Scaglia Toscana Research Articles

Late Cretaceous black shales from the Tuscan Sedimentary Succession (northern Tuscany, Italy): geochemistry and ore mineralogy

We report on the first geochemical and mineralogical study of the Late Cretaceous black shales and black phyllites occurring within the basal portion of the “Scaglia toscana” and “Scisti sericitici” formations, respectively (Northern Apennines, northern Tuscany, Italy). The black shales occurring within the “Scaglia toscana” Formation are interbedded with red and greenish shales and form cm-thick layers; in some localities they are characterized by the occurrence of cm- sized pyrite nodules. Black phyllites and meta-cherts in the “Scisti sericitici” Formation are associated with Cu ores and with a small pyrite-molybdenite mineralization. These rocks are made of variable amounts of quartz, “chlorite”, illite/muscovite, pyrite ± calcite ± albite plus accessory amounts of baryte, apatite, sulfides and sulfosalts. In addition, they contain abundant carbonaceous matter (2-12 wt% total organic carbon). Whole-rock analyses by ICP-MS reveal a marked enrichment of Cd, Ag, Zn, Sb, Cu, Mo, V, Pb, and Tl with respect to the average marine shale and to the more typical shales of the “Scaglia toscana” fm. The distribution of these elements in the studied samples is compatible with a strongly anoxic and euxinic depositional environment. The hyper-enrichment of Cd, Ag, Zn, Sb and Cu strongly suggests that besides from seawater these elements were extracted from additional sources, most likely hydrothermal vents.

The Scaglia Toscana Formation of the Monti del Chianti: new lithostratigraphic and biostratigraphic data

The Scaglia Toscana Formation (Scisti Policromi Auctt.) is one of the most investigated formation of the Tuscane Nappe. The Formation is widely exposed in the Chianti Mounts and despite the number of studies in this area, some aspects remain poorly known and debated. In this paper new litho- and bio-stratigraphic data from eight key-sections distributed over the entire area are provided and discussed in order to clarify the stratigraphic relationshpis among different lithostratigraphic members, as well as the depositional ages of each member. The Formation deposited in the Cretaceous-Oligocene time interval and it can be subdivided into five lithostratigraphic members: i) the Argilliti di Brolio (wine-red shales with sporadic siliceous calcilutites and rare interbedded cherts); ii) the Marne del Sugame (red and pink marls, calcareous marls and marly limestones with interbedded calcarenitic beds and ruditic lens-shaped bodies including calcareous-siliceous clasts); iii) the Argilliti di Cintoia (grey-green to black shales, locally with manganese-rich siliceous calcilutites and cherts); iv) the Calcareniti di Montegrossi (thin beds of calcilutites and calcarenites with varicoloured shaly-marly interbeds); and v) the Argilliti e Calcareniti di Dudda (alternating thin beds of calcilutites and calcarenites with varicoloured shaly-marly interbeds). These members deposited in a marine environment and have been interpreted as deposited in a turbiditic system, in which shaly and calcareous turbiditic members have been attributed to a basin plain below the CCD, whereas the marls and marly limestones of the Marne del Sugame Member can be settled in a slope/ramp environment above or close to the CCD. Furthermore, the combination of these new data with structural informations coming from literatures allowed to a better paleogeographic reconstruction of the paleobasin. In order to better explain these data, the paper is accompanied by two geological maps realized in the past but never distributed. The two geological maps, at the scale of 1:25,000, cover the whole area from the Cintoia (south of Florence) to the San Gusme (north of Siena) villages.

Geochemistry of groundwater in a sector of the Colline Metallifere mining district (Tuscany, Italy)

