Gatuncillo Formation

Not to be confused with Gatún Formation.

The Gatuncillo Formation (Tgo)^[1] is a geologic formation in central Panama. The formation is exposed in the Panama Canal Zone and surrounding areas. It preserves fossils dating back to the Middle to Late Eocene period.^[2]

Gatuncillo Formation
Stratigraphic range: Middle-Late Eocene
Type	Formation
Underlies	Caimito, Bohío & Panama Formations
Overlies	Cretaceous basement
Thickness	150–800 m (490–2,620 ft)
Lithology
Primary	Mudstone, siltstone
Other	Limestone, sandstone, conglomerate
Location
Coordinates	9.3°N 79.7°W / 9.3; -79.7
Approximate paleocoordinates	6.8°N 77.3°W / 6.8; -77.3
Region	Panamá Province
Country	Panama
Extent	Panama Basin
Type section
Named for	Gatuncillo River
Named by	Thompson
Year defined	1944
Gatuncillo Formation (Panama)

Description

The Gatuncillo Formation is the oldest sedimentary unit of the Panama Canal Zone, unconformably resting on Cretaceous basement. The formation was defined as Gatuncillo Shale by Thompson in 1944, who named it after the Gatuncillo River. The estimated thickness ranges from 150 to 800 metres (490 to 2,620 ft).^[3]

Though the Gatuncillo consists chiefly of mudstone and siltstone, it includes bentonitic mudstone, sandstone, and limestone, and at the base a conglomerate of variable thickness.^[4]

Fossil content

• Zamia nelliae^[5]
• Podocnemididae indet.^[6]

See also

• List of fossiliferous stratigraphic units in Panama