Genesis and evolution of 'pseudocarniole': preliminary observations from the Susa Valley (Western...

Genesis and evolution of ‘pseudocarniole’: preliminary

observations from the Susa Valley (Western Alps)

W. ALBERTO, F. CARRARO, M. GIARDINO & D. TIRANTI

University of Torino, Earth Sciences Department, Via Valperga Caluso, 35.

I-10125, Torino, Italy (e-mail: [email protected])

Abstract: In the Alpine geological literature some particular carbonate rocks having a vuggyappearance, associated with evaporite rocks, have a controversial origin and diversified,uneven, nomenclature. In this paper they are provisionally called ‘pseudocarniole’. An excellentexposure along the Susa Valley (Italian Western Alps) permitted a relatively full analysis of agroup of such vuggy rocks in situ. Five main lithologies have been identified with respect totheir nature, shape, dimensions and organization of the clasts, also according to the matrix andthe composition of the cements.

Utilizing the interpretation of geological and geomorphological field data that cover thesedeposits, detailed stratigraphical descriptions and laboratory microanalyses (optical microscopeand cathode-luminescence), a genetic interpretative model is proposed. The main formationalprocess is dissolution, starting from solution of gypsum and anhydrite; then the processes affectingcarbonate ‘parental residual rocks’ are considered. Thereafter a general instability of the rockmasses is introduced with a consequent gravitational collapse. Other general processes areusually associated: tectonics, gravity and Plio-Quaternary karst phenomena. Finally, a particularlyyoung age for the formation of the pseudocarniole deposits is noted, based on palynological data,Plio-Quaternary.

This paper deals with carbonate rocks having avuggy appearance, commonly grey to yellowishcoloured, widely distributed in the Western Alpsin association with evaporitic Triassic rocks, hereprovisionally called ‘pseudocarniole’. Formerly(Zaccagna et al. 1911a, b), these rocks were inter-preted as ‘true carniole’, in that they are normallyassociated with gypsum formations. More recentlythey have been distinguished from these last andinterpreted as ‘carbonate breccias’ of unknownage and/or as ‘residual breccias’ of Pliocene–Upper Holocene age (Polino et al. 2002).

In the present study these rocks have beendescribed, from both lithological and structuralpoints of view, in comparison with other similaralpine rocks (Rauhwacken, carniole, cornieules,cargneules) and Apenninic rocks (CalcareCavernoso, in: Ciarapica 1985; Ciarapica et al.1987; Gandin et al. 2000) of controversial originand diversified nomenclature.

Throughout the geological literature it is poss-ible to recognize the different interpretativemodels for the genesis and age of these much-discussed carbonate breccias and conglomerates inthe Alps. Schematically the hypothesis for theorigins of these rocks can be gathered into threemain groups:

(1) ‘sedimentary origin’ (from late Neogene) due totheir unconformity with respect to Paleogenestructural elements and/or because they also

rework late Eocene or Oligocene sedimentsin (Grandjacquet & Haccard 1973, 1975;Patacca et al. 1973; Federici & Raggi 1974);

(2) ‘direct tectonic origin’ (e.g. cataclastites) orof ‘indirect tectonic origin’, e.g. reworked tec-tonic clasts (Leine 1971; Masson 1972;Debelmas et al. 1980; Fudral 1998);

(3) breccias derived from alteration or weatheringof carbonate rocks, i.e. processes followingsedimentation and tectonics (Bruckner 1941;Ellenberger 1954), also from recent genesis,for instance climate-controlled processesrelated to alternate advances and retreat ofglaciers (Debenedetti & Turi 1975).

Lastly, other studies offer an intermediary viewon the matter, pointing out a ‘mixed’ origin for themuch-discussed carbonate breccias and conglomer-ates: ‘sedimentary and tectonic’ (Wiesender 1971)or ‘tectonic and alteration’ (Warrak 1974; Muller1982; Richards & Vearnecombe 1984) becausethe last process commonly overlaps the tectonicbrecciation (also see sedimentation, tectonics andweathering; in Warren 1999).

