RENDlCONTI DELLA SOCIETA ITALlANA Dl MlNERALOGlA E PETROLOGlA, 1':l8':l, Vol. 4).}, pp. 7)},741

Petrofacies and petrologic characteristics of lower-middleMiocene sandstones of southern Calabria

WlLUAM CAVAZZA*

Department of Earth and Space Scicll«$, University of California, Los Angeles, CA 90024, U.S.A.

ABSnACT. - 1ne Slilo . Capo d'OrlaOOo Formationis a Mioccnc sedimentary unit croppina OUt exclusivelyaIona the: soo.i1he:m S«tor of the: Calabria·Pdoritani Arc(southttnmon Caiabria and Sicily). h is composed ofcong!ommm:, sandstone and mudrode mostly depositedin a decpomarinc e:nvironment,

Sandstonc:s of lhe: Stilo ' Capo d'Orlando Fm are:arkoses (i.e., quanz.fe:k1spt.rs'rich are:niles), Averagesandstone is composed of 4'9& quarlz, 489& fcldsparsand 79& lithic fragme:nts lteCllculated to QFLpercentagesl, PTovenance WIS primlrily from granitoidplutonic rocks and Iow.to-medium·grade: me:tamorphicrocks. Most common Iphlnitk lithic fragments arephyllite:s; schisu and a few volcanic lithics are: alsopresent. LocaDy, utraooinal C2tbonate lilhic fragmentsmay represem a significant detrital componem.

Point-count data documem a direct corrc:1ationbetween detrital mode:s of Slilo· Capo d'Orlando Fmsandstones and present basement lilhologies. Twodifferent petrofacies arc present. 1'he northe:n petrofacics(StHo and Allaro stratigraphic sections) has apredominantly plutoniclastic composition and wasderived from the Se:rre massif, located directly 10 thewest of the study Brea Bnd mostly composed ofHercynillO granitoid plutons. The southe:rn petrofBcies(Amendole:a seedon) has metamorphiclastic compositionand was derived from the Aspromonte massif, locateddirectly to the: north of the study area and mainlycomposed of middle:.to·high.grade metamorphic rocks.1'hese dala indicate 'direct provenance of the Stilo· Capod'Orlando Fm from the same rock types presentlycropping oot as the _geologic btockbone .. of the southernseetor of the Calabria·Pcloritani Arc. No exoticprovenance has been documented,

K~.worth: CaIabria·Pdoritlni Atc. Stilo . CIPOd'Orlando Formalion, slndStOne, petrofacies, pointcounting,

Ru.ssuNTO. - La Formazione di Stilo· CIPO d'Orlan·do eun'unita sedimentaria di e:11. miocenicl affionmelungo iI seuore maidionalc: dc::U'Arco caJabro-pelorillno(Calabria mcridion.aJ.e e Skill&). Eua Co composta cb con­glomerali. arenarie e pditi deposilalisi prevakntemc:n­le in ambieme mlrino profondo.

Le an:narie dcUa Formazione di Stilo . Capo d'Or­lando sono dassirlCabili come: ar\to$e: (ooe arerUli <j\Ian.G­

feldspalichc:). Esse sono composte mediamenle da ',,9&quano, 48% fddspati e 79& frammenti litid (percen.lUaii rkalcolate sulla somma QFLl. La provenienza eprincipa]mente da tocce plutoniche granitoidi e da me·tamorfiti di grado variabile da bano I medio. I fram­menti litid afanitid piu comuni sono di fil1adi; scisti e:vulcaniti sono molto menD comuni. Localmenle, i fram­menli [hid carbonatici extrlbacinali possono eS5Cre unacomponente detrilica qUlntitltivamente significativa.

