Llanquihue glaciation

View of the Chilean Lake District where the Llanquihue glaciation has been defined.

The last glacial period and its associated glaciation is known in southern Chile as the Llanquihue glaciation (Spanish: Glaciación de Llanquihue).[1] In its type area west of Llanquihue Lake where various drifts or end moraine systems belonging to the Llanquihue glaciation have been identified.[2] The preceding interglacial is known as the Valdivia interglacial after its type locality of Valdivia.[3]

Development of the glaciation

Palynological analysis in Chiloé reveal the existence of at least three warm periods, or interstadials, during the Llanquihue glaciation. One interstadial begun 57,000 years before present (yrs BP) and ended no later than 49.000 yrs BP, another that begun 50,000 yrs BP and ended no later than 47,000 yrs BP and a third one from 45,000 to 35,000 yrs BP.[4] During the interstadials of the glaciation the conifers Fitzroya and Pilgerodendron had much greater geographical extent than at present growing during that time in the Chilean Central Valley at latitudes between 41° and 43° S.[4] There is evidence for five westward advances of glacier lobes of the Patagonian Ice Sheet. These advances occurred at ~33,600, ~30,800, ~26,900, ~26,000 and 17,700–18,100 years before present.[5]

The ice-free areas of Patagonia east of the Andes formed periglacial features like ice wedges, patterned ground, pingos, rock glaciers, palsas, soil cryoturbation, solifluction deposits during the Llanquihue glaciation.[6][upper-alpha 1]

The coast of Chile north of 42° S and much of the Chilean Coast Range remained glacier-free and free from periglaciation though the glaciation. These regions, and in particular Cordillera de Nahuelbuta, are believed to have served as refugia for Valdivian temperate rainforest.[7]

Last Glacial Maximum

During the Last Glacial Maximum valley glaciers merged and descended from the Andes occupying lacustrine and marine basins where they spread out forming large piedmont glacier lobes. Glaciers extended about 7 km west of the modern Llanquihue Lake but not more than 2 to 3 km south of it. Nahuel Huapi Lake in Argentina was also glaciated by the same time.[8] Despite glacier advances much of the area west of Llanquihue Lake was still ice-free during the Last Glacial Maximum and had sparsely distributed vegetation dominated by Nothofagus species.[9] Valdivian temperate rainforest proper was reduced to scattered remnants in the western side of the Andes.[9]

Little is known about the extent of glaciers during Last Glacial Maximum north of the Chilean Lake District. To the north, in the dry Andes of Central and northern Chile the Last Glacial Maximum is associated with increased humidity and the advance of some glaciers. Further north in more arid regions some high mountains (>5000) have remained ice-free trough the whole Quaternary period.[10]

Deglaciation

Rapid warming started 17,800 years before present leading to interglacial temperatures within 1000 years accompanied by the retreat of glaciers and the rapid colonization of Nothofagus dombeyi and the subsequent development of Valdivian temperate rainforest in the formerly glaciated area. Magellanic moorland species that had thrived in unglaciated areas during the 1,500 year long cold interval that preceded deglaciation were largely wiped out as conditions changed from hyper-humid to humid.[5] The deglaciation pulse that begun in 17,800 was paralleled by similar events in New Zealand.[5] The warming that caused and followed the deglaciation is though to have caused conifer forest to lose ground to other vegetation types over much of the lowlands and obtaining its modern discontinuous distribution in the cool heights of the Chilean Coast Range and the Andes.[4]

Notes

  1. ↑ However, not all these reported features have been verified.[6]

References

  1. ↑ Heusser, C.J. (1974). "Vegetation and climate of the southern Chilean Lake District during and since the last interglaciation". Quaternary Research. 4 (3): 290–315.
  2. ↑ Porter, Stephen C. (1981). "Pleistocene glaciation in the southern Lake District of Chile". Quaternary Research. 16 (3): 263–292. doi:10.1016/0033-5894(81)90013-2.
  3. ↑ Astorga, G. and Pino, M. (2011). "Fossil leaves from the last interglacial in Central-Southern Chile: Inferences regarding the vegetation and paleoclimate". Geologica Acta. 9 (1): 45–54.
  4. 1 2 3 Villagrán, Carolina; León, Ana; Roig, Fidel A. (2004). "Paleodistribución del alerce y ciprés de las Guaitecas durante períodos interestadiales de la Glaciación Llanquihue: provincias de Llanquihue y Chiloé, Región de Los Lagos, Chile". Revista geológica de Chile (in Spanish). 31 (1): 133–151.
  5. 1 2 3 Moreno, Patricio I.; Denton, Geoge H.; Moreno, Hugo; Lowell, Thomas V.; Putnam, Aaron E.; Kaplan, Michael R. (2015). "Radiocarbon chronology of the last glacial maximum and its termination in northwestern Patagonia". Quaternary Science Reviews. 122: 233–249.
  6. 1 2 Trombotto Liaudat, Darío (2008). "Geocryology of Southern South America". In Rabassa, J. The Late Cenozoic of Patagonia and Tierra del Fuego. pp. 255–268. ISBN 978-0-444-52954-1.
  7. ↑ Villagrán, Carolina; Hinojosa, Luis Felipe (2005). "Esquema biogeográfico de Chile". In Llorente Bousquests, Jorge; Morrone, Juan J. Regionalización Biogeográfica en Iberoámeríca y tópicos afines (in Spanish). Mexico: Ediciones de la Universidad Nacional Autónoma de México, Jiménez Editores.
  8. ↑ Hausser, C.J. (2004). Ice Age Southern Andes. pp. 25–27.
  9. 1 2 Adams, Jonathan. "South America during the last 150,000 years".
  10. ↑ Harrison, Stephan (2004). "The Pleistocene glaciations of Chile". In Ehlers, J.; Gibbard, P.L. Quaternary Glaciations - Extent and Chronology: Part III: South America, Asia, Africa, Australasia, Antarctica. pp. 91–97.
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