Epiligurian Succession Research Articles

An outline of the geology of the Northern Apennines (Italy), with geological map at 1:250,000 scale

An outline of the geology of the Italian Northern Apennines, to accompany a geological map at 1:250,000 scale covering the Emilia- Romagna, Marche, Tuscany and Umbria regions, is presented herein. The map is intended as a first result of a longer term project carried out by the Geological Surveys of the above regions, aimed to create a common geological map at 1:10,000 scale, useful for environmental planning and management.The lithostratigraphic units are grouped in domains and successions (with references to main tectonic units), and a special effort was made to correlate similar lithostratigraphic units across the area. The enclosed geological map distinguishes stratigraphic successions deposited in: a) Ligurian Domain (Internal and External Ligurian domains); b) Subligurian Domain; c) Tuscan Domain (Tuscan Succession, Tuscan Metamorphic Succession, Cervarola- Falterona Succession, Modino Succession, Rentella Succession, Pseudoverrucano Succession); Umbria-Marche-Romagna Domain. Tectonic units derived from regional tectonic mélanges and shear zones (Sestola-Vidiciatico Unit), and units affected by HP metamorphism in the Tuscan Archipelago and southern Tuscany have been mapped. Distinguished younger successions are: a) Epiligurian Succession; b) Miocene-Pleistocene succession of the Tyrrhenian margin; c) Miocene- Pleistocene succession of the Po Plain and Adriatic margin. The main outcrops of magmatic rocks (Miocene-Pleistocene in age) and Quaternary alluvial, continental and coastal deposits have also been mapped. Main tectonic contacts (high-angle normal faults, main thrust and low-angle normal faults) are indicated. The 1:250,000 geological map of the Northern Apennines is freely available as PDF, raster and vector GIS data from the web site: https://www.geological-map.it.

Oligocene-Miocene volcanism in the Apennines: discovery and characterization of a baryte and Ba-rich phillipsite bed in the lower part of the Ranzano Formation (Reggio Emilia, Italy)

This work reports the biostratigraphic assessment and the chemical and mineralogical characterization of a zeolitized and barium-rich volcanic pyroclastic bed outcropping in the lower Secchia Valley (Northern Apennines, Italy), very close to the boundary between the Ranzano and the Monte Piano Formations. To our knowledge, it is the older so far documented in the Emilian Epiligurian Succession as, through nannofossil biostratigraphy, we have documented an early Oligocene age (Rupelian CNO1 nannofossil zone) for the enclosing sediments. The chemical and mineralogical composition, the latter obtained through a multi- analytical approach combining X-ray powder diffraction (Rietveld- RIR method) with thermal analyses coupled with evolved gas mass spectrometry, revealed large amounts of Ba-rich phillipsite, baryte, volcanic glass and subordinate quantities of sanidine and plagioclase; on the other hand, phlogopite, idiomorphic plagioclase and femic minerals, frequently found in younger volcanic layers of the Ranzano Formation, here are absent. The quantitative mineralogical assessment together with mineral associations suggest that diagenesis did not play a relevant role in the crystallization of phillipsite, but its role cannot be neglected for the crystallization of baryte. Hypothesis on the genesis and transformation of the original material and on the possible correlation with the coeval calc-alkaline magmatic sources in the circum-Mediterranean area were considered, but no definitive conclusion has been reached.

Depositional history of the Epiligurian wedge-top basin in the Val Marecchia area (northern Apennines, Italy): a revision of the Burdigalian-Tortonian succession

The Burdigalian-Tortonian Epiligurian succession in the Val Marecchia area comprehends different lithostratigraphic units deposited in a wedge-top basin during the northeastern migration of the thrust belt. The succession includes shallow-water carbonates passing to mixed carbonate-siliciclastic and to fine-grained politic sediments, capped by fluvio-deltaic coarse-grained deposits. Detailed field work and stratigraphy has allowed to characterize depositional units and unconformities and to delineate the sedimentary and tectonic evolution of the basin. Tectonics exerted a primary control at different stages. During the Burdigalian, a general uplift of the area allowed the onset of shelfal carbonate sedimentation on underlying Ligurian and Epiligurian deep-water sediments. At the Serravallian the sedimentation was influenced by the thrust reactivations which caused a marked asymmetry in the basin geometry and fill. The subsidence increase in the rear part of the basin determined the deposition of a thick succession of relatively deep fine-grained sediments (up to 800 m water-depth) (Serravallian, MNN6a through MNN6b subzones based on nannofossil biostratigraphy) and fossiliferous clays (lower Tortonian, biozones MNN8b-MNN9). Conversely, uplift is activated in the frontal part of the basin, causing the partial erosion of the Burdigalian-Langhian shallow-water carbonates. A relevant amount of this carbonate detritus is delivered to the foredeep, supplying the Marnoso-arenacea Fm. A general uplift of the area in the late Tortonian leads to the deposition of fluvio-deltaic conglomerates supplied by emerged rear sectors of the basin.

