Optical parameters of maturity of organic matter dispersed in sediments: first results from the Central Apennines (Italy)

Levels of organic maturity of Mesozoic and Tertiary sequences outcropping in the Central Apennines have been established, using vitrinite reflectance techniques, the Thermal Alteration Index and fluorescence colours of organic matter dispersed in sediments. These results provide new constraints throughout the Meso-Cenozoic evolution of this crustal sector. In exploration geology, vitrinite reflectance provides data on hydrocarbon maturation by constraining organic matter maturity. In sedimentary basin modelling, it is adopted to define the palaeothermal regime. Vitrinite reflectance (R_o) also provides information on the burial history of sedimentary basins and may be employed to estimate tectonic uplift and erosion rates. Thermal Alteration Index (TAI) and fluorescence colour values can be correlated with R_o and may be used to estimate the degree of maturation when vitrinite is absent. Samples derived from the Sabini and Tiburtini Mts, in slope facies between the Latium–Abruzzi carbonate Platform and the Umbria–Marche pelagic Basin; from the Simbruini and Ernici Mts, in carbonate Platform facies, and from upper Miocene turbiditic deposits outcropping between the Olevano–Antrodoco Une, towards the West, and the Marsica slope facies, towards the East. Both the pre-terrigenous Meso-Cenozoic sequences show a low grade of organic maturity: the Sabini and Tiburtini Mts show R_o values that are less than 0.4%, and the Simbruini–Ernici Range show R_o values that range between 0.5% and 0.65%. Field analysis indicates that the cause of these low maturity levels is that thick sequences of turbidites were never deposited during the Neogene evolution of the Apennine thrust belt. Moreover, Upper Miocene turbiditic deposits also show low maturity levels, with R_o values that are less than 0.5%, indicating that these deposits were never overthrusted by huge volumes of rocks, during the chain building. The slight increase in the maturity level recorded in the Marsica area may be related to local heating along shear zones in areas of strike-slip tectonics.     

Thermal and tectonic evolution of the southern Alps (northern Italy) rifting: Coupled organic matter maturity analysis and thermokinematic modeling

The Pearl River Mouth Basin (PRMB) is one of the most petroliferous basins on the northern margin of the South China Sea. Knowledge of the thermal history of the PRMB is significant for understanding its tectonic evolution and for unraveling its poorly studied source-rock maturation history. Our investigations in this study are based on apatite fission-track (AFT) thermochronology analysis of 12 cutting samples from 4 boreholes. Both AFT ages and length data suggested that the PRMB has experienced quite complicated thermal evolution. Thermal history modeling results unraveled four successive events of heating separated by three stages of cooling since the early Middle Eocene. The cooling events occurred approximately in the Late Eocene, early Oligocene, and the Late Miocene, possibly attributed to the Zhuqiong II Event, Nanhai Event, and Dongsha Event, respectively. The erosion amount during the first cooling stage is roughly estimated to be about 455–712 m, with an erosion rate of 0.08–0.12 mm/a. The second erosion-driven cooling is stronger than the first one, with an erosion amount of about 747–814 m and an erosion rate between about 0.13–0.21 mm/a. The erosion amount calculated related to the third cooling event varies from 800 m to 3419 m, which is speculative due to the possible influence of the magmatic activity.     

Activity maps of multi-source mudslides from the Daunia Apennines (Apulia,southern Italy)

Natural Hazards - Flooding poses a serious public health hazard throughout the world. Flood modeling is an important tool for emergency preparedness and response, but some common methods require a...     

Influence of syn-sedimentary faults on orogenic structures in a collisional belt: Insights from the inner zone of the Northern Apennines (Italy)

