Tephrochronology and chronostratigraphy of the Miocene Chilcatay and Pisco formations (East Pisco Basin, Peru)

Bosio, Giulia; Malinverno, Elisa; Villa, Igor Maria; Di Celma, Claudio; Gariboldi, Karen; Gioncada, Anna; Barberini, Valentina; Urbina, Mario; Bianucci, Giovanni (2020). Tephrochronology and chronostratigraphy of the Miocene Chilcatay and Pisco formations (East Pisco Basin, Peru). Newsletters on stratigraphy, 53(2), pp. 213-247. Schweizerbart science publishers 10.1127/nos/2019/0525

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Strata of Chilcatay and Pisco formations exposed in the Ica Desert (East Pisco Basin, southern Peru) preserve one of the most complete and rich records of Miocene marine vertebrates of the world. Despite its exceptional importance, the chronostratigraphy of these fossil-bearing deposits has been only sporadically studied in the literature until recently. This work presents a detailed reconstruction of the chronostratigraphic framework, achieved by mapping and measuring of seven sections (totaling a height of almost 1000 m) of the Miocene Chilcatay and Pisco formations along the western side of the Ica River. The Chilcatay Formation consists of two allomembers, namely Ct1 and Ct2, bounded at the base by unconformities CE0.1 and CE0.2, respectively. Similarly, the immediately overlying Pisco Formation is divided into allomembers P0, P1, and P2, bounded at the base by unconformities PE0.0, PE0.1 and PE0.2, respectively. The new 39Ar–40Ar results presented here, combined with ages of previous work, provide precise constraints on the age of several stratigraphically referenced volcanic ash layers intercalated in the studied fossil-bearing succession, placing its vertebrate fossil fauna within a refined temporal framework and laying the solid ground for its detailed regional and global comparison. The ages of the allomembers, and thus their associated faunas, can be reliably estimated by the combination of 39Ar–40Ar dating on tephra layers with diatom biostratigraphy. In the study area, two methods are mutually consistent and constrain the deposition of the Chilcatay Formation between 19.2 and 18.0 Ma, that of P1 between 9.5 and 8.6 Ma, and that of P2 between 8.4 and 6.7 Ma. In the absence of direct dating of the P0 allomember, which lacks both preserved tephra suitable for 39Ar–40Ar dating and microfossils, its age can be constrained to the temporal gap between the youngest age available from the underlying Chilcatay strata (18.0 Ma) and the oldest age available from the overlying P1 strata (9.5 Ma).

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Institute of Geological Sciences
08 Faculty of Science > Institute of Geological Sciences > Isotope Geology
08 Faculty of Science > Other Institutions > Emeriti, Faculty of Science

UniBE Contributor:

Villa, Igor Maria


500 Science > 550 Earth sciences & geology
500 Science > 560 Fossils & prehistoric life




Schweizerbart science publishers


[UNSPECIFIED] Ministero dell'Istruzione, Università e Ricerca




Igor Maria Villa-Toscani

Date Deposited:

15 Apr 2021 09:20

Last Modified:

05 Dec 2022 15:50

Publisher DOI:


Web of Science ID:


Uncontrolled Keywords:

tephrochronology, tephrostratigraphy, 39Ar–40Ar dating, biostratigraphy, Miocene, PiscoBasin





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