Recently, the complexity and the variety of pro-cesses related to these diverse rock formations hasalso been recognized as being dependent on localfactors. This way it is possible to have many differ-ent breccia types, depending on texture, structure,geometry of the rock body and relationships withsurrounding rocks (Jeanbourquin 1988; Amieux &

From: SCHREIBER, B. C., LUGLI, S. & BABEL, M. (eds) Evaporites Through Space and Time.Geological Society, London, Special Publications, 285, 155–168.DOI: 10.1144/SP285.9 0305-8719/07/$15.00 # The Geological Society of London 2007.

Jeanbourquin 1989; Giardino 1995; Schaad 1995;Carraro et al. 2002; Polino et al. 2002).

In the Susa valley (Fig. 1) detailed macro- andmicroscopical analyses of this group of rocks havebeen conducted (Alberto 2004; Alberto et al.2005). A complex but organic framework resultedfrom these analyses: all the studied pseudocarnioleare carbonate rocks (breccias, conglomerates, cal-carenites, travertine crusts) of vuggy appearance(often enhanced by centimetric carbonate crusts)similar to that of the above-mentioned ‘true car-niole’, i.e. from Triassic evaporites (Zaccagnaet al. 1911a, b).

For this group of rocks a genetic model and arelative classification scheme are here proposed:the provisional name of ‘pseudocarniole’ indicatesthe similarity of appearance but the differentorigin and age with respect to the ‘true carniole’and also to the deformed sulphate evaporites(Passeri 1975; Malavieille & Ritz 1989; Nury &Schreiber 1997; Schreiber & Helman 2005).

In the Susa Valley the pseudocarniole aretypically associated with Triassic successions oflimestones and dolomites (Fig. 2a–c), being gener-ally located above gypsum/anhydrite rock masses(Fig. 3) and/or along tectonic contacts. The Susavalley pseudocarniole genesis is here interpretedas a consequence of the relevant volume reductioninduced by dissolution of gypsum/anhydrite rockmasses: the complex story of pseudocarniole devel-opment seems to start with hydrothermal fluidascension and consequent dissolution. As conse-quence of this, the overlying dolomite and carbon-ate rocks are deeply transformed by means ofgravity collapse; hydrothermal fluid activities andassociated dissolution can both be followed bylater karst phenomena. The sector is characterizedby a significant degree of reworking of the originalcarbonate rocks so that their earlier structures andtextures are completely obliterated. Thus newrocks are created, necessitating the introduction ofthe new name, pseudocarniole.

Fig. 1. Structural geology of the Western Alps and locations of case studies in the Susa Valley: wA, Bardonecchia(E 315.556 m, N 4.990.889); wB, Seguret (E 328.920, N 4994.109); wC, Thuras Valley (E 329.651, N 4.975.035).Geographic coordinates UTM 32 ED 50.

W. ALBERTO ET AL.156

Fig. 2. Geomorphological context of the pseudocarniole and geometrical relationships between the pseudocarnioleand other lithological units (pc, pseudocarniole; gy, gypsum; cs, calcschistes; do, dolomites). (a) Best outcrop ofgypsum–pseudocarniole association near Bardonecchia. (b) Steep landforms characterizing the geomorphologicallandscape of the Val Thuras pseudocarniole. (c) Karst caves (Grotta dei Saraceni) into the Seguret Dolomites (middleTriassic); detrital pseudocarniole outcrops at the cave’s exit.

GENESIS AND EVOLUTION OF PSEUDOCARNIOLE 157

Other processes are usually associated withdissolution: these are connected to tectonics(usually normal or strike–slip faulting), gravity(deep hollow collapse and slope dynamics) andkarst (shallow dissolution and re-precipitation). Inconsequence of all these different possible formationprocesses, many types of pseudocarniole havebeen recognized and described, which constituterock bodies with different dimensions, geometriesand lithofacies associations. Finally, a particularlyyoung age for some facies of pseudocarniole inthis area has been suggested: Plio-Quaternary,from preliminary palynological data.

Methodology

The data collection was first developed on thefield: detailed geological maps and sections weremade, and stratigraphical descriptions, logs andsamples were collected. Subsequently, further

studies have been carried out in the laboratory,using thin-section optical microanalysis of thesamples, some of which were also examined bycathode luminescence (CL).

The pseudocarniole

The main object of the research presented in thispaper is the geological data concerning the diversemembers of the group pseudocarniole, interpretedand organized in such a way as to create a functionalclassification, present the evidence and possiblysolve some interpretative problems concerningtheir origin.

