The San Juan Formation (Spanish: Formación San Juan) is a geologic formation in Argentina. The formation comprising limestones, mudstones and marls was deposited in a shallow marine reefal environment and preserves many fossils dating back to the Ordovician period. The formation overlies the La Silla Formation and crops out in the Precordillera of San Juan Province.[1]
| San Juan Formation | |
|---|---|
| Stratigraphic range: Ordovician | |
| Type | Formation |
| Overlies | La Silla Formation |
| Thickness | 300–400 m (980–1,310 ft) |
| Lithology | |
| Primary | Limestone, marl |
| Other | Mudstone |
| Location | |
| Coordinates | 30°18′S 68°12′W / 30.3°S 68.2°W |
| Approximate paleocoordinates | 35°24′S 132°48′W / 35.4°S 132.8°W |
| Region | San Juan Province |
| Country |  Argentina |
| Extent | Precordillera |
| Type section | |
| Named for | San Juan Province |
  San Juan Formation, Argentina (Argentina) | |
The oldest calcareous microfossils, known as calcisphers or calcitarchs, were found in the Early Ordovician (Floian) strata of this formation. Trilobites, gastropods and echinoderm Nuia sibiria have been collected from the same deposits.[2]
See also
editReferences
edit- ^ Sánchez, Teresa M.; Carrera, Marcelo G.; Benedetto, Juan Luis (1996). "Variaciones faunísticas en el techo de la formación San Juan (Ordovícico Temprano, Precordillera Argentina): Significado paleoambiental". Ameghiniana (in Spanish). 33 (2): 185–200.
- ^ Florencia Moreno, Ana Mestre, Susana Heredia (May 2023). "Lower Ordovician calcareous microfossils from the San Juan Formation, Argentina: A new type of calcitarch and its paleoenvironmental implications". Andean Geology. 50 (2): 302—317. doi:10.5027/andgeoV50n2-3469. hdl:11336/223379.
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Further reading
edit- J. L. Benedetto. 2012. Gatosella, a new basal plectambonitoid brachiopod with undercut cardinal process from Middle Ordovician limestones of the Precordillera terrane, Argentina. Journal of Systematic Palaeontology 10(3):435-443
- M. G. Carrera. 2006. The new genus Multispongia (Porifera) from the Lower Ordovician limestones of the Argentine Precordillera. Ameghiniana 43(2):493-498
- M. G. Carrera. 2000. Epizoan-sponge Interactions in the Early Ordovician of the Argentine Precordillera. Palaios 15:261-272
- B. Kröger, M. S. Beresi, and E. Landing. 2007. Early orthoceratoid cephalopods from the Argentine Precordillera (Lower-Middle Ordovician). Journal of Paleontology 81(6):1266-1283
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