A note on diatom stratigraphic markers in upper Miocene sediments of the Pisco Formation, Peru, and description of Delphineis urbinai sp. nov.

Abstract

With the aim of preparing the ground for a comprehensive stratigraphic work on the Mio-Pliocene Pisco Formation, Peru, diatom marker species from the upper Miocene sites of Cerro Colorado (CC) and Cerro Los Quesos (CLQ) were investigated. Samples were collected along two composite stratigraphic sections and prepared for microscope analysis. Marker species are listed and described; their ranges and taxonomy are discussed in the light of recent works on Pacific diatom biostratigraphy and compared to findings in previous works from the 1980s on the Pisco Formation. Subsequently, marker species ranges and taxonomy have been significantly revised, suggesting that age-attributions based on sediments of the Pisco Formation should also be corrected. Examples are: (1) Koizumia tatsunokuchiensis, which was known as a Pliocene marker, but is now known to first appear in the late Miocene; (2) Thalassiosira cf. flexuosa, which was reported in early works on the Pisco Formation biostratigraphy as Coscinodiscus plicatus; (3) Thalassiora antiqua, which is found both at CC and CLQ, although typical of cold waters. The need to build a specific diatom biozonation for this Pacific region is thus highlighted. In addition, a new species, Delphineis urbinai, is described. This species is not a biostratigraphic marker but its sporadic presence may help with the correlation of stratigraphic sections within the Pisco Formation.

Keywords:

• Pisco Formation
• upper Miocene
• Pacific diatom biostratigraphy
• stratigraphic markers
• Delphineis urbinai

Acknowledgements

I would like to thank Professor Andrey Gladenkov and Professor John Barron for fruitful discussions and suggestions on Tropical Pacific Diatom Biostratigraphy. I also would like to thank Professor John Barron, an anonymous Reviewer, Professor Masao Iwai and Dr Eileen Cox for the valuable help they gave me in improving the manuscript. My thankfulness goes to Dr Elisa Malinverno and Professor Igor Villa for encouraging me in writing this short note; to Dr Caludio Di Celma for his inestimable help in revising the manuscript; to Dr Giovanni Bianucci, Dr Anna Gioncada, Dr Claudio Di Celma and Dr Elisa Malinverno for supporting me and for their precious work and help in the field; to Dr Roberto Albani and Mr Franco Colarieti for their help with LM, SEM, stubs preparation and, above all, for their kindness and helpfulness; to Dr Salvatore Iaccarino for his constant support.

Additional information

Funding

This research was supported by the Italian Ministero dell'Istruzione dell'Università e della Ricerca under PRIN Project 2012YJSBMK to Dr G. Bianucci; and by National Geographic Society Committee on Research Exploration under grant 9410–13 to Dr G. Bianucci.