open access

https://hdl.handle.net/2115/36780

Diatomaceous Sediments Along the Pacific Coastal Areas of South America and their Evaluation

英語

1992-08

Hokkaido University

Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy

23(2)

227-245

The Tertiary diatomaceous sediments in the sequences along the continental margin from Ecuador to Chile are recognized in 4 horizons at the last stage of transgression-regression cycle. (1) The uppermost Eocene Chira Formation in Bayovar of northern Peru was resulted from high-latitude cooling and consequently strengthened oceanic circulation, the Terminal Eocene Event. (2) The Caballas Formation in Cerro Las Salinas of Pisco consists of calcareous siltstone and sandstone with interbedded diatomaceous intervals. It is assigned to the late Oligocene to early Miocene based on diatom biostratigraphy. The diatom assemblages contain many tropic to equatorial species. (3) The significant diatomaceous sediments in Ecuador, Peru, and Chile occur in early middle Miocene at 14 to 12 Ma. They were triggered by intensified coastal upwelling and oceanic circulation from pole to equatorial zone caused by the increased thermal gradients resulted from the permanent establishment of the major East Antarctic ice sheet. Sedimentary facies changes simultaneously both in the Pacific coastal area of South America and in the North Pacific region. (4) The upper Miocene to Pliocene diatomaceous sediments such as Pisco Formation in Pisco-Ice of Peru contain abundantly coastal upwelling-related genus Thalassionema and Chaetoceros, and suggest high productivity conditions linked to coastal upwelling. Tertiary diatomaceous sediments along the Pacific coastal areas of South America are related to the global climatic and oceanic events.

紀要論文

Version of Record

0018-3474