Purilactis Group | |
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Stratigraphic range: Upper Cretaceous– Upper Eocene | |
Type | Geological group |
Unit of | Salar de Atacama basin |
Thickness | >6,000 m (20,000 ft) [1] |
Lithology | |
Primary | Conglomerate, basaltic andesite lava, rhyolitic ignimbrite |
Other | Gypsum |
Location | |
Coordinates | 22°45′56″S 68°27′47″W / 22.76556°S 68.46306°W |
Region | Antofagasta Region |
Country | Chile |
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]
From top to bottom, the main units (formations) of the group outlined by Mpodozis and co-worders in 1999 are: [1]
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]