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| Titel |
Sedimentology, paleontology and age of the Ayacara and Lago Ranco formations (south-central Chile, 40º- 42ºS). Tectonic implications. |
| VerfasserIn |
Alfonso Encinas, Patricio Zambrano, Pablo Bernabe, Kenneth Finger, Luis Buatois, Paul Duhart, Victor Valencia, M. Fanning, Francisco Hervé |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036711
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| Zusammenfassung |
| Deep-marine, Mio-Pliocene strata correlative with the Navidad Formation crop out in different areas along the forearc of south-central Chile (~34º-41º) and have also been recognized in boreholes drilles on the continental shelf. However, at Lago Ranco (40ºS) and Ayacara (42º) there are outcrops of marine strata whose age and correlation with these units remain uncertain. These deposits consist of rhythmic successions of sandstone and siltstone representing facies similar to those of the Navidad and correlative formations. These marine successions are known ase the Estratos de Lago Ranco and Ayacara formations. They both crop out in the western Andean Cordillera near the limit with the Intermediate Depression at Lago Ranco and the submerged equivalent of this physiographic unit at Ayacara. There are very few studies carried out on these units and most of them consist on internal reports and unpublished theses.In order to unravel the sedimentary enviroment, age and tectonic history of this area during the Neogene we carried out sedimentological, ichnological and micropaleontological studies. In addition, we carried out U-Pb dating in detrital zircons (LAICPMS and SHRIMP).
Our studies show the presence of sedimentary features and ichnofacies typical of deposition in a deep-marine environment for these units..In agreement, benthic foraminifers (Ciclamina incisa and Siphonodosaria sangrinensis) indicate lower bathial depths (1500 m). U-Pb (LAICPMS and SHRIMP) indicate a maximum depositional age of around 20 Ma for these units. In agreement, the occurrence of the planktic foraminifer species Globorotalia siakensis (P22-N14), Globigerinoides quadrilobatus (N6-Recent) and Globigerinoides sikanus (N8-N9) in strata of the Ayacara Formation suggest an early-middle Miocene age for this unit.
These data indicate that the area corresponding to the western Main Andean Cordillera in south central Chile, was subjeted to major subsidence during the early-middle Miocene. Major subsidence of the margin has been attributed to an important event of subduction erosion that would have removed the underside of the upper continental plate and caused its thinning. |
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