Chaicayán Group is a group of poorly defined

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

strata found in

Taitao Peninsula The Taitao Peninsula (Spanish: ''Península de Taitao'') is a westward projection of the mainland of Chile, with which it is connected by the narrow Isthmus of Ofqui, over which the natives and early missionaries were accustomed to carry their bo ...

in the west coast of

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

. The most common rock types are siltstone and

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

. Conglomerate occur but is less common. Study of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s and

uranium–lead dating Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routi ...

of detrital zircons indicate a

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

age, at least for the upper sequences. The Chaicayán Group deposited likely as a result of a

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

that drowned much of Patagonia and Central Chile in the

Late Oligocene The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/ Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...

and

. The group is

intruded Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March 2 ...

by porphyritic stocks and sills of

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Geology of Chile The geology of Chile is a characterized by processes linked to subduction such as volcanism, earthquakes and orogeny. The buildings blocks of Chile's geology assembled during the Paleozoic Era. Chile was by then the southwestern margin of the su ...

Ayacara Formation The Ayacara Formation is a sedimentary formation made up of interbedded sand and siltstone cropping out around Hornopirén and Ayacara Peninsula in western Los Lagos Region, Chile. Less common rocks are tuff and conglomerate. The formation dates ...

La Cascada Formation La Cascada Formation a sedimentary formation near Futaleufú in the western Patagonian Andes of southern Chile. Lithologies vary from sandstone, siltstone and conglomerate. The sediment that now forms the rock deposited during the Oligocene and ...

Puduhuapi Formation The Puduhuapi Formation is a sedimentary formation whose only known outcrops are on Puduhuapi Island of the Chiloé Archipelago, west of Chaitén in western Patagonia, Chile. Lithologies vary from sandstone and siltstone to conglomerate. The sed ...

Vargas Formation The Vargas Formation is a sedimentary formation on the left bank of Palena River in the western Patagonian Andes of southern Chile. The formation is made of black shale and sandstone that deposited in the Late Oligocene or Early Miocene epoch some ...

References

{{Geology of Chile Geologic groups of South America Geologic formations of Chile Miocene Series of South America Neogene Chile Sandstone formations Siltstone formations Geology of Aysén Region Taitao Peninsula