| Osorno–Llanquihue Basin | |
| Other Name: | Cuenca de Osorno-Llanquihue |
| Named For: | Osorno and Llanquihue Lake |
| Pushpin Map: | Chile |
| Pushpin Relief: | 1 |
| Coordinates: | -40.7121°N -73.1092°W |
| Location: | Southwestern South America |
| State: | Los Ríos Region Los Lagos Region |
| Onoffshore: | Southern tip is offshore |
| Boundaries: | Chilean Coast Range (W) Andes (E) |
| Seas: | Eastern Pacific Ocean |
| Rivers: | Bueno, Negro, Pilmaiquén, Rahue, Damas |
| Lakes: | Llanquihue, Laguna Las Ortigas and the westernmost portions of Rupanco, Puyehue and Ranco |
| Basin Type: | Forearc basin |
| Orogeny: | Andean |
| Age: | Oligocene-Pleistocene |
| Fields: | Chilean coal |
The Osorno–Llanquihue Basin (Spanish; Castilian: Cuenca Osorno-Llanquihue) is a sedimentary basin located in south-central Chile in the forearc region of the Andes. From north to south the basin spans and area from Catamutún to Reloncaví Sound (40–42° S).[1] The deepest part of the basin lie to the east.[2] The lower levels of the basin are occupied by coal-bearing Cheuquemó Formation among other units while the Miocene-aged marine Santo Domingo Formation makes up much of the upper stratigraphy.[2] The uppermost levels are made of sediments of Quaternary age of glacial, glaci-fluvial, glaci-lacustrine and volcanic character.[3] The thickness of Quaternary sediments is greater to the south reaching almost 1300m (4,300feet) in Puerto Montt.[3] Sediments in the western part of the basin are roughly estimated to have reached during burial and diagenesis.[4]