Paleontological and sedimentological records in Pliocene distal alluvial fan deposits a Cava Toppetti (Todi, central Italy).

The Tiberino Basin is a Plio-Quaternary intermontane basin located in Central Italy (Umbria). This paper deals with the sedimentological, mammalofaunistical, and palynological aspects of the deposits of the Ponte Naja Formation (Late Pliocene), outcropping at Cava Toppetti and with the magnetostratigraphical data from the underlying Fosso Bianco Formation (Middle-Late Pliocene) outcropping at the same site. In the Ponte Naja Formation, sheet flow deposits and paleosols constitute 98% of the sedimentological succession and they alternate with each other cyclically. The plausible short development time of the paleosols made it possible to identify each couplet as a high frequency cyclical depositional sequence. From these sediments scattered, fragmented large and small mammal remains were found. Taking into consideration the inferred high sedimentation rate, the faunal assemblage may be considered as a local fauna which, owing to its taxonomic composition and in particular to the occurrence of the deer Pseudodama cf. P. rhenana can be attributed to the Middle Villafranchian. Paleomagnetic analysis of the underlying Fosso Bianco Formation, is in agreement with the mammal biochronology of the Ponte Naja Formation, restricting chronological attribution to the time interval of the Late Pliocene, more recent than the Reunion event, judging from the deposition of the alluvial fan deposits. All the mammal bones occur in the paleosols, except for a scapula of a rhino which comes from sheet flow deposits. The sheet-flow deposits have a rich and diversified pollen assemblage; paleosols are very poor in pollen grains, whereas Pteridophyta spores (mainly Pteridaceae) are abundant. The occurrence of selective degradation in some paleosols explains the strong difference between their palynomorph content and that of the sheet-flow deposits. Nevertheless, climatic influence cannot be ignored. Throughout the succession a complete climatic cycle and part of the following one can be established should further more detailed analyses support the climatic interpretation.