Preliminary water flow monitoring of a vertical fractures system in a sandstone rock mass

Fractured sandstone by tectonic and gravity actions could be classified as aquitard or aquifer according to the number and aperture of the fractures inside the rock mass. This kind of rock mass outcrops not frequently and sparsely in the Apennine and Alps chains. In the Emilian Apennines, which is mainly composed by sedimentary rocks (rich in clay), this type of rock is part of the Epiligurian Succession that outcrops for a 20% of the chain. The aim of the paper is to highlight the first results of the semi-continuous water flow monitoring (discharge, electrical conductivity and temperature) of the spring that represents the drainage point of a vertical fractures system. This network joint characterizes the vertical scarp of a sandstone slab with thickness of 100 meters. The results shows that the spring flow rate, the water electrical conductivity and temperature are influenced by the rainfall distribution pattern. Consequently every rainfall event the spring discharge and water electrical conductivity increase, while the water temperature decreases. The new infiltrate water reacts the spring with a delay of 10-60 hours. The discharge variability index is around 270%. The fractured system is characterized by replacement effect of the preexistent groundwater. During the infiltration event, dissolution phenomena are observed along the wall of the fractures. A preliminary groundwater budget calculation highlights that only a potential infiltration coefficient higher that 75% is admitted to justify the total annual volume discharge from the fractures.

Relationships between seep-carbonates, mud volcanism and basin geometry in the Late Miocene of the northern Apennines of Italy: the Montardone mélange

The Montardone melange (Mm) is a chaotic, block-in-matrix unit outcropping in the Montebaranzone syncline in the northern Apennines. The Mm occurs in the uppermost part of the Termina Fm, the Middle-Late Miocene interval of a succession deposited in a wedge-top slope basin (Epiligurian succession). The Mm is closely associated with bodies of authigenic carbonates, charac- terized by negative values of d 13 C (from -18.22 to -39.05 % PDB) and chemosynthetic benthic fauna (lucinid and vesicomyid bivalves). In this paper, we propose that the Mm is a mud volcano originated by the post-deposi- tional reactivation and rising of a stratigraphically lower mud-rich mass transport body (Canossa-Val Tiepido sed- imentary melange or olistostrome) triggered by fluid overpressure. We base our conclusion on (1) the Mm pierces the entire Termina Fm and older Epiligurian units and represents the direct continuation of the underlying Canossa-Val Tiepido melange; (2) the geometry and facies distribution of the Montebaranzone sandstone body, which are compatible with a confined basin controlled by the rising of the Mm; (3) the systematic presence of large-scale (lateral extension 300-400 m) seep-carbonates associated with the melange, suggesting a persistent gas-enriched fluid vent from the ascending overpressured mud; (4) blocks and clasts sourced from the Mm, hosted by the authigenic carbonates, conveyed by ascending mud and gas-enriched fluids. The Mm represents one of the few fossil examples of reactivation of a basin-scale sedimentary melange (olistostrome); a three-stage model showing mechanisms of Mm raising is proposed.

Le Brecce argillose di Musigliano (Appennino Vogherese – Tortonese): dati stratigrafici preliminari