These detailed studies have permitted us tospecify relationships between different types ofpseudocarniole, depending on characteristics andmutual relationships between different carbonatecements found in them. It has also allowed a com-plete description of the nature of constituent clasts

Fig. 3. Thuras Valley case study: geological map and cross-sections.


present in all the varieties of pseudocarniole, thereconstruction of the sedimentary processes thathave determined or conditioned their origin, aswell as the influences of the deformation processeson their texture and structure.

The field data collection, supported by labora-tory data and results, has resulted in the establish-ment of five principal facies and to the elaborationof a general genetic model for the pseudocarnioleof the Upper Susa Valley. Several related sub-faciesalso have been recognized, which correspond toseveral other genetic mechanisms: the complexhierarchy is summarized in Table 1, and detaileddescriptions are presented in the following pages.

(A) Carbonate breccias from dissolution

Carbonate breccias from dissolution are constitutedby monogenetic breccias (calcareous or dolomitic);the fragments are always angular, do not show anykind of transport or indications of rotation, and havevarying dimensions from less than a centimetre tosome metres and generally a chaotic distribution.Macroscopically, most of the carbonate brecciasshow a vuggy fabric and an inhomogeneousgreyish colour. Locally, dolomitic remnants of theoriginal clasts are characterized by a poor degreeof cohesion, which can decrease until they form adolomitic powder; generally they show a peculiarboxwork structure, made of angular moulds individ-uated by prominent calcite walls and selectiveerosion of incoherent dolomite powder (Fig. 4).

Sometimes they preserve traces of stratification,more or less disguised by the fractures, inheritedfrom the original ‘parent rock’. In some casesempty interstitial spaces between fragments havebeen described. The analyses in CL have shownthe presence of several phases of cementation thatalternate with dissolution and fracturing phases forthe genesis of carbonate breccias from dissolution.

Calcite cements are present (sparry, clear orturbid in transmitted light; sometimes zonedyellow, mustard, brown in CL), as well as dolomitecements (sparry, also in pluri-millimetre crystals,generally turbid and not zoned); in some caseswithin these last phases there are sparse fluoritecrystals present.

As discussed below in the proposed interpret-ative model, this facies is here interpreted as theproduct of the partial dissolution and alteration ofthe dolomite and calcareous parent rocks, aftermassive dissolution of gypsum/anhydrite rocksand consequent volume reduction, thus carbonatebreccias are formed: they are genetically connectedto the slow re-arrangement of overhanging dolomiteand calcareous rocks; the original sedimentarystructures are largely preserved (McWhae 1953).

(B) Residual pseudocarniole from

dissolution and collapse

Residual pseudocarniole from dissolution andcollapse are made up of monogenetic breccias(calcareous or dolomitic), more rarely polygenetic(containing minor calc-schist and quartzite clasts),with angular, not selected fragments; they arealways associated with typical yellowish, seldomreddish, matrix locally showing a weak stratifica-tion. The residual pseudocarniole also show avuggy fabric locally characterized by a boxworkstructure (Fig. 5).

They generally include lithosomes of carbonatebreccias from dissolution with varying dimensions,up to 10 m long. The residual pseudocarniole arebounded from the underlying rocks (carbonate brec-cias from dissolution, dolomites) by means ofunconformities often underlain by accumulationsof insoluble products (Fig. 5c).

The analyses of samples using CL also demon-strate the existence of cement phases having

Table 1. Hierarchy of pseudocarniole facies and sub-facies

(A) Carbonate breccias from dissolution(B) Residual pseudocarniole from dissolution and collapse

(C) Detrital pseudocarniole

(C1) Detrital sub-facies withoutevidence of transport

(C2A) Detrital sub-facies, by channelledwater transport

(C2) Detrital sub-facies withevidence of transport

(C2B) Detrital sub-facies, formed bystream water transport

(C2C) Detrital sub-facies, by stream waterfrom infill of subterranean karst cavities

(D) Encrustingpseudocamiole

(E) ‘Tectonic’ pseudocarniole

f f


Fig. 4. Carbonatic breccias from dissolution. Note the stratification inherited by the genetical process, the poorlyvacuolar detrital aspect and the heterogeneity in the dimensions of the clasts. (a) Outcrop view; (b) detailed view.