1 risultati del conleggio dei punti documemano un le­game diretto fra le mode detritiche delle Irenarie dellaFormazione di Stilo· CIPO d'OrIando e le litologie delbasamento affioNJlte attualmente. Sono presenti due dif­ferenti petrofacies arenae«. La petrofacies settentrio·nale (corrispondente alle sezioni nratigufiche Stilo eAllaro) ha composizione principalme:nll: plutonodasti.ca ed edetivau dall'erosione delle Serre, situlte imme·dialamente: ad ovesl deU'arel studiata e ptcvalentememecomposte da plutonili erciniche di composizione guni·toide. La petrofacies meridionale (sezione Amendolea)ha composizione metlmorfoclasticl cd ederivata dal·I'Aspromome, SitultO immediatamente I nord dell'areastudiau e prevalentememe composto dl metamorfiti digrado me<!io-allo, Questi dlti iodicano unl provenien.za diretu e locale delll Formazionc di Stilo· CIPO d'Or·lando dagli Slessi lilotipi che formano attullmente IIstrunura portante del setlore meridionale dell'Arcocaiabro-pelorilano. Contributi dauid e:sodd non sonosllti documenlati.

.. Present address: Dip, di Scienze Minttalogiche, Un. di Bologna, Piazza di Porta S. OonalO, 1 1·40127 Bolog:na

734 W. CAVAZZA

Parole chiave: Areo calabro.peJorilal1O, Formazione diStilo . Capo d'Orlando, arenaria, petrofacies, conleg­gio dei pumi.

Introduction

The Calabria·Peloritani Arc (ePA) is aforeing element in the Apennic-Maghrebian

which subsequently completely overthrust theApennines-Maghrebides orogen.

The ePA may be divided into two sectors(BONARDI et al., 1979). Several argumentsseem to point out different geologic historiesfor the two sectors of the epA. In fact, mostof che rock units present in the northernsector are strictly comparable to the eo-Alpineunits of the Western Alps and northeastern

BIANCO

15km

~ 605r'i)'·;',! 4_3N5'12f;'~-;I 1

Fig. 1. - Simplified geologic map of southern Calabria (modified from BoNARDI Cl al., 1981). Legend: 1) basementrocks of Aspromonte and Serre; 2) Meso:wk sedimentary cover; 3) Stilo· Capo d'Orlando Formation; 4) «argiUevarkolori,.; 5) younger sedimentary deposits (middle Miocene to Holocene); 6) locations of studied sections.

scenario. The Apennines and Maghrebides aretwo distinct segments of the Neogene Africa­verging chain mosdy composed of decollementnappes made up of Mesozoic and Tertiarysedimentary rocks. The CPA, on the contrary,mainly consists of pre-Triassic crystalline rockspartly affected by Alpine metamorphism.There exists general agreement among authors(ALVAREZ et al., 1974; AMODIO-MoRELU etal., 1976; SCANDONE, 1982) that at least partof the CPA is a fragment of the Cretaceous­Paleogene, Europe·verging Alpine chain,

Corsica (AMODIO-MoRELLI et al., 1976;SCANDONE, 1980), whereas the rock units ofthe southern sector have been hardly affectedby Alpine metamorphism. Ophiolite-bearingnappes are present only in the northern sector.Furthermore, the southern sector (southernCalabria and Peloritani Mountains of Sicily)was a single continuous belt starting at leastfrom latest Oligocene time (BONARDI et al.,1981). In fact, all crystalline units arestratigraphically overlain by the same lower­middle Miocene sedimentary unit: the Stilo

PETROfACTES AND PETROLOGIC CIIARACTERISTlCS Of LC/IlUER·MIOOLE MIOCENE. ETC. 735

- Capo d'Orlando Formation, the subject ofthis paper, which is significantly absent in thenorthern sector of the CPA.

The Stilo - Cape d'Orlando Form.tion

The Stilo - Capo d'Orlando Formation(SCa Fm) is a clastic unit composed ofconglomerate, sandstone and mudrockdeposited in a deep-marine environment. Itcrops out as a virtually continuous belt alongthe eastern and southern coasts of southernCalabria (Fig. 1). Is is also present in Sicilyalong a wide belt crossing the northeasterncorner of the island with WNW-ESE trend.Maximum thickness of the SCO Fm is about700 m. The age is late Aquitanian - Langhian,based on planktonic foraminifera andnannoplankton (BONARDJ et al., 1981).

The lower boundary is a nonconformityseparating the SCO Fm from the basementrocks of the southern sector of the CPA. Ina few places, the sca Fm overlies the PalizziFormation (lower Oligocene), a very thin,shallow-marine so:limemary deposit (BotnulNet al., 1985). The basement is composed oflow-to-high-grade metamorphic rocks intrudedby granitoid plutons of Hercynian age, bothlocally covered by a thin and discontinuousveneer of Mesozoic carbonates. The sca Fmis overlain by a chaotic terrain of Cretaceous­Paleogene age, which has been informallynamed _argille varicolori If by AMoDJo­MOREUl et al. (1976). The «argille varicolori ..are absent in the northern sector of theCalabria-Peloritani Arc.

