Angelida Di Staso

The age of the oceanic accretionary wedge and onset of continental collision in the Sicilian Maghrebian Chain

New biostratigraphic data from the formations unconformably lying above the tectonic units resulting from the Flysch Basin Domain (FBD) in the Sicilian Maghrebids are here reported. The FBD constituted a southern branch of the western Tethys, separating during the Jurassic to Paleogene a Mesomediterranean Microplate from the African Plate. The age of the youngest sediments involved in the nappes and that of the unconformable terrains deposited in thrust-top basins on these tectonic units, allow to define both the age of deformation of the oceanic realm and the onset of the continental collision. The deformation migrated from internal to external areas of FBD starting from the latest Burdigalian-Langhian to Serravallian. Therefore, the previously proposed Eocene-Oligocene mesoalpine deformation of the Maghrebian FBD cannot be supported. The continental collision started during the Serravallian and it was accomplished in the late Tortonian, when clastic deposits sealed the boundaries of the tectonic units originated from all the paleogeographic domains of the Maghrebian Chain. The steps of the tectonic evolution in the Sicilian Maghrebids are now very well constrained and the proposed tectonic evolution may be extended to the whole Maghrebian Chain, as far as to the western Betic Cordilleras and to the southern Apennines, where most of the tectonic events show highly similar features and ages.

The Lower Miocene volcaniclastic sedimentation in the Sicilian sector of the Maghrebian Flysch Basin: geodynamic implications

Abstract Volcaniclastic debris-rich formations, characterising the Troina–Tusa Unit in the Sicilian Maghrebian Chain, are examined. The Troina–Tusa Unit terrains sedimented in the Maghrebian Flysch Basin, which, from Jurassic to Early Miocene, constituted the southernmost branch of the Western Tethys, located between Africa and the Mesomediterranean Terrane margins. New field, biostratigraphic and petrographic data enable a reconstruction of the palaeogeographic and structural evolution of the Flysch Basin immediately before its deformation. All the studied formations transpired to be Burdigalian in age. The sandstone compositions, showing different source areas (magmatic arc, recycled orogen and continental block), indicate a provenance for the clastic material from a crystalline basement with an active volcanic arc, replaced by a remnant volcanic arc, which was rapidly completely eroded. The source area that has been considered is Sardinia, where Upper Oligocene–Aquitanian calc-alkaline volcanites are widespread, but the sedimentological characteristics and the Burdigalian age do not fit with this provenance. The Burdigalian calc-alkaline arc should be located on the internal side of the Troina–Tusa Basin, above the already stacked Peloritanian units. A migration of the volcanic activity, connected with the subduction plain roll-back, can be envisaged from the Sardinia Block to the Peloritanian Chain, this latter still docked to the Sardinia–Corsica massif.

New biostratigraphic and petrographic data from the Poggio Carnaio Sandstone Fm (Val Marecchia Nappe): insights into the tectonic evolution of the Northern Apennines

In the Northern Apennines, the Poggio Carnaio Sandstone Formation consists of sandy-clayey turbidites, cropping out in the northernmost corner of the Val Marecchia Nappe.The formation has been considered Oligocene in age and is commonly interpreted as an Epiligurian unit, unconformably deposited above the Val Marecchia Nappe during its transport towards the Adriatic foreland.The Poggio Carnaio Sandstone Fm rests on the Argille Varicolori Fm of the Val Marecchia Nappe, but field data do not allow it to be recognized wherever it abruptly replaces the pelagic sediments of the Argille Varicolori Fm, thus testifying to the foredeep evolution of the basin, or where it unconformably overlies this latter formation.Nannofossil assemblages are characterized by abundant reworked Cretaceous and Paleogene taxa and by some taxa, whose first occurrence is reported in the upper part of the NN4 Zone = upper part of the CN3 Zone. Therefore the formation must be considered not older than Langhian.Detrital modes of arenites revealed a quartz-feldspathic composition and the lithic component includes mainly metamorphic fragments and minor plutonic, sedimentary, ophiolithic and volcanic clasts. The presence of clasts of garnet, sillimanite, hornblende and glaucophane is significant. Biostratigraphic as well as petrographic data agree with the interpretation of the Poggio Carnaio Sandstone Fm as an Epiligurian succession.Rock fragments indicate source areas characterized by Ligurian-, Pennidic- and Australpine-type units. Sedimentary facies and textural features of arenites, revealing a rapid erosion and deposition of clasts in a basin close to the source area of the clastic supply, indicate that the Alps cannot be considered as the source area of these arenites, as frequently argued for many North-Apennine clastic formations. Ligurian-, Pennidic- and Australpine-type units were located close to the Poggio Carnaio Sandstone basin, probably representing the geometrically highest units of the Palaeo-Apennine Chain.