Fig. 5. Residual pseudocarniole from dissolution and collapse. The monogenetic clasts of carbonatic rocks (heredolomites), angular and not sorted, are separated by discontinuous and irregular portions of yellow matrix. (a) Outcropview. (b) Sample of polygenetic breccia, note the vacuolar aspect (scale is in centimetres). (c) Insoluble productaccumulation at the lower boundary of carbonatic breccias from dissolution.


various compositions: several dolomitic phaseswith large turbid spars (turbid, also in transmittedlight), with some neo-formed crystals of quartzand thin dolomite veins, that appear weakly zonedin CL; at least one calcite cement phase has beenidentified, made up of clear spar, as seen in planepolarized light, but zoned in CL. Like the carbonatebreccias from dissolution, the residual pseudocar-niole also do not show evidence of ‘ductile’ defor-mation while the carbonate ‘parent rocks’, aregenerally deformed.

We consider the residual pseudocarniolefrom dissolution and collapse to originate due togravity collapse, by complete re-arrangement ofrock mass at an advanced stage of dissolution andby accumulation of residual products largely insubsurface environments.

(C) Detrital pseudocarniole

Detrital pseudocarniole are made up either by poly-genetic breccias (clast- or matrix-supported, withfragments of varying dimensions and lithology,matrix always present) or by fine sand-silt sedi-ments. They show a vuggy fabric, but are seldomcharacterized by boxwork structure. Macroscopi-cally the rock colour ranges from yellowish toorange (Fig. 6).

Depending on the textural variability, it is poss-ible to make a further subdivision into a number ofsub-facies with different genetic mechanisms.

(C1) Detrital sub-facies without evidence oftransport. These are breccias with polygeneticclasts,mainlyangularandpoorlysorted,withvaryingdimensions from few centimetres to meters. Thetexture varies from clast-supported to the rarematrix-supported. The matrix introduces a highvariability in grain dimension, from silts to gravellysands; the grains have the same composition as theclasts. It is possible to observe rare sedimentarystructures (e.g. gradation); the cementation bycalcite and volume of accumulation vary notablyfrom place to place. This sub-facies can be inter-preted as cemented detrital material from thecarbonates of the circulating groundwaters.

(C2) Detrital sub-facies with evidence of trans-port. This sub-facies is represented by brecciasor micro-breccias, evolving with the intermediarycompositions to conglomerates or micro-conglomerates; the clasts can be polygenetic ormonogenetic. The C2 sub-facies includes matrix-supported, strongly cemented by calcite pseudocar-niole characterized by such sedimentary structuresas ripples, laminations and well-orientated clasts;the clasts are equal-dimensioned, a few centimetresin size. The very fine and well-sorted carbonate

sediments (silts to sands) commonly act as amatrix with respect to the coarsest clasts, or canconstitute homo-metric lenses.

All of these characteristics give a non-homogeneous appearance to the C2 sub-faciespseudocarniole. Commonly they constitute theexhumed infill of subterranean karst forms: sedi-ments that are entirely or partially fill-in channels;and spindle-shaped tubes and cavities. Inside thissub-facies a further subdivision has been recog-nized (three parts):

(C2A) Detrital sub-facies by channelled watertransport: the sub-facies is represented by well-sorted carbonate sediments, with grain sizesranging from clayey silts to coarse sands. Thefinest-grain deposits, clayey silts to silts, showplane-parallel or parallel-undulating laminationsbut sedimentary structures formed by currentaction were not noticed. As the grain dimensionsincrease, more complex sedimentary structureshave been observed: from silts to fine sands, inwhich low angle laminations and ripples (eitherasymmetrical or symmetrical) are preserved.The sand size sediments include more markedstructures such as festoons and convolute lami-nations, concave erosion surfaces and evidentnormal gradations. This sub-facies is the mostwidely distributed and abundant among the detri-tal pseudocarniole types. Its fine sediments havea broad distribution: they seem to represent theonly preserved record of a long sedimentaryphase in the evolution of the pseudocarniole.The C2A sub-facies is significant because finesediments are associated with almost all theother sub-facies, representing the final localproduct of their karst reworking. Although rare,the presence of water splash-marks on thestrata surfaces suggests genesis within a subterra-nean karst environment, where the drippingfrom the ceilings of cavities and into channelswas a common event. The different facies geo-metries and internal structures mark variousenvironments of sedimentation: from one side,diffuse depositional sedimentary structures dueto current action (either on the fine isolateddeposits or on other constituent of the sub-faciesmatrix) indicate a high-energy underwaterenvironment sedimentation. On the other hand,the distribution across wide areas seems to rep-resent the deposition by subterranean watersheets. Finally, the C2A sub-facies also fills infractures and small dissolution cavities in thesubstratum or in other types of pseudocarniole(Fig. 6c).