BONARDI et al. (1981) established the name«Formazione di Stilo - Capo d'Orlando» anddescribed several of its best outcrops inCalabria and in Sicily. That paper reorganizedthe confusing stratigraphic nomenclaturepreviously used, and represented a startingpoint for subsequent research. Nevertheless,in spite of the excellent outcroppingconditions of the SCO Fm, very little researchhas been done on this unit. FEJlli\ and AtAtMo(1976) studied the petrology of theconglomerate dasrs in the PeloritaniMountains of northeastern Sicily.CARMISClANO and PuGUSI (1978, 1982)defined sandstone detrital modes and

attempted a broad fades analysis in the samearea. Sedimentary fades analyses andpetrologic studies of the SCO Fm in Calabriaare lacking. The purpose of this study is toassess sandstone compositional parameters ofthis significam unit in Calabria, in order toreconstruct provenance. This contribution ispart of a larger project aimed at thesedimentologic-petrologic characterization ofthe sca Fm (and to its eventualstructural/geodynamk implications) over itsentire outcropping area (Calabria and Sicily).

Methods

Thirty-two sandstone samples were selectedthroughout the stratigraphic thickness of theSCO Fm along three stratigraphic sectionswhose locations are shown in Fig. 1. Studiedsections represent the best outcrops of thesca Fm in Calabria. Thin sections were cutperpendicular to bedding and stained for bothcalcium plagioclase and potassium feldspar.

Sandstone point counts were preceded byinspection of the basement rocks of theCalabria-Peloritani Arc. Over sixty basementsamples of different lithologies were taken andexamined in thin section, in order to be ableto eventually recognize them as lithicfragments within the seo Fm sandstones. Inaddition, about thirty seo Fm conglomeratedast of various rocks types were thin­sectioned and examined for the same reason.

Sandstone point counts were performedfollowing the procedures independentlyproposed by GAZZI (1966) and DICKINSON(1970), and discussed by GAZZI et al. (1973)and INGERSOLL et al. (1984). The peculiarityof the Gazzi-Dickinson point-countingmethod is that monomineralic crystals andother polymineralic grains of sand size(> .0625 mm) that occur within larger rockfragments are assigned to the category of thecrystal or other grain, rather than to thecategory of the larger rock fragment. In thisway, the effect of grain-size variations onsand/sandstone composition is minimizedUNGERSOLL et al., 1984). Unsorted samplesof any sand size may be used for modalanalysis, eliminating the need for sieving and

736 W. CAVAZZA

Eg. 2. _ QFL and QmFLI ternary diqrams showingcompos.iciolU of Stilo C.po d'Orlando uodstones insouthern Cal.bri•. Sce T.ble 1 for explan.tion ofsymbols. For both diagrams, c:ros.ses and polygonsrepresent means and uandard devi.tions of the samplepopulation, n indicates number of samples. Sce leXI for• discuuion of d.l. distribution.

statistically rigorous values because the datasets are constant-sum and constrained.Nevettheless, means and standard deviationfields are useful in illustrating visually theoverall petrologic characteristics of sandstonesample populations (lNGERSOLL and SUCZEK,1979).

The QFL plot (Fig. 2a) illustrates thequartzo.feldspathic nature of the samplepopulation. In fact, sea Fm sandstones couldbe broadly classified as arkoses (i.e. quartz­feldspar-rich arenites). The average SCO Fmsandstone is composed of 45% quartz, 48%feldspars and 7% lithic fragments,recakulated to QFL percentages ITable 2). Onthe QFL diagram, the studied sandstonesamples show similar composition, as also

L

Lt

A.

B.