This paper reports the results of a geochemical study of groundwater in the Montioni area, a sector of the Colline Metallifere mining district (Tuscany, Italy). The aim of the study was to distinguish the hydrochemical facies of groundwater, to define their origin and flow systems, and to identify the main geochemical processes ruling their chemical composition. The physico-chemical parameters (temperature, pH, electrical conductivity and redox potential) and concentrations of major ions (Na, K, Ca, Mg, Cl, HCO3 and SO4) measured in 203 groundwater samples collected in the period 1996-2014 from four springs and three piezometers, were used for this study. The analytical data suggests that the Montioni area is characterized by a complex hydrogeological system consisting of three main groundwater types: (1) Ca-SO4 waters of the deep regional aquifer system hosted by Triassic carbonate-evaporite formations, rising through fractures and faults; (2) Ca(Na)-HCO3 and Na-HCO3(Cl) waters fed by recent meteoric recharge and characterized by shallow circulation within calcareous-siliceous and clayey-calcareous-arenaceous formations of the Tuscan Nappe, respectively; (3) Ca-SO4-HCO3 waters arising by mixing of deep Ca-SO4 fluids and shallow Ca(Na)-HCO3 groundwater. The main processes determining the geochemical features of groundwater in the study area are: (1) carbonate dissolution (mainly calcite) in the surface recharge zone, as well as sulphate (gypsum and anhydrite) and carbonate (calcite and dolomite) dissolution in the deep aquifer hosted by Triassic carbonate-evaporite lithologies; (2) ion exchange reactions occurring in the surface water circulation system within clayey rocks of the Tuscan Nappe (Scaglia Toscana Group); (3) mixing of deep and shallow groundwater.

Paleomagnetic evidence for a post‐Eocene 90° CCW rotation of internal Apennine units: A linkage with Corsica‐Sardinia rotation?

AbstractWe report on an extensive paleomagnetic study (36 sites) of the Tuscan Nappe succession from the Northern Apennines Arc, aimed to reconstruct the tectonic evolution of the internal sector of this chain. We analyzed Eocene pelagic foreland ramp deposits (Scaglia Toscana Formation) and Oligocene–lower Miocene siliciclastic turbidites (Macigno and Falterona Formations). Paleomagnetic results show that the internal sector of the Northern Apennines underwent large counterclockwise (CCW) rotations with respect to the Adria‐Africa foreland. A decrease in the rotation magnitude was observed from the southern to the northern sector of the arc (from 91 to 36°). This trend is opposite to that observed in the more external units of Northern Apennines and demonstrates that the oroclinal bending model, which has been proposed for the external units of the chain, is not appropriate to explain the evolution of the internal sector of the arc. On the basis of the observed paleomagnetic pattern, we propose a new tectonic model in which the Tuscan and Falterona‐Cervarola units in the southern area were first rotated CCW along with the Corsica‐Sardinia block during its lower Miocene rotational drifting and were later involved in the main phases of rotational emplacement and translation toward the outermost sector (Umbria domain), thus yielding the final curved shape of the Northern Apennines chain. Data from this study represent the first paleomagnetic evidence of the influence of the Corsica‐Sardinia CCW rotation in the Apennines orogenic wedge deformation, in the general framework of the geodynamic evolution of the Central Mediterranean subduction system.

An outer ramp to basin plain transect: Interacting pelagic and calciturbidite deposition in the Eocene–Oligocene of the Tuscan Domain, Adria Microplate (Italy)

The interaction of ramps, basin plains and turbidite systems on the scale of tens of km has been rarely observed in fossil examples. Deep marine Eocene–Oligocene beds are exposed in the axial zone of the Chianti Mountains, Italy, and compose a regionally continue stratigraphic succession known as the Scaglia Toscana Formation. The formation was deposited in the Tuscan Domain of the Adria Microplate. This research aims at depicting its depositional architecture and evolution in the type area. Stratigraphic and sedimentologic analyses were performed on a ca. 25km-long transect that includes depositional systems sectioned both in the down- and along-dip directions. Shaly-carbonate deposits compose a complex of interacting ramps, basin plains and turbidite floor fan systems. Ramp deposits accumulated above the lysocline and in oxic conditions. Basin plain beds were deposited below the lysocline and were subject to episodes of oxygen depletion. Turbidity flows fed elongate fan lobes characterized by poor channelisation. The basin palaeogeography hampered the development of slope apron turbidite systems.The Eocene–Oligocene geodynamic setting of the Tuscan Domain was characterized by the evolution of a peripheral bulge and by the early structuring of a foredeep basin. Syn-sedimentary tectonism acted a primary role in the basin-scale arrangement. However other mechanisms also contributed to the local facies distribution, including the disposition of sediment-source areas and intrabasinal confinement morphologies, as well as relative oscillations of the depositional surface with respect to the lysocline and oxycline.