The Musigliano argillaceous Breccias (Voghera and Tortona Apennines): preliminary stratigraphic data.An integrated biostratigraphic study based on foraminifers and calcareous nannofossils has been performed on two chaotic bodies involved within the Epiligurian pelitic sequence outcropping in the Alessandria and Pavia Apennines (M. Penola & M. Vallassa area), allowing to define the age of their emplacement. The investigated deposits mainly consist of strongly tectonized sediments ensuing from the Ligurian substratum mainly through submarine cohesive mud flows and lithic debris. These chaotic bodies have been previously considered (Gelati et al., 1974; Gelati & Vercesi, 1994) as involved within the Antognola Formation and correlated with similar Lower Miocene deposits widespread in Northern Apennines (Canossa Olistostrome, Val Tiepido-Canossa argillaceous Breccias). Dissenting from previous interpretations, our study shows that these chaotic bodies, named here as “Musigliano argillaceous Breccias” were displaced in an interval between Late Eocene and Early Oligocene. In fact, the biostratigraphic analyses of the marlstones under the chaotic bodies indicate they are attributable to the P15 and P16 planktonic foraminifer biozones of Berggren et al., (1995) corresponding to the G. semiinvoluta and T. cerroazulensis biozones of Mancin et al. (2003). The same pelitic rocks are relatable to the MNP19/20 nannofossil biozone of Catanzariti et al. (1997), corresponding to the NP19/20 of Martini (1971). The Epiligurian marlstones and turbiditic mudstones upon the Musigliano argillaceous Breccias fall in the P19 p.p. / P20 (corresponding to the G. ampliapertura biozone, Mancin et al., 2003) corresponding to the MNP23 biozone (Catanzariti et al., 1997) and to the NP23 biozone of Martini(1971). We correlate the pelitic rocks under the Musigliano argillaceous Breccias to the uppermost part of the Monte Piano Marls (“grey lithofacies” according to Mancin & Cobianchi, 2000 and Panini et al., 2002), and the marlstones and turbiditic mudstones upon the sedimentary chaotic bodies to the Ranzano Formation, on the basis of lithologic features and age. The displacement of the Musigliano chaotic breccias marks a strong stratigraphic break in the Epiligurian sequence; it could be related to events (probably of tectonic nature) previously reported as affecting the lower part of the Epiligurian succession and the coeval sequence of the Tertiary Piedmont Basin (Mutti et al., 1995; Catanzariti et al.,1997; Martelli et al., 1998; Ottria et al., 2001). As in the Emilia south-easternmost Apennines, the Oligocene-Lower Miocene Epiligurian sedimentary record seems to be devoid of typical resedimented arenaceous bodies generally characterizing the Ranzano Formation also in the studied area.

Tectonic and sedimentary evolution of the frontal part of an ancient subduction complex at the transition from accretion to erosion: The case of the Ligurian wedge of the northern Apennines, Italy

Subduction can be associated either with accretion or with removal of material from the overriding plate. These two processes can either coexist or alternate in time along the same margin. Their inception has the potential to change the dynamic equilibrium of a marginal wedge resulting in the development of out-of-sequence thrusts, normal and strike-slip faults, or large submarine landslides in the frontal part of the subduction zone. In this work we investigate the effects of the transition from frontal accretion to frontal erosion on the stability of a subduction complex through the study of an ancient example from the northern Apennines (Ligurian subduction complex). New structural data suggest that in the early Neogene (Aquitanian), the removal and underthrusting of the toe of the wedge, formed by both the accreted oceanic sediments and the overlying wedge-top basin fill (i.e., the Subligurian units), implied a process of frontal tectonic erosion. The presence, on top of the subduction complex, of a complete succession of mid-late Eocene to late Miocene slope-apron sediments—i.e., the Epiligurian succession—facilitates a reconstruction of the sedimentary response to this event. In the Aquitanian, large areas of the wedge were denuded from the lower-slope sedimentary cover through extensive gravitational mass movements. The subsequent deposition of a thick body of submarine debris flows is documented. The mass-wasting deposits are interpreted as the sedimentary response to the underthrusting of the frontal part of the Ligurian subduction complex formed by the Subligurian units.

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 Romagna Apennines, Italy: an eroded duplex

AbstractThe study of clast composition carried out on the alluvial gravels of the Romagna Apennines of northern Italy has provided evidence for an extensive covering of allochthonous units (Ligurian nappe and Epiligurian succession) above the Miocene foredeep deposits (Marnoso‐Arenacea Formation), which has been subsequently eroded during the Late Miocene–Pleistocene uplift. This result is confirmed by the burial history outlined in the Marnoso‐Arenacea Formation through vitrinite reflectance and apatite fission‐track analyses. The Romagna Apennines represent, therefore, a regional tectonic window where the thrust system that displaced the Marnoso‐Arenacea Formation crops out. The geometric relations between this thrust system and the basal thrust of the Ligurian nappe, exposed at the boundaries of the Romagna Apennines (Sillaro Zone and Val Marecchia klippe), are consistent with a duplex structure. Thus, the Romagna Apennines thrust system is an eroded duplex. The duplex roof‐thrust corresponds to the surface of the synsedimentary overthrust of the Ligurian nappe on the Marnoso‐Arenacea Formation; the floor‐thrust is located in the pelagic pre‐foredeep deposits (Schlier Formation). Copyright © 2001 John Wiley & Sons, Ltd.

