The East Pisco Basin of southern Peru is renowned worldwide for its exceptionally well-pre- served marine vertebrate fossils, recovered from sedimentary successions spanning the middle Eocene to the early Pliocene. Although the lower Eocene–Oligocene deposits of the Otuma Formation have been exten- sively investigated, the uppermost Eocene to lower Oligocene strata remain comparatively understudied. Notably, these strata encompass the Eocene–Oligocene transition (~ 34 Ma), a critical interval characterized by profound global climatic and ecological changes. This study presents an integrated biostratigraphic analy- sis of the Otuma Formation based on calcareous nannofossils, diatoms, and silicoflagellates. The investigated deposits were laid down in two distinct sub-basins: an eastern, land-proximal sub-basin at Cerro Tiza and a western, more distal sub-basin at Quebrada Perdida (Media Luna). In addition, 39Ar–40Ar dating of a vol- canic ash layer provides an independent chronological tie point for the age model at Cerro Tiza. At both lo- calities, the Otuma Formation comprises calcareous siltstones and diatomite layers deposited from the Pria- bonian (37.71–33.90 Ma) to the Rupelian (33.90–27.82 Ma). Sedimentation rates derived from the age model average 75.5 m/My at Cerro Tiza and 8.1 m/My at Media Luna. A progressive shift from calcareous nannofossil-dominated assemblages to diatom-dominated assemblages throughout the sections reflects a general trend toward cooler conditions and increased nutrient availability, consistent with global patterns dur- ing this interval. However, diatom assemblages do not indicate the establishment of permanently eutrophic conditions. Differences in microfossil assemblages, together with an order-of-magnitude contrast in sedimen- tation rates between Cerro Tiza and Media Luna, point to markedly distinct palaeoenvironmental conditions in the two sub-basins. These differences are interpreted as the result of tectonic controls and contrasting posi- tions within the Peruvian forearc system.
The stratigraphic record of the Eocene–Oligocene transition in the East Pisco Basin (Peru): a phytoplankton perspective
Di Celma C.;Mazzoli S.;
In corso di stampa
Abstract
The East Pisco Basin of southern Peru is renowned worldwide for its exceptionally well-pre- served marine vertebrate fossils, recovered from sedimentary successions spanning the middle Eocene to the early Pliocene. Although the lower Eocene–Oligocene deposits of the Otuma Formation have been exten- sively investigated, the uppermost Eocene to lower Oligocene strata remain comparatively understudied. Notably, these strata encompass the Eocene–Oligocene transition (~ 34 Ma), a critical interval characterized by profound global climatic and ecological changes. This study presents an integrated biostratigraphic analy- sis of the Otuma Formation based on calcareous nannofossils, diatoms, and silicoflagellates. The investigated deposits were laid down in two distinct sub-basins: an eastern, land-proximal sub-basin at Cerro Tiza and a western, more distal sub-basin at Quebrada Perdida (Media Luna). In addition, 39Ar–40Ar dating of a vol- canic ash layer provides an independent chronological tie point for the age model at Cerro Tiza. At both lo- calities, the Otuma Formation comprises calcareous siltstones and diatomite layers deposited from the Pria- bonian (37.71–33.90 Ma) to the Rupelian (33.90–27.82 Ma). Sedimentation rates derived from the age model average 75.5 m/My at Cerro Tiza and 8.1 m/My at Media Luna. A progressive shift from calcareous nannofossil-dominated assemblages to diatom-dominated assemblages throughout the sections reflects a general trend toward cooler conditions and increased nutrient availability, consistent with global patterns dur- ing this interval. However, diatom assemblages do not indicate the establishment of permanently eutrophic conditions. Differences in microfossil assemblages, together with an order-of-magnitude contrast in sedimen- tation rates between Cerro Tiza and Media Luna, point to markedly distinct palaeoenvironmental conditions in the two sub-basins. These differences are interpreted as the result of tectonic controls and contrasting posi- tions within the Peruvian forearc system.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
