FACIES 35 163-208 P|.39-s4 18 Figs. 2Tab. ERLANGEN 1996
Dasycladaleans and Depositional Environments of the UpperTriassic-Liassic Platformof the GranSasso Garbonate (CentralApennines,ltaly) FilippoBarattolo,NapoliandAnnaBigozzi,Potenza KEYWORDS: FACIESANALYSIS - MICROPALAEONTOLOGY(DASYCLADALES,NEW TAXA) - PALAEOECOLOGYCARBONATEPLATFORM- CENTRAL APENNINE(ITALY) - UPPERTRIASSIC-LOWERruRASSIC
CONTENTS Summary - Riassunto 1 Introduction 2 L,ocationand geological setting 3 Previous works 4 Investigatedsuccessions 5 Dolomia Principale 5.1 Microfacies 5.2 SedimentaryCycles 5.3 Origin of cycles 5.4 Algal assemblages 5.5 Depositional environment. 6 Calcare Massiccio 6.1 Microfacies 6.2 SedimentaryCycles 6.3 Algal assemblages 6.4 Depositional environment 7 Stratigraphicaldistribution of algae 8 Paleontology 8.1 Genus Tersella Monelr-er in Monr:lr-r:r& Tr.ns 1951 8.1.l Tersella genoti n.sp. 8.2 Gcnus Farcsella Cnos & Lpvornr 196ó ex GnnNutn& Delorrne 1993 8.2.1 Fanesella sokaci n.sp. 8.3 Other taxa 8.3.7 P a laeodasy c ladus mediter r aneus (Pta) 8.3.2 Palaeodasycladus gracili.s Cnos & Leuorue 8.3.3 Petrascula? heraki Soxec & Nxlnn 9 Conclusions References
SUMMARY Sedimentological and paleontological stutlies carried out on the Upper TriassicDolomia Principaleand on the Lower Liassic CalcareMassicciocarbonateplatform successionsof the Gran Sassoarea (Central Apennine, Italy) allowed to recognize several microfacies types arrangedin three different types of high frequency cycles,subtidal,peritidal and diagenetic.The cyclescan be attributed to high frequency sea-leveloscillations on a fifth and fourth order scale.
Fivealgalassemblages havebeenidentified: l. Gyroporella vesiculifera, 2. Griphoporella curvata,3.Palaeodasycladus spp.,4. Palaeodasycladus andTheumatoporella,and 5. Tersella genoti andFanesellasokaciassemblage. In this latter assemblage two new species(Tersellagenoti n.sp. and Fanesellasokacin.sp.)are described,both from Liassic beds.Tersellagenotidifîersfrom theotherTersellaspecies for a less'differentiated'club shapedthallus,the shapeof secondarybranchesandsize.Fanesellasokacidiffers from other speciesof the samegenusin shapeand size of the branches, sizeof thethallusanddegreeof calcification. A re-evaluationof the genusTersel/a Mons[Er considersMorellet'soriginal diagnosisto be apterthanthe subsequentemendations. A discussionon several"Terselliform" (D taxa i ssocladella creti ca,Linoporella lucasi,D issocladella iberica andDissocladellaebroensrs)is supplied. Somecomments on thegenusF aneseI laCnos& Lruonm Palaeodasycladus gracilis Cros & Lsì.rorhrE and aregiven. Severalfaciesunitshavebeenidentifiedon the basisof frequencyanddistributionofalgal assemblages andtypeof cycle,eachunit recordinga differentdepositionalpaleoenvironment. In the DolomiaPrincipaleFormation two main depositionalenvironments havebeenrecognized: - a shelflagoonfaciescharacterized by subtidalandperitidal cycles dominatedby the Gyroporella vesiculiftra algal assemblage; - a backmarginfaciesmarkedby peritidal and diagenetic cyclesin whichtheGriphoporellacurvataalgalassemblage is widespread. In theCalcareMassiccioFormationthefollowing depositionalenvironments havebeenrecognized: - a back-marginfaciescharacterizedby diageneticcycles with high energysubtidalunits and thePalaeodasycladus spp.algalassemblage. Thepresence of thePalaeodasy cladus and Thaumatoporellaalgal assemblageindicatesa local transitionto a moreprotectedopenlagoonenvironment.
Addresses: Prof.F. Barattolo,Dipartimentodi Paleontologia, Universitàdi NapoliFedericoII - IangoSanMarcellino,10, I-80138Napoli;Fax-39-81-5520971. Dr. A. Bigozzi,Centrodi Geodinamica, UniversitàdellaBasilicata,Via Anzio,10, I-85100Potenza
r64
Fl
c*uooate platform
N
Nl
n"nsi" sequences
-\
stop. and proximal basin Thrusts
Fig. l. Facies distibution map of central Apennines showing the location of the snrdied area.
- a margin faciescharacterizedby oolites and bioclastic sandyshoals,with minor contributionsof reef-building organisms,andby a very poor cyclothemicorganization. This faciesis markedby thewidespreadoccurrenceof the Tersellagenortmd Fanesellasokncialgal assemblage The environmentaldistribution of subtidal,peritidal anddiageneticcycleswithin thefaciesunitswereprobably controlledmoreby therelativepositionto themarginthan by the amplitudeof the high frequencysealevel fluctuations. Thedisribution of faciesunitsallowedthereconsrruction of the paleoenvironmental evolutionof the shallow water facies in this area during the Late Triassic-Early Liassic interval. In the Late Triassica shallow watercarbonatefacies (from lagoonalto backmargin)extendedin the western and southernparts of the Gran Sassoarea.In the Early Liassic the platform faciesreEograded,and the margin movedbackto the westand southof theGranSassoarea. In the Middle Liassic, extensionaltectonicsfragmented theCalcareMassiccioplatform.Largeplatformareaswere drowned,andshallowwatersedimentation retreatedto the Southof the Gran Sassorange.
del CalcareMassiccio(Lias inferiore)dell'area del Gran Sasso(Appenninocentrale,Italia), al fine di precisarneI'assettostratigrafico,il contenutoalgale, la distribuzionedelle faciese dei paleoambienú. Lo studio paleontologicoha messoin luce un riccocontenutoalgalerappresentato da5 associazioni ad alghe verdi dasicladalitra le quali sono súate riconosciutedue nuove specie,entrambedel Lias Tersellagenotin.sp.eF anesellasokacin.sp.Tersella genotidifferiscedallealtre specieaffini per un tallo claviforme meno "differenziato",per la forma dei rami secondarie le dimensionidelle varie parti del tallo.FanesellasokacidifferiscedallealtreFaneselle perlaformaeledimensioni deirami,perledimensioni del tallo nonché per I'andamentoed il grado di Vengonofornite,inoltre,osservazioni calcificazione. sui generiTersellaMonrrrE'r in Monru-r'r & Tsns l95l e FanesellaCnos& Lnuotrva1966ex Gtlr.urn & Dnor, ne 1993. L' analisi sedimentologica ha evidenziatouna notevolevarietà di microfaciessia nella Dolomia Principale lacuidisribuzione chenelCalcareMassiccio verticaledefiniscequasisempreun assettociclico con ciclicità ad alta frequenzadi quartoe quinto ordine.Tre diversitipi di cicli, subtidali,diagenetici e peritidalisonostati identificati.I cicli appaiono conrollati daoscillazionieustatiche adaltafrequenza. La distribuzione la frequenza e dellemicrofacies, dei tipi di cicli e delleassocciazioni algalipresenti, identificanovarie facies deposizionaliindicanti differenti paleoambienti.
Nella DolomiaPrincipalesonostatiriconosciutidue ambientideposizionali; - faciesdi lagunaoccasionalmente ristret[a, a circolazione presenzadi cicli a caratteresubtidalee caratfeîizzatadalla peritidalee dallapredominanza algalea dcll' associazione Gyroporella vesiculift ra. - faciesdi retromargine,caratterizzata da cicli peritidalie diageneticie dall' associazionealgale a Griphoporella curvata. Nel CalcareMassicciosonostatiinvecericonosciutii seguentiambientideposizionali: - faciesdi retromargine,caratterizzata da cicli diagenetici conintervallosubtidale di altaenergiae dallaassociazione algalea Paleodasycladus spp.La presenzaoccasionalein questafaciesdellaassociazione algalea Paleodasycladus e Thaumatoporellaindica la transizionead un ambiente relativamentepiù protettodi lagunaaperta. - faciesdi margine,caratfeizzatada barre oolitico-bioclastichecon modesticontributidi organismicostruttori cheprobabilmenteformavanopiccoli pctch reefsin prosinoltre simitàdell' areamarginale.La faciessi caratterizza per la scarsaorganizzazione ciclica e per la dominanza dell' associazionealgale a Tersella genoti e Fqnesella RIASSUNTO sokaci. E' stata condotta un analisi sedimentologicae La distribuzionedei cicli (cicli subtidali,peritidalie micropaleontologicasulle successionidi piattaforma diagenetici)neipaleoambienti deposizionaliappareprincicarbonaticadella Dolomia Principale(Trias superiore)e palmentecontrollatada differenzenel rilievo topografico
165
\\\\t
I
-v
)omo Grmde -
c4À4Po
IMPERA TORf
S, Stcfilo
di Sessilio
Fig. 2. Topographic sketch of the Gran Sasso area (Central Italy), showing the position of the main stratigraphic sections which Upper Triassic- Lower Liassic dasycladaleancome from.
deglistessi,piuttosfoched allaampiezzadelle oscillazioni eustatichead altafrequenza. La distribuzionedelle facies nel tempo, ha inoltre consentitodi ricostruire I' evoluzionepaleoambientale dell'area. Nel Trias superiorefaciescarbonatiche di maresottilo si deponevano nellaporzioneoccidentaledellacatenadel Gran Sassoe a Sud di essa(CampoImperatore),in un ambientevariabileda lagunareristrettoal retromargine. Nel Lias inferiorele faciesdi piattaformaarretraronoe facies di margine si stabilirono al Corno Grande e immediatamente a Suddella catenadel Gran Sasso. Nel Lias medio, in seguito ad un importantefase estensionale, la piattaformadel CalcareMassiccioannegò in tutta I' areadel GranSasso.
of the Gran Sassorange(Gutsrrrl et al., 1990:Btcozn 1994). On account of the strong late dolomitizationextensively affectingtheDolomia Principale(D.P.)andpartially the Calcare Massiccio(C.M.), theGranSassoareahad notbeenobjectof detailedbiosratigraphical andsedimentological studiesupnow.Even thefossilcontent(expeciallyalgae)isknown l94l;Crnoccuu, 1977; onlyin part(Berveo, CruoccsrNr & MnNcwrlu, 1978). The purposeof the presentpaperis to supplyfurtherdataconcerningfaciestypes, algalbiotaandpaleogeographic settingof of the Gran the shallowwatersediments SassoareaduringtheLateTriassic- Early Liassic. The sedimentological and micropaleontologicalanalysisallow to discussthe faciesdistributionandpaleoenvironmental reconstructions. Therichdasycladalean assemblagessupply also somc intcrcsting biosnatigraphical data.
2 LOCATION AND GI.]OLOGICAL SETTING
TheGranSassoareais locatedat thenorthernmargin platform,a largesediof the Latium-Abruzzicarbonate mentarybody,about200 km wide,whichconstitutes the mountain range(Fig.l). The coreoftheCentralApennine Latium-Abruzziplatformconsistsof a thick scquence of shallow-water carbonates, depositedalongthe Southern margin of Tethys,from the Late Triassicto Miocene (Cor-rcrccn,1987). Thegeologichistoryof theGranSassoarca,asmostof theItalianpeninsula, recordstheevolutionof thismargin whichhasbeeninterpreted asa promontoryof theAfrican continenlalmarginor asan isolatedmicroplateknownas Adria(Csmxsv et al, 1979: DrRcornretal. I 986,Srr upelr & Prnavurr,1993). During the Late Triassicthe westernMediterranean region,thatwasstill partof anundiffercntiated continental block formedby Europe,Africa andNorth America,un1 INTRODUCTION derwentcrustalextension westward dueto theprogressive TheLateTriassic-EarlyLiassicof theGranSassoarea openingof theNeotethysocean(ZrEclrn1988;Marcoux is characterized by carbonatesediments,of platform and et al. 1993).Theextensional regimedetcrmined thetransbasinalfacies(Btcozz, 1987;Dun.mrrrr, 1987;Ao.lrvrollet gressions of shallowseasoverpartofthiscontinentand the al., 1990;Bigozzi etal.,1992). The shallowwaterfacies developmentof wide carbonateplatforms (Zaerarrnnl arerepresented by theNorian-Raethian DolomiaPrincipale 1990). Fm.andbytheLowerLiassic CalcareMassiccioFm. They During the Norian, evaporiticto peritidal carbonates outcropwidely along the westernpart of the Gran Sasso sedimented overmuchof theItalianpeninsula; localeuxinic range and southwardsin the Mt. Meta-Capole Serre- troughsdeveloped aspullapartbasins, relatedto transcurrent Ofenaarea.The basinalfaciesarerepresented by "Norian movements associated with theriftingphase(Znmnrenna, BituminousDolomitespassingupwardsto thin bedded 1990). dolomites"@aethianp.p.),"SpottedLimestones andCherty At this time in theGranSassoarea,two depositional Limestoneswith scatteredturbiditic calcarenites"(lower environments platform,in weredifferentiated: a carbonatc Lias).Thesebasinalfaciesspreadout in theeasternsector whichtheshallowwaterfaciesof theDolomiaPrincipale
166
Sella dei due Corni
Corno Grande
Mt. Capo l-c Scrre
Mt.Meta Calcare Massiccio
7
Calcare MÍtsslcclo
?Dolomia Principale
Dolomia Principale
-
Ofena
*l:t'Í"ffiL*'
,|
Dolomia Principale
,! /
ffi
shelf dolomites and calcareousdolomites
ffiilTll.*, ffi
basinallimestonesand cherty limestones
Fig. 3. Chronostratigraphic correlation of the Upper Triassic-[,ower Liassic investigated successions(Gran Sassoarea,Central Italy).
sedimented, and an euxinic trough,theGranSassobasin, The rifting phasein centralItaly endedin the middle in which bituminousdolomitesdeposited(Ao.r,uolret al., Jurassicwith the openingof the Ligurid ocean(Zncun, l99O; Btcozn et al., 1992;Brcozn, 1994). 1988;AsnerEet al., 1992;ENrv et al., 1993).The Gran In the Early Jurassicnew extensionalphasesaffected Sassoareathenbecamepartof theAfrican passivemargin thewholeItalianregioncausingtheopeningof newrifting which existeduntil the Oligocenewhen it was incorpobasinsandthefragmentationandprogressivedrowningof ratedin the Apenninefold and thrustbelt. someplatforms(Bnssotrm-ret al., 1993;Wnrrrnnn& BoseLLrM, 1981;Smn etal,1992). 3 PREVIOUSWORKS During theearlyLiassicthis extensionalregimedeterminedthe expansionof the Gran Sassobasin,which was The Upper Triassic-LowerLiassic sequencesof the connectedto the Ionian and Bellunobasins,and in the GranSassoareahavebeen ignoredfor almostcompletely middleLiassicthe breakup and successive drowningof alongtime.Thisfactispartiallyjustifiedbythestronglate the CalcareMassicciocarbonateplatform (Z.lmrrrnu, dolomitizationthat,affectsthesesuccessions. 1990;AnruolI et al., 1978;Brcozn, 1993;1994). A certaininterest,for its miningvalue,is manifestedin The Italian paleogeographic situationwas substan- thefirsthalfpartofthiscenturyfortle"ScistiBituminosi", tially modified at the end of the middle Liassic;platform a bituminousdolomitic succession, which outcropsin the areasrilerestronglyreducedand the pelagicdomainex- easternsideoftheGranSassorange,andthatisdoubtfully tendedfrom the SouthernAlps to theNorthernApennine, assignedto theLateTriassicby Bei.iso(1941).Significant evenup to the Adriatic region.Shallowwatersedimenta- stratigraphicdataon the region are given by severalautionhowevercontinuedintheCenral Apennine, thors,expeciallyon occasionof thegeologicalmappingat andSoufhem in theLatium-Abruzziplatform,whicharosein thisperiod scalel:100,000of theSheets TeramorespecSulmonaand as a distinctpaleogeographic unit. tively (M.rrvrrnorr.u, 1958, 1959;Scmssu 1953, 1954, Startingfrom the middleLiassic,the GranSassobe- 1955a, 1955b, 1958, 1959).Theseauthorsrecognize camea transitionzonebetweenthenewly formedUmbria- UpperTriassicplatformfaciesonly in theOfenaarea,but MarcheanpelagicbasinandtheLatium-Abruzziplatform they misunderstand all the otherTriassicoutcropsof the (AonuorIef.al.,l982a):slopetoproximalbasinsedimen-Gran Sassoareaattributingtlem to tle lower Liassic tationresultedin the depositionof chertylimestoneswith CalcareMassiccioFm. Howeverin their tentativepalaeogeographicreconstruction abundantmegabreccias andcalcareousturbidites. theGranSassoareais correctly
r67
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o
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codiaceans solenoporaceans dasycladrcemalgae oncoids ammonites radiolarians sPongesPicules foraminifers gatroPods
Fig. 4. Suatigraphic sketch of Corno Grande succession (Gran Sasso area, Central Italy) showing litholory, sedimentary cycles, dasycladalean algae and depositional paleoenvironments distribution. A, subtidal cycles; Bl, incomplete peritidal cycles; 82, complete peritidal cycles; C, diagenetic cycles.
