Hettangian Ammonites and Radiolarians in the Mt

Home , Arietitidae, Schlotheimiidae, Vermiceras

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HETTANGIAN AMMONITES AND RADIOLARIANS IN THE MT. CAMICIA (GRAN SASSO, CENTRAL APENNINES)

ANG E,LA BE,RTINE,LLI', CARI-O NANNARONE', LE,ONSEVERO PASSERI' & T;EDI]RICO VENTURI'

ll.t'tt'it't'd Scptcnrbcr 19, 20a2: rc(?ltcd ()rntbcr (.),2A0-)

\ù7est Ke1, -onrr1t, Aurnronitcs, IL;rdiol,rrirns, [:uxirrrc f.rcrcs, Hcttiìr]giirì, fronr Er.rst to durine the Lirte Triassic - Early Lias- L;rrc Trirrssic, Tctlrvs, Gr,rn S,rsso, Ccntr.rì Apennirrcs. Itrrh: sic. Thc first trcnd defines the transition between the Lat- iunr-Abruz-zi Cirrbonate Plltfornr (to the south) and the Abstr'tct. The V.rllone cli Vr;rdd;r striìrii{rrìphic secti()rl ;\ situ.rt.'cl in the c;.rstcrn plrt o1 tlre Grrrn Srrsso rrìngc il.ìd shos's thc triurs;ti()rl Tlrscr.rnv-Un.rbriar-Mtrrche Basin (to the north) which was froÌ1l l-rÌte Trirrssic curinic flcies to L.:rrlv l.iassic opcn prcl;rgìc irrcics. connected durins the Jur:rssic with the Liguria-Piedmont This p;rper"cic'scribes Micltllc encl [-rìrc Hcttiìng;rrt rnrrttoltitc rncl lrrtlio- Occrrn. The second trend records the existence of early lirri:rn;rsser.nblrscs fonncl in tìrc uppcr prrt oi thc succcssiotr. Tlrc cr- euxirlic b,rsins ,rnd seiì-w:lys probably loosely connected, istencc oi,rn ,rnoxic cvcnt bckru thc Middlc Hett;rngi;rn bccls is notcti. bnt serretic,rlly related, rvith the Late Triassic - Jurassic Assenrblr{Ìes of snrlll-siz-ed M icldle Hettrrn girttr ;rrnronitcs sLr ggcsr 5()r ì rc

