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| Peladahue Formation | |
|---|---|
| Name | Peladahue Formation |
| Type | Geological formation |
| Period | Paleogene–Neogene |
| Primary lithology | Mudstone, sandstone, conglomerate |
| Other lithology | Tuff, volcaniclastics |
| Region | Los Ríos Region, Los Lagos Region |
| Country | Chile |
| Named for | Peladahue Bay |
| Thickness | up to several hundred metres |
Peladahue Formation The Peladahue Formation is a sedimentary and volcaniclastic succession exposed in the Los Ríos Region, Los Lagos Region of southern Chile, notable for its record of Paleogene–Neogene marine and volcaniclastic deposition proximal to the Andean orogeny. It crops out along the eastern margin of Chiloé Island and the adjacent mainland, preserving lithologies and fossils that link regional tectonics, Nazca Plate subduction dynamics, and Paleogene–Neogene paleogeography of western South America. Research on the unit has connected it to wider sedimentary basins, volcanic arcs, and biogeographic shifts recorded across the Patagonian Andes and Austral Basin.
The formation occupies structural positions related to the forearc and retroarc domains influenced by the Andean orogeny and ongoing convergence of the Nazca Plate beneath the South American Plate. Its exposures are controlled by fault systems correlated with the Liquiñe-Ofqui Fault Zone and secondary structures connecting to the Puyehue-Cordón Caulle volcanic complex and the Chaitén volcanic center. Regional mapping links the unit to the sedimentary architecture of the Austral Basin, interactions with the Magallanes Basin, and proximal inputs from uplifted blocks associated with the Patagonian Batholith.
Stratigraphically, the succession comprises interbedded mudstone, siltstone, heterolithic sandstone, and local conglomerate with intercalations of tuff and volcaniclastic layers attributed to contemporaneous activity of the South Volcanic Zone and scattered vents such as Mocho-Choshuenco. Clast-supported units locally grade into matrix-supported conglomerates, while fine-grained horizons include bioturbated mudstones and organic-rich layers comparable to facies described in the Golfo de Corcovado and Arauco Basin. Tuffaceous horizons bear mineral assemblages consistent with intermediate to acidic volcanic sources related to arc magmatism recorded at the Coastal Cordillera.
Biostratigraphic constraints and radiometric dates indicate deposition across the late Paleogene to early Neogene, with inferred age brackets overlapping the Oligocene–Miocene boundary. Fossil assemblages used for dating include marine invertebrates and microfauna comparable to records from the Marambio Island and Jaramillo sites, while K–Ar and ^40Ar/^39Ar ages from intercalated tuffs provide absolute constraints correlated to regional chronostratigraphic frameworks such as the South American Land Mammal Ages and magnetostratigraphic ties to the Chron C5–Chron C4 intervals.
Fossil contents include marine mollusks, foraminifera, and trace fossils indicative of outer shelf to slope environments; assemblages show affinities with taxa recorded at Seymour Island, Punta Arenas, and the Beagle Channel region. Macrofauna include bivalves and gastropods with genera comparable to collections from Valdivia and Chiloé Island Pleistocene–Neogene sequences, while microfaunal studies have employed benthic and planktonic foraminiferal zonations used elsewhere in the Southern Hemisphere Neogene. Trace fossil suites include ichnotaxa analogous to those described from the Taltal Formation and other Chilean marine units, aiding paleoenvironmental reconstructions and correlation.
Sediment provenance analyses implicate sources from the uplifted Patagonian Andes and erosional inputs from arc-related plutonic and volcanic rocks of the Patagonian Batholith and Chilean Coastal Range. Heavy mineral spectra and detrital zircon U–Pb age populations record contributions matching Grenville-age to Andean magmatic suites, similar to provenance signals recognized in the Magallanes Basin and Neuquén Basin. The tectonic framework reflects forearc basin development during progressive subduction of the Nazca Plate and interactions with plate reorganizations documented at chronostratigraphic boundaries linked to the Andean uplift pulses.
Facies interpretations indicate deposition in a marine shelf to upper slope setting punctuated by episodic volcanic ash fallout and mass-wasting events delivering coarse volcaniclastic debris. Sedimentary structures and ichnofauna point to deposition under varying energy regimes comparable to shelf deposits described from Chilean Patagonia and the Falkland Islands–Malvinas distal margin correlation. Volcaniclastic inputs and tuff layers record contemporaneous activity of the South Volcanic Zone, with pyroclastic dispersal patterns consistent with prevailing paleowind reconstructions tied to Neogene climatic shifts.
The formation hosts tuffaceous horizons and organic-rich intervals that have been evaluated for unconventional hydrocarbon source potential analogous to plays in the Arauco Basin and Magallanes Basin. Aggregates and construction materials have local economic value, while volcaniclastics contain minerals of interest for industrial applications similar to those exploited near the Llaima and Osorno volcanoes. Hydrogeological settings associated with the unit influence groundwater reservoirs utilized by municipalities such as Valdivia and Osorno, and potential geothermal gradients related to nearby volcanic centers inform renewable energy assessments linked to the regional Geothermal energy initiatives.
Category:Geologic formations of Chile Category:Paleogene geology Category:Neogene geology