Autonn^ tp. Tiasinahantkcni crinoids Megatodonsp. corals sponges bivalves
nz1 angularbioclasts O lithoclasts
600
E9" 96
bioturbatiom $ |I ' 1 Paleokant arrar stromatolltes channels \*, gmcrsionbreccias .i^^ ! \ ^
DlacK peooles tepe€
"un6hg6ementqusts
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dolomite
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thickueaaea calcareuos dolomits
interpretedas a transitionalzone betweeenthe LatiumAbruzzi carbonateplatform and the Umbria-Marchean pelagicbasin(Fig. 1). The earliestsignificantpaleontological data on the Triassicterrainsareprovidedby AmssnxoRr et al. (1968). The fossilsdocumented the presenceof UpperTriassic platformfaciesin the westernsideof CornoGrande. Aortvtot-t etal. (1978,1982a,1982b, 1984),CHroccunir (1977)andCHroccHNr (1978),carriedout & MANCTNELLT newstratigraphic andmicropaleontological studiesof the Triassic-Jurassic successions. They recognizethe presenceof Triassicshallow-water faciesin theMt. Meta-Mt. CapoLe SeneÍuea,at thebaseof Mt. Prenaanddoubtfully at Vradda(eastemsideofthe GranSassorange).Theyalso providea paleogeographic reconstructionwith a wideLate Triassic-EarlyLias carbonateplatform, which is fragmentedanddrowned in theMiddleLiassicby animportant phase. extensional Recentcontributions by Brctozz(1987),DuncNr ( I 987), ADAMoLT et al. (1990)andBtcozztetal.(1992)givefurther dataon stratigraphyandpalaeogeography ofthis area.The presenceof carbonateplatformandbasinalfaciesis recognizedandthedetaileddistributionof UpperTriassic-lower LiassicterrainsalongtheGran Sassorangeis workedout on thebasisof micropaleontological andsedimentological data.Btcozn et al. (1992) describethe following three successions: - Valle dell' Inferno-CornoGrandesuccession which is entirelycharacterizedby carbonateplatform facies;
thin beddcd cherty limeslones
- Canala-Mt.Prenasuccession which is characterized by a platform to basin transitionat t}rebaseand by platform faciesin the upperpart; - Vradda sequencewhich is entirely characterizedby basinalfaciesfrom the Late Triassicup to Late Jurassic. Btcozzt(1990)hascarriedout a studyon the cyclicity of the CornoGrandeLate Triassic-earlyLiassicplatform documenting of orbitally succession, theprobablepresence forcingcyclicity referableto theprecessional-eccentricity variations.Brcozn (1993, 1994)describedthe sequential evolutionof theGranSassoareain theLateTriassic-Early Liassicinterval,while Gursrrr et al. (1990)and VezzlNt et al. (1993)providednew geologicalmapsof the Gran Sassoareaat thescale1:25,000and l:100,000. 4 INVESTIGATED SUCCESSIONS Five UpperTriassic-lower Liassicshallow-water successionshavebeeninvestigated:CornoGrande,Selladei dueCorni,Mt. Meta,Mt. Capole SerreandOfena(Figs. 2-3).Thesesuccessions belongto thesametectonicunitso relationsamongthese that the original palaeogeographic successions areroughly preserved(Vrzzlr.net al., 1993). Corno Grandesuccession The Corno Grandesuccession(Fig. 4), locatedat the easternslopeof this relief alongthe Valle dell' Infernoin thewesternsideof theGranSassorange,is 1,200m thick. Itrestson thehangingwall of a splaythrust(Gurseruetal.,
168 mw
ithology
rge b{
Mt. Capo le Serre
30{h
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alcal li(fríhiltion
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C
2q)
îtt
c
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ts
B:
U*U
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Fig. 6. Stratigraphicsketchof Mt. Meta succession(Gran Sassoare4 CentralItaly) showinglithology, sedimentary cycles and dasycladaleanalgae distribution, and the (for symbolsseeFig.4). depositionalpaleoenvironments Mt. Meta succession The Mt. Meta succession(Fig. 6) hasbeen sampled along the southern slope, corresponding to the SouthEast side of Campo Imperatore. It is composed of about 200 m. of Dolomia Pricipale cut at the baseby a normal fault. About 120 samples have been collected frequently showing a rich dasyclad assemblage.
J4 I
Fig. 5. Stratigraphicsketchof Mt. Capo le Serresuccesslon (Gran Sassoarea,CentralItaly) showinglithology, sedimentary cycles and dasycladaleanalgae distribution, and the (for symbolssee Fig. 4). depositionalpaleoenvironments
Lithology
age
followed by 600 m of CalcareMassiccio.About 300 sampleshave been collected,but only in the Calcare alMassiccioformation well-preserveddasycladacean gaehavebeenfound.The DolomiaPrincipalecontainsa quite exclusivelyby higly poor assemblage,'represented (probably GriphoporeI la dolomitized dasycladaceans curvata).The top of the successionis truncatedby the the Selladei dueCorni splaythrustwhich superimposes sequenceuponit. Mt. Capo Le Serre succession (Fig. 5) is located The Ml CapoLe Serresuccession at the South-Eastside of CampoImperatore.It is composedof about350 m of DolomiaPricipaleandof 300 m by a normalfault. The of CalcareMasssiccio,separated sequenceis limited downwardsand upwardsby normal faults. About 70 sampleswith a frequentdasycladcontent havebeencollected. Plate Fig. l.
Fig.2. Fig.3.
Fig.4.
39
o at
alsal distrìbution
o o
z
NÈS
Ofena
è. 1990) and is composed of 600 m of Dolomia Principale
m w p g l c)rlc
B: Br
S .llr
P È-s
!.; rîP
F.E ó90 Epa !rz
E B v)3
Fig. 7. Stratigraphic sketch of Ofena succession (òran Sassoarea, Central Italy) showing lithology, sedimentary cycles and dasycladalean algae distibution, and the depositional paleoenvironments (explanation of symbols in Fig. 4).
Ofenasuccession (Fig. 7), exposednorth of Ofena The Ofenasuccession village, consistsof about 150 m of Dolomia Principale limited downwardsandupwardsby normalfaults.55 samples havebeencollectedin this sequence. Selladei due Corni succession The Sella dei due Comi succession(Fig. 8) is located betweenthe Corno Grandeand the Corno Piccolo mountains,on thehangingwall of thesplaythrustswhichoverlies
Upper Triassicmicrofacies(DolomiaPricipale;Gran Sasso,CentralItaly). Oncolitic packstone(DP6).Oncolitescanreachseveralmillimetersin lenght.Their nucleiaremadeboth of lithoclasts and bioclasts.The muddy matrix contains peloids and small bioclasts (mainly shell fragments).In the upperportion stylolites,enrichedin siltitic residualmaterialwith scatteredcrystalsof pyrite, are visible. Monte Meta.TA105.b.x 8.3 lithoclasts,textulariid forams,pelecypodshell Peloidal.bioclasticgrainstone(DP9). In the assemblage fragmentsand gastropodscanbe observed.MonteCapole Serre;thin sectionCS3.x 13.3 Bioclasticgrainstone(DP9).Particlesaremicritizedfragmentsof molluscshells,Griphoporellacurvata in additionfo Aulotortzssp. andotherforaminifers,and smalllithoclasts.The andotherdasycladaleans, grainshavebeenvariouslyabradedandrounded.Monte Meta; thin sectionCM6. x 13.3 Foraminiferalgrainstone(DP8).In themicrofaciesTriasinahantkeni,Aulotortussp.andlithoclasts;in the Monte assemblage, but not in the figure, gastropodsand small inegular thalli of thaumatoporellaleans. Meta;thin sectionCM2. x 13.3
Plate
39
169
170
ithology
lge
mwp g r
cyclc
algaldistribution
Selladei dueCorni o
o
o
a)
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o o
o
slslÈ,È 6
the CornoGrandesequence. The sectionis 100thick and is composed of 50 m of CalcareMassicciofollowedby 70 m of Pliensbachian basinalchertylimestones belongingto the CorniolaFormation.The boundarybetweenthis two Formationshasbeenaffectedby late dolomitizationthat partially masksthe originally stratigraphicrelationsbetweentheCalcareMassiccioandthe Corniola.In this area Bigozzi (1992)recognizedtracesofa prolongedsubaerial exposureat the top of the CalcareMassiccio.From this formation about 20 samples,frequentlycontaining dasycladaleans, havebeencollected. 5 DOLOMIA PRINCIPALE In the Gran Sassoareathe DolomiaPrincipaleFm. (D.P.)outcropsat Como Grande,Mt. Brancastello, Mt. Infornace,Mt. Prena,Fornaca,Mt. Meta, Mt. Capo le SerreandOfenaareas(Vrzznuret al. 1993).TheD.P.has a maximumthickness of 600m. At Mt. Prena(Aoruor-ret al. 1984) and Fornacaoverliesbasinaleuxinic facies represented by bituminousdolomites("Dolomie Bituminose",Ao.q,Nror-r et al., 1990).At Corno Grandeand Mt.Capo le Serrethe D.P. is overlainby the Calcare MassiccioFm.,while nearFornacait is overlainby lower Liassicbasinalfacies(Brcozzr,1994; Y uzztn et al, 1993). Two maindepositionalfaciescanbe distinguished: a cyclothemicanda massivefacies(Btaozn,1993;1994). The first facies crops out at Corno Grande,Mt. Brancastello, Mt. Infornace,Mt. Meta,Mt. Capole Serre andOfenaandin the upperpartof the Mt. Prenasuccession, over the massivefacies.It is characterized by a cyclicalsedimentation. Themassivefaciesis knownonly atthebaseof Mt. Prenasuccession andin theFornacaarea. It has beenreferredto a marginalarea(Dunavt, 1987; Aoavorretal., 1990;Btcozzrefal.,1992).Themarginwas characterized by thepresence ofbioclasticsandshoalsthat were stabilized and colonized by encrustingand reef-
Plate Fig. l.
Fig.2. Fig.3.
40
Fig. 8. Stratigraphic sketch of Sella dei due Corni succession (Gran Sasso area, Central Italy) showing lithology, sedimentary cycles and dasycladalean algae distribution, and the depositional paleoenvironments. (explanation of symbols in Fig.4).
building organisme.g. calcareoussponges,and by foraminifers,algae,incertae sedis organismsand dasyThisfaciesis extremelydolomitizedandis not cladaleans. subjectto the presentpaper,as no algaehavefound. The sedimentological and biostratigraphicalanalyses mainly focus on the cyclothemicfacies of the Corno Grande, Mt. Meta,Mt. Capole SerreandOfena successions, thatturnouttobebetteipreserved fromlatedolomitization. 5.1 Microfacies l3 microfaciestypes,relatedto different subenvironments,havebeenidentifiedin theD.P.cyclothemicfacies on thebasisof grains,texturesandbiota: DP1 - bioclastic wackestone DP2 - peloidal wackestone-packstone DP3 - megalodon wackestone DP4 - bioclastic packstone DP5 - lithoclastic packstone DP6 - oncolitic packstone-grainstone DP1 - aggregatelumps packstone-grainstone DP8 - foraminiferal grainstone DP9 - bioclastic grainstone DP10 - algal bindstone DPll - loferite DPl2 - pisolitic dolostone DP13 - dolomitic breccia
DPI - bioclasticwackestone. Allochemsconsistmainlyof smallbioclastscomposed of pelecypod shells,gastropods, dasycladalean algaeandpeloids.Themicrofaciesarecharacterizedmainly by the Griphoporellc curvataalgal assemblageand the Gyroporellavesiculiftraalgal assemblage.Thedepositional is a restricted lagoon. environment DP2 - peloidal wackestone-packstone. It is characteristically composedof peloids in a muddy matrix. Other allochemsare represented by green algae (thaumatoporellaleans),rare foraminifersand gastropods.This
UpperTriassicmicrofacies(DolomiaPricipale;GranSasso,Centralltaly). Lithoclasticwackestone-packstone (DP5),withAulotortzssp.andotherforams,anddasycladalean algae in a muddypeloidalmatrix.Lithoclastsare composedof bioclasticpackstones. Part of the grainsare oxidized.Fenestralcavitiesarepresent.MonteMeta;thin sectionTA37.a.x 11 Loferite(DP1l) with laminoidfenestrae probablyenlargedby disssolution. Noticethelargespecimen of Aulotortussp.in the middleleft. MonteMela;thin sectionM4. x 6.7 Dolomiticbreccia(DPl3). Lithoclastsare composedof algalbindstones andby lithoclastic-bioclastic packstone.They areborderedby dog toothcements.Cavitiesarecompletelyfilled by vadosesilt. Ofena; thin sectionOF43.x 5.3
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172 microfaciesis theproductofa shallowsubtidaldeposition to a shallow subtidal setting, with moderateto intense in alow-energyenvironment,probablyarestrictedlagoon, circulation,proximal to the shelf edge, into which the lagoonalaggegategrainswere transported. by the low-diversitybiota . as suggested It is characterized DP3 - Megalodonwackestone. by large megalodontidshellsin life position.Thematrixconsistsof mud,oftenintensely bioturbated,with peloids and rare bioclasts.The microfaciesdescribesa subtidalenvironmentundermoderatewatermovementsin a lagoonalto a back marginarea.
DP8 - foraminiferalgrainstone(Pl. 39/4). Foraminifers form up to the 60 Voof theallochems.Other constituents fragments(Griphoporella anddasycladacean arepelecypod curvata) . Fossils are usually well-rounded,and wellsorted.Themicrofaciesis relatedto a high energyshallow subtidalto intertidal environment,proximal to the shelf edge,wheresomelagoonalforaminiferswere sweptin.