The Ligurian Helminthoid flysch units of the Emilian Apennines: stratigraphic and petrographic features, paleogeographic restoration and structural evolution

This work deals with the Cretaceous–Tertiary Helminthoid flysch successions of the Emilian Apennines and related basal complexes (Mt. Caio, Val Baganza, Solignano, Mt. Venere–Monghidoro and Mt. Cassio Units): it is based on an integrated approach which included stratigraphic, petrographic and structural observations. Detailed stratigraphic sections measured in the various successions evidenced the specific features of the different flysch formations. The main framework composition analysis of the arenites pointed out a partly ‘oceanic’ alimentation for the Mt. Caio Flysch Fm; the Mt. Venere–Monghidoro, and Mt. Cassio Flysch Fms have been alimented exclusively by a terrigenous detritus mainly derived from continental basement source areas. The heavy mineral assemblage of the Mt. Caio Flysch Fm is characterized by picotite, that of the Mt. Venere–Monghidoro, Solignano and Mt. Cassio Flysch Fms commonly contains straurolite, garnet and chloritoid, generally considered to be typical products of the Adriatic continental margin. The calcareous nannofossils biostratigraphy indicated that the flysch sedimentation started during the Late Campanian and ended between the Paleocene (Mt. Cassio Flysch Fm and Mt. Venere–Monghidoro Fms) and the Middle Eocene (Mt. Caio Flysch Fm). We propose a schematic paleogeographic restoration for the External Ligurian Domain which implies a more internal position for the Mt. Caio succession and a more external one for the Mt. Venere–Monghidoro and Mt. Cassio successions. The Helminthoid flyschs sedimented after and during deformation and subduction phases in perched and fore-arc basins partly overlying the marginal part of the Adriatic plate. The External Ligurian nappes’ stacking consists, in the study area, from the bottom, of the following units: Caio Unit, Val Baganza Ophiolitic Unit, Monghidoro Unit, Cassio Unit. This pile of thrust-nappes, sealed by the Epiligurian succession, has been already realized before Late Eocene. In our opinion it was generated by a frontal west-verging frontal accretion process (offscraping), which let the flysch successions remain, in this phase, quite undeformed. This westverging thrusting phase, starting from the Middle-Late Eocene, has been followed by an important folding event which generated striking hectometric and kilometric ‘Apenninic’ reverse folds, sometimes associated with NE-verging thrust surfaces. The Oligocene and post-Oligocene evolution is characterized by a block-translation of the Ligurian staking over the Subligurian, Tuscan and Umbrian Domains, associated with a new generation of minor thrusts and thrust related Apenninic folds.

The Ligurian Helminthoid flysch units of the Emilian Apennines: stratigraphic and petrographic features, paleogeographic restoration and structural evolution

This work deals with the Cretaceous-Tertiary Helminthoid flysch successions of the Emilian Apennines and related basal complexes (Mt. Caio, Val Baganza, Solignano, Mt. Venere-Monghidoro and Mt. Cassio Units): it is based on an integrated approach which included stratigraphic, petrographic and structural observations. Detailed stratigraphic sections measured in the various successions evidenced the specific features of the different flysch formations. The main framework composition analysis of the arenites pointed out a partly ‘oceanic’ alimentation for the Mt. Caio Flysch Fm; the Mt. Venere-Monghidoro, and Mt. Cassio Flysch Fms have been alimented exclusively by a terrigenous detritus mainly derived from continental basement source areas. The heavy mineral assemblage of the Mt. Caio Flysch Fm is characterized by picotite, that of the Mt. Venere-Monghidoro, Solignano and Mt. Cassio Flysch Fms commonly contains straurolite, garnet and chloritoid, generally considered to be typical products of the Adriatic continental margin. The calcareous nannofossils biostratigraphy indicated that the flysch sedimentation started during the Late Campanian and ended between the Paleocene (Mt. Cassio Flysch Fm and Mt. Venere-Monghidoro Fms) and the Middle Eocene (Mt. Caio Flysch Fm). We propose a schematic paleogeographic restoration for the External Ligurian Domain which implies a more internal position for the Mt. Caio succession and a more external one for the Mt. Venere-Monghidoro and Mt. Cassio successions. The Helminthoid flyschs sedimented after and during deformation and subduction phases in perched and fore-arc basins partly overlying the marginal part of the Adriatic plate. The External Ligurian nappes’ stacking consists, in the study area, from the bottom, of the following units: Caio Unit, Val Baganza Ophiolitic Unit, Monghidoro Unit, Cassio Unit. This pile of thrust-nappes, sealed by the Epiligurian succession, has been already realized before Late Eocene. In our opinion it was generated by a frontal west-verging frontal accretion process (offscraping), which let the flysch successions remain, in this phase, quite undeformed. This westverging thrusting phase, starting from the Middle-Late Eocene, has been followed by an important folding event which generated striking hectometric and kilometric ‘Apenninic’ reverse folds, sometimes associated with NE-verging thrust surfaces. The Oligocene and post-Oligocene evolution is characterized by a block-translation of the Ligurian staking over the Subligurian, Tuscan and Umbrian Domains, associated with a new generation of minor thrusts and thrust related Apenninic folds. © 2000 Éditions scientifiques et médicales Elsevier SAS