trxononlic innov:rtion u itlrin thc e ,rr'l\ [-\ r')ccrrtinr: ,{ún. n. (l)le uro.t- l.:rsoncsro B,rsin of the Southern Apennines (Ciarapica canthitidac') and Anil)'tocertr rr. sp. indct. l{lliol.rri,rns iountl togcthcr & Prrsscri 1998,2002). The Late ti:rssic - Early Liassic t,ith ;rnrnronitcs inrprove thc knowlcclgc of Hett.rrrsi.rn rrrclioìrtrirtn rrs- f,rcìes of the Gr;rn Sirsso range are referable to a carbonate senrbl,rgcs of t]re l,cstcrn Tctlrvs. plrrtforrrr environment in the western part (Corno Grande iìrer) rlnd :rn euxinic-to-open pelagic basin in the east- RiLrssLrnto. È Lrrc. enr",.rt" tlescritt.r lrr succcssiorre dcl Vrllonc tlì to Vradcl;l (parte orient;rlc dcll;r crrtcn,r tle I Grrn Srsso) che corltie nc i.rcics crn parrt (Mt. C;rn-ricia area). dl er,rrinichc r bacin;rliepc'rtc, rile ribili :rll'irrtervrrlkt Tli.rs superiorc - l.irrs The Corno Grrrnde 21rea is charircterized by the inferiore. Lrr prrrte princìprlc rlcl l,tvoro ò de'cììc.rta.rll.r clcscrizìonc clclle Dolonri,r Principale Fornr:rtion in the Late Triassic and ricche irssocirrzioni rìd irlln.ìoniti e r.rcliol;rri clcll'Hctt:rrrgi,rno treclio e b), tl.r" C,rlcare M:rssiccio Fm. in the Early Liassic. Both superiore, tror':rtc rrcllrr prìrte irltJ cli rlLrcst.r succcssiotrc. Un cvcnto rrnos- sico è segnrrllto sorto glìstrrrti tlcll'Hr'tt.rrrgirtno ntcdìo. I-e .trrt'ci.rzir'ni fornr:'rtions shorv sedin.renî;rry cycles with repeated emer- rr piccole lrrrloniti dell'Hcttlrrgi;rrro nredio suggcriscono rìcunc rtoliti sior.r surfrrces. The Dolomia Principale contains massive trssonomichc ncl c;rnrpo tlcllc [-r.tocentinr prinritivc: *e n. rr. (f)leuror- bcds, oiten with nregalodontids, xnd stromxtolitic layers c!ìnthiticlxe) e Anall'tocarts n. sp. irrclct. I r.tclìol,rri tf()\'rti insicnlt rgli il,ith fcncstrae ; the Calcare Massiccio is mainly composed :rnrnroniti pcnlcttor.ro cli nrigliorirrc le conoscenzc sullc.rsroe i.ru-iuni .r radiol,rri hcttrnsi,rni tlclh Tetidc occiclent.tlc. oi n-rrrssìvc beds often separated by layers with vadose pi- soids (Alessandri et al. 1968; Adamoli et il.1978; Bigoz- zi '99A). Thc trirr.rsition between Dolon-ria Principale and Massiccio, r,isible ;1long the SE wall of the Introduction C,rlc,rrc Corno Gr,rrrdc bclorv the B:rfile hut, is affected by late diagenetic The Gran Sasso thrust belt is n'rirdc r,rp of :1n inrbri- corlrsc-crvst:llli ne dolomitiz:rtion. The Calc:rre Massiccio cate stack of tector-ric elcrrre nts, the nurrber :rrrd bor,rndr- is ovcrl;rirr by Middle and Late Liassic open nlarine facies ries of which chirnge accordins to thc irrtcrprctirtiorl of (Corniol,.r înd Verde Anrnronitico) formations of the Tus- different irurhors (Adrrnroli cr al. l98lb, 1990; Ghisetti c,rnr'-U nrbria-M,rrche Basin. & Yezzani, 1986). This thrust bclt sl.ron's frrcies vrrrirr- L:.rte'Irir'rssic - E:rrly Liassic facies in the Mt. Ca- tions fron.r South to North sincc thc Middlc Li,rssic ,rrrd rricirr rrrc'rr rrre represented by bituninous layers, dolos-

I Diplrtinre nto cli Scicnze dcll;r Tcrn, Univcrsrtì di [)crusi.t, Pi.rzzr Urircrsitì. l.I - 06 IOO I)e rr-rgia, Itrrlr: E-nr;ril: angib(r libero.ìt 2 Diprrtinrcnto cli Scicnzc dclll Tcrrrr, Univcrsitì tli Pcnrgir, I)irrzz.t L.Jnir crsitì. l. I - 06 100 I)crugia, lt,rh. E-rr,ril: lprtn(rr rrrub;r.it 3 Diprrtinrcnto cli Scienze dcllrr Tcrr.r, Univtrsitì .li I)erugir. I)i.rzz.r Unìr'crsìr;ì. l.l - O6 IC0 Pcrugir. Itrh. E-rrail: Ipasseri(rrunipg.it .l Diprrtinrcrrto cli Scicnz-c cle lh Tcrru. Unive rsitì cìi I)cnrgi,r. [)irzz.r Unircrsitì. l.l - 06 ICO I)crugi.r, It.rh. Ll-nr,ril: r'e nturi(,r unìps.it 88 ,4. []ertinelli. C. Nattttaronc, L. Passari X F. \lentttrt

