Bortolotti, Valerio

Chiari, M.

Marcucci, Marta

Principi, Gianfranco

English

Florence Research

INTRODUCTIONIn the Albanian sector of the Dinaric-Hellenic Chain, theophiolites have been subdivided into two parallel belts: theWestern Belt (WB) and the Eastern Belt, due to their differ-ent stratigraphical, petrological and geochemical character-istics: WB represents oceanic lithosphere generated at amid-oceanic ridge (MOR ophiolites), EB represents anoceanic basin developed over a subduction zone (SSZ ophi-olites) (ISPGJ-IGJN, 1990; Beccaluva et al., 1994; Bortolot-ti et al., 1996, and bibl. therein). EB overthrust westwardsWB. The radiolarian cherts (Kalur Cherts) covering the vol-canites of both the successions have the same ages, com-prised between latest Bajocian-early Bathonian (UAZones 5of Baumgartner et al., 1995) and middle Callovian-earlyOxfordian (UAZones 8) (Chiari et al., 2004, and bibl. there-in). Thin levels of radiolarian cherts intercalated in thebasalts of EB have late Bajocian to latest Bajocian-earlyBathonian ages (UAZones 4-5) (Chiari et al., 1994 andChiari et al., 2004).A “blocks in matrix-type” sedimentary mélange, the Si-moni Mélange, unconformably covers both the successions,indistinctly lying on the radiolarian cherts or on the upperportions of the underlying volcanites (Bortolotti et al., 1996;Carosi et al., 1996). It grades upwards to the Firza Flysch(latest Tithonian-Valanginian age after Shallo 1991; Gardinet al., 1996), a pelagic sediment with frequent ophiolite-bearing polimict pebbly sandstones and mudstone intercala-tions. The mélange includes blocks of different sizes (up toseveral hundred meters) of continental derived (predomi-nant) and ocean derived rocks, in a shaly matrix. It can beinterpreted as “syn-orogenic....deposited after the inceptionof ophiolite deformation” (Bortolotti et al., 1996). The ageof the mélange was indirectly determined, being comprisedbetween middle Callovian-early Oxfordian, the more recentage found at the top of the Kalur Cherts (Marcucci andPrela, 1996), and the latest Tithonian-early Berriasian?,found at the base of the Firza Flysch (Gardin et al., 1996). The aim of this note is to present new biostratigraphicaldata that define a more precise age of the Simoni Mélange,dating a cherty-silty level found at the top of the KalurCherts near the Lumi i Zi (northern Albania). THE LUMI I ZI SECTIONIn the Lumi i Zi area, south of Puke, Mirdita (Fig. 1),Marcucci and Prela (1996) dated a section of Kalur Chertsat the top of the volcanites of the Eastern Belt. Moreover,they wrote that on top of the Kalur Cherts, a 12 meters thicklevel of “green siltstones and tuffites with unfossiliferousgreen cherts” was present.This locality was the only one in which sediments withcherty beds, conformably covering the Kalur Cherts, werefound. On this account, a successive sampling of this levelwas performed, and furnished significative radiolarian as-semblages.The sampled section, reported in Fig. 2, from the baseupwards consists of:1- pillow lavas, extending downwards for some hundredmeters;2- thin beds of red radiolarian cherts regularly alternatingwith thinner shale beds (the Kalur Cherts), with at theOfioliti, 2007, 32 (1), 53-56 53SHORT NOTENEW DATA ON THE AGE OF THE SIMONI MELANGE, NORTHERN MIRDITA OPHIOLITE NAPPE, ALBANIAMarco Chiari°, Valerio Bortolotti*,, Marta Marcucci*,° and Gianfranco Principi*,°° Istituto di Geoscienze e Georisorse, Unità di Firenze, Via G. La Pira 4, 50121 Firenze, Italy. * Dipartimento di Scienze della Terra, Università di Firenze, Via G. La Pira 4, 50121, Firenze, Italy. Corresponding author, e-mail: valerio.bortolotti@geo.unifi.it.Keywords: Simoni Mélange, Kalur Cherts, radiolarian, biostratigraphy, Mirdita Ophiolite Nappe, Late Jurassic. Albania.Fig. 1 - Schematic geologic map of the northern Albania with the site ofthe studied section (modified from Bortolotti et al. (2004).base 2 meters of red siliceous shales. For this level (5 mthick) Marcucci and Prela (1996) obtained a late Bathon-ian-early Callovian age (UAZones 7) at the