DP4 - bioclastic packstone(Pl. 4212).Allochems are usually composedof shell fragments,dasycladaceans, DP9 - bioclasticgrainstoneQl.3913-4).Allochemsare bivalves, gastropods, foraminifersandlithoclasts.Oftenadistincttypeof biogenic composedof dasycladaleans, with veryrarelithoclasts.Usuallochemis dominant.The matrixconsistsof mud,fine- foraminifers,echinoderms, grainedbioclastsand/orpeloids. ally onedistinctgroupof organismsdominateandform up Like in DPl the Griphoporellacurvataalgalassem- to 70Voof the allochems.The grains are set in a spary blageand the Gyroporellavesiculiftra algalassemblage mosaic,or are surroundedby isopachousrims of fibrous in thismicrofaciestypeinterpreted "dirty" cementsthat suggestan early diagenesisin a areequallyrepresented Late sparcalcitefills theremaining as a depositof shallowsubtidalenvironmentproximal to marineenvironment. theshelfedge,undera moderateto intensewater-energy. interparticleporositybut intraparticleandvuggyporosity mainly canbe preserved.The algalcontentis represented (Pl.40/1).Themicrofacies DP5- lithoclasticpackstone is by theGriphoporellacurvatqassemblage. composedof angularlithoclasts(A 0.5-5mm)consisting in a shallowsubtidal,highThismicrofacies deposited of peloidalor bioclasticpackstones; black pebblesand with on tidalbars,shoalsor beaches, energyenvironment, oxidatedlithoclastshavebeenobservedaswell. Theeleandforaminifers Dasycladaleans anactiveearlydiagenesis. mentsare immersedin a muddypeloidalmatrix.Somewheretransportedfrom adjacentlagoonalsetting. times fenestralfabricsarerecorded. is foundalsoin 10-20cm thismicrofacies Occasionally The microfaciesis an intertidal to shallow subtidal thick layers inside the DPl to DP4 microfacies.One transgressivelag deposit. Black pebblesand oxidated distinct group of organisms,especiallydasycladaleans, probablycomefromanearliercemented lithoclasts substrate dominatesin theselayersinterpretedas stormdeposits. which had undergonesubaerialexposure. DP10 - algal
[email protected]/I). It is composedof (Pl.39/1).Theoncolites, DP6- oncolitepackstone-grainstone stromatoliticlayers,with eitherLLH or planaralgallamioftenup to 2 mm,of variousshape,havefossilsorrounded nae, trapping mud or peloids. Laminoid fenestraeand lithoclastsasnuclei.Thelithoclastsarepeloidalorbioclastic is Thismicrofacies areobserved. evidenceofdessiccation wackestones-packstones. Otherallochemsarerepresented referredto an intertidalto supratidaldepositin a tidal flat by shell fragments.The matrix consistsof fine-grained environment. peloidsorbioclasts.Whenthematrixis lacking,thegrains are usually surroundedby thin envelopesof fibrous ce- DPll - loferite (Pl. 4012).The lithofaciesconsistsof ments.Dissolutioncavitiescansometimes with birdseyes andfenestral bepresent. The peloidalpackstone-grainstones, microfaciesis interpretedasa depositof a shallowsubtidal fabrics.Otherallochems by rareforaminifers arerepresented environmentundermoderatelyhigh water-energycondi- and gastropods. Plain bed laminae,0.5-1.5cm thick, of tions,probablylagoonalchannelsor shoals.Thelithoclasts gradedpeloids can be present.The voids, sometimes wereprobablyerodedfroma weaklyconsolidated substrate enlargedby dissolution,areusuallyfilled by latesparite. from leeves The lithofaciesbelongsto an intertidal to supratidaldeor the of thechannels. posit on tidal flats. DP7 - aggregate lumpspackstone-grainstone. Allochems Themicrofacies arecomposed lumps,2-5 mm in size,some- DP12- pisoliticdolostone of aggregate @ls.412,4411). timeswith thin micriticenvelopes. Thegrainscomefrom is characterized by pisoidsand thin cementcrustswhich mud or peloidalaggregations in a muddymatrix.Rimsof canbeindifferentlysuperimposed on theprecedingmicrofibrous cementssometimessurroundingthe grains are faciestypes.Fenestralfabric,birdseyesand/ordissolution Themicrofacies interpretedas an effect.of winnowing.Aggregatelumps cavitieswith geopetaltexturesarepresent. were formed in a restrictedlagoon under very modest is interpretedas the productof vadosediagenesisdue to watermovement(Flúgel,1982).Themicrofacies is related subaerialexposure. P I a t e 41 Fig. 1. Fig. 2.
UpperTriassicmicrofacies(DolomiaPricipale;GranSasso,CentralItaly). Algal bindstone(DPl0). Noticethetepeestructures, in thecenter.MonteMeta;thin sectionMM7. x 6.8 of bioclasticPisoliticdolostone(DPl2). Vadosediagenesis hasaffectedan originalsedimentcomposed peloidalpackstone. MonteMeta;thin sectionM3. x 8.3
Plat e 47
t13
ffi
ll, "t.
t74 Cyclesfromthe UpperTriassic- LowerJurassic Sedimentary in the GranSassoArea Calcare Masslcrlo Dolomla Prlnclpalo
Fig.9. Schematic colunmof sedimentary cycles from the DolomiaPrincipale (DP) and the Calcare Massiccio (CM) formations (Gran Sasso area, Central Apennines). A) subtidal interval, B) intersupratidal interval, C) supratidal interval. TheDolomiaPrincipale Formation shows subtidal cycles (composedorùy by the A interval), peritidal cycles either complete or incomplete (respectively composed of A, B, C and A, B intervals) and diagenetic cycles (formed by A, C intervals). In the calcare Massiccio Formation diagenetic cycles prevail. Laterally the detail of the subtidal interval from a marginal facies is shown (microfacies type CM6).
5.2 Sedimentarycycles
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In the studiedareathe microfaciesare cyclicallyarranged(Fig. 9). Thecyclesare from 40 cm up to 3-5 m thick andgenerally exhibit a shallowing upwardscharacter. Threemaintypesofcycleshavebeenidentified: - subtidalcycles,with only subtidalunits (DPl, 2, 3): theupperboundarygenerally coincideswith a maximumfloodingsurface; - peritidalcycles,whichcanbecompleteor incomplete.In the first casetheyarecomposedof a subtidalbasal unit (DP3-9), overlainby an intertidalunit (DPl0, l1) unit(DPl2, l3); andfinallyby a supratidal incompletecycleslack the supratidalunit at thetop of thecycle; - diagenetic cycles(asdefinedbyBoSELLINI & llanore,1985),in which the supratidal interval (DP12, 13) is directly superimposedon the subtidalportion (DP3-9). upwards Cycleswithpartiallydeepening charactersare rare. Thesecycles have a intervalreprebasalintertidaltrasgressive sentedby the DPl1 microfaciestype.
resoluLacking a goodbiostratigraphic tion the duration of cycles can be only Btcozz (1990)gavean averagetime DPl3 - dolomiticbreccia(Pl. 40/3). It is composedof roughlyestimated. in a greento yellowishcoarsedolomite spanof 20-40Kyr for the cyclesof CornoGrande.This angularlithoclasts, cyclothemic matrix.This lithofaciesis interpretedasa collapsebreccia seemsconfirmedalsofor theotherisochronous area. of the investigated sequences due to subaerialexposure.
Plate Fig.1.
Fig.2.
42
UpperTriassicmicrofacies(DolomiaPricipale;GranSasso,CentralItaly). by a Gyroporellavesiculiftra Pisoliticdolostone(DPl2). Theoriginalsedimentwasprobablyrepresented peloidal-bioclastic (Gùr"mel)packstone-grainstone matrix.Noticethethick pisolitic envelopesaround in a thegrainswhich alsotrappartof thesediment.Fenestralcavitiespartiallyenlargedby dissolution. Ofena; thin sectionOF32.4(= BA.594.4).x13.3 thalli of thistaxon packstone(DP4).Notethedifferentsizeof calcareous Griphoporellacurvata(Gùr'rnrr-) andsmalllithoclastsarealso sp.),gastropods in respectto thoseof theFig. 1. Foraminifers(Aulotortu.e present. MonteMeta;thin sectionTAl6.3 (= 8A.592.3).x 13.3
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176 5.1.3 Origin of thecycles
probablyoccurredin restrictedlagoon thattheassociation andin near-margin environments @anarrolo, I 99I ; Fig.I 0i Many authorshaveparallelizedhigh-frequency, meter A), wherethealgaecoveredtheshallow subtidalsubstrate scalecyclesof manyshallow-waterplatformsuccessions by a more or lessdensemeadow.Very restrictedcondito orbitally forcedsea-levelvariationswith Milankovitch tionsarerecordedfor thisalga(MlnrrN & Drlc,rno, 1980). frequencies.The origin of meterscalecyclesis still under Gr iphoporeIIa curvata is refen eÀtotheNorian-Rhaetian discussion(seeGomuruurR et al., 1993andDnurr.ruout & (Brnnrroro et al, 1993); the associationwith Triasina WnKrNSoN, 1993,for a recentreview). The confioversial hantkeni and Aulotortus sinuosus(Dn Crsrno, I990a; debatebetweenautocyclicor allocyclic mechanisms, in- Mlncoux et al., 1993) is typical for the late Norianvoking progradationprocessese.g. Ginsburg'sautocycle Rhaetian. (Ginsburg,I971), or reversalhigh-frequencytectonic,is still open. 2. Gyr oporeIIa vesiculifera assemblage (Pl. 42/l) . Peritidal cycles record the lateral progradationof a The assemblage is oligotypic; calcareousskeletonsof tidal flat environmentover a subtidal shelfJagoonbut otherundeterminable dasycladsoccurseldom.The fauna cannotruleoutthepossibilityof anautocyclicmechanism. consistscommonlyof gastropodsandforaminifers(AuloSimpleprogradationmodelscannotexplainthe presence tortus sp.).This algalassemblage is frequentin bioclastic of diageneticcaps,at thetop of thecycles,which recorda wackestones-packstones (microfaciestypes:DPl, 4) where prolongedsubaerialexposure,or the origin of diagenetic it can constitutethe lOÙVoof the fossil content. This cycleswhich lack an intertidal interval at the top of the assemblage is rarerthantheprecedingone.The two algal subtidalportion.Diageneticcycleswitnessin fact sudden assemblages werepresumablyvicariantin quietprotected relativesea-levelfalls that shouldbe controlledby either areascharacferizedby restrictedcirculation,as the relasomeallocyclicmechanismof high-frequency sea-level tivelylow diversityof associat€dbiota suggests. Gyroporella variations(with Milankovitch frequency)or reversaltec- vesiculiferaassemblage mostlikely populatedtransitional tonic. Eventhe subtidalcycles,as suggested by Emrcr & areasbetweena restricted lagoon and a back margin Rrm (1991),needanallocyclicprocessfor theirexplana- (Fig. 10/A). In thisenvironmentGrip hop or ell a curvata, if tion. present,is alwayssubordinate. Brcozn (1990),on thebasisof differenrtypes,distribuThealgalassemblage is typicalof theNorian-Rhaetian tion andorganizationof cycles,referredthecyclicity of the ageevenif Gyroporellavesiculiftra is doubtfully known Late Triassic-EarlyLiassic Corno Grandesuccessionto from younger strata (lower Liassic: Cnos & LruorNE, high-frequencysea-levelvariationson the Milankovitch 1967;seealsochapter6). band. A similar interpretationseemsto fit to all Dolomia 5.4 Depositionalenvironment Principalecyclothemicfacies. Two main faciescan be differentiatedbasedon type, distribution and frequencyof microfacies,algal assem5.3 Algal assemblages blageand cycle, eachrecordinga particulardepositional l. Grip hop oreIIa curvata assemblage(Pl. 42 12). paleoenvironment: Theassemblage is oligotypic,andthenominal[axonis always dominant. Foraminifers(Triasina hantkeni and - shelflagoonfacies. The prevailingmicrofaciesarerepAulotortussinuosus),thaumatoporellaleans andraremol- resented by bioclasticandpeloidalwackestones (DPl, 2), luscshellscanbe present.Thesedimentconsistsof either megalodon (DP3),algalbindstones wackestones andloferites (microfaciesDPI) or packstones (DP10, l l) and rare bioclasticpackstones(DP4). The bioclasticwackestone and grainstones(microfaciesDP4, DP9) wherethe alga Gyroporellavesiculiftra algal assemblage dominatesin may constitutelhe 707oof the allochems.This suggests respectto fheGriphoporellacurvaîa algalassemblage.
Plate 43 Fig. I
Fig.2.
Fig.3.. Fig.4.
Lower Liassicmicrofacies(CalcareMassiccioFm.;GranSasso,CentralItaly). Aggregategrainsgrainstone(CM5). Cayeuxia-likealgaeandshellfragmentsarcpresentThegrainsshow thin envelopesof fibrous "dirty" cements.Remainingvoids are filled by late sparcalcitebut some interparticleporosityis still preserved. ComoGrande;thin sectionpSC5.x 8.3 Coralsframestone(CM9). Corals,in life positions,arepartially recristallizedandencrustedby incertae sedis organisms,probablered algae. Intergranularspaceis filled by peloidal mudstone,containing scattered bioclasts,mainlycomposed of shellfragments. CornoGrande;thin sectionPSCIl. x 10.4 Birdseyeslimestone(CMl0). Theoriginalsedimentis a peloidalpackstone. Largercavitiesenlargedby dissolution.CornoGrande;thin sectionBA7. x 10.4. Pisoliticlimestone(CMl l). Theoriginalsedimentis a peloidalpackstone-grainstone. Reworkedpisoids andthetypical "drop" like structure,with downwardgrowthof somepisoids(center).Geopetalstructures within a pisoidcanbe alsoobserved(lowerleft). CornoGrande;thin sectionBA2. x 10.4
Plat e 43
r11
178 LateTrlasslc
A
\\ \\ subtidal cycles
Fig. I 0. Paleogeographicprofiles showing the facies distribution in the Gran Sassoareain the Late Triassic (A) and in the early Liassic (B). The Corno Grande is characterized by outer lagoon facies during the Late Triassic and by marginal facies during the early Liassic (see also Fig. lllA and Fig. lllB). Note the occurrence of different type of cycles moving westward, from the margin to the lagoon (explanation of symbols in Fig. 4).
\ \ \ \ \ \ \ \
peritidal diagenetic bioclastic sand shoals cycles cycles and banks
with encrustingorganisms Gyropore lla vesiculifera a.a. Griphopore lla curvata & a.
EarlyLiassic
diaeenetic -;;i;;
a
oolitic.bioclastic sandshoals
Terselh genoti - Fanesella sokaci a.a.
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Paleodasycladusspp. a.a.
b
Paleodasycladusand ThaumatoporeIIa a.a.
Shallowingupwardscycles(3 m thick in average) are usuallyobservedin this facies.Subtidaland complete peritidal cycles, sharply prevail over completeperitidal cyclesanddiageneticcycles(Figs.a-10lA). This facies, althoughlargely dolomitized,is wellrepresented at the Corno Grandesuccession(middle-upper portion of the D.P terms)and in the Ofenaarea(Figs. 4-7). The depositionalenvironmentis a protectedlagoon characterizedby modestto moderatewater energy.The
Plate 44 Fig. 1.
Fig.2.
pelagic limestones with turbidites
onsetof restrictedcirculationis witnessedby the occasionaloccurrence of low diversitybiota.Algalbindstones and loferites(DP10, l1) suggestthe periodicdevelopmentof tidalflatswith cyanobacterians andstromatolites. The cyclicityof this facieswasmainlycontrolledby high frequencysealevel oscillationswhich determined restrictionin the circulation pattern inside the lagoon, progradationof peritidal faciesover the subtidallagoon and occasionaltemporaryemersions. Howeverthe predominance ofthesubtidalandperiúdalcyclesoverdiagenetic
LowerLiassicmicrofacies(Calcare MassiccioFm.; GranSasso,CentralItaly). (CM3)containingPalaeodasycladus Bioclasticpackstone muddypeloidal-fine andThaumatoporellaina bioclasticmatrix.Largedissolutioncavitiesandscatteredcrystalsof dolomitearepresent.Como Grande; thin sectionD2.8 (= BA.588.8);x 10.4 Lithoclastic-bioclastic rudstone(CM8). Lithoclastsare composedof peloidaland oncoliticpackstonegrainstoneand are rounded to subrounded.Bioclasts consist of Palaeodasycladussp., gastropods, Cayeuxia-likealgae,shell fragmentsandforaminifers.The grainsare surroundedby isopachousfibrous porosityis filled by latesparcalcite.CornoGrande;thin sectionFC3.4 cements. Remaininginterparticle (= 84.598.3).x 8.3
Plate
rl9
44
h-
: ,;,3?.