This paper discusses the possible influence of syn-sedimentary structures on the development of orogenic structures during positive tectonic inversion in the inner Northern Apennines (Italy). Examples from key areas located in southern Tuscany provided original cartographic, structural and kinematics data for Late Oligocene-Early Miocene thrusts, organized in duplex systems, verging in the opposite direction of the foreland propagation (back-thrusts), which affected the Late Triassic-Oligocene sedimentary succession of the Tuscan Domain, previously affected by pre-orogenic structures. These latter consist of mesoscopic-to cartographic-scale Jurassic syn-sedimentary normal faults and extensional structures, which gave rise to effective stratigraphic lateral variation and mechanical heterogeneities. Structural analysis of both syn-sedimentary faults and back-thrusts were therefore compared in order to discuss the possible role of the pre-existing anisotropies in influencing the evolution of the back-thrusts. As a result, it can be reasonably proposed that back-thrusts trajectories and stacking pattern were controlled by relevant syn-sedimentary normal faults; these latter were reactivated, in some cases, if properly oriented. Such an issue adds new inputs for discussing the potential role of structural inheritance during tectonic inversions, and helps to better understand the processes suitable for the development of back-thrusts in the inner zones of orogenic belts, as it is the case of the inner Northern Apennines.     

Recent and active tectonics of the external zone of the Northern Apennines (Italy)

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.     

Lateral variations in tectonic style across cross-strike discontinuities: an example from the Central Apennines belt (Italy)

In foreland thrust belts, abrupt lateral changes in tectonic style, structural–stratigraphic features, and topography usually occur across cross-strike faults. The Central Apennines of Italy offer an exceptional scenario of lateral variations in tectonic setting. Here, the Sangro Volturno oblique thrust ramp (SVOTR) represents the outer thrust front of the Pliocene–Quaternary foreland thrust system, confining southward the axial culmination of the orogen that occurs in the Central Apennines. We present an interpretation of the Pliocene–Quaternary evolution of this cross-strike fault through an integrated dataset including structural-geological mapping and subsurface onshore seismic reflection profiles. The interpretation of the structural framework is augmented by the analysis of low-temperature thermochronometers from 32 new sites extending across the subsurface transverse structure. As evidenced by seismic line interpretation, the localization and development of the SVOTR have been influenced by inherited extensional faults within a positive inversion tectonics context. The regional distribution of the maximum paleotemperature values across the SVOTR constrains the original extent of the allochthonous thrust sheet over all its hanging-wall and footwall blocks. The Pliocene–Quaternary thrusting and inversion of SVOTR caused the strong hanging-wall uplift, which brought to the complete erosion of the allochthonous units and the exhumation of the Adria units. The integrated analysis of low-temperature thermochronometers and structural evidence as applied in the study case can define the role of major cross-strike discontinuities in foreland thrust belts, by constraining and verifying their tectonics inversion significance and the amount of related exhumation.     

A major geodynamic change revealed by Quaternary stress patterns in the southern Apennines (Italy)

In southern Italy, analysis of fault slip data sets, in particular from Quaternary formations, provides evidence for a recent change of the stress field. During the Early Pleistocene, the horizontal maximum stress axes were ENE-WSW trending. The deformation was ENE-WSW compression near the front of the chain, and NNW-SSE extension close to the back-arc basin. Some time after the Early Pleistocene, the direction of the largest horizontal stress axes changed to northwest-southeast. Only extensional deformation (σ₂, NW-SE trending; σ₃, NE-SW trending) is observed for this phase and focal mechanisms indicate that it is still active. This NE-SW extension invaded areas previously affected by compression or NNW-SSE extension and coincides with major uplift of Pleistocene marine sediments in the chain and the foredeep up to 700 m above sea level. This change in the stress regime corresponds to the end of accretion processes that had prevailed since the Middle-Late Miocene. As a consequence of this discovery of a recent regional stress and deformational style change, the present-day normal and strike-slip faulting earthquake focal mechanisms in the Southern Apennines should not be considered representative of Tyrrhenian Sea opening and Apennines accretion.     

Structural style and deformation mechanism of the southern Dabashan foreland fold-and-thrust belt, central China