base of thecherts and a middle Callovian-early Oxfordian age (UA-Zones 8) at the top.3- tufites and greenish siltites, with green and more rarelyreddish cherty beds. In this level (12 m thick) the new ra-diolarian assemblages have been found.RADIOLARIAN BIOSTRATIGRAPHYFour samples have been examined for radiolarian analy-sis (LU 1 - LU 4). We adopted also for this study the UAZones proposed byBaumgartner et al. (1995).Sample LU 1 (2 m from the top of the Kalur Cherts)yielded the following species: Archaeodictyomitra primige-na Pessagno and Whalen, Emiluvia sedecimporata (Rüst),Podocapsa amphitreptera Foreman. The age is middle-lateOxfordian to late Kimmeridgian-early Tithonian (UAZones9-11) for the presence of Podocapsa amphitreptera andEmiluvia sedecimporata. After Pessagno and Whalen (1982) the age range of Ar-chaeodictyomitra primigena is late Bathonian. O’Doghertyet al. (2006) found this taxon in a sample of middle Bathon-ian age. Considering also the age of the sample LU 1 wherethis taxon occurs, the range of Archaeodictyomitra primige-na could be extended from middle Bathonian to middle-lateOxfordian or from middle Bathonian to late Oxfordian-earlyKimmeridgian.The sample LU 3 (8 m upside) yielded the followingspecies: Archaeospongoprunum sp., Emiluvia orea ultimaBaumgartner and Dumitrica, Emiluvia sedecimporata(Rüst), Emiluvia sp. cf. E. orea s.l. Baumgartner, Mirifususdianae s.l. (Karrer), Paronaella kotura Baumgartner,Podobursa sp., Podocapsa amphitreptera Foreman, Prae-conosphaera sphaeroconus (Rüst), Protunuma japonicusYao, Sethocapsa sp., Syringocapsa spinellifera Baumgart-ner, Triactoma foremanae Muzavor, Zhamoidellum ovumDumitrica. The age is late Oxfordian-early Kimmeridgian(UAZones 10) due to the presence of Emiluvia orea ultima,Praeconosphaera sphaeroconus with Paronaella kotura. Inthis work we consider for Praeconosphaera sphaeroconus alate Oxfordian-early Kimmeridgian to Neocomian age rangeas reported in Chiari et al. (2007).The sample LU 4 collected in the same level of LU 3yielded the following species: Archaeospongoprunum sp. cf.A. imlayi Pessagno, Emiluvia ordinaria Ozvoldova, Hexasat-urnalis nakasekoi Dumitrica and Dumitrica-Jud, Perispyridi-um sp., Praeconosphaera sphaeroconus (Rüst), Tritrabs sp.cf. T. ewingi s.l. (Pessagno). The age of this last sample islate Oxfordian-early Kimmeridgian to late Kimmeridgian-early Tithonian (UAZones 10-11), for the presence of Emilu-via ordinaria and Praeconosphaera sphaeroconus. In this sample the taxon Hexasaturnalis nakasekoioccurs, its first appearance is during the lower Bathonianand its last occurrence probably at the end of the Kimmerid-gian or lowermost Berriasian, after Dumitrica and Dumitri-ca-Jud (2005).CONCLUSIONSThe age span in which the Simoni Mélange was deposited,previously considered to be comprised between late Callov-ian-early Oxfordian and latest Tithonian-early Berriasian?Can be now restricted to the interval late Oxfordian-earlyKimmeridgian and latest Tithonian-early Berriasian?, a timespan of about 10-15 my (Gradstein et al., 2004 time scale). Even if this age span has been slightly restricted, a largesedimentary gap between the cherty sedimentation and theoverlying Simoni Mélange formation, is clearly present.AKNOWLEDGEMENTSWe express our thanks to Simone Corti and Ivan Aiello,which, during a geological mission in Albania, collected thesamples studied in this article.BIBLIOGRAPHYBaumgartner P.O., Bartolini, A.C., Carter E.S., Conti M., CorteseG., Danelian T., De Wever P., Dumitrica P., Dumitrica-Jud R.,Gorican S., Guex J., Hull D.M., Kito N., Marcucci M., Matsuo-ka A., Murchey B., O’Dogherty L., Savary J., Vishnevskaya V.,Widz D. and Yao A. 1995: Middle Jurassic to Early CretaceousRadiolarian biochronology of Tethys based on Unitary Associa-tions. In: P.O. Baumgartner et al. (Eds.), Mém. Géol., Lau-sanne, 23: 1013-1048.Beccaluva L., Coltorti M., Premti I., Saccani E., Siena F. and ZedaO. 