lrig. I - Rcl.rri,tnshipr bcts ecn thc Corno Grande Corno (ì r.rntlc c.rrlronrtc pl.ìt- fornr.rntl thc Vr,rcld,r b.tsin r \\ ( \t( t n .rrtrl e.trtrr-rt p.trt ,,t the (ìr.rn Srss() r..lnge) clur- ing rhr [..rte Tli.rssic rnd l:erlv l-irssicr rhr upper pert of \lt. J'rert.t 'tt, e. ..i, 'tt i. rtti..irtl ior crrrsion (.rfter Bigozzr ct al. 1991, nrodifìed). T. - l-rtc Trirssic. l. =l'l.rrìr' l-iessic.

tones, nodullr lir.nestones and chertv linrestonesl these ;rnd c:rlc;rre nites \\'ith iulrìr()nitcs (Anrnronitic beds f rl.); lithoflcies are referred to a basinal cnvironnrent evolvirrg 5) chcrtv linrestones (Corniolir Fn'r.). lrom euxinic to opcn nlarine conditions (Acl;rnroli et ,r1., I) Iìitunrinous (Scisti Dolornie bitumi- l98lr, 1984, 1990; Ciarapica 1990; Bis.t-l/.2l et ;rl. I99 ll dolostones bitunrinosi. nose) -'l'ìre nrosr tvpicrl litht,îrcics rrc bl:rck rrntl s hite rhvtlrmitcs in ve n D:rnrirni er al. 199 l). thin I.rnrin.rr ()l cJrL)()nirtc .rntl 0rg.rnic Dìirttcrt thìs lith0frcic: irrc'guìrrrìr' The lrrteral trensition fronr the Lirte Tri:rssic Dolonri:r rltcrn.rtcs sitìr rrrlssi'c cit,lt,stoncs. Thc IJitunrinous tlolostoncs shou Principale platfornr f,rcies of the Corno Grande to\\':ìrcl rvnsctli:ltntrrv nricroirults, cortloltrtc I.rnrinrti,rn.. slunrpirru rnd vrrious thc Mt. Crrmicia clrxinic b;rsinal fircies occurs bv rrc.irrr .,f kincis of svnsrrìinrentrrv rngulrr bitunrinous [rrecci.rsr lhcsc structurcs rre rcl.rterl t() c()nlpirction, fluids crc.rpc ancl gr.rvin nrovcnrcnts. Asvrtt- nliss;ve coarse-crystrlline dolostoncs proilrxdins ()n the nrctrìc.rl ripplcs, uitlr,r slrort l.rrc Ie nqth, lcrt obscrrcd.rt one lcvel (in bitunrinous dolostor-rcsl thc massive clolostoncs cr)nt.rin thc I,,s cr prrr) rntl cr,tss lrrnirrrti,rn\ rre unc()nlnlort. Sonrc :nrrll prrts r:1re iorams, algac:rncl ghosts of encrusting organlsnls; oi thc lJitrnninous tloiostoncs rrc silicified rntl thc tilicilicrtion occurrttl the prcscnce of storn'r-lavers in the bitunrinous dolostoncs bcfttrc thc I.rtt gcncr.rtion ol co.ìrsc-crvsr.lllinc tlolonrìtc. 'l suggcst the existence of r c;rrbonatc rrnrp. The Errrlv l.i:rs- hc entirc se'ction is strolrglr rrctonìzcd nr.rking it cliflicult trt distìngLrish tht prinrrn sctlinrcnt.rrv structures lront thc tcct(,nic (rnc\; sic part of this transition is not visible (Fiu. l). the thickcst tlrlostone bctls (rr.rnv tlnt) h,u c r brittlc bchrrviour rrnrl arc olttn c.t.rcl.rrtic. uhilc tht thirr-bcddccl bitunrinous rhvthnritcs uere

