Cour. Forsch.-Inst. Scnckcnberg I 245 I 281-313 I 7 Figs, 4 Pls I FrankfUJ1 a. M., 30. 12.2003 ----------------------------------------------------------------- Conodonts across the Permian-Triassic boundary in the Southern Alps With 7 figs, 4 pls Maria Cristina PFRRI & Enzo FARABEGOLI Abstract The Tesero and Hulla sections (Dolomites, Italy) currently considered 01' pivotal importance l'or thc l'er- mian- Triassic (P-T) boundary in the western Tethys were characterised hy a medium to high rate of shal- low-marine sedimentation (5-]() cm k.y.-'). The thin, uppermost carbonate facies ofthe Permian Bellerophon Fmn (here named the "Bulla Mem- ber") is bounded regionally by unconformable surfaces. The upper unconforrnity coincides with the base of the Werfen Fmn historically identificd with the P-T boundary. In the Bulla scction, it slightIy antedates (by 1.3 m) the P-T boundary-defined hy conodonts, specifically the firs! appearance of Hìndeodus parvus. The Bulla Mbr yielded Hì. typicalis and Hi. praeparvus, extending their ranges above the P-T boundary into the Wcrfcn Fmn The conodont associations l'rom the lower part ofthe Werfen Fmn consist mainly ofhindcodids and isarciccllids showing graduai morphological change up-scction. The thickness and swcll1l1g ofthe basai cavity anù of th.e attachment area of the denticlcs-giving the conodont a swollen appearance-has been considercd laxonomically significant for ùefining rorms to be grouped in Isareìee/la. Four ncw specics are describcd: Ifindeodus pìsai. Isareicella lobala. Is. m(lala and Is. peculiaris. Seven conodont biozoncs have been discriminated, three are defined for the first time: Lower and Upper praeparvlIs. parvlIs. loba!a. slaeseheì, ìsareica and aeqllabì/is zones. A possible lincagc between the genera Hindeodus and [mreicclla is suggested. JJi. praeparvus has been considered the anccstor of Hi. parvus, the last represcntativc offlindc- odus in the Southern Alps. Ili. praeparvIIs is also ancestral to Isarcicella prìsea tÌ'om which the subsequent Isarcìcefla lineage evolved, namely Is. prìsca to Is. turgida, Is. lobata, lI'. s!aeschei and Is. isarciea. The carbonate-terrigenous deposits around the P-T boundary oceur in thin (dm-m thick) depositional cycles, recording superimposed high frequency, fourth- (l 00 k.y. period) and fifth- (\ 0-25 k.y.) order cy- cles driven by short-terrn sea-Ievel fluctuations. The main mass-extinction event occurred dunng the rapid sea-Ievel fall followed by sea-Ievel rise at the contact of the Belferophon and Werfen Fmns. The lowstand exhumed the top of the Bellerophon Fmn shallow-watcr carbonates resulting in moderate weathering and erosion ofbcdrock. Many remanié Perrnian fossils occur in the basai Werfen Fmn transgrcssive trae!. The high conodont diversity in the lower Tesero \llbr accords with rapid adaptative radiation following c1imatic change. On the basis ofour resu\ts, we propose thallhe Bulla section---(;haracterised by relatively abundant conodonts prccisely located in readily discriminahle high- depositional cycles-is the mosl rcliahle paras- tratotype scction for the P-T boundary in the western Palaeotethys. K e y w o r d s: conodonts, Permian-Triassic boundary, Southern Alps, Italy. Introduction Since the nineteenth century, the Perrnian-Triassic bound- ary (P- T boundary) in the Southem Alps (Italy, Austria) has been equated with the lithostratigraphic boundary between the Bellerophol1 Fmn (below) and Werfen Fmn (above) (RICHTHOFEN 1860, LEPSIUS 1878, MOJSISOVICS 1879, MERL;\ 1930, LEOI\\RI)I I935, PIA) 937, BOSELLINI 1964, ASSERFTO et al. 1973), two units cropping out exten- sively (fig. l) over an area of about 40,000 sq. km. VENZO (1957) and subsequently PASINI (1985) found that the oldest layers ofthe Werfen Fmn produced foraminifers, fusulinids and calcareous algae ofPerrnian aspect. Attribution ofthe lowermost Werfen Fmn to the Pcrrnian, supported by ad- ditional palaeontologic data (NERI & P\SI'i1 1985, BROGLIO LORIGA et al. 1986, POSENATO 1988), became genera\1y ac- cepted during the last decade when more than 20 detailed contributions to litho- and hiostratigraphy, sedimentology and depositional architecturc around the P T boundary have been proposed for correlation between the Southem Authors' addresses: Dipartimento di Scienze della Terra e Geologico-Ambientali, University of Bologna, Italy. Fax: 0039 051 2094522. >perri@;geomi.n.unibo.it<, >fàra@geomin.unibo.it<