The Daba Mountains define the southern margin of the East Qinling orogenic belt, and form the boundary of the Sichuan basin in the north and northeast. The Daba Mountains can be divided into two structural belts by the NW-striking Chengkou fault, namely the northern Dabashan thrust-nappe belt and the southern Dabashan foreland fold-and-thrust belt. The southern Dabashan fold-and-thrust belt is a southwestward extruding thin-skinned thrust wedge, showing obvious belted change in deformation style and deformation intensity along the dip direction, and can be divided further into three sub-belts, i.e. the imbricate thrust sub-belt characterized by imbricate stepped-thrust sheets, the thrust-fold sub-belt characterized by the combination of the equally-developed thrusts and related folds, and the detachment-fold sub-belt characterized by box folds and closed overturned-isoclinal folds on the outcrops. Several kinds of structures have been recognized or inferred, including imbricate thrust system, passive-roof duplex (triangle zone), fault-related folds, back-thrust system and pop-up structure. The NE-SW compressive stress from the Qinling orogenic belt and detachment layers in the covering strata are the two most important determinants of deformation style. After the collision between the North China block and Yangtze block at the end of the Middle Triassic, the northward intracontinental subduction along the southern edge of the Qinling orogenic belt was initiated, which led to the corresponding southward thrusting in the upper crust. The thrusting propagated towards the foreland through the Jurassic and extended to the southernmost part of the southern Daba Mountains around the end of the Early Cretaceous, with thrusting deformation to be preferentially developed along major detachment layers and progressing upwards from the Lower Sinian through the Lower Cambrian and Silurian to Middle-Lower Triassic. Translated from Geotectonica et Metallogenia, 2006, 30(3): 294–304 [译自: 大地构造与成矿学]     

On the tectonics of the Ligurian Apennines (northern Italy)

Four nappes have been recognized in the Ligurian Apennines. In the Lavagna Nappe very low-grade metamorphism is combined with very large, originally W-facing isoclinal folds. In the other nappes, no evidence for metamorphism is found and all eutectonic folding was originally E- to NE-facing. Tectonic transport along the major nappe contacts was in an E- to NE-direction. A tectonic model is presented, which explains the generation of the large, originally W-facing folds as a result of originally E-inclined subduction within a young oceanic basin. Young oceanic lithosphere (maximum age approximately 25 Ma) subducted beneath oceanic lithosphere with a maximum age of approximately 40 Ma, under the influence of horizontally oriented compressional forces. Within the tectonic wedge, associated with the subduction, originally W-facing isoclinal folding and metamorphism occurred. Decrease and/or termination of compression resulted in the cessation of the subduction movements, followed by uplift of the region above the subducted plate by means of buoyancy. This uplift formed a slope from which sequences slid in an E- to NE-direction, causing E- to NE-facing folds. Ultimately, detachment and thrusting of gravitational nappes took place, by which process rock sequences of oceanic origin have been externally transported to attain ensialic (continental) domains. The Triassic-Early Oligocene tectonic events recognized in the Ligurian Apennines correlate quite well with the events that preceded the collision phase of the Alps.     

Convective support of long-wavelength topography in the Apennines (Italy)

Bio-alteration of basaltic glass in the oceanic crust has lately attained much attention. One of the many questions related to this topic is the depth at which bio-alteration presently takes place in the oceanic crust. For this purpose we have investigated samples from the deepest drill hole, i.e. Hole 540B at the Costa Rica Rift in the eastern equatorial Pacific. The glassy rim of pillow lava samples show alteration textures and δ¹³C values compatible with microbial activity throughout the upper 500 m part of the volcanic succession. The concentration and distribution patterns of carbon and potassium within the microbially altered parts, however, indicate that microbes presently interact with the fresh glass to depths of about 380 m into the volcanic basement, at temperatures up to ≈100 °C.     

Triassic metasedimentary successions across the boundary between the southern Apennines and the Calabrian Arc (northern Calabria,Italy)

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.     

The Mesozoic continental rifting in the Mediterranean area: insights from the Verrucano tectofacies of southern Tuscany (Northern Apennines,Italy)

In the Alpine-Mediterranean region, the continental redbeds and shallow-marine siliciclastics related to the early depositional phases of the Late Permian-Mesozoic continental rifting are referred to as the most common representative of the “Verrucano tectofacies”. The Verrucano-type successions exposed in southern Tuscany are diachronous, spanning from Triassic to earliest Jurassic in age, and accumulated within the Tuscan domain, a paleogeographic region of continental crust that due to the opening of the Piedmont–Ligurian ocean formed part of the Adria passive-margin. They belong to the metamorphic Verrucano Group and the non-metamorphic Pseudoverrucano fm. Viewed overall, these Verrucano-type successions appear to manifest five episodes or pulses of an ongoing continental rifting. With the exception of the first episode that developed entirely within a terrestrial setting, each one is represented by basal Verrucano-type continental siliciclastics overlain by compositionally mixed marine deposits, which resulted from four diachronous, post-Middle Triassic transgressions. This suite of tectonic pulses produced the progressive westward widening (backstepping) of the Tuscan domain in the rifting south-Tuscany area.     