(C2B) Detrital sub-facies formed by stream watertransport: this is constituted of matrix supportedmicro-breccias, poorly cemented and dense; in a


Fig. 6. Detrital pseudocarniole. (a) Outcrop view; note the rounded clasts into the detrital sub-facies by stream waterfrom infill of subterranean karst cavities (C2C). (b) Sample of stratified polygenetic breccia of detrital sub-faciesformed by stream water transport (C2B), scale in centimetres; the clasts vary from sub-angular to sub-rounded; thehand-sample in the upper portion is composed by fine detrital sub-facies sediments. (c) Geometrical relationships detailamong different facies of the pseudocarniole: detrital sub-facies by channelled water transport (C2A) that fills in openfractures within the carbonatic breccias from dissolution.


sandy-silt matrix, poorly sorted, polygeneticclasts are found, up to centimetre-size. The sedi-ment is organized in heterogeneous layers ofdifferent thicknesses and irregular shapes, eventhough parallel lamination surfaces are alsofound. The clasts of small dimensions (up tomillimetres in size) are sub-rounded and orga-nized in ‘stone-lines’, while the larger clastsare angular, have a chaotic disposition and arewrapped by the lamination surfaces. The C2Bsub-facies forms rock bodies with an irregulargeometry articulated in a series of smalllobes. The angle of lamination-dip is entirelyconcordant with the depositional slope. Thissub-facies is thought to have originated fromsedimentary deposition in channels and bystream water transport, through localized flowmechanisms. The coarse material comes fromthe dismantlement of the detrital sub-facies, bythe action of channelled waters throughout thekarst flow path.

(C2C) Detrital sub-facies, by stream water frominfill of subterranean karst cavities: this is com-posed of poorly sorted and strongly cemented bycalcite deposits, matrix- or clast-supported. Thepolygenetic clasts are heterogeneous in dimen-sion and form: ranging from big blocks, tabularand angular or sub-spherical and rounded, tosmoothed pebbles, or equidimensional or pris-matic angular clasts inside a silt/sand to sand/gravel matrix. The clast composition is verydiverse and includes fragments of bedrock,other pseudocarniole deposits (residual and det-rital) and material from surface formations.Isolated C2C sub-facies rock bodies showcharacteristic pinnacle morphology. Local devel-opment of inverted relief morphology is facili-tated by poor mechanical conditions of therocks caused by the morphology of the karst inwhich they formed. The C2C sub-facies rep-resents the sediments deposed in funnel-likesockets, probably representing small subterra-nean karst landforms: these are modelled in thecarbonate bedrocks or in the carbonate brecciasfrom dissolution and residual pseudocarniolefrom dissolution and collapse facies after theirexhumation. Accumulation and cementation pro-cesses have made these pseudocarniole moreresistant to weathering and erosion in compari-son to their bedrocks.

(D) Encrusting pseudocarniole

These pseudocarniole show abundant quantities ofcarbonate polygenetic cement, polychrome(various yellow and white shades), with smallangular fragments of different lithological natures.They also show a typical vuggy aspect. This

facies is quite diffuse and forms thin layers (thick-ness up to 30 cm) on exposed surfaces of othertypes of pseudocarniole, disguising their realaspect and therefore making them appear appar-ently similar. The encrusting pseudocarniole canalso constitute small bodies, up to 50 cm high, atthe base of the rock walls (Fig. 7).

The origin of this facies can be comparedwith that of the detrital travertines (D’Argenio &Ferreri 1987): both are the result of the calciumcarbonate precipitation contained in the surfacestream waters. The thickness of the mineral crustlayers directly depends on the exposure time ofthe pseudocarniole to meteoric agents.

