Along the Peruvian coast, the sedimentary succession of the East Pisco Basin is exposed in the Ica Desert. At Cerro Los Quesos, laterally continuous dolomite layers characterise the diatomaceous sediments of the P2 sequence of the Miocene Pisco Formation, where a large number of marine vertebrates are exceptionally preserved, many enclosed in dolomite nodules. In this work, cemented layers from this sequence were described and sampled for petrographic, chemical, microscopic and isotopic analyses. Dolomite occurs in continuous 10–50 cm thick well cemented layers, formed by sediment of different nature: biogenic, terrigenous, volcanoclastic, and phosphatic. The underlying sediments exhibit a yellow layer with sparse dolomite crystals, a black layer with abundant Mn-oxides, and a reddish layer rich in Fe-oxides, indicating redox-related fronts. Two generations of dolomite can be recognised: an early diagenetic microcrystalline one, and a sparry one, filling the large cavities. As observed in both thin sections and on broken surfaces, microcrystalline dolomite also fills the inner spaces of the diatom areolae replicating their finest ultrastructure, such as foramina and cribra and replace calcite shells of foraminifera. δ18O and δ13C values from the microcrystalline dolomite of two layers, selected based on the absence of other carbonate phases (e.g. calcite) and the lack of sparry cement, are in agreement with those reported for the Peru margin and fall in the fields of either sulphate-reduction or methanogenesis. All the data point to dolomite precipitation associated with low-temperature early diagenesis that typically occurs in upwelling settings, where high surface water productivity is responsible for high rates of organic carbon flux to the sea bottom and for the cyclical oxygen depletion at the bottom. Such conditions also promote high abundances of marine vertebrates and the exceptional preservation of their skeletons in the sediments.

Malinverno, E., Bosio, G., Gioncada, A., Cimo, R., Ando, S., Mariani, L., et al. (2023). Laterally-continuous dolomite layers of the Miocene Pisco Formation (East Pisco Basin, Peru): A window into past cyclical changes of the diagenetic environment. MARINE AND PETROLEUM GEOLOGY, 147(January 2023) [10.1016/j.marpetgeo.2022.105977].

Laterally-continuous dolomite layers of the Miocene Pisco Formation (East Pisco Basin, Peru): A window into past cyclical changes of the diagenetic environment

Malinverno E.
Primo
;
Bosio G.;Sergio Ando;Mariani L.;Coletti G.;Galimberti L.;
2023

Abstract

Along the Peruvian coast, the sedimentary succession of the East Pisco Basin is exposed in the Ica Desert. At Cerro Los Quesos, laterally continuous dolomite layers characterise the diatomaceous sediments of the P2 sequence of the Miocene Pisco Formation, where a large number of marine vertebrates are exceptionally preserved, many enclosed in dolomite nodules. In this work, cemented layers from this sequence were described and sampled for petrographic, chemical, microscopic and isotopic analyses. Dolomite occurs in continuous 10–50 cm thick well cemented layers, formed by sediment of different nature: biogenic, terrigenous, volcanoclastic, and phosphatic. The underlying sediments exhibit a yellow layer with sparse dolomite crystals, a black layer with abundant Mn-oxides, and a reddish layer rich in Fe-oxides, indicating redox-related fronts. Two generations of dolomite can be recognised: an early diagenetic microcrystalline one, and a sparry one, filling the large cavities. As observed in both thin sections and on broken surfaces, microcrystalline dolomite also fills the inner spaces of the diatom areolae replicating their finest ultrastructure, such as foramina and cribra and replace calcite shells of foraminifera. δ18O and δ13C values from the microcrystalline dolomite of two layers, selected based on the absence of other carbonate phases (e.g. calcite) and the lack of sparry cement, are in agreement with those reported for the Peru margin and fall in the fields of either sulphate-reduction or methanogenesis. All the data point to dolomite precipitation associated with low-temperature early diagenesis that typically occurs in upwelling settings, where high surface water productivity is responsible for high rates of organic carbon flux to the sea bottom and for the cyclical oxygen depletion at the bottom. Such conditions also promote high abundances of marine vertebrates and the exceptional preservation of their skeletons in the sediments.
Articolo in rivista - Articolo scientifico
Dolomite; Early diagenesis; East Pisco Basin; Stable isotopes; XRD analyses;
English
19-ott-2022
2023
147
January 2023
105977
reserved
Malinverno, E., Bosio, G., Gioncada, A., Cimo, R., Ando, S., Mariani, L., et al. (2023). Laterally-continuous dolomite layers of the Miocene Pisco Formation (East Pisco Basin, Peru): A window into past cyclical changes of the diagenetic environment. MARINE AND PETROLEUM GEOLOGY, 147(January 2023) [10.1016/j.marpetgeo.2022.105977].
File in questo prodotto:
File Dimensione Formato  
Malinverno-2023-Marine Petroleum Geology-VoR.pdf

Solo gestori archivio

Descrizione: Research article
Tipologia di allegato: Publisher’s Version (Version of Record, VoR)
Licenza: Tutti i diritti riservati
Dimensione 1.93 MB
Formato Adobe PDF
1.93 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/10281/396572
Citazioni
  • Scopus 3
  • ???jsp.display-item.citation.isi??? 1
Social impact