The Eocene sediment successions of the East Pisco Basin (southern Peru) host an exceptionally rich and well-preserved assemblage of vertebrate fossils. However, due to the dearth of geochronological and biostratigraphic controls as well as of stratigraphic correlations, our understanding of these rocks and their fossil content remains elusive. This paper provides a comprehensive calcareous nannofossil, diatom, and silicoflagellate biostratigraphic framework for the Eocene strata exposed at four localities along the Ica River Valley, permitting a robust chronological calibration of the marine vertebrate fauna entombed therein and a better definition of important appearance/ extinction events. The Paracas Formation, deposited directly on top of the Proterozoic and Paleozoic rocks of the crystalline basement, is formed by a siliciclastic- bioclastic gravel-sized deposit (Los Choros member) and calcareous-terrigenous siltstone (Yumaque member) that was deposited from the Lutetian (47.8-41.2 Ma) through the Bartonian (41.2-37.7 Ma) to the early Priabonian (37.7-33.9 Ma). The unconformably overlying Otuma Formation consists of a basal sand, followed by calcareous siltstone intercalated by diatomite layers towards the top. In the study area, the Otuma Formation is Priabonian in age and is truncated at the top by an unconformity at the base of the overlying Miocene Chilcatay Formation. Due to the angular nature of the unconformity, the upper Otuma strata reach the Oligocene elsewhere. Average sedimentation rates range from 17 to 24 m/My in the Yumaque member of the Paracas Formation and increase to 147-170 m/My in the Otuma Formation. The microfossil assemblages witness a coastal setting with warm-temperate conditions for the Paracas Formation that become slightly cooler (though still temperate) in the upper Otuma Formation. Diatomaceous layers in the upper Otuma Formation indicate an overall increase in nutrient availability, which could reflect the global reorganization of ocean currents at the Eocene-Oligocene transition. However, the taxonomic composition of the diatom assemblage suggests seasonal rather than persistent upwelling conditions.

(Bio)stratigraphic overview and paleoclimatic-paleoceanographic implications of the middle-upper Eocene deposits from the Ica River Valley (East Pisco Basin, Peru)

Di Celma C.;Pierantoni P. P.;
2021-01-01

Abstract

The Eocene sediment successions of the East Pisco Basin (southern Peru) host an exceptionally rich and well-preserved assemblage of vertebrate fossils. However, due to the dearth of geochronological and biostratigraphic controls as well as of stratigraphic correlations, our understanding of these rocks and their fossil content remains elusive. This paper provides a comprehensive calcareous nannofossil, diatom, and silicoflagellate biostratigraphic framework for the Eocene strata exposed at four localities along the Ica River Valley, permitting a robust chronological calibration of the marine vertebrate fauna entombed therein and a better definition of important appearance/ extinction events. The Paracas Formation, deposited directly on top of the Proterozoic and Paleozoic rocks of the crystalline basement, is formed by a siliciclastic- bioclastic gravel-sized deposit (Los Choros member) and calcareous-terrigenous siltstone (Yumaque member) that was deposited from the Lutetian (47.8-41.2 Ma) through the Bartonian (41.2-37.7 Ma) to the early Priabonian (37.7-33.9 Ma). The unconformably overlying Otuma Formation consists of a basal sand, followed by calcareous siltstone intercalated by diatomite layers towards the top. In the study area, the Otuma Formation is Priabonian in age and is truncated at the top by an unconformity at the base of the overlying Miocene Chilcatay Formation. Due to the angular nature of the unconformity, the upper Otuma strata reach the Oligocene elsewhere. Average sedimentation rates range from 17 to 24 m/My in the Yumaque member of the Paracas Formation and increase to 147-170 m/My in the Otuma Formation. The microfossil assemblages witness a coastal setting with warm-temperate conditions for the Paracas Formation that become slightly cooler (though still temperate) in the upper Otuma Formation. Diatomaceous layers in the upper Otuma Formation indicate an overall increase in nutrient availability, which could reflect the global reorganization of ocean currents at the Eocene-Oligocene transition. However, the taxonomic composition of the diatom assemblage suggests seasonal rather than persistent upwelling conditions.
2021
File in questo prodotto:
File Dimensione Formato  
PDFsam_PALAEO-D-21-00018_R2.pdf

accesso aperto

Descrizione: Articolo principale
Tipologia: Documento in Post-print
Licenza: DRM non definito
Dimensione 3.56 MB
Formato Adobe PDF
3.56 MB Adobe PDF Visualizza/Apri
Malinverno et al 2021 Supp 1_Fig A1.xlsx

accesso aperto

Descrizione: Supplementary Material Figure A.1
Tipologia: Altro materiale allegato
Licenza: DRM non definito
Dimensione 13.51 kB
Formato Microsoft Excel XML
13.51 kB Microsoft Excel XML Visualizza/Apri
Malinverno et al 2021 Supp 2_Fig A2.xlsx

accesso aperto

Descrizione: Supplementary Material Figure A.2
Tipologia: Altro materiale allegato
Licenza: DRM non definito
Dimensione 11.72 kB
Formato Microsoft Excel XML
11.72 kB Microsoft Excel XML Visualizza/Apri
Malinverno et al 2021 Supp 3_Fig A3.xlsx

accesso aperto

Descrizione: Supplementary Material Figure A.3
Tipologia: Altro materiale allegato
Licenza: DRM non definito
Dimensione 13.51 kB
Formato Microsoft Excel XML
13.51 kB Microsoft Excel XML Visualizza/Apri
(Bio)stratigraphic overview and paleoclimatic-paleoceanographic implications of the middle-upper Eocene deposits from the Ica River Valley (East Pisco Basin, Peru)_compressed (1).pdf

solo gestori di archivio

Tipologia: Versione Editoriale
Licenza: NON PUBBLICO - Accesso privato/ristretto
Dimensione 1.28 MB
Formato Adobe PDF
1.28 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11581/452648
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 8
  • ???jsp.display-item.citation.isi??? 6
social impact