Q

Qm

,~'--AMEI\OOlEA

., SECTIONill (n.'O)

.' ""SRO & ALLAROSECTIONS (n.22)

F

M£NDOLEASECTION

(n·101

STlLO &ALLAROSECTIONS(n.221

TABLE 1Explanation ofpetrographic parameters for Table

2 and Figures 2 and J

o.QiI.c. - • ._--~ . , • --~ ._--,... ~ - , ._--• ._--• ._--

u ••• 0, - .. ._---, ._----L ...... L.o ~

-~ ._---.. · 0'..'___ -.. ._---,·l_.__ ,.... : ,,."*, ' _....._- *,---,_.Q.,., .... "" -" ._-,--­...._----multiple counts of different size fractions.Furthermore, use of the Gazzi-Dickinsonmethod of point counting facilitates theapplication of aClualistic petrologic modelsrelating detrital composition to tectonicsetting because it allows direct comparisonbetw~n modern sands and poorly sortedancient sandstones.

For each thin section, 500 points werecounted. using the maximum grid spacing thatresulted in coverage of the entire slide. Allof the point-counted thin sections do not showevidence of quantitatively significantdiagenetic replacement of framework grains,and virtually all grains were recognized withcertainty. Therefore, 500 counts per sectionprovided statistically significant values for allparameters (VAN DER pus and TOBI, 1965).Criteria used for distinguishing lithic types,matrix types and other comIXlnents of samplesare those of DICKINSON (1970) and GRAHAMet al. (1976). Point counts were perfomed withsample locations ad ages unknown to avoidbias.

Petrologic results

Point-counted grains were originallyclassified according to twenty-nine categories.Point<ount data were then recalculated toproduce the grain parameters indicated inTable 1. The resulting modes appear in Table2. Four types of triangular plots wereconstructed from these data (Figs. 2 and }).Means and standard deviations listed in Table2 and plotted on Figs. 2 and 3 are not

PETROFACIES AND PETROLOGIC CHARACTERlSTICS OF LOW'ER·MIDDLE MIOCENE, ETC. 7J 7

this diagram is also used because it is astandard representation of sandstone detritalmodes (e.g. DICKlNSON and SUCZEK, 1979;DtCKINSON et al., 1983) and, therefore, allowscomparison with published data.

Phaneritic granitoid and gneissic rockfragments are very common within the scaFm sandstones; they are the primary sourceof Qm and F. Aphanitic lithic populations aredominated by metasedimentary rock types:slates, phyllites and, subordinately, quartz­mica schisu. Carbonate Iithics and volcaniclithics with felsitic and microlitic textures aregenerally minor detrital components.Aphanitic rock fragments are relatively scarcein sandstones of the Stilo - Capo d'OrlandoFormation (average QFL%L = 7). Thissituation reduces the statistical significanceof any plot based on these components, andcreates some scatter of data. Several diagramsbased on lithic populations have beendesigned. The LmLvLs and QpLvrnLsmtriangular plots were introduced by INGERSOlland SUCZEK (1979) as useful indicators ofprovenance. On these plots (Fig. 3a, b),detrital modes of the studied samples showpredominance of metamorphic (particularlymetasedimentary) lithic fragments. On bothplots, in spite of a considerable overlap,samples from the Amendolea section arerichest in metamorphic lithic components.

LmAMENOOlEAseCTION--J'-,

(n.1O)

STLO&ALlAROseCTIONS

(n.22)

AMENOOlEAseCTION

(n.1O)

STLO & AllAROSECTIONS (n.22) '-I--;~'-

LvmFig. J. - LmLvLs .nd QpLvmLsm ternary diagramsshowing ('OlIlpo$itions of 5tilo . C.po d'Orlaodosandstones in southc'm Cal.bri•. See T.ble 1 forexplanation of symboh. For both diagruns, cro5SC'5 andpolygons rC'pI"C'SCIIt means and standard devi.tions of thesample popul.tion, n incliClltes number of samples. Seetexl for discussion.

•

Discussion

indicated by very low values of the standarddeviation. Nevertheless, it is possible to definetwo populations with significantly differentcompositional parameters. Samples from theStilo and Allaro stratigraphic sections havevirtually identical composition, whereas thosefrom the Amendolea section have higherquartz and lower feldspars contents. In alldiagrams (Figs. 2 and 3), all samples areindicated by the same symbol to stress theoverall compositional similarity, whereasregional differences are emphasized by meansand fields of standard deviation.

