant NNE–SSW compression direction. The oldest structure is represented by the NNE‐verging Acquerino Unit duplex structure, the roof thrust of which is represented by the Ligurian stacking basal thrust. The interpretation of this structure as a large‐scale duplex is supported by the presence in the outer sectors of the Northern Apennines belt of Ligurian Units directly overthrust on younger Foredeep Units. In the second deformation stage the NNE‐verging Tavaiano Thrust developed. This regionally significant tectonic surface juxtaposes the Acquerino Unit (already developed as a duplex) and the overlying Ligurian Units, onto the Carigiola Unit. During this stage the fault pattern of the Carigiola Unit was also developed, characterized by two conjugate fault systems, coherent with a NNE–SSW maximum compression direction. During the last deformation stage, a backthrusting with a top‐to‐the SSW sense of movement (the Marcoiano Backthrust) brings the Carigiola Unit and its tectonic cover over the Acquerino and Ligurian Units, with the development of a large footwall syncline. The deformation history presented here differs from previous studies, and so provides a contribution to the debate on Northern Apennines tectonic evolution. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

20.
The Hoh Xil Basin, lying in the central Tibetan Plateau, is key to understanding the Cenozoic tectonics, paleoelevation and paleoclimate changes that have occurred in the Tibetan Plateau since the collision of the Indian and Asian tectonic plates. However, the stratigraphic age and paleoelevation indicated by the sediments of the Hoh Xil Basin remain hotly debated. Here we report on one palynological record from the TTH-C section, extracted from the Yaxicuo Group (the stratigraphic unit between the Fenghuoshan and Wudaoliang groups), and analyze its implications for stratigraphic age, paleoclimate and paleoelevation in the Hoh Xil Basin. The record shows that palynological taxa are mainly dominated by xerophytic Ephedripites, Nitrariadites (Nitrariapollis) and Chenopodipollis, with few ferns and conifers. Rich morphologies correspond well with those in the Xia Ganchaigou Formation (Fm) of the Qaidam Basin to the north. Palynological percentages are well correlated with the middle member of the Xia Ganchaigou Fm in the Qaidam Basin as well as the lower member of the Mahalagou Fm in the Xining Basin to the northeast. The ages of the middle member of the Xia Ganchaigou and lower member of the Mahalagou Fms from these two basins are both identical to the Bartonian Stage (~ 40–37 Ma) of the Late Eocene, according to their respective high-resolution magnetostratigraphic dating. This means that the age of the Yaxicuo Group at least covers the Bartonian Stage. Besides the Qaidam and Xining basins, the palynological assemblages of the TTH-C section are also similar to those of three other sites (the Jiuquan, Tu-ha and Hetao basins), indicating similarly arid climates dominated by a northwestern Chinese subtropical high, and a relatively low paleoelevation in the Hoh Xil Basin (mostly < 2000 m a.s.l.) in the Late Eocene.  相似文献   

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