AMS fabric and tectonic evolution of Quaternary intramontane extensional basins in the Picentini Mountains (southern Apennines, Italy)

In this work, we report the results of combined geological, structural, and anisotropy of magnetic susceptibility (AMS) studies carried out on Quaternary deposits in the Picentini Mountains, southern Apennines (Italy). The study concerns four small continental basins, Acerno, Tizzano, Iumaiano, and Piano del Gaudo, related to fluvial–lacustrine depositional environments, ranging in altitude from 600 to 1,200 m a.s.l. and strongly incised during recent time. Stratigraphic and structural analyses, integrated by low- and high-field anisotropy of magnetic susceptibility (AMS), show that the formation of these basins has been controlled by extensional and transtensional tectonics. Most of the AMS sites exhibit a well-defined magnetic foliation parallel to the bedding planes. A well-defined magnetic lineation has also been measured within the foliation planes. In the Iumaiano, Tizzano, and Piano del Gaudo basins, magnetic lineations cluster around NNE–SSW trend and are parallel to the stretching directions inferred by structural analysis of faults and fractures. On the basis of structural, sedimentological, and high-field AMS data, we suggest a tectonic origin for the magnetic lineation, analogously to what has been observed in other weakly deformed sediments from Neogene and Quaternary extensional basins of the Mediterranean region. Our results demonstrate that onset and the evolution of the investigated basins have been mainly controlled since lower Pleistocene by NW–SE normal and transtensional faults. This deformation pattern is consistent with a prevalent NE–SW extensional tectonic regime, still active in southern Apennines, as revealed by seismological and geodetic data.     

Microstructures of intergrown phyllosilicate grains from Verrucano metasediments (northern Apennines, Italy)

Interleaved phyllosilicate grains (IPG) of various compositions are widespread in low-grade Verrucano metasediments of the northern Apennines (Italy). They are ellipsoidal or barrel shaped, up to 300–400 μm long and they are often kinked and folded; phyllosilicate packets occur as continuous lamellae or as wedge-shaped layers terminating inside the grain. Using electron microscopy techniques (SEM, TEM) six types of IPG have been distinguished on the basis of their mineralogical composition: (1) Chl+Ms ± Kln; (2) Chl+ Ms+Pg ± Kln; (3) Ms+Prl ± Pg; (4) Ms+Prl+Su; (5) Ms+Prl+Chl+Su; (6) Su+Ms. Types (1) and (2) are mainly composed of chlorite, with Ms and Pg as minor phases; Kln grows on Ms in highly weathered samples. Types (3), (4), (5), and (6) are composed of muscovite, with intergrown Prl, Chl, Su and new-formed muscovite. The IPG show all kinds of contacts: from coherent grain boundaries with parallel basal planes and along-layer transitions to low- and high-angle grain boundaries. The IPG formed on pristine minerals such as chlorite and muscovite. The transformations took place during the prograde and retrograde metamorphic path of the rocks: they were facilitated by deformation and they occurred in equilibrium with a fluid phase, which allowed cation diffusion. Prograde reactions [Chl = Ms (or Pg); Ms = Prl; Ms = Chl] involve dehydration and sometimes a decrease in volume, whereas retrograde reactions (Ms = Kln; Ms = Su) involve hydration and an increase in volume. These transformations do not simply occur through an interchange of cations, but often involve deep structural changes: transitions from one phyllosilicate to another generally proceed through dissolution-recrystallization reactions. In conclusion, Verrucano IPG represent microstructural sites which have not completely equilibrated with the whole rock and whose mineral assemblage depends on the original composition of the microstructural sites. Received: 20 June 1996 / Accepted: 3 February 1997     

Tethyan heritage in the development of the Neogene Umbria-Marche fold-and-thrust belt, Italy: a 3D approach

