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. The group has a stratigraphic thickness of more than 6000 m. The group overlies basement rocks of Late Paleozoic age. The north-south El Bordo Escarpment of Cordillera Domeyko contain the main outcrops of the group. The group has been difficult to date in detail since it hosts few fossils and dateable minerals. 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.
From top to bottom, the main units (formations) of the group outlined by Mpodozis and co-worders in 1999 are:
- 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. The Tonel Formation exhibit at some localities diapirism in its gypsum layers. 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. Other tectonic movements have thrust the older Paleozoic basement over the top of the southern part of the Purilactis Group. These movements account to a phase of tectonic inversion beloning to the "Incaic Phase" of the Andean orogeny.
References
- ^ 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.
- ^ 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.
- ^ 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.
