TRACE ELEMENT CLASSIFICATION DIAGRAMS OF PYROCLASTIC ROCKS FROM THE VOLCANIC DISTRICTS OF CENTRAL ITALY: THE CASE STUDY OF THE ANCIENT ROMAN SHIPS OF PISA*

摘要

Identification of the volcanic material (pozzolan) stored in a Roman ship of the fourth to third century BCE, wrecked in the ancient harbour of Pisa (central Italy), was based on ratios of selected trace elements. The compositions of the major volcanic products erupted by the volcanoes of the Roman province, including the volcanic districts of Latium (Vulsini, Vico, Monti Sabatini and the Alban Hills) and Campania (Roccamonfina, the Phlegraean Fields, Ischia, Procida and Vesuvius) are compared with the pozzolan from the Pisa ship. Superposition of the Zr/Y, Nb/Y and Nb/Zr ratios of the pyroclastic material from the wrecked ship (computed from the published literature) allows correlation with the products of the Onano eruption from the Vulsini Volcanic District. The Vulsini rocks outcrop extensively in a sector drained by the hydrographic network of the Fiora River, which has been a well-developed commercial water trade route since Etruscan times, with a river port and a sea port connected to the important town of Vulci, and, since 273 BCE, part of the larger Roman harbour system of Cosa.