The QmFLt triangular diagram (Fig. 2b)depicts a similar distribution. This is due tothe scarcity of polycrystalline quartz grainswithin the sample population. Nevertheless,

Petrologic characteristics of the sca Fmsandstones suggest that provenance of thesample population was primarily fromcrystalline basement terranes, mostly ofgranitoid composition, as well as fromextensive low·to·high-grade metasedimentaryterranes.

Although detrital modes of sandstonesamples from the same section are veryconsistent throughout its stratigraphicthickness, a few variables display significantvertical trends. For example, in the AlIarosection, the total percentage of carbonateextrabasinal detritus decreases abruptly withinthe first 200 meters of section (Fig. 4). Thisdecrease was producm by rapid erosion of thethin Mesozoic sedimentary cover overlying

n8 W. CAVAZZA

TABLE 2

Racakuloted modal point-count dotll (see Tabk I for expltmation of symbols)

M.t.~ aFL. QmFL\iI FIlMWiI Lmlvld QpLvmLsmilSompls Abovs '"Hllrnb.... 6ess , , l 'm , Cl " lm Lv Co Q1IlvmLlm

AmendDles sectlon116-113 "" " " ,

'" ", ,., 1.19 "

, , • • ..1l6-112 ." " " ,

" ", ,.. '25 " .. • • " "l!J6-1I1 ,,.

" ",

" " , 15.11 '25 ", , ,

" "116-110 ". " .. ," .. , ,.. 1.17 la, , , , ,

"116-79 '" " " ",.

" " ,., 1.54 n , , • " "86·711 '",. .. , ,. .. , ,.. 1.36 " " "

," ..

86-77 '" " " • " " • .., 1.47 " ", ,

" ..116-76 " " "

," " , >.Z 1.76 n , .. " " "116-75 ., ., .. 1 .. .. ,

" 0.94 n ", ,

" ..116-74 • ,. 'l ,

" 'l , .., 1.31 " " 0 .. .. ", ,. .. , ,. .. , .., 1.38 " " 1 , .. "" • • , • • , ,.. 0.25 , , , , ,"

"l1ero wctlon(l6-~1l 'l' .. " • .. " • .- 0.e4 " " • ,

" "06-" '" " ,. ," " 1 ,., 0.73 eo " • , " "8&-39 ". "

,. ," " , .. 0.69 " " " '" "86-311 '" " "

," "

, .., 0.95 " ", '" "86-37 '" " "

," " , ,.. 0.54 "

, 1 , " "86-36 '" 'l ", .. " 1 ,., 0.76 n "

,"" "!l6-35 '" " "

," "

, ,.. 0.6l " ",

" " "!l6-34 '" " ",

" " • ,.• 0.70 " " " 20 13 "1I11-JJ '" .. ", .. "

, ,., 0.90 .. .. 0 ... ..86-31 " " " " " " " ,., 0.74 " "

, , " ", .. ",

" ", .., 0.15 " " " '" "" • • , • • ,

" 0,12 " " " , " "SI11, SlIet Ion86-28 '" " "

," "

, .., ,." " " • '" "1\6-27 '" .. ", .. "

," '.06 .. " " , .. "86-2<1 '" .. " • " "

, .., ,... .. , ,"" "86-22 '" .. "

," " " •., 1.10 " "

, '" "116-21 .., " " " " .. " " 0.90 .. ",

1 " "116-20 '" " " " " " " " 0.73 " ",

1 " "tl6-19 ". .. " 0 .. ", 00 0.96 " " " 12 14 "06-111 '" " " ,

" ", U 0.74 " "

,'" "116-1" '" " " .. " " " ,.. 0.70 "

, ,1 " "116-16 '" " " 1 " " • ••• 0.66 " "

, , " "86-15 " " " • " ", ,.. 0.67 " " 0 o " "116-14 " "

,." "

,." ,., 0.66 .. 1 ,

",

", 'l " • .. " , ,., 0.79 " ", 0 " "" • • , • • , '.0 O. '" " " 1 1 "

,SIll0 end Al1llnl aeetlon Combined, .. " 1 .. " • '-' 0.71 " "

, 1 " "" • • , • • ," 0.13 " " " 1 " "

Totol, .. .. 1 .. " 1 " 0.96 " ",

'" "" • 1 , • 1 ," 0.::13 " " " 1 " "