pl.rst ic.rl lv rlelornr.'ci lncl sonrct i ntcs strctchecl i n boutli ns. The Vradda section (Mt. Camicia area) 'l ht'prlcontologicrl e,,ntcnt is vcrr-poor, r,nlv sorle ostrrcotis, thin-shcllcd lrclecrpods.rnri lcrr ionnrs lC)lonospirt'llt sp.) sere founcl. This strrtisraphic section was srrllpled rlong thc V;rl- This lithol.rcics is reierrctl 1o thc l..rtc Trirrssic rrrinlr',,n tlrc brsis ol prl- lonc di Vradda :lnd on the western sidc of Mt. Trenrousi.r vnonrorpìrs rcportcrl ìn Acl.rrrroli ct rl. ( I990) .rntl l),rnri.rni ct :rl. ( I99I) (Contllint t/,rssrrir/r,s Pllug, (-. ntt'i'cri,tttt Klrus, (-r,r,,//lrta sp., Dupli (Figs. 2, 3). It is charactcrized b1, the following lithologi- cryrrrrrlrs srtttrtlfits Lcschik, I)ul,litisp,,rites sp., I)rtt'tìrculirn grattiJtt' cal intervirls (Fie. a): bituminous dolostones ;rnd bitr.r- l) I-.'schik. !)rtt,t irur I itt t syt. ). nrinolrs l;r1.e rs (Bitr"rniinous dolostoncs inr.); 2) thin be cl- Tlre lJirunrinous ,lolr,rt,,nc, .rre vrsi[rlc for .r thickncss oi lS0 ded dolostones (Vr.rdd;r dolostones fnr.); 3) noclul;rr;rr.rcl rr. trrrt tlricliness is unknorr n bccrusc thcr ovcrtlrrustttl the vc;unger spottccl lir.r.restones (Spotted linrcstoncs fnr.); 4) nricrite iornrrtions oi rhe Corniolr rntl Vcrclc A:rrnroniticr,. 2) Vradde dolostones - l'hin-Lrc.ldcd. lìnc-:rninctl rLrlostone s, hckin{ biturrrinous l.rvcr' rntl s ith clrern notlulrs. 'l'hc Lrppcr prrt i. c.rtrcirrric. l'ìrickncss is rround I l0 nr. 3) Spottcd lirnestoncs (Celcari macul:1ti) -'l'lro .rre ch,rr.rc- terizctl Lrv tìtc lrrescncc of nrrttlrtl.rntl noclulrr pinÌi linrcstones lntl shou s,,ntc thickcnin!Ì uplrrtl evclcs (-lO-50 nr thicli). T'hcsc srrf,tf, ;lrc

lji,' I THettangian faunas from the Gran Sasso range

mina); d) a black bed of felted organic matter ("bituminous layer", 40 60 l cm); e) thin-bedded calcarenites and micrites (14 m) with many levels *L containing small-sized, silicified ammonites (Ammonitic beds s.s.). Interwals c, d, e are somewhat weathered and often covered by f detritus. The detailed stratigraphic log of the ammonitic levels (Fig. 5) was achieved by combination of several short sections cropping out in different gullies along the western side of Mt. Tremoggia. 5) Corniola - The lower part of this formation (Corniola A) is @n a well-bedded cherty mudstones, similar to the typical Corniola Fm., but devoid of calcirudites and calcarenites. Corniola A overlies the Am- 6q monitic beds; a double system of faults, marked by cataclastic dolostones, separates these cherty limestones from the typical Corniola Fm. cropping out up to the Mt. Tremoggia ridge.