Stratigraphic architecture of an outer ramp/basinal turbidite fan carbonate system in a foreland basin (“Scaglia Toscana” Fm., Chianti Mts, Northern Apennines, Italy)

The Chianti Mts, part of the Northern Apennines orogen, represent an ideal case study to depict the relationships between outer carbonate ramps and basin plain carbonate turbidite systemsin foreland basins. The main object of this research is the Scaglia Toscana Fm., a ca. 200 metres thick Eocene-Oligocene succession of polychromous shales, marls, pelagic limestones and turbidite calcarenites, with marked lateral/vertical complexity, having its type-section in the Chianti Mts. During fi eldwork, the fm. has been subdivided in four partially interfingered members (from the bottom and northernmost): Sugame Marls; Cintoia Shales; Montegrossi Calcarenites; Dudda Shales and Limestones. The formation relates to three depositional systems: a middle to outer carbonate ramp dominated by hemipelagic deposition; a basinal plain whose sediments distribution was mainly forced by redox/oxic conditions and calcite-lysocline fluctuations; a thinning- and fining-upward, coarse- to fine-grained carbonate turbidite system. The Scaglia Toscana basin was located on the Adria continental micro-plate, foreland of the developing Northern Apennines orogen, whose facies distribution was mainly controlled by block faulting and differential subsidence. The Chianti Mts. represent then a crucial sector, since they expose the junction between a northern SSE-dipping ramp and a southern basinal plain with turbidite fl oor fans. A general southwardand upward-shift from ramp, basinal plain and turbidite fan facies has been recognized and remarked since the pioneering studies of the 1960s. Nonetheless, an exhaustive facies and architectural analysis is still lacking in literature. To fill this gap, the partial and preliminary results of a field logging, integrated with sedimentary facies analysis are reported here.

Geologia dell’area di Rapolano Terme in Provincia di Siena (Appennino Settentrionale)

Geologia dell’area di Rapolano Terme in Provincia di Siena (Appennino Settentrionale)

Oligocene-Miocene foredeep depositsin the Lake Trasimeno area (Central Italy):insights into the evolution of the Northern Apennines

In the Trasimeno Lake area (Umbria Region), several thrust sheets belonging to the Sansepolcro-Monte Filoncio and Rentella Units, are interposed between the Tuscan Nappe (in the hanging-wall) and the Umbria-Romagna Unit (in the footwall). The thrust sheets succession of the Sansepolcro-Monte Filoncio Unit is made up of Rupelian-Chattian Scaglia toscana Fm. and Chattian-Aquitanian foredeep deposits of Macigno Fm.; the base of the siliciclastic succession becomes gradually younger eastward. The compositional mode of the fine-grained rock fragments in the arenaceous turbidites is comparable with that of the upper part of the Macigno Fm. in the Tuscan Nappe. The succession of the Rentella Unit includes Rupelian-Aquitanian Monte Rentella Fm. and Aquitanian-Burdigalian foredeep siliciclastic turbidites of the Montagnaccia Fm.. In the lower portion of the Montagnaccia Fm. a level of black cherty horizons is present, as detected in all Aquitanian-Burdigalian successions of the Northern Apennines. The compositional mode of the fine-grained rock fragments in the turbidites is comparable with that of Marnoso-Arenacea Fm.. All these data allow an Oligocene-Miocene paleogeographic reconstruction of the Northern Apennines foredeep. Based on the age, the compositional mode and structural position, the Rentella and Sansepolcro-Monte Filoncio Units can be compared to the Carigiola and Acquerino Units cropping out in the Tuscan-Emilian Apennines.

