San Juan Formation, Argentina

For other uses, see San Juan Formation.

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	30.3°S 68.2°W / -30.3; -68.2
Approximate paleocoordinates	35.4°S 132.8°W / -35.4; -132.8
Region	San Juan Province
Country	Argentina
Extent	Precordillera
Type section
Named for	San Juan Province
San Juan Formation, Argentina (Argentina)

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]

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

• Geological history of the Precordillera terrane
• Mesón Group

References

1. 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.
2. 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.

Further reading

• 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