(E) ‘Tectonic’ pseudocarniole

These are made up of monogenetic breccias (calcar-eous or dolomitic), more rarely polygenetic, withangular, not selected fragments; they are alwaysassociated to matrix of varied colours; they showa vuggy fabric commonly characterized by aboxwork structure.

The ‘tectonic’ facies shows characteristic vari-ation in texture, with a typical tabular geometryand distribution, following a sort of parallel bandaround fault planes and shear zones. Inside therock it is possible to recognize some deformationmarkers (boudin lithons, minor shear zones) aswell as non-deformed portions (Fig. 8a & b).

In fact, it is possible to observe in thin-sectionstudy the presence of hydrothermal minerals thathave grown in the matrix pores (hydrothermalalbite, quartz and/or ankerite). At outcrop-scalethe hydrothermal activity is underlined by a highconcentration of hydrothermal products as infill ofthe fracture systems involving the pseudocarnioleformations (hematite crusts, Fe- and Pb-sulfideveins or other mineralogic associations such asalbite, hematite, ankerite, quartz (Fig. 8c) and/ordolomite, quartz, chalcedony and fluorite).

All these characteristics suggest that E faciespseudocarniole are formed and evolved in anenvironment influenced by tectonic activity, eitherdirectly or indirectly. Some pseudocarniole portionscan be absolutely considered rock shear zones, witha syn-deformation genesis. Moreover, the genesisof some pseudocarniole would seem to be influ-enced by chemical processes induced by possiblehydrothermal fluids flowing along the structuraldiscontinuities.

Interpretative model

The analysis of stratigraphical, sedimentologicaland geomorphological characteristics of pseudocar-niole pointed out different types of relationships


between single lithofacies and geological elementsand processes:

† with their bedrock (calcareous-dolomitic rockunits, i.e. their ‘parent rocks’);

† with the ‘ductile’ (plastic) deformation;† with events of ‘brittle’ (cataclastic) deformation;† with fluid flow – ascending (hydrothermal) and

descending (karst).

The complex variations of the key features(texture, cementation, corrosion, alteration)observed through different pseudocarniole facies,or inside the same facies, or even in a single

sub-facies, testify to a diverse and differential sedi-mentological/lithological evolution, even in nearbyportions of the same rock body.

From a general point of view, considering thechemical and physical modifications responsiblefor the transformation of carbonate parent rocksinto pseudocarniole, the fluids occupy a primarydeterminant role.

The change of the original gypsum/dolomite/calcareous rocks into pseudocarniole is carriedout through several stages of progressive transform-ation (Fig. 9) In the first stage, after gypsum/anhydrite rocks’ massive dissolution and

Fig. 7. Encrusting pseudocarniole. Mineral crusts and travertine formation on the aerial exposure surfaces.


consequent volume reduction, carbonate brecciasare formed (carbonate breccias from dissolution):they are genetically connected to the slowre-arrangement of overhanging dolomite and cal-careous rocks. The original sedimentary structuresare largely preserved.

Subsequently, by means of sulphate-ion richfluids, induced dissolution extended to include dolo-mite and calcareous rocks, local reworking of rockmasses goes on; an intense leaching of Ca-sulphateby waters could have caused the enrichment inCa2þ and SO22

4 ions in the circulating fluids,resulting in the progressive dissolution of dolomiteand the precipitation of calcite associated withdedolomitization (Bischoff et al. 1994; Canaveraset al. 1996).

Dedolomitization processes induce very import-ant transformation of parent rock and new facies areformed, characterized by progressively strongerinternal re-arrangement and by accumulation ofresidual insoluble products (residual pseudocar-niole from dissolution and collapse).

After uplift of the local Alpine structures, andlocal processes of exhumation and relief formation,a karst landscape forms. The karst flow pathsmainly involve the previously formed pseudocar-niole. Some rock masses are further reworked bymeans of transport and sedimentation processes,

typical of the hypogenic karst environment, asshown by the close association of sedimentarystructures: fill-in channels, spindle-shaped tubesand cavities, laminations and ripples, and watersplashmarks on the strata surfaces (detritalpseudocarniole).

