Farellones Formation

Farellones Formation Stratigraphic range: Miocene
Sub-units	Upper member Lower member
Overlies	Abanico Formation
Thickness	>3,000 m (9,800 ft)
Lithology
Primary	Rhyolitic ignimbrite, rhyolitic tuff, andesitic lava, basaltic lava
Other	Breccia
Location
Region	Valparaíso Region Santiago Metropolitan Region O'Higgins Region
Country	Chile
Type section
Named for	Farellones
Named by	Carlos Klohn (1960)

Farellones Formation (Spanish: Formación Farellones) is a geological formation of Miocene age in the Andes of Central Chile up almost entirely of volcanic and volcaniclastic rocks. At some location reaches thicknesses in excess of 3,000 metres (9,800 ft). It overlies the Oligo–Miocene Abanico Formation across a diachronous unconformity. The best exposure of the formation is said to be at the ski resort of Farellones east of Santiago. From the latitude of Santiago to Rancagua the base of the formation becomes progressively younger and outcrops more scarce. In the mentioned latitudes the formation has been deformed by a diachronous tectonic inversion that produced reverse faults and destroyed the extensional sedimentary basin were the rocks deposited and contributed to the uplift of the Andes in the Late Miocene.

Rivano and co-workers define two sub-units of the formation: a lower member made up of rather fresh rhyolitic ignimbrite and tuff, and an upper member made up of lavas of basaltic and andesitic composition. The volcanic rocks of Farellones Formation have mostly a calc-alkaline character contrasting with the mostly tholeiitic Abanico Formation.

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