The Oued Dayr Formation: first evidence of a new Miocene late-orogenic cycle on the Ghomaride complex (Internal Domains of the Rifian Maghrebian Chain, Morocco)

This work deals with the first evidence in the Rifian Maghrebids of a Miocene clastic succession, named Oued Dayr Fm, uncorformably resting on the Ghomaride Complex. The formation starts with polymictic conglomerates, consisting of clasts coming from all the Rifian Internal Units, sharply or gradationally evolving to graded and stratified calcareous sandstones, siltstones and massive marls. The occurrence of nannofossils starting from the NN5 Biozone of Martini indicates an age no older than middle Langhian. However, considering the possible reworking of taxa and the regional framework, the possibility of a younger age cannot be excluded. The sedimentary evolution points out a subsidence rate exceeding the detritic supply, within a thrust-top basin originated during an extensional tectonic phase, affecting the exhumed internal nappe stack. The Oued Dayr Fm constitutes the first evidence of a new Miocene late-orogenic sedimentary cycle resting on the Rifian Internal Units, intermediate between the Burdigalian Oued Gharraq-Sidi Abdeslam cycle and the Pliocene deposits. In a regional framework, no middle Miocene unconformable deposits are known on the Internal Units of both the Betic Cordillera and Maghrebian Chain, while Tortonian deposits everywhere occur. A Tortonian age, therefore, can be suggested for the Oued Dayr Fm, but data demonstrating this hypothesis at present are lacking.

The succession of the Val Marecchia Nappe (Northern Apennines, Italy) in the light of new field and biostratigraphic data

This paper challenges the classical idea that the Val Marecchia Nappe, the highest of the north-eastern Apennines, is a nappe that originated from the External Ligurian Domain and consisting of Upper Cretaceous–Middle Eocene rocks, accreted to the Palaeo-Apenninic Chain in the Middle-Late Eocene due to the Ligurian tectonic phase. Its succession comprises a Middle-Late Jurassic ophiolitic substratum and its sedimentary cover of Late Jurassic to Early Miocene age. This succession is quite similar to those of the North-Calabrian and Parasicilide Units of the Southern Apennines and of many Maghrebian and Betic Flysch Domain Units, all originating from the Western Tethys and deformed since the Early Miocene. The Val Marecchia Nappe succession was likely deposited in an oceanic realm that differs from that of the Ligurian Domain and was located in a more external palaeogeographic position with respect to that of the Ligurian Domain. The oceanic realm of the Val Marecchia Nappe constituted the northwards extension of the Maghrebian Flysch Basin-Lucanian Ocean system.

New stratigraphic data for the Poggio Carnaio Sandstone Fm (Northern Apennines; Italy)

A revision of field data and new biostratigraphic analyses have highlighted that the lowest part of the Poggio Carnaio Sandstone Fm consists of greyish marls, formerly attributed to the Antognola Marl Fm, and that calcareous nannofossil assemblages from these marls as well as from the overlying turbiditic sandstones are characterized by some taxa first occurring in Tortonian. Moreover, the occurrence of Discoaster cf. berggrenii could suggest an age not older than late Tortonian for the studied succession. The Poggio Carnaio Sandstone Fm, therefore, from its base is not older than Tortonian and constitutes a thrust-top basin unconformable succession, deposited on sub-ligurian units.

Stratigraphic revision of the Cenozoic deposits of the Lungro-Verbicaro Unit (Northern Calabria): new data for the reconstruction of tectonic evolution of the southern Apennines

Field and biostratigraphic data from Cenozoic metasedimentary succession («breccia a selce», Colle Trodo and «Scisti del Fiume Lao» Formations) of Lungro-Verbicaro Unit are reported. The «Scisti del Fiume Lao» Formation, formerly included in the ophiolite-bearing Frido Unit, defined at the Calabria-Lucania border area, is interpreted as the stratigraphic uppermost part of the above Cenozoic succession. Therefore, the occurrence of nannofossil assemblage not older than late Aquitanian, represents the minimum age constrain both to the deformation and to the HP/LT metamorphic event affecting the Lungro-Verbicaro Unit. This age is in agreement with the Burdigalian radiometric age recognized in metavolcanic and metapelitic rocks of Lungro-Verbicaro Unit.