Arqueros Formation
Geological formation in northern Chile
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Arqueros Formation (Spanish: Formación Arqueros) is a geological formation composed of alternations of volcanic and volcaniclastic rock layers and limestone of marine origin in inland Coquimbo Region, northern Chile.[1][2] The formation has been dated to the Early Cretaceous,[3] more specifically to the Hauterivian and Barremian.[2] The volcanic rocks of the formation are of andesitic composition.[2] The formation has a stratigraphic thickness of 1020 m.[2] The exposed parts of the formation run as a belt from north to south through the central part of the region.[4][5] There are large outcrops of the formation in mountain plateaux north of Quebrada Marquesa, a tributary of Elqui River.[2] These outcrops are thought to have originated by uplift of the region bounded by one normal fault to the west and one to the east.[2]
| Arqueros Formation | |
|---|---|
| Stratigraphic range: Hauterivian-Barremian | |
| Type | Geological formation |
| Underlies | Quebrada Marquesa Formation |
| Overlies | La Negra Formation |
| Thickness | 1020 m |
| Lithology | |
| Primary | Porphyritic andesite, limestone, calcareous sandstone, volcanic sandstone |
| Other | Manganese deposits |
| Location | |
| Coordinates | 24°1′51.70″S 68°11′44.79″W |
| Region | Coquimbo Region |
| Country | Chile |
  Arqueros Formation (Chile) | |
The work of Aguirre and Egert (1970) found that five members could be identified in the formation, beginning with porphyritic andesites in the bottom (Ka1),[2] overlaid by cherts, sandstones and limestones (Ka2), again overlain by a layer of porphyritic andesites (Ka3) and then followed by limestones, sandstones and andesites (Ka4). The stratigraphically uppermost layer, Mn1, is made of volcanic sandstones and manto-type copper and manto-type manganese deposits.[2] The manganese-bearing beds of the Mn1 member lie typically 30 m from the roof of the formation, and thus lie close to Quebrada Marquesa Formation that overlies it.[4]
Arqueros Formation is underlaid by La Negra Formation.[5]