. "",x*. 'ù..{
ì
180 onesindicatesthat the subtidaldepositionprevailedover CornoGrande,Mt. Aquila, Mt. Capole Serreand northall othersub-environments andthatthesealevelvariations wardofCasteldelMontevillage.ThisFormation is locally weremoderate. affectedby strongdiageneticalterations,which canlimit thesedimentological andbiostratigraphical analysis. Only - back margin facies: packstonesand grainstoneswith the mostcontinuousandbestpreservedsequences will be bioclasts,foraminifera,oncolites,lithoclastsand aggre- treatedin thepresentpaper:Corno Grande,Selladei due gate lumps as well as algal bindstonesand dolomitic Corni and Mt. Capole Serresuccessions. breccias(DP3 to DP13 microfacies)mark this environTheCalcareMassiccioreachesa maximumthickness ment.TheGriphoporellacurvataalgalassemblage anda of 600m. It overliestheDolomiaPrincipaleFormationat cyclic organizationare the most usualand strikingele- Corno Grandeand is overlain by the Corniola basinal mentsof this facies. formationattheSelladeidueCorniandMt.CapoLe Serre. Cycles,about2.5 metresthick in average,exhibit a shallowingupwardspattern.Completeperitidalcyclesas 6,1 Microfacies well asdiagenetic cyclesarerecorded;subtidalcyclesare absent(Fig. 10/A).This facies,moreor lessdolomitized, Theanalysisof grains,sedimentary texturesandbiota (Fig.6) aswell asatMt. allowstorecognize occursattheMt. Metasuccession thefollowingmicrofacies eachrecordCapole Serre(Fig.5) andCornoGrande(lowerintervalof inga depositional subenvironment in theCalcareMassiccio theDolomiaPrincipale,Fig. 4). Formation: The depositional environment wascharacterized by a CMI - bioclastic wackestone moderateto intensewater movement.It was strongly CM2 - peloidal packstone influencedby high frequencysealevel fluctuationsand CM3 - bioclastic packstone thusperiodicallyevolvedto high energytidal flatswhere CM4 - oncolitic packstone-grainstone peloidal-bioclasúc sandswereaccumulated andlarertrapped CM5 - aggregategrain packstone-grainstone CM6 oolitic grainstone by cyanobacterial algalmats@ig. l0/A). CM7 - bioclastic grainstone-rudstone The more frequentoccurrenceof diageneticand of CM8 - lithoclastic grainstone-rudstone completeperitidalcycleswithin thisback-margin area,in CM9 - coral framestone comparisonto the lagoonalcycles,can be relatedto its CM10 - birdseyeslimestone highermorphological elevation.Indeed,topographycally CM11 - pisolitic limestone higherareas,like the margin and the back margin,often CMI - bioclasticwackestone. Allochemscan form 30underwenta subaerialexposurein response to a sealevel 40 7oof the whole rock. They are represented by a great fall , comparedto the inner anddeeperlagoonalareas. variety of grains (mainly fossils) amongwhich dasyTheoccurrence of intertidaldepositsoverthesubtidal cladaleans,Cayeuxia-llkethalli, peloids, pelecypods, intervaldependson the rate and amplitudeof sealevel ostracodsand gastropods.The Palaeodasycladusdrop.A slowrateof sea-level fall (or minorsealevelfalls) Thaumatop or eIIa algal assemblageis characteristic.The produceda subaerialexposureonly in marginalareas, microfacies belongsto a subtidalsettingwith only modest whileperitidalcyclesformedin thebackmargin area,and to moderatewaterenergy,presumablyrelatedto an open subtidalconditionsdevelopingcorresponding cyclesper- lagoonenvironment. sistedin the shelfinterior.A fastrateof sealevelfall (or major sealevel drops)resultedin suddenexposures of C}l{z - peloidalpackstone.It is characteizedbythepresmargin and backmarginarea which yield widespread enceof peloidsin a muddymatrix.Thaumatoporellaceans, Thismicrofacies canbepresent. diagenetic cycleswhiletidalflatenvironments withperitidal foraminifersandgastropods is interpreted as in a moderate a shallow subtidal deposit cyclic sedimentation developed overlagoonalareas. energyenvironmentas a shelflagoon,or a back margin tidal flat. 6 CALCAREMASSICCIO CM3 - bioclasticpackstone(Pl. 44/l). Allochemsare The CalcareMassiccioFm. is well represented in the composedof pelecypods,gastropods,dasycladaceans GranSassoarea.It is widely exposedatPizzoCefalone, (Palaeodasycladusspp.),Cayeuxia-likethalli,echinoderms,
Plate Fig. l.
Fig.2.
45
LowerLiassicmicrofacies(CalcareMassiccioFm.; GranSasso,CentralItaly). Dasycladalean rudstone(CM6). Grainsare composedof dasycladacean algae(Tersellagenotin.sp.), gastropods andlithoclasts andaresurrounded by onegeneration of isopachous fibrouscements. Remaining interparticleporosity is filled by late sparcalcite,someintergranularand intragranularporosity is still preserved. CornoGrande;thin sectionFR13.4(= BA591.4).x 6.7 Dasycladalean rudstone(Tersellagenotin.sp.and,Fanesella sokacin.sp.; CM6).Grainsaresurrounded by severalgenerations fibrouscements. of isopachous porosityis filled by latespar Remaininginterparticles calcite,someintergranular porosityis preserved. CornoGrande;thin sectionCG2.3(= BA.598.3).x 6.7
Plate
181
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-.
r82 foraminifersand lithoclasts.Rudite-sizedshells,consist- thin generationof isopachousfibrous cementenvelopes. ing of disarticulatedvalvesof pelecypodsimmersedin a Theremaininginterparticlescavitiesarepaflially filled by muddydetritalmatrix, sometimesoccur.Theselevelsare latesparcalcite(Pl.45| l). 2) thegrainsarelessfrequently interpretedasbasalsedimentsof stormdeposits. in directcontactandareconstantlysurroundedby several ThePalaeodasycladusspp.assemblage andtheTersella generations of isopachous fibrouscements.Theremaining genoti- Fanesellasokaciassemblage arebothwell repre- interparticlevoids are filled by late spar or part of tlte sented,althoughthefirst seemsmorewidespreadthanthe intraparticleand interparticleporosityis preserved. is second.Themicrofaciesis interpretedasa shallowsubtidal The Tersellagenoti - Fanesellasoksciassemblage depositcharacterized by a moderatelyhigh waterenergy. characteristicfor this microfaciesalthoughthe PalaeoAn openlagoonproximalto theshelfedgecanbe inferred dasycladusspp.assemblage is also moderatelyfrequent. The microfaciesbelongsto a shallow subtidalhighas depositionalenvironment. energy setting with active early diagenesis,in a sandy CM4 - oncoliticpackstone-grainstone. Oncoids(@< 2 mm) shoaldepositionalenvironmentnextto theshelfedge.The form up to the607oof therock.Peloidsandshellfragments first textural type mentionedabovedepositedin a more occur.Theinterparticlespaceis filled by apeloidalmuddy protectedposition within the margin, under a moderate matrix or by sparry calcitic cement.The beds with this water circulation; the latter depositedin an energetic microfaciessometimesarelimited downwardsby an ero- foremarginenvironment,characterized by a more active Themicrofacies indicatesashallow sionalboundary. subtidal earlydiagenesis, inducedby a strongerwatermovement. settingwith a moderately highwaterenergy.A migrating Allochems(upto 807o)arewelllagoonchannel,or a tidal bar or even a back-margin CM7 - ooliticgrainstone. with multiplecoatingsandrounded sorted tangential ooids depositis possible. bioclasts(pelecypods andgastropods). (Pl. 43ll). CM5 - aggregategrain packstone-grainstone The depositionalenvironmentis a shallowsubtidal Aggregategrains(@0.5 to 5 mm) cancomposeover60Vo settingwith intensewatermovement,as on tidal barsor of allochems.Peloids,mollusc shells(pelecypodsand ooliteshoals. gastropods), dasycladaleans, solenoporaceans and solitarycoralsarealsorecorded. Thegrainssometimes exhibit CM8 lithoclasticbreccia(Pl. 4412).The elementsare (1 cm to 15 cm) centimeter-size envelopesof fibrous cements.Medium to coarsesized angularto subrounded, packstones-grainstones lithoclasts, consisting of bioclastic scattered dolomiticrhombsoccurseldominsidetheaggreimmersedin a sandymatrix.This gategrains.The Palaeodasycladus spp. assemblage and or oolitic grainstones, lateral microfacies shows andverticaltransitionto CM6, the lersella genoti Fanesellasokaci assemblageare microfacies or CM9 types. CM7 widelyspreadin thismicrofacies, especiallythefirst one. is The consistingof shelf margin sediment a breccia grains Aggregate arereferredto a restrictedlagoonwith in frontof theshelfedge,at orjust (Flùorl, 1982).Thecomposi- material,depositedjust moderate watermovements wave base. above the grains, tionoftheaggregate aswell asthepresence ofhighenergyorganisms(corals,solenoporacean algae),sug- CM9 - coralframestone (Pl. 43/2).ltconsistsof colonial gestsa shallowsubtidalenvironment influencedby mod- coralsin growthposition.They can be encrusted by red eratelyhigh waterenergyconditions(e.g.a back margin algae.The intraparticlespacesare filled by mud or fine lagoon). peloidalbioclasticsand.This microfaciesbelongsto a shallowsubtidalhighenergysettingin frontorjustbehind (Pl.4511-2). CM6-bioclasticgrainstone-rudstone Allochems theplatformmargin. are composedof pelecypods,gastropods,solitarycorals, (P1.4313).It is composed of calcareoussponges,dasycladaceans, limestones solenoporaceans,CMl0 - birdseyes gminstones foraminifers withbirdseyes echinoderms, andlithoclasts. Dasycladaleans oolititicand/orpeloidalpackstone(I' erseI la genoti, F aneseI Ia sokaci andPalaeodasycladus andfenestralfabricsandwith thin algallaminae.Thevoids spp.)sometimesdominate formingupto707oof allochems. areusuallyfilled with sparcalcite.Birdseyestexturesare Thin sectionanalysisshowstwo differenttextures:1) the typicalfor tidalfl ats,althoughwhentheyoccurin gainstones grainsshowfrequentgrain-to-graincontactsandonly one they are supposedto be depositedin a shallow subtidal
P I a t e 46 Figs.1,3.
Liassicdasycladales from CalcareMassiccioFm. (GranSasso,Centralltaly): Tersellagenoti n.sp.
Isotypes.Transversal-obliquesectionsprobablycutbetweenthestalkandtheheadpartofthethallus;no the well definedswollenend of primarybranches. Fig. l: thin section8A.589.6,Fig. 3: thin section 8A.589.5.CornoGrande.x 12 Figs.2,4-5. Isotypes.Transversal-obliquesectionsprobablycutintheheadpartofthethallus;Insectionprimarypore arerepresented widely openedinward.Fig.2: thin section8A.589.4,Fig. 4: thin section assemicircles 84.589.11,Fig. 5: thin section8A.589.6.CornoGrande.x 12
Plate
183
46
-
d.g.*f
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qf .s
tr
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.-tl *f ir,
184 (Shinn,1982).Thepresence environment This assemblage is well represented of algallaminaat theGranSasso, tion hereis diagnosticfor a peritidal setting. whereonlylowerLiassicmembersof ttreCalcareMassiccio occur. CMll - pisolitic limestone(P1.43/4).The presenceof pisoidsandthin cementscrustsusuallysuperimposed on Palaeodasycladus (Pl. 44/2) It exhibits spp.assemblage the preceedingCMI to CMl0 microfaciesis typical. the highestdiversitycontainingPalaeodasycladus mediFenestralfabrics,and/or dissolutioncavitieswith geopetal terraneus@ia),Palaeodasycladusgracili sCnos& Lruonw, texturescanbe present. Palaeodasy cladussp.,Ter sellagenotin.sp.andPeftascula The lithofaciesis the productof a vadosediagenesis ? herakiSoxdc& NKLsn.NodularCcyeuxia-llkethalliare due to subaerialexposure. a commoncomponent.The faunaconsistsof bivalves, gastropods,echinoderms, calcareousspongesandcorals. 6.2 Sedimentarycycles Among the gastropods,nerineidsbelongingto the genus PseudonerineaQl. 44/2) occur.Foraminifersare repreThe verticaldistributionof microfacieswitnesses the sentedby Rectocyclammina sp.(Pl. aaQ). cyclicalorganization of theCalcareMassicciosuccessions This algal assemblage is very frequentin bioclastic (Fig.9).Thecyclesaregenerallycomposed of shallowing grainstones (microfaciestype:CM2,CM6). andpackstones upwardsdiageneticcycles formed of a basal subtidal It thrivedon highenergy,shallowsubtidalsettings,with interval(CMl-9) directlyoverlainby a supratidal interval waterandopencirculationwhich favouredthe high (CMl l). Peritidalcycles,althoughpoorly spread,occur. clear was floral and faunaldiversity.The paleoenvironment They are characterized by an intertidalinterval(CMll) probablythe backmarginarea(Fig.l0/B). that is interposedbetweena lower subtidaland an upper layer.Transgressive supratidal intertidalunitatthebottom PalaeodasycIadus and Thaumatop or eIIa assemblage of the subtidalunit arerare. (Pl.44/l).It is a moderately high diversityalgalassemThe diageneticcycles of the CalcareMassiccioat blage,even if its contentneverexceedsin richnessthe ComoGrandehavebeeninterpretedby Bigozzi(1990)as previousdescribedone.Palaeodasycladus is represented allocyclescontrolledby high-frequencyeustaticvaria- by the speciesP. mediterraneusandP. gracilis. Other (4ù and5ù order). dasyclads(Petrascula? heraki Sox,qc& Nxlrn) may tionswith Milankovitchcharacteristics Basedon thesedimentological dataa similarinterpretation occur,alwayslessfrequent.Molluscshellsandforaminifers couldbe extendedto theC.M. cyclothemicfaciesinvesti- (mainlysiphonatevalvulinids)arerecordedin the faunal gatedin the presentpaper. Thaumatoporellales assemblage. arerepresented by small globularto irregularthalli. Someof them,especiallyirregularones, wereencrusting skeletalgrainsandlithoclasts 5.2.3 Algal assemblages or arefoundinsideskeletalcavities,others,mainlyglobu(Pl. 45llTersellagenoti- Fanesellasokaciassemblage lar forms, were probablyfree rolling on the bottom (De 2). The assemblage is oligotypic.Besidesthe two index Castro,1990b). gracilis Cnos & LnÀaonqs taxa,Palaeodasycladus occurs Thisalgalassemblage ispresent in bioclasticwackestones althoughlessfrequently.In addition,nodularCayeuxia- and packstones (microfaciesCMI). It occursin shallow like thalli and aggregate-grains have beenobserved(Pl. subtidalsettings,in an openlagoonwith opencirculation 43ll). The fauna is represented by bivalve shells.The andmoderatewatermovement. presenceof nerineidsreferableto the genusTrochalia is noteworthy. environment 5.2.4 Depositional Thisalgalassemblage characterizes bioclasticgrainstones (microfacies CM6),whereit canrepresent themostimporpopulatedshallowsubtidal tantfossilgroup.Theassociation areasmarkedby opencirculationconditions, with intense watermovementandstrongearlydiagenesis. It probably flourishedin smallpatchreefsin front or just behindthe shelfedge(Fig.10/B).
Plate
47
Figs. l-2. Fig.3.
Fig.4.