Dissolution can be accompanied by other pro-cesses (strike–slip or normal faulting, gravitationaltectonic) that can act independently, repeatedly andin different moments, with varying intensity. Therocks resulting from these processes are indicatedas ‘tectonic’ pseudocarniole.

The different types of pseudocarniole constitutebodies with different dimensions, geometries andassociations, each characterized by key-featuresleft behind by the conditioning processes.Through the pseudocarniole and parent rockoutcrops, the Ca-carbonate precipitation from thecirculating waters and the surface streams hascaused travertine formation with the developmentof cemented crusts, up to decimetres thick: the‘encrusting pseudocarniole’.

Chronology

Some comments concerning the chronologicalsignificance of the Susa Valley pseudocarniole are

Fig. 8. ‘Tectonic’ pseudocarniole. (a) In the outcrop, local diagenesis of the dolomitic wall along a shear zone; brecciaaccumulated along some fault planes, altered because of the circulating fluids. (b) ‘Tectonic pseudocarniole’ sample(scale in centimetres); note the partial cementation and the general vacuolar aspect. (c) Microscopic view of hematite,ankerite and quartz cements in a tectonic pseudocarniole (this section, photo taken under crossed polars).


possible. First of all, the presented data pointed outthe objective interpretation problems: at present,there are neither ‘time zero’ nor significant‘time steps’ in the formation process that can beabsolutely placed either on climatic and/or tectonicchronologies. Nevertheless, a general framingof the pseudocarniole is possible through indirectdating evidences; for instance the total lack ofalpine metamorphism or alpine deformationthroughout the pseudocarniole deposits (Alberto2004; Alberto et al. 2005), the unconformityof pseudocarniole units present on different alpinedeformational structures (Polino et al. 2002;Alberto et al. 2005) and the residual pseudo-carniole containing clasts of deformed alpinemetamorphic rocks (Alberto et al. 2005). Theabove mentioned evidence represents post-quemelements indicating a post-Lower Oligocene agefor pseudocarniole.

In this study, some results of more precise datesfor pseudocarniole development have been furn-ished by preliminary pollen analysis (carried outby L. Cattani, Ferrara University) and detailed stra-tigraphical studies. Collected samples of detritalsub-facies by stream water transport containedpollen of Upper Pliocene–Early Pleistocene arbor-eal taxa from coastal environments. Moreover, therelationships among the detrital sub-facies bystream waters and natural landforms or man-madestructures indicate that the genetic process ofpseudocarniole formation took place between theUpper Pliocene and the present. In this way it ispossible to ascertain that the genesis of the pseudo-carniole does not correspond to the Triassic as thetime of formation of ‘true’ carnioles, but that itmight have started much more recently, at thevery begining of the recent evolution of the present-day Alpine relief.

Fig. 9. Outline of possibile processes and products relationships in the proposed model for pseudocarniole genesis.


Conclusions

After the collection and analysis of the collecteddata and their comparison with the informationfrom the geological literature, the provisionalterm of ‘pseudocarniole’ has been introduced toindicate carbonate breccias and conglomeratesof vuggy appearance, in the past interpreted as‘true carniole’ of the Susa Valley and assimilatedto other alpine rocks of controversial origin anddiversified nomenclature.

A classification of the pseudocarniole of theSusa Valley (Western Alps) has been proposed.This is articulated in five major facies, and furthersub-facies, the divisions depending on their tex-tural, structural and geometrical characteristics.The genesis of every facies has been inserted in ageneral evolutional model starting from the Triassiccarbonates (particularly dolomitic) and evaporitesuccessions, that are widely distributed in theWestern Alps.

The genesis of pseudocarnioles is connected tothe interaction and to the superimposition ofvarious processes. The dissolution and alterationof carbonate rocks are induced by a sulphate-richfluid, which apparently acts as the main mechanism.The dissolution induces a general instability anddisaggregation of the bedrock with a consequentgravitational settlement. Other processes are alsoassociated with dissolution; these are connected totectonics (extensional or strike–slip faults),gravity and karst development.

Because of all these many processes, many typesof pseudocarniole have been described, which con-stitute rock bodies with different dimensions, geo-metries and lithofacies associations. Finally, aparticularly young age for the pseudocarniolefacies have been suggested: Plio-Quaternary,based on palynological data.

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