Ammonites of the Vradda section

Several levels with small, silicified ammonites were found in the Ammonitic beds; the specimens lie on the bedding plane, do not sho\il sutures and probably preserve part of their original shell. Four lithologic discontinuous ammonite-bearing intervals were identified in different gullies, separated by detritic and grassy areas (Fig. 5). The first interval (1 m) lacks ammonires, but contains a characteristic black bed of felted organic matter. The second interval contains six horizons with ammonites (Fig. 5): - horizon 1 contains very small specimens (few mm diameter) of gen. indet. cf. Protoqtmbites; Middle Het- tangian; horizon 2 (2 m above) contains many specimens, f, 'coRNtoLA A" - (CHERTY MUDSTONES) almost 1 cm large, of two species: gen. n. (Pleuroacan- e. AMMONITIC BEDS thitidae) and Discampbiceras sp. indet.; the first one is d. SPOTTED LII\,4ESTONES dominant; Middle Hettangian; c. CATACLASTIC DOLOSTONES b. VRADDADOLOSTONES - horizon 3 (40 cm above) contains small specimens a. BITUMINOUS DOLOSTONES of gen. indet. (Pleuroacanthitida e) , Karnmerharites sp. in- 6 ammonites :] det. and an indeterminate genus of Schlotheimiidae; Kam- U radiolarians merh.arites is the most common; Middle Hettangian;

Fig. 4 - The Vradda stratigraphic section and detail of the transition - horizon 4 contains many larger specimens, mostly from the Sported Limestone to the Corniola fm.; 1-8: am- Kammerbarites sp. indet. and Psewdoaetornoceras sp. indet. monitic horizons illustrated in Fie. 5. and a gen. indet. of Schlotheimiidae; this assemblage can be assigned to both the Middle and Late Hettangian; - horizon 5 contains small and medium-sized specimens of Schlotheimia sp. indet.; Middle or Late Hettang- wackestone and packstone with pellets, coated grains, echinoid plates ian; and rare forams; the upper part contains radiolarians, sponge spicules, - horizon 6 shows dominant Analytoceras n. sp.r algae such as Thaumatoporella paruoaesiculfera (Prainerr) and forams fewer Discampbiceras sp. indet. and rare Paracaloceras (Siphonovalztulina sp. and Nodosariidae). The thickness of the Spot- ted limestones reaches 160 m. cf. centawroides (Savi Er Meneghini, 1851). Specimens of 4) Ammonitic beds - They are typically represented by thin- Analytoceras n. sp. are very different from the species of bedded micrites and calcarenites with even lamina, thin beds of chert this genus described by \flàhner (1894); Middle or Late and ammonites of Middle and Late Hettangian age. Ammonitic beds Hettangian. crop out along the weslern side of Mt. Tremoggia and are marked by The Z) species: a characteristic grassy ledge between the cliffs of Spotted limestones third interval (horizon contains two and cherty limestones of the Corniola fm. Sunrisites sp. indet. and Paracalocerds sp. indet.; it is prob- Along the sampled section the Spotted limestones are overlain ably referable to the Late Hettangian. by: a) thin bedded limestones (1 7 m) made up of packstone, wackestone The fourth interval (horizon 8) contains dominant and mudstone containing pellets, thin-shelled pelecypods, echinoid Gyrophiocera.s, some Schlotheimia sp. indet. andrare Kam- plates, sponge spicules, radiolarians and some forams (Textulariidae); b) thin bedded calcarenites (6 m) with yellow and grey beds; c) a thin merkaroceras? sp. indet.; it is assigned to the Late Het- level (10 cm) of pebbly mudstone with encrusting forams (Tolypam- tangian. 9A A. Bertinelli. C. Nttilttttt'oila, L. P,rsscri Ei F. Venturi

z 8+ (, z I Gyrophioceras praespiratissimum ruJ Lrl 7- F\ \ j\

3,8 u..* 5

3 a\

AnalyÍoceras n. sp. and "Saxoceras" ffiffi z /n z2 F ,\ [' -Lr-t n uJ oJ Kammerkarlles so. ind. o * .*lF"rÈk;; u#tlT ,'

4 \d '\ Gen. n. ind. (Pleuroacanthitidae?) ffi ffiìj Gen. n. ind. cf. Protocymbites l\* 1"À'l tÉtt"-t'." .1.. vt,.tt J.!)-.ì/ /,r/ri5c

