Types of rocks of the precolumbian objects

Sedimentary clastic rocks

Other pre-Columbian artifacts were also elaborated from sedimentary clastic rocks from Curré and Térraba formations.  These rocks consist of particles or clasts derived from pre-existing rocks and are subdivided according to the particles’ size:

• Shale: particles of clay and silt with a size under  1/16 mm
• Sandstone: particles of sand, size 1/16 mm to 2 mm
• Conglomerates and breccia: fragments of gravel with a size over 2 mm.

The Curré Formation is a sequence of brown sandstones, interstratified with conglomerates and shales.Outcrops of these rocks can be observed along the Térraba River, between the Curré and La Escuadra homesteads. Its age is Middle-Upper Miocene.

The Térraba Formation is composed of shales, siltstones and calcarean sandstones of dark grey to black colors. There are outcrops along the Térraba River, between the Chánguena’s river confluence and the crossing at El Cajón.  Its age, Oligocene to Lower Miocene, was determined based upon its fossiliferous content.