Santa Juana Formation
Stratigraphic range: Carnian ~235–222 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Sub-units	Talcamávida-Gomero, Unihue & Quilacoya Members
Overlies	Coastal Batholith of central Chile
Thickness	Unknown
Lithology
Primary	Conglomerate, sandstone, siltstone
Other	Arkosic sandstone, mudstone, volcanic rock, anthracite
Location
Coordinates	37°12′S 73°00′W / 37.2°S 73.0°W / -37.2; -73.0
Approximate paleocoordinates	53°48′S 39°54′W / 53.8°S 39.9°W / -53.8; -39.9
Region	Bío Bío Region
Country	Chile
Type section
Named for	Santa Juana
Named by	Ferraris
Year defined	1981
Santa Juana Formation (Chile)

Santa Juana Formation a Late Triassic (Carnian stage) sedimentary rock formation near Santa Juana in the lower course of the Biobío River in south-central Chile.^[1] Lithologies range from conglomerate sandstone, arkosic sandstone, siltstone and mudstone.^[2]

Description

The sediments that consolidate into the rocks of the formation deposited in alluvial, fluvial, lacustrine and playa lake environment. Overall, the formation is rich in plant fossils.^[2]

The formation was deposited over the rocks of the Coastal Batholith of central Chile in a sedimentary basin that formed along the Gastre Fault. It has been posited that the basin developed as a rift during the early break-up of Gondwana in the Triassic.^[2]

Fossil content

The following fossils have been reported from the formation:^[1]

Flora

Insects

Branchiopoda

• Polygrapta troncosoi^[4]
• Menucoestheria terneraensis^[4]