Features of the Vradda ammonites Gyrophioceras supraspiratum Wahner 1885 and G. (in stratigraphic order) praespiratissimws Wahner 1882 (horizon 8) - This genus was distinguished from Vermiceras by Bloos (1994, Gen. n. cf. Protoqtmbites sp. indet. (horizon 1) - It 1996);ir was recognized by the very evolute conch, sub- has been identified for the typical subglobular conch, but rounded section of the whorl, absence of ventral grooves is different lrom Protocymbites because of the large ribs and blunt keel; rectiradiate and strong ribs terminate or that cross the venter without interruption (in Protocym- become very feeble on the venter. Inner whorls of the bites the venter is smooth). Vradda specimens are smooth, while \fahner's speci- Gen. n. indet. (Pleuroacanthitidae) (horizon 2, 3) - mens are ribbed. This genus has been referred to the Pleuroacanthitidae for Kammerkaroceras? sp. indet. (horizon 8) - The the presence of ventrolateral parabolic nodes in the inner identification of these specimens is uncertain because whorl at the end of the ribs; coiiing is similar to the one of the ribs are numerous, dense and cross the venter. the Pleuroacanthitidae, but the conch is more compressed. Kammerkarites sp. indet. (horizon 3) - The specimens are characterized by evolute coiling, a compressed whorl, Hettangian ammonites in ltaly and in the Austrian Alps rectiradiate ribs and by a subrounded venter without keel. Gen. indet. (Schlotheimiidae) sp. indet. (horizons Important contributions to the knowledge of the 3, 4, 5,6) - They are strongly ribbed with ventral groove Hettangian ammonites of the Tethys are due to Wàhner or smooth band. The specimens have varying compressed (1882 - 1898) who documented Middle and Late Het- conches and varied strong ribs; some can be referred to tangian and Early Sinemurian in the condensed cephalo- the genus Schlotheimia. pod limestones of the basal Lias (Northern Calcareous Psewdoaetomocerds sp. indet. (horizon 4) - Only one Alps, Austria). Later the same succession was studied by specimen was found; ribs are similar to those of Kam- Dommergues et al. (1995) who documenred the pres- merkarites, but the conch is very involute (mainly on rhe ence of hiatuses in the Hettangian Scblotheimia marmo- inner whorl) and the venter is sharp. The inner whorls rea Zone. of this specimen are smooth up to a diameter of 9 mm. Hettangian ammonites coming from the La Spezia Analytoceras sp. n. indet. (horizon 6) - The attribution to area (Northern Apennines) were first described by Ca- this genus is due to the presence of conspicuous parabolic navari (1882, 1888) who ascribed them to Early Liassic nodes on the inner whorls. in seneral. Later other ammonites coming from the same Discamphiceras spp. indet. (horizons 4, 6) - Speci- succession and preserved in the Palaeontological Museum mens are very small but recognizable for the subglobu- of Bologna University (Capellini collection), were revised lar conch with involute coiling in the inner whorls. Some by Venturi (1985) who suggested the presence of the Late specimens have ribs on the whorl sides with large and Hettangian and Early Sinemurian. smooth venter, others are completely smooth. Cantaluppi & Lualdi (1983) studied the Early Li- Schlotheimia sp. indet. (horizons 6, 8) - It is recos- assic in the Ligurian Alps finding a large hiatus between nizedby compressed conch and ribs interrupted by ven- the Early Hettangian and the Early Sinemurian. tral groove; ribs are less strong than in other genera of Gaetani (1970) contributed to the knowledge of Schlotheimiidae. Hettangian ammonites with a study on Sedrina Lime- Sunrisites sp. indet. (horizon Z) - Some specimens stone (Bergamo area, Lombardian Basin, Italy) where the have been referred to this genus for the intermediate invo- described ammonites are considered Late Hettangian in lute conch, the round section of the whorl, ribs developed aee (gen. Schlotheimia). only on the sides and the large and smooth venter. One Adamoli et al. (1990) described the succession of strongly ribbed specimen can be referredrc Sunrisites sutt- Vradda where, at that time, only a few ammonitic levels risensis Guex (type species of the genus; Guex, 1995). had been found (belonging exclusively to the Gyrophi- Paracaloceras spp. indet. (horizons 6, 7) - Specimens oceras hortzon). During this new research more levels small; recognizedby the intermediate evolute conch, de- were documented and at present the Vradda section ap- pressed whorl, ribs only on the sides, smooth venter and pears to be the most complete Italian stratigraphic suc- blunt keel. cession of Hettangian ammonites.

