Comment on Palombo et al. The Lost MIS 11c Mammalian Fauna from Via dell’Impero (Rome, Italy). Quaternary 2024, 7, 54

Abstract

Palombo et al. provide a paleontological study of the large mammal remains recovered in the historical center of Rome and attempt to provide age constraints through a geochemical study on the pumice fragments adhering to the faunal remains.

I would like to remark that the authors neglected the two 40Ar/39Ar ages performed on a pumice fallout layer cropping out in Via dell’Impero within the sedimentary deposits in which the faunal remains were excavated, even though these ages have been repeatedly reported on in the literature since the year 1998. Moreover, they did not frame the sediments in which the faunal remains and the pumice they analyzed are embedded within the proper chronostratigraphic context represented by the San Paolo Formation. This short comment aims at proving the geologic context and direct 40Ar/39Ar dating to the investigated faunal assemblage, which may represent a useful integration for the scientific audience interested in the topic discussed by [1].

I read the paper by [1] with great interest, in which the authors provided a paleontological study of the large mammal remains recovered in the historical center of Rome and attempted to provide age constraints through an excellent geochemical study on the pumice fragments adhering to the faunal remains.

However, I was surprised in noting that the authors neglected the two 40Ar/39Ar ages performed on a pumice fallout layer cropping out in Via dell’Impero within the sedimentary deposits in which the faunal remains were excavated, even though these ages have been repeatedly reported on in the literature since the year 1998 [2,3,4,5,6,7,8].

The pumice layer is intercalated within fluvial sandy clay deposits of the San Paolo Formation [9] cropping out on the western slopes of the Capitoline Hill within the Forum of Caesar, along the Via dell’Impero (the modern Via dei Fori Imperiali) (Figure 1a). The dating, published by [2] (sample SPQR-51), gave an original age of 413 ± 11 ka (2σ), later reported in [4], as “Bedded pumice, Tiber River”, and recalculated as 416 ± 11 ka (2σ). This dating, together with others carried out in the Rome area, was used by [3] to formalize the correlation between the local aggradational succession represented by the fining upward sedimentary succession of the San Paolo Formation and the sea-level rise during glacial termination V, leading to the MIS 11c highstand (Figure 1b).

It is frankly incomprehensible that [1] attribute the faunal remains to MIS 11c in the title without mentioning the 40Ar/39Ar age consenting this correlation, nor any of the above-mentioned works.

Also incomprehensibly, the authors do not frame the sediments in which the faunal remains and the pumice they analyzed are embedded within the proper chronostratigraphic context represented by the San Paolo Formation.

The age of the pumice layer cropping out in Via dell’Impero, together with the stratigraphic scheme showing the correlation between the different geological sections hosting the deposits of the San Paolo Formation between Rome and the coast, was republished in [6] Marra et al. (2016) to demonstrate the excellent correlation with the glacial termination V and the subsequent MIS 11c. Before that, the same pumice, resampled by me, was redated at the Rare Gas Laboratory of the Wisconsin University, and an age of 414.8 ± 6.0 ka (2σ) was published in [5] together with the stratigraphic scheme showing its position within the San Paolo Formation outcropping on the eastern flank of the Capitoline Hill.

Finally, the detailed reconstruction of the stratigraphic setting along Via dell’Impero, showing the complex interbedding among three different aggradational successions, including the Santa Cecilia Formation (MIS 15), the Valle Giulia Formation (MIS 13), and the San Palo Formation (MIS 11), was presented in [7] (Figure 1a).

It is unfortunate that, in the face of an extensive bibliography of other works by the writer and all the scholars who have worked in the Roman area, the authors did not precisely cite the works that had a direct relationship with their subject of study. They both neglected to refer the deposits in which the faunal remains were found to the San Paolo Formation and, above all, ignored the existence of a fundamental chronostratigraphic constraint for the dating of the deposits, which would have provided direct support to the excellent chemostratigraphic work performed on the pumice they analyzed.

Finally, the age of 415 ka yielded by the bedded pumice cropping out in Via dell’Impero provided a straightforward correlation with the Vico α eruption, as opposed to the attribution to Vico β (406 ka) based on the interpretation of the geochemical composition of the pumice adhering to the faunal remains, a fact that deserved at least to be discussed.