Nott; Valuts Ihown art ba~d on '00 /owl grain poinn pn sampk. X and SD indica~ mtan and ont lumd4rd dtviationfrom tht mtan. Point-eOllnling raw d4w. and n:m:t location 0/ sampln art /Wdi/JJbk from tht author upon rrqum

PETROFACIES AND PETROLOGIC CHARACTERISTICS OF LOWER-MIDDLE MIOCENE. ETC. 739

Fig. 4. - Histogram showing an example of verticalcompositional variation within sandstones of the Stilo· Capo d'Orlando Formation. n indicates number ofsamples. Note how the total amOUnt of carbonate gninsrelative to the total framework grains (FRMW9&CARB)decreases abruptly within the first 200 meters of theAllaro section. 'This trend refleclS relatively quick erosionof a thin Mesozoic carbonate cover overlying thebasement in the sediment source area (unrooflngsequence).

the basement rocks and, therefore, documentsunroofing of the source terranes.

Compositions of sandstone samples fromthe Stilo and Allaro sections·combined andfrom the Amendolea section differsignificantly. For example, samples from theAmendolea section have higher proportionsof quartz (average QFL%Q = 54 versus 41 forthe Stilo and AlIaro sections combined) and,accordingly, lower proportions of feldspars(average QLF%F = 40 versus 52) (see Table2). Another petrologic parameterdiscriminating the two groups of sample is therelative amount of monocrystallinephyllosilicates (FRMW%M). This parameterhas a mean of 3.1 and 4.3, respectively, forthe Stilo and AlIaro sections, and 8.0 for theAmendolea section.

The relatively higher quartz contentof the Amendolea section is probably theresult of a different provenance. In fact,the south-central Serre massif (most likely,the sediment source area for the northern Stilo- Capo d'Orlando Formation, as alsosupported by paleocurrent data yet to bepublished) is mostly composed of Hercyniangranitoid intrusions (mostly granodiorites,with subordinate tonalites and granites)

Allllro sectIon

characterized by a quartz/feldspars ratio (QfF)ranging from 0.49 to 0.58 (see ROTTURA etal., 1986, p. 24, for list of data sources).On the other hand, the Aspromonte massifis mainly composed of middle - grademetamorphic rocks (mostly gneisses andsubordinate micaschists) (BONAROI et al.,1979; CRISeI et al., 1982). Modal analysesof the Aspromonte basement rocks arerare. They are instead available for thebasement rocks of the easternmost PeloritaniMountains, which are considered to beequivalent of those of Aspromonte (D'AMIcoet al., 1973; AMODIO-MoRELLI et al., 1976).They have a quartz/feldspars ratio rangingfrom 0.68 and 1.55, most commonly greaterthan 1.0 (D'A~nco et al., 1972; ATZORI et al.,1976; ATZORJ and La GruDIcE, 1982).Therefore, these is close correspondencebetween petrologi,. parameters of the SCO Fmand those of the basement terranes fromwhich it was evidently derived, and the Q/Fratio represents a significant «petrologictracer» for the delineation of the Miocenesediment dispersal routes in southernCalabria.

The higher percentage of phyUosilicategrains (FRMW%M) of the Amendoleasection samples is another clue to a local butsignificant metamorphic detrital input. A largesouthern metamorphiclastic input is indicatedalso by the LmLvLs and QpLvmLsm plots(Figs. 3a, b) depicting a shift for theAmendolea section subpopulation towardsmetamorphic lithics and sedimentary­metasedimentary lithks, respectively.

On these grounds, in spite of the overallsimilarity in composition, sandstones of thesca Fm in Calabria can be divided into twodifferent petrofacies (MANSFIELD, 1971) (Le.,rock bodies characterized by distinctivepetrologic parameters). A northernpetrofacies, including the samples from theStilo and Allaro sections, and a southern one,including the samples from the Amendoleasection. Several petrologic parameters allowdiscrimination of the two petrofacies. Thenorthern petrofacies is characterized bya lower percentage of quartz (averageQFL%Q = 41, versus 54 of the southern one),a relatively larger amount of feldspars (average

••

(n= 10)

, .FRMW'hCRRB

,

""'"u.