The Umbria-Marche fold-and-thrust belt (Northern Apennines, Italy), provides excellent opportunities to evaluate the structural heritage of the opening of the Mesozoic Tethys Ocean in the 3D geometry of the Neogene compressional structures related to the Alpine Orogeny. The structure and evolution of a portion of the southernmost belt, between the Nera River and the Rieti Basin, are described as a field example, and the kinematics along well-exposed Mesozoic extension structures are provided. Cross-section restoration shows a close coincidence between these extension structures and the Neogene thrust ramps, thus suggesting that the geometry of the latter was controlled by the map distribution of the former. Sequential balancing also allows for the definition of the geometrical pattern of pre-existing normal faults, which were produced in response to a unidirectional or a two-directional extension stress field. The inferred direction of principal extension, corrected for the effects of late deformation, is consistent with that proposed for the northern margin of the Adria Promontory in global-scale plate tectonic reconstructions.     

Normal faulting, transcrustal permeability and seismogenesis in the Apennines (Italy)

Late Pliocene–Pleistocene tectonic evolution of the Apennines is driven by progressive eastward migration of extensional downfaulting superposed onto the Late Miocene–Early Pliocene compressional thrust belt. This process has led to distinct structural domains that show decreasing transcrustal permeability from conditions of pervasive mixing between deep and surface fluids in the hinterland (west) to conditions of restricted fluid circulation and overpressuring in the foreland (east). At present, the highest rates of normal faulting and the strongest seismicity occur in the area bounded by stretched, highly permeable crust to the west and thick, poorly permeable crust to the east. In this area, the seismogenic sources of the largest earthquakes (5<M_s<7) are potentially related to mature normal faults that deeply penetrate thick brittle upper crust, and act as transient high-permeability channels during seismic activity. In this framework, it is plausible that domains of overpressuring govern progressive inception of normal faulting and fluid redistribution in the crust, leading to eastward migration of the belt of maximum seismicity with time.     

Tectonic burial and exhumation in a foreland fold and thrust belt: the Monte Alpi case history (Southern Apennines,Italy)

The Monte Alpi area of the Southern Apennines represents the only sector of the thrust belt where the reservoir rocks (i.e. Apulian Platform carbonates) for major hydrocarbon accumulations in southern Italy are interpreted to crop out. Tectonic evolution and exhumation of this area were analysed by integrating stratigraphic and structural data with different organic and inorganic parameters which record the burial and thermal evolution of the sediments (vitrinite reflectance, fluid inclusions, and I/S mixed layers in clayey sediments). Our analyses suggest that the presently exposed Monte Alpi structure suffered a loading of ca. 4000 m, owing to the emplacement of allochthonous units in Early Pliocene times. Available geological data indicate that erosion of the tectonic load occurred since the Late Pliocene, when the area first emerged. This implies an average exhumation rate in excess of 1 mm/year. A model can be constructed which matches the maturity indices and also takes into account intermediate stages of the evolution, resulting from combined structural and fluid inclusion data. By this model, a first stage of exhumation would have taken place at an average rate of about 0.36 mm/year. This was controlled by uplift and erosion associated with both: (i) thrusting at depth within the Apulian carbonates (Late Pliocene), and (ii) strike-slip faulting (Early Pleistocene). A second exhumation stage would have occurred in the last 700 ky at a much faster rate (ca. 4 mm/year) as a result of extensional tectonics.     

Statistical occurrence analysis and spatio-temporal distribution of earthquakes in the Apennines (Italy)

We present two examples of statistical analysis of seismicity conducted by integrating geological, geophysical and seismological data with the aim to characterize the active stress field and to define the spatio-temporal distribution of large earthquakes. Moreover, our data will help to improve the knowledge of the “seismogenic behavior” of the areas and to provide useful information for seismic hazard evaluation.The earthquakes are described by two non-parametric statistical procedures integrating also tectonic-physical parameters to study the spatio-temporal variability.The results show that the areas are characterized by: 1) a stress regime with mainly extensional kinematics; 2) tectonic structures mainly oriented with the active stress field (S_hmin = N44° ± 18° in the southern Apennines and S_hmin = N50° ± 17° in the central Apennines); 3) cluster distribution of seismicity and 4) a high probability of earthquake occurrence (M > 5.5) in the next 10 years.