Radiolarian fauna

The most important papers on Hettangian radiolarians are by Pessagno et al. (1982) who made a preliminary radiolarian zonation for the of North Fì1;. 5 - Four litholosic intervals corresponding to a pxrt of the An.r- Jurassic monitic beds of F-is. 4. Onlv the most abundant specics lre America; Carter, Whalen & Guex (1998) who proposed illustrated. Leneth of scale bars : 1 cm. a more detailed zonation of Hettansian and Sinemurian 92 A. Bcrtittclli, C. Nttltnttrone, L. Passeri k F. Voúun radiolarians of Queen Charlotte Island, British Coltrnr- Conclusions bia, defined by Unitary Associations (UA; Guex, 1977); The Vradda section shows the tr;rnsition from eux- Hori (1990) who proposed a radiolarian zonrrtion for thc inic to open-m,rrine facies. Hettangian ammonites in the Lower of SW Other authors, :rs Dunritri- Jurassic Japan. Lrpper pilrt of this section confirn.r the existence of a ma- ca (1970, 1985, 1995), De Wever (1982), Matsr-rok:r & rine trough running to the east of the Calcare Massic- Yao (1986), Takemura (1986), Kozur & Mostler (1990), cio cirrbon:rte platforr.n older than the post-Hettansian Gorican (1994), Sugiyama (1997), Yeh & Cheng (1998) Tuscirny-LJrrrbrir-Mirrche pelagic basin. Drill cores in the and Tekin (2002) have siven virluirblc cor.rtributions to Adri:,rtic off-shore indicate this trough w:ìs probably con- the systematics of the EarlyJurassic (mainlv Hettansian nected with the Emma basin. and Sinemurian) r:rdiolrrirns. The presence of two olìgotypic assemblages of The Arnmonitic beds of the Vraddir secuon are srrall-sized Anrmonites (horizons 2 md 6) sugsests the rich in ammonites and radiol,rrians. Many rirdiolariirns existence of tr partially isolated basin during the transition are caicified. However, rvell-preserved faun,rs rvith sili- fron.r the L:rte Triassic euxinic environment to open-ma- ceous tests have been found in two oLrt of the cieht ho- rine conditions in the Middle Liassic. rizons sampled. This is the first tinre th:rt lvell preserved The Vraddar sect;on contains several levels of Het- radiolarians and ammonites have been for.rnd tosether ir.ì t:rngian ar.r.rlnonites in stratieraphic succession and, at the Hettangian of the western Tethys. Preservation of present, it is the nlost inlportant section in the Apen- nines for studies on the Hettangian ammonites. the radiolarians is cenerally excellent. The spc'cinrens lre Sonre ammonites in the Vradda section suggest tax- very fragile, with well defined n.reshwork: nlost :lre ell- onon'ric innovaltions within the early Lytoceratina during tire, others have frasile spines, sometinles brokcn. Thesc the Middle Hettangian: sen. n. (Pleuroacanthitidae) and assemblages are rich in spherical and irresulirrlv spinose Analytoceras n. sp. indet.; their phyletic relations with the forms, often with tubercles. l,rrger specin.rens described by Canavari (1882, 1888) and The lowest level containins siliccous radiol:rri,rns Wàhner (1882-1888) have stillto be studied. occurs in the second amr.nonitic horizon (with Pler"rro,r- The recovery of siliceous radiolarians in the ammo- canthitidae and Discamphiceras - Middle Hettirngi:rn): nitic levels of the Vrtrdda section is important, because this these radiolarians are less well preserved then those in is the first tilne that well-preserved Hettangian radiolarians the hieher level. The second level rich in r,rdiolarians is and ar.rrr.nonites were found together in the western Tethys. horizon Z, which contains Sunrisites and Paracaloceras l.nd Further studies are necessary to evaluate the importance could be referred to the Late Hettangian. of the arnoxic level inside the ammonitic succession. Spumellarians dominate in both Middle and Lirte

