Sabatino Ciarcia

On the tectonic evolution of the Ligurian accretionary complex in southern Italy

Unraveling the deformation pattern characterizing the transition from final oceanic subduction stages to early stages of deformation of a foreland continental margin is crucial for a better understanding of the geodynamic processes taking place at convergent plate boundaries. In particular, the combined role of internal wedge dynamics and continental-margin architecture in controlling the tectonic evolution of an accretionary complex during its final emplacement onto the foreland continent is discussed in this study. To this purpose, we conducted integrated structural, stratigraphic, and low-temperature thermochronometric analyses on the Ligurian accretionary complex units exposed in the Campania region (Italy) and on continental-margin successions located in their footwall, as well as on related foredeep and wedge-top basin deposits. Our results point out a series of late early Miocene (Burdigalian) shortening events, also involving buttressing of the accretionary wedge against the crustal ramp of the foreland continental margin. Emplacement of the overthickened accretionary complex onto the distal part of the continental margin was followed by horizontal extension and wedge thinning, aiding the development of wedge-top depocenters. Extension may have been either related to reduced subduction rates during the middle Miocene, or to a period of subduction erosion (known to have occurred in the Northern Apennines in the same time frame). Early Miocene NW-SE shortening recorded by Ligurian accretionary complex units was completely unrelated to later (late Miocene to Pleistocene) NE-directed thrusting in the Apennines, which was coeval with backarc extension in the Tyrrhenian Sea. Therefore, our results emphasize the occurrence of a major discontinuity in the Neogene geodynamic evolution of the Southern Apennines, the tectonic history of which may be clearly subdivided, from a kinematic point of view, into pre- and syn-Tyrrhenian backarc extension stages.

The northward tectonic transport in the southern Apennines: examples from the Capri Island and western Sorrento Peninsula (Italy)

We analyzed a thrust fault system located in the western Sorrento Peninsula and Capri Island (southern Italy) where several mesoscale structures related to the main thrusts, such as Riedel shear planes, overturned folds, minor thrust and back-thrust faults, suggest a dominant northward tectonic transport. Major and minor thrust faults, generally characterized by a ramp-flat geometry, involved the Mesozoic Apennine carbonates, the Middle Miocene foredeep, and the unconformable thrust-top basin deposits. The biostratigraphic analysis of calcareous nannoplankton assemblages on the thrust-top basin sediments indicates an age not older than late Tortonian. We propose that this out-of-sequence thrusting stage was related to a regional tectonic event widespread in the entire southern Apennines, probably occurred in the Pliocene time simultaneously with the activity of deep-seated thrust faults that involved the buried carbonates of the Apulian platform. These out-of-sequence thrust faults, here referred to as “envelopment thrusts,” were enucleated in a lower structural level with respect to the allochthonous wedge, representing the W–E segments of large regional arcuate structures.

Stratigrafia della Formazione del Ponticello (Miocene superiore, Appennino campano)

The Ponticello formation is represented by a siliciclastic and calciclastic sedimentary succession, outcropping in the campanian sector of the Southern Apennines, and structured in four main sequences (lithozones). A transition interval is localized in the upper portion of the sedimentary record. A lithozone CTS (Calcarenitic Turbiditic Sequence), with dominant marly deposits is constituted by yellow, medium, sometimes coarse grained stratified calcarenites, occasionally weakly cemented. The bed thickness varies from a few centimeters to several decimeters, with many showing the Bouma Sequence. In the Arenara and Melito Vecchia locations frequent intervals of marls, marly limestones, and rarely «pseudo-saccharoidal» limestones crop out. An intense bioturbation is present. The deposits of this interval are approximately 25 meters thick and originated by turbiditic processes. A lithozone SCS (Sandy-microConglomeratic Sequence), with dominant arenaceous-conglomeratic deposits, comprises alternations of medium-coarse grained yellow-brownish sands with quartzo-feldspathic composition, and paraconglomerates. In places this interval includes some layers of granular conglomerates, with sub-rounded polygenic clasts, immersed in a sandy matrix. The sands are organized in layers some decimetres thick. The paraconglomerates are usually organized in fining-up sequences. The thickness of this lithozone is approximately 40 meters, the significant exposures being in the Vallone dei Morti. The deposits of this lithozone can be interpreted as formed by submarine mass flows and gravity flows. A lithozone MCS (Marly-Calcareous Sequence), with marly-limestone dominant, consists of alternations of marls, calcareous marls and white marly limestones, ordered in layers which generally have a maximum thickness of 10–15 centimeters, and usually contain an abundant planktonic microfauna. The thickness of this lithozone seems to exceed 50 meters in the Incoronata and Felette locations. The sediments of this interval can be considered as the result of depositional processes that occur along a submarine slope. Above the lithozone MCS lies a transitional stratigraphic interval, well exposed along the Vallone Ponticello, and characterized by two dominant components: a calciclastic portion (TCC), in the lower part, and a siliciclastic fraction (TSC), in the upper part. The lower part, about 20 meters thick, crops out in the C. Sterpara and Pretalonga locations, shows alternations of partially recrystallized calcarenites and calcareous brecciola. This last lithotype is characterized by lithoclastic (calcilutites, oolithic limestones, etc.) and bioclastic ( Lithothamnium and briozoarians, pectinids, etc.) elements, granule to fine pebble size and frequently angular-shaped, inter-bedded with marly limestones and marls. In the C. Sterpara location, the upper transition interval (TSC), approximately 25 meters thick, also outcrops. It is constituted by sandstones, siltstones and marls, with very frequent intercalations of alternating of light grey muddy marls and brownish muddy silts, outcropping in Incoronata location. Here a polygenetic orthoconglomerate horizon more than one meter thick is present, containing an important crystalline fraction (mostly granitoids). The clast dimensions are commonly larger than ten centimetres, the sorting is moderate, and a short supply of the arenaceous-microconglomeratic matrix is manifest. The transition interval can be interpreted as connected to processes of detritic sedimentation in proximal sectors of the marine basin, near the coastline. A lithozone ATS (Arenaceous Turbiditic Sequence) with arenaceous-pelitic compositions dominant, consists of brownish-yellow, [or yellowish-brown!] medium to fine grained, quartzo-feldspathic sandstones and laminated muds. Usually the complete Bouma Sequence is recognizable. The best exposure is in the C. Sterpara location, where this interval reaches a thickness of approximately 30 meters. This interval can be interpreted as the result of submarine turbiditic flows. The planktonic foraminifera (biozone G. o. extremus ) and nannoplankton (biozone CN9a) associations indicate a middle-upper Tortonian age. The calciclastic fraction originates from the erosion of several units of the Southern Apennine chain. The supply areas of the calcareous clasts are identifiable with the Mesozoic carbonate platform unit, mainly from outer positions. In the lower part of the transition interval (TCC) the presence of fragments of limestones with Lithothamnium and briozoarians indicates the probable erosion of Miocene successions (Formazione di Cusano and Formazione di Longano, Selli, 1957) overlying some external platforms. The source areas of the siliciclastic sediments, instead, derive from the erosion of deposits previously involved in the orogenic transport. The rich presence of crystalline clasts in the upper portion of the transition interval (TSC), is due to probable reworking of inner units of the sudappennine chain (cfr. Gruppo del Cilento, Amore et alii , 1988). The supra-Miocene deposits of the Ponticello Formation are the expression of an intermontane basin, carried on the Southern Apennine nappes, in thrust-top position.

