Stratigraphical and palaeontological data from the Early Pleistocene Pirro 10 site of Pirro Nord (Puglia, south eastern Italy)

摘要

The Pirro Nord palaeontological and archaeological locality has been the object of recent field research to investigate the fossil content of its Early Pleistocene vertebrate palaeocommunities, and to understand the genesis of the karst network and related deposits that delivered the lithic industry representing the earliest human occupation of Europe known so far, spanning 1.7-1.3 Ma. The succession of the Pirro 10 site has been described in terms of facies and fossil vertebrate content of the 37 distinguished Sedimentary Units (SU). On the whole, the succession is made of chemical and clastic sediments that include debris fall and alluvial deposits. SU are distinguished according to lithology, colour, discontinuities, lamination, fossil concentration, and taphonomical parameters. Palaeomagnetic data and bio-chronological characteristics refer the Pirro 10 site to the latest Late Villafranchian Mammal Age of the Italian biochronological mammal scale. The fossil content is quite homogenous. Common taxa are Axis eurygonos, Hystrix refossa, Ursus etruscus, Canis mosbachensis together with small mammal remains mainly represented by Chiroptera and the arvicolid Microtus (Allophaiomys) ex gr. ruffoi. A significant change in the taxonomic record occurs in SU 22 and 108, where a clear increase of Equus altidens and Bison (Eobison) degiulii remains indicates shifting towards drier and more open environments and possibly deteriorating local climatic conditions. In general, for all phases, taphonomic evidence suggests that (1) bone accumulation results from carcass transport into the cave system by accident, (2) skeletons were decomposed and partially disarticulated near the cave entrance, (3) the cave environment caused corrosion, desquamation and pitting, and (4) bones were moved within the cave system by water flow, usually for short distances. Pirro 10, Pirro 13 and all karst structures of the Pirro Nord locality during Early Pleistocene were part of a complex interconnected karst system. Dissolution was more effective along the highly fractured core-zones of the Pliocene fault that bounded the "Apricena horst" to the south, where Pirro 10 gallery and Pirro 13 shaft are located. At that time, Pirro 10 was developed within the vadose zone whereas Pirro 13 represented a vertical structure connecting the surface to an underground karst floor. In general, the filling of Pirro 10 indicates fluctuations of the base level: water flow circulation in phreatic and epiphreatic conditions led to the deposition of clastic sediments, whereas flowstones reflect base level lowerings.