Purilactis Group

Purilactis Group (Spanish: Grupo Purilactis) is a heterogeneous group of volcanic, volcano-sedimentary and formations of Cretaceous to Eocene age in Salar de Atacama basin, northern Chile.[1] The group has a stratigraphic thickness of more than 6000 m.[1] The group overlies basement rocks of Late Paleozoic age.[1][2] The north-south El Bordo Escarpment of Cordillera Domeyko contain the main outcrops of the group.[1] The group has been difficult to date in detail since it hosts few fossils and dateable minerals.[1] The sediments of the group deposited when volcanism in the area was mainly occurring to the west of it, rather than to east as in the present-day. In geological terms this qualifies the basin as a back-arc basin.[2]

Purilactis Group
Stratigraphic range: Upper Cretaceous–Upper Eocene
TypeGeological group
Unit ofSalar de Atacama basin
Thickness>6,000 m (20,000 ft)[1]
Lithology
PrimaryConglomerate, basaltic andesite lava, rhyolitic ignimbrite
OtherGypsum
Location
Coordinates22°45′56″S 68°27′47″W
RegionAntofagasta Region
CountryChile
Purilactis Group is located in Chile
Purilactis Group
Purilactis Group (Chile)

From top to bottom, the main units (formations) of the group outlined by Mpodozis and co-worders in 1999 are:[1]

  • Cerro Puntiagudo Strata
  • Loma Amarilla Strata
  • "Orange" Unit
  • Cerro Totola Strata
  • Barros Arana Strata
  • Purilactis Formation
    • Río Grande Member
    • Serilao Member
    • Vizcachita Member
    • Licán Member
    • Limón Verde Member
  • Tonel Formation

Tonel Formation is separated from Purilactis Formation by a fault, while the remaining first-order units are separated from each other by disconformities.[1] The Tonel Formation exhibit at some localities diapirism in its gypsum layers.[2] Tectonic movements have tilted the northern part of Purilactis Group into an near-vertical position with the stratigraphically higher parts being located in the east.[2] Other tectonic movements have thrust the older Paleozoic basement over the top of the southern part of the Purilactis Group.[2] These movements account to a phase of tectonic inversion beloning to the "Incaic Phase" of the Andean orogeny.[3]

References
  1. Mpodozis, Constantino; Arriagada, César; Roperch, Pierrick (1999-10-06). Cretaceous to Paleogene geology of the Salar de Atacama basin, northern Chile: A reappraisal of the Purilactis Group stratigraphy. Fourth ISAG, Goettingen. Goettingen, Germany.
  2. Charrier, Reynaldo; Reutter, Klaus-J. (1990). "The Purilactis Group of Northern Chile: Boundary Between Arc and Backarc from Late Cretaceous to Eocene". In Reutter, Klaus-Joachim; Scheuber, Ekkehard; Wigger, Peter J. (eds.). Tectonics of the Southern Central Andes. Springer, Berlin, Heidelberg. pp. 189–202. doi:10.1007/978-3-642-77353-2. ISBN 978-3-642-77353-2.
  3. Flint, Stephen S.; Hartley, A.J.; Rex, David C.; Guise, P.; Turner, Peter (1989). "Geochronology of the Purilactis Formation, Northern Chile: an insight into late cretaceous/early tertiary basin dynamics of the central Andes". Revista Geológica de Chile. 16 (2): 241–246.
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