PLIOCENE PARALIC ENVIRONMENTS OF IRPINIA-DAUNIA BASIN (BARONIA MOUNTAINS, SOUTHERN APENNINES, ITALY)

This report describes and interprets two stratigraphic sections across the regressive part of Baronia Synthem, located near the villages of Flumeri and Vallesaccarda (Ariano Irpino area, Southern Italy). Four different depositional environments have been recognized: fluvial, lagoon, foreshore and shoreface. Fluvial deposits, occurring in the Flumeri section, consist of clast-supported conglomerates, horizontal laminated sands and muddy silts with freshwater ostracod assemblages, indicating deposition in braided river low-sinuosity channels. In the Flumeri section lagoonal deposits are generally represented by structureless layers of dark clay including ostracods of brackish coastal lagoon connected with shallow-marine waters. In the Vallesaccarda section lagoonal sediments only occur as muddy clasts. Foreshore deposits are represented by well sorted yellow sands with low-angle cross lamination; a horizontal layer of stratified gravels outcrops in Vallesaccarda section. The shoreface deposits consist of poorly sorted sands with trough cross stratification formed in a bar and trough system, of symmetric ripples layers, and of abundant mollusc shell debris; in the Vallesaccarda section a tempestite interval generated by storm activity has been found. In Flumeri section littoral and lagoonal facies assemblages alternate; in Vallesaccarda section only nearshore sediments crop out. Nearshore deposits denote a wave-dominated coastal marine environments. These data contribute to a better knowledge of the distribution of paralic facies on the Western margin of the Pliocene Irpinia-Daunia Basin.

Tectono-stratigraphic setting of the Campania region (southern Italy)

ABSTRACT This paper furnishes a brief, but exhaustive, description of the tectonics and stratigraphy of the Campania region (southern Italy). The attached geological map (Main Map) at 1:250,000 scale should be considered as a first attempt to provide a more detailed geological cartography of the entire region, with respect to the available literature, in the light of scientific advances in stratigraphy and tectonics reached in the last years. The geological setting, proposed in this study, is the result of a review and reinterpretation of the current geological knowledge plus original surveys carried out in some key sectors of the area. We also include a schematic stratigraphic chart and three geological cross-sections illustrating the tectonic architecture in depth for the internal and external zones. The geodatabase was compiled in GIS format and subsequently imported in vector graphic software to allow a classical cartographic design.

Evoluzione tettono-sedimentaria del Complesso d’Accrezione Liguride in Appennino Meridionale

Tectono-sedimentary evolution of the Ligurian Accretionary Complex in the southern Apennines.Aim of this paper is the structural and stratigraphic analyses of the Ligurian Accretionary Complex exposed in the Campania region (Italy) in order to unraveling the deformation pattern characterizing the transition from the final oceanic subduction stages to the early stages of deformation of the foreland continental margin. Our results outline a sequence of late Early Miocene (Burdigalian) shortening events, also involving buttressing of the accretionary wedge against the crustal ramp of the foreland continental margin. Emplacement of the overthickened accretionary complex onto the distal part of the continental margin was followed by horizontal extension and wedge thinning, aiding the development of wedge-top depocenters. Early Miocene NW-SE shortening recorded by Ligurian Accretionary Complex units is completely unrelated with later (Late Miocene to Pleistocene) NE-directed thrusting in the Apennines, which was coeval with back-arc extension in the Tyrrhenian Sea. Therefore, our results emphasize the occurrence of a major discontinuity in the Neogene geodynamic evolution of the southern Apennines, whose tectonic history may be clearly subdivided, from a kinematic point of view, into pre- and syn-Tyrrhenian back-arc extension stages.