Nuovi dati litostratigrafici e biostratigrafici sulla Scaglia Toscana nella Toscana meridionale (area di Rapolano Terme)

Nuovi dati litostratigrafici e biostratigrafici sulla Scaglia Toscana nella Toscana meridionale (area di Rapolano Terme)

Evolution, formation mechanism and kinematics of a contractional shallow shear zone within sedimentary rocks of the Northern Apennines (Italy)

Integration of a meso- and microstructural study with illite-cristallinity, X-ray and SEM analyses allow us to describe the fabric, kinematics, evolution and formation mechanism of a shallow level shear zone, developed during thrusting within the Tuscan Nappe, the deepest non metamorphic tectonic unit of the Northern Apennines. This shear zone has been described for the Mt. Aquilaia area, located west of the Mt. Amiata geothermal area. Shearing took place during the Late Oligocene-Early Miocene and accompanied the superimposition of Middle Jurassic carbonate rocks (Marne a Posidonomya Fm.) on the Eocene-Oligocene pelagic sequence (Scaglia Toscana Fm.). The shear zone, less then 10 m in thickness, consists of strongly deformed rocks which can be subdivided in three shear zone domains characterised by different structures indicating top-to-the-east shearing. The A domain (about 1 m thick) is characterised by an highly damaged zone composed of a clayey gouge with centimetre and decimetre limestone clasts dispersed within the clayey “matrix”. The B domain (max 4 m thick) consists of detached and overturned decimetre folds, a pervasive tectonic foliation, reverse faults and s-c structures which affected the Jurassic calcareous rocks. The C-domain (max 2 m thick) consists of s-c structures. The shear zone developed through two uninterrupted stages of a single episode of deformation: the first stage produced the highly damaged zone within the Scaglia Toscana clayey rocks (A-domain) and the folding within the Marne a Posidonomya calcareous rocks (B-domain); the second stage concentrated on the A-domain, caused the detachment of the folds and the development of reverse faults within the B-domain, and produced the development of S-C structures within the C-domain. During shearing, strain was partitioned. Strain partitioning was mainly controlled by different processes, such as: (a) lithological contrast, (b) lithological anisotropy and (c) fluid-assisted deformation and related metamorphic reactions. Pressure solution and solution transfer are the mechanisms which produced the S1 foliation. A very low-grade metamorphism affected only the very strongly deformed pelitic dominantly rocks. The metamorphism produced the development of new clay minerals (illite-illite/smectite), only developed within the cleavage domains of the folded rocks. This has been interpreted as mainly due to deformation heating, coupled with fluid circulation associated with cleavage development.

THE VARICOLOURED SLATES OF THE GRÀSSERA UNIT (CENTRAL-EASTERN ELBA, TUSCANY): PETROGRAPHICAL-MINERALOGICAL DATA AND COMPARISONS WITH OTHER TUSCAN AND LIGURIAN-PIEDMONTESE UNITS

The varicoloured slates of the Cavo Formation in the Grassera Unit represent a succession of debated stratigraphic and paleogeographic pertinence (Tuscan Domain, Ligurian or Ligurian-Piedmontese Units) within the complex tectonic puzzle of the Elba Island. With this in mind, the authors carried out petrographical, illite crystallinity and mineralogical analyses on the slates of the Grassera Unit and on the pelites of some other Tuscan, Ligurian and Ligurian- Piedmontese units cropping out in the Eastern Elba Island (the Tuscan Verrucano Group, Varicoloured Sericitc Schists and Posidonia Marlstones Fm. and the Ligurian Palombini Shales) and in Southern Tuscany (the “Scaglia Toscana” Fm. and the “Schistes Lustres” of the Argentario Promontory). The Cavo Fm. slates show a mineralogical association of illite+chlorite+quartz (±chlorite-vermiculite) and IC values in the anchimetamorphic field (°D2q = 0.28¸0.39). The local hydrothermal circulation and heating processes due to the Neogene magmatic intrusions locally increase the IC and vary the phyllosilicates association. The comparison of these data with those obtained from the other units ruled out the correlation of the Cavo Fm. with the pelitic rocks either of both the Tuscan Nappe (Posidonia Marlstones and Tuscan Scaglia Fms.) and the Ophiolitic unit (Palombini Shales Fm.). The correlation with the metapelites of the Monticiano- Roccastrada Unit (e.g. “Verrucano” Group) is not clear, whereas the attribution of the Cavo Fm. slates to a shallow-buried Ligurian-Piedmontese Unit succession seems more probable because of some lithological and mineralogical analogies with the “Schistes Lustres” of the Argentario Promontory.