Rivista Italiana di Paleontologia e Stratigrafia volume luj numero 3 pagrne 369-388 Dtcembre 7997 BIOCHRONOLOGY OF SELECTED MAMMALS, MOLLUSCS AND OSTRACODS FROM THE MIDDLE PLIOCENE TO THE LATE PLEISTOCENE IN ITALY. THE STATE OF THE ART E. GLTOZZII, L. ABBAZZI2,P. ARGENTI3, A. AZZAROLI2,L. CALOI4, L. CAPASSO BARBATO4, G. DI STEFANO4, D. ESU4, G. FICCARELLI2, O. GIROTTI4, T. KOTSAKISS, F. MASINI6, P. MAZZA2, c. MEZZABOTTA2, M. R. PALOMBO4, C. PETRONIO4, L. ROOK2, B. SALA/, R. SARDELLA4, E. ZANALDAO & D. TORRE' Key-uords: Continental biochronology, Plio-Pleistocene, large the mammal ages used for the biochronological scale of and micro mammals, molluscs, ostracods. the large mammals are aiso used (mainly for historical reasons) biochronology molluscs and Riassunto, Gli Autori hanno elaborato quattro tavole di distri for the of the buzione cronologica delle faune a mammiferi (macro e micrQ, a mol- ostracods. luschi e ad ostracodi di acqua dolce e salmastra, prendendo in consi- The species distribution charts refer to the Faunal derazione i più significativi giacimenti del Plio-Pleistocene della peni- Units (F.U.) succession (Azzaroli, 1977; Azzaroli et al., sola italiana. In questo lavoro viene istituita una nuova Età a Mammi- feri (Aureliano) correlabile con la pane superiore del Pleistocene Me- 7982, 1988). This succession constitutes the biochrono- dio e con il Pieistocene Superiore: di questa età sono state definite logical scale for the continental succession in the Italian due Unità Faunistiche (Torre in Pietra e Vitinia) per l'Aureliano infe- peninsula, and is calibrated with the geochronological riore e medio, mentre nessun giacimento è stato considerato rappre- scale by means of radiometric and palaeomagnetic da- sentativo per I'Aureliano superiore. k unità biocronologiche sono state calibrate con la magnetostratigrafia, con le scale isotopiche ting. Successive faunal units are not separated by a dell' ossi geno e attraverso éataziom radiometriche. boundary because of the impossibility of defining them with precision. The unreiiability of the boundaries deri- Abstract. The Authors have elaborated four range chans of ves from two causes of a different order: mammalian (large and small), molluscs and fresh-water and brackish continental successions are largely disconti- ostracodes faunas, for the selected Plio-Pleistocene fossiliferous locali- ") ties of the Italy. A new Mamnal Age (Aurelian) correlatable to late nuous and mammal remains afe usualiy concentrated in Middle and Late Pleistocene has been defined. Inside this age two horizons with a punctual distribution in stratigraphic Faunal Units (Torre in Pietra and Vitinia) have been defined as char- successions. Therefore only exceptionally can the transi- acteristic for early and middle Aurelian, while no gisements have been chosen for the late Aurelian. Biochronological units are calibra- tion to the next association be recognised in strati- ted on magnetostratigraphic and isotopic scales and by radiometric graphic succession. datings. b) the definition of F.U., which is based on all the species from local faunas selected as typical associations. This latter point merits a brief discussion. Faunal lntroduction. Units in biochronology correspond to what in biostrati- Present day knowledge about the terrestrial mam- graphy are coenozones and, in the same way, their li- mal faunas, non marine molluscs and freshwater brac- mits are not definable with precision. The distinction kish ostracods of the Italian Plio-Pleistocene enables us between successive coenozones is not based on single to attempt to construct an integrated biochronology. faxa bioevents, but on diffe- ^ppearance,/disappearance This has been achieved by means of constructing four rent associations of characteristic taxa. In fact bioevents distribution charts of selected taxa from the most signi- characterising successive F.lJ. occur during the transition ficant Italian localities. It is worthwhile underlining that between the two F.U., and their calibration is conse- 1l C..r' St".li^ ^.r il Quaternario e I'Evoluzione ambientale CNR c/o Dipanimento di Scienze della Terra, Università degli Studi "La Sapienza" di Roma p.le A. Moro 5, 00185 Roma, Italy. 2) Dipanimento di Scienze della Terra, Università degli Studi di Firenze. 3) Dipanimen- to di Scienze della Terra, Università degli Studi di Perugia. 4) Dipanimento di Scienze della Terra, Università degli Studi "La Sapienza" di Roma. 5) Dipanimento di Scienze Geologiche, Università degli Studi di Roma Tre. 6) Dipanimento di Geologia e Geodesia, Università degli Studi di Palermo. 7) Dipanimento di Geologia e Paieontologia, Università degli Studi di Ferrara. 8) Dipanimento di Scienze della Terra, Università degli Studi di Miiano. 