Arqueros Formation

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 volcanic sandstones 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]