Jurassic marine sediments buried under Patagonian plateau contain major oil reserves. Seismic imaging shows ancient submarine fans that channeled organic-rich sediments into traps.
A Sea Below the Steppe
Beneath the semi-arid plains of Patagonia lies a vast petroleum system, its origins tracing back to the Jurassic period. The Austral Basin, a 200,000 square kilometer depression, formed as the supercontinent Gondwana began to fracture. This initial rifting created a series of deep valleys and half-grabens. As sea levels rose, the Atlantic Ocean flooded these newly formed troughs, creating a restricted marine environment.
In these oxygen-poor waters, enormous quantities of organic material, mostly algae and bacteria, accumulated on the seafloor. Over millions of years these deposits became the Palermo Aike Formation, the primary source rock for the basin's hydrocarbons. This formation consists of black shales with total organic carbon content between 0.6% and 2.5%, primarily containing Type II kerogen, which generates both oil and gas. As subsequent layers of sediment buried these shales, increasing heat and pressure cooked the organic matter transforming it into petroleum. The "oil window," where generation begins, is typically reached at depths between 2,200 and 2,500 meters.
Trapped in Ancient Valleys
The petroleum migrated from the Palermo Aike source rock into an overlying sandstone layer known as the Springhill Formation. This Early Cretaceous unit is the basin's primary conventional reservoir. The sandstones of the Springhill Formation were deposited in a complex network of estuaries and submarine channels that filled the incised valleys created during the earlier rifting phase. This pre-existing topography created perfect conditions for trapping oil and gas.
The hydrocarbons are held in place by both structural and stratigraphic traps. The ancient valleys funneled migrating oil into porous sandstone bodies, which were then sealed by overlying, impermeable marine shales of the Río Mayer Formation. Faults created during the later transition to a foreland basin, caused by the rise of the Andes mountains, also formed barriers that stopped the oil's upward movement. Geologists use 3D seismic imaging to map these deeply buried valley systems, some of which are located up to 3,200 meters below the surface. This technology allows them to pinpoint potential reservoirs before drilling. Hydrocarbon production in the basin dates back to 1945, and estimates for the Palermo Aike shale alone suggest recoverable resources could exceed 10 billion barrels of oil equivalent.
💡Fun Facts
The Austral Basin is also known as the Magallanes Basin, particularly in the parts that extend into neighboring Chile.
The main source rock, the Palermo Aike Formation, is considered the southernmost effective petroleum source rock in the world.
The basin's geology is directly linked to the opening of the South Atlantic Ocean during the breakup of Gondwana.
The Springhill Formation, the primary reservoir, was named after a discovery well drilled in Chile, not Argentina.
This is a widespread industrial region, not a specific tourist site. Public roads pass through the area, but oil field facilities are not accessible to the public.
Admission
Free to travel through the region on public roads.
Accessibility
The terrain is typical Patagonian steppe—vast, semi-arid, and subject to strong winds and rapidly changing weather. Many roads outside of main towns are unpaved.