The-Geology-Of-The-Mt-Etna-Basament
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Man. Soc. GeoL I t., (1982),7-25, 23 11 ff. THE GEOLOGY OF THE MT. ETNA BASEMENT by Faero LENrtNr (*) RIASSUNTO The Iblean Foreland consists of a Dredominantlv lhick carbonalesuccession wirh repearedvolcanic iri- tercalations.This successiondatel from Nel substrato dell'Etna sono riconoscibili Lre Triassic to elementi Ouaternary. lt does not appear in rhe map of Ml. Filgipali slrutrurali : I Avampaeseibleo, I A- Erna, present (see tanfcsa buL is in lhe iubsurlace i:300,000 Gela-Cataniae la CatenaSetientrionale. scale profile). L Avampaese è costituito da una potente serie The Cela-CataniaForedeep is crtooatica estesadal Trias al Quaternirio e interes- . lhe externalpart of da rip€tute LheCalranisselra Trough and is elongaredin NE-SW -|' manifestazioni vulcaniche basiche. direcrion.Ir Esco non affìora is limited loward the SE by rhe progres- nella carta dell'Etna. ma aooare nel sive platèau a scala 1:300.000 downfaulting of the Iblean a;d-dis- Fofrlo disegnalonella caria. appears L Avanfossa toward the NW below the Sicilian fold-belt of Cela-Caraniarappresenra la pdrte the Northern pir) 6rerna della Fossadi Caltanissetta Chain. This foredeep contains the Gela ed è allungara Nappe, which reprcscnts in direzione NE-SW. Verso SE essa è delimitattdaÌ the mosi southerly extent of lhe Northern Chain rhrusts and oargine del Plateau ibleo e si immerge verso NW con is buried'under the Quaternarl deposils sisremi di faglia gradinara". sparendoal disolto "a The NorthernChain. linking èlle collri della Catena.Tl tronre piu atajjzaLo que- . LheApennines Lo lhe ol ALlasMounLains ol Norrh Africtis st€ colri è costituirodalla Falda di Cela che si inseri- namedrhe Apenni- nian-Maghrebian Chain, and consists sce fra i depositi plio-quaternari dell'avanfossa,che in of a seiies of Parte ne mascherano la presenza. k Catena Settentrionale, che rappresenta la con- tEione ha l'Appennino e le catené moniuose del Nord-Africa e che pertanto prende il nome di Catena Appenninico-Maghrebide, consisLein una serie di col- tri di ricoprimento, costiluite da unità stratigrafico- smttturali a loro volta riconducibili a ditferentiaree paleogeografiche.Le varie unità sono oggi il risultato di fasi di deformazione succeduLesidàll'Eocene al Ksy woros: Stratigraphy, tectonics, Eastem (ltratemario con un progressivo spostamenlo del fron- Sicily. L di deformazioneandando da Nord versoSud. Ven- Epoo p€rtanto brevemente descritte le varie unità ini- ziando da quelle esterne e terminando con quelle piu rDtenre- INTRODUCTORYREMARKS ABSTRACT The volcanic complex of Mt. Etna is lo- cated between two main structural units: the In the Mt. Etna substralum three main structural Iblean Foreland and the Northern Chain. units are recognizable: the Iblean Foreland, the Gela- The Iblean Foreland, lying in the south- Catania Foredeepand the Northern Chain. easter-n.part of Sicily, does not appear in the ---Ìi) map of Mt. Etna, but lies in the subsurface, Isti,,r,o Scienze della Terra - Università di as is seen in the 1:300,000 scale profile. Catania. It repr4eíts part of the margin of the FABIO TENTINI Ft8. I ' Schematic structural cross-sectionof Eastern Sicily, west of the Mt Etna area. A = Iblean Foreland; F = Gela-CataniaForedeep; c=celaNappe; J = Mr. Judica Unit; I= Iúerese Unit; N: Numidian p : Flvsch:-"Calabride PanormideUnit; S = Sicilide Unit; SN = Sicilide + Numidian Flysch;MS = Mt.SoroUnit; C: Units; Cl = Capo S. Andrea U.; C, = 16.t*i-luormina U.j Cr = S. Marco U.; R = Rocca Novara U.; Ca = Mandaaici U.; Cr = 45p.o*ottte Unit; RF = Reitano Flysch; O = Capo d'Orlando Flysch; VC : Variegaìed clays (Antisicilide unit); Fc = Floresta calcarenites; pr : (posrorogènous) units (afier inrrru tr vriz,uq, 1978. modified). African Plate, which has remained relatively northeast tilting towards the southwest. Thus undisturbed save by predominantly normil towards the northeast the section becomes faulting. The progressive downfaulting of the thinner, gaps develop and locally emergence northwestern part of the Iblean Foreland by occurs, whereas to the southwest oelaeic a system of NE-SW trending faults in Cene- sedimentation is continuous. zoic times led to the formation of an asym- The pattern is little changed in the Up- metric trough: the Caltanissetta Trough, the per Miocene with volcanoclasticsof phreato- southeastern part of which is referred to as magmatic origin intercalated with coral the Gela-Catania Foredeep. bioherms. Lower Messinian limestones with The Northern Chain linking the Apen- a restricted fauna indicate a shallow-water nines to the mountains of North Africa and environment which grades up into continen- part of the Alpine orogen is commonly refer- tal conditions. red to as the Apenninian-Maghrebian Chain. From the Miocene-Pliocene boundarv the It consists of a series of thrust sheets made palaeogeographicpattem js totaìly differenr. up of sediments originally deposiîed along The present one is the result of three tectonic the old cratonic