Polyphase thrusting in piggy-back deposits: the example of epi-Ligurian Succession (northern Apennines, Italy)

Abstract A Lower Aquitanian thrusting phase has been recognized for the first time within the piggy-back deposits of the northern Apennines (epi-Ligurian Succession) outcropping in the Enza Valley. This result, together with previous structural and biostratigraphical data, indicates the existence of thrusting at the uppermost structural level and allows us to delineate a polyphase tectono-sedimentary evolution of the Middle Eocene–Lower Miocene epi-Ligurian Succession characterized by two successive northeast-thrusting phases (Rupelian and Lower Aquitanian) separated by unconformable deposits developed between Rupelian and Chattian. These thrust tectonics, at lower structural levels, can be related to the northeast-verging overthrusting of the Ligurian Units onto the Subligurian Units.

Lower Oligocene thrust-system in the epi-Ligurian succession: evidence from the Enza Valley (northern Apennines, Italy)

Within the lower part (Upper Eocene–Oligocene) of the epi-Ligurian succession, outcropping in the Emilian side of the northern Apennines (Enza Valley), duplications by thrust tectonics were recognized through the systematic integration of field geology with calcareous nannofossil biostratigraphy. This thrust system, derived from the overthrusting of two thrust-sheets over a footwall, is unconformably overlain by a Rupelian succession. The thrust structure of the Enza Valley, affected by a subsequent wide overturned syncline together with the unconformable succession, shows a remarkable Lower Oligocene contractional tectonics, previously not recognized in the northern Apennines.The comparison of this thrust system with other outcropping areas of the epi-Ligurian succession makes probable the widespread occurrence of the Lower Oligocene tectonics in the uppermost structural levels of the chain (epi-Ligurian domain).In a regional tectonic framework, the Rupelian thrust tectonics affecting the epi-Ligurian succession can be related to the Lower Oligocene closure of the innermost portion of the Subligurian basin (Aveto-Petrignacola Formation) due to the NE-verging overthrusting of the External Ligurian Units. In this context the unconformable succession of the Enza Valley seems correlable with the basal portion of the Subligurian Bratica Sandstone (Rupelian–Chattian) which unconformably overlies a deformed substratum (Mesoalpine Phase). © Elsevier, Paris

Lower Oligocene thrust-system in the epi-Ligurian succession: evidence from the Enza Valley (northern Apennines, Italy)

Within the lower part (Upper Eocene-Oligocene) of the epi-Ligurian succession, outcropping in the Emilian side of the northern Apennines (Enza Valley), duplications by thrust tectonics were recognized through the systematic integration of field geology with calcareous nannofossil biostratigraphy. This thrust system, derived from the overthrusting of two thrust-sheets over a footwall, is unconformably overlain by a Rupelian succession. The thrust structure of the Enza Valley, affected by a subsequent wide overturned syncline together vith the unconformable succession, shows a remarkable Lower Oligocene contractional tectonics, previously not recognized in the northern Apennines. The comparison of this thrust system with other outcropping areas of the epi-Ligurian succession makes probable the wide-spread occurrence of the Lower Oligocene tectonics in the uppermost structural levels of the chain (epi-Ligurian domain). In a regional tectonic framework, the Rupelian thrust tectonics affecting the epi-Ligurian succession can be related to the Lower Oligocene closure of the innermost portion of the Subligurian basin (Aveto-Petrignacola Formation) due to the NE-verging overthrusting of the External Ligurian Units. In this context the unconformable succession of the Enza Valley seems correlable with the basal portion of the Subligurian Eratica Sandstone (Rupelian-Chattian) which unconformably overlies a deformed substratum (Mesoalpine Phase).