Basedon microfaciesand algalassemblage distributionandtheirrelativefrequency twomainpaleoenvironmental faciescanbe identified: - backmarginfacies. It is characterized by diagenetic cycleswith high-energysubtidalunits (Fig. l0lB). The
Liassicdasycladales from CalcareMassiccioFm. (GranSasso,Centrallfaly): Tersellagenoti n.sp. Isotypes. probablyacrossthestalkpartofthethallus.Fig .l: thin sectionBA.589.4,fig.2: Obliquesections thin section84.589.5.CornoGrande.x 12 Holotype.Longitudinal-oblique sectioncuttingthe stalk and the headpart of the thallus;the section crosses,althougha little peripherally,the apicalzone(top of figure).Thin sectionBA.589.11.Corno Grande.x 12 Isotype.Longitudinal-oblique sectionintersecting theheadpartof thethallusaswell astheapex(seealso Pl. 50/1).Thin sectionBA.591.4(= FRl3). CornoGrande. x 12
Plate
185
47
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*.
', * , .fJ erl
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186 microfaciesconsist of packstonesand grainstoneswith formedof oolitic and bioclasticsandshoals,with some oncolites,bioclasts,aggregate lumps(microfacies CM3- scarcecontributionof reef building organisms,such as 5) and of pisolitic limestones(CMll). Less frequently corals, spongesand solenoporacean algaeTheseorganpeloidalpackstones, (CM1-2)and ismsformedsmallpatch-reefs bioclasticwackestones behindorjust in frontof the (CMl0) occur. birdseyeslimestones platformmarginwherethey founda morefirm and stable The Palaeodasycladus spp. and Petrascula? heraki substrate.Formationof a continuousbarrier reef can be algalassemblage dominatebut,Tersellagenoti- F anesella excluded. sokaci algal assemblagecan also be present,while the Sealevel changesstronglycontrolledthedepositional PalaeodasycladusandThaumatop oreIIaalgalassemblage environment, assuggested by thenumerousevidences of is rare. subaerial exposure. However,theabsence ofa pronounced Cycles have an averagethicknessof 2.5 m and a cyclical stackingpatterncan be due to the erosionof the shallowingupwardscharacter.Peritidalcyclesas well as shelfedgeeitherduringlow stand,or earlytransgressive deepeningupwardcyclesarealmostcompletelyabsent. phases,which could havereducedthe preservation of a This faciesoccursin the lower portionof the C. M. at goodeustaticsignal. Como Grandeand the lower portionof the C.M. at Mt. Accordingto thedistributionof shelf,marginandslope CapoLe Serre(Figs.4-5). faciesin theGranSassoduringtheLateTriassic- middle Thepaleoenvironmental datasuggestthattheareawas Liassicit ispossibleto supplya tentative palaeogeographic subjectto intensewatermovementandconditionsof open mapof thearea(Fig.l l). In theearlyLiassic,themarginal circulation,confirmedby the high-diverse biota.It was faciesbecomesmorewidespreadand migrateswestward mostlikely intersected by migratingtidalchannelswhere in respectto the Late Triassicscenery.In the middle oncolitic packstoneswere deposited.Locally protected Liassicmostpartof the studiedareawasdrowned. areas,probablyrepresentingtransitionalenvironments betweenbackmarginand the lagoon,were populatedby 6 STRATIGRAPHICALDISTRIBUTIONOF thePalaeodasy porella algalassemcladus andThaumato ALGAE peloidal blageandarecharacterized by bioclasticwackstonespackstones (CMl-2 microfacies). The depositional enviGyroporella vesiculiftra has been observedin the ronmentwasstronglyinfluencedby sea-level oscillations (Fig.7).In thisseriesonlyAtlotortussp. Ofena succession whichcausedtheperiodicexposure of thebackmarginand is present,the age can be genericallyassignedto the the formationof diageneticcycles(Bosellrm & H.lnorr, Norian-Rhaetian, thatis alsothe stratigraphical distribule85). tion recognized for Gyroporella vesiculifera,if adoubtful - shelfedgefacies.Thefaciesshowsa lesspronounced Lower Jurassicrecord(Cros & Leuolue,1966)is necyclicitywittrrespect, úothebackmargin faciesbutdiagenetic glected. cyclescanbestill present(Fig. lO/B).Themicrofacies are Griphoporellacurvatahasbeenfoundin theDolomia characterized by grainstones and rudstoneswith oolites, Principaleof Mt. Meta(Fig.6), Mt. Capole Serre(Fig.5), bioclastsand lithoclasts,by coral framestones (CM6-9 as well as,but dolomitized,in the DolomiaPrincipaleof microfacies)andby pisoliticlimestone(CMl l). CornoGrande(Fig. 4). In this lastsuccession the algais The Tersella genoti - Fanesellasokaci andPalaeo- accompanied byAulotortusfr iedli,bothof themoccurring dasycladus spp.algalassemblages dominatebutPalaeo- duringthewholeformation.In the Mt. Capole Serrethe dasycladusand Thaumathoporellaalgal assemblage can algaoccursin all theDolomiaPrincipale; it is associated occasionally be found. at the basewith Aulotortusfriedli, while in the middleThe presentfaciesoutcropsat CornoGrande(upper upperpafi it. occurstogheterwith Triasina hantkeni.At termsof the CalcareMassiccioFm., Fig. 4), at the basal Mt. MetaGriphoporellacurvatais presentthroughout the partof Selladei dueCorni succession (Fig.8) andat Mt. DolomiaPrincipale, alwaysw ith I. hantke ni andA.fr iedli. Capole Serre(upperpartof C.M. Fm.,Fig. 5). TheNorian-Rhaetian in literature. ageis generallyaccepted Thedepositional environment wassubjectto anintense Although the CalcareMassiccio(about600-700m watermovementandanearlydiagenesis. Themarginwas complexivelythick)is foundin severalprofiles(Mt. Meta,
Plate 48 Figs.l-3.
Fig.4. Fig. 5.
Liassicdasycladales from CalcareMassiccioFm. (GranSasso,Centralltaly): Tersellagenoti n.sp. Isotypes.Transversal-oblique sections primaryand cuttingthestalkpartof thethallus.Notetheelongated thesmallsecondary Fig. l: thin section8A.597.2,Fig.2:thin section8A.591.5(= FRl3); Fig. branches. 3: thin section8A.598.6.CornoGrande.x 12 Isotype.Longitudinal-oblique sectionfrom a "poorlydifferentiated" thallus.Thin sectionBA.589.a.4(= CG3).CornoGrande.x 12 Isotype.Longitudinal-oblique sectioncuttingthestalkandtheheadpartof thethallusaswell astheapex. Thin section8A.591.3(= FRl3). CornoGrande. x 12
Plate
r87
48
fud'
t
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188 EarlyLiassic
L-ateTriassic
shelf
MiddleLiassic
margin
-l
%ffi
m
slope
Fig I l. Schematic sketch of facies distribution in the Gran Sassoareaduring the Late Triassic (A), early Liassic (B) and middle Liassic (C). In the early Liassic, the marginal facies becomes more widespread and migrates westward with respect to the Late Triassic scenery. In the middle Liassic most pzìrt of the studied area is drowned.
Fig.6; MtCapole Serre,Fig.5; SelladeidueCorni,Fig .8) Griphoporella curvata. The upper boundary can only be the only one rich in dasycladsand exibitingthe contact dated because of the overlying Corniola Fm, which conwith theunderlyingformationis theCornoGrandesucces- tains Carixian nannofossils and Domerian ammonites (Prof. (PalaeodasycladusVenturi,pers.comm.).A Sinemurian sion(Fig.4). Herethe first dasyclads ageof thetop of the gracilis and Tersellagenoti n.sp)appearabout 100 m CalcareMassicciomaybe assumed because of theoccurabovethe DolomiaPrincipale/Calcare Massicciobound- renceofcharacteristic of Liassicalgaeandby theabsence ary,whilePalaeodasycladus mediterraneusappears 150m typicalmiddleLiassicforaminifera. higher.Fanesellasokacin.sp.is foundin the last 100m, In the carbonaticsequences of the Central-Southern i.e. 500 m abovethe boundary.This algaoccursalsoat ApenninesPalaeodasycladusmediterraneusappears150(Fig.8) whereitreachesthe 300m overthe lastbedscontainingAulotortus SelladeidueCornisuccession sinuosus, top of theCalcareMassiccioFm. markedby an emersion Griphoporella curvataandTriasinahantkeni(DuCnsrno, surfaceandoverlainby theCorniolaFm..Theglobalrange l99l; Curoccunrefal. 1995),almostatthesametimeasP. of the Calcare Massiccio Fm. covers the Hettangian- gracilis (sub?Teutloporellaelongatula:Cutoccslrul et al. Sinemurianinterval.The lower limit conespondsto the 1995).Accordingto De Crsrno (1987,1991)theageof disappearance of Aulotortusfriedli,Triasinahantkeniand appearance is Hettangianp.p.- lowermost,Sinemurian;
Plate Figs.l-2 Fig.3. Fig.4.
49
Liassicdasycladales from CalcareMassiccioFm. (GranSasso,Central[taly): Tersellagenoti n.sp. Isotypes.Longitudinalsections. Fig.l: thinsection8A.597.1,fig.2:thinsectionB\.597 .3(= FCI). Corno Grande.x 12 Isotype.Detailof a longitudinal-oblique poresin sectionthatshowstheshapeof primaryandsecondary (= theheadpartof thecalcareous Thin BA.597.5 x20.9 skeleton. section FCI). CornoGrande. Isotype.Detailof a transversal poresin the head sectionthatshowsthe shapeofprimary andsecondary partof thecalcareous (= skeleton.Thin sectionBA.597.5 FCI). CornoGrande.x20.9
189
49
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190 accordingto CrnoccHnvr et al. (1995)it is a little older (upperSimemurian).If we agreewith De Castrothe lower portionof theCalcareMassicciobeforetheappearance of gracilis has to be ascribedtotally or Palaeodasycladus partly to the Hettangian. The stratigraphicaldistributionof the new algal taxa (TersellagenotiandF anesellasokaci)canbeinferredwith reasonableconfidenceonly from their first appearance becausethe top of the formation is cu[ by an emersion surfaceandcoveredby deep-water sediments. According to thestratigîaphicaldalaTersellagenotin.sp.exhibitsan Hettangianp.p.- Sinemurianinterval,while Fanesella sokacin.sp.seemsto be limited to the Sinemurian.
sisbut proposea description(p.2a\ sressingthedifferentiationof calcareousskeletoninto a lower stalkedpart andan upperhead.This characteris evidentonly in some in the specimens ofT. alpinabut absent(neverobserved) (7. hypothetically typespecies incompletc),whereit was assumedby Cnos& LrMoNe (1967). CuslvNEs& DnlorTnr (1984)establisheda new species,Tersellaquercyensis,from the Toarcianof France (CentralMassif).TheauthorsemendedthegenusTersella givingthefollowingdiagnosis:" Le manchoncalcairese qui présentecommeunetige cylindriquebiendéveloppée s'élargitpour donnerun renflementen massue.Celle-ci estouverteò sonsommetpour permettrele passagede la continuationde la tige et la formation d'une nouvelle massuesuperposée. Les pores dans l'epaisseurdu test 8 PALEONTOLOGY de ramifiindiquentl'existencede deuxordressuccessifs cations." (The calcareousskeletondisplaysa well developed Themostabundantfossilremainsfoundin thestudied areabelongto greenalgae(dasycladales) andto molluscs cylindricalstemthat flaresgiving rise to a club-shaped (bivalvesandgastropods). As a second,but occasionally swelling.Thislatteris openat thetopin orderto allowthe abundant,important part of the fossil assemblage, stemto passandmakea new superimposed club-shaped foraminifers,cyanobacteria andthaumatoporellaleans skeletonshowthe oc- unit. The poresinsidethe calcareous cur.Echinoderms, calcareous sponges andcoralsarerare. presence of two ordersof branches.) The followingdasyclads areof specialinterest. V/hichtaxonomical weightshouldbe attributedto the skeletonoîTersellais upper"opening"of thecalcareous matter If interpretedas the largely a interpretation. of 8.1Genuslersel/a Monnllnrin Monnllnr & Tnns1"951 passage of the centralstem,as in moniliformthalli (e.g. ThegenusTersellawasestablishedby JeanMoneI-I-er Cymopolia),then its taxonomicalvalue must be high in l95l (Monrner & Trns, 1951)in a study on some (genericlevel). This was first discussedby Monrnrr dasycladtaxafrom theHettangianof Vendée@rance).He (1951:p. e7).However he himselfthoughtit to be supplieda comprehensive diagnosisfor thegenusandits unfikelybecause thearticlesof Cymopolianevershowa (Tersellaincompleta).In MornLLrr'sopinion well-roundedtop and a taperedbottom as in Tersella type-species thealgais characterized by a club-shaped, thincalcareous incompleta(actuallyclavatearticleswere pointedout skeleton, openat bothends.Thelowestorderbranches are later: e.g. CymopoliainflataramosaSecoxzac).Afterarranged in whorlsbutarecalcifiedonlyat.theirdistalend. wardsthe"moniliformhypotesis" wasespousedbyCun.lnms Eachbranchramifiesintophloiophorous branches of next & Dslorrnr (1984),which they foundedtheir generic higherorder that show a subterminalnarrowingbefore emendation on. flaringout to form a sortof networkof polygonalmeshes On theotherhandif we explaintheupper"opening"as at theirdistalend(mostlikely a cortex). a lack of calcificationthenits taxonomicalvaluemustbe In 1967Cnos& Lruowsestablished thespeciesTersella verylow (belowthespecificlevel).In factin severalextant alpina from the Liassic of NorthernItaly (Dolomites, genera(e.g.Bornetella,Neomeris,Cymopolia)the apex, AsiagoPlateau).Theyagreewith theMonrLLrr'sdiagno- whenit still holdshair-likebranches. is uncalcified.
Plate Fig. l.
Fig.2.
Fig. 3-4.
50
Liassicdasycladales from CalcareMassiccioFm. (GranSasso,Cehtral[taly):Tersellagenoti n.sp. Isotype.Derailof Pl. 4714showingtheapicalzone.Notethereductionin sizeof thesecondary branches againstthethickeningof calcificationandelongation of primarypores.Calcificationstopsjust beforethe apex.Thin section84.591.7.CornoGrande;x 20.9 Isotype.Detailofa longitudinalsectionbetweenthestalkandheadpartofthe calcareous skeletonin order pores.Notice how the calcareous to show the changein shapeand/orsizeof primaryand secondary skeletonbecomesthinnerandthinnerupwards.Thin section8A.591.2(= FRl3). CornoGrande.x209 Isotypes.Obliquesectionsin highermagnificationshowingtheelongated primarybranchesin the stalk part of the thallus.Fig.4:theinnersurfaceof thecalcareous skeletonis regularandsmoothdownwards (probablybecauseit touchedthe centralstem)but irregularupwards(mostlikely becauseit departsfrom thecentralstem).Thin sections8A.597.6andBA.597.8(= FCI) respectively. CornoGrande.x 20.9
Plate
t97
50
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t92 Actually,for the time being,no clearevidenceexists not differ significantly from each other and that they that the type-species, and by reflex the genus,showsa representdifferent sectionsof a single, slightly clubmoniliformthallus. shaped,terselliformspecies. Cnos& Lruorxe (1967)consideredthe presenceof a Few yearsago Drlorrre & Lalott.a (1990)attributed stalkedskeletonas a genericcharacterin Tersella.This to Palaeodasycladus mediterraneusPl,q,somealgaefrom characterseemsto be too much restrictive,especially theLotharingianof Morocco.AccordingtoBaraifoloet al. whensucha shapecan notbediscerned in thetype-species. (1994)this taxonbelongsto anotherspecies.Actually the On theotherhandextantgenerashowa widevariabilityon Moroccospecieslooksvery similarto îersella genoti n.sp. this regard.The genusBornetella,for example,includes Only a somewhatbiggersizeof the calcareous skeleton both club-shapedand sphericalspecies. and the smallersizeof theprimarybranchesdo not allow For thesereasonsit is, at the moment,betterto stick to a clearattributionto the new species. MoneLLsr'soriginal diagnosis. Moretaxonomicuncertaintycanarisefor thosespecies that showsquat,fingerJike,cylindricalto slightlyclubDiscussion on other comparable taxa. According to shapedthalli exhibitingtwo orderof branchesanda distal MoRrLLrr'sdiagnosisthecharactersof TersellaÍìrerather cacificationof primarybranches (e.g.Dissocladellacretica closeto Dissocladellaha in Reo & Prn1936.Also if the Orr andLinoporella/zccsiCnos& Lruolur). differencesbetweenthe genera not indicatedby Dissocladellacreticawasestablished by Ott in 1965 "vereof the thallusand Morellettheyare fundedon the shape for somedasyclads comingfromtheLiassicof Crete(Kom primarypores.The thallusis club-shaped, often differen- & Orr, 1977).I hadtheopportunityto seethetypematerial tiatedin a stalkandan ovoidheadinTersella,cylindrical duringthe Alpine Algae meeting(September 1993);alto slightlyclub-shaped in Dissocladella. thoughthe stateof preservationis ratherpoor mostof the Primary branchesare largely unknown in Tersella datasuppliedby Orr (1965)canbe confirmed.The alga because uncalcifiedfor themostextent,excepttheirdistal showsa slightlyclub-shaped calcareous skeleton,tapered end.TheyareshortandswollenoutwardsinDissocladella, and openat both ends.The centralcavity is wide and the (Dissocladellasavitriae shortswollenprimaryporesdo not show,in their axial almostsphericalin thetype-species Pn in Rao & Pta 1936). section,anyinnernarrowingreferableto a junctionpoint, Thetype-species of thetwo generaarenotwell knoùn. Thereforethe primary porescorrespondto the calcifed A re-studyon a richer materialis necessaryto judge the terminalpart.ofprimarybranchesasin Tersellaincompleta validityof thegenusTersellain respectto Dissocladella. andT.genotin.sp.Forthisreasonweproposeherethenew Althougha simplevariationin thedegreeof calcification combinationTersellacretica(On). can not be usedto differentiatethe genera,at the present (1967) showsa Linoporella /zcasl Cros & Ler\aorNE stateof knowledgeit seemsbefterto keepseparate thetwo cylindricalcalcareous skeletonclearlytaperedat thebotgenera.This fact will permitto give a genericstatusto a l.omwherecalcificationbecomesstronger(Cnos& Lrwell definedgroup of species,sharinga more or less rraorNp,l967: pl. I fig. 5). Theprimarybranches arecalcidifferentiated club-shaped thallus. fied only at theirdisralendandaremoderatelythick.As In thepaleoalgological literaturesomeLiassicspecies, affirmedby theauthors,somesectionslook like thoseof currentlyascribedto other genera,can be tentatively T'ersella alpinawhichoccursin thesameassemblage. The placedin the genusTersella. shapeof the thallusand the characters of the branches Dn.ccA.sraN & Tnappr(1986)describedtwo new spe- hardlypermita positionin thegenusLinoporella(seefor cies(Dissoc/adella iberica andD. ebroensls)fromaLiassic exampleBenarrolo, 1991b).This is why someauthors sequence of IberianChain(Spain)associated with some questioned theattibutiontoLinoporella(Bnssoulare/ c/., (Cxos& otherspecimens indicatedasDissocladellalucasi 1978) and othersproposeda transferinto the genus Lruonr), Sestrosphaera liasinahA.andGyr oporellar etica Dissocladella (DRrcasraN 1986).Thepossibil& Tnappe, (Zrr.nxBunr).The photographs andthe descriptions sup- ity that this taxoncould representa Tersellacannotbe pliedby theauthorsgivetheimpression thatall thetaxado excluded.
Plate
5l
Liassicdasycladales fromCalcareMassiccioFm.(GranSasso, CentralItaly):Fanesellasokaci n.sp.
F i g s .l - 4 , 6 . Isotypes.Transversal-oblique sections.Figs.2-4 showa calcificationthat reachesthe centralstem.In
Fig.5.
Figs.l,4 calcificationcoverspartof theprimarybranches upto quaternaries. Fig. l: thinsection8A.589.9, Fig.2: thin sectionBA.589.8,Fig. 3: thin sectionBA.589.6,Fig.4: thin section8A,589.8,Fig. 6: thin sectionB4.589.3.CornoGrande.x l5 Isotype.Obliquesection.Noticethenarrowcentralstemandits weakcalcification.Thin sectionBA.589.4. CornoGrande.x 15
Plate
193
- 5I
"
ffi' 't*
o
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À.
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194 Fí9. 1,2. Geographic setting of the typelocality of Tersella genotin.sp. urd F anesella sokaci n.sp. The ubication of the sample BA.589 is indicated by an Íurow.
8.1.1 Tersellagenotin.sp.(Pls.45-50) Origin of the name. The species is dedicated to the colleague Patrick Genot, Department of Earth Sciences, University of Nantes, forhis contributions to knowledge of fossil algae. Holotype. Specimens in longitudinal section figured in
Pl. 4713.Thin section8A.589.1l. Isotypes.Secimens of the sampleBA.589(= CG2 of the Bigozzisampling): BA.589.1- BA.589.11. thinsections Othermaterialis represented by the samplesBA.589.a (=CG3),BA.59l (= pR.13), BA.597(=FCl) andBA.598 (FC3). Type-locality.Northern slope of Corno Grande (Gran Sasso,Centralltaly), at about 2700 metresof altitude fig.12). Type-level.Thick beddedwhitebioclasticpackstones (see microfaciesCM3). Plate
52
F i g s .1 , 3 . Fig.2.
Fig.4.
Depository.Thematerialis depositedat theDepartmentof Palaeontology, Universityof NaplesFedericoII @arattolo collection). Diagnosis.Club-shapedsimple thallus with a moderate differentiationinto a subcylindricallower paÌt (the stalk) andan enlargedellipsoidalupperhead.Primarybranches anangedin closeverticilsandaltematingin thefollowing ones.Theyaresetalmostperpendicularly to themainaxis. However,movingto thetopof thethallus,primarybranches bendmoreandmoreupwardssothattheyaresetvertically neartheapex.Primarybranchesof thestalkaremoderately long andwidenedoutwards,with a circularcrosssection. Only disralendsof primarybranchescalcify in theheadof thethallus,resultingin globularprimarypores.Secondary pertuft,roughlykeepthesameinclinationas branches,4-5 the primaries.In their calcified paÍ they are short and slightly widenedoutwards.They probablywerephloio-
Liassicdasycladales from CalcareMassiccioFm. (GranSasso,CentralIfaly): Fanesellasokaci n.sp. Isotypes.Oblique sectionsshowinga calcificationmainly restrictedto secondary-quaternary branches. Fig. l: thin sectionBA.589.10, Fig. 3: thin section8A.589.10.CornoGrande.x 15 Holotype.Longitudinal-oblique section.Noticethestrongprimarybranchesandthefact thatcalcification becomesweakerupwardsenvelopingonly thebranchesof higherorder.Thin section8A.589.7.Corno Grande.x 15 Isotype.Tangential-oblique sectionshowingsecondary branches,tufts of three-fourtertiarybranchesand a peripheralzone with crowdedporesmost likely conespondingto quaternarybranches.Thin section 84.589.3.CornoGrande.x l5
Plate
195
52
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196 SDec. Thin s€ction
1A589.8 2 14.589.8 J 14589.8 14589.8
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0.57 0,39
0.37
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0.+5
0.20,
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0.30| 0,27 0.I7t 0.22 0,27 0.20,
0.32 0.62 0.21 0.3.1
0.25 0-16
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0.52 2(. 0.1 2El n ?t o.17 0.+t 0..14 0.6! vH 0.42 0.44 0.25 5.6 0.5( o.2 0.3t 0,4{ 0,34 25 6 0.62 u.l u-J o,37 0,2( u-ta. 0.60 ;+H )-J 4, o 3.t o) 0.22 0..r.f 0.62 0.64 3 0,t0 0,1 0,20 0,1 I5 0,36 I, 4,94 0.35 0,10 0,30 0.61 0,19 0,ó6 3I 0,81 7.8 0.89 0,2s 6. 42 4I 4t 30 tó 4. 42 1 I 5,068ó5 3,93670 0,56597 0.t7J71 0.36510 0.31230 23.06667 0 . 5 3 t 8 2| 0 . 2 1 ó 4 20.31687 L5911I L 5 7 5 0 J 0.09557 0.01I8 I 0.06309 0.I 3083 4,093I 7 0.12859 0,0J619| 0,09858 7 5.
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o.37
Table I . Main biometric parameters of Tersella genoti n.sp. For each specimen is supplied the thin section number, the part of the thallus sectioned (S: stalk; H: head, S/H: intermediate part between S and H; S+H: section of both parts, measurementsrefer to H) and the dimensional values., Therurge(min. andmax.), the number of measurements,the averageandthe standarddeviation foreach parameter are given at the bottom of the table. All size parameters are in millimeters. D: outer diameter of the calcareous skeleton; d: inner diameter of the calcareous skeleton; pd: inner width of primary branches;pd: distal width of primary branches; /: Ienght of primary branches; w: number of primary branchesper whorl; ft: height between whorls; p': width of secondary branches; /': lenght of secondary branches.
phorousand constituteda distal cortex.No reproductive ary branches,while it is thinneraroundthe head,whereit organshavebeenobserved,they wereplacedmostprob- envelopesthe distalendsof theprimarybranchesandthe ablyinthemainstemorintheprimarybranches(endosporatesecondary branches. type or cladosporate-type). The most significantbiometric values,takenfrom a The calcareousskeletonis thicker along the stalk, singlesample(BA.589),are suppliedin Tab. 1. whereit envelopes almostentirelytheprimaryandsecondP I a t e 53 Fig. l. Fig.2. Fig. 3.
Liassicdasycladales fromCalcareMassiccioFm. (GranSasso, Centralltaly):Fanesellasokaci n.sp. Isotype.longitudinal-oblique. Thin sectionBA.589.9.ComoGrande.x l5 Holotype.Detail of Pl. 5212.Primary,secondaryand tertiary branchesare clearly visible. Thin section 84.589.7.CornoGrande.x 48 Isotype.Detail of Pl. 5 l/l . Notice the weaklycalcifiedprimary andsecondarybranchesand the tertiary branches. Very peripherallyquaternarybranchescan be distinguished. Thin sectionBA.589.9.Corno Grande.x 48
Plate
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Generalfeaturesofthe calcareousskeleton.The calcareousskeletonis simple,continuousandwithoutanytraceof annulationor intusannulation.It exhibitsa moderatedifferentiationinto a subcylindricallowerpart(thestalk)and an enlargedellipsoidalupperpart (the head).The head, when differentiated,representsin lenght 70-807oof the wholecalcareousskeleton.The shapeof the headis ellipsoidal to ovoidal, rather elongated- the outer diameter being0.5-0.7timesthelenght- with themoretaperedend directeddownward.In the headthe calcificationis rather thin andenvelopsthe distal endof primaryporesand the poresup to theirdistalswelling.Nearthetopits secondary thicknessincreases envelopingthinnerprimaryporesfora longer extent (Pl. 50/l). At the apex the calcification leavinga cavityof I .5-I .8 mmin diameter.The disappears It stalkis rathershort,cylindricalto slightly cone-shaped. usually showsa calcification thicker than in the head, envelopingtheprimarypores(thinnerthanin thehead)for a longerextentand the secondaryporesup to their distal swelling.Transversalandobliquesections,probablycutting thestalkportion,oftenexhibit a regularinnersurface (Pl. 50/4middle-lowerpart). This fact indicatesthat the calcareous skeletonwasherevery closethecentralstemor touchedit. Rarelythetwoparts(headandstalk)areundifferentiated or not well differentiated(Pl. aUù. ln this case the calcareousskeletonlooks like an elongatedclub and the calcificationshowsalmost the samethicknessfrom the lower to the upperpart of the thallus. The calcareousskeletonwas probably aragonitic,it in calciteor dolomitized. appea$alwaysrecrystallized The inner diameteris 0.9-3.7mm in the stalk portion (ds) and 3.7-6.7mm in the headportion(dh); the outer diameteris1.7-5.Lmmin thesúalkportion(Ds)and4.9-7.8 mm in the headpofion (Dh).
I
rrrr
attaaoot.tI
J .t.
f
ttl
7 Fig. 13. Tersella genotin.sp. Outer diameter of the calcareous skeleton (D, below), number of pores per whorl (w, centre) and distal width of primary pores (po, ap) against the irurer diameter of the calcareous skeleton (d). Specimens in thin section belonging to the stalk partofthe calcareousskeleton (.), the head (r) and the intermediate part between the stalk and head (o) are specified.
Plate
54
Pr imaryp ores.Theprimaryporesareroughlyperpendicular to themainaxisalongthegreatestextentof thethallus; but, in the uppermostpart of it, their inclinationdecreases until theystandverticallyneart}
[email protected]/l). The primary pores are arrangedin simple whorls (euspondyle whorls type;Pl. 48/1,5; Pl. 47 13).Subsequent positionevenifnot exhibitbranches anangedin alternate properlyregulareL 47/3).
Liassicdasycladales from CalcareMassiccioFm. (GranSasso,CentralItaly)
gracilisCnos& Lsr"rorr.rs. Figs.1-2,4-5.Palaeodasycladus (Fig.l; Fig.5,specimen Obliquesections. Smallspecimens at the top) exhibit a strongercalcificationprobablyreachingthecentralstemandthreeorderofbranches. Medium to big sizedspecimens (figs. 2, 4-5) show a wider centralcavity, their calcareous skeleton represents thecalcificationaroundthesecondary andtertiarybranchesor aroundtheselastonesonly. Thin sections: 8A.598.5,BA.598.4,8A.598.7,8A.598.3respectively. ComoGrande.x 30 Fig. 3. Palaeodasycladus sp.Obliquesection.Thin sectionBA.598.2.CornoGrande.x 15 Figs.6-7. Petrascula? herakiSorac & NKr-sn.Obliquesections. Thin sections:BA.598.7andBA.598.4respectively. CornoGrande.x 15
Plate
r99
,54
-w
'ij'{ l.o. ld
r 'fÉ' .,
t.*
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200 outer part that in turn usually exhibits a well-defined globularshape.It is rarelyobservedthattheveryproximal part is joined to the central stem (Pl. 50/4). The cross sectionof the poresis circular,its size0. 1-0.25mm (p-) and0.20-0.34mm (pa")in theinneranddistalpartrespectively. The lenghtof the primary poresin the stalk (ls) is 0.27-0.51mm. The primary poresin the headare nearlyglobular.In thin section they appearsometimesas moderatelybig circlesor semicircles
[email protected]/l-2,4), sometimesas largearcs(Pl. 4615).This canbe explained asdueto a calcificationrestrictedto thedistalglobularpart of primarybranches.The diameteris 034-049mm (pat). In the uppermostpart of the calcareousskeletonprimary pores are club-shaped,decreasein size and are calcified for a greatextent;practicallythey look like the onesof thelower partof thethallus.Thisindicatesthatthe primary branchesof the head were phloiophorousand club-shaped(for a fartherreachingdiscussionseereconstruction,Fig. 14). pores.Secondary poresarecylindricalor slightly Secondary widenedoutwards.In rare placesthey are seenclosely packedat tho outer surfaceof the calcareousskeleton (Pl. 47/4). This observationallowstheassumptionthatthe secondarybranchesflared in their distal part, usually uncalcified,and formed a cortex. The secondarypores originatefrom thedistalpart of primarybranches,3-5 per tuft. Theyincreasein sizefrom the stalkto theheadof the thallus.In the stalkthey are0.08-0.2lmmwide (p'")and 0.06-0.42mm long (/'") while in the headtheyare0.170.29mm wide (p'o)and0.25-0.58mm long (/'r). Reproductive organs.No reproductive organshavebeen in thecalcareous observed skeleton.Howevertheprimary branchesarenotparticularlystrongto infer a reproductive function.The greatestpart of theprimarybranchesof the head (usually the main fertile part of the thallus) was uncalcified,we thereforehave few argumentsto judge where the reproductiveorgansof Tersella genoti n.sp. were situated.A reproductionof endosporate-type or cladosporate-type seemsto be possible. Reconstuction(Figs.14, 15). Theuppermostpartof theheadandthestalkoftenshow Fig 14. Tersella genoti n.sp. Reconstruction of the thallus in a calcification touchingor very closeto the centralstem. longitudinal vi ew.Left side: primary branches,secondarybranches Therefore for these two regionsof the thalluswe cantake and calcification (black) in axial section. Right side: longinudinal view of the branches without calcification and the central stem the inner diameterof the calcareousskeletonas a good showing the junctions of primary branches; in the middle part a proxyfor thediameterof theaxialstem.It comesout that perspectiveview of the branchesand the cortex is drawn. (x 12.7) partof theheadthediameterof theaxial in theuppermost stemis equalor a little wider thanin the stalk. The stalk portionexhibitsa slightlyclub shapedcentralstem. In our Theheightbetweenwhorls(h) is abour0.36-0.81mm. reconstructionwe supposethatthecentralstemkeepsthis Thenumberof poresin a whorl(w) is aboutl4-31,butthis shapefrom the baseto the apexof the thallus.Our interparameterseemsto increaseslightly upwards,i.e.from the pretationis consistentwith what said abovefor the stem stalk to the apex. diameterin theuppermostpartof theheadandis basedon Theprimaryporesin thestalkarephloiophorous thatprimarybranches longerand becomes and theassumption (Pl. 49ll: Pl. 5013-4).They often show an longerin the headbeforegettingshorteragaintowardthe club-shaped inner portion,subcylindricalin shape,that is about0.6- apex. 0.75 timesthe total lenght.This part is thinnerthanthe Someevidenceindicatesthattheprimarybranches of
201
A
B
Srlrltt ;'ì
;"
r
.{
1 {
J
C
C Fig 15.Tersella genoti n.sp. Reconstruction in transversal v iew of the stalked p art (below) and the head (up) of the thallus. A: transversal section at whorl level showing the calcareous skeleton.(x L2.7) B: transversal section at whorl level showing primary and secondarybranches and the calcification(blac&). C: central stem and branchesin transversalview. (x 12.7)
the headhada shapesimilar to thoseof thestalk.Primary pores,if axially cut,arealwaysbroadlyopenedinwardand nowhere(except in the stalk) a structurereliable to a junctionpointhasbeenobserved. placed Primarybranches at bothendsofthe calcareous skeleton,stalkandtop,are very similar.The thicknessof calcificationclearlyand quickly decreases betweenstalk and head.Here the primaryporesbecomeshorterandshorter.The innersurface of thecalcareousskeletonheregraduallydepartsfrom the centralstem leaving the akrophorouspart of the branch uncalcified.The branches nevershowan appreciable increasein size that could be correlatedto a specialization (e.g. reproductive;Pl. 50/2). Accordinglyrhe primary branches havebeen drawnwith equalshapebutincreasing in size upwards.They reducetheir size and inclination againwhenapproachingthe top.
Accordingto theshapeandinclinationof thebranches closeto the top of the calcareousskeleton,and basedon whatobserved in club-shaped dasyclads withphloiophorous branches(e.9.Neomeris)the apicalzoneis consideredto be constructedby branchesclosedtogetherto form a sort of bud. It may be inferredthat the bottom of the thallus wasarathershortbranchlessstalk-likepart of the siphon. Comparisons. Tersellagenotidiffers from the type species,Tersella incompletaMonrlr-r-r (Hettangian),in the presenceof a moderatelylongstalkregion,in theshapeof thesecondary pores(cylindricalor slightly widenedoutwardsversus porescharacterized by a subterminalnarrowingjustbefore thecorticalswelling)andfor a smallernumberof poresin a whorl(14-31versus30-40). The new speciesdiffers from Tersellaalpina Cnos& Lsl,rontE(Liassic) andTersella quercyensisCusrvr.{Es & Delonrne(Toarcian)in a less"differentiated" clubshaped skeleton;in additionthestalkportionis far lesselongated. MoreoverTersellagenoti ismuchsmallerthanT.quercyensis (4.9-7.8mm versus10-24mm). Tersellagenoti dfffers from T'ersellaalpina also in the larger size of primary pores(0.34-0.49 mm versus0.25mm),andin theshapeof pores(cylindricalor slightlywidenedoutwards secondary insteadof swollen at the base and then regularly phloiophorous). Thenewspecies differsîromTersella/uccsi(Cnos& Lruorxe) (Liassic)in the shapeof the skeleton(clubshapedmoderatelystalkedversuscylindrical)and in a generallylargercalcareous skeleton(4.9-7.8mm versus 2.4-3.1mm} T. genoti differs from Tersella cretica (Orr) (lower Liassic)for the shapeof the calcareous skeleton(clubshapedmoderatelystalkedversuscylindrical to clubshaped).Moreoverin T. cretica the calcificationnever reaches thestemwall, andprimaryporesareglobularand do not show a club shape.The primary and secondary poresare, in average,smallerthan in T. genoti (0.220.42mm versus0.34-0.49 mm). T.genotidiffersfromDissocladellaibericaDnacrstnN & Tnrppr (and assembledallied forms; Liassic) for a generalbiggersizeof thebiometricalparameters. 7.2 GenusFanesellaCnos& Lrrvrorxn1966 ex Gnaxrnn& Delonnnn1993 The genusFanesella,and its type-species Fanesella dolomitica,wereestablished by Cnos& Lruolue in 1966 whenstudyingan algal-richmaterialfrom the Liassicof NorthemItaly (Dolomitesand AsiagoPlateau).According to the two authorsthe genus is characterizedby a Primarybranches cylindricalcalcareous skeleton. areswollen and laterally compressed,arrangedin whorls. They are specializedfor reproduction(cladosporate-type). Each primarybranchdividesinto secondary brancheswithout anynarrowingat thejunction.Tuftsof tertiaryandquaternarybranchesarepresent. Thesebranches shownarrowings at thejunctionpoint.
202
pd (mm)
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o
a
order,this dependingwhethernippleJike projectionare consideredasreal ramificationsor not. The fact that more thanonenipple-like projectionperprimary branchoccurs, andthateachof themis theorigin ofa tuft ofbranchescan leadto theconclusionthattheyrepresentpropersecondary branches. In the genericdiagnosisCnos & Lruorm (1966) remark the absenceof a narrowing at the proximal end of Howeverthiscanbedueto thelackof secondary branches. calcification for thecloselypackedprimary andsecondary branches.A similar phenomenonfrequentlyhappens,for example,amongtheprimarybranchesof a samewhorl of F. dolomiticaresultingin a lateral fusion of primary pores into a sortof annularchannel(Cros & Lruorm, 1966,p1.2 figs.4-5).This is confirmedby exampleswherethe primary poresof the samewhorl areseparatedonefrom each other(CRos& LeMoNe,1966,p1.2fig.3). The absenceof narrowingsat the inner end of secondaryporesis of no laxonomicimportance. At thepresentstateof knowledgethe genusFanesella differs ftomPalaeodasycladushtmainly in thepresence of four ordersof branchesinsteadof threeandsecondlyin type species the somewhatthickerprimarybranches.The in theporesof lastorder. of F aneseI Ia lacksa segmentation
7.2.1 Fanesellasoluci n.sp.(Pl.452;Pls.51-53)
d (mm) a
Origin of the name.The speciesis dedicatedto the colleagueBrankoSokac,Institut za GeoloskaIsrazivanija of Zagreb (Croatia) for his contributions o knowledge of fossil algae. a o Holotype.Specimens in longitudinalsectionfiguredin Pl. D (mm) 52/3.Thin sectionBA.589.7. I sotypes.Specimens of the sampleBA.589 (= CG2 of the 3,8 3,4 4.2 4.6 3,0 5,0 Bigozzisampling): BA.589.1- 84.589.1l. thinsections Fig. 16. Fancsella soitaci n.sp. Irmer diameter of the calcareous Type-locality.Northern slope of Corno Grande (Gran skeleton (d, below), number of pores per whorl (w, centre) and Sasso,CentralItaly), at about 2700 metresof altitude distal width of primary pores (po, zp) against the outer diameter @ig. 12). of the calcareous skeleton (D). (see Type-level.Thickbeddedwhitebioclasticpackstones Brx.uovr (1976)describedthe speciesFanesella? microfaciesCM3). Same locality as Tersella genoti urgonicafrom tle LowerCrehceousof Bulgary.Accordn.sp. ing to thisauthorthespeciesshowsthreeordersof ramifi- Depository.Thematerialis depositedat theDepartmentof cations;actuallythe occunenceof tertiarybranchesis Palaeontology, Universityof NaplesFedericoII @aratolo higly questionable. The "secondary branches" figuredby collection) Ber.tovn (1976; pl.1 fig.4= detailof therightsideof pl.l fig.3) can be interpretedas primary pores of the same Diagnosis.Cylindrical simple thallus.Primary branches whorl formingan annularcavity(a fact thatis evidentin arrangedin closewhorlsandalternatingin following ones. theholotype:B*.uov.r 1916,p1.1, fig.l). On theleft side They aresetat an angleof 70-90oto thecentralstem,and (p1.1, primarypores the branchesof higher order tend to maintain îhe same of the samesection fig.3),separated present areverythick,phloiophorous. arevisible.In agreement with the interpretationthe inclination.Primarybranches They primary can be sraight or slightly curvedupwardor downoccurrenceof strong branchesand secondary general gradually ward. In verticillar the secúonincreases branchescanbe infened, thereforethis speciesshouldbe vertical The (tentatively remains genus outward but the section constant ascribedto another to Triploporella) inner vertically fransversal section looks like a elongated not andwill be considered here. Sorrc ( 1988)established ,F. anaeîromrhelowerLiassic rectanglewhile theouteroneis similarbut wider.Second(Velebit of Croatia Ms.). The speciesis characterized by ary branchesare akrophorous,moderatelysquat,4-6 per bulbousprimarybranchesthat continueinto 3-5 nipple- tuft. They often are laterally compressed,expecially in like projectionsand ramificationsup to third or fourth their inner part, with a subtriangularto subquadrangular a
a
a
a
a
203
,DCC.
Thin scction
D
d.
8 4 . 5 8 9 .I 84.589.2
3..1 46
8 4 . 5 8 9 . -3 B A . 5 8 9 . i--
1
an.3r.l.i eA..irv.+ria.siq.i ''
l'ó
0.9{
D-.112
t.2+
0.82
h
DId
0.32
0.++ __9.4? 0.38
l_.38
22 25 t1
0.42
n.nri .
0.4.1
0.76
{)J.l
- -
0,1 0,26 0,20
-rq .1),99 ta
0.25 0,25
l
p'
I'
I
!7
_._3,.0 8A.5S9.5 4.5 3.4 84.589.6 1.114 I 1 1 0,79 l . lt 3. 8A.58t.6 + 84.589.6 o,qg . f . + I 3.6 8A.51ì9.7 _ -5.0 84.5n9.7 BA.51t9.tì , t.pt . t.t: I It 1.26 llA.5tì9.(, .ì,6 3.0 o.77 - , l . r l uA.-589.9 8A.589.9 {.0 l.o.,e !.41 84.589.10 8 A . 5 8 9I.O --sî BA.-51t9.10 t) 84.589.1() -t,13 -..J:! - " 0,77 I,11 Iatx t,r2 ,\unbct _ __ 'l|araqc -_ Sl. Devi0lion
D$d 0.19
ti..ru
0.44
l1 2T l8 t2 24 l8 22
0,54
p" 0 . tI I 0,135 0,123 0,098
p"' \r.t, I
0,30 0,32
u.l) 0.37
0.09E
0,25
_, q,oE!
q3_{
fl,s2
9,_!2! ___flge8 q,9?!.--..9,J! 0.54 0,.!6 0,70
0, l6
0.lll
0,2t
0,086
0,l5 0 ,t 5
0,098
0,3(
_1r!11
0,1 0.10
0.33
0,069
0,1
0,1 0.27
0.0,ó2 0.08(r 0,0ó2
0.1 0.1
rì11 0,1? o.42
0.tll _ q,!4
0.1 0.1 0 ,l 0
0.!l o o98
0 ,1 9
0.3
0.20
0,u 0.21 _ _9,9q6
(,.2I 0.t6 0.5.f
t"'
tr,(róo 0.1il
9.?l 0,20
0.32 0.3
0 . 1I
0.il 1 0,lll
- 0 . ! 2 1- __,0_.!ll
0.42
0.062 0.0E6 o iiqt 0.123 n )) 0,t0 U , T ) 0,062 u_'19. 0 . 1 U,UóO _.. . , 0,1i Q'9e ;a o51 0,37 0,1 0,il 1 0,t35 !) 0.70 0.2ó 0,41 0.62 0.76 I 7 14 I8 7 I l1 9 7 5 9 20 3 , u|7! 0,e32_l ! , 2 8 2 2 i),ssio ,0/107. 0.7257 19.6t51 0 . 5 7I 7 0 , t 8 5 0 0,3137 0 , tt 1 1 0 , 2 8 1 8 0,0828 _g,Lq6! 0.ó59310.138610. I I 5(t5 0.096Iu 0 , 0 9 3 5 20.052I 8 3 , 5 9 l t t 7 0,09076 0.02988 0.08913 0 . 0 t1 3 9 0 . 0 8 1 7 10 . 0 t 5 1 9 0,07790 0.62
O.CrZ
0.123
q,ul
Table 2. Main biometric parametcrs oî Fanesella sokaci n.sp.. For each specimen is supplied the thin section number and the dimensional values. The range (min. and max.), the number of measurements, the average and the standard deviation for each parÍìmeter are given in italics at the bottom of the table . All size parameters are in millimeters. D: outer diameter of the calcareous skeleton; d: inner diameter of the calcareous skeleton; p*r: distal whorly width of primary branches; p"d: distal vertical width of primary branches; l: lenght of primary branches; w: number of primary branches per whorl; à: height between whorls; p': width of secondary branches; /': lenght of secondary branches; p": width of tertiary branches; /": lenght of tertiary branches; p"': width of quaternarybranches;/"': lenght ofquatemary branches.
transversal section.Tertiarybranches areratherthin, cylindricalin shape,2-4 pertuft.Sometimes theyshowsome crosspartitionsinside.Thebranchesof highestorderare thinnerandshorterthanthetertiaries,in tuftsof 2-3.They probablywere distally widenedto form a cortex. No reproductiveorgans have been observedin the plant,theywereplacedmostlikely in theprimarybranches (cladosporate-type). The calcareous skeletonis ratherthick, it usuallyenvelopsthe distalpafl of the primarybranchesup to the corticalquaternarybranches. It rarelyreachesinwardto themainaxis. Themostsignificantbiometricdataaresummarized in Tab.I . Theyhavebeentakenfroma singlcsample (BA.589).
tinuoushorizontalchannelsseparated by scallopedcalcified
[email protected]/5;Pl. 53/l). Thesebandsrepresentthe interspacebetweenwhorls that sometimescan be recognizedup to the zonewith tertiaryporesas a thin poreless band inside the calcareousskeleton(P1.5213;Pl. 53/1). Some evidencesfrom longitudinal sections@1. 52/3) showthatcalcificationis thickerin thelower regionof the thallus(from the centralstemup to the quaternarypores) andbecomesthinnerin the upperregion(from secondary to quaternarypores). The innerdiameter(d) is 0.77-l.l mm and the outer diameter(D) is 3.0-5.3mm.
Primarypores.Primaryporesare generallysetat 60-700 as to the main axis. Usually they benddownwardsin the Generalfeaturesof thecalcereous Thecalcare- very innerpartandthenupwardin theouterpart(Pl. $n), skeleton. ousskeletonis simple,cylindrical,continuous andwithout sometimesdownwardsagainin thevery distalend(Pl. 53/ anytraceof annulationor intusannulation. A greatamount l). The primary pores are arranged in close whorls type;Pl. 5 li5). Theheightbetweenwhorls(ft) of sectionsexhibitsa widecentralcaviry(Pl. 52ll-2); the (euspondyle is 0.46-0.70mm. The numberof poresin a whorl (w) is calcificationenvelopsthe distal part of primary poresor the secondaryporesup to the quaternarypores,probably approx.L2-25. The primary poresare phloiophorous(Pl. 51/1). The just beforetheircorticalswelling.Somesectionsshowsa width of the vertical section (Dr Crsrno, 1995) of the narrowcentralcavitywith a strongercalcificationthatcan pores is nearlyconstantfor mostof theporelenght(Pl. 53/ touchthecentralstem(Pl. 5l/3-5).ln this casea certain 2), while the width of the verticillar section increases degreeof calcificationoccursat both endsof primary (Pl. radially 53/3). The cross sectionof a pore is subporesandin the spacebetweenwhorls,but,almost,never quadrangular, passingoutwardsinto a roundedvertical betweentheporesof thesamewhorl,probablybecause of rectangle. The lenght (/) of the primary pores is 0.69theclosepackingof theprimaryporesthatdoesnot leave (p,) and the verticillar (p) width mm. vertical 0.76 The spaceenoughfor calcification.For thisreasonin oblique are0.32-0.61mm and0.22-0.44mm. or tangentialsectionthe whorls are represented by con-
204
A
A
B =-b + =/
B
J
c c
Fig 18. Fancsella sokaci n.sp. Reconstruction of the thallus in transversalview. A: transversal section at whorl level showing the calcareous skeleton. B: transversal section at whorl level showing primary to quaternary branches and the calcification (black). C: central stem and branchesin transversalview. (x 11.5) and becomes round in the distal one. Often l-3 transversal
D
Fig 17. Faresella soÈaci n.sp. Reconstruction of the thallus in longitudinal view. A: calcareous skeleton in axial section. B: central stem, primary to quatemary branchesand calcification (black) in axial section. C: longitudinal view of the thallus without calcification; the central stem shows the junctions of primary branches. D: perspective view of the branches and the cortex. (x I 1.5)
Secondarypores. The secondarypores are roughly subcylindrical,moreor lesslaterallycompressed leading to oval to subquadrangular transversalshapes.In some oblique sectionssecondaryporesseemto be slightly taperedoutwards(Pl. part;Pl. 53/3).It is difficult 5213lower to judge if this fact is real or just a resultof calcification. The secondaryporesoriginatein thedistalpartof primary pores,4-6, usuallyfive per tuft, . Theyare0.15-0.26mm wide (p) and0.27-0.54mm long (/).
septaare seeninside the pores.Howeverthey maintain their cylindrical shapeand no remarkableconstrictionis combinedwith eachseptum(P1.53/2:P1.522).Tertiary poresare0.09-0.13mm wide (p") and0.15-0.42mm long
(v').
Quaternarypores.The compactionof tertiary pores,the occurrenceof crosspartitions inside and the erosionor diageneticdamages(micritizationand/ordolomitization) of the outer surfaceof the calcareousskeletonmake it Some ofhigherorderpores. difficult to detectthepresence pores quaternary preserved reveal least at well specimens (Pl. 53/3).Quaternaryporesareshort,roughlycylindrical mostof their lenght,slightly wideningoutwardsat their distalend.Very probablytwo quaternaryporesstemfrom eachtertiarypore. The closepacking,thedisralwideningandsomeevidenceof polygonalpores near the outer surfaceof the calcareousskeletonfrom specimenscut in tangentialand oblique sectionsmake it probablethat quaternarypores form a cortexat their distal end. Reproductiveorgans.No clear tracesof reproductiveorganshavebeenobservedin thecalcareousskeleton.Howeverprimarybranchesappearstrongenoughfor carrying a reproductivefunction.For this reasona reproductionof is highlyprobable. cladosporate-type
Reconstruction @igs.17, 18).Unfossilizedor questionablepartsareconsideredhere:i.e. the top andthe bottom Tertíarypores.At the distal end of the secondaryporesa of thethallus. tuft of two or threetertiaryporesoriginates.Thesepores According to observationsin cylindrical dasyclads moderately long. Their are cylindrical and transversal with phloiophorousbranches(e.g.NeomerisandD asycladus) proximal part theapicalzoneis consideredto consistof branchesformsectionis triangularto subpolygonalin the
205 ing a bud.The basalpartof thethalluswasa rathershort branchless stalk-likeportionof thesiphon. Comparisons. F anesellasokacin.sp.canbedifferentiated from F. dolomiticaCnos& LsMol.{Eby its weakercalcification.ln F. sokacicalcificationdoesnot oftenreachthe central stem but,it is restrictedfrom the outer parts of secondaryto quaternarybranches.Thenewspeciesshows higherbiometricaldataof thethallus(e.g.D = 3.0-5.3mm versus2.6-3.3mm; d = 0.77-l.l mm insteadof 0.41.0mm).Evenif theprimarybranches showcomparable sizes,thesecondary branches areusuallylonger(l' =0.270.54mm versus0.15-0.30mm) andlargerin diameter(p' = 0.14-0.25mm versus0.15 mm).Tertiarybranchesare longer(1" = 0.15-0.42mm versus0.15 mm) but show (p" = 0.086-0.13 similardiameters mm versus0.10mm). Fanesellasokacin.sp.differsfrom,lî.anceSor.qcin a general biggersize(e.g.D = 3.0-5.3mm versus1.48-2,85 mm;d = 0.77-l.l mm versus0.35-0.48 mm)anda weaker calcification.The primary branchesoî F.sokaci. are phloiophorous with a constantverticalwidth while they are globularand much shorterin F. anae.The tertiary branchesof F. anaearebv far moreslenderthanthoseof thenew species.
8.3 Other taxa (Pra)(Pl. 44ll-2) 8.3.1Palaeodasycladus mediterraneus
for nomenclaturcreasonsby Gralurn & Delorrna (1993), a taxonomic review is also given by Bnn,tTrol-o et al. (1994). An analysisof the figured original material and of our specimensallows a new interpretationon somecharacters of the alga (thallus morphology, calcification and ramifications)partly differing from the descriptionsupplied by Cnos & Leuorlw (1967). Judgingfrom Pl.l/2 ofCnos &Lruom (1967:Pl.l12), that is the lectotype (Gn.nr.,rrn& Dpr-oprnr,l993), the thallusappearsdistinctly club-shapedand not cylindrical. (1967, Moreover, as alreadyaffirmed by Cnos & LeNaotNIs p. 251), this specimenalso shows that intusannulationis not anywherepresentalong the thallus;in fact it is lacking or undistinctin the lower part ol the figure, contrary to the upper part where it is clearly visible. This might suggest Lhatintusannulationhas a regional range and is growth dependent,similarly to what happensin P alaeodasycl adus mediterraneu.r (Bnnarrolo et al., 1994). Cnos & LuvorNe (1967, p. 251) think that each intusannulationinvolvestwo or three whorls of primary brancheswhose distal ends continue into the calcareous skeleton(Cnos & Lerrrorm,1967: fig.4). We supposethat the primary branchesof Cnos & Lprtroruaare to be consideredsecondarybranches.While Pl. l/2 of Cnos & Lauotm (1967) shows continuous horizontal channels (i.e. intusannulations), Pl. 1/4 shows that those figuresbreak downwardsinto singlerows (i.e.one whorl) of moderately large pores (secrninglyprimary pores).In thc Gran Sasso material this fact occurs too (Pl. 5414).Regardingcalcification Palaeodasycladusgracilis behaves like Palaeodasycladusmediterraneus(B,tnn'rrolo et al., 1994: p.3). Problemswill consequentlyarisein the discussionabout the order of ramifications of Palaeodasycladusgracilis (four?, five ?; seeCnos & Leuonc, 1967: îig.4). The calcareousskeleton of the specimens from the Gran Sasso,which were originally aragonitic,usuallyare recrystallizedin sparitic c:rlciteand only rarely micritized
This taxonhasrecentlybeentheobjectof a scientific debateinvolvingits specificstatusandgenericcharacterization (Drr-orrne& LA.corLA, 1990;BlnerroI-o et al., 1994). This speciesis largelyspreadin lagoonaland shelf marginfaciesof the Liassicof the Tethys(Bannrrolo, l99la). In theGranSassoareait is usedto definetwoalgal (Palaeodasycladus assemblages spp. algal assemblage andPalaeodasy cladusandThaumatop orella algalaSSerì: blage). (Pt.3et4). Dasycladsidentifiableas P. mediterraneusare rather numerousin thestudiedarea,althoughtheirmorphology 8.3.3 Petrascula?heraki Soxac & Nxran (Pl. 54/6-7) may differ from the type material(e.g.Benerrolo et al, 1994).Two extrememorphologies occur.One showsa Somespecimensfrom CM I , CM3 andCM5 microfacies smallersize,thinnersecondarybranches, but last order arereferredto this taxon.Thcy occur in tie Palaeodasycladus (Pl. 44/l-2). The sec- and Thaumatoporella algal assemblage, and Palaeobranchesdistinctlyphloiophorous ond morphologyexhibits rather stout and denselyset dasycladusspp. algal assemblage. varietyof secondary andtertiarybranches . A continuous The sizeofourspecimens fits well to thatofP. ? heraki. intermediate morphologies is recorded, butonlyrarelytwo The charactersofprimary and secondarybranches,as well distinctmorphologies areintermingledin the samesam- asthenumberofsecondariesper tuft, alsofit the variability ple. deducedfrom the Sokac& Nikler's photosand description. Waiting for an accuratequantitativestudyand comHoweverour specimensclearly show tertiarybranches, parisonof theseveralmorphologies, theseformsarecon- which havenot beenobservedin P. ? heraki.evenifSoxac sideredasa singletaxon. & Nrxlrn (1969, p. I I I ) do not exclude their occurrence. Although somephotos(Soxac & Nxt-sn, 1969: pl.2îigs4gracilisCnos& Larraou.m 8.3.2 Palaeodasycladus 1967 5) show tracesof tertiary branches,the stateof preservaex GnaMsn& Derorrnr1993(Pl.54ll-2,4-5;P1.4412) tion of the original materialdoesnotallow fartherreaching discussion.The attribution of our material to the taxon is given with somereservation. PalaeodasycIadusgracili s (= Palaeodasycladus medi In agreemcntwith B,qssou-lEretal. (1978)theposition terr aneusv aî.eIongalulusPnnrunr.oN) hasbeenreinstated
206 in the genusPetrasculais doubtful, but the taxonis not believedto be a junior synonymof Faneselladolomitica Cnos& Lrlrorxs as supposedby Orr (1974) 9 CONCLUSIONS
vesiculiferaalgal assemblage dominates; . a backmarginfaciesmarkedby completeperitidal cycles andby diageneticcycles.In thisfaciestheGriplwporella is present. curvataalgal assemblage
In theCalcareMassiccioFm.thefollowingdepositional wererecognized: environments Sedimentologicaland paleontologicalanalysishave . faciescharacterized a back-margin by diageneticcycles been carried out in the Dolomia Principaleand in the with high energy subtidal units and by the PalaeoCalcareMassiccioshallow water carbonatesuccessions In dasycladus spp. algal assemblage. this areathepresfrom the Upper Triassic and lower Liassic of the Gran Palaeodasycladus of and Thaumatoporella algal ence Sassoarea (Cennal Apennine,Italy) in order to define interpreted local to a assemblage can be as a transition stratigraphy,algal content,faciesdistributionand paleoprotected more lagoonal environment. environments. by oolitesandbioclasticsand The paleontologicalstudy has revealeda rich algal . marginfaciescharacterized with minor shoals contribution of reef-buildingorgangreenalgal assemcontentin which five dasycladacean isms and dasyas corals, sponges, solenoporaceans blageshavebeenrecognized.Theyhavebeenusedbothas genoti Fanesella algae Tersella and, cladacean of the indicators. biosrratigraphical and paleoenvironmenf,al probably formed These s o ka c i algal usemblage. organisms Two newalgalspecies, Iersella genoti n,sp.andFanesella patch-reefs in front behind the shelfedge. small and/or .rokacin.sp.,bothfromLiassicbedshavebeenestablished. The faciesrarely showsa cyclothemicorganization. Tersellagenoti differs from the other allied speciesin a "differentiated" less club shapedthallus,the shapeof The cyclicity of the shallowwaterunits is referredto secondarybranchesand size. Fanesellasokaci differs high frequencysealevel fluctuations.The distributionof fromotherspecies ofthe samegenusin theshapeandsize peritidalanddiageneticcycleswithin the facies subtidal, of thebranches, the sizeof the thallusand the degreeof mainlycontrolledby thetopographicpositionof units was calcification. environmentrelativeto themarginalarea the depositional The paleontological studyhasallowedsomenew obless and by the amplitudeof high frequencysea level servationson the genusTersellaMoneI-t-rrwhich leadto variations. considerMorellet'soriginaldiagnosismoreapt thanthe subsequentemendationsThe descriptionof Tersellaas The facies distribution has allowed ùo constructa havinga well-marked, stalkedthallusproposed by Cros& paleoenvironmental model for the Gran Sassoarea. (1967) Lemoine seemsto be too muchrestrictive,espeIn Late Triassic the shallow water platform facies when not cially sucha shapecan be discerned in thetypespecies.The assignment of a moniliformthallus,as sug- extendedin tìe westernand southernparts of the Gran gestedby CuBAyNEs & Delornnr(1984),cannotbeverified Sassoarea,with a lagoonalto backmarginfacies(Fig. 1ll A). In the early Liassic the shallow water faciesretrofor thetype-species, andthe genus. graded, andthe marginalareamovedbackto tlte western A discussion onseveral"terselliform"raxa(Dissocladella partsof the Gran Sassoarea(Fig. 1llB). In and southem cretica, Linoporella lucasi, Dissocladella iberica and Dissocladellaebroensis) is suppliedandsomecomments the middle Liassic, after the break up of the Calcare genus Fanesel/aCnos & Lruoltts and Palaeo- Massiccioplatform,largeshelf areasweredrowned,and on the retreatedto the Southof the shallowwatersedimentation gracilis dasycladus Cnos& LsN,rohiE aregiven. (Fig. range I l/C). Gran Sasso point Thesedimentological analysishasallowedto out a varietyof microfaciesin theDolomiaPrincipaleandin the CalcareMassiccioUnits defininga high frequency ACKNOWLEDGMENTS cyclic pattern.Threedifferenttypesof cycleswereobhasbeenfundedby grantsMURST Thepresentresearch served:subtidalcyclescomposed only by a subtidalunit, (scientific responsible Filippo Barattolo)and CNR 607o peritidalcyclesformedby a subtidalunitoverlained by an (scientific responsible Piero De Castro). (incomintersupratidal unit andrarelyby a supratidalunit geological The field and the sedimentological studies pleteandcompleteperitidalcycles)anddiagenetic cycles pertain Anna Bigozzi while to thepalaeontological aspects madeof a subtidalunit directlyoverlained by a supratidal Filippo Barattolo. The and the to stratigraphical study unit. joined palaeocological results from a analysis. come Microfacies,typesof cyclesand frequencyanddistriThe authorsare very grateful to Prof. E. Ott who bution of algal assemblageshave been used to define allowed to one of us (Barattolo)a comparativestudyon patterns facies anddepositional environments. Dissocladellacretica during the Alpine Algae Meeting In theDolomiaPrincipaleFm. two maindepositional (Sept.1993), who madeitpossiandto Dr. E. Moussavian wererecognized: of Earth environments Cirilli, Department ble.A thankto Dr. Simonetta . a shelflagoonfaciesoccasionallycharacterized by re- Sciences, UniversityofPerugia,for theusefulsuggestions strictedcirculation.In this faciessubtidaland incom- on somesedimentological aspects.Ioan Bucur and an pleteperitidalcyclesare presentand the Gyroporella anonvmous reviewercontributedvaluablecomments.
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