margin of Africa and prog- phases following the regional Upper Miocene ressively thrust over one another between uplift and referred to Early-Middle Pliocene, Eocene and Quaternary (fig. 1). Plio-Pleistocene and Middle Pleistocene- Recent age, which influenced the tectonic evolution of the present Ionian coast and the Syracuse-Malta Scarp (Carnoue TIIE IBLEAN FORELAND et alii,1982). l Sedimentation of the Iblean Foreland I from Triassic to Tertiary times was predomi- THE GELA-CATANIA FOREDEEP nantly one of carbonate deposition, both of limestone and dolomite. Information about all horizons below the Upper Cretaceous is only available foom boreholes. The lowest horizon penetrated by the drill is Triassic, so that nothing is known of the pre-Triassic basement. An interpretation of the subsur- face data is available îrorrl PATAc;:Aet alii (1979), who reviewed the core material. A distinction in facies has been studied in surface outcrop, in the Creaceous to near Mineo. Miocene sections, by Gnesso et atii (1979), Gnesso, Lerrrm & PEDLEY(1981), etc. In conclusion, the pattern which seems to characterize the Cenozoic of the Iblean Foreland is that of a structural hieh to the THE GEOLOGY OF TIIE MT. ETNA BASEMENT Mt. JUDICA UNIT ( Sicanianor lmcrcrc domain) VARIEGAIEDCLAYS Sc.gli. l.ci.. E-O CALIAVUIURQF'n. E-O G-C Cozzo Cucca Scction TI Mt- Gzr'rbarrera Succcsrion Mt. Jud.ica .s.crion (af..ì catt{taN -300fi LENTINI,tCz4) FIYSCH (or /rìUFAIA Fn.) -o M., Scalpcl,o Sccalorr l0 FABIO LENTINI posed, for it is always buried under Quater- running approximately from South to North nary depositsand its recognition has to await orovides an account of the structural- the drill. itratigraphic units from the external to the The nappe is made up of Pliocene and internal zones. pre-Pliocenesediments and rests upon Mid- dle Pliocene layers in the northwest of the foredeep (Rabbito n. 1) to horizons as young Tse Mr. Juprcl UNrr (Leurrxr & Vezzeu, as Quaternary at its furthest advance to the 1978). (Gelan. 1). southeast The lowermost stratigraphical level of Well data indicate that the floor of the this unit consists of shales with rare interca- the nappe is made up of a car- trough under lations of sandstones and marly limestones bonate sequencetypical of the Iblean region containing faunas of the Aonoides and Sub- followed by Upper Miocene evaporites, bullatus zones (Lprrrrr, 1974). This forma- PlioceneoTrubi", and sandsand marls of the tion has been assigned to the Mufara Forma- Plio-Pleistocene.Only in the region of Cata- tion bv Scsurpt nr FnrnpeeR.c & Tnovò of the foredeep formed of nia is the base (19ó2),'but is also known in the literature as Triassic carbonatesdirectly, becausethe Cre- the uFlysch Carnicoo ("Carnian Flysch,). members are lacking and taceous-Miocene The succeeding 200-300 m thick cherty the Jurassic is very much reduced in thick- limestones witJù Halobia styriaca ar lhe base ness. This is covered by a Pliocene- and H.norica at the top are of Norian- pelitic series with intercalated Quaternary Rhetian age. They are followed by 50-100 m basic lavas (Catania No. 10 Well). of cherty shales and radiolarites with interca- lations of submarine basic volcanic rocks, Jurassic-Cretaceous in age. THE NORTIIERN CHAIN On the top of these beds rest Middle- Eocene to Lower Oligocene red marls and The Northern Chain is a fragment of the marly limestones of the Caltavuturo Forma- Apenninian-MaghrebianChain. It consistsof tion containing microfaunas with Glaborota- a pile of superposednappes of sîrucîural- lia ceftoazulen!;is at the base and with Glo- stratigraphic units, which originated from bigerina oligocenica at the top. Some rare different basins or platforms. With certain brèccias, conglomerates and slumps occur exceptions, the units which are structurally between Cretaceous radiolarites and Eocene the highest originated from the more internal marls. These breccias and conglomerates zones. The profile of the structural scheme were interpreted as a transgressive interval. Fig. 3 - Upper Triassic cherty limestones of the Mt. Judica Unit, cropping out in the Mt. Scalpello area. THE GEOLOCY OF THE MT, ETNA BASEMENT 11 and Middle Miocene horizons and to en- croach on the external zone. THe Iupnpse UNrr: rge Nuuroreu Fr_yscn turo Formation is about 100 m. This unit is made up o[ a succession similar to the Mr, Judica one in Triassic- Jurassic levels, but different due to the pre_ sence of a thick flyschoid series (Numiàian Flysch), the only part out-cropping in the geological map of Mt. Etna. Tectonically resting upon this sedimen_ tary succession is the Numidian Flysch and the Varicoloured ClayS(Variegared ót^v"t ter a tectonic phase referable to Middle_"i_ tavuturo Formation and the silty shales of the Portella Colla Formation bf Eoc.rr"_ Oligocene age (Cf Gnesso et atii, 1979). s_ection,not more than 15 m thick, belongs to the Mt. Judica-type sequence, and repreénts the most condensedsuccession. Fi& 4 - Jurassic-CretaceousradioÌarites with breccias and conglomerates at the top. Mt. Judica Unit.