'"~ 302~

• =• ,,,

W. (AVAZZA

OIF

Fig. ,. - FRMW911M.QJF diagram of Stilo . C.pod'Orlando sandstones in Calabria. FRMW9bM indkaresdle paa'nl~ of monocrySlallinc pbyllo:silie-tc grains,QfF indiates the ntion between Iota! quanz grains andtOlal fdckpu grain5, n indicates number of samples. Note'how the oorthan (Stilo and Aflaro sccrions) and $OUthemIAmcndolca section} peuof.cies are unequivocallydiscriminated using~ petrologic parameters. Sce lexlfor diKuSsion.

QFL%F = 52 versus 40), a smaller amount ofmonocrystalline phyllosilicate grains (averageFRMW9bM = 3.6 versus 8.0), and a smalleramount of metamorphic lithic grains (Figs~ 3a,b).

The two parameters which bestdiscriminate the two petrofacies~ the ratiobetween total quartzose grains and totalfeldspar grains (OfF) and the percentage ofmonocrysulline .phyllosilicate grains(FRMW%M) (Fig. 5). Combined use of these[WO parameters produces a significantdiscrimination of the sample population.

REFERENCES

Ad~"owld",,~tJ. - This paper is based on part of aPh.D. dis5Crtation al veLA under the supervision ofR.V. INGERSOLL, whose guidance is gralefullyacknowledged. Sludy of the Sdlo - Capo d'OrlanooFormation WlIS originally suggested by G.G. ZUFFA.Discussion with G. BONARDI, D. PUGLlSI and A.ROTTURA tontributed greatly 10 lhis research G.GANDOLFI, R.V. INGERSOLL. L. PAGANELLI,G.B. VAI and two anonymous reviewers are thankedfor the critical reading of the manuscript. Fiddwork wassupported by grants·in.aid of reseatth from TheGeological Society of Amerita and Sigma Xi·TheScienlific Research Society.

ALVAU2 W., CocozzA T., WEZEL F.C. (1974) ­F1tl""~J4tio" 0/tM A/pi,,~ orovnic btiJ by micropltmdispm4l. Nature, 23', 10).10'.

MlODlo-MoRELU L., BoNARDI G., CoLONNA V.,DIETlUCII D., GIUNTA G., IPPOLrTO F., LIGUORl V.,LORENZONI 5., PAGLlONICO A., PEI.RONE V.,

soU[hern petrofacies was derived from themostly metamorphic terranes of theAspromonte.

Exotic detrital inputs have not bet:ndocumented. Some peculiar rock types, whichare present in the northern sector of theCalabria-Peloritani Arc (e.g., serpentinites andassociated rocks of the Gimigliano andDiamame-Terranova units; AMODlO-MoRELLl

et aI., 1976), have not been documentedduring this study as detrital components ofthe Stilo . Capo d'Orlando Fm sandstones.These northern detrital components might beabsent: i) because the northern sector was toofar away to act as a sediment source area; ii)because they were: not yet exposed; or iii)because the sediment paleodispersal systemcarried the detritus eroded from those peculiarunits to a different sedimentary basin.

There is a close similarity between thecompositional parameters of the SCO Fmsandstones of southern Calabria and chose ofthe corresponding basement rocks in the sameregion. This fact indicates that bothdocumented petrofacies had a localprovenance and that, during early Miocenetime, sediment source areas (the Serre andAspromonte regions) were already composedof the same rock units cropping out today.

••

southernpetrofedes/ (n"IO)

• •• •

740

"•

northem~ pelrofecles •.. (11=22)3 "~ \ •~

~

Conclusions

Sandstones of the Stilo· Capo d'OrlandoFormation have quartzo-feldspathiccomposition and, broadly speaking, have amixed plutonic-metamorphic provenance. Inspite of the rather homogeneous detritalmodes, there: are several petrologic parameterswhich allow discrimination of two differentpetrofacies. Detrital modes of the twopetrofacies can be matched with presentbasement lithologies in the adjacent sourceareas. The nonhern petrofacies reflectsprovenance from granitoid plutonic rocksforming the bulk of the Serre, whereas the

PETROFACIES AND PETROLOGIC CHARACTERISTICS OF LOWER·MIDDLE MIOCENE, ETC. 741

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