374 E. Gliozzi et al. quently affected by some inaccuracy (for a wider discus- few cases is it possible to reconstruct the relative chro- sion on this subject we refer the reader to De Giuli et. nological position of each local fauna within a faunal aL, 1986; Lindsay, 1990). Clearly this facror generates a unit. For this reason local faunas in a faunal unit are certain "background noise" in the contents of the distri- conventionally reported in alphabetical order and bution charts. In addition an even more important bias first/last occurrences of taxa are conventionally placed is caused by the fact that different Faunal IJnits are nor at the base of each faunal unit, represented by a dotted homogeneous from the point of view of the diversity of line. The synchrony of events observable on the distri occurring species. bution chart is attributable to this graphic convenrions. An example of this is given by the faunal renewal For the reasons discussed above, the temporal gap that occurred at the beginning of the Middle Pleistoce- between appearances is sometimes emphasised by the ne, between the Colle Curti and the Slivia Faunal Units. scarcity of local faunas, especially in the older part. In fact the few species occurring at Colle Curti - which Furthermore, the scale of the faunal renewal (measured in any case are indicative of a renewal - does not make it by the number of new appearances) is biased by the possible to establish whether this faunai change was al- gîeafer or lesser richness of the local faunas which make ready under way previous to this faunal unit. up each faunal unit. Despite these limitations, the picture which re- sults from this work gives reasonably acceptable infor- mation about the timing of the faunal renewals during Large mammals. the Plio-Pleistocene. Villafranchian Mammal Age. The distribution charts. The oldest fauna we are dealing with is the Triver- The unreliability of biochronologies based on sa F.IJ., which dates back to the Middle Pliocene. Early mammal assemblages mentioned above forced us to use Pliocene mammals in Italy are exrremely poorly repre- some graphic conventions and symbols in the distribu- sented. A few fossils were collected in the Val di Pugna tion charts which need some explanation. (Siena), assigned a Stepbanorhinus megarhinus, Sus mi- On the left in Fig. 1 and 2 are the composire cur- nor, Alephis liryx and Felsinotherium gerztaisi (Azzaroli et ve of oxygen isotopes modified from Shackleton (1995), al., 1988). A further find of this age is a fragmentary the chronologically calibrated magnetostratigraphic scale metapodial of Alephis liryx {rom the fluviolacustrine ba- (Baksi, 1993) and the geochronological scale. The sin of Montecarlo near Lucca (Dallan Nardi, 1988). Ear- boundary between the middle and the late Pliocene is ly Pliocene mammais are not sufficiently well repre- placed at isotopic stage 103, just before the beginning of sented in Italy to be included in the distribution chart. the marked cooling event which took place at about 2.5 The fauna of the Triversa F.U. (the first faunal Ma (R.io et al., 1994). The boundary between the eady unit of the early Villafranchian) show a marked renewal and the Middle Pleistocene is placed close to isotopic with respect to previous associations which are well stage 25, following the proposal made by Cita 6c Casrra- characterised in localities of Spain and southern France dori (1994). The boundary between the Middle and the (see Azzaroli et al., 1988, with references) and which are Late Pleistocene is placed at isotopic stage 5e (Aguirre & composed of taxa which are typical of humid and dense Pasini, 1985). forested environments. Faunal units calibrated by radiometric and/or pa- The Triversa F.U. is characterised by the assembla- laeomagnetic analyses are reported in the column "Cali- ge of fossils from various sites in the Villafranca d'Asti brated local faunas". The graphic convention indicating area (S. Paolo, Solbrito, Dusino, Fornace R.D.B., Casa the transition between Mammai Ages is a vertical bar Crotino, Casa Cassinotta, Arboschio, Arondelli) and ta- which covers the space between the last and the first kes its name from a small river in the area. The verte- faunal unit of two successive mammal ages. The same brate bearing fluvio-lacustrine succession lies on Early graphic convention is used rc indicate the base of selec- Pliocene (MPL 4) marine clays. The age of this F.U. ted events, which is placed in an intermediate position should be around 3.2};,4a, as suggested by palaeomagne- between two successive faunai units. tic analyses at Fornace R.D.B. (Lindsay et al., 1980), The distribution of the taxa is represenred by a although new analyses by Lindsay et al. (1995, and oral continuous vertical line when the presence of taxa is do- communication) suggest that the Fornace R.D.B. section cumented. \When the presence of a taxon is inferred or should be attributed to the upper parr of the Gilbert is documented by scarce or fragmentary material, it is magnetochronoznîe. The first date has however been represented by a domed line. The precise succession of confirmed by the palaeomagnetic survey recently carri- the appearance,/disappearance of each taxon charac- ed out at Santa Barbara near Casrelnuovo dei Sabbioni terising successive faunal units is not known.