1994. Mid-ocean ridge and supra-subduction affinities inophiolitic belts from Albania. In: L. Beccaluva (Ed.), Albanianophiolites: state of the art and perspectives. Ofioliti, 19: 77-96.Bortolotti V., Kodra A., Marroni M., Faruk M., Pandolfi L., Prin-cipi G. and Saccani E., 1996. Geology and petrology of ophi-olitic sequences in the Mirdita region (Northern Albania). Ofi-oliti, 21: 3-20.Bortolotti V., Chiari M., Kodra A., Marcucci M., Mustafa F., Prin-cipi G. and Saccani E., 2004. New evidences for TriassicMORB magmatism in the northern Mirdita zone ophiolites (Al-bania). Ofioliti, 29 (2): 243-246.54Fig. 2 - Lithological column of the Lumi i Zi section.Carosi R., Kodra A., Marroni M. and Mustafa F., 1996. Deforma-tion history of Jurassic Kalur Cherts from the Mirdita nappe,Albanian ophiolites. Ofioliti, 21 (1): 41-46.Chiari M., Cobianchi M. and Picotti V. 2007. Integrated biostratig-raphy of Jurassic successions in the Southern Alps. Palaeo.Palaeo. Palaeo., 249: 233-270.Chiari M., Marcucci M. and Prela M., 1994. Mirdita ophiolitesProject: 2- Radiolarian assemblages in the cherts at Fushe Arrezand Shebaj (Mirdita area, Albania). Ofioliti, 19 (2a): 313-318.Chiari M., Marcucci M. and Prela M. 2004. Radiolarian assem-blages from the Jurassic cherts of Albania: new data. Ofioliti,29: 95-105.Dumitrica P. and Dumitrica-Jud R., 2005. Hexasaturnalisnakasekoi nov. sp., a Jurassic saturnalid radiolarian species fre-quently confounded with Hexasaturnalis suboblongus (Yao).Rev Micropal., 48: 159-168.Gardin S., Kiçi V., Marroni M., Mustafa F., Pandolfi L., Pirdeni A.and Xhomo A., 1996. Litho- and biostratigraphy of the FirzaFlysch, ophiolite Mirdita Nappe, Albania. Ofioliti, 21: 47-54.Gradstein F.M., Ogg J.G., Smith A.G., Bleeker W: and LourensL.J. 2004. A new Geologic Time Scale, with special referenceto Precambrian and Neogene. Episodes, 27: 83-100.ISPGJ-IGJN, 1990. Geologjia e RPSSH. MMKS, Tirana, Albania Marcucci M. and Prela M., 1996. The Lumi i Zi (Puke) section ofthe Kalur Cherts: radiolarian assemblages and comparison withother sections in nortern Albania. Ofioliti, 21 (1): 71-76.O’Dogherty L., Bill M., Gorican S., Dumitrica P. and Masson H..2006. Bathonian radiolarians from an ophiolitic mélange of theAlpine Tethys (Gets Nappe, Swiss-French Alps). Micropal., 51(6): 425-485.Pessagno E.A. and Whalen P.A. 1982. Lower and Middle JurassicRadiolaria (multicyrtid Nassellariina) from California, east-cen-tral Oregon and the Queen Charlotte Islands, B.C. Micropal.,28 (2): 111-169.Shallo M., 1991. Ophiolitic mélange and flyschoidal sediment ofthe Tithonian-Lower Cretaceous in Albania. Terra Nova, 2:476-483.55Received, April 30, 2007 Accepted, June 4, 200756Plate 1 - 1) Archaeodictyomitra primigena Pessagno and Whalen, LU 1, x265; 2) Archaeospongoprunum sp. cf. A. imlayi Pessagno, LU 4, x160; 3) Ar-chaeospongoprunum sp., LU 3, x150; 4) Emiluvia ordinaria Ozvoldova, LU 4, x140; 5) Emiluvia orea ultima Baumgartner and Dumitrica, LU 3, x120; 6)Emiluvia sedecimporata (Rüst), LU 3, x150; 7) Emiluvia sp. cf. E. orea s.l. Baumgartner, LU 3, x145; 8) Hexasaturnalis nakasekoi Dumitrica and Dumitrica-Jud, LU 4, x175; 9) Mirifusus dianae s.l. (Karrer), LU 3, x100; 10) Paronaella kotura Baumgartner, LU 3, x145; 11) Perispyridium sp., LU 4, x175; 12)Podobursa sp., LU 3, x150; 13) Podocapsa amphitreptera Foreman, LU 3, x150; 14) Praeconosphaera sphaeroconus (Rüst), LU 3, x155; 15) Protunumajaponicus Yao, LU 3, x235; 16) Sethocapsa sp., LU 3, x175; 17) Syringocapsa spinellifera Baumgartner, LU 3, x110; 18) Triactoma foremanae Muzavor,LU 3, x120; 19) Tritrabs sp. cf. T. ewingi s.l. (Pessagno), LU 4, x150; 20) Zhamoidellum ovum Dumitrica LU 3, x205.

New data on the age of the Simoni M&#233;lange, Northern Mirdita Ophiolitic Nappe, Albania.

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New data on the age of the Simoni Mélange, Northern Mirdita Ophiolitic Nappe, Albania.

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New data on the age of the Simoni M&#233;lange, Northern Mirdita Ophiolitic Nappe, Albania.

Abstract

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New data on the age of the Simoni Mélange, Northern Mirdita Ophiolitic Nappe, Albania.