La Chilca Formation

La Chilca Formation ({{langx|es|Formación La Chilca}}) is a geological formation that crops out in the Precordillera of San Juan Province, Argentina. Rocks of the formation are mostly shale and sandstone that deposited during the Ordovician and Silurian periods. The formation contains a high diversity of graptolite fossils.{{Cite journal |title=New insights on the Silurian graptolite biostratigraphy of the La Chilca Formation, Poblete Norte section, Central Precordillera of San Juan, Argentina: faunal replacement and paleoenvironmental implications |journal=Andean Geology |url=https://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062023000200201&lng=en&nrm=iso&tlng=en |last1=Lopez |first1=Fernando Enrique |issue=2 |volume=50 |last2=Kaufmann |first2=Cintia |doi=10.5027/andgeov50n2-3617 |year=2023|page=201 |doi-access=free }}{{cite journal|last1=Serra|first1=F.|last2=Feltes|first2=N.A.|last3=Mango|first3=M.J.|last4=Henderson|first4=M.A.|last5=Albanesi|first5=G.L.|last6=Ortega|first6=G.D.C.|year=2020|title=Darriwilian (Middle ordovician) conodonts and graptolites from the cerro la chilca section, central precordillera, Argentina|journal=Andean Geology|volume=47|issue=1|pages=125–143|doi=10.5027/andgeoV47n1-3229|doi-access=free}} Graptolite fossil taxa found include:

{{linked species list

|Monograptus priodon|

|Retiolites geinitzianus|

|Stimulograptus sedgwickii|

|Metaclimacograptus asejradi|

|Pseudoplegmatograptus reticulatus|

|Talacastograptus leanzai|

|Coronograptus|

|Pristiograptus|

|Stimulograptus|

|Pristiograptus|

}}