Micropaleontological analysis of the “Pietra di Vicenza” from the Cathedral and the Ghirlandina Tower of Modena (N Italy): a tool for provenance recognition.

A comprehensive survey of the stones covering the external walls of the Cathedral and the Ghirlandina Tower in Modena, both built between the XI and the XIV century, has been recently completed as a part of the scientific background needed for the restoration works, which are still in progress.The map shows the presence, among others, of numerous slabs of the stone commercially known as Pietra di Vicenza, which includes Paleogene limestones coming from the Lessini-Berici area (Veneto, northern Italy). Since the Middle Age, re-use of stones coming from the despoliation of Roman monuments is attested by documents, we can hypothesize that at least part of the Pietra di Vicenza was originally quarried out in Roman times. On the other hand, the presence of different varieties of Pietra di Vicenza suggests that it has been used also for later restorations.The micropaleontological analysis of the fossil content has been used as a powerful tool to identify the provenance of the stones, allowing to distinguish different ages and depositional paleoenvironments.The observation of thin sections allowed to recognize at least 4 different microfacies.The microfacies 1 and 2 have been dated to the Early Oligocene, according to the presence of the index fossils Nummulites cf. fichteli, N. cf. vascus, Asterigerina rotula haeringensis, and Praerhapydionina delicata. Facies 1 contains abundant miliolids and articulate coralline algae, whereas facies 2 is dominated by crustose coralline fragments, with less miliolids. The depositional paleoenvironment was very shallow, probably in the back-reef, with microfacies 2 slightly more distal than microfacies 1.The microfacies 3 contains quite frequent nummulites (some of them large-sized), abundant crustose coralline algae (rhodoliths are common), and some large fossils such as bivalves, echinoids, corals, etc. Its age is not always the same, varying from the Middle Eocene (with Nummulites cf. ptukhiani) to the Late Eocene (with Nummulites cf. fabianii); Early Oligocene index fossils have also been identified (Nummulites cf. vascus, Asterigerina rotula haeringensis). These characteristics indicate a “shoal” facies in the middle-outer platform/ramp.The microfacies 4 is dominated by Discocyclina, Orbitoclypeus, Asterocyclina, rather large Nummulites, and some planktonic foraminifera. The age is limited to the Eocene but no index fossils were recognized. The paleoenvironment could be in the outer platform/ramp, near the transition to the basin.The examination of ornamental stones coming from archaeological excavations in the Modena area allowed to determine that most of the Pietra di Vicenza quarried by the Romans belongs to microfacies 1 and rarely to n. 2 or 3. After fieldwork and sampling in the Lessini and Berici Mts., we recognized the microfacies 1 and 2 only in the basal levels of a quarry active since pre-Roman times near the village of Costozza (Berici Mts.).The microfacies 3 has been found in several localities both of Lessini and Berici Mts., usually in quarries only recently exploited. The microfacies 4 is very similar to the commercial Pietra di Nanto, presently extracted near the homonymous village in the Berici Mts. The historical documentation attests its use for restorations of the Cathedral only during the restoration work of 1898-1903.