Hettangian assenrblages. Diversity is low, but incrcascs in Ackttott'letlgenelts. Authors lre grateful to the reviewers G. the Late Hettangian. Spherical Spunrell,rrians with strong- lìloos (Stuttsrr-t) encl E. S. C,rrtcr (Portland-Oregon) for the useful ly raised nodes (similar to the ser.s Praeconocrnlontmll suggc'stiorrs:rncl thev ivish to thlnk elso: G. Cilrepicl (Perueia) for her sLrpp()rt ìn thc fielcl ,rncl dr.rring thc org;lniz;rtion of the paper, J. Guex Pessagno) are the n.rost abundirnt in both levels. (l-rrusrrrrrc) for the r-rsefr-rl clìscussion on thc'Hettlngiln anrmonites, M. The first level with siliceous radiolirriirns (horizon Mirrclìcc; (lìircnzc), M. Chiari (liircnze) ;rnd S. Gorican (Ljubljana) for 2 - Middle Hettangian) presents irn assemblirse (Fig. 6, tlrcir,rssist,rrrce lith the ncliol.rri:rn stuclies,rnd R. Ferri (Perugia) for his contribr,rtion in the lield;rnd for the rnrrrlonites photographs. This 22-25) with many specimens of Spunrellrrria een. et sp. re scirrch s:rs c;rrriecl or.rt ri,ith the financial suDDorr of the COFIN 20OO genus indet. (most are sin-rilar to PraeconoctnVotlnltd irnd Ploject (l-. P,rsscri coord.). others to Spum. gen. et sp. indet A) and r,vith the generi'r Charlottea Whalen 8r Carter; Archaeocenospbrtera Pessit- gno tr Yang, Thurstonia Vhalen & Carter, ,rnd l ferv ir.r- determinate Nassellaria. The second level (horizon 7 - Lirtc Hettlngi:rn) presents a very rich assenlbltlge (Fie. 6, 1-2 I ) u'itl.r scr'- eral senera (in decreasing order of rrbundance): dorri- nant Spun-ìellari:r sen. et sp. indet. (irs in the first lo'el); Thurstonia Whalen 8t Carter, Arnurìa Wh,rle n & Cirrt- l;ig. 6 - Scrrrrrring t'lectron rricrorr;rplrs of r,rcliol;rri;rns found in the er, Kungalaria \Whalen 8c Carter, Charlottea Vh,rlen .\ horizolrs 2 irrìd 7: 1-2 I belone to horiz-on 7 (Late Hettang- i.rn) rrnd 22-25 to horiz.on 2 (Middle Hettangiirn). Leni;th Carter; rare Pdntanellium Pessttgno Blonre, Paronael/rt & oi sc,rìe brrr : O,I nrnr. Pessagno, Crucella Pessasno, Llclalia \fhalen & C;rrter; |-lì: Spunrell:rri:r inclet.; 9-I0:,4rtut'ia sp.: I I: Nasselleria in- very rare Anaticapitula Dur.r.ritric:r 8: Zùgel, Bipetlis Dc det.; ll-l-l: llntanelliuxt spp.; l6: Clurlottea ? sp.;15, l7-18: Spunrellrrria indet.; l9: Uddlia sp.;20-2 l: Spumell:rria indet.; \fiever and Farcus Pessasno, Vhi-rlen cY Yeh. Their study 22: llrch,te ocenosPh.lerd sp.: 23:, Cbarlottet sp.:24: Tburstonìa is still in nr^oress sp.; 25: Nlsselllria inclet. 9-l 94 A. Bertìnellì